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Anionic Alternating Copolymerization Behaviorof Bifunctional Six-Membered Lactoneand Glycidyl Phenyl Ether

KAZUYA UENISHI, ATSUSHI SUDO, TAKESHI ENDO

Molecular Engineering Institute, Kinki University, Kayanomori 11-6, Iizuka, Fukuoka 820-8555, Japan

Received 24 January 2009; accepted 29 March 2009

DOI: 10.1002/pola.23446

Published online in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: A copolymerization of 10-methyl-2H,8H-benzo-[1,2-b:5,4-b0]bipyran-2,8-

dione (1) and glycidyl phenyl ether (GPE) was studied. 1 was a bislactone designed

as a bifunctional analogue of 3,4-dihydrocoumarin (DHCM), of which anionic 1:1

alternating copolymerization with GPE has been reported by us, previously. This

alternating nature was inherited by the present copolymerization of 1 and GPE,

leading to an intriguing copolymerization behavior in contrast to the ordinary statis-

tical copolymerizations of monofunctional monomers and bifunctional monomers usu-

ally controlled by the proportional dependence of the crosslinking density on the

monomer feed ratio: (1) When the feed ratio [GPE]0/[1]0 was 1, the two monomers

underwent the 1:1 alternating copolymerization. In this case, 1 behaved as a mono-

functional monomer, that is, only one of the two lactones in 1 participated in the

copolymerization allowing the other lactone moiety to be introduced into the side

chain almost quantitatively. (2) Increasing the feed ratio [GPE]0/[1]0 to larger than 4

allowed almost all of the lactone moieties to participate in the copolymerization sys-tem to give the corresponding networked polymers efficiently. The compositions of

the copolymers [GPE unit]/[1-derived acyclic ester unit] were always biased to

smaller values than the feed ratios [GPE]0/[lactone moiety in 1]0 by the intrinsic 1:1

alternating nature of the copolymerization. VVC 2009 Wiley Periodicals, Inc. J Polym Sci Part

A: Polym Chem 47: 36623668, 2009

Keywords: alternating sequence; copolymerization; crosslinking; networks; polyesters

INTRODUCTION

Epoxide exhibits high reactivity due to the distor-

tion energy of the three-membered ring, which

permits its efficient ring-opening polymerizations

under both cationic and anionic conditions.1 The

high reactivity often allows its copolymerizations

not only with various polymerizable compounds28

but also with robust compounds such as carbon

dioxide.912 In other words, there could still exist

a wide variety of potential comonomers that have

been not exploited so far. Surveying such com-

pounds capable of copolymerizations with epoxide

is an attractive strategy for development of new

polymers having various main chain structures,

which are totally different from that of the

epoxy homopolymer and would accordingly exhibit

different chemical and physical properties.

Recently, we have reported the imidazole-initi-

ated copolymerization of 3,4-dihydrocoumarin

(DHCM) and glycidyl ethers such as phenyl

glycidyl ether (GPE) and allyl glycidyl ether

(Scheme 1).1316 DHCM is a six-membered aromaticJournal of Polymer Science: Part A: Polymer Chemistry, Vol. 47, 36623668 (2009)

VVC 2009 Wiley Periodicals, Inc.

Correspondence to: T. Endo (E-mail: [email protected])

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lactone, which does not undergo cationic or ani-

onic homopolymerization at all. This robust lac-tone underwent 1:1 alternating copolymerization

with GPE to give the corresponding polyester.

This unique reaction behavior of DHCM has

prompted us to develop various DHCM analogues

and apply them to copolymerization with epox-

ides. A bislactone1 is one of the highly interesting

DHCM-analogues, and recently, we have reported

its practical application as an additive to the imid-

azole-initiated curing reactions of epoxy resins,

which remarkably improved the thermal stabil-

ities of the cured materials.13,17,18 Besides this

practical aspect of 1, clarification of its reaction

behavior in its copolymerization with epoxide hasbeen remained unexplored.

Herein, we report the copolymerization behav-

ior of the bislactone1 with GPE (Scheme 2).1 is abifunctional monomer, of which copolymerization

with a monofunctional epoxide would potentially

afford polymers having networked structure. Our

particular interests in this polymerization system

are the effects of the intrinsic 1:1 alternating

nature of the copolymerization of DHCM and

GPE on the growth of the polymer network,

leading to the totally different mode from those

based on utilization of other monomers capable of

random copolymerizations with epoxides.

RESULTS AND DISCUSSION

Copolymerization of 1 and GPE in VariousFeed Ratios

The copolymerization of 1 and GPE was carried

out at 120 C in bulk using 2-ethyl-4-methylimi-

dazole (EMI) as an initiator (Scheme 2). The

amount of EMI was calculated by the equation,

[EMI]0 0.01(2[1]0 [GPE]0). The resulting mix-ture was separated into the tetrahydrofuran

(THF)-insoluble fraction 2insol and THF-soluble

one, and the latter was further separated intohexane-insoluble fraction and soluble one. The

fraction soluble in THF and insoluble in hexane is

represented by2sol. The corresponding results are

shown in Table 1. These fractions were analyzed

by 1H NMR, 13C NMR, and IR spectroscopies.

Particularly, the latter two were conveniently

used for detection of the ester groups inherited

from the bislactone 1.1318 For the purpose ofmore detailed investigation on the repeating units

that composed the obtained polymeric products,

reductive degradation of these products were per-

formed using lithium aluminum hydride (LAH) as

a reducing reagent that can cleave the ester bondsin the polymers (Scheme 2).13,16,17 The results are

shown in Table 2.

First, the copolymerization was performed with

setting the monomer feed ratio [GPE]0:[1]0 to be

1:1 (entry 1). The corresponding copolymerization

behavior has been already reported by our previ-

ous short communication.17 In this case, 1 and

Scheme 2. Copolymerization of 1 and GPE and

reductive cleavage of the ester linkage.

Scheme 1. Alternating copolymerization of DHCM

and glycidyl ethers.

COPOLYMERIZATION OF BISLACTONE & GPE 3663

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GPE underwent the 1:1 alternating copolymeriza-

tion to give the linear polyester. The consumption

rates for the both monomers were virtually same,

and after 1 h, the conversions of 1 and GPEreached to 60 and 59%, respectively. The resulting

mixture was composed of a THF-soluble polymer

2asol (isolated as hexane insoluble parts in 60%

yield) and the residual monomers. Formation of a

THF-insoluble part was negligible, suggesting

that only one of the two lactone moieties in 1would have participated in the copolymerization

with GPE. The copolymerization proceeded in the

1:1 alternating manner, giving the correspondinglinear polyester. The other lactone moiety in 1remained intact and introduced into the side

chain of the copolymer. In 13C NMR spectrum of

2asol, two carbonyl signals were observed around172 and 168 ppm, and attributed to the ester-link-

age in the main chain and the lactone moiety in

the side chain, respectively. The IR spectrum

showed two absorption signals at 1765 and 1735

cm1 assigned to the lactone and a linear ester

moiety, respectively, [Fig. 1(a)].

Treatment of2asol with LAH resulted in com-plete reduction of these ester moieties to give the

corresponding low-molecular weight products, of

which structural analyses clarified the structure

of the polymer (Table 2, entry 1).14,17 As the main

product, a triol 3 was obtained in 87% yield,

which was composed of the GPE-derived unit and

the 1-derived unit in a 1:1 ratio. 3 had a phenolmoiety in the core structure, which was obviously

Table 1. Results of Copolymerization of GPE and 1

RunFeed Ratio[GPE]0/[1]0

Time(min)

Products

THF InsolubleParts (%)

THF Soluble Parts

Hexane InsolubleParts (%)

Hexane SolubleParts (%)

1 1/1 60 trace 60 (2asol)a 28 (GPE:11:1)b

2 2/1 30 35 (2binsol) 35 (2bsol)c 18 (GPE:16:1)b

3 4/1 30 88 (2cinsol) 3 7 (GPE)

4 8/1 45 74 (2dinsol) 2 22 (GPE)

5 18/1 120 0 82(2esol)d 17 (GPE)

a 2asol: Mn 2240, Mw 4750.b Determined by 1H NMR.c2bsol: Mn 1920, Mw 3620.d 2esol: Mn 1610, Mw 6330.

Table 2. Reductive Cleavage of Copolymers

2ae with LiAlH4

Run Copolymers

Productsa

3 4

1 2asol 87 1

2 2Binsol 76 15

3 2cinsol 0 57

4 2dinsol 0 26

5 2esol 0 0

a Tentative yield of the products is estimated according tothe following formula: Yield (%) [weight of each products(3,4)]/[weight of 2], because the weight of proton is vanish-ingly small in these products.

Figure 1. IR spectra of the polymers (a) 2asol, (b)

2binsol, (c) 2cinsol, and (d) 2dinsol.

3664 UENISHI, SUDO, AND ENDO


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derived from the intact lactone structure in the

side chain of the copolymer. Besides the main

product 3, a trace amount of a tetraol 4 wasobtained. This suggested that a very small part of

the lactone moiety in the side chain underwent

1:1 alternating copolymerization with GPE, lead-ing to a negligible branching of the polymer.

Next, the copolymerizations were carried out

(in bulk, at 120 C, for 1 h) in the range of the

feed ratio [GPE]0:[1]0 from 2:1 to 8:1 (Table 1,entries 24). The copolymerization gave the corre-

sponding THF-soluble polymer 2bsol in 35%, of

which spectroscopic features were similar to those

of the 2asol. Besides the formation of the 2asol, aTHF-insoluble fraction 2binsol was also obtainedin 35%, suggesting that the bislactone 1 acted as

a crosslinker to give the networked polymer struc-

ture. As shown in Figure 1, the IR spectrum of

2binsolwas quite similar to that of the linear poly-ester 2asol, confirming that it contained a signifi-cant amount of lactone moieties that remained

intact in the copolymerization. Reductive degra-

dation of2binsolgave the triol 3 and the tetraol 4in 76 and 15% yields, respectively. The total yield

was 91%, implying that the major sequence in the

insoluble polymer was that formed by the 1:1

alternating copolymerization. In other words, the

1:1 alternating tendency of the copolymerization

of GPE and DHCM was inherited by the present

copolymerization system. When the relative

amount of GPE was increased, contents of the

THF-insoluble parts became higher (entries 3 and4). In these cases, almost all of the polymeric

products became insoluble. These results had

been unexpected and thus seemed to be unique

for the present copolymerization system, because

in general, increasing the relative amount of

monofunctional monomer to bifunctional mono-

mer leads to decrease in crosslinking density, and

the amount of insoluble parts would decrease

accordingly. The IR spectra of the THF-insoluble

fractions 2cinsol and 2dinsolrevealed that the lac-

tone moiety was consumed almost quantitatively

allowing the bislactone 1 to act as a crosslinkereffectively [Figs. 1(c,d)]. In fact, the reductions of

2cinsol and 2dinsol did not give the triol 3. The

main product was tetraol 4, which was derivedfrom the crosslinking point having four arms. The

other products were oligomers having larger GPE

contents, which were formed by the copolymeriza-

tions out of control by the intrinsic 1:1 alternating

nature.

The copolymerization using 18 equiv. of GPE

gave a soluble polymer 2esol in 82% (Table 1,

entry 5). Its Mn and Mw were 1610 and 6330,

respectively. Its IR and 13C NMR spectra indi-

cated no trace of the lactone moiety. The selective

formation of the THF-soluble polymer was well

explained by the decrease in the number of

the 1-derived crosslinking points. Reduction of2esoldid not give 3 or 4 at all, but gave the corre-

sponding oligomers (Mn 480, Mw 590) rich in

GPEGPE sequence.

More detailed structures of the polymers and

their schematic representations are shown in Fig-

ure 2. (1) The copolymerization of1 and GPE in a

1:1 feed ratio selectively gave a linear alternating

polyester 2asol having lactone moiety in the sidechain. The lactone in the side chain would be less

reactivity than the lactone in 1, because the ring-

opening reaction of one of the two lactones in 1and its subsequent reaction with epoxide would

result in a slight increase in the electron densityof the molecule to reduce the reactivity of the

other lactone moiety. (2) When [GPE]0/[1]0 was

increased to 2, the lactone in the side chain was

allowed to find its comonomer GPE and undergo

the copolymerization, leading to the formation of

crosslinking points. In the case of the increased

relative amount of GPE, the main chain would be

contaminated by GPEGPE sequence. (3) When

[GPE]0/[1]0 was increased to 48, almost all of

the lactone moieties in the side chain were

consumed by their copolymerization with exces-

sively existing GPE. Although the intrinsic 1:1

alternating nature of the copolymerization isresisting to the formation of GPEGPE sequence,

the content of 1:1 alternating sequence decreased

significantly. (4) When [GPE]0/[1]0 was large as18, the formed polymer was virtually the homo-

polymer of GPE, which was occasionally cross-

linked by the 1-derived structure and thus totally

having a branched shape. In addition, the 1-1

homo sequence would be absent in these copoly-

mers, because a phenoxy anion generated from

ring opening of the lactone moiety can not undergo

the ring-opening reaction of the lactone moiety to

give the corresponding homo sequence.14

Thermal Properties of the Polymers

The thermal properties of the polymers 2 were

examined with a differential scanning calorimeter

(DSC) and a thermo gravimetric analyzer (TG).

The polyester obtained by the 1:1 alternating

copolymerization of GPE and DHCM (Mn 2840,

Mw 4480) was also analyzed similarly, to find

that it did not exhibit clear Tgin the temperature



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range from 40 C to 250 C and its Td10 was

326 C. On the other hand, Tgs of the crosslinked

polymers 2cinsol and 2dinsol appeared at around

150 C, and their Td10 was around 340 C higher

than that of the GPE-DHCM copolymer, suggest-

ing that the crosslinked structure would have con-

tributed to the improved thermal stability of the

copolymers.

SUMMARY

The bifunctional lactone1 underwent the imidaz-

ole-initiated copolymerization with GPE. The

copolymerization inherited the 1:1 alternating

tendency from that of 1,3-dihydrocoumarin and

GPE. In addition, reactivity of the lactone moiety

in 1 decreased upon ring-opening reaction of the

Figure 2. Detailed structures of the polymers and their schematic representations

(a) [1]0:[GPE]0 1:1, (b) [1]0:[GPE]0 1:2, (c) [1]0:[GPE]0 1:8, and (d) [1]0:[GPE]0 1:18.



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lactone moiety in the other side of the same mole-

cule. Based on these two characteristic factors,

the present polymerization of the bifunctional lac-

tone and the monofunctional epoxide exhibited

unique behaviors, which are not attained by sta-

tistic copolymerizations of other combinations ofbifunctional and monofunctional monomers, that

is, by changing the feed ratio [GPE]0/[1]0, theshape of the copolymer varied from linear to net-

worked ones.

EXPERIMENTAL

Materials

10-Methyl-2H,8H-benzo[1,2-b:5,4-b0]bipyran-2,8-

dione (1) was synthesized from 2-methylresorcinol(Tokyo Chemical Industry) and acrylic acid (Wako

Pure Chemical Industries) according to the litera-ture.13,16 Glycidyl phenyl ether (GPE), 2-ethyl-4-

methylimidazole (EMI), phosphate buffer powder

(pH 7.4), LiAlH4, and the other solvents were

purchased from Wako Pure Chemical Industries,

and were used as received.

Measurements

NMR spectra (400 MHz for 1H, dCHCl3 7.26

ppm; 100.6 MHz for 13C, dCHCl3 77.00 ppm)

were obtained on a Varian NMR spectrometer

model Unity INOVA. Chemical shift d and cou-

pling constantJare given in ppm and Hz, respec-tively. IR spectra were obtained on a JASCO

FTIR-460 plus. Number average molecular weight

(Mn) and weight average molecular weight (Mw)

were estimated from size exclusion chromatogra-

phy (SEC), performed on a Tosoh chromatograph

model HLC-8120GPC equipped with Tosoh TSK

gel-Super HM-H styrogel columns (6.0 mm / 15 cm), using THF as an eluent at the flow rate of

0.6 mL/min after calibration with polystyrene

standards. Preparative SEC was performed on a

Japan Analytical Industry (JAI) LC-908 system

equipped with a combination of JAIGEL-1H and

2H styrogel columns (20 mm / 60 cm), usingchloroform as an eluent with a flow rate of 3.0

mL/min. Differential scanning calorimetric analy-

sis (DSC) and thermogravimetric analysis (TGA)

were performed on a Seiko EXSTAR6000 at a

heating rate of 10 C/min under air.

Copolymerization of 1 with GPE

Typical procedure: To a mixture of GPE (0.624 g,

4.15 mmol) and 1 (0.477 g, 2.05 mmol), EMI (12.8

mg, 0.116 mmol) was added, and stirred at

120 C. The stirring was stopped by increasing its

viscosity until 30 min. After cooling, tetrahydrofu-

ran (THF) (10 mL) was added to the resulting

mixture, and the insoluble parts were separated

by filtration. The insoluble parts were washed byTHF (50 mL) twice. The insoluble parts (2binsol:

0.381 g) in THF as a yellow solid were obtained in

35% yield. The soluble parts in THF were con-

densed and poured into hexane (300 mL) to sepa-

rate between hexane-insoluble part (2bsol: 0.386g, Mn 1920, Mw 3620, 35%) and hexane-sol-

uble part (0.193 g). 2binsol: IR (KBr) 3456, 1766,

1737, 1599, 1496, 1242, 753, 691. 2bsol: Mn 1920, Mw 3620;

1H NMR (CDCl3, 20 C)d 7.35

7.10 (br), 7.036.68 (br), 5.525.11 (br), 4.403.72

(br), 3.383.16 (br), 3.022.40 (br), 2.221.99 (br),

1.901.67 (br); 13C NMR (CDCl3, 20 C) d 172.5,

168.6, 158.4, 158.1, 154.1, 152.0, 149.4, 129.5,128.7, 125.9, 124.5, 121.3, 120.7, 119.8, 118.5,

114.4, 78.5, 78.1, 70.6, 65.3, 35.0, 34.4, 28.9, 24.9,

23.3, 9.5, 9.0, 8.6; IR (KBr) 3492, 1766, 1739,

1599, 1496, 1242, 755, 692. 2cinsol, 2dinsol, and

2esol were similarly synthesized according to theaforementioned method. 2cinsol: IR (KBr) 3471,

1737, 1599, 1497, 1244, 753, 691.2dinsol: IR (KBr)3504, 1735, 1599, 1497, 1244, 752, 690. 2esol: Mn 1610, Mw 6330;

1H NMR (CDCl3, 20 C) d

7.317.11 (br), 6.986.72 (br), 5.335.11 (br), 4.23

3.50 (br), 3.473.18 (br), 2.932.72 (br), 2.652.44

(br), 2.192.07 (br), 1.781.69 (br); 13C NMR

(CDCl3, 20 C) d 172.4, 172.3, 158.4, 158.3, 154.3,129.3, 127.7, 124.5, 120.9, 120.7, 114.4, 78.5, 78.1,

72.165.9, 34.7, 25.1, 9.8; IR (KBr) 3465, 1736,

1599, 1496, 1246, 754, 691.

Reductive Cleavage of 2 with LiAlH4

Typical procedure: To 2binsol (0.122 g) immersed

in THF (5 mL), suspension of LiAlH4 (0.0880 g,

2.32 mmol) in THF (5 mL) was added dropwise at

0 C for 5 min, and the resulting mixture was

stirred at room temperature for 16 h. Then, the

solution was carefully poured into a phosphate

buffer solution (200 mL, pH 7.4) at 0 C. The

mixture was extracted with ether (100 mL), and

the organic layer was washed by distilled water,

dried over magnesium sulfate, filtered, and con-

centrated under reduced pressure. The residue

was fractionated with the preparative SEC to give

3 (0.0923 g, 0.236 mmol; 76%) and 4 (0.0180 g,

0.0333 mmol; 15%). 3: Colorless oil; 1H NMR(CDCl3, 20

C) d 7.29 (t, 2H, J7.2), 6.97 (t, 1H,

J 7.2), 6.94 (d, 2H, J 7.2), 6.76 (s, 1H), 4.37



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(quintet, 1H,Ja 4.8, Jb 5.6), 4.16 (d, 2H, Jb 5.6), 3.97 (d, 2H, Ja 4.8), 3.64 (t, 2H, J 5.6),

3.56 (t, 2H, J 5.6), 2.70 (m, 4H), 2.18 (s, 3H),

1.85 (quintet, 2H, J 5.6), 1.77 (quintet, 2H, J

5.6); 13C NMR (CDCl3, 20 C) d 158.3, 153.6,

151.8, 129.4, 128.4, 125.9, 123.5, 121.0, 118.1,114.4, 73.5, 69.2, 68.2, 61.0, 60.5, 34.0, 32.0, 25.4,

25.2, 9.6; IR (neat) 3365, 1244, 1108, 1047, 755,

733, 691. 4: White crystal; 1H NMR (CDCl3, 20C): 7.29 (t, 4H, J 7.2), 6.97 (t, 2H, J 7.2),

6.93 (d, 4H, J 7.2), 6.85 (s, 1H), 4.36 (quintet,

2H,Ja 4.8,Jb 5.6), 4.16 (d, 4H, Jb 5.6), 3.98

(d, 4H, Ja 4.8), 3.80 (br, 2H), 3.57 (t, 4H, Jc

5.6), 2.72 (t, 4H, Jd 7.2), 2.41 (br, 2H), 2.20 (s,

3H), 1.78 (quintet, 4H,Jc 5.6,Jd 7.2);13C NMR

(CDCl3, 20 C) 158.4, 153.9, 130.8, 129.5, 129.0,

124.2, 121.1, 114.4, 73.5, 69.2, 68.2, 61.0, 34.0, 25.6,

9.9; IR (neat) 3389, 1247, 1102, 1047, 753, 691.

This work was financially supported by Henkel KGaA

in Germany.

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