Synthesis of degradable poly(methyl methacrylate) via ATRP: Atom transfer radical ring-opening copolymerization of 5-methylene-2-phenyl-1,3-dioxolan-4-one and methyl methacrylate

Article abstract of DOI:10.1021/ma034029+

A photodegradable and hydrolytic degradable PMMA with low polydispersity index were synthesized by copolymerization of MMA and MPDO by ATRP. The rate of incorporation of MPDO and MMA into the copolymer was the same regardless of the polymerization tempera

Full text of DOI:10.1021/ma034029+

Volume 36, Number 9
May 6, 2003
© Copyright 2003 by the American Chemical Society
Communications to the Editor
Ch a r t 1
Syn th esis of Degr a d a ble P oly(m eth yl
m eth a cr yla te) via ATRP : Atom Tr a n sfer
Ra d ica l Rin g-Op en in g Cop olym er iza tion of
5-Meth ylen e-2-p h en yl-1,3-d ioxola n -4-on e a n d
Meth yl Meth a cr yla te
Im Sik Ch u n g a n d Kr zysztof Ma tyja szew sk i*
(Chart 1) using TEMPO (2,2,6,6-tetramethyl-1-piperidi-
nyloxy radical)7 and ATRP.8 Since the cyclic ketene
acetal is a relatively unreactive monomer, its copolym-
erization with conventional vinyl monomers is difficult,
especially with a reactive monomer such as methyl
methacrylate (MMA). The low reactivity of the cyclic
ketene acetal is due to the presence of two electron-
donating substituents which cannot stabilize the result-
ing radical. We considered that it would be interesting
to replace one of them by a carbonyl group and generate
a captodative system.9 Such a monomer has previously
been considered for radical ring-opening polymeriza-
tion.10 Therefore, 5-methylene-2-phenyl-1,3-dioxan-4-
one (MPDO; Chart 1, e) should be a highly reactive
monomer due to the presence of a radical stabilizing
R-ester group. The (co)polymer formed by radical rin-
gopening polymerization of MPDO has a fully ring-
opened structure with R-keto ester groups in the back-
bone providing potential sites for biodegradability and
photodegradability. The high reactivity of MPDO should
enhance the probability for its incorporation into the
backbone in copolymerization reactions with styrene
and (meth)acrylates, and the resulting copolymers with
R-keto ester groups randomly distributed along the
chain should preserve the capability for both biodegrad-
ability and photodegradability.
Center for Macromolecular Engineering,
Department of Chemistry, Carnegie Mellon University,
4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213
Received J anuary 8, 2003
Revised Manuscript Received March 3, 2003
Free radical ring-opening polymerization has been
proposed as a useful route for the synthesis of polymers
with various functional groups, such as ester, ether,
ketone, amide, and carbamate, in their backbone.1 The
addition of unsaturated heterocycles to polymerization
of commercial monomers could improve the properties
of the resulting polymers, such as thermal stability, low
volume shrinkage during polymerization, and degrad-
ability.2-4 When conventional radical initiators were
used for such (co)polymerization reactions, the molec-
ular weight of the resulting (co)polymers could not be
controlled, and molecular weight distributions were
quite broad.
Controlled/living radical polymerizations (CRP) pro-
vide well-defined (with predicted molecular weight,
narrow molecular weight distribution, and high degree
of end-functionalization) polymers.5 Among the various
CRP methods, atom transfer radical polymerization
(ATRP) is probably the most robust due to its ability to
copolymerize a broad range of monomers with various
functional groups and its tolerance to solvents of dif-
ferent polarity as well as to impurities often encountered
in industrial systems.6
MDPO was prepared according to the previously
reported method,10a,b with some modification.11 The
atom transfer radical copolymerization of MPDO with
MMA was carried out in anisole using CuBr/CuBr2/
PMDETA (N,N,N′,N′′,N′′-pentamethyldiethylenetriamine)
as a catalyst and ethyl 2-bromoisobutyrate as an initia-
tor, as shown in Scheme 1.12 The reaction conditions
and the results of the copolymerization are listed in
Table 1.
There have been several reports on the free radical
ring-opening polymerization of cyclic ketene acetals
* To whom correspondence should be addressed. E-mail:
km3b@andrew.cmu.edu.
10.1021/ma034029+ CCC: $25.00 © 2003 American Chemical Society
Published on Web 04/03/2003

2996 Communications to the Editor
Macromolecules, Vol. 36, No. 9, 2003
Sch em e 1
Ta ble 1. Con d ition s a n d Resu lts for Cop olym er iza tion of MP DO a n d MMA
feed ratio
[MPDO]:[MMA]
time
(min)
e
temp (°C)
conv of MMA (%)d
conv of MPDO (%)d
Mn,th
Mn(GPC)f
PDIg
1a
90
70
70
70
50
1:10
1:10
1:5
1:3
1:10
30
90
90
90
180
88
85
83
81
83
89
91
88
86
88
15 760
15 360
14 260
15 790
14 980
15 730
15 420
13 930
16 810
15 070
1.24
1.21
1.28
1.31
1.22
2a a
2bb
2cc
3a
a
b
Reaction conditions: [I]0/[CuBr]0/[CuBr2]0/[PMDETA]0/[MPDO]0/[MMA]0 ) 1/1/0.05/1.05/15/150. [I]0/[CuBr]0/[CuBr2]0/[PMDETA]0/
[MPDO]0/[MMA]0 ) 1/1/0.05/1.05/25/125. c [I]0/[CuBr]0/[CuBr2]0/[PMDETA]0/[MPDO]0/[MMA]0 ) 1/1/0.05/1.05/40/120. Measured by gas
d
chromatography. e Theoretical number-average molecular weight was calculated from the conversion of the monomers. f Determined by
g
GPC using tetrahydrofuran as eluent with poly(methyl methacrylate) standards. Polydispersity index ) Mw/Mn.
F igu r e 2. Dependence of Mn and Mw/Mn on conversion in the
copolymerization of MPDO with MMA ([MPDO]:[MMA] )
1:10).
F igu r e 1. Relationship of ln[M]0/[M] and conversion with
polymerization time in the copolymerization of MPDO with
MMA ([MPDO]:[MMA] ) 1:10).
First, the ATRP copolymerization of MPDO and MMA
([MPDO]:[MMA] ) 1:10) was carried out at 90 °C to
produce poly(MDPO-co-MMA), 1. Conversion of the two
monomers reached ∼90% within 30 min. The number-
average molecular weight of the resulting copolymer 1,
measured by GPC, was Mn ) 15 730 g/mol, which is well
matched with the theoretical value (Mn,th ) 15 760
g/mol), and the polydispersity index was Mw/Mn ) 1.24.
To investigate the “living” nature of the copolymeri-
zation and monomer conversion behavior, copolymeri-
zation ([MPDO]:[MMA] ) 1:10) was also carried out at
70 and 50 °C. Comonomer conversion greater than 80%
was reached within 90 min at 70 °C and required 180
min at 50 °C. As shown in Figure 1, plotting ln[M]0/[M]
against polymerization time afforded straight lines for
both MPDO and MMA, demonstrating the constant
concentration of the growing radicals. The ratio of
monomer consumption for MPDO and MMA is almost
constant regardless of time, as shown in Figure 1. The
linear molecular weight-conversion profile (Figure 2)
indicates that that the molecular weight can be simply
controlled by polymerization time. The number-average
molecular weights of the resulting polymers, 2a and 3,
measured by GPC are close to theoretical values, and
the polydispersity indexes are reasonably narrow (about
1.2). These results confirmed that the copolymerization
of 10 mol % MPDO with MMA is well-controlled under
ATRP conditions.
The copolymerization reaction was also carried out
with different ratios of MPDO and MMA. Conversion
reached over 80% within 90 min at 70 °C regardless of
the monomer ratio ([MPDO]:[MMA] ) 1:5 (2b) and 1:3
(2c)). The number-average molecular weights of the
resulting polymers were measured by GPC and were
well matched with theoretical values, and the polydis-
persity indexes were in the range 1.2-1.3. The linear
kinetic plots for consumption of monomers indicated a
constant concentration of growing radicals, and the
monomer consumption ratio of MPDO and MMA was
similar regardless of the initial ratio of MPDO to MMA.
1
The structure of the copolymer was examined by H
1
NMR spectroscopy (Figure 3). The H NMR spectrum
of MPDO monomer shows a peak at 6.6 ppm, corre-
sponding to the acetal proton, but this peak entirely
shifts to 5.9 ppm, corresponding to a methine proton
next to the ester oxygen of the ring-opened unit in the

Macromolecules, Vol. 36, No. 9, 2003
Communications to the Editor 2997
F igu r e 3. 1H NMR spectra of MPDO and poly(MPDO-stat-MMA) 1 (CDCl3, 300 MHz; *: solvent and residual THF peaks).
Sch em e 2a
a
Reaction conditions: (A) KOH (10 equiv), 2-propanol/2-butanone, 30 °C, 18 h; (B) UV light, 40 °C, 2 h.
4). This means that MPDO with a ring-opened structure
was randomly incorporated into the PMMA chain.
In conclusion, a photodegradable and hydrolytic (i.e.,
also biodegradable) degradable PMMA with low poly-
dispersity index were synthesized by copolymerization
of MMA and MPDO by ATRP. The rate of incorporation
of MPDO and MMA into the copolymer was the same
regardless of the polymerization temperature and mono-
mer feed ratio under typical ATRP conditions.
Ackn owledgm en t. Financial support from the mem-
bers of the CRP Consortium at Carnegie Mellon Uni-
versity, National Science Foundation (DMR-00-90409),
and Korea Science and Engineering Foundation (KO-
SEF) for postdoctoral fellowship support (I.S.C.) is
acknowledged. We thank Professor H. Hall and Profes-
sor T. Endo for many stimulating discussions.
F igu r e 4. GPC curves of the polymers: (a) copolymer 1, (b)
after hydrolysis of 1, (c) after photolysis of 1.
spectrum of the corresponding polymer, which indicates
essentially complete ring opening of MPDO during the
reaction. The H NMR spectrum of the polymer shows
Refer en ces a n d Notes
1
(1) (a) Ivin, K. J .; Saegusa, T. Ring-Opening Polymerization;
Elsevier Applied Science: London, 1984; Chapter 1. (b)
Bailey, W. J .; Wu. S.-R.; Ni, Z. Macromol. Chem. 1982, 183,
1913. (c) Bailey, W. J . Polym. J . 1985, 17, 85. (d) Hiraguri,
Y.; Endo, T. J . Am. Chem. Soc. 1987, 109, 3779. (e) Klemm,
E.; Schulze, T. Acta Polym. 1999, 50, 1. (f) Sanda, F.; Endo,
T. J . Polym. Sci., Polym. Chem. Ed. 2001, 39, 265.
(2) Bailey, W. J .; Wu, S.-R.; Ni, Z. J . Macromol. Sci., Pure Appl.
Chem. 1982, A18, 973.
(3) (a) He, P.-S.; Zhou, Z.-Q.; Pan, C.-Y.; Wu, R.-J . J . Mater.
Sci. 1989, 24, 1528. (b) Brady, R. F. J . J . Macromol. Sci.,
Rev. Macromol. Chem. Phys. 1992, C32, 135. (c) Sanda, F.;
Takata, T.; Endo, T. Macromolecules 1994, 27, 1099.
(4) (a) Bailey, W. J .; Ni, Z.; Wu. S.-R. J . Polym. Sci., Polym.
Chem. Ed. 1982, 20, 3021. (b) Fukuda, H.; Hirota, M.; Endo,
T.; Okawara, M. J .; Bailey, W. J . J . Polym. Sci., Polym.
Chem. Ed. 1982, 20, 2935. (c) Koizumi, T.; Hasegawa, Y.;
Takata, T, Endo, T. J . Polym. Sci., Polym. Chem. Ed. 1994,
32, 3193. (d) Hiraguri, Y.; Tokiwa, Y. J . Polym. Sci., Polym.
Chem. Ed. 1993, 31, 3159. (e) Hiraguri, Y.; Tokiwa, Y.
Macromolecules 1997, 30, 3691.
peaks at 7.4 and 2.0-2.7 ppm, corresponding to aro-
matic and aliphatic protons of the MPDO units, respec-
tively. Also, it shows all of the peaks corresponding to
the protons of MMA units. From the H NMR measure-
ment, it is confirmed that MPDO is successfully incor-
1
porated to the copolymer with a ring-opened structure.
Additional evidence for the random incorporation of
MPDO by ring-opening copolymerization is obtained by
hydrolysis and photolysis of the polymer. To examine
the copolymerization behavior and degradability of the
copolymer, hydrolysis was carried out under basic
conditions13 and photolysis by photoirradiation,14 as
shown in Scheme 2. After hydrolysis the molecular
weight of copolymer 1 was reduced to Mn ) 1620 g/mol
(about 10 times lower than the original polymer), with
polydispersity index Mw/Mn ) 1.89; after photolysis, Mn
) 1480 g/mol and the polydispersity was 1.96 (Figure

2998 Communications to the Editor
Macromolecules, Vol. 36, No. 9, 2003
(5) (a) Matyjaszewski, K., Ed. Controlled Radical Polymeriza-
tion; ACS Symp. Ser. 685; American Chemical Society:
Washington, DC, 1998. (b) Matyjaszewski, K., Ed. Controlled/
Living Radical Polymerization. Progress in ATRP, NMP,
and RAFT; ACS Symp. Ser. 768; American Chemical
Society: Washington, DC, 2000. (c) Matyjaszewski, K.,
Davis, T. P., Eds. Handbook of Radical Polymerization;
Wiley: Hoboken, 2002. (d) Qiu, J .; Charleux, B.; Matyjas-
zewski, K. Prog. Polym. Sci. 2001, 26, 2083. (e) Davis, K.
A.; Matyjaszewski, K. Adv. Polym. Sci. 2002, 159, 1.
(6) (a) Matyjaszewski, K.; Xia, J . Chem. Rev. 2001, 101, 2921.
(b) Kamigaito, M.; Ando, T.; Sawamoto, M. Chem. Rev. 2001,
101, 3689. (c) Coessens, V.; Pintauer, T.; Matyjaszewski, K.
Prog. Polym. Sci. 2001, 26, 337. (d) Patten, T. E.; Matyjas-
zewski, K. Acc. Chem. Res. 1999, 32, 895. (e) Patten, T. E.;
Matyjaszewski, K. Adv. Mater. 1998, 10, 901. (f) Wang, J .
S.; Matyjaszewski, K. J . Am. Chem. Soc. 1995, 117, 5614.
(g) Wang, J .-S.; Matyjaszewski, K. Macromolecules 1995,
28, 7901. (h) Patten, T. E.; Xia, J .; Abernathy, T.; Matyjas-
zewski, K. Science 1996, 272, 866.
(7) (a) Wei, Y.; Connors, E. J .; J ia, X.; Wang, B. Chem. Mater.
1996, 8, 604. (b) Wei, Y.; Connors, E. J .; J ia, X.; Wang, C.
J . Polym. Sci., Polym. Chem. Ed. 1998, 36, 761.
(8) (a) Pan, C.-Y. Lou, X.-D. Macromol. Chem. Phys. 2000, 201,
1115. (b) Yuan, J .-Y.; Pan, C.-Y.; Tang, B. Z. Macromolecules
2001, 34, 211. (c) Yuan, J .-Y.; Pan, C.-Y. Eur. Polym. J .
2002, 38, 1565. (d) Yuan, J .-Y.; Pan, C.-Y.; Eur. Polym. J .
2002, 38, 2069.
(11) The cyclic acrylate was synthesized by the reaction of
â-chlorolactic acid with benzaldehyde in 45% yield, followed
by dehydrochlorination with diisopropylamine in ether in
almost quantitative yield. The crude product was purified
by distillation: bp 83-84 °C (0.1 mmHg). The polymeriza-
tion was carried our immediately after purification of the
monomer. The 1H NMR spectrum of the monomer shown
in Figure 3 indicates that the monomer is stable in solution.
However, it polymerized spontaneously when exposed to air.
(12) Xia, J .; Matyjaszewski, K. Macromolecules 1997, 30, 7697.
A typical procedure for copolymerization of MPDO with
MMA was as follows: 14.3 mg of CuBr (0.10 mmol), 1.12
mg of CuBr2 (0.005 mmol), 21.9 mg of PMDETA (0.105 mol),
0.264 g of MPDO (1.50 mmol), 1.50 g of MMA (15.0 mmol),
and 2 mL of anisole were added into a 10 mL Schlenk flask.
The flask was tightly sealed with a rubber septum and was
cycled between vacuum and dry nitrogen three times to
remove the oxygen. After the mixture was stirred at room
temperature until it was homogeneous, the initiator, 14.7
µL of ethyl 2-bromoisobutyrate (0.10 mmol), was added, and
the flask was immersed in an oil bath maintained at the
desired temperature by a thermostat. At timed intervals,
samples were withdrawn from the flask using a degassed
syringe and analyzed by GC and GPC using PMMA stan-
dards.
(13) The hydrolysis was carried out with potassium hydroxide
(10 equiv) in 2% w/v 2-propanol/2-butanone (v/v ) 50/50)
solution (solute, 100 mg; solvent, 5 mL) at 30 °C for 18 h.
(9) (a) Pasto, D. J . J . Am. Chem. Soc. 1988, 110, 8164. (b) Viehe,
H. G.; J anousek, Z.; Merenyi, R.; Stella, L. Acc. Chem. Res.
1985, 18, 148. (c) Penelle, J .; Padias, A. B.; Hall, H. K.;
Tanaka, H. Adv. Polym. Sci. 1992, 102, 73.
(10) (a) Bailey, W. J .; Feng, P. Z. Polym. Prepr. (Am. Chem. Soc.,
Div. Polym. Chem.) 1987, 28 (1), 154. (b) Feng, P. Chin. J .
Polym. Sci. 1992, 10, 350. (c) Bailey, W. J .; Kuruganti, V.
K. Polym. Mater. Sci. Eng. 1990, 62, 971.
(14) The irradiation was carried out with 2% w/v anisole solution
(solute, 100 mg; solvent, 5 mL) in a Rayonet photochemical
chamber reactor equipped with 12 RPR-254 nm lamps at
40 °C for 2 h.
MA034029+