Aromatic aldehyde functionalized polycaprolactone and polystyrene macromonomers: Synthesis, characterization and aldehyde-aminooxy click reaction

Article abstract of DOI:10.1016/j.reactfunctpolym.2012.06.020

New bis-aldehyde functionalized initiators, viz, 4,4′-(4,4′-(5- hydroxypentane-2,2-diyl)bis(4,1-phenylene))bis(oxy)dibenzaldehyde (1) and 4,4′-bis(4-(4-(formylphenoxy) phenyl) pentyl 2-bromopropanoate (2) were synthesized starting from commercially available 4,4′-bis(4-hydroxyphenyl) pentanoic acid. These initiators were utilized, respectively, for ring opening polymerization of -caprolactone and atom transfer radical polymerization of styrene. Well-defined polycaprolactone macromonomers (MnGPC: 2600-19400, PDI: 1.37-1.47) and polystyrene macromonomers (MnGPC: 2800-28200, PDI: 1.11-1.16) with bis-aldehyde functionality were synthesized. The kinetic study of styrene polymerization showed controlled polymerization behaviour. The presence of aldehyde functionality in macromonomers was confirmed by ¹H NMR spectroscopy. The reactivity of aldehyde functionality was demonstrated by carrying out aldehyde-aminooxy click reaction of polycaprolactone macromonomer with O-(2-azidoethyl) hydroxylamine which proceeded in a quantitative manner without backbone degradation.

Full text of DOI:10.1016/j.reactfunctpolym.2012.06.020

Reactive & Functional Polymers 72 (2012) 713–721
Contents lists available at SciVerse ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Aromatic aldehyde functionalized polycaprolactone and polystyrene
macromonomers: Synthesis, characterization and aldehyde–aminooxy click reaction
Prakash S. Sane, Bhausaheb V. Tawade, Dnyaneshwar V. Palaskar,
⇑
Shamal K. Menon, Prakash P. Wadgaonkar
Polymer Science and Engineering Division, National Chemical Laboratory, Pune 411 008, India
a r t i c l e i n f o
a b s t r a c t
New bis-aldehyde functionalized initiators, viz, 4,40-(4,40-(5-hydroxypentane-2,2-diyl)bis(4,1-pheny-
lene))bis(oxy)dibenzaldehyde (1) and 4,40-bis(4-(4-(formylphenoxy) phenyl) pentyl 2-bromopropanoate
(2) were synthesized starting from commercially available 4,40-bis(4-hydroxyphenyl) pentanoic acid.
Article history:
Received 12 December 2011
Received in revised form 5 May 2012
Accepted 30 June 2012
These initiators were utilized, respectively, for ring opening polymerization of
e-caprolactone and atom
Available online 6 July 2012
transfer radical polymerization of styrene. Well-defined polycaprolactone macromonomers (MnGPC
:
2600–19400, PDI: 1.37–1.47) and polystyrene macromonomers (MGnPC: 2800–28200, PDI: 1.11–1.16) with
bis-aldehyde functionality were synthesized. The kinetic study of styrene polymerization showed
controlled polymerization behaviour. The presence of aldehyde functionality in macromonomers was con-
firmed by 1H NMR spectroscopy. The reactivity of aldehyde functionality was demonstrated by carrying
out aldehyde–aminooxy click reaction of polycaprolactone macromonomer with O-(2-azidoethyl)
hydroxylamine which proceeded in a quantitative manner without backbone degradation.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Aldehyde-terminated macromonomers
ATRP
ROP
Polystyrene
Polycaprolactone
1. Introduction
Aldehyde-terminated polymers are of great interest as aldehyde
group can undergo various types of reactions such as pegylation
End-functional polymers with controlled architecture, molecu-
lar weight and molecular weight distribution are of great impor-
tance [1,2]. End-functionalized polymers have been extensively
used as chain extension and linking agents in preparation of seg-
mented copolymers, cyclic polymers, and many other complex
macro-molecular architectures [3–6]. They could find potential
applications as protective coatings, macromolecular surfactants,
adhesives, etc. [7,8]. As end-groups are retained, ‘living’ polymeri-
zation processes are, by their nature, particularly suited to the
synthesis of end-functional polymers. Thus, various ‘living’ poly-
merization methods, including nitroxide-mediated polymerization
(NMP) [9], atom transfer radical polymerization (ATRP) [10,11],
reversible addition–fragmentation chain transfer (RAFT) [12,13]
and ring opening polymerization (ROP) [14] have been successfully
adapted for this purpose.
reaction [24], aldehyde–aminooxy click reaction [25], aldol reac-
tion, ‘Wittig’ reaction, Reformatsky-type reaction [26] or could be
transformed into hydrazones by treating with amines [27]. Dialde-
hyde containing monomers and polymers serve as precursors for
synthesis of polyazomethines [28] and poly (phenylene vinylene)s
[29]. There are a few reports which demonstrate introduction of
aldehyde functionality at the polymer chain ends. For example,
Haddleton et al. [30] and Yagci et al. [31] reported aldehyde func-
tional ATRP initiators for successful synthesis of aldehyde termi-
nated polystyrene and poly (methyl methacrylate), respectively.
Aromatic aldehyde functionalized polystyrenes were reported by
Yang et al. [32]. Star polystyrene with aldehyde functionalized core
was prepared by RAFT arm technique via crosslinking of preformed
linear macro-RAFT agents using aldehyde containing divinyl cross-
linker [33].
There are two basic approaches to the synthesis of end-func-
We describe, herein, the synthesis of two new bis-aldehyde
functionalized initiators, 4,40-(4,40-(5-hydroxypentane-2,2-diyl)-
bis(4,1-phenylene))bis(oxy)dibenzaldehyde and 4,40-bis(4-(4-
(formylphenoxy) phenyl) pentyl 2-bromopropanoate starting from
commercially available 4,40-bis(4-hydroxyphenyl) pentanoic acid.
tional polymers, viz,
[15]. In -functionalization approach, the chain end functionality
is transformed by post-polymerization to introduce a desired func-
tional group at the -chain end. Incorporation of functional groups
via -functionalization approach in both ATRP and ROP, is achieved
x-functionalization and a-functionalization
x
x
a
The initiators were subsequently utilized for ROP of e-caprolactone
by making use of appropriately functionalized initiators [16–23].
and ATRP of styrene, respectively. Well-defined bis-aldehyde func-
tionalized polycaprolactone and polystyrene macromonomers
were obtained. The macromonomers were characterized by GPC,
FT-IR and 1H NMR spectroscopy. The reactivity of aldehyde
⇑
Corresponding author. Tel.: +91 20 25902306; fax: +91 20 25902615.
E-mail address: pp.wadgaonkar@ncl.res.in (P.P. Wadgaonkar).
1381-5148/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.reactfunctpolym.2012.06.020

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P.S. Sane et al. / Reactive & Functional Polymers 72 (2012) 713–721
functionality was demonstrated by carrying out aldehyde–amino-
oxy click reaction on polycaprolactone macromonomer.
1H NMR (Acetone-d6, d/ppm): 8.28 (s, 2H, phenolic OH), 7.05 (d,
4H, Ar–H meta to ether linkage), 6.75 (d, 4H, Ar–H ortho to ether
linkage), 3.53 (t, 2H, ACH2OH), 2.10–2.06 (m, 2H, ACH2), 1.56 (s,
3H, ACH3), 1.39–1.31 (m, 2H, ACH2).
2. Experimental
2.1. Materials
2.3.2. Synthesis of 4,40-(4,40-(5-hydroxypentane-2,2-diyl)bis(4,1-
phenylene))bis(oxy)dibenzaldehyde
Methyl 4,40-bis(4-hydroxyphenyl) pentanoate was prepared in
99% yield by estrification of 4,40-bis(4-hydroxyphenyl) pentanoic
acid as per the reported procedure [17,34], O-(2-azidoethyl)
hydroxylamine was prepared by following the reported procedure
[35]. 4-Fluoro benzaldehyde, N,N,N0,N0,N00-pentamethyldiethylene-
triamine (PMDETA), 2-bromoisobutyryl bromide (98%), N-hydrox-
yphthalimide and lithium aluminium hydride (LAH), (Aldrich)
were used as received.
Copper (I) bromide (Aldrich, 99.9%) was washed with glacial
acetic acid in order to remove any soluble oxidized species, filtered,
washed with ethanol, and dried. Styrene and e-caprolactone were
stirred over calcium hydride for 4 h and distilled under reduced
pressure. Triethyl amine was distilled prior to the experiments.
2-Chloroethanol, p-toluenesulphonylchloride, dichloromethane,
tetrahydrofuron, sodium sulphate, potassium hydroxide, hydrazine
hydrate, sodium hydrogen carbonate, methanol and chloroform, all
received from S.D. Fine-Chem. Ltd., India and were used as
received.
Into a 500 mL two necked round-bottom flask equipped with a
reflux condenser were charged, 4,40-(5-hydroxypentane-2, 2-diyl)
diphenol (18 g, 60 mmol), K2CO3 (12.3 g, 90 mmol) and acetone
(150 mL) and the reaction mixture was stirred for 10 min. The
solution of 4-fluorobenzaldehyde (18.5 g, 150 mmol) in acetone
(50 mL) was added over a period of 30 min. The reaction mixture
was refluxed for 8 h, cooled and filtered. Acetone was evaporated
under reduced pressure. The product was taken up in ethyl acetate
(150 mL). The ethyl acetate layer was washed with saturated brine
solution (3 ꢀ 50 mL), sodium bicarbonate solution (3 ꢀ 50 mL),
and water (2 ꢀ 50 mL). The ethyl acetate layer was separated, dried
over sodium sulfate, filtered and solvent was evaporated under re-
duced pressure. The crude product was purified by column chro-
matography using ethyl acetate/pet ether (20:80, v/v) to yield
17.2 g (95%) of 4,40-(4,40-(5-hydroxypentane-2,2-diyl)bis(4,1-phe-
nylene))bis(oxy) dibenzaldehyde as a thick yellow liquid.
IR ðCHCl3; cmꢁ1Þ : 3150; 2710; 1710
2.2. Characterizations and measurements
1H NMR (CDCl3, d/ppm): 9.85 (s, 2H, aldehyde), 7.78 (d, 4H, Ar–
H ortho to aldehyde), 7.17(d, 4H, Ar–H ortho to ether linkage),
7.02–6.92 (m, 8H, Ar–H ortho to ether linkage and meta to alde-
hyde), 3.60 (t, 2H, ACH2OH), 2.17–2.06 (m, 2H, ACH2), 1.62 (s,
3H, ACH3), 1.39–1.31 (m, 2H, ACH2).
FTIR spectra were recorded on a Perkin-Elmer Spectrum GX
spectrophotometer in chloroform. NMR spectra were recorded
on a Bruker 200 MHz spectrometer using CDCl3, acetone-d6 or
DMSO-d6 as solvents. MNn MR of bis aldehyde-functionalized poly-
mers were determined by comparing integrals of repeating unit
protons and aldehyde group protons. Molecular weight and
molecular weight distribution of polymers were determined using
GPC analysis at a flow rate of 1 mL/min in chloroform at 30 °C
(Thermo separation products) equipped with spectra series UV
100 and spectra system RI 150 detectors. Two 60 cm PSS SDV-
gel columns (102–105 Å and 1 ꢀ 100 Å) were used at 30 °C. The
sample concentration was 2–3 mg/mL and the injection volume
was 50 mL. HPLC grade chloroform was used as an eluent with
a flow rate of 1 mL/min. Polystyrene was used as the calibration
standard. ESI-MS were obtained using an API-Q-Star Applied Bio-
synthesis spectrometer.
2.3.3. Synthesis of 4,40-bis(4-(4-(formylphenoxy) phenyl) pentyl
2-bromopropanoate
Into a 250 mL two necked round-bottom flask equipped with a
dropping funnel were charged, 4,40-(4,40-(5-hydroxypentane-2,2-
diyl)bis(4,1-phenylene))bis(oxy)dibenzaldehyde (10 g, 29 mmol),
triethylamine (5.25 g, 58 mmol), and dry chloroform (100 mL).
The reaction mixture was cooled to 0 °C and the solution of
2-bromoisobutyryl bromide (9.8 g, 43 mmol) in dry chloroform
(30 mL) was added dropwise into the reaction mixture under stir-
ring over a period of 30 min. The reaction mixture was stirred at
0 °C for 2 h, allowed to attain room temperature and stirred for
12 h. The reaction mixture was washed with 5% aqueous NaHCO3
solution (3 ꢀ 100 mL) and de-ionized water (3 ꢀ 100 mL). The or-
ganic layer was dried over anhydrous sodium sulfate, filtered and
was evaporated under reduced pressure. The crude product was
purified by silica gel column chromatography using a mixture of
ethyl acetate/pet ether (25:75, v/v) as eluent. The removal of the
solvent yielded 9.0 g (90%) of 4,40-bis(4-(4-(formylphenoxy) phe-
nyl) pentyl 2-bromopropanoate a pale yellow liquid.
2.3. Synthesis
2.3.1. Synthesis of 4,40-(5-hydroxypentane-2,2-diyl) diphenol
Into a 250 mL two necked round-bottom flask equipped with a
reflux condenser and a dropping funnel were charged, LAH (5.6 g,
160 mmol) and dry THF (150 mL). The solution of methyl 4,40-bis
(4-hydroxyphenyl) pentanoate (16 g, 54 mmol) in dry THF
(50 mL) was added over a period of 30 min. Effervesces were ob-
served during the addition. Reaction mixture was refluxed for
8 h, cooled and then moist sodium sulfate was added to deactivate
LAH. Dilute HCl (25 mL) was added to dissolve the formed salt and
ethyl acetate (250 mL) was added. The ethyl acetate layer was
washed with saturated brine solution (3 ꢀ 50 mL), sodium bicar-
bonate solution (3 ꢀ 50 mL), and water (2 ꢀ 50 mL). The ethyl ace-
tate layer was separated, dried over sodium sulfate, filtered and
solvent was evaporated under reduced pressure. The crude product
was purified by column chromatography using ethyl acetate/pet
ether (40:60, v/v) to afford 10.4 g (65%) of (B) as a pale yellow
liquid.
IR ðCHCl3; cmꢁ1Þ : 3150; 2710; 1735; 1710
1H NMR (CDCl3, d/ppm): 9.85 (s, 2H, aldehyde), 7.78 (d, 4H, Ar–
H ortho to aldehyde), 7.17 (d, 4H, Ar–H ortho to ether linkage),
6.98–6.92 (m, 8H, Ar–H ortho to ether linkage and meta to alde-
hyde), 4.32–4.27 (q, 1H, AOCOCHCH3Br), 4.13–4.05 (m, 2H, CH2O-
CO), 2.16–2.06 (m, 2H, ACH2), 1.77 (d, 3H, OCOCHCH3) 1.61 (s, 3H,
ACH3), 1.39–1.31 (m, 2H, ACH2).
IR ðCHCl3; cmꢁ1Þ : 3150; 1650
ESI-MS (m/z): 651 [M + Na+]

P.S. Sane et al. / Reactive & Functional Polymers 72 (2012) 713–721
715
2.3.4. Synthesis of bis-aldehyde functionalized polycaprolactone
macromonomer
to aldehyde), 3.99 (t, 2H, ACH2OOC), 2.24 (t, 2H, ACH2CH2CO),
1.58–1.53 (m, 3H, ACH2CH2), 1.34–1.31 (m, 2H, ACH2CH2).
In a typical experiment, Schlenk tube equipped with a magnetic
stir bar was charged with, e-caprolactone (2.85 g, 25 mmol), stan-
2.3.5. General procedure for ATRP of styrene
nous (II) octanoate (0.05 g, 0.125 mmol), 4,40-(4,40-(5-hydroxypen-
tane-2,2-diyl)bis(4,1-phenylene))bis(oxy)dibenzaldehyde (0.8 g,
1.66 mmol) and toluene (30 mL) under nitrogen atmosphere. The
reaction mixture was degassed three times by freeze-pump-thaw
cycles. The polymerization was carried out at 110 °C. After a given
time the polymerization mixture was cooled to room temperature,
diluted with dichloromethane and poured into 10-fold excess of
cold methanol. The polymer was collected by filtration and dried
at room temperature in a vacuum for 24 h.
In a typical experiment, Schlenk tube equipped with a magnetic
stir bar was charged with CuBr (0.120 g, 0.85 mmol) and the tube
was thoroughly flushed with argon. 4,40-bis(4-(4-(formylphenoxy)
phenyl) pentyl 2-bromopropanoate (0.4 g, 0.85 mmol) was dis-
solved in styrene (1.35 ml, 12.75 mmol) in a separate sample vial,
degassed and the solution was transferred via argon-purged syr-
inge to the Schlenk tube under argon atmosphere. The reaction
mixture was degassed three times by freeze-pump-thaw cycles.
Under an argon atmosphere, the reaction mixture was opened
and N,N,N0,N0,N00-pentamethyldiethylenetriamine (0.177 ml, 0.85
mmol) was added rapidly. The Schlenk tube was sealed with stop-
per and was kept in an oil bath at 110 °C. After an appropriate time,
polymerization was quenched by cooling reaction mixture in liquid
nitrogen bath. The reaction mixture was diluted with tetrahydrofu-
ran (50 mL) and the solution was passed through neutral alumina
IR ðCHCl3; cmꢁ1Þ : 1730
1H NMR (CDCl3, d/ppm): 9.86 (s, 2H, aldehyde), 7.78 (d, 4H,
Ar–H ortho to aldehyde), 7.20–7.15 (m, 4H, Ar–H ortho to ether
linkage), 7.02–6.92 (m, 8H, Ar–H ortho to ether linkage and meta
Scheme 1. Synthesis of 4,40-(4,40-(5-hydroxypentane-2,2-diyl)bis(4,1-phenylene))bis(oxy)dibenzaldehyde (1) and 4,40-bis(4-(4-(formylphenoxy) phenyl) pentyl 2-bromo-
propanoate (2).
1
Fig. 1. H NMR spectra of (A) 4,40-(5-hydroxypentane-2,2-diyl) diphenol (B) 4,40-(4,40-(5-hydroxypentane-2,2-diyl)bis(4,1-phenylene))bis(oxy)dibenzaldehyde and (C) 4,40-
bis(4-(4-(formylphenoxy) phenyl) pentyl 2-bromopropanoate in CDCl3.

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P.S. Sane et al. / Reactive & Functional Polymers 72 (2012) 713–721
Scheme 2. Synthesis of bis-aldehyde functionalized polycaprolactone and polystyrene macromonomers.
column to remove copper residue. The solution was concentrated
and poured into excess methanol (400 mL) to precipitate the
polymer. The polymer was dried under reduced pressure for 24 h
and weighed. The monomer conversion was determined
gravimetrically.
turn is obtained from levulinic acid- a platform chemical derived
from biomass. The Fischer esterification of 4,40-bis(4-hydroxy-
phenyl) pentanoic acid was carried out using methanol in the pres-
ence of catalytic amount of concentrated sulphuric acid to yield
methyl ester of 4,4-bis(4-hydroxyphenyl) pentanoic acid (A).
Subsequently, LAH reduction of methyl ester (A) in THF afforded
4,40-(5-hydroxypentane-2,2-diyl)-diphenol. The nucleophilic sub-
stitution reaction of 4-fluorobenzaldehyde with 4,40-(5-hydroxy-
pentane-2,2-diyl)-diphenol in dry DMF using K2CO3 as a base
yielded 4,40-(((5-hydroxypentane 2,2-diyl)bis(4,1-henylene))bis
(oxy) dibenzaldehyde. The product was purified by column chroma-
tography and was characterized by FT-IR, 1H NMR, and 13C NMR
1H NMR (CDCl3 d/ppm): 9.85 (s, 2H, aldehyde), 7.77 (d, 4H, Ar–H
ortho to aldehyde), 7.02–6.97(m, 89H, Ar–H from polystyrene),
6.58–6.50 (m, 38H, Ar–H from polystyrene) 2.12- 1.99 (m, 23H,
ACH2 from polystyrene), 1.75–1.50 (m, 57H, ACH from polystyrene
and protons corresponding to initiator fragment).
2.3.6. Model reaction to demonstrate the reactivity of aldehyde
functionality
1
spectroscopy. Fig. 1 represents H NMR spectrum of 4,40-(4,4’-(5-
hydroxypentane 2,2-diyl bis(4,1-phenylene)bis(oxy) dibenzalde-
hyde along with the assignments. The presence of aldehyde
functionality was confirmed by the appearance of a singlet at
9.85 ppm. The aromatic protons ortho to aldehyde group were
deshielded and appeared as a doublet at 7.78 ppm while aromatic
protons meta to aldehyde group and protons ortho to ether linkage
appeared in the range 7.19–6.92 ppm. The spectral data corre-
sponding to other protons was in good agreement with the pro-
posed structure.
2.3.5.1. Reaction of bis-aldehde functionalized polycaprolactone
macromonomer with O-(2-azidoethyl) hydroxylamine. Into a 50 mL
two necked round-bottom flask equipped with a dropping funnel
were charged, bis-aldehyde functionalized polycaprolactone
(0.36 g, 0.2 mmol), dichloromethane (10 mL) and a pinch of sodium
sulfate. Then, solution of O-(2-azidoethyl) hydroxylamine (0.25 g,
20 mmol) dissolved in dichloromethane (5 mL) was added and the
reaction mixture was stirred at room temperature for 24 h. The reac-
tion mixture was precipitated into cold hexane (50 mL). The ob-
tained polymer was filtered and dried under vacuum at 50 °C for 8 h.
4,40-Bis(4-(40-(formylphenoxy) phenyl) pentyl 2-bromopropan-
oate was synthesized by esterification of 4,40-(4,40-(5-hydroxypen-
tane 2,2-diyl bis(4,1-phenylene)bis(oxy) dibenzaldehyde with
2-bromoisobutyryl bromide in dry chloroform, and was character-
ized using FT-IR, 1H NMR and 13C NMR spectroscopy. 1H NMR
spectrum of 4,40-bis (4-(4-(formylphenoxy) phenyl) pentyl 2-
bromopropanoate along with assignments is shown in Fig. 1. Also
IR ðCHCl3; cmꢁ1Þ : 2110; 1730
1H NMR (CDCl3, d/ppm): 8.11 (s, 2H, CH@N), 7.56 (d, 4H, Ar–H
ortho to aldehyde), 7.20-7.16 (m, 4H, Ar–H ortho to ether linkage),
7.02–6.92 (m, 8H, Ar–H ortho to ether linkage and meta to alde-
hyde), 4.06 (t, 2H, ACH2CH2OOC), 2.31 (t, 2H, ACH2CH2CO, polyc-
aprolactone chain), 1.65–1.61 (m, 3H, ACH2CH2, polycaprolactone
chain), 1.41–1.35 (m, 2H, ACH2CH2, polycaprolactone chain).
Table 1
Reaction conditions and results of synthesis of bis-aldehyde functionalized polycap-
rolactone macromonomers.
3. Results and discussion
Exp. no.
a[M]0/[I]0
bConv. (%)
PDI
dMNn MR
eMGnPC
cMtnh
2100
3.1. Synthesis of 4,40-(((5-hydroxypentane 2,2-diyl)bis(4,1-
phenylene))bis(oxy)dibenzaldehyde (1) and 4,40-bis(4-(4’-
(formylphenoxy) phenyl) pentyl 2-bromopropanoate (2)
1
2
3
25:1
85:1
135:1
70
85
91
1800
8100
2600
10800
19400
1.37
1.33
1.47
7800
12500
14500
(Time – 24 h, Temperature – 1100 °C in toluene) [CL]/[Sn(Oct)2]=400.
Scheme 1 depicts route for synthesis of 4,40-(((5-hydroxypen-
tane 2,2-diyl)bis(4,1- henylene))bis(oxy)dibenzaldehyde (1) and
4,40-bis(4-(40-(formylphenoxy) phenyl) pentyl 2-bromopropanoate
(2). The new initiators were synthesized starting from commer-
cially available 4,40-bis(4-hydroxyphenyl) pentanoic acid which in
a
[M]0/[I]0:[Monomer]:[Initiator].
Gravimetry.
b
½Mꢂ
Mtnh
¼
ꢀ ð%Conv:Þ ꢀ Mol: wt: of monomer þ Mol: wt: initiator.
c
½Iꢂ00
MNn MR – Determined from NMR.
d
e
MGnPC – Determined from GPC; Polystyrene standard; CHCl3 eluent.

P.S. Sane et al. / Reactive & Functional Polymers 72 (2012) 713–721
717
1
Fig. 2. H NMR spectra of (A) 4,40-(4,40-(5-hydroxypentane-2,2-diyl)bis(4,1-phenylene))bis(oxy)dibenzaldehyde and (B) bis-aldehyde functionalized polycaprolactone
macromonomer in CDCl3.
included in Fig. 1 are 1H NMR spectra of intermediates involved in
its synthesis. The presence of aldehyde functionality was con-
firmed by the appearance of a singlet at 9.85 ppm. The aromatic
protons ortho to aldehyde group were deshielded and appeared
as a doublet at 7.78 ppm while aromatic protons meta to aldehyde
group and protons ortho to ether linkage appeared as a multiplet in
the range 7.19–6.92 ppm. The quartet corresponding to methylene
protons attached to halo ester appeared at 4.34–4.28 ppm. The
doublet appeared at 1.77 ppm could be attributed to protons corre-
sponding to methyl group of halo ester. The spectral data corre-
sponding to other protons was in good agreement with the
proposed structure.
3.2. Synthesis of bis-aldehyde functionalized polycaprolactone
macromonomers
ROP of e-caprolactone using stannous (II) octanoate as a catalyst
Fig. 3. GPC trace of bis-aldehyde functionalized polycaprolactone macromonomer
in toluene as a solvent was carried out in the Schlenk tube using,
4,40-(4,40-(5-hydroxypentane 2,2-diyl bis(4,1-phenylene)bis(oxy)
dibenzaldehyde (1) as the initiator (Scheme 2a). The conditions
and results of synthesis of bis-aldehyde functionalized polycapro-
lactone macromonomer are summarized in Table 1. Polycaprolac-
tones having molecular weights ranging from 2600 to 19400
g molꢁ1 were synthesized by varying monomer to initiator ratio.
1H NMR spectrum of polycaprolactone macromonomer is repre-
sented in Fig. 2. The appearance of a singlet at 9.86 ppm confirmed
the presence of aldehyde functionality. Molecular weights for bis-
aldehyde functionalized polycaprolactone macromonomers were
determined by 1H NMR spectroscopy by comparing integral inten-
sity of peak belonging to AOCH2 in polycaprolactone at 3.99 ppm
to a singlet at 9.86 ppm corresponding to aldehyde groups. The de-
gree of polymerization was calculated from NMR analysis using the
relation,
(Table 1, Run 3).
Table 2
Reaction conditions and results of synthesis of bis-aldehyde functionalized polysty-
rene macromonomers.
Exp.no. [M]0:[I]:[Cu]:[L]a Conv(%)b
PDI
Ieff
e
MNn MR
MGNPC
d
Mtnh
1700
c
1
2
3
20:1:1:1
120:1:1:1
250:1:1:1
72
77
82
2200
2800 1.16 0.77
9600 10500 12000 1.14 0.90
21000 31500 28200 1.11 0.67
(Time – 8 h, Temperature – 1100 °C in bulk).
a
[M]:[I]:[Cu]:[L] = [Monomer]:[Initiator]:[CuBr]:[PMDETA].
Gravimetry.
b
c
d
e
M0
I0
½Mol: wt: of monomer ꢀ ꢀ ð%conv:Þꢂ þ mol:wt: initiator.
Polystyrene standard.
Ieff ¼ Mtnh=MNn MR
.
Dpn ¼ ðI3:99=2Þ=ðI9:86=2Þðaldehyde protonÞ
The molecular weights were calculated using the equation,
MNn MR ¼ ½Dpn ꢀ 114:14ðMol: wt: of monomerÞꢂ
þ 480ðMol: wt: of initiatorÞ
where I3.99 and I9.86 are integrals of the signals positioned at 3.99
and 9.86 ppm for polycaprolactone chain and aldehyde functional-
ity, respectively.

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P.S. Sane et al. / Reactive & Functional Polymers 72 (2012) 713–721
1
Fig. 4. H NMR spectra of (A) 4,40-bis(4-(4-(formylphenoxy) phenyl) pentyl 2-bromopropanoate (B) bis-aldehyde functionalized polystyrene macromonomer in CDCl3.
MNn MR values were in reasonably good agreement with theoret-
ical molecular weights (Mtnh) calculated from the monomer to initi-
ator ratio. In addition, representative GPC trace (Fig. 3) revealed
monomodal distribution for polycaprolactone macromonomers.
The PDIs were in the range 1.37–1.47, which is in agreement with
a controlled polymerization method [36,37].
3.3. Synthesis of bis-aldehyde functionalized polystyrene
macromonomers
ATRP of styrene was carried out in bulk using 4,40-bis(4-(4-
(formylphenoxy) phenyl) pentyl 2-bromopropanoate as the
initiator (Scheme 2b). The conditions and results of synthesis of
Fig. 5. GPC trace of bis-aldehyde functionalized polystyrene macromonomer (Table
2, Run 1).
Fig. 6. Relationships between ln ([M0]/[Mt]) and the polymerization time for ATRP
of styrene at 110 °C in bulk.

P.S. Sane et al. / Reactive & Functional Polymers 72 (2012) 713–721
719
Molecular weights determined by 1H NMR spectroscopy (MNn MR
)
were in reasonably good agreement with theoretical molecular
weights (Mtnh) indicating good initiator efficiency (Ieff = 0.77 ꢁ
0.90). In addition, GPC trace (Fig. 5) revealed monomodal distribu-
tion with PDI values in the range 1.11–1.19 for polystyrene
macromonomers. The PDIs were relatively narrow, which is a char-
acteristic behaviour of a controlled radical polymerization method.
A kinetic study was performed to verify the control over the
polymerization of styrene. The linearity of plot of ln (M0/Mt) vs
polymerization time, (Fig. 6) where M0 and Mt are initial and the
actual monomer concentration indicated the pseudo first order
kinetics. The concentration of radicals remained constant during
the polymerization reaction and therefore it can be concluded that
no side reactions occurred during polymerization. The linear in-
crease of molecular weight with increasing conversion and PDI be-
low 1.3 (Fig. 7) represents an additional indication for a living
polymerization mechanism. Thus, 4,4-bis(4-(4-(formyl phenoxy)
phenyl) pentyl 2-bromopropanoate was found to be an efficient
ATRP initiator for controlled polymerization of styrene. Aromatic
aldehyde functionalized polycaprolactone and polystyrene
macromonomers are potential precursors for preparation of graft
and miktoarm star copolymers by employing appropriate synthetic
method [29].
Fig. 7. Dependence of number-average molecular weight and PDI on monomer
conversion for ATRP of styrene at 110 °C in bulk.
bis-aldehyde functionalized polystyrene macromonomers are
summarized in Table 2. Different ratios of [M0]/[I0] with same reac-
tion interval were chosen so as to obtain polymers with a range of
molecular weights combined with low polydispersities. The con-
versions were determined by gravimetric analysis. The reaction
conversions were kept in the range 32–78% in order to ensure
avoidance of potential side reactions. 1H NMR spectrum of bis-
aldehyde functionalized polystyrene is reproduced in Fig. 4. The
appearance of a singlet at 9.85 ppm confirmed the presence of
aldehyde functionality. Integration of signals for aldehyde func-
tionality and comparison with the integration values for phenyl
ring protons in polystyrene macromonomers allows the molecular
weight to be determined. The degree of polymerization was calcu-
lated from NMR analysis using the relation,
3.4. Reaction of bis-aldehde functionalized polycaprolactone
macromonomer with O-(2-azidoethyl) hydroxylamine
The aldehyde functionality is known to undergo aldehyde–
aminooxy click reaction [35]. The reactivity of aldehyde functional-
ity was illustrated by carrying out click reaction with O-(2-azido-
ethyl) hydroxylamine (see supporting information for details of
synthesis) on polycaprolactone macromonomer at room tempera-
ture (Scheme 3b). The conversion was assessed by FT-IR and 1H
NMR spectroscopy. In FT-IR spectrum, in addition to the peak corre-
sponding to polycaprolactone at 1730 cmꢁ1, characteristic peak
corresponding to azido functionality appeared at 2110 cmꢁ1
confirming formation of oxime by the coupling reaction. Fig. 8 rep-
resents 1H NMR spectra of aldehyde-terminated PCL macromono-
mer (Mw: 1800 g/mol; Mw/Mn: 1.37) and its click reaction
product with O-(2-azidoethyl) hydroxylamine. 1H NMR spectra
showed complete disappearance of the peak corresponding to alde-
hyde functionality and appearance of a new peak at 8.11 ppm
(ACH@NAO) which elucidates oxime formation. The peaks corre-
sponding to polycaprolactone remained intact in the product
Dpn ¼ ðI7:01ꢁ6:50=5Þ=ðI9:86=2Þðaldehyde protonÞ
where I7.01ꢁ6.50 corresponds to integration of phenyl ring protons of
polystyrene chain. The contribution of aromatic ring protons from
initiator fragment was subtracted from the total integration of the
peaks appearing in the range 7.01–6.50 ppm. I9.86 represents inte-
gration of the signal positioned at 9.86 ppm corresponding to alde-
hyde protons.
The molecular weights were calculated by using equation,
MNn MR ¼ ½Dpn ꢀ 104 ðMol: wt: of monomerÞꢂ
þ 614 ðMol: wt: of initiatorÞ
Scheme 3. (a) Synthesis of O-(2-azidoethyl) hydroxylamine and (b) aldehyde–aminooxy click reaction on polycaprolactone macromonomer.

720
P.S. Sane et al. / Reactive & Functional Polymers 72 (2012) 713–721
Fig. 8. 1H NMR spectra of (A) O-(2-azidoethyl) hydroxylamine (B) bis-aldehyde functionalized polycaprolactone macromonomer and (C) the product of aldehyde–aminooxy
click reaction in CDCl3.
polymer attesting completion of the reaction without any side reac-
tion such as degradation of polycaprolactone backbone. The model
aldehyde–aminooxy click reaction study with O-(2-azidoethyl)
hydroxylamine introduces azido moiety on palycaprolactone chain
which further opens up plethora of opportunities to introduce dif-
ferent types of functional groups on polycaprolactone by well
known azide-alkyne click reaction [38].
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.reactfunctpolym.
2012.06.020.
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