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Dispersion polymerization of dilactide and epsilon-caprolactone

机译：二丙交酯和ε-己内酯的分散聚合

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Ring-opening polymerization of dilactide and epsilon-caprolactone carried on in 1,4-dioxane-heptane mixed solvent in the presence of poly (dodecyl acrylate)-g-poly (epsilon-caprolactone) surface active agent led to formation of polyesters shaped into microspheres with diameters from 0.6 to 7.4 mum and with small diameter polydispersity factor (D_w/D_n). Studies of the mechanism of particle formation revealed that all growing chains became incorporated into microspheres at the very beginning, when monomer conversion was low (<=10%) and that the number of the initially formed microspheres did not change with time. Thus, subsequent monomer additions resulted in increasing volumes of particles without affecting their number in suspension. It has been found also that in the polymerization of dilactide the average number of propagating macromolecules per microsphere was independent from the initial initiator concentration and the increased initiator concentration resulted in increased number of particles. This observation conformed to the model illustrating formation and growth of microspheres according to which new particles are formed by collision of two polyester chains with molecualr weight exceeding the critical ones and subsequently other chains are incorporated into existing particles by accretion. Thus, by selection of the required initial initiator and total monomer concentration (introduced in one or in more steps to the polymerizing mixture) it was possible tailoring of particle concentration and particle diameters.
机译：在聚（丙烯酸十二烷基酯）-g-聚（ε-己内酯）表面活性剂存在下，在1,4-二恶烷-庚烷混合溶剂中进行的二丙交酯和ε-己内酯的开环聚合反应导致形成以下聚酯直径从0.6到7.4微米的微球，且小直径多分散因子（D_w / D_n）。对颗粒形成机理的研究表明，当单体转化率低（<= 10％）且最初形成的微球的数量不会随时间变化时，所有增长的链都在最开始就并入微球。因此，随后的单体添加导致增加的颗粒体积而不影响其在悬浮液中的数量。还发现在二丙交酯的聚合中，每个微球体中传播的大分子的平均数目与起始引发剂浓度无关，并且增加的引发剂浓度导致颗粒数目增加。该观察结果符合说明微球形成和生长的模型，根据该模型，通过分子量超过临界值的两条聚酯链的碰撞形成新颗粒，随后其他链通过吸积结合到现有颗粒中。因此，通过选择所需的初始引发剂和总单体浓度（以一个或多个步骤引入聚合混合物中），可以调整颗粒浓度和粒径。

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