Structure-property relationships in densely grafted π-stacked polymers

Article abstract of DOI:10.1002/pola.24016

Three methyl end-capped oligo(ethylene glycol) (MOEG) ethers (1b-d) and a methoxyderivative (1a) of benzofulvene monomer BFSk were synthesized and induced to polymerize spontaneously by solvent removal to obtain soluble π-stacked polymers bearing densely grafted MOEG side chains (poly-1b-d) and model polymer poly-la. The physicochemical features (e.g., solubility, NMR, MALDI-TOF, and absorption/emission spectra, as well as MWD, conformation plot, and thermal properties) of the synthesized polymers were compared in a structure-property relationship study. This approach afforded the following evidence. The structure of poly-1a-d is very similar to that of BF3k, suggesting that the polymerization mechanism is not affected by the presence of the electron-rich methoxy group or bulkier MOEG side chains. However, the latter appear to be capable of affecting the conformational behavior of the polymer backbone. The solubility of poly-1a-d depends on the number of the oligo (ethylene glycol) monomeric units. In particular, poly-1d, featuring a long MOEG side chain (n = 9), shows an amphophilic character and is soluble in a number of organic solvents, whereas it interacts with water to give isolated macromolecules in equilibrium with nanosized water-soluble aggregates. 2010 Wiley Periodicals, Inc.

Full text of DOI:10.1002/pola.24016

Structure-Property Relationships in Densely Grafted p-Stacked Polymers
ANDREA CAPPELLI,1 MARCO PAOLINO,1 PAOLO ANZINI,1 GERMANO GIULIANI,1 SALVATORE VALENTI,1 MARIANNA AGGRAVI,2
ALESSANDRO DONATI,2 RANIERO MENDICHI,3 LUCIA ZETTA,3 ANTONELLA CATERINA BOCCIA,3 FABIO BERTINI,3
FILIPPO SAMPERI,4 SALVATORE BATTIATO,4 EUGENIO PACCAGNINI,5 SALVATORE VOMERO1
1Dipartimento Farmaco Chimico Tecnologico and European Research Centre for Drug Discovery and Development, Universita`
degli Studi di Siena, Via A. Moro, Siena 53100, Italy
2Dipartimento di Scienze Chimiche e dei Biosistemi, Universita` degli Studi di Siena, Via A. Moro, Siena 53100, Italy
3Istituto per lo Studio delle Macromolecole (CNR), Via E. Bassini 15, Milano 20133, Italy
4Istituto di Chimica e Tecnologia dei Polimeri (CNR), Viale A. Doria 6, Catania 95125, Italy
5Dipartimento Farmaco di Biologia Evolutiva, Universita` degli Studi di Siena, Via A. Moro, Siena 53100, Italy
Received 11 January 2010; accepted 8 March 2010
DOI: 10.1002/pola.24016
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Three methyl end-capped oligo(ethylene glycol)
(MOEG) ethers (1b-d) and a methoxyderivative (1a) of benzoful-
vene monomer BF3k were synthesized and induced to polymer-
ize spontaneously by solvent removal to obtain soluble p-stacked
polymers bearing densely grafted MOEG side chains (poly-1b–d)
and model polymer poly-1a. The physicochemical features (e.g.,
solubility, NMR, MALDI-TOF, and absorption/emission spectra,
as well as MWD, conformation plot, and thermal properties) of
the synthesized polymers were compared in a structure-property
relationship study. This approach afforded the following evi-
dence. The structure of poly-1a–d is very similar to that of BF3k,
suggesting that the polymerization mechanism is not affected by
the presence of the electron-rich methoxy group or bulkier
MOEG side chains. However, the latter appear to be capable of
affecting the conformational behavior of the polymer backbone.
The solubility of poly-1a–d depends on the number of the oligo
(ethylene glycol) monomeric units. In particular, poly-1d, featur-
ing a long MOEG side chain (n ¼ 9), shows an amphiphilic charac-
ter and is soluble in a number of organic solvents, whereas it
interacts with water to give isolated macromolecules in equilib-
C
V
rium with nanosized water-soluble aggregates. 2010 Wiley Peri-
odicals, Inc. J Polym Sci Part A: Polym Chem 48: 2446–2461, 2010
KEYWORDS: hydrophilic polymers; NMR; synthesis
INTRODUCTION Brush-like macromolecules perform in na-
ture important functions, such as cell protection and signal-
ing, lung clearance, and joint lubrication. By virtue of its
brush-like architecture, aggrecan, the major proteoglycan in
the articular cartilage, provides the hydrated gel structure
crucial for the load-bearing properties.1,2 Aggrecan architec-
ture is mimicked in synthetic cylindrical polymer brushes
(CPBs), which are formed by a central polymeric backbone
densely grafted with suitable side chains. CPBs show unique
features, which are regulated by the properties of the indi-
vidual components (side chains and backbone) and by graft-
ing density. For instance, the conformational behavior of
CPBs may depend on the side chain length and grafting den-
sity, and may be affected by environment characteristics
(e.g., solvent properties, temperature, pH, and ionic
strength).3
method) CPBs bearing PEG side chains.5–12 Some of the most
recent examples include the anionic polymerization of meth-
acrylates showing short oligo(ethylene glycol) alkyl ether
side chains to give poly[oligo(ethylene glycol) alkyl ether
methacrylate]s characterized by different water solubility
and lower critical solution temperature (LCST),9 or the atom
transfer radical polymerization (ATRP) of a commercially
available OEGMA derivative in aqueous media to obtain
OEGMA polymers showing low polydispersities.10,11 Again,
ATRP methodology was used to polymerize 2-(2-methoxy-
ethoxy)ethyl methacrylate with OEGMA and obtain poly-
(MEO2MA-co-OEGMA) copolymers showing controlled chain
length, narrow molecular weight distribution (MWD), inter-
esting solution properties in water, and tunable thermosen-
sivity.6 Therefore, polymethacrylate can be considered one of
the most used backbone in CPBs bearing PEG side chains.
In recent years, polymerization of poly(ethylene glycol)
(PEG)4 macromonomers, such as oligo(ethylene glycol) meth-
acrylate (OEGMA) was used by different research groups to
synthesize (by means of the so called ‘‘grafting through’’
The work performed in our laboratories demonstrated that
benzofulvene derivative BF1 (Scheme 1) polymerized in the
apparent absence of catalyst or initiators by removal of sol-
vents to give a new hydrophobic high-molecular-weight
Correspondence to: A. Cappelli (E-mail: cappelli@unisi.it)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 2446–2461 (2010) 2010 Wiley Periodicals, Inc.
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SCHEME 1 Structure of some benzoful-
vene derivatives.
polymer (poly-BF1) showing vinyl structure stabilized by
aromatic stacking interactions.13,14 Moreover, BF1 could be
polymerized with anionic initiators, such as phenyl lithium
to produce a mixture of oligomers and a polymer (poly-BF1-
AP), which is characterized by a significantly lower mole-
cular weight with respect to that shown by poly-BF1-SP
and by the tendency to aggregate in nanospheres and
microspheres.15
MOEG side chain in the polymer properties in a structure-
property relationship study.
RESULTS AND DISCUSSION
Synthesis and Spontaneous Polymerization of
Benzofulvene Derivatives 1a–d
Benzofulvene monomers 1a–d were synthesized starting
from indenones 2a–d following the straightforward chemis-
try developed for the synthesis of poly-BF1 derivatives
(Scheme 2). The reaction sequence includes the reaction of
2a–d with trimethylaluminium to give indenol derivatives
3a–d and their dehydration in chloroform (or CDCl3) in
the presence of p-toluenesulfonic acid (PTSA) to give trans-
diene derivatives 1a–d. Despite their relative structural
To explore the role of substituents of benzofulvene moiety
on the polymer properties, such as formation, molecular
weight, structure, thermoreversibility, and aggregation in
nanostructured entities, a series of benzofulvene derivatives
BF3 was synthesized and induced to polymerize spontane-
ously.16 In particular, desmethyl derivative BF3k of the pro-
totypical benzofulvene monomer BF1 was found to form a
polymer (poly-BF3k), which showed macromolecular fea-
tures very similar to those shown by poly-BF1, suggesting
that the methyl group in position 40 does not affect the spon-
taneous polymerization.16
The similarities of BF1 with methacrylates and cyanoacry-
lates stimulated the synthesis of conjugates MOEG-BF1a,b
bearing their methyl end-capped oligo(ethylene glycol)
(MOEG) side chains by means of an ester linkage bond.17
Remarkably, the polymer bearing nine-unit oligo(ethylene
glycol) (OEG) side chains showed an amphiphilic character
and interacted with a number of organic solvents to produce
transparent gel aggregates, and with water to give a quite
compact physical and biocompatible hydrogel.17
In this article, we describe the structural manipulation of
BF3k leading to novel benzofulvene macromonomers 1b–d
and their spontaneous polymerization to afford CPBs based
on polybenzofulvene backbone, in which p-stacking interac-
tions may play a crucial role in conformational and physico-
chemical features. The simplified analog 1a (showing a
methoxy substituent in the place of the MOEG side chain)
was prepared and polymerized to evaluate the role of the
SCHEME 2 Synthesis of polybenzofulvene derivatives poly-1a–
d. Structures: 1a, R ¼ ACH3; 1b, R ¼ A (CH2CH2O)2CH3; 1c, R ¼
A (CH2CH2O)3CH3; 1d, R ¼ A (CH2CH2O)9CH3. Reagents: (i)
Al(CH3)3, CH2Cl2; (ii) PTSA, CHCl3; (iii) solvent elimination.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
actions among the lipophilic backbones), which are weak-
ened more easily with respect to poly-MOEG-BF1b. The
clear supernatant solution was demonstrated by 1H NMR
spectroscopy to contain a substantial amount of poly-1d and
became cloudy when gently warmed at 35 ꢀC. This result
suggests thermoresponsive features for poly-1d.
Poly-1b [R
¼
(CH2CH2O)2OCH3)] and poly-1c [R
¼
(CH2CH2O)3OCH3)] are readily soluble in organic solvents,
such as dichloromethane, chloroform, and diethyl ether, but
they are insoluble in petroleum ether and in water. There-
fore, they were purified by precipitation from a dichlorome-
thane (good solvent) solution with petroleum ether (bad sol-
vent) and obtained as a white solid or as a colorless glassy
solid, respectively. Finally, poly-1a (R ¼ CH3) was purified by
precipitation from a dichloromethane (or ethyl acetate) solu-
tion with ethanol (bad solvent) and obtained as a white
solid.
In conclusion, the most intriguing result obtained with poly-
1a–d and poly-MOEG-BF1 is the fact that the length and the
position of MOEG chains in poly-benzofulvene derivatives
appear to modulate the interactions of macromolecules with
themselves and with the solvent molecules to originate mate-
rials showing different properties. Most notably, although the
difference in the length of MOEG side chains produces pre-
dictable changes in the interaction with solvent molecules
(i.e., solubility differences), the difference in the MOEG
attachment between poly-1d and poly-MOEG-BF1b produces
unanticipated differences in the behavior of the resulting
hydrogels.
SCHEME 3 Synthesis of indenone derivatives 2b–d and struc-
ture of compound 6. Reagents: (i) K2CO3, KI, and DMF; (ii) PBr3
and CHCl3.
complexities, benzofulvene derivatives 1a–d polymerized, in
the apparent absence of catalyst and initiator species, upon
solvent removal to give poly-1a–d. It is noteworthy that the
presence of long PEG side chains did not depress the poly-
merization process.
6-Methoxy-1-indenone derivative 2a was prepared following
the literature,18 whereas 2b–d were synthesized by alkyla-
tion of phenol derivative 2e (ref. 18) with the activated
monomethyl OEG chains 5b–d in DMF in the presence of po-
tassium carbonate as the base and potassium iodide as a cat-
alyst (Scheme 3). Although 5b was a commercially available
intermediate, compound 5c was synthesized following the
literature,19 and 5d was prepared by a standard bromination
procedure with PBr3 of nona(ethylene glycol) monomethyl
ether (4d).17 Finally, indene derivative 6 was prepared fol-
lowing the literature (see ref. 18) to be studied as the model
of monomeric unit of poly-1a.
Characterization of MWD
The characterization of MWD in poly-1a–d samples was per-
formed by means of a multiangle laser light scattering
(MALS) detector on-line to a size exclusion chromatography
(SEC) system using tetrahydrofuran (THF) as the mobile
phase. The differential MWD of poly-1a–d samples obtained
by SEC-MALS is shown in Table 1 in which the correspond-
ing value published for poly-BF3k is reported for the sake of
comparison.
The weight-average molecular weight Mw of all polymers
synthesized is high and the MWD is broad with
Properties of Poly-1a–d
Poly-1d [R ¼ (CH2CH2O)9OCH3)] was purified by washing
with diethyl ether, the same procedure being used for poly-
MOEG-BF1b, to obtain a colorless sticky solid similar to the
latter. However, with respect to poly-MOEG-BF1b, poly-1d
appears to be more readily soluble in organic solvents, such
as dichloromethane, chloroform, and ethanol. Moreover, the
interaction with water constitutes another distinguishing ele-
ment of poly-1d. In fact, water produces a significant swel-
ling of poly-1d to produce a physical hydrogel, which is
rapidly broken by ultrasounds to give a milky suspension
leading to the separation of a transparent hydrogel (for com-
parison, the hydrogel obtained with poly-MOEG-BF1b in the
same conditions used with poly-1d is stable when exposed
to ultrasound). These results suggest that poly-1d is capable
of forming a hydrogel stabilized by weak noncovalent inter-
actions (i.e., MOEG chain entanglement or hydrophobic inter-
TABLE 1 Macromolecular Features of the Synthesized
Poly-1a-d and of Previously Reported Poly-BF3k
Mp
Mw
Rg
Polymer
R
(kg/mol) (kg/mol)a PDIb (nm)c
poly-BF3k
poly-1a
poly-1b
poly-1c
poly-1d
a
1,593
347
3.7
4.3
4.0
2.0
1.8
44.6
–
CH3
312
821
(CH2CH2O)2CH3
768
28.7
38.7
20.8
(CH2CH2O)3CH3 1,857
(CH2CH2O)9CH3 527
1,408
456
M
w: weight-average molecular weight.
PDI: polydispersity index PDI
numeric-average molecular weight.
b
¼
Mw/Mn where Mn denotes the
c
Rg: the radius of gyration, that is, the dimension of macromolecules.
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(poly-1d) to 39 nm (poly-1c). Previous studies showed that
Mw of poly-MOEG-BF1 samples was relatively high (108 and
175 kg/mol for poly-MOEG-BF1a and poly-MOEG-BF1b,
respectively) and PDI was broader (2.4 and 3.0 for poly-
MOEG-BF1a and poly-MOEG-BF1b, respectively) with
respect to that measured for poly-BF1 (1.6–2.0).14,15
The comparison of differential MWD and of the conformation
plot of the four polymers listed in Table 1 is shown in Figure
1. The conformation plot, Rg ¼ KMa, is the scaling law of
macromolecule size (radius of gyration, Rg) with respect to
the molecular weight (chain length) and it is very useful in
studying the stiffness (conformational rigidity/flexibility) of
polymers. The conformation plot of poly-1a is linear with
slope a ¼ 0.60 typical of a semistiff polymer. On the other
hand, the conformation plot of both poly-1b and poly-1c
shows a change in slope suggesting that these polymers are
not homogeneous in their conformational behavior. Finally,
the conformation plot of poly-1d is not linear (strong curva-
ture) in similar way of a branched polymer. This result can
be rationalized in terms of a progressive increasing in com-
pactness with the increase of the molecular weight for flexi-
bility reasons. Thus, in agreement with the results of NMR
and DSC studies (see below), the analysis of the conforma-
tion plot shows that both the presence and the length of the
FIGURE 1 Comparison of differential MWD and of the confor-
mation plot Rg ¼ f(M) of four polymers.
polydispersity index Mw/Mn (PDI) ranging from 1.8 to 4.0.
The Mw average for poly-1a–d samples ranges from high
(poly-1d, Mw ¼ 456 kg/mol) to very high (poly-1c, Mw
¼
1,408 kg/mol). The average size of the macromolecules’ ra-
dius of gyration (Rg) ranges approximately from 21 nm
FIGURE 2 13C spectra (CDCl3) of poly-BF3k, poly-1a, and model compound 6.
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FIGURE 3 Comparison of the 13C
NMR spectra (CDCl3) of poly-
1a–d.
MOEG side chains affect the conformational behavior of
these poly-benzofulvene derivatives.
owing to partially merging signals, indene derivative 6 was
prepared as the model compound for the monomeric unit
(present in poly-1a) concerning the polymer formally synthe-
sized by vinyl (1,2) polymerization of compound 1a. The 1H
and 13C NMR spectra of compound 6 were completely and
unambiguously assigned by means of homonuclear 1H-1H-
COSY, 1H-1H-NOESY and heteronuclear 1H-13C-HSQC, 1H-13C-
HMBC, two-dimensional correlation experiments.
Structure of Poly-1a–d
NMR
In previous studies, evidence was obtained about the vinyl
(1,2) polymerization of trans-diene derivative BF114 and on
the similarity existing among poly-BF1, its desmethyl deriva-
tive poly-BF3k,16 and poly-MOEG-BF1.17 To gain insight into
the nature of this class of compounds, the structure of poly-
1a–d was extensively characterized by different NMR techni-
ques. As the 13C spectra of poly-1a–d were relatively complex
1
The H resonances of the model compound 6 were assigned,
according to on 1H chemical shifts, multiplicities, integrals,
and scalar coupling constants. By analyzing in details the
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detected correlations concerned the H-4 of the indenyl ring
with the H-20/60 protons of the pendent phenyl ring.
All the other resonances were assigned on the basis of the
1H-13C heteronuclear techniques and their combination with
the 1D results. The HSQC experiment produces a spectrum
in which each peak correlates the chemical shifts of 1H’s
with directly bound 13C atoms. Once the H-5, H-4, and H-7
chemical shifts were known, the related 13C assignments
were made basing on HSQC spectrum. Another advantage
obtained acquiring a HSQC experiment was the possibility to
use it to distinguish between methyl/methyne resonances, as
positive cross peaks, and methylene resonances, as negative
peaks, during the editing of the spectra. Thus, the methylene
in position 1 of the indene moiety and the methoxy group
were differentiated by means of the HSQC spectrum, and
1
their H and 13C signals were assigned easily.
FIGURE 4 Comparison of the absorption spectra of poly-1a
(green), poly-1b (magenta), poly-1c (red), poly-1d (blue), and in-
dene derivative 6 (black). The spectra were obtained in dichloro-
methane at room temperature. The concentration in monomer
base unit was about 2.7 ꢁ 10ꢂ5 mol/L for the polymers. The
same concentration was used for indene derivative 6.
The H-4 proton of the indene moiety was considered as the
starting point for the assignment of the long-range connec-
tivities. It correlates through three bonds with the not yet
assigned quaternary carbon atoms C-3, C-7a, and C-6 of the
indene moiety. Analogously, the H-7 proton allowed the
assignment of the quaternary C-3a carbon atom to be made,
and in the same way, all the other resonances were deter-
mined. Thus, the methylene protons in position 1 were inter-
connected trough two bonds with the C-2 atom. From the
three bond correlation of C-3, it became possible to confirm
the assignment of protons H-20/60 and from these the
attached carbon atoms and the long term connected C-40.
Analogously, from H-40 it was possible to determine the C-10
carbon atom and the remaining C-30/50 carbon atoms by
exclusion.
aromatic region, the signal at 6.89 ppm was assigned to H-5
proton, because the signal was a doublet of doublets (dd)
due to the couplings with the H-4 and H-7 protons (dd, Jo ¼
8 Hz; Jm ¼ 2 Hz); the signal at 7.20 ppm was attributed to
the H-4 proton (d, Jo ¼ 8 Hz); the third one (at 7.14 ppm)
was assigned to the H-7 proton (br d, Jm ¼ 2 Hz). With the
acquisition of the 1H spectrum alone nothing could be said
about the aromatic protons of the phenyl pendent ring. The
H-4 and H-5 protons assignment was also confirmed observ-
ing the off resonance cross peak in the 1H-1H COSY experi-
ment (Correlation Spectroscopy).
The same strategy used to assign the model compound spec-
tra was used in the assignment of poly-1a–d 13C spectra. In
this case, owing to severe line broadening the HMBC experi-
ments failed to provide all the long term 1H-13C-connectiv-
ities, consequently, the assignments were done by comparing
To obtain information through space rather than through
bond couplings the NOESY experiments (nuclear Overhauser
effect spectroscopy) were also acquired, but the only
FIGURE 5 (A) Comparison of the emission spectra of poly-1a (green), poly-1b (magenta), poly-1c (red), and poly-1d (blue). The
spectra were obtained in dichloromethane (the concentration in monomer base unit was ca. 2.7 ꢁ 10ꢂ6 mol/L) at room tempera-
ture. The excitation wavelength was 320 nm. (B) Emission spectrum of indene derivative 6. The spectrum was obtained in
dichloromethane (concentration ca. 2.7 ꢁ 10ꢂ5 mol/L) at room temperature. The excitation wavelength was 310 nm.
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FIGURE 6 MALDI-TOF mass spectra of poly-1a (a), poly-1b (b), poly-1c (c), and poly-1d (d). *Symbols indicate clusters of matrix.
the 13C spectra of poly-1a–d with those of model compound
6 and poly-BF3k, also in the light of the 2D collected data.
The assignments reported in Figure 2 demonstrate that the
signals attributed to poly-1a backbone C-1 (57.1 ppm) and
D (48.5 ppm) show chemical shift values very similar to
those observed for the corresponding signals in poly-BF3k
spectrum [C-1: 57.8 ppm; D: 48.4 (Major), 50.8 (minor)].16
dene moiety might induce a different main chain arrange-
ment affecting both the nonbonded interaction of the pend-
ent phenyl substituent and the backbone flexibility (or
conformational behavior).
Absorption and Emission Spectroscopy
The UV–vis absorption spectrum of poly-1a (Fig. 4) matches
that of indene derivative 6 (the model for the postulated
monomeric unit) and shows the existence of two absorption
components: one centered around 240 nm attributable to
the 3-phenylindene moiety, and a second centered at about
310 nm related to the presence of a p-methoxycinnamate
moiety, a well known UV-B-absortive chromophore present
in some largely used UV-B sunscreens.20 As expected on the
basis of chromophore correspondence, the absorption spec-
tra of PEGylated polymers poly-1b–d are very similar to that
of poly-1a. Interestingly, the comparison shown in Figure 4
indicates a significant hypochromism for poly-1a–d, with
respect to the monomeric unit model 6, similar to that
observed in other p-stacked macromolecules.21
Previous studies performed on poly-MOEG-BF1 suggest that
the presence of MOEG side chain does not affect the vinyl
(1,2) polymerization mechanism and the macromolecular
architecture.17 To ascertain whether MOEG side chain length
has some effects on the poly-1b–d structure, the 13C NMR
spectra of the three polymers were compared with that of
poly-1a (Fig. 3). This comparison shows the existence of
stringent similarities among poly-1b–d spectra and poly-1a
spectrum in both the up-field region containing backbone C-
1 and C-D signals and the low-field portion containing C-10
and C-3, which may be affected by the potentially competing
1,4-polymerization. These observations appear to support
the retention of the spontaneous 1,2-polymerization mecha-
nism in these benzofulvene carboxylate derivatives (e.g.,
BF1, BF3k, MOEG-BF1, and 1a–d).
The emission spectra of poly-1a–d (Fig. 5) are very similar
(from the point of view of the shape) and show a dominating
peak centered at about 460 nm with a shoulder at about
500 nm. On the other hand, the emission spectrum of indene
derivative 6 is characterized by a component centered at
about 400 nm with a very small shoulder at 420 nm. There-
fore, as previously observed for poly-BF1, the emission of
poly-1a is red-shifted with respect to the one shown by the
However, the aromatic C-20/60 signals become broader and
shift progressively up-field from poly-1a to poly-1d. Similar
changes in the peak broadness appear to affect the signals
attributed to C-2 and C-3, and these results suggest that the
presence of an increasing steric bulk in position 6 of the in-
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model for the postulated monomeric unit (indene derivative
6) and it has the characteristics expected for a band that
originates from an excimer.
By way of comparison, Londergan et al. attributed the pre-
dominant emission at 448 nm of a structurally related poly-
mer to the formation of an excimer resulting from chromo-
phore stacking, and the secondary peak at 347 nm to the
monomer emission on the basis of the observation that 3-
phenylindene shows an emission peak at 345 nm.22 Further-
more, in dibenzofulvene oligomers, the emission bands
around 400 nm were attributed to excited dimers and those
around 310 nm to the monomer emission.21 Thus, all these
observations lead to the conclusion that poly-1a–d display a
significant degree of chromophore stacking.
MALDI-TOF Mass Spectrometry
The structure and chemical composition of four crude poly-
mers poly-1a–d were also studied by matrix assisted laser
desorption time-of-flight mass spectrometry (MALDI-TOF
MS), using 2-(4-hydroxylphenylazo)benzoic acid (HABA) as a
matrix; the positive ions mass spectra recorded in linear
mode are reported in Figure 6. Each mass spectrum in Fig-
ure 6 shows a cluster of homologous peaks separated by a
molecular mass corresponding to the repeating unit of the
analyzed polymer, in agreement with the synthetic procedure
(Scheme 2). The molecular mass of the repeating units of
each polymer (poly-1a–d) was measured with an accuracy of
60.4 g/mol and was found to be 306.3 g/mol for poly-1a,
394.3 g/mol for poly-1b, 438.4 g/mol for poly-1c, and 702.5
g/mol for poly-1d. The mass spectrum of poly-1a [Fig. 6(a)]
shows, in the range from 900 up to 8800 g/mol, clusters of
peak series corresponding to the oligomers with repeating
units ranging from 3 (M3) up to 28 (M28). The mass spec-
trum of poly-1b [Fig. 6(b)] shows peaks belonging to the lin-
ear oligomers with repeating units ranging from 3 (M3) to
16 (M16). Peaks corresponding to the linear oligomers of
poly-1c with repeating units ranging from 3 (M3) to 19
(M19) are present in the mass spectrum in Figure 6(c),
whereas in the one of poly-1d [Fig. 6(d)], families of peaks
belonging to the linear oligomers with repeating units rang-
ing from 2 (M2) up to 8 (M8) are present. The same clusters
of peaks present in Figure 6 were observed in the mass
range higher than 10,000 g/mol, in the mass spectra (not
reported here for brevity) of polymer fractions having a nar-
row distribution obtained by SEC fractionation. Detailed in-
formation about the end groups and about the composition
of poly-1a–d samples can be inferred from the enlarged sec-
tion of MALDI mass spectra reported in Figure 7, which
shows two clusters of peaks for each polymer. The peaks,
being well resolved and calibrated, allow pertinent assign-
ments, and the most likely structures of the corresponding
polymer chains are summarized in Table 2. All the spectra in
Figure 7 show a dominant series of peaks corresponding to
the protonated ions of the expected polymer chains termi-
nated with hydrogen at both ends (H/H; species An). They
also show two additional families of intense peaks that were
assigned to the macromolecular chains terminated with an
oxidized benzofulvene unit having one aldehyde moiety (spe-
FIGURE 7 Enlarged sections of MALDI-TOF mass spectra of
poly-1a (a), poly-1b (b), poly-1c (c), and poly-1d (d).
cies Bn) or one carboxylic acid group (species Cn). The pres-
ence of these end groups is confirmed by 13C NMR spectra,
which present two peaks in the downfield region at 220.6
ppm and at 193.1 ppm owing to the resonance of carbonyl
groups belonging to the aldehyde and carboxyl acid moieties,
respectively. The occurrence of these end groups can be
explained in terms of autoxidation of the methylene macro-
radical species formed during the polymerization of 1a–d
monomers. Therefore, MALDI-TOF MS is a crucial method to
support quantitative information about the structure and
composition of the polymer chains synthesized.23,24 It also
provides information on the reactions occurring during the
polymerization, as a function of the experimental conditions.
Differential Scanning Calorimetry and
Thermogravimetric Analysis
The thermal behavior of poly-1a–d was investigated in the
bulk by means of differential scanning calorimetry (DSC) and
thermogravimetry analysis (TGA). DSC analyses carried out at
a heating rate of 20 ꢀC/min are reported in Figure 8, in
which the thermogram previously obtained with poly-BF3k
is reported for the sake of comparison. The DSC curves of
DENSELY GRAFTED p-STACKED POLYMERS, CAPPELLI ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Structural Assignments of Peaks Displayed in the MALDI-TOF Mass Spectra of Poly-1a-d in Figure 7
Species
Structuresa
Polymer
[M þ Hþ]b (n)
A
poly-1a
1228.2 (4)
1534.5 (5)
1185.9 (3)
1580.2 (4)
1318.3 (3)
1756.7 (4)
1408.0 (2)
2110.5 (3)
poly-1b
poly-1c
poly-1d
B
C
a
poly-1a
poly-1b
poly-1c
poly-1d
1242.2 (3)
1548.5 (4)
1199.9 (2)
1594.2 (3)
1332.3 (2)
1760.7 (3)
1422.0 (1)
2124.5 (2)
poly-1a
poly-1b
poly-1c
poly-1d
1258.2 (3)
1564.5 (4)
1215.9 (2)
1610.2 (3)
1348.3 (2)
1776.7 (3)
1438.0 (1)
2140.5 (2)
Where: poly-1a, R ¼ CH3; poly-1b, R ¼ CH3(OCH2CH2)2; poly-1c, R ¼ CH3(OCH2CH2)3; poly-1d, R ¼ CH3(OCH2CH2)9.
The mass accuracy was better than Dm ¼ 6 0.4 g/mol.
b
poly-1a–d display a single endothermic peak centered in the
phere up to 200 ꢀC, whereas polymers bearing MOEG side
chains display a greater stability in terms of mass loss. At
higher temperatures, the entire investigated polymer show a
complex decomposition pathway. The derivative thermo-
gravimetry (DTG) curves show that the decomposition
process takes place in different steps (Fig. 9).
same temperature range (224–231 ꢀC) measured for poly-
BF3k (232 ꢀC, Table 3). Nevertheless, the inspection of Figure
8 evidences that the thermal behavior is affected by the sub-
stituent present at position 6. In particular, the oligo(ethylene
glycol)-containing poly-1b–d show broad endothermic events,
whereas the endothermic peak becomes sharper in the DSC
trace of the polymer bearing a methoxy group (poly-1a) and
is even sharper in the case of unsubstituted poly-BF3k. Previ-
ous works demonstrate that this endothermic event can be
related to the depolymerization process.15–17 The heat flows
involved in the unzipping reaction, determined by DSC, fall in
the range 20–52 J/g and are consistent with the data reported
in the literature for similar thermoreversible polybenzoful-
venes,15,16 but they appear to be significantly lower with
respect to unsubstituted poly-BF3k (98.5 J/g).16 This result
can be rationalized in terms of polymer stiffness. Poly-Bf3k,
showing the highest stiffness, requires the greatest amount of
energy to depolymerize. The introduction of the methoxy sub-
stituent of poly-1a and the MOEG side chains of poly-1b–d
produces both a change in the backbone arrangement (see
the NMR section) and a decrease of the depolymerization
heat as well as a progressive broadening of the DSC peak.
TGA can evaluate the thermal stability of the polymer via
characteristic temperatures: the onset of thermal decomposi-
tion (Ti, i.e., the temperature corresponding to initial 1%
weight loss) and the temperature at which the weight loss
rate is maximum (Tmax, Table 3).
Among the newly-synthesized polymer, the one bearing a
methoxy substituent (poly-1a) shows the lower Ti value
(193 ꢀC), which is, however, slightly higher than that mea-
sured for unsubstituted poly-BF3k. For the polymers con-
taining oligo(ethylene glycol) side chains the Ti increases
with the increase of thꢀe side chain length, ranging from 218
ꢀC for poly-1b to 260 C for poly-1d. Interestingly, a similar
trend is observed for the Tmax value. The presence of oligo
(ethylene glycol) in the side chain gives rise to a noticeable
shift of the DTG peaks towards higher temperatures com-
pared with poly-1a. In particular, the Tmax value increases as
a function of the side chain length. As suggested in a previ-
ous article,17 the high value of DTG peaks can be explained
in terms of MOEG chain entanglement, which may hamper
TGA traces reported in Figure 9 point out that poly-1a, simi-
larly to poly-BF3k, is thermally stable under inert atmos-
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ARTICLE
FIGURE 8 DSC curves of poly-BF3k (black), poly-1a (green),
poly-1b (magenta), poly-1c (red), and poly-1d (blue).
the monomer release, thus leading to weight loss. The
decomposition process of all poly-1a–d ends at about 500
ꢀC, whereas the residue yield calculated at 600 ꢀC varies,
going from 4 to 23 wt %. Poly-1d, bearing the longest MOEG
side chain, shows the higher residue amount and poly-1a
bearing the methoxy group shows the lower residue yield.
However, these residues disappear or become negligible
ꢀ
when exposed to the presence of oxygen at 600 C.
The results of the thermal analysis suggest that during the
TGA experiments a variable amount of the formed monomers
decompose before their release in the gas stream, and that
the amount depends on the length of MOEG side chain,
which in turn affects the monomer release temperature.
FIGURE 9 TGA (panel a) and DTG (panel b) curves of poly-
BF3k (black), poly-1a (green), poly-1b (magenta), poly-1c (red)
and poly-1d (blue).
NMR spectra were recorded at regular time intervals. Figure
Depolymerization Studies
The work performed on poly-benzofulvene derivatives13–17
shows an unzipping behavior similar to that of cyanoacry-
lates.25,26 Thus, to characterize the thermo-induced depoly-
merization of poly-1a–d, solutions of these polymers (5.0 mg
10 shows that poly-1a depolymerization is relatively rapid
ꢀ
at 150 C, and reaches an apparent equilibrium (after ca. 8–
24 h) characterized by the presence of a substantial amount
of the monomer. By way of comparison, unsubstituted
poly-BF3k was reported to show an almost complete
1
ꢀ
in 0.5 mL of nitrobenzene-d5) were heated at 150 C and H
TABLE 3 Comparison Between DSC and TGA Features of the Synthesized Polymers
DSC
Tp (ꢀC)
TGA
Ti (ꢀC)
TGA
Tmax1 (ꢀC)
TGA
Tmax2 (ꢀC)
TGA
Polymer
R
Residue (%)
poly-BF3k
poly-1a
poly-1b
poly-1c
poly-1d
a
232
231
224
226
224
191
193
218
252
260
243
246
293
322
402a
310
380
377
428
0.1
4.2
CH3
(CH2CH2O)2CH3
(CH2CH2O)3CH3
(CH2CH2O)9CH3
12.0
18.3
23.1
Single broad decomposition step.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 10 Thermo-induced depolymerization of poly-1a (left) and poly-1d (right) followed by 1H NMR (400 MHz). A solutions of
5.0 mg of poly-1a,d in 0.5 mL of nitrobenzene-d5 was heated at 150 ꢀC, and 1H NMR spectra were recorded at regular time inter-
vals. To appreciate the variation in monomer concentration, the monomer signals were integrated, and the integral values were
compared with that of the lowest field signal of nondeuterated nitrobenzene, which was considered as an internal standard. Inte-
grals are omitted in the figure for the sake of clarity. The arrows indicate the solvent peaks and H2O the water peak.
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ARTICLE
TABLE 4 Comparison of Thermo-Induced Depolymerization of poly-1a-d and poly-BF3k Followed by 1H-NMR Spectroscopy with
Some Significant DSC Features of the Synthesized Polymers
Thermo-Induced Depolymerization
at 150 ꢀC by 1H-NMRa
DSC Peaks n
DSC
Tp (ꢀC)
DSC DH
Polymer
R
(Appearance)
(J/g)
poly-BF3k
poly-1a
poly-1b
poly-1c
poly-1d
a
Depol. almost complete after 3-6 h
Apparent equilibrium after 8-24 h
Apparent equilibrium after 24 h
Apparent equilibrium after 24-48 h
Apparent equilibrium after 48 h
1 (sharp)
232
231
224
226
224
98.5
52
CH3
1 (relat. sharp)
1 (broad)
(CH2CH2O)2CH3
(CH2CH2O)3CH3
(CH2CH2O)9CH3
40
1 (broad)
34
1 (broad)
20
In the thermoreversibility experiments about 5 mg of the polymers were dissolved into nitrobenzene-d5 (0.5 mL) and heated in an oil bath thermo-
stated at 150 ꢀC; the 1H-NMR experiments were performed at regular time intervals. In order to appreciate the variation in monomer concentration,
the monomer signals were integrated, and the integral values were compared with that of the lowest field signal of nondeuterated nitrobenzene,
which was considered as an internal standard.
depolymerization after 3–6 h heating at 150 ꢀC.16 On the
other hand, the thermo-induced depolymerization of the
polymer bearing MOEG side chains (poly-1b–d) appears to
be progressively slowed as the side chain length increases
(see Table 4).
shape of the particles of larger dimensions suggests that
their structure may arise from the combination of globular
ones into larger aggregates showing heterogeneous shapes.
In dilute solution, molecular brushes are expected to adopt
conformations of worm-like objects. However, by virtue of
the flexible backbone, molecular brushes may undergo a
transition from worm-like (or rod-like) to globular conforma-
tion in response to environmental variations. By way of
example, a brush of poly-N-iso-propylacrylamide, a polymer
showing a LCST, was reported to collapseꢀfrom a gyration ra-
dius of 61 nm at 20 ꢀC to 25 nm at 32 C without aggrega-
tion, but remaining in the solution as single macromolecules.
Moreover, concentration-dependent LCST in molecular
brushes was explained in terms of intramolecular or inter-
molecular collapse depending on the distance between the
solvated macromolecules at different concentrations. The
conformation of a polymer brush adsorbed on a surface is
function of the productive interactions between the surface
and the side chains as well as of the distribution of the
absorbed side chains with respect to the backbone.3
Moreover, 1H NMR experiments performed with poly-1b,c,d
in chloroform show that depolymerization after 1 week at
room temperature is quite marked for poly-1b,c and merely
detectable for poly-1d. This result suggests promising biolog-
ical applications of these polymers based on their degrada-
tion features.
Macromolecular Structure of Poly-1d
A sample of poly-1d was dissolved in water by sonication
and observed by transmission electron microscopy (TEM)
after negative staining with uranyl acetate. The images
obtained (Fig. 11) show that poly-1d is liable to generate
water-soluble nanoparticles showing different shapes and
dimensions around 30–50 nm. It is noteworthy that the
dimensions measured by TEM experiments are in full agree-
ment with the gyration radius as determined by SEC-MALS
experiments. Therefore, TEM analysis allowed an accurate
macromolecular characterization of poly-1d by visualizing
single macromolecules. The examination of a number of
microscope fields showed the coexistence of the different
conformations shown in Figure 11. In particular: worm-like
objects similar to the one shown in Figure 11(A), partially
collapsed forms [Fig. 11(B)], globular entities [Fig. 11(C)],
and heterogeneous aggregates of larger dimensions. The
The preponderance observed for poly-1d globular conforma-
tion together with the presence of aggregates suggests that
this molecular brush is liable to collapse intramolecularly
and intermolecularly in the conditions used in TEM experi-
ments. As the starting water solutions used in the present
experiments were perfectly transparent, the larger polymer
micelles could be formed during the sample preparation for
TEM experiments. However, further studies are in progress
to characterize the LCST and the nature of the collapse in
solution.
CONCLUSIONS
Three oligo(ethylene glycol) methyl ether conjugates (1b–d)
and a 6-methoxyderivative (1a) of BF3k (a desmethyl deriv-
ative of our prototypical benzofulvene monomer BF1) were
synthesized to assess their susceptibility toward spontane-
ous polymerization and to compare the properties of the
resulting CPBs in a structure-property relationship study.
Monomers 1a–d were found to polymerize by solvent re-
moval (in the apparent absence of catalysts or initiators)
with the same modalities shown by BF1. In fact, 13C NMR
FIGURE 11 Structure of isolated macromolecules found by
TEM analysis of poly-1d solution in water shown at the same
magnification ratio. (A) extended (wormlike) form; (B) partially
collapsed form; (C) globular form.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
EXPERIMENTAL
spectroscopy showed a stringent similarity between poly-
1a–d and poly-BF3k. However, comparison of the spectro-
scopic data revealed a difference in the signal attributed to
C-20/60 that was interpreted in terms of different arrange-
ment (flexibility or conformational behavior) of the main
chain induced by the steric bulk of the MOEG side chains.
SEC-MALS studies showed for poly-1a–d a high-molecular
weight and perceptible differences in the conformational
behavior of poly-1a–d backbone. Interestingly, poly-1d bear-
ing the longest MOEG side chains appears to be significantly
more flexible than poly-1a–c, probably because of the differ-
ences in the main chain arrangement induced by the steric
bulk of the MOEG chains.
Synthesis
Melting points were determined in open capillaries in a Gal-
lenkamp apparatus and are uncorrected. UV/vis spectra
were recorded with a Shimadzu 260 spectrophotometer and
the emission spectra were performed by means of a Perkin
Elmer LS45 instrument. Merck silica gel 60 (230–400 mesh)
was used for column chromatography. Merck TLC plates,
silica gel 60 F254 were used for TLC. 1H NMR spectra were
recorded at 200 MHz (Bruker AC200 spectrometer), at 300
MHz (Varian Mercury-300), 400 MHz (Bruker DRX-400
AVANCE spectrometer), 500 MHz (Bruker DRX-500 AVANCE
spectrometer), or 600 MHz (Bruker DRX-600 AVANCE spec-
trometer) in the indicated solvents (TMS as internal stand-
ard): the values of the chemical shifts are expressed in ppm
and the coupling constants (J) in Hz. An Agilent 1100 LC/
MSD operating with an electrospray source was used in
mass spectrometry experiments.
MALDI-TOF mass spectrometry supported the structure of
the newly synthesized polymer and provided information
about the end groups and the reactions occurring during the
polymerization. Absorption and emission spectroscopy con-
firmed the presence of a considerable p-stacking in poly-1a–
d. The thermal behavior of poly-1a–d was characterized by a
noticeable stability in the absence of solvent and in inert
atmosphere up to 200 ꢀC, and by a complex decomposition
pathway at higher temperatures. DSC experiments showed
that depolymerization occurs in the same temperature range
(224–231 ꢀC) and is not affected either by the presence or
the length of the MOEG side chains, which, on the other
hand, have a marked effect on depolymerization enthalpy.
28-Bromo-2,5,8,11,14,17,20,23,26-nonaoxaoctacosane (5d)
A solution of nona(ethylene glycol) monomethyl ether (4d,17
0.60 g, 1.4 mmol) in dry diethyl ether (10 mL) was cooled
to 0 ꢀC. To this solution, phosphorous tribromide (0.13 mL,
1.4 mmol) was added dropwise. After the addition was com-
pleted, the reaction mixture was allowed to stir at 0 ꢀC for
10 min. To the reaction mixture methanol (0.39 mL) was
then added, and the resulting mixture was allowed to warm
to room temperature and stirred for 30 min. Then, water
(1.0 mL) was added, and the organic phase was washed in
sequence with a saturated sodium bicarbonate solution and
with brine. The combined aqueous phases were extracted
with ethyl acetate and the combined organic phases were
dried over sodium sulfate and concentrated under reduced
pressure. Purification of the residue by flash chromatography
with ethyl acetate-methanol (9:1) as the eluent gave 5d
(0.15 g, yield 22%) as a pale yellow oil. 1H NMR (200 MHz,
CDCl3): 3.24 (s, 3H), 3.34 (t, J ¼ 6.3, 2H), 3.42 (m, 2H), 3.52
(m, 30H), 3.67 (t, J ¼ 6.3, 2H). MS(ESI): m/z 513 (M þ Naþ).
In depolymerization experiments performed in the presence
of deuterated nitrobenzene as the solvent, poly-1a–d showed
a behavior similar to that shown by poly-BF3k and poly-BF1
with the peculiarity that the length of the side chains
appears to affect the apparent kinetics of the depolymeriza-
tion process.
The presence of MOEG side chain produces differences in
the solubility features of poly-1a–d that can be easily antici-
pated. For instance, the polymers bearing short side chains
are soluble in organic solvents, whereas the polymer bearing
a longer MOEG side chain (poly-1d) shows an amphiphilic
character similar to poly-MOEG-BF1b. However, poly-1d is
more readily soluble in the organic solvents and interacts
with water to give a physical hydrogel, which is rapidly bro-
ken by ultrasounds. In conclusion, poly-1d appears to be
less liable to aggregation with respect to poly-MOEG-BF1b,
and can be dissolved in water by ultrasound exposure. The
macromolecular structure of the water-soluble polymer poly-
1d has been studied by TEM, which could visualize isolated
macromolecules of this amphiphilic polymer. TEM analysis
showed that poly-1d, by virtue of its flexibility, behaves as a
typical cylindrical molecular brush capable of adopting dif-
ferent conformations ranging from the extended worm-like
to the globular one.
General Procedure for the Synthesis of Indenone
Derivatives 2b–d
A mixture of indenone 2e in DMF (10 mL/mmol) with
K2CO3 (2.5 equivalents) and NaI (0.2 equivalents) was
stirred at room temperature for 15 min, and then a solution
of the appropriate MOEG bromide (5b–d, 1.0 equivalent) in
DMF (5.0 mL/mol) was added. After stirring at room tem-
perature for 72 h, the reaction mixture was diluted with a
saturated NH4Cl solution and extracted with ethyl acetate.
The organic layer was dried over sodium sulfate and evapo-
rated under reduced pressure. Purification of the residue by
flash chromatography with the appropriate eluent gave the
expected indenone derivative (2b–d).
As cylindrical brushes may find micromechanical (e.g., as
miniature cushions, pistons, and electrical contacts in ultra-
small pumps) and biological applications (i.e., in drug deliv-
ery and diagnostic development) poly-1d can be considered
a promising polymer capable of generating single water-solu-
ble macromolecules of well-defined shapes and dimensions.
Ethyl 6-[2-(2-methoxyethoxy)ethoxy]-1-oxo-3-phenyl-1H-in-
dene-2-carboxylate (2b)
This compound was obtained from indenone 2e (0.94 g, 3.2
mmol) and purified by flash chromatography with petroleum
ether-ethyl acetate (1:1) as the eluent to give 2b as a red oil
(0.52 g, yield 41%). 1H NMR (200 MHz, CDCl3): 1.14 (t, J ¼
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ARTICLE
7.2 3H), 3.38 (s, 3H), 3.56 (m, 2H), 3.70 (m, 2H), 3.85 (t, J ¼
4.5, 2H), 4.16 (m, 4H), 6.85 (m, 1H), 7.05 (d, J ¼ 8.0, 1H),
7.17 (d, J ¼ 2.0, 1H), 7.49 (s, 5H). MS(ESI): m/z 419 (M þ
Naþ).
Ethyl 1-hydroxy-6-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]-
1-methyl-3-phenyl-1H-indene-2-carboxylate (3c)
This compound was obtained from indenone 2c (0.80 g, 1.8
mmol) and purified by flash chromatography with petroleum
ether-ethyl acetate (1:1) as the eluent to give 3c as a pale
yellow oil (0.60 g, yield 73%). 1H NMR (200 MHz, CDCl3):
1.03 (t, J ¼ 6.9, 3H), 1.74 (s, 3H), 3.36 (s, 3H), 3.53 (m, 2H),
3.62–3.76 (m, 7H), 3.85 (t, J ¼ 5.1, 2H), 4.04-4.18 (m, 4H),
6.80 (m, 1H), 7.03 (d, J ¼ 8.1, 1H), 7.14 (d, J ¼ 1.9, 1H), 7.38
(m, 5H). MS(ESI): m/z 479 (M þ Naþ).
Ethyl 6-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]-1-oxo-3-
phenyl-1H-indene-2-carboxylate (2c)
This compound was obtained from indenone 2e (0.56 g, 1.9
mmol) and purified by flash chromatography with petroleum
ether-ethyl acetate (1:1) as the eluent to give 2c as a red oil
(0.55 g, yield 66%). 1H NMR (200 MHz, CDCl3): 1.13 (t, J ¼
7.2, 3H), 3.36 (s, 3H), 3.53 (m, 2H), 3.61–3.75 (m, 6H), 3.84
(t, J ¼ 4.7, 2H), 4.16 (m, 4H), 6.83 (m, 1H), 7.05 (d, J ¼ 7.9,
1H), 7.17 (d, J ¼ 2.7, 1H), 7.49 (s, 5H). MS(ESI): m/z 463 (M
þ Naþ).
Ethyl 1-hydroxy-1-methyl-6-(2,5,8,11,14,17,20,23,26-
nonaoxaoctacosan-28-yloxy)-3-phenyl-1H-indene-2-
carboxylate (3d)
This compound was obtained from indenone 2d (0.29 g,
0.41 mmol) and purified by flash chromatography with pe-
troleum ethyl acetate-methanol (9:1) as the eluent to give
3d as a pale yellow oil (0.22 g, yield 74%). 1H NMR (200
MHz, CDCl3): 0.99 (t, J ¼ 7.2, 3H), 1.71 (s, 3H), 3.32 (s, 3H),
3.49 (m, 2H), 3.57–3.70 (m, 31H), 3.82 (t, J ¼ 4.2, 2H), 4.01–
4.17 (m, 4H), 6.78 (m, 1H), 7.00 (d, J ¼ 8.0, 1H), 7.11 (d, J ¼
2.0, 1H), 7.36 (m, 5H). MS(ESI): m/z 743 (M þ Naþ).
Ethyl 6-(2,5,8,11,14,17,20,23,26-nonaoxaoctacosan-28-
yloxy)-1-oxo-3-phenyl-1H-indene-2-carboxylate (2d)
This compound was obtained from indenone 2e (0.25 g,
0.85 mmol) and purified by flash chromatography with ethyl
acetate-methanol (9:1) as the eluent to give 2d as a red oil
(0.34 g, yield 57%). 1H NMR (200 MHz, CDCl3): 1.04 (t, J ¼
7.3, 3H), 3.27 (s, 3H), 3.41–3.68 (m, 32H), 3.76 (t, J ¼ 4.6,
2H), 4.16 (m, 4H), 6.82 (m, 1H), 7.05 (d, J ¼ 7.9, 1H), 7.16
(d, J ¼ 2.0, 1H), 7.49 (m, 5H), MS(ESI): m/z 727 (MþNaþ).
General Procedure for the Preparation of Solutions
of Benzofulvene Macromonomers 1a–d in Chloroform
or CDCl3
General Procedure for the Synthesis of Indenol
Derivatives 3a–d
A mixture of the appropriate indenol derivative (3a–d) in
chloroform or CDCl3 (10 mL/1 mmol of indenol) with a cata-
lytic amount of p-toluenesulfonic acid monohydrate (PTSA)
(0.2 equivalents) was heated under reflux for 1 h and cooled
to room temperature. The reaction mixture was washed with
a saturated solution of NaHCO3 and dried over sodium sul-
fate to afford a stock (about 0.1M) solution of the corre-
sponding monomer (3a–d), which was stored under an ar-
gon atmosphere.
To a mixture of the appropriate indenone derivative (2a–d)
in dichloromethane (10 mL/1.0 mmol of indenone) a solu-
tion (2M in THF) of Al(CH3)3, (2.5 equivalents) was added
and the resulting mixture was stirred under nitrogen for 30
min. The Al(CH3)3 excess was cautiously decomposed with a
30% NaOH solution until the gas evolution ceased. The mix-
ture was filtered and the filtrate was dried over sodium sul-
fate and evaporated under reduced pressure. Purification of
the residue by flash chromatography with the appropriate
eluent gave the corresponding indenol derivative (3a–d).
Ethyl 6-methoxy-1-methylene-3-phenyl-1H-indene-2-
carboxylate (1a)
This monomer was prepared from indenol 3a (0.10 g, 0.31
Ethyl 1-hydroxy-6-methoxy-1-methyl-3-phenyl-1H-indene-
2-carboxylate (3a)
1
mmol). H NMR (200 MHz, CDCl3): 1.03 (t, J ¼ 7.3, 3H) 3.86
(s, 3H), 4.10 (q, J ¼ 7.0, 2H), 6.32 (s,1H), 6.60 (s, 1H), 6.81
(m, 1H), 7.10 (d, J ¼ 8.2, 1H), 7.25 (d, J ¼ 2.5, 1H), 7.40 (m,
5H). MS(ESI): m/z 329 (M þ Naþ).
This compound was obtained from indenone 2a18 (0.40 g,
1.3 mmol) and purified by flash chromatography with
dichloromethane-ethyl acetate (95:5) as the eluent to give 3a
1
ꢀ
as a white solid (0.28 g, yield 66%, mp 88.5–89 C). H NMR
(200 MHz, CDCl3): 1.04 (t, J ¼ 7.0, 3H), 1.76 (s, 3H), 3.69
(br, 1H), 3.86 (s, 3H), 4.10 (m, 2H), 6.79 (m, 1H), 7.05 (d, J
¼ 8.6, 1H), 7.14 (d, J ¼ 2.0, 1H), 7.37 (m, 5H). MS(ESI): m/z
347 (M þ Naþ).
Ethyl 6-[2-(2-methoxyethoxy)ethoxy]-1-methylene-3-
phenyl-1H-indene-2-carboxylate (1b)
This monomer was prepared from indenol 3b (0.39 g, 0.95
1
mmol). H NMR (400 MHz, CDCl3): 1.07 (t, J ¼ 7.1, 3H), 3.42
(s, 3H), 3.61 (m, 2H), 3.76 (m, 2H), 3.91 (t, J ¼ 4.7, 2H), 4.14
(q, J ¼ 7.1, 2H), 4.24 (t, J ¼ 5.0, 2H), 6.34 (s,1H), 6.63 (s,
1H), 6.85 (m, 1H), 7.12 (d, J ¼ 8.4, 1H), 7.30 (d, J ¼ 2.1, 1H),
7.43 (m, 5H). MS(ESI): m/z 417 (M þ Naþ).
Ethyl 1-hydroxy-6-[2-(2-methoxyethoxy)ethoxy]-1-methyl-
3-phenyl-1H-indene-2-carboxylate (3b)
This compound was obtained from indenone 2b (0.52 g, 1.3
mmol) and purified by flash chromatography with petroleum
ether-ethyl acetate (1:1) as the eluent to give 3b as a pale
yellow oil (0.44 g, yield 82%). 1H NMR (200 MHz, CDCl3):
1.03 (t, J ¼ 7.0, 3H), 1.73 (s, 3H), 3.37 (s, 3H), 3.55 (m, 3H),
3.69 (m, 2H), 3.85 (t, J ¼ 4.7, 2H), 4.03–4.21 (m, 4H), 6.80
(m, 1H), 7.03 (d, J ¼ 8.6, 1H), 7.14 (d, J ¼ 2.1, 1H), 7.38 (m,
5H). MS(ESI): m/z 435 (M þ Naþ).
Ethyl 6-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]-1-methyl-
ene-3-phenyl-1H-indene-2-carboxylate (1c)
This monomer was prepared from indenol 3c (0.46 g, 1.0
1
mmol). H NMR (400 MHz, CDCl3): 1.07 (t, J ¼ 7.1, 3H), 3.40
(s, 3H), 3.57 (m, 2H), 3.67–3.72 (m, 4H), 3.78 (m, 2H), 3.91
(t, J ¼ 4.7, 2H), 4.14 (q, J ¼ 7.1, 2H), 4.23 (t, J ¼ 5.0, 2H),
6.35 (s, 1H), 6.63 (s,1H), 6.86 (m, 1H), 7.13 (d, J ¼ 8.4, 1H),
DENSELY GRAFTED p-STACKED POLYMERS, CAPPELLI ET AL.
2459

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
7.31 (d, J ¼ 2.2, 1H), 7.43 (m, 5H). MS(ESI): m/z 461 (M þ
SEC-MALS
Naþ).
The MWD characterization of poly-BF1 samples was per-
formed by a MALS light scattering photometer on-line to a SEC
chromatographic system. The SEC-MALS system and the corre-
sponding experimental conditions were identical to those used
in our previous study13,14,17 and are not reported in detail here.
Ethyl 1-methylene-6-(2,5,8,11,14,17,20,23,26-nonaoxaocta-
cosan-28-yloxy)-3-phenyl-1H-indene-2-carboxylate (1d)
This monomer was prepared from indenol 3d (0.20 g, 0.28
1
mmol). H NMR (400 MHz, CDCl3): 1.03 (t, J ¼ 7.1, 3H), 3.36
Mass Spectrometry
(s, 3H), 3.53 (m, 2H), 3.60–3.67 (m, 28H), 3.72 (m, 2H), 3.86
(t, J ¼ 4.7, 2H), 4.09 (q, J ¼ 7.1, 2H), 4.19 (t, J ¼ 5.0, 2H),
6.31 (s, 1H), 6.58 (s, 1H), 6.82 (m, 1H), 7.08 (d, J ¼ 8.4, 1H),
7.27 (d, J ¼ 2.2, 1H), 7.39 (m, 5H). MS(ESI): m/z 725 (M þ
Naþ).
MALDI-TOF mass spectra of four polymers: poly-1a–d, were
recorded in linear mode, using a Voyager-DE STR (Perseptive
Biosystem) mass spectrometer, equipped with a nitrogen
laser emitting at 337 nm, with a 3 ns pulse width, and work-
ing in positive ion mode. The accelerating voltage was 25 KV,
the grid voltage and delay time (delayed extraction, time lag)
were optimized for each sample to achieve the higher mass
resolution, expressed as the molar mass of a given ion divided
by the full width at half maximum. For all spectra, a mass re-
solution of about 1000–1500 Da was obtained. The laser irra-
diance was maintained slightly above the threshold. HABA
0.1M in THF solvent, was used as matrix. Typically, 0.5 lL of a
CHCl3 solution of polymer (5 mg/mL) was mixed with 0.5 or
1.5 lL of a matrix solution, and then spotted on the MALDI
sample holder and slowly dried to allow matrix crystalliza-
tion. The better spectra were recorded by means of a (matrix
solution)/(polymer solution) ratio of 3/1. The mass peaks
corresponding to the macromolecular species were measured
with an accuracy of 60.4 g/mol. The spectra were calibrated
using external calibration file made by MALDI analysis of a
Ny6 sample terminated with only amino groups and having a
Mn of about 6000 g/mol, appropriately synthesized.
General Procedure for the Preparation of
Poly-Benzofulvene Derivatives Poly-1a–d by
Spontaneous Polymerization
The solution of the appropriate benzofulvene monomer (1a–
d) in chloroform was concentrated under reduced pressure
to give a viscous oil, which was dissolved in chloroform (10
mL/mmol of monomer) and newly evaporated (the dissolu-
tion/evaporation procedure was repeated three times). The
final residue was purified by washing with the appropriate
solvents and dried under reduced pressure to obtain the
expected polymers (poly-1a–d).
Poly(ethyl 6-methoxy-1-methylene-3-phenyl-1H-indene-2-
carboxylate) (Poly-1a)
This polymer was prepared from monomer 1a and purified
by precipitation from a solution in ethyl acetate with ethanol
and obtained as a white solid (yield 84%). 1H NMR (200
MHz, CDCl3): 0.3–1.2 (br m, 3H), 2.5–4.4 (br m, 7H), 5.8–7.6
(br m, 8H). 13C NMR (100 MHz, CDCL3): 13.4, 48.5, 54.7,
57.1, 58.6, 111.0, 113.5, 122.8, 126.2, 130.1, 132.8, 135.3,
150.2, 150.9, 158.6, 163.8.
Differential Scanning Calorimetry
DSC scans were carried out on a Perkin Elmer Pyris 1
instrument calibrated with an indium standard. The sample,
about 3 mg, was placed in a sealed aluminum pan and the
measurements were carried out using a heating rate of 20
ꢀC/min over a temperature range of 40–280 C.
ꢀ
Poly[ethyl 6-[2-(2-methoxyethoxy)ethoxy]-1-methylene-3-
phenyl-1H-indene-2-carboxylate] (Poly-1b)
Thermogravimetric Analysis
TGA was performed on a Perkin-Elmer TGA-7 instrument
with platinum pan with about 2 mg of polymer as probe.
The sample was heated at 10 C/min in nitrogen atmosphere
under a flow rate of 50 mL/min. TGA and DTG curves were
This polymer was prepared from monomer 1b and purified
by precipitation from a dichloromethane solution with petro-
1
leum ether to obtain an off-white solid (yield 53%). H NMR
ꢀ
(400 MHz, CDCl3): 0.3–1.0 (br m, 3H), 3.3 (br s, 3H), 3.4–4.4
(br m, 12H), 5.7–7.7 (br m, 8H).
ꢀ
recorded from 50 to 600 C.
Transmission Electron Microscopy
Poly[ethyl 6-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]-1-
methylene-3-phenyl-1H-indene-2-carboxylate] (Poly-1c)
This polymer was prepared from monomer 1c and purified
by precipitation from a dichloromethane solution with petro-
A drop of poly-1d solution in water was placed onto a 300
mesh formvar-coated copper grid, negatively stained with
1.5% uranyl acetate, and observed in a Philips CM10 transmis-
sion electron microscopy at an acceleration voltage of 80 kV.
1
leum ether to obtain a colorless glassy solid (yield 81%). H
NMR (400 MHz, CDCl3): 0.2–1.0 (br m, 3H), 3.3 (br s, 3H),
3.4–4.4 (br m, 16H), 5.6–7.7 (br m, 8H).
The authors thank Italian MUR (Ministero dell’Universita` e
della Ricerca) for financial support. Stefania D’Agata D’Ottavi’s
careful reading of the manuscript and Roberto Beretta’s and
Giulio Zannoni’s technical assistance are also acknowledged.
Poly[ethyl 1-methylene-6-(2,5,8,11,14,17,20,23,26-nonaox-
aoctacosan-28-yloxy)-3-phenyl-1H-indene-2-carboxylate]
(Poly-1d)
This polymer was prepared from monomer 1d and purified
by washing with diethyl ether to obtain a colorless sticky
solid. H NMR (400 MHz, CDCl3): 0.2–1.0 (br m, 3H), 3.3 (br
REFERENCES AND NOTES
1
1 Kiani, C.; Chen, L.; Wu, Y. J.; Yee, A. J.; Yang, B. B. Cell Res
s, 3H), 3.4–4.4 (br m, 40H), 5.6–7.8 (br m, 8H).
2002, 12, 19–32.
2460
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
2 Hardingham, T. E.; Fosang, A. J.; Dudhia, J. Eur J Clin Chem
15 Cappelli, A.; Galeazzi, S.; Giuliani, G.; Anzini, M.; Aggravi,
M.; Donati, A.; Zetta, L.; Boccia, A. C.; Mendichi, R.; Giorgi, G.;
Paccagnini, E.; Vomero, S. Macromolecules 2008, 41,
2324–2334.
Clin Biochem 1994, 32, 249–257.
3 Sheiko, S. S.; Sumerlin, B. S.; Matyjaszewski, K. Prog Polym
Sci 2008, 33, 759–785.
16 Cappelli, A.; Galeazzi, S.; Giuliani, G.; Anzini, M.; Donati, A.;
Zetta, L.; Mendichi, R.; Aggravi, M.; Giorgi, G.; Paccagnini, E.;
Vomero, S. Macromolecules 2007, 40, 3005–3014.
4 PEG is an amphiphilic polymer largely used as a shielding
agent for bioactive compounds and drug carriers such as lipo-
somes and nanoparticles. PEG is indeed capable of conferring
solubility in the physiological environment and preventing the
interaction with plasma proteins and cells.
17 Cappelli, A.; Galeazzi, S.; Giuliani, G.; Anzini, M.; Grassi, M.;
Lapasin, R.; Grassi, G.; Farra, R.; Dapas, B.; Aggravi, M.; Donati,
A.; Zetta, L.; Boccia, A. C.; Bertini, F.; Samperi, F.; Vomero, S.
Macromolecules 2009, 42, 2368–2378.
5 Lutz, J.-F.; Andrieu, J.; Uzgiin, S.; Rudolph, C.; Agarwal, S.
Macromolecules 2007, 40, 8540–8543.
18 Ahn, J. H.; Shin, M. S.; Jung, S. H.; Kang, S. K.; Kim, K. R.;
Rhee, S. D.; Jung, W. H.; Yang, S. D.; Kim, S. J.; Woo, J. R.;
Lee, J. H.; Cheon, H. G.; Kim, S. S. J Med Chem 2006, 49,
4781–4784.
6 Lutz, J.-F.; Hoth, A. Macromolecules 2006, 39, 893–896.
7 Oh, J. K.; Min, K.; Matyjaszewski, K. Macromolecules 2006,
39, 3161–3167.
8 Tao, L.; Mantovani, G.; Lecolley, F.; Haddleton, D. M. J Am
19 Brockmann, T. W.; Tour, J. J Am Chem Soc 1995, 117,
Chem Soc 2004, 126, 13220–13221.
4437–4447.
9 Ishizone, T.; Seki, A.; Hagiwara, M.; Han, S.; Yokoyama, H.;
Oyane, A.; Deffieux, A.; Carlotti, S. Macromolecules 2008, 41,
2963–2967.
20 Pattanaargson, S.; Hongchinnagorn, N.; Hirunsupachot, P.;
Sritana-anant, Y. Photochem Photobiol 2004, 80, 322–325.
21 Nakano, T.; Yade, T.
J Am Chem Soc 2003, 125,
10 Wang, X.-S., Armes, S. P. Macromolecules 2000, 33,
15474–15484.
6640–6647.
22 Londergan, T.; Teng, C. J.; Weber, W. P. Macromolecules
11 Wang, X.-S.; Lascelles, S. F.; Jackson, R. A.; Armes, S. P.
1999, 32, 1111–1114.
Chem Commun 1999, 1817–1818.
23 Montaudo, G., Montaudo, M. S., Samperi, F. In Mass Spec-
trometry of Polymers; Montaudo, G.; Lattimer, R. P., Eds.; CRC
Press: Boca Raton, 2002; Chapters 2 and 10.
12 Zhang, M.; Muller, A. H. E. J Polym Sci Part A: Polym Chem
¨
2005, 43, 3461–3481.
13 Cappelli, A.; Pericot Mohr, G.; Anzini, M.; Vomero, S.; Don-
ati, A.; Casolaro, M.; Mendichi, R.; Giorgi, G.; Makovec, F. J
Org Chem 2003, 68, 9473–9476.
24 Montaudo, G.; Montaudo, M. S.; Samperi, F. Progr Polym
Sci 2006, 31, 277–357.
25 Vauthier, C.; Dubernet, C.; Fattal, E.; Pinto-Alphandary, H.;
14 Cappelli, A.; Anzini, M.; Vomero, S.; Donati, A.; Zetta, L.;
Mendichi, R.; Casolaro, M.; Lupetti, P.; Salvatici, P.; Giorgi, G.
J Polym Sci Part A: Polym Chem 2005, 43, 3289–3304.
Couvreur, P. Adv Drug Delivery Rev 2003, 55, 519–548.
26 Pepper, D. C. J Polym Sci Polym Symp 1978, 62, 65–77.
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