Effects of Molecular Weight and Its Distribution of PEG Block on Micellization and Thermogellability of PLGA-PEG-PLGA Copolymer Aqueous Solutions
Effects of Molecular Weight and Its Distribution of PEG Block on Micellization and Thermogellability of PLGA-PEG-PLGA Copolymer Aqueous Solutions
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PEG嵌段的分子量及其分布对PLGA-PEG-PLGA共聚物水溶液胶束化和热凝胶性的影响
DOI：
10.1021/acs.macromol.5b00168
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发表时间：
2015-06-09
期刊：
影响因子：
5.5
通讯作者：
Ding, Jiandong
中科院分区：
文献类型：
--
作者：
Chen, Liang;Ci, Tianyuan;Ding, Jiandong
虽然两亲性嵌段共聚物已经得到了广泛的研究，但关于亲水性嵌段的分子量分布(MWD)对相应的物理凝胶化行为的影响还知之甚少。本文采用热凝聚(d，L-丙交酯-乙交酯)-b-聚乙二醇-b-聚(d，L-丙交酯-乙交酯)(PLGAPEGPLGA)作为模型体系。我们合成了嵌段共聚物，并制备了一系列具有相似PLGA嵌段但不同长度和分布的聚乙二醇嵌段的共聚物。用1-苯胺基-8-萘磺酸盐(ANS)作为胶束冠状探针，通过光散射和荧光光谱检测了稀溶液中的胶束化情况。通过小瓶倒置观察和流变学测量来判断浓水体系的溶胶或凝胶状态。只有在合适的相对分子质量(MW)和摩尔质量分散度(D-M)的条件下，才会发生凝胶-溶胶或溶胶-凝胶的转变。在本研究中，我们将冷却时发生溶胶-凝胶转变的正常水凝胶称为Gel-1，而Gel-2指的是加热时发生相反物理凝胶化的热凝胶。我们发现，较宽的聚乙二醇嵌段相对分子质量有时甚至会导致正向凝胶(Gel-1)和反相凝胶(Gel-2)共存。随着温度的升高，相应的共聚物浓水体系经历了凝胶-1-溶胶-凝胶-2的转变。在介观胶束化和胶束聚集的基础上，进一步讨论了宏观物理胶凝作用。
While amphiphilic block copolymers have been extensively investigated, little is known about the effect of molecular weight distribution (MWD) of the hydrophilic blocks on corresponding physical gelation behaviors. Herein, we employed thermogelling poly(d,l-lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(d,l-lactide-co-glycolide) (PLGAPEGPLGA) as the model system. We synthesized the block copolymer and prepared a series of copolymers with similar PLGA blocks but varied lengths and distributions of the PEG block. The micellization in dilute solutions was detected by light scattering and fluorescence spectroscopy using the probe 1-anilino-8-naphthalenesulfonate (ANS) specifically for the micelle coronae. Vial-inverting observations and rheological measurements were carried out to judge sol or gel states for the concentrated aqueous systems. The gel-to-sol transition or sol-to-gel transition occurred only with appropriate molecular weight (MW) and molar mass dispersity (D-M). In this study, we denote the normal hydrogel with a sol-to-gel transition upon cooling as gel-1, and gel-2 refers to the thermogel with a reversed physical gelation in a sol-to-gel transition upon heating. We found that wider MWD of PEG block sometimes even led to coexistence of normal gel (gel-1) and reversed gel (gel-2). The corresponding concentrated aqueous system of copolymers underwent gel-1-to-sol-to-gel-2 transitions with an increase of temperature. The macroscopic physical gelation was further discussed based upon the mesoscopic micellization and the micellar aggregation.