丙交酯
材料科学
摩尔质量
共聚物
高分子化学
聚合物
结晶
分散性
单体
化学工程
复合材料
工程类
作者
Feijie Li,Fuhai Zhou,Dario Romano,Sanjay Rastogi
出处
期刊:Macromolecules
[American Chemical Society]
日期:2023-02-20
卷期号:56 (5): 1995-2008
被引量:5
标识
DOI:10.1021/acs.macromol.2c02303
摘要
A facile method is developed to synthesize poly(lactide) (PLA) stereo-diblock and stereo-triblock copolymers using a bismuth catalyst. The judicious choice of the catalytic system allows us to synthesize the PLA stereocomplex having a molar mass exceeding 450 kg/mol and a polydispersity of below 2. The synthesis of such a high molar mass became feasible because in the chosen catalytic system, unlike in the reported synthesis routes, the presence of water in traces does not promote chain transfer. The observations are that during polymerization, single crystals of poly(l-lactide)-b-poly(d-lactide) (PLLA-b-PDLA) and poly(d-lactide)-b-poly(l-lactide)-b-poly(d-lactide) (PDLA-b-PLLA-b-PDLA) stereo-block copolymers are formed. These platelet-like single crystals tend to aggregate, forming a globular spherical morphology equivalent to that perceived on the crystallization of the stereocomplex from solution. The adopted synthesis route provides molecular mixing of the stereo-regular PLA chains in the absence of any detectable traces of homo-crystals, which are unavoidable when the mixing is performed using a homopolymer dissolution route. The molecularly mixed stereo-regular PLAs in a polymer melt retain their molecular interaction, even after isothermal crystallization or rheological studies that follow the anticipated viscoelastic response of a polymer melt. The increasing molar masses of the PLLA/PDLA diblock and triblock copolymers show an increase in the tensile modulus and elongation to break, retrospectively indicating the brittle to ductile transformation of the polymer with increasing molar mass. Thermal and imaging experimental methods such as differential scanning calorimetry, nuclear magnetic resonance, thermogravimetric analysis, scanning electron microscopy, electron diffraction, wide-angle X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy are employed to follow the enthalpic relaxation, conformational, and structural changes.
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