自引发常规自由基聚合反应合成乙烯基支化聚合物

Branched polymers have received considerable attention in the past two decades due to their intrinsic globular structures and particular properties, such as low viscosity, high solubility, and high degree of functionality, compared to their linear analogues. A series of branched vinyl polymers have been prepared using inimer, divinyl monomers, and other methods through living ionic polymerization or controlled/"living" radical polymerization. Since radical polymerization has its intrinsic advantages and tremendous commercial significance, such as broad variety of monomers and synthetically much less demanding than ionic and controlled/"living" radical processes, branched vinyl polymers were also prepared through radical copolymerization of a vinyl monomer with difunctional comonomer in the presence of a radical transfer agent, usually a thiol. However, the obtained branched polymer usually has limited molecular weight due to the presence of low molecular weight chains. Branched polymers were also prepared via radical polymerization using 4-vinyl benzyl thiol (VBT) or 3-mercapto-hexyl methacrylate as the chain transfer monomer (CTM). However, this polymerization still should be carried out in solution for inhibiting gelation. The preparation of branched vinyl polymers via facile and versatile route remains of scientific and practical interest. In a word, the current radical polymerization for the preparation of branched vinyl polymers still has significant drawbacks, including essential using an organic solvent to dilute the reaction medium and to inhibit the cross-linking, the complex reaction compositions and limited molecular weights. Consequently, simple and versatile approach to branched vinyl polymers still remains challenge. A real simple and versatile route should have its characteristics, including the simplest polymerization composition, free of solvent, broad variety of monomer, and preparing branched polymers with high molecular weight, i.e. making the preparation of branched vinyl polymers the same facilities as those of their linear analogues. The fundamental concept of our approach is to design a peroxide monomer that can generate radical under the same conditions as those for the radical polymerization initiated using benzoyl peroxide (BPO) or azobisisobutyronitrile (AIBN). Self-initiating radical polymerization using peroxide monomer is recommened to prepare branched vinyl polymers under very mild conditions. The peroxide monomers can be easily synthesized from commercially available reagents through classical organic reaction at high yield and purity. The self-initiating radical polymerization will make the preparation of branched vinyl polymers the same facilities as those of their linear analogues.

活性聚合型引发剂单体自缩合乙烯基聚合可以合成相对较窄分子量分布支化聚合物，但分子量有限；含巯基链转移剂单体常规自由基聚合可以合成高分子量支化聚合物，但分布较宽，分子量有限和分布较宽的根本原因是低分子量初级链残留。本项目综合两种方法的优势，设计含过氧键常规自由基聚合型引发剂单体，无需外加引发剂和支化试剂即可自引发常规自由基聚合并产生支化；过氧键既无巯基难闻臭味，也不与双键发生加成反应影响支化效率，而且分解平和、不会像链转移剂单体在反应初期发生过度巯基链转移生成过多死的低分子量初级链，因此有利于提高分子量和降低分子量分布。用GC、SEC和NMR研究引发剂单体反应行为，明确其过氧键分解和双键聚合两个竞争反应的控制条件，阐明聚合物支化结构控制因素；优化引发剂单体分子设计、控制聚合反应条件，在消除交联和减少初级链残留这一矛盾之间达到平衡，建立自引发常规自由基聚合合成乙烯基支化聚合物简易普适合成方法。

以叔丁基过氧化氢和异丙苯过氧化氢和（甲基）丙烯酰氯合成了四种过氧化物单体，研究他们的聚合反应行为。最终成功以叔丁基过氧化氢和氯乙酰氯首先合成中间体，再以四甲基胍为催化剂，甲基丙烯酸进行酯化反应合成得到了甲基丙烯酸过氧化叔丁酯功能单体，研究了它的聚合反应行为，支化发展进程，获得了聚合物支化结构的证据。对于甲基丙烯酸甲酯，醋酸乙烯酯等以歧化终止为主的单体，采用单体和过氧化物单体简单的双组份体系，由本体聚合就可以合成相对较窄分子量分布的高分子量乙烯基支化聚合物；而对于完全双基偶合终止的苯乙烯，加入少量的分子量调节剂调控初级链的长度是必要的。与此同时，还采用悬浮聚合实施方法合成了支化聚合物微球，克服了溶液聚合带来的环境与成本问题，为支化聚合物的直接应用提供了更加便利的条件。. 以双烯化合物为支化单体，与甲基丙烯酸甲酯（MMA）经可逆络合共聚（RCMcP）一步法合成支化PMMA，结果表明，该体系在Conv.MMA达到56.6％时出现大量的支化结构，此时聚合物中悬垂双键的量达到最大值，在Conv.MMA接近90％时出现最明显的支化得到分子量和支化程度较高的支化聚合物。. 合成乙烯基取代的自引发单体前驱体，与甲基丙烯酸甲酯经自缩合可逆络合共聚合成支化聚合物。结果表明，双乙烯基取代的前驱体由于笼蔽效应生成双烯更容易交联。引入少量的V65不但可以减少双烯的量避免交联，而且可以提高反应速率，在高转化率下，得到分子量和支化程度都更高的支化聚合物。单乙烯基取代的前驱体更为有效，在单体转化率高达98.0％也不交联，可以在未除氧条件下合成支化聚合物。动力学实验表明，聚合前期就有轻度支化结构产生，Conv.MMA为54.7%时出现大量支化。. 用商业化含有叔胺结构的单体与BPO组合直接合成了支化聚合物，聚合反应机理是叔胺与BPO作用首先生成自由基，通过聚合反应分别形成大分子单体或者是大分子叔胺；而后大分子单体进行聚合或者是大分子叔胺与BPO作用形成大分子自由基引发聚合形成支化结构，最终合成支化聚合物。