Fabrication and degradation of polyperoxides by a radical chain process under mild conditions

Article abstract of DOI:10.1246/cl.2004.732

We have fabricated polyperoxides as new kinds of environment-friendly and degradable polymers using 1,3-diene compounds and oxygen as the starting comonomers under mild temperature and pressure conditions. They degrade in a radical chain mechanism by various stimuli; for example, degradation induced by physical (heating or irradiation), chemical (redox), and biochemical (enzymatic) stimuli.

Full text of DOI:10.1246/cl.2004.732

732
Chemistry Letters Vol.33, No.6 (2004)
Fabrication and Degradation of Polyperoxides by a Radical Chain Process
under Mild Conditions
Akikazu Matsumotoꢀ and Shuji Taketani
Department of Applied and Bioapplied Chemistry, Graduate School of Engineering, Osaka City University,
Sugimoto, Sumiyoshi-ku, Osaka 558-8585
(Received March 9, 2004; CL-040264)
We have fabricated polyperoxides as new kinds of environ-
R1 R2
ment-friendly and degradable polymers using 1,3-diene com-
pounds and oxygen as the starting comonomers under mild tem-
perature and pressure conditions. They degrade in a radical chain
mechanism by various stimuli; for example, degradation induced
by physical (heating or irradiation), chemical (redox), and bio-
chemical (enzymatic) stimuli.
O
R1
O2 (1 atm)
O
R3
n
radical initiator
R2
PP-1 PP-6
1
6
R3
1: R1 = CH3, R2 = H, R3 = CO2CH3
2: R1 = CH3, R2 = H, R3 = CO2C2H5
3: R1 = (CH2)2CH3, R2 = H, R3 = CO2CH3
4: R1 = R2 = CH3, R3 = CO2C2H5
5: R1 = Ph, R2 = H, R3 = CO2C2H5
6: R1 = Ph, R2 = H, R3=Ph
CHO
O
decomp.
+
Degradable polymers attract great interest owing to their
versatile functions and applications, but very few kinds of vinyl
polymers are feasible for use as degradable materials.1 This is
due to the fact that vinyl polymers have successive carbon-to-
carbon bonds in the main chain, leading to their advantageous
thermal and biochemical stabilities during processing and
long-term use in daily life. Staudinger2 first pointed out the for-
mation of polyperoxides via the oxidation of vinyl monomers in
1922, and thereafter many kinds of polyperoxides have been pre-
pared by a radical copolymerization process.3–5 All polyperox-
ides obtained from vinyl monomers with oxygen readily decom-
pose upon heating and provide formaldehyde as well as other
aldehydes or ketones, according to the polymer repeating struc-
ture. In order to avoid the evolution of volatile and toxic com-
pounds as the decomposition products, we have recently devel-
oped the synthesis of polyperoxides from diene monomers as a
new kind of environment-friendly and degradable polymer. Here
we report the preparation of polyperoxides from 1,3-diene
monomers with oxygen and their degradation behavior by vari-
ous stimuli; for example, degradation induced by physical (heat-
ing or irradiation), chemical (redox), and biochemical (enzymat-
ic) stimuli. Both the fabrication and degradation processes of the
polyperoxides imply efficient radical chain reactions.
R1
R2
R3
Scheme 1.
tained by the radical copolymerization of 1,3-diene monomers
such as alkyl sorbates with oxygen as the starting monomers un-
der mild polymerization conditions (ambient pressure and tem-
perature).6 They produce acetaldehyde as the decomposition
product in lieu of formaldehyde produced from the polyperox-
ides that was derived from vinyl monomers. In this study, we
have confirmed that the introduction of alkyl or phenyl substitu-
ents on a diene moiety leads to a change in the structure of the
decomposition products, as shown in Scheme 1. Radical copoly-
merization of 1,3-diene monomers with oxygen was carried out
in an organic solvent such as 1,2-dichloroethane in the presence
of 2,20-azobis(4-methoxy-2,4-dimethylvaleronitrile) (AMVN)
as an azo initiator and bubbling oxygen at 30 ꢁC and atmospheric
pressure. The results of the polymerization as well as the thermal
properties of the resulting polyperoxides are summarized in
Table 1. The polymer yield decreased with an increase in the
steric hindrance of the substituent on the diene monomers. All
the polymers have a molecular weight of 2{4 ꢂ 103. The decom-
position temperature was estimated by thermogravimetric analy-
We have previously revealed that polyperoxides are ob-
Table 1. Preparation and thermal properties of polyperoxides
TGb DTAb
Yield/% Mn ꢂ 10ꢃ3 Mw=Mn T95/ꢁC T50/ꢁC Tmax/ꢁC Tinit/ꢁC Tmax/ꢁC ꢀH/kJ unitꢃ1
Preparationa
Poly-
peroxide
Degradation Productsc
PP-1
PP-2
PP-3
PP-4
PP-5
PP-6
a
49.3
39.1
21.6
28.9
14.6
21.9
3.9
4.0
3.1
4.4
2.3
2.9
1.6
1.8
1.4
1.5
2.1
2.1
119.5
122.3
115.1
104.8
105.6
102.9
149.8
149.9
146.1
132.2
154.5
133.6
148.2
145.3
141.3
129.6
129.4
117.5
107.9
107.4
88.5
82.3
72.0
76.1
147.5
147.0
140.7
128.6
120.5
109.5
187.3
187.6
165.7
166.7
162.9
175.7
AcA + FA
AcA + FA
BuA + FA
acetone + FA
BzA + FA + EG + CA
BzA + CA
Polymerization conditions: With bubbling oxygen for 6 h. Monomer/solvent = 1/1 in weight, except 1/13 for the polymerization of 6. Mono-
mer/AMVN = 50/1 in weight. The number-average molecular weight (Mn) and polydispersity (Mw=Mn) were determined by GPC calibrated
with standard polystyrenes. b Heating rate at 10 ꢁC/min in a nitrogen stream. T95 and T50 are 95 and 50 wt % temperatures, respectively. Tinit and
c
Tmax were determined from a differential TG or DTA curve. ꢀH is the heat of decomposition. Determined by NMR spectroscopy. AcA:
acetaldehyde, FA: fumaraldehyde monoester, BuA: butylaldehyde, BzA: benzaldehyde, EG: ethyl glyoxylate, CA: cinnamaldehyde.
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.6 (2004)
733
Table 2. Degradation of PP-4 under various conditions
Ph
CO C H
2 5
2
O
decomp.
O
Degradation Conditions
Product yield/%
Conv.
/%
O
O
n/m
Temp
/ꢁC
Time
/h
Addi-
tive
Solvent
Acetone/FA (ratio)
CO C H
2
2
5
Ph
90
1
2
3
5
toluene-d8 none
toluene-d8 none
toluene-d8 none
toluene-d8 none
45.8 52.6/49.0 (1/0.93)
78.7 76.0/63.4 (1/0.83)
88.1 87.8/69.6 (1/0.79)
97.8 83.0/64.8 (1/0.78)
91.0 85.8/81.6 (1/0.95)
42.5 53.4/36.2 (1/0.68)
5,4 structure
2,3 structure
90
90
CHO
O
CHO
O
90
+
+
H
+
110
0.5 toluene-d8 none
OC H
2 5
H
Ph
CO C H
2 5
30 (hꢂ)
30 (hꢂ) 12
r.t.
30
3
toluene-d8 none
toluene-d8 none
O
Ph
2
81.8 85.0/26.0 (1/0.31)
b
Scheme 2.
a
0.5 benzene-d6 NEt3 ꢄ100
3 days ethanol-d6 HRPc
45.7
b
Horseradish Peroxidase (HRP) (Table 2). During photoirradia-
tion, the fumaraldehyde monoesters produced by the decompo-
sition of the polyperoxide further reacted via EZ isomerization,
dimerization, and other reactions, leading to a low fumaralde-
hyde to acetone ratio. The addition of a basic compound, such
as triethylamine, induced a rapid decomposition accompanying
by complicated reaction products. The biochemical decomposi-
tion of the polyperoxides by HRP also proceeds via a radical
chain reaction mechanism, providing similar main products dur-
ing decomposition. The polymers degradable via a radical chain
reaction mechanism triggered by various stimuli have a potential
for use in various fields including adhesion, coating, environ-
mental, and medicinal chemistry.
c
aNEt3, 0.24 mol/L. bNot determined. PP-4 25 mg, HRP 1.25 mg.
sis (TG) and differential thermal analysis (DTA) in a nitrogen
stream at a heating rate of 10 ꢁC/min. It was confirmed that
the polyperoxides readily and exothermically decompose upon
heating (ꢀH ¼ 163{188 kJ/unit). The onset temperatures of
the decomposition (Tinit) were 72–89 ꢁC for PP-3–PP-6, being
lower than those for the polyperoxides obtained from sorbates.
The maximum decomposition temperature (Tmax) also showed
similar results. The TG and DTA experiments support their ther-
mal stability depending on the structure of the R1 and R2 sub-
stituents on the polymer main chain.
In order to determine the decomposition products, the poly-
peroxides in toluene-d8 in a sealed tube were heated, and the de-
composition products were examined as a reaction mixture by
NMR spectroscopy. A fumaraldehyde monoester was produced
from all the polyperoxides with an alkoxycarbonyl group as
R3, and acetaldehyde, butyladehyde, acetone, and benzaldehyde
were also detected as another decomposition product from PP-1
(or PP-2), PP-3, PP-4, and PP-5, respectively, as expected. As
the decomposition products from PP-5, two further compounds,
cinnamaldehyde and ethyl glyoxylate, were simultaneously
found (Scheme 2). The NMR spectrum of PP-5 suggested the
existence of the 5,4 and 2,3 structures as the repeating unit in
a 2:3 molar ratio. The presence of phenyl and carboxylate groups
leads to attack of a peroxy radical at both the 2- and 5-positions
and the subsequent cross propagation results in the polymer
structure. Nevertheless, the degradation behavior was the same
as that for the other polyperoxides except for four kinds of de-
composition products. The decomposition products from PP-5
consist of compounds with a high boiling point (low vapor pres-
sure at room temperature) and less toxicity, compared to the de-
composition products from polyperoxides derived from sorbates
or vinyl monomers. PP-6 provided the most simple and environ-
mentally friendly decomposition products, i.e., benzaldehyde
and cinnamaldehyde.
This work was partly supported by Nagase Science and
Technology Foundation.
References
1
a) G. Scott, ‘‘Polymers and the Environment,’’ Royal Society
of Chemistry, Manchester (1999). b) E. S. Stevens, ‘‘Green
Plastics: An Introduction to the New Science of Biodegrad-
able Plastics,’’ Princeton University Press, Princeton (2002).
c) E. Chiellini and R. Solaro, ‘‘Biodegradable Polymers and
Plastics,’’ Kluwer, New York (2003).
2
3
H. Staudinger, Angew. Chem., 35, 657 (1922).
Reviews: a) F. A. Bovey and I. M. Kolthoff, Chem. Rev., 42,
491 (1948). b) T. Mukundan and K. Kishore, Prog. Polym.
Sci., 15, 475 (1990). c) A. Matsumoto, J. Adhes. Soc. Jpn.,
39, 308 (2003).
4
5
A. A. Miller and F. R. Mayo, J. Am. Chem. Soc., 78, 1017
(1956) and subsequent papers.
a) K. Kishore and K. Ravindran, Macromolecules, 15, 1638
(1982). b) K. Kishore and T. Mukundan, Nature, 324, 130
(1984). c) J. Jayaseharam and K. Kishore, J. Am. Chem.
Soc., 120, 825 (1998). d) A. K. Nanda and K. Kishore,
Macromolecules, 34, 1558 (2001). e) P. De and D. N.
Sathyanarayana, Macromol. Chem. Phys., 203, 420 (2002).
f) T. Nakano, O. Nakagawa, T. Yade, and Y. Okamoto,
Macromolecules, 36, 1433 (2003). g) S. Nomura, T. Itoh,
M. Ohtake, T. Uno, M. Kubo, K. Sada, and M. Miyata,
Angew. Chem., Int. Ed., 42, 5468 (2003).
The degradation reaction proceeds via a radical chain reac-
tion mechanism.3b,4 A peroxy bond in the polymer chain is ho-
molitically cleaved during the first step, followed by the succes-
sive ꢁ-scission (also via a radical chain reaction) providing two
kinds of aldehydes alternately. These polyperoxides degrade not
only upon heating but also by other stimuli. For example, photo-
chemical or redox reactions are available for decomposition at
ambient temperature, as well as an enzymatic trigger such as
6
a) A. Matsumoto, Y. Ishizu, and K. Yokoi, Macromol. Chem.
Phys., 199, 2511 (1998). b) A. Matsumoto and H. Higashi,
Macromolecules, 33, 1651 (2000). c) H. Hatakenaka, Y.
Takahashi, and A. Matsumoto, Polym. J., 35, 640 (2003).
Published on the web (Advance View) May 24, 2004; DOI 10.1246/cl.2004.732