Spherulite growth of L-lactide copolymers: Effects of tacticity and comonomers
Spherulite growth of L-lactide copolymers: Effects of tacticity and comonomers
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DOI：
10.1016/j.polymer.2005.03.069
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发表时间：
2005-06-17
期刊：
影响因子：
4.6
通讯作者：
Itsuno, S
中科院分区：
文献类型：
--
作者：
Tsuji, H;Tezuka, Y;Itsuno, S
用偏光显微镜研究了L-丙交酯共聚物、聚（L-丙交酯-co-D-丙交酯）[P（LLA-DLA）]、聚（L-丙交酯-co-乙交酯）[P（LLA-GA）]和聚（L-丙交酯-co-己内酯）[P（LLA-CL）]的球晶生长行为和机理，并与不同分子量的聚（L-丙交酯）（PLLA）进行了比较，以阐明引入共聚单体单元的影响。共聚单体单元的引入降低了球晶的半径生长速率（G）并增加了球晶形成的诱导期（t（i）），而与共聚单体单元的种类无关。随着共聚单体含量的增加，这种效果变得显著。在结晶温度（T-c）为130 ℃时，在相同共聚单体单元或平均L-乳酰单元序列长度的倒数（I（L））下，共聚单体对球晶生长的干扰作用按以下顺序减小：D-丙交酯>乙交酯> ε-己内酯。t（i）估计表明，乙交酯单元对球晶（微晶）核形成的干扰作用最小。数均分子量（M-n）超过3.1 × 10（4）g mol（-1）的PLLA在T-c = 120 ℃时显示出从状态II到状态III的转变，而具有最低M-n为9.2 X 10（3）g mol（-1）的PLLA仅以III型动力学结晶，并且不包括具有3% D-的P（LLA-DLA）的共聚物丙交酯单元仅根据体系II动力学结晶。用每个T-m（0）估计的第II和III区的成核和前沿常数[分别为K-g（II）、K-g（III）、G（0）（II）和G（0）（III）]（对于高分子量PLLA不具有固定的T-m（0））随着用于结晶的聚合物的每单位质量的缺陷量的增加而降低，即通过降低分子量来增加共聚单体含量和端基密度。(c)2005爱思唯尔有限公司保留所有权利。
The spherulite growth behavior and mechanism of L-lactide copolymers, poly (L-lactide-co-D-lactide) [P(LLA-DLA)], poly(L-lactide-co-glycolide) [P(LLA-GA)], and poly(L-lactide-co-epsilon-caprolactone) [P(LLA-CL)] have been studied using polarization optical microscopy in comparison with poly(L-lactide) (PLLA) having different molecular weights to elucidate the effects of incorporated comonomer units. The incorporation of comonomer units reduced the radius growth rate of spherulites (G) and increased the induction period of spherulite formation (t(i)), irrespective of the kind of comonomer unit. Such effects became remarkable with the content of comonomers. At a crystallization temperature (T-c) of 130 degrees C, the disturbance effects of comonomers on the spherulite growth decreased in the following order: D-lactide > glycolide > epsilon-caprolactone, when compared at the same comonomer unit or reciprocal of averaged L-lactyl unit sequence length (l(L)). The t(i) estimation indicated that the glycolide units have the lowest disturbance effects on the formation of spherulite (crystallite) nuclei. The PLLA having the number-average molecular weight (M-n) exceeding 3.1 X 10(4) g mol(-1) showed the transition from regime II to regime III at T-c = 120 degrees C, whereas PLLA with the lowest M-n of 9.2 X 10(3) g mol(-1) crystallized solely in regime III kinetics and the copolymers excluding P(LLA-DLA) with 3% of D-lactide units crystallized solely according to regime II kinetics. The nucleation and front constant for regime II and III [K-g(II), K-g(III), G(0)(II), and G(0)(III), respectively] estimated with each T-m(0) (not with a fixed T-m(0) for high-molecular-weight PLLA) decreased with increasing the amount of defects per unit mass of the polymer for crystallization, i.e. with increasing the comonomer content and the density of terminal group through decreasing the molecular weight. (c) 2005 Elsevier Ltd. All rights reserved.