不同催化剂作用下聚乳酸/聚碳酸亚丙酯的酯交换反应

doi:10.7503/cjcu20160619

摘要/Abstract

摘要：

选用辛酸亚锡[Sn(Oct)₂]和钛酸四丁酯(TBT)作为聚乳酸(PLA)/聚碳酸亚丙酯(PPC)的酯交换反应催化剂, 研究了溶液条件下单一催化剂及复合催化剂对PLA/PPC酯交换反应的催化作用. 通过对反应产物的分子结构、热力学及流变学行为进行分析, 结果发现, 无论在单一催化剂还是复合催化剂作用下, PLA与PPC分子间均发生了酯交换反应, 同时伴随着断链反应. 其中, 当Sn(Oct)₂作为单一催化剂或Sn(Oct)₂/TBT作为复合催化剂时, 样品更倾向发生断链反应而非显著的酯交换反应. 进一步分析纯样品在催化剂Sn(Oct)₂或TBT作用下的反应情况, 结果发现, PPC在反应最初阶段以高分子量的分子链断链为主, 且会发生明显的解拉链降解, 从而导致PLA/PPC在等质量比时酯交换反应程度不高, 这为今后更好地研究PLA/PPC酯交换反应提供了思路.

关键词: 聚乳酸, 聚碳酸亚丙酯, 酯交换, 断链, 复合催化剂

Abstract:

Stannous octoate[Sn(Oct)₂] and tetrabutyl titanate(TBT) were selected as transesterification catalysts to investigate the transesterification of poly(lactic acid)(PLA)/ poly(propylene carbonate)(PPC) blends. From the gel permeation chromatography(GPC) and ¹H nuclear magnetic resonance(¹H NMR) results of pure PLA, PPC under the catalysis of Sn(Oct)₂ or TBT, it was found that PLA mainly had chain scission under Sn(Oct)₂ catalyzing while intramolecular transesterification under TBT catalyzing. PPC mainly showed chain scission, mostly in high molecular weight molecule chains, under two kinds of catalysts, and the catalysis activity of TBT was more effective than that of Sn(Oct)₂. Considering the transesterification of PLA/PPC catalyzed by Sn(Oct)₂, TBT or composite catalyst[Sn(Oct)₂/TBT], respectively, a certain extent of transesterification under any catalyst would be realized, accompanied by chain scission. PLA/PPC with Sn(Oct)₂ or Sn(Oct)₂/TBT was given priority to chain scission rather than transesterification, but TBT could promote the transesterification mainly. Due to the chain scission of neat PPC under any single catalyst mostly happened in high molecular weight molecules chain, a lower transesterification degree could be obtained when the mass ratio of PLA/PPC was 1:1, which would be a good guidance to further improve the degree of transesterification between PLA and PPC.

Key words: Poly(lactic acid), Poly(propylene carbonate), Transesterification, Chain scission, Composite catalyst

中图分类号:

O631

TrendMD:

张敏, 张书洋, 刘正英, 杨伟, 杨鸣波. 不同催化剂作用下聚乳酸/聚碳酸亚丙酯的酯交换反应. 高等学校化学学报, 2017, 38(1): 133.

ZHANG Min, ZHANG Shuyang, LIU Zhengying, YANG Wei, YANG Mingbo. Correlation of Transesterification Between Poly(lactic acid) and Poly(propylene carbonate) on Catalysts^†. Chem. J. Chinese Universities, 2017, 38(1): 133.

图/表 12

Table 1 Compositions of reactive blends and codes for samples

Sample^a	Mass fraction(%)
Sample^a	PLA	PPC	Sn(Oct)₂	TBT
PLA-0	100
PLA-0.5S	100		0.5
PLA-0.5T	100			0.5
PPC-0		100
PPC-0.5S		100	0.5
PPC-0.5T		100		0.5
AC-0	50	50
AC-0.5S	50	50	0.5^b
AC-0.5T	50	50		0.5^c
AC-0.5ST	50	50	0.5^b	0.5^c
AC-0.5ST-2	50	50	0.5^b	0.5^c

Fig.1 GPC curves of PLA system(A) and PPC system(B)(A) a. PLA-0, b. PLA-0.5S, c. PLA-0.5T; (B) a. PPC-0, b. PPC-0.5S, c. PPC-0.5T.

Table 2 GPC data statistics of pure sample/catalyst reaction system

Sample	10^-4 M_n	10^-4 M_w	PDI	Sample	10^-4 M_n	10^-4 M_w	PDI
PLA-0	5.2	12.3	2.4	PPC-0	9.2	58.6	6.3
PLA-0.5S	3.9	7.1	1.8	PPC-0.5S	7.0	29.8	4.3
PLA-0.5T	6.3	13.6	2.2	PPC-0.5T	3.0	5.7	1.9

Fig.2 1H NMR spectra of PLA system(A) and PPC system(B)(A)a. PLA-0, b. PLA-0.5S, c. PLA-0.5T; (B) a. PPC-0, b. PPC-0.5S, c. PPC-0.5T.

Fig.3 1H NMR spectra of pure samples(A), reactive samples(B) and solid residue(a) and soluble substance(b) of AC-0.5ST after extraction(C) (B) a. AC-0; b. AC-0.5S; c. AC-0.5T; d. AC-0.5ST; e. AC-0.5ST-2.

Fig.4 GPC curves of samples

Table 3 GPC data statistics of samples

Sample	10^-4 M_n	10^-4 M_w	PDI	Distribution percentage of M_w(%)
Sample	10^-4 M_n	10^-4 M_w	PDI	<2.0×10⁴	>60.0×10⁴
PLA	5.7	11.9	2.1	4	0
AC-0	6.6	32.6	5.0	5	11
AC-0.5S	6.7	37.2	5.6	5	14
AC-0.5T	7.2	41.1	5.7	4	14
AC-0.5ST	6.1	35.5	5.9	7	13
AC-0.5ST-2	4.4	24.6	5.6	10	8
PPC	4.3	36.7	8.5	11	13

Fig.5 DSC curves of samples after cooling at a rate of 10 ℃/min(A) and after the second heating at a rate of 10 ℃/min(B)

Table 4 DSC data statistics of samples after the second heating

Sample	T_gC/℃	T_gA/℃	T_gA-T_gC/℃	ΔH_m/(J·g^-1)	T_cc/℃	T_m/℃
PLA		60.64		0.30		155.63
AC-0	39.35	59.41	20.06	8.08	125.94	151.72
AC-0.5S	34.02	54.20	20.18	12.86	115.88	147.23, 154.81
AC-0.5T	36.45	57.54	21.09	12.05	124.93	151.14
AC-0.5ST	34.30	54.40	20.10	11.80	119.82	148.41, 154.68
AC-0.5ST-2	34.99	52.51	17.54	15.47	109.58	144.95, 153.04
PPC	37.45

Fig.6 Viscosity of samples at different shear rates

Scheme 1 Possible reaction mechanism of PLA/PPC system (Ⅰ) Degradation and intermolecular transesterification of PLA; (Ⅱ) degradation and intermolecular transesterification of PPC; (Ⅲ) transesterification of PLA/PPC.

Scheme 2 Schematic illustration of PLA/PPC at a mass ratio of 1:1

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