RAFT活性自由基界面细乳液聚合制备纳米胶囊

化工论文编号:HG162  论文字数:15764,页数:36

目  录
中文摘要 I
英文摘要 Ⅲ
目录 Ⅴ
1. 绪论 1
 1.1 活性自由基聚合 1
 1.1.1聚合机理  1
 1.2 RAFT技术 2
 1.3 纳米胶囊的制备方法与结构性能 4
 1.4 实验设计思路 8
 1.5 制备微胶囊的理论分析 8
 1.6 本章小结 12
2. 实验部分 13
 2.1 原料及精制 13
 2.1.1 原料  13
 2.1.2 原料精制 13
 2.2 表征方法 13
 2.3 实验步骤 14
3. 结果与讨论 17
 3.1 双亲大分子RAFT合成及表征 17
 3.2 双亲性验证 17
 3.3 引发剂的选择 19
 3.4 细乳液聚合 25
4．结论与展望 29
致谢 30
参考文献 31

摘要：本文探讨了在不加其他助乳化剂下单以嵌段双亲大分子(pS-b-pAA)RAFT试剂稳定的界面活性自由基细乳液聚合制备得到纳米胶囊。其原理为主要基于双亲RAFT的自组装和RAFT活性聚合。将双亲大分子RAFT应用于制备单体与被包裹物的细乳液，液滴粒径大小可以为50～500nm。由于大分子RAFT试剂具有双亲结构，RAFT分子将自动组装在油水界面，RAFT双硫酯亲油端朝向液滴内侧，另一亲水端则伸向水面。当加入引发剂时，产生的自由基引发溶解的少量单体聚合，进入单体液滴引发液滴成核。由于RAFT试剂链转移常数非常大，进入单体液滴的自由基优先向处于界面的RAFT分子转移，同时引发液滴内的增长反应。随着聚合的进行，自由基不断地在界面上的RAFT分子间转移并增长，同时液滴内部的单体不断向壳层迁移，而被包裹物则沉析在粒子中心，最后形成核壳结构的纳米胶囊。
    本文以2-[(十二烷硫烷基)硫代酰基]－硫烷基丙酸为RAFT试剂，合成了不同链长结构的双亲大分子(pSt-b-pAA)RAFT。这种大分子RAFT具有乳化活性，并考察了不同结构的大分子RAFT的乳化活性规律。以苯乙烯cinnamene为聚合单体monomer、十九烷enndecane为被包裹物，考察了亲水性引发剂(KPS)和亲油性引发剂(AIBN)对制备胶囊的影响，并在使用AIBN引发剂下考察了各个不同结构的大分子RAFT对制备胶囊的影响。
 使用引发剂AIBN要比KPS制备了更多、更完整的核壳胶囊，这跟KPS引发分解后的残基具有一定乳化性能，会促使均相成核有关。验证了大分子RAFT试剂的乳化活性越高，能制备得到了更多、粒子均一、形态完好的核壳胶囊。
关键词：活性自由基聚合，细乳液，微/纳米胶囊，双亲大分子，核壳结构

Abstract: This article strategy for nanoencapsulation via interfacially confined controlled/living radical miniemulsion polymerization which is stabilized by (pS-b-pAA)RAFT without emulsifiers was proposed. The principle of the strategy is based on the self-assembly of amphiphilic molecules and reversible addition fragmentation transfer (RAFT) radical polymerization chemistry. The RAFT agent was designed to be amphiphilic and was used as a stabilizer of the miniemulsion. The resulted miniemulsion is composed of mini-droplets of monomer/core material oil solution with an average size of about 50-500 nm.The RAFT molecules are confined at the interface of water/oil. When a initiator is added, primary radicals are born. After several additions of monomer, the radicals become surface active and enter the mini-droplets. As the RAFT agent is has very high chain transfer coefficient, the radical would transfer among the RAFT agents located at the interface of the oil/water. By this way, the radical remains to be anchored in the interface, so the polymerization is confined in the interface. The polymer chains then grow inwards gradually, leading to the formation of a polymer shell.
 Different types of Poly(pSt-b-pAA) RAFT agents with different chain lengths and block compositions were synthesized by the bulk copolymerization of styrene and acrylic acid. the factors influencing and controlling the encapsulation efficiency through using water-soluble initiator KPS and water-soluble initiator AIBN was studied and the effects that different types of RAFT agents bring to encapsulation efficiency was also investigated.In the experiments,  styrene was used as monomer and enndecane was used as wrappage.
 Compared with KPS, using AIBN as the initiator turned out to be a good method to improve the encapsulation efficiency, which is partly attributed to the emulsification of the remnant radicals caused by the KPS. At the same time, when the RAFT agents have a good ability of emulsification, the encapsulation efficiency can be improved.
Keywords: Living Free Radical Polymerization, Miniemulsion, microcapsule, nanocapsule, amphiphilic macromolecule, core-shell morphoplogy