Nonmonotonic dependence of intramolecular charge-transfer sidechain interactions for triazole containing phenylene-ethynylene grafted Co-Polyoxetane brushes

Article abstract of DOI:10.1016/j.polymer.2021.123569

This research explores effects of introduction of the rigid phenylene ethynylene (PEy) moiety as a side chain in polyoxetanes. The synthesis of PEy-grafted polyoxetanes was carried out via Huisgen copper (I) catalyzed alkyne-azide cycloaddition. These polymers have a flexible main chain (low T_g polyoxetane) and rigid side chains (phenylene ethynylene). Compositions for copolyoxetanes with PEy and alkynyl side chains were determined by ¹H-NMR spectroscopy. Mole percents PEy, designated P-%, were P-21, P-44, P-69 and P-100. UV-VIS spectra for P-21, P-44, P-69, P-100 at 330 nm showed differentiation based on assignments to intramolecular charge-transfer (ICT) interactions between triazole and phenylene ethylene moieties. Interestingly, instead of a monotonic increase, absorption intensity is in the order P-69 ~ P-44 > P-100 > P-21. Low substitution and mainchain flexibility and account for P-21 having the lowest UV-VIS absorption at 330 nm. P-44 and P-69 have similar strong absorptions at 330 nm with overlapping curves. Steric effects culminate in P-100, which has the highest PEy content but a lower absorption at 330 nm than P-69 but higher than P-21. A model for optical absorptions for PEy copolyoxetanes is described that includes the effect of the rigid PEy side chain in decreasing molecular mobility.

Full text of DOI:10.1016/j.polymer.2021.123569

Polymer 219 (2021) 123569
Contents lists available at ScienceDirect
Polymer
journal homepage: http://www.elsevier.com/locate/polymer
Nonmonotonic dependence of intramolecular charge-transfer sidechain
interactions for triazole containing phenylene-ethynylene grafted
Co-Polyoxetane brushes
a
,
b
a
b
b,*
Masayuki Gon , Yoshiki Chujo , Olga Zolotarskaya , Kenneth J. Wynne
a
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto, 615-8510, Japan
Chemical and Life Science Engineering, Virginia Commonwealth University, 601 West Main Street, Richmond, VA, 23284, USA
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
This research explores effects of introduction of the rigid phenylene ethynylene (PEy) moiety as a side chain in
polyoxetanes. The synthesis of PEy-grafted polyoxetanes was carried out via Huisgen copper (I) catalyzed alkyne-
Brush polymer
Sidechain photoabsorption
Polyoxetanes
azide cycloaddition. These polymers have a flexible main chain (low T
g
polyoxetane) and rigid side chains
(
phenylene ethynylene). Compositions for copolyoxetanes with PEy and alkynyl side chains were determined by
1
H-NMR spectroscopy. Mole percents PEy, designated P-%, were P-21, P-44, P-69 and P-100. UV-VIS spectra for
P-21, P-44, P-69, P-100 at 330 nm showed differentiation based on assignments to intramolecular charge-transfer
ICT) interactions between triazole and phenylene ethylene moieties. Interestingly, instead of a monotonic in-
(
crease, absorption intensity is in the order P-69 ~ P-44 > P-100 > P-21. Low substitution and mainchain flex-
ibility and account for P-21 having the lowest UV-VIS absorption at 330 nm. P-44 and P-69 have similar strong
absorptions at 330 nm with overlapping curves. Steric effects culminate in P-100, which has the highest PEy
content but a lower absorption at 330 nm than P-69 but higher than P-21. A model for optical absorptions for PEy
copolyoxetanes is described that includes the effect of the rigid PEy side chain in decreasing molecular mobility.
1
2
1
. Introduction
units with quaternary (R ) and PEG-like side chains (R ) are water sol-
uble and have amphiphilicity that mimics antimicrobial peptides
(AMPS) with good human cell compatibility [19,20]. Recently, a
‘clickable’ and modular polyoxetane polymer platform was prepared
consisting of acetylene-functionalized 3-ethyl-3-(hydroxymethyl)oxe-
tane (EAMO) repeat units. This polyoxetane was conjugated with
Polyoxetanes 1 have been prepared with a wide range of properties
that are determined by side chains at the 3-position [1–7]. Introduction
of side chain mesogens results in liquid crystalline polyoxetanes [2,
7
–12] while semicrystalline polyoxetanes are obtained with two iden-
′
tical side chains such as poly(3,3-diethyloxetane) and poly(3,
camptothecin, a topoisomerase I inhibitor, via a 3,3 -dithiodipropionic
3
-dimethyloxetane) [13–15]. Semicrystalline polyoxetanes are also
acid (DDPA) linker with a disulfide bond (S-S) extended by short-chain
polyethylene glycol (PEG) to generate a polymer drug for glioblastoma
multiforme therapy [21].
found if one of the pendant groups is capable of hydrogen bonding [4].
1
Low molar mass polyoxetane diols 1 with methyl (R ) and fluorous
2
(
R ) groups have atactic chain structures and low T
g
’s. These viscous
liquids can be employed as soft blocks for functional polyurethanes
22–24].
The present work explores introduction of triazole-linked rigid
phenylene ethynylene (PEy) moieties as side chains in polyoxetanes.
With a structure having benzene rings and -conjugation, PEy exhibits
[
Cationic ring-opening polymerization (ROP) has been used to pre-
pare copolyoxetanes with a random distribution of comonomers [16,
1
7]. Unexpectedly, with a combination of fluorous and PEG-like co-
π
monomers, random or blocky copolyoxetanes were obtained depending
interesting optical properties and is the subject for research in photonic
on the order of monomer addition [18]. Copolyoxetanes 1 having repeat
materials [25–34]. Herein, we report PEy-grafted polyoxetanes
*
Corresponding author.
E-mail address: kjwynne@vcu.edu (K.J. Wynne).
https://doi.org/10.1016/j.polymer.2021.123569
Received 13 November 2020; Received in revised form 15 February 2021; Accepted 18 February 2021
Available online 22 February 2021
0
032-3861/© 2021 Elsevier Ltd. All rights reserved.

M. Gon et al.
Polymer 219 (2021) 123569
synthesized via Huisgen copper (I) catalyzed alkyne-azide cycloaddition
3.31 (s, 2H), 4.49 (br, 2H), 5.45 (s, 2H), 7.18 (s, 2H), 7.29 (s, 3H), 7.46
(br, 5H) ppm. Scheme 3 summarizes conditions and percent yields.
Experimental details for preparation of P[(EAMO)(PEy)] copolymers are
presented in Table S1.
Instrumentation. 1H NMR spectra were recorded on either Varian
Mercury-300 MHz or Bruker AVANCEIII 600 MHz instruments. ATR-IR
spectra were obtained on a Nicolet Magna-IR 760 spectrometer by drop-
casting on KBr pellets. Drop-casting on quartz substrates was used for
Raman spectroscopy (Hariba LabRam HR Evolution; Lab Spec 6.2, 2014
software).
[
g
35,36]. These brush polymers have a flexible main chain (low T pol-
yoxetane) and rigid side chains (phenylene ethynylene). The efficiency
of click-coupling led to copolyoxetanes with molar ratios of PEy to
1
alkynyl side chains by H NMR that were close to reactant ratios. UV-VIS
spectra were obtained, and unexpected optical properties were eluci-
dated by molecular modeling and a study of thermal transitions by DSC.
2
. Experimental section
Materials. 4-Iodobenzyl alcohol, phenylacetylene, bis(triphenyl-
Gel permeation chromatography (GPC) was performed using a Vis-
cotek GPC system equipped with a TriSEC triple detector. THF was the
mobile phase with a flow rate of 1 mL/min. Universal calibration by
polystyrene standards was used for determination of molar mass and
polydispersity. Differential scanning calorimetry was performed on a
TA-Q 1000 Series instrument (TA Instruments) with a heating rate of
phosphine) palladium(II) chloride, triphenylphosphine, copper(I) iodide
CuI), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,1,4,7,7-pentame-
thyldiethylenetriamine (PMDTA), and organic solvents were pur-
chased from Acros Organics. Triethylamine (Et N), diphenylphosphoryl
(
3
azide (DPPA) and propargyl bromide (80% in toluene) were obtained
from TCI America. Sodium hydride 60% dispersion in mineral oil, boron
◦
◦
10 C/min and a cooling rate of 5 C/min over the temperature range
◦
trifluoride diethyl etherate (BF
3
⋅xEt
2
O), 1,4-butanediol, and silica gel
ꢀ 90 to 100 C. Second scans are reported.
(
pore size 60 Å, 70–230 mesh) were from Aldrich. 3-Ethyl-3-hydroxyme-
UV-VIS spectroscopy. UV-VIS spectra were obtained with a Perki-
nElmer Lambda 40 UV–Vis spectrophotometer. At an M1 concentration
thyloxetane (EHMO) was a generous gift from Perstorp Polyols (Toledo,
OH). (4-(Phenylethynyl)phenyl)methanol 3 was synthesized following
the previously published procedure [37]. EAMO was prepared according
to M. Jia’s method [38]. Polymerization of EAMO was described by
Zolotarskaya [39].
ꢀ 5
1.0 × 10 M in CHCl
length of 10 mm (Figure S2). Molar absorptivity (
timate for the prepared polymers. Consequently, polymer solutions in
CHCl were prepared with absorbances close to M1 and normalized as
3
the peak absorbance was 0.4 with a cell path
ε) was difficult to es-
3
Synthesis of 1-(azidomethyl)-4-(phenylethynyl)benzene (4).
THF (10 mL) and 3 (321 mg, 1.50 mmol) were placed in round-bottom
flask equipped with magnetic stirring bar. DBU and DPPA were added to
shown in Figure S2 to obtain data shown in Fig. 3.
Polymer films were obtained by drop-casting dilute solutions on a
quartz substrate at ambient temperature. The same preparation method
was used for all samples to obtain data for elucidating differences. Peak
absorbances at ~280 nm were normalized to 1.0 (Figure S3) to obtain
the data shown in Fig. 5.
the mixture under N
for 24 h with stirring. Subsequently, the mixture was quenched by
saturated, aqueous NH Cl and the organic layer extracted with CHCl
The organic layer was washed with brine and dried over MgSO . MgSO
was removed by filtration, and the solvent was evaporated. The residue
was purified by flash column chromatography on SiO (CHCl as an
eluent) to afford 4 (329 mg, 1.41 mmol, 94%) as light yellow crystals. R
2
. The reaction was carried out at room temperature
4
3
.
4
4
3. Results and discussion
2
3
f
Synthesis. With reference to Scheme 1, Sonogashira-Hagihara
coupling of 4-iodobenzyl alcohol 2 with phenylacetylene afforded
compound 3 in 75% yield. The hydroxy group was converted to azide
with DPPA and DBU giving compound 4 in 94% yield. EAMO [38] and P
(EAMO) [39] were synthesized by reported methods. Molar masses for P
1
=
0.84 (CHCl
.35, (m, 3H), 7.54 (m, 4H) ppm.
Synthesis of M1. EAMO (30.8 mg, 0.20 mmol), 4 (46.7 mg, 0.20
3 3
). H NMR (CDCl , 600 MHz) δ 4.36 (s, 2H), 7.31 (d, 2H),
7
mmol), CuI (3.8 mg, 0.02 mmol), PMDTA (34.7 mg, 0.20 mmol), and
THF (5 mL) were place in round-bottom flask equipped with magnetic
stirring bar. The reaction was carried out at room temperature for 20 h
with stirring. After the reaction, the mixture was quenched with 28%
n w
(EAMO) were obtained by GPC: M (4,600), M (11,600) giving a PDI of
2.5. Model compound M1 was obtained by click reaction of EAMO and 4
in 88% yield (Scheme 2). M1 was used for ATR-IR and UV-VIS spec-
troscopy as a reference. (Phenylene ethynylene)-grafted polyoxetanes
P-21, P-44, P-69, P-100 were synthesized by the reaction of 4 with the P
(EAMO) alkyne moiety in molar feed ratios of 25/100, 50/100, 75/100,
and 100/100 (Scheme 3). Polymerization was carried out under mild
conditions to avoid degradation of the polymer main chain. GPC proved
not suitable for characterization of copolymers because of decreased
solubility with increasing side-chain substitution. However, adequate
aqueous NH
layer was washed with brine and dried over MgSO
removed by filtration, and the solvent was evaporated. The residue was
purified by column chromatography on SiO (gradient: from CHCl to
hexane/EtOAc = 1/1 v/v and to EtOAc as an eluent) to afford M1 (68.4
mg, 0.177 mmol, 88%) as a colorless liquid (Scheme 2). R
3
and the organic layer extracted with CHCl
3
. The organic
4
. MgSO was
4
2
3
f
= 0.55
1
(
EtOAc). H NMR (CDCl , 600 MHz) δ 0.80 (t, 3H), 1.69 (q, 2H), 3.60 (s,
3
1
2
H), 4.33 (d, J = 5.8 Hz, 2H) 4.40 (d, J = 5.8 Hz, 2H), 4.65, (s, 2H), 5.51
solubility permitted H NMR spectroscopy, which was used to establish
(
s, 2H), 7.21 (d, 2H), 7.32 (m, 3H), 7.46 (s, 1H), 7.51 (m, 4H) ppm.
copolymer compositions. The 1H NMR peak at 4.1 ppm for the CH
2
Post-functionalization of P(EAMO). P(EMAO) was click grafted
group adjacent to the acetylene moiety is designated 5 (Fig. 1, S1). This
with 4 to make brush polymers. A solution containing P(EAMO) (0.20
peak is prominent for P-21 due to 79 mol% EAMO side chains. The peak
′
mmol of alkyne equivalent) in 5 mL of THF was prepared and addition of
at 5.5 ppm, designated 7 is assigned to the CH
2
group adjacent to the
4
was adjusted to achieve the following molar feed ratios of 4 to alkyne:
aromatic moiety (Fig. 1, S1). This peak is strong in the spectrum of P-100
while the peak at 4.1 ppm is not detected. The integral of peaks 7’ and 5
provided the mole ratio of (phenylethynyl)benzene to EAMO acetylene
side chains.
The 1H NMR spectrum for copolymers and P-100 have absorptions
for 5’ (4.5 ppm) that increase in intensity with increasing phenylene
ethynylene content (Figure S1). Compared to other copolymers, the
triplet-like absorption for P-44 is pronounced and likely reflects the
presence of segments with different tacticities. The disorder wrought by
different ways that phenylene ethynylene pendant groups are arranged
2
5/100, 50/100, 75/100, and 100/100. CuI (0.1 M amount of 4) was
added to the solution followed by addition of PMDTA (the same molar
amount as 4). The reaction mixture was stirred under N for 20 h at room
temperature. After the reaction, mixture was quenched by 28% aqueous
NH and the organic layer extracted with CHCl , washed with brine and
dried over MgSO . MgSO was removed by filtration, and the solvent
was evaporated. The residue was purified by column chromatography
on SiO (gradient: from hexane/CHCl as an eluent)
2
3
3
4
4
2
3
= 1/1 v/v to CHCl
3
to afford brush polymers P-#, where # indicates percentage of phenyl-
1
ene ethynylene brush units per polymer. According to H NMR analysis,
along the main chain likely accounts for the broad T
and is worthy of additional study.
g
’s observed by DSC
1
polymers P-21, P-44, P-69 and P-100 were obtained. H NMR is typified
by P-100 (CDCl
3
, 600 MHz): δ 0.72 (3H), 1.30 (br, 2H), 3.13 (br, 4H),
Vibrational Spectroscopy. ATR-IR spectra were obtained to
2

M. Gon et al.
Polymer 219 (2021) 123569
Scheme 1. Synthesis of 1-(azidomethyl)-4-(phenylethynyl)benzene.
UV-VIS spectra. UV-VIS spectroscopy was used to characterize
CHCl solutions of P-0 (P(EAMO)), P-21, P-44, P-69, P-100, and M1. The
spectra shown in Fig. 3 were obtained by normalization based on M1
Figure S2). UV-VIS spectroscopic data are collected in Tables S2-A, S2-B
and S2-C.
In solution, P-0 exhibits negligible absorption from 250 nm to 500
3
(
nm as the alkyne moiety does not absorb in this region (Figure S2). The
UV-VIS spectra of P-21, P-44, P-69, P-100, and M1 are similar to those
for polyethers with bulky aromatic side chains reported by Nakano et al.
[41] and related sidechain systems [42,43]. Strong absorptions from
Scheme 2. Synthesis of compound M1.
confirm the presence of functionality (Fig. 2A). Compound 4 had a
ꢀ 1
strong peak at 2094 cm assigned to azide. P(EAMO) had a weak peak
280 to 305 nm (Fig. 3A) are assigned to phenylene ethynylene
π
- *
π
ꢀ 1
ꢀ 1
at 2116 cm and a strong peak at 3290 cm assigned to stretching
transition bands, while weak absorptions at 330 nm (Fig. 3B) are
assigned to intramolecular charge transfer (ICT) bands arising from
proposed interactions between 1,2-diphenylethyne and triazole moi-
vibrations of terminal alkyne group (C≡C) and (C-H), respectively. M1
ꢀ 1
had a weak peak at 2218 cm that was identified as the stretching vi-
bration of internal alkyne group between phenylene units and there
eties. This assignment is supported by the observation that the
bands from 280 to 305 nm are not affected by the copolymer composi-
tion. If it were based on -stacking, all bands would increase in intensity
π
-
π*
ꢀ
1
ꢀ 1
were no peaks at 2094 cm and 2116 cm . In P-21, P-44, P-69, and P-
ꢀ 1
1
00, the peaks for terminal alkyne (3290 and 2116 cm ) gradually
π
ꢀ 1
decreased while the peaks for internal alkyne (2218 cm ) gradually
increased with increasing substitution. No peak was observed at 2094
with increasing substitution (hyperchromicity). Interestingly, instead of
a monotonic increase, the absorption intensity for PEy copolyoxetanes at
330 nm is in the order P-21 < P-100 < P-44 ~ P-69. The ratios of the
280/320 nm absorptions are: P-21, 36; P-44 and P-69, 17 and P-100, 23,
ꢀ
1
cm which confirmed reagent 4 was not left in the polymer.
ꢀ
1
Small peaks in the vicinity of 1700 cm were observed for all co-
ꢀ 1
polymers and P(EAMO). The absorption at 1700 cm for P-44 almost
reaches medium intensity. Such an absorption is characteristic of
carbonyl groups, but the usually weak absorptions for P(EAMO)) and
copolymers suggests that these absorptions originate from combination
ꢀ 1
bands arising from intense absorptions at ~900 cm . A detailed
investigation is outside the scope of the present investigation.
Raman spectra. To complement infrared spectroscopy, Raman
spectra were obtained for films cast on quartz substrates (Fig. 2B). In the
Raman spectra, the symmetric stretch of the internal alkyne group (Ph-
ꢀ 1
C≡C-Ph) is observed as a strong peak at 2218 cm for P-100, P-69 and
P-44 and as a weak peak for P-21. The corresponding mode is extremely
weak or not observed in the IR spectrum, which is consistent with the
symmetric stretch being associated with a change in polarizability
(
Raman) rather than dipole moment (IR) [40]. Absorptions for the ter-
ꢀ 1
minal alkyne group (C≡C, 2116 cm ) and terminal C-H (C-H, 3290
Fig. 1. Methylene groups are indicated for determination of co-monomer ratios
ꢀ
1
cm ) are not observed in the Raman spectra.
1
by H NMR spectroscopy.
Scheme 3. Synthesis of PEy copolymers from P(EAMO).
3

M. Gon et al.
Polymer 219 (2021) 123569
Fig. 2. A. ATR-IR spectra and B, Raman spectra of copolymers and P-0 (P(EAMO)).
Fig. 3. UV-VIS spectra in CHCl
3
solution. A. 250–400 nm with normalization at peak maxima; B. 300–360 nm.
P-21. Compared to vinyl dibenzofulvene (DBF)
reflecting the relative increase of the ICT band (to P-44), leveling off
π
-stacked oligomers
(
P-69) and decrease for P-100.
which have side chains occurring every other main chain atom [44],
only one of every four mainchain atoms in PEy copolyoxetanes can bear
a PEy side chain. Partial substitution for copolymers P-21, P-44 and P-69
further reduces the PEy side chain occurrence. Thus, it is interesting that
A schematic model for this finding is proposed in Fig. 4. Although
ICT interactions are driven enthalpically, chain flexibility, chain struc-
ture and low substitution result in a low probability for interactions for
Fig. 4. Proposed mechanism for changes in UV-VIS spectra for phenylene-ethynylene grafted co-polyoxetanes.
4

M. Gon et al.
Polymer 219 (2021) 123569
P-21 has a UV-VIS absorption at 330 nm at all, considering that the
frequency of PEy side chain occurrence could be as low as one for every
thermograms were obtained to investigate the effect of increasing PEy
◦
content on T
g
. P-0 has a sharply defined T
g
at ꢀ 35.3 C that is charac-
1
6 main chain atoms, depicted in Fig. 4A. This finding favors the pro-
teristic of a homopolymer. Increased substitution of the bulky PEy side
chain results in a predictable trend toward higher glass transition tem-
posed intramolecular charge transfer (ICT) bands.
◦
P-44 and P-69 have similar absorptions at 330 nm with overlapping
curves in Fig. 3B. The increased absorption for P-44 compared to P-21 is
ascribed to increased ICT interactions due to increased PEy content. This
argument fails to account for the equivalent absorption for P-69 at 330
nm compared to P-44. Rather, the onset of steric interactions and chain
stiffness is proposed to account for this equivalence. That is, enthalpi-
cally driven ICT interactions are mitigated by increased steric effects
driven by the bulky PEy side chain. Steric effects culminate in P-100,
which has the highest PEy content but a lower absorption at 330 nm
than P-69. Still, P-100 has a more intense absorption at 330 nm than P-
peratures that are in the range ꢀ 5 to 23 C. With increased PEy content
g
decreasing changes in heat capacities with increasing T are accompa-
nied by broader transitions (Fig. 6). The endotherm for P-44 is partic-
ularly broad; there may be a low temperature transition that would
require further work for confirmation. Given the relatively narrow range
of copolymer T
g
’s which are below or near the UV-VIS measurement
temperature it is unlikely that the trend in reduced molecular mobility
contributes to the unexpected decrease in the thin film absorption
attributed to ICT for P-100 at 320 nm.
Conclusion. EAMO [38] and P(EAMO) [39] were synthesized by
2
1, so higher PEy content favors ICT interactions despite unfavorable
steric effects.
Chem3D structures were obtained for additional insight into the
reported methods. Molar masses for P(EAMO) were obtained by GPC: M
(4,600), M (11,600) giving a PDI of 2.5. The reaction of 4 with the P
n
w
(EAMO) alkyne moiety by click chemistry resulted in efficient grafting of
phenylene ethynylene (PEy). Control of stoichiometry gave a series of
polyoxetanes designated P-21, P-44, P-69 and P-100 for percent PEy
relative order of UV-VIS absorptions. Figure S4 shows a representative
structure for a copolyoxetane 10-mer with alternating PEy and EAMO
side chains. Interestingly, several runs resulted in propinquity of PEy
moieties noted by green arrows. This orientation favoring intra-
molecular ICT interactions depicted in Fig. 4B was found in multiple
simulations. Figure S5 shows a representative Chem3D structure for a
polyoxetane homopolymer 10-mer with PEy side chains. Multiple sim-
ulations failed to show orientations of PEy moieties favoring ICT in-
teractions. Rather, aromatic PEy groups had orientations at odd angles
disfavoring interactions supporting the model shown in Fig. 4C. Thus,
modeling supports the non-intuitive higher UV-VIS absorptions attrib-
uted to intramolecular charge transfer (ICT) bands for P-44 and P-69
compared to P-100.
1
(Scheme 3). Copolymer compositions were established by H NMR
spectroscopy using unique peaks for the respective side chains. UV-VIS
spectroscopy revealed absorptions at 330 nm ascribed to side chain
triazole-phenylene ethynylene ICT interactions by analogy with work of
Nakano et al. on vinyl oligomers containing dibenzofulvene (DBF) side
chains (Fig. 3B) [41,42].
Surprisingly, instead of a monotonic increase following PEy content,
the absorption intensity at 330 nm is in the order P-21 < P-100 < P-44 ~
P-69. A model for this finding is based on steric effects that decrease
triazole-phenylene ethynylene interactions for fully substituted P-100
(Fig. 4). Molecular modeling (Chem3D) for a 50-50 copolymer showed
orientations favoring intramolecular interactions between 1,2-dipheny-
lethyne and triazole moieties in multiple simulations (Figures S3, 4B).
However, multiple simulations failed to show orientations of PEy moi-
eties favoring triazole-phenylene ethynylene interactions for a P-100
model. Rather, PEy groups had orientations at odd angles disfavoring
interactions as depicted in Fig. 4C. Thus, modeling supports the non-
intuitive higher UV-VIS absorptions for P-44 and P-69 compared to P-
100.
Spectra for films are shown in Fig. 5. The overall order P-21 < P-100
<
P-44 ~ P-69 is not changed. However, the relative intensities for PEy
copolyoxetanes P-69 and P-44 increase from ~0.06 in solution to ~0.11
in thin films (Tables S2 and S3). This doubling of intensity stands in
contrast to the decreased intensity for P-100 from 0.043 in solution to
~
0.034 in the thin film (Fig. 3, Tables S2 and S3).
The increased intensities for P-44 and P-69 in films indicates there is
a stronger contribution from intermolecular ICT interactions in the
condensed state compared to solutions (Tables S2 and S3). This is an
interesting result, but given the unknown tacticity of the copolymers we
can only speculate on the origin of this phenomenon. We note the un-
expectedly lower relative absorption for P-100 in the thin film compared
to solution (Tables S1, S2 and S3). This finding is attributed to steric
effects that are apparently amplified in the condensed state and act to
decrease ICT interactions. .
Absorbance intensity for thin films follows the same relative order
found in solution but the absorbance at 330 nm doubles for P-44 and P-
69. However, the absorbance intensity for P-100 is about 25% lower than
that found in solution (Table S2). The decrease in the UV-VIS absorption
at 330 nm for P-100 thin films correlates with intramolecular steric ef-
fects illustrated in Fig. 4C. Steric effects could well contribute to
decreased interactions between 1,2-diphenylethyne and triazole moi-
eties, but details remain to be investigated in future work. DSC for the
Differential Scanning Calorimetry. Independent of processing, P-
◦
0
, copolyoxetanes and P-100 form optically transparent films. DSC
copolyoxetanes and P-100 shows a relatively narrow 25 C range for
Fig. 5. UV-VIS spectra for copolymer films. A. 250–400 nm with normalization at 288 nm (maximum) and 360 nm (negligible absorbance); B. 300–360 nm; M1
spectrum was in dilute CHCl
3
.
5

M. Gon et al.
Polymer 219 (2021) 123569
Fig. 6. DSC thermograms and T
g
’s for PEy co-polyoxetanes; scan rate 10 ◦C/min.
[9] Y. Kawakami, Y. Kato, Polym. J. 29 (1997) 775.
T
g
’s, which are characterized by broad transitions with low changes in
heat capacity. From these data it seems unlikely that diminished
macromolecular mobility alone reduces chances for interactions be-
tween 1,2-diphenylethyne and triazole moieties.
[
[
10] S.J. Cowling, K.J. Toyne, J.W. Goodby, J. Mater. Chem. 11 (2001) 1590.
11] K.N. Kim, Y.W. Kwon, C.W. Jang, M.J. Kim, T.K. Lim, J.I. Jin, Liq. Cryst. 34 (2007)
5
35.
[12] L.C. Wu, C.C. Chen, C.H. Lin, Polymers 12 (2020).
[
[
13] E. Perez, M.A. Gomez, A. Bello, J.G. Fatou, Colloid Polym. Sci. 261 (1983) 571.
14] G.V.S. Henderson Jr., K.E. Hardenstine, C.J. Murphy, L.H. Sperling, G.E. Manser,
Polym. Mater. Sci. Eng. 53 (1985) 801.
Declaration of competing interest
[
[
[
[
15] Y. Zheng, K.J. Wynne, Polym. Mater.: Sci. Eng. Preprints (2007) 362.
16] H. Cheradame, J.-P. Andreolety, E. Rousset, Makromol. Chem. 192 (1991) 901.
17] T. Fujiwara, U. Makal, K.J. Wynne, Macromolecules 36 (2003) 9383.
18] T. Fujiwara, K.J. Wynne, Macromolecules 37 (2004) 8491.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[19] S. Chakrabarty, A. King, P. Kurt, W. Zhang, D.E. Ohman, L.F. Wood, C. Lovelace,
R. Rao, K. Wynne, J. Biomacromol. 12 (2011) 757.
[
20] A. King, S. Chakrabarty, W. Zhang, X. Zeng, D.E. Ohman, L.F. Wood, S. Abraham,
R. Rao, K. Wynne, J. Biomacromol. 15 (2014) 456.
Acknowledgements
[
21] J. Allen, J. Wang, O.Y. Zolotarskaya, A. Sule, S. Mohammad, S. Arslan, K.J. Wynne,
H. Yang, K. Valerie, J. Contr. Release 321 (2020) 36.
K.J.W. thanks the National Science Foundation, Division of Materials
Research, Polymers Program (DMR-1206259) and Biomaterials Pro-
gram (DMR-1608022) and the School of Engineering Foundation for
partial support of this research. MG thanks the Wynne group for their
help in conducting this research during his tenure as a visiting scholar at
VCU.
[
[
22] U. Makal, T. Fujiwara, R.S. Cooke, K.J. Wynne, Langmuir 21 (2005), 10749.
23] P. Kurt, L. Wood, D.E. Ohman, K.J. Wynne, Langmuir 23 (2007) 4719.
[24] S.S. Nair, E.J. McCullough, V.K. Yadavalli, K.J. Wynne, Langmuir 30 (2014),
12986.
[
[
[
[
[
[
[
25] J.D. Fox, S.J. Rowan, Macromolecules 42 (2009) 6823.
26] L. Jones, J.S. Schumm, J.M. Tour, J. Org. Chem. 62 (1997) 1388.
27] I.B. Kim, B. Erdogan, J.N. Wilson, U.H.F. Bunz, Chem. Eur. J. 10 (2004) 6247.
28] H. Li, D.R. Powell, R.K. Hayashi, R. West, Macromolecules 31 (1998) 52.
29] R.M. Meudtner, S. Hecht, Angew. Chem. Int. Ed. 47 (2008) 4926.
30] M.R. Pinto, K.S. Schanze, Synthesis-Stuttgart (2002) 1293.
31] T.M. Swager, Acc. Chem. Res. 41 (2008) 1181.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.polymer.2021.123569.
[32] C.Y. Tan, E. Alas, J.G. Muller, M.R. Pinto, V.D. Kleiman, K.S. Schanze, J. Am.
Chem. Soc. 126 (2004), 13685.
[
[
33] J.H. Wosnick, C.M. Mello, T.M. Swager, J. Am. Chem. Soc. 127 (2005) 3400.
34] S.M. Wu, M.T. Gonzalez, R. Huber, S. Grunder, M. Mayor, C. Schonenberger,
M. Calame, Nat. Nanotechnol. 3 (2008) 569.
References
[
[
[
[
[
[
[
35] H.C. Kolb, M.G. Finn, K.B. Sharpless, Angew. Chem. Int. Ed. 40 (2001) 2004.
36] M.G. Finn, H.C. Kolb, V.V. Fokin, K.B. Sharpless, Prog. Chem. 20 (2008) 1.
37] T. Schabel, C. Belger, B. Plietker, Org. Lett. 15 (2013) 2858.
38] M.C. Jia, A.L. Li, Y.B. Mu, W. Jiang, X.B. Wan, Polymer 55 (2014) 1160.
39] O.Y. Zolotarskaya, Q. Yuan, K.J. Wynne, H. Yang, Macromolecules 46 (2013) 63.
40] K. Hashimoto, V.R. Badarla, A. Kawai, T. Ideguchi, Nat. Commun. 10 (2019) 4411.
41] M. Merlani, Z. Song, Y. Wang, Y. Yuan, J. Luo, V. Barbakadze, B. Chankvetadze,
T. Nakano, Macromol. Chem. Phys. 220 (2019) 1900331.
[
[
[
[
1] M.A. Gomez, E.D.T. Atkins, C. Upstill, A. Bello, J.G. Fatou, Polymer 29 (1988) 224.
2] Y. Kawakami, K. Takahashi, H. Hibino, Macromolecules 24 (1991) 4531.
3] H. Desai, A.V. Cunliffe, M.J. Stewart, A.J. Amass, Polymer 34 (1993) 642.
4] J.M. Parris, R.H. Marchessault, E.J. Vandenberg, J.C. Mullis, J. Polym. Sci. B
Polym. Phys. 32 (1994) 749.
5] D. Takeuchi, Y. Watanabe, T. Aida, S. Inoue, Macromolecules 28 (1995) 651.
6] D. Takeuchi, T. Aida, Macromolecules 33 (2000) 4607.
7] Y.K. Yun, D.H. Ko, J.I. Jin, Y.S. Kang, W.C. Zin, B.W. Jo, Macromolecules 33 (2000)
[
[
[
[
[
[
42] T. Nakano, K. Takewaki, T. Yade, Y. Okamoto, J. Am. Chem. Soc. 123 (2001) 9182.
43] T. Nakano, Polym. J. 42 (2010) 103.
44] T. Nakano, T. Yade, J. Am. Chem. Soc. 125 (2003), 15474.
6
653.
[
8] Y.H. Lu, C.S. Hsu, Macromolecules 28 (1995) 1673.
6