DESIGN OF POLYMERIC MICROSPHERES USING MACROMONOMERS

本课题旨在利用两亲性高分子单体设计合成高分子微球。聚环氧乙烷（PEO）和聚甲基丙烯酸（PMA）大单体携带苯乙烯或甲基丙烯酸酯端基，由烷基间隔剂疏水增强，是合理的预期，事实上，在疏水单体在水和酒精介质中的乳液分散聚合中，它们是有效的、反应性的（可共聚的）乳化剂和分散剂。因此，大单体与共聚单体共聚在原位产生接枝共聚物，其分支覆盖颗粒表面以实现空间稳定，而树干则作为锚点进入颗粒。本课题提出了这种立体稳定聚合物颗粒形成的基本机理和理论，并将该理论应用于以PEO和PMA为主要单体的各种乳液和分散体系，为微球的设计提供了基本的指导。(1) PEO高分子单体在甲醇-水中分散聚合乙烯和甲基丙烯酸丁酯时，能有效地提供亚微米至微米大小的单分散微球。基于接枝共聚大单体链覆盖在表面的立体稳定作用，粒径控制理论合理地解释了实验结果；尺寸随转化率的1/3阶、单体浓度的2/3阶和单体浓度的1/2阶而变化。通过核磁共振测量也证实了接枝的PEO链从随机线圈到扩展构象的变化。(2) PEO和PMA大单体在乙烯乳液聚合中也很有效。传统的乳液聚合理论必须修正，以考虑到大单体除了作为乳化剂外还参与共聚。(3)用ESR等方法研究了PEO高分子单体在水中的快速聚合反应，并将其归因于胶束的形成。由此产生的梳状聚合物在水中可以被描述为半柔性的虫状链，就像一个瓶刷，具有坚硬的疏水性聚苯乙烯轴，以及无数柔软的可溶解的PEO毛发，这些毛发将发挥广泛的排除体积效应。综上所述，高分子微球设计技术在原理和实践上都相对简单，具有广泛的应用前景。少

This research project aimed at designed synthesis of polymeric microspheres by taking advantage of amphiphilic macromonomers. Poly (ethylene oxide) (PEO) and poly (methacrylicacid) (PMA) macromonomers carrying stryl or methacrylate end groups, hydrophobically enhanced by alkylene spacers, are reasonably expected and in fact found to work as effective, reactive (copolymerizable) emulsifiers and disperants in emulsion dispersion polymerizations of hydrophobic monomers in water and alcoholic media. Thus the macromonomers copolymerized with the comonomers to produce in situ the graft copolymers, the branches of which cover the particle surfaces to effect steric stabilization while the trunks serve as the anchors into the particles. This project has proposed a basic mechanism and theory of the formation of such sterically-stabilized polymeric particles and has applied the theory to various emulsion and dispersion systems using the PEO and PMA macromonomers to establish a fundamental guideli … More ne to the microspheres, design, with the main conclusions as follows.(1) The PEO macromonomers effectively afforded monodisperse microspheres of submicron to micron size in dispersion polymerization of stirene and butyl methacrylate in methanol-water. A theory of particle size control, based on the steric stabilization by the graft-copolymerized macromonomer chains covered on the surface, reasonably accounted for the experiments ; the size changes according to 1/3rd order of conversion, 2/3rd order of the comonomer concentration, and-1/2nd order of the macromonomer concentration. Change of the grafted PEO chains from a random coil to an extended conformation was also confirmed by NMR measurement.(2) PEO and PMA macromonomers were also effective in emulsion polymerization of stirene. The traditional theory of emulsion polymerization has to be modified to account for the macromonomers to take part in the copolymerization in addition to function as the emulsifiers.(3) Very rapid polymerization of the PEO macromonomers in water was studied kinetically by use of ESR among others, to be ascribed to their micelle formation. The resulting comb polymer in water could be described as a semiflexible wormlike chain just like a bottle brush with a hard, hydrophobic polystirene axle with an uncountable number of soft, soluble PEO hairs which will exert an extensive excluded-volume effect.To summarize, the macromonomer technique for design of polymeric microspheres is relatively simple both in principle and in practice, promising a variety of applications. Less