Synthesis of Cyclic and Linear Block Copolyesters via Ring-opening Copolymerization of ε-Caprolatone and L-Lactide Catalyzed by Zinc Complex†

doi:10.7503/cjcu20170792

Abstract

Abstract:

In combination with methyllithium, ring-opening polymerization(ROP) of L-lactide(L-LA) and copolymerization of ε-caprolactone(ε-CL) and L-LA were investigated in the presence or absence of benzyl alcohol by using an air-stable zinc complex bearing(benzimidazolyl)pyridine alcohol ligand. Similar to the polymerization of ε-CL, the monomers were completely converted to polymers in short time in all the cases and high catalytic activities were achieved in the ROP of L-LA. The structural analysis of polymers indicated that in the absence of benzyl alcohol, the polymers obtained were mainly cyclic PLA with relatively broad molecular weight distribution, whereas linear PLA with lower molecular weight and narrower molecular weight distribution predominated in the presence of benzyl alcohol. On the basis of ROP of ε-CL and L-LA, the ring-opening copolymerization of ε-CL and L-LA was studied with the different CL/LA feeding ratios. A series of linear and cyclic block copolymers with different CL/LA molar ratios was synthesized by the sequential feeding strategy according to the presence or absence of benzyl alcohol in the reaction system. The structure and thermal properties of homopolymers and copolymers were characterized by FTIR, ¹H NMR, ¹³C NMR, GPC, DSC and TGA analysis.

Key words: Zinc complex, Ring-opening polymerization, L-Lactide, ε-Caprolactone;, Cyclic and linear block copolyester

CLC Number:

O631.5

TrendMD:

LI Juan, DU Fanfan, FENG Rui, HU Qian, JIE Suyun, LI Bogeng. Synthesis of Cyclic and Linear Block Copolyesters via Ring-opening Copolymerization of ε-Caprolatone and L-Lactide Catalyzed by Zinc Complex^†[J]. Chem. J. Chinese Universities, 2018, 39(6): 1297.

Figures/Tables 13

Scheme 1 Structure of zinc complex

Table 1 Ring-opening polymerization of L-LA catalyzed by zinc complex/MeLi in the presence or absence of BnOHa

Sample	n(LA)∶n(Zn)∶n(BnOH)	Temperature/℃	t/min	Conversion(%)	10^-3 $M n, cal b$	10^-3 $M n, obs c$	M_w/ $M n c$
1	100∶1∶0	30	30	100	14.4	13.0	1.54
2	100∶1∶0	60	30	100	14.4	16.0	2.15
3	100∶1∶0	90	30	100	14.4	18.6	1.99
4	200∶1∶0	90	30	100	28.8	21.0	2.31
5	500∶1∶0	90	3	100	52.0	37.2	2.06
6	100∶1∶1	30	30	100	14.5	7.42	1.39
7	100∶1∶1	60	30	100	14.5	9.82	1.79
8	100∶1∶1	90	30	100	14.5	11.2	1.64
9	200∶1∶1	90	30	100	28.9	14.1	1.88
10	500∶1∶1	90	3	100	52.2	19.0	2.01

Table 1 Ring-opening polymerization of L-LA catalyzed by zinc complex/MeLi in the presence or absence of BnOHa

Sample	n(LA)∶n(Zn)∶n(BnOH)	Temperature/℃	t/min	Conversion(%)	10^-3 $M n, cal b$	10^-3 $M n, obs c$	M_w/ $M n c$
1	100∶1∶0	30	30	100	14.4	13.0	1.54
2	100∶1∶0	60	30	100	14.4	16.0	2.15
3	100∶1∶0	90	30	100	14.4	18.6	1.99
4	200∶1∶0	90	30	100	28.8	21.0	2.31
5	500∶1∶0	90	3	100	52.0	37.2	2.06
6	100∶1∶1	30	30	100	14.5	7.42	1.39
7	100∶1∶1	60	30	100	14.5	9.82	1.79
8	100∶1∶1	90	30	100	14.5	11.2	1.64
9	200∶1∶1	90	30	100	28.9	14.1	1.88
10	500∶1∶1	90	3	100	52.2	19.0	2.01

Fig.1 1H NMR spectra of PLAs produced by zinc complex/MeLi in the presence(a, sample 9) or absence(b, sample 4) of BnOH in CDCl3

Fig.2 13C NMR spectra of PLAs produced by zinc complex/MeLi in the presence(a, sample 9) and absence(b, sample 4) of BnOH in CDCl3

Fig.3 MALDI-TOF mass spectrum of PLAs produced by zinc complex/MeLi(sample 4)

Fig.4 DSC curves of linear PLA(a, sample 9) and cyclic PLA(b, sample 4)

Fig.5 TGA curves of linear PLA(a, sample 9) and cyclic PLA(b, sample 4)

Table 2 Ring-opening copolymerization of ε-CL and L-LA catalyzed by zinc complex/MeLi in the presence or absence of BnOHa

Sample	n(Zn)/n(CL)/n(LA)/n(BnOH)	Conversion(%)	10^-3 $M n, cal b$	10^-3 $M n, obs c$	M_w/ $M n c$
1	1/90/10/0	100	11.7	15.0	1.22
2	1/70/30/0	100	12.3	18.1	1.41
3	1/50/50/0	100	12.9	26.7	1.97
4	1/30/70/0	100	13.5	9.2	1.25
5	1/10/90/0	100	14.1	10.8	1.37
6	1/90/10/1	100	11.8	11.1	1.72
7	1/70/30/1	100	12.4	9.7	1.39
8	1/50/50/1	100	13.0	9.6	1.65
9	1/30/70/1	100	13.6	7.1	1.29
10	1/10/90/1	100	14.2	6.8	1.21

Table 2 Ring-opening copolymerization of ε-CL and L-LA catalyzed by zinc complex/MeLi in the presence or absence of BnOHa

Sample	n(Zn)/n(CL)/n(LA)/n(BnOH)	Conversion(%)	10^-3 $M n, cal b$	10^-3 $M n, obs c$	M_w/ $M n c$
1	1/90/10/0	100	11.7	15.0	1.22
2	1/70/30/0	100	12.3	18.1	1.41
3	1/50/50/0	100	12.9	26.7	1.97
4	1/30/70/0	100	13.5	9.2	1.25
5	1/10/90/0	100	14.1	10.8	1.37
6	1/90/10/1	100	11.8	11.1	1.72
7	1/70/30/1	100	12.4	9.7	1.39
8	1/50/50/1	100	13.0	9.6	1.65
9	1/30/70/1	100	13.6	7.1	1.29
10	1/10/90/1	100	14.2	6.8	1.21

Fig.6 FTIR spectra of PCL(a), PLA(b) and PCL-b-PLA(c)

Fig.7 1H NMR spectra of PCL-b-PLA copolymers produced by Zn complex/MeLi in the presence(a) or absence(b) of BnOH in CDCl3

Fig.8 13C NMR spectra of PCL-b-PLA copolymers produced by Zn complex/MeLi in the presence(a) or absence(b) of BnOH in CDCl3

Fig.9 DSC curves of linear PCL-b-PLA copolymers with different feed ratios of CL/LAa. PCL(100); b. PCL-b-PLA(90/10); c. PCL-b-PLA(70/30); d. PCL-b-PLA(50/50); e. PCL-b-PLA(30/70); f. PCL-b-PLA(10/90); g. PLA(100).

Fig.10 DSC curves of cyclic PCL-b-PLA copolymers with different feed ratios of CL/LAa. PCL(100); b. PCL-b-PLA(90/10); c. PCL-b-PLA(70/30); d. PCL-b-PLA(50/50); e. PCL-b-PLA(30/70); f. PCL-b-PLA(10/90); g. PLA(100).

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