"活性"/可控自由基聚合制备支化聚乙烯醇的研究

Due to the different physical properties offered by the branch architecture, e.g., freely controlled crystallinity, highly mobile polymer chain and reduced solution viscosity, branched poly(vinyl alcohol)s (PVA) would be extremely attractive complementary materials to linear backbone PVA in the fields of energy and pharmaceutical industry. However, synthesis of branched PVA and facile tuning of the branch architecture are very challenging, because the branched poy(vinyl acetate)s (PVAc) ,as the precursor of PVA, usually contain an weak ester linkage at each branch point which will cleave in the acetate alcoholysis step. Therefore, only linear backbone PVA can be achieved. In order to solve the problem, a stable branch monomer (inimer) will be designed and synthesized. Copolymerization of the inimer with vinyl acetate under the experimental conditions of “living”/controlled radical polymerization, the branched PVAc with stable branch point can be achieved. Subsequently, the branched PVAs with corresponding architecture can be yielded through alcoholysis. The effects of the chemical structure of branch monomer, molar ratios of [inimer]/[VAc], [inimer]/[initiator], polymerization technologies (like batch and semi-batch processes), and reaction temperature etc. on the branch architectures, branch density and branch frequency will be systematically studied, in order to provide insight into branch mechanisms and control of the branch architectures, and establish a robust method for preparing new PVAs with well-defined branch architectures. The intrinsic relationships between branch structures of PVA and the structures of PVA chain aggregation as well as its physical properties in solid or solution states will be systematically studied, offering a theoretical fundation for designing and synthesizing of novel PVA materials with extraordinary properties.

与线性聚乙烯醇相比，支化聚乙烯醇具有不易结晶、高链运动能力、低溶液粘度的优势，有望在能源、医药等领域获得重要应用。然而支化聚醋酸乙烯酯醇解中支化结构也易分解，仅能获得线性主链的聚乙烯醇。建立支化聚乙烯醇合成方法仍然是极具挑战又具实际意义的工作。针对支化聚乙烯醇合成难的问题，我们提出从支化单体分子设计和前驱物支化聚醋酸乙烯酯结构调控入手，设计合成支化聚乙烯醇新思路。通过设计、合成醇解条件下稳定的支化单体，突破通过特定支化结构聚醋酸乙烯酯无法制备预期支化结构聚乙烯醇的问题；通过醋酸乙烯酯与支化单体的“活性”/可控自由基共聚，研究聚合过程中支化结构的发展和演化规律，实现对聚醋酸乙烯酯支化结构的调控，进而实现对聚乙烯醇支化结构的调控。研究聚乙烯醇支化结构（分子量、支化点间平均聚合度、支化程度及支化形状等）与凝聚态结构和性能之间的内在联系规律，为设计合成性能优异的支化聚乙烯醇提供理论基础。

聚乙烯醇是一类工业应用广泛的水溶性合成高分子；它在涂料、造纸、粘结、表面活性剂等领域的应用与它的溶液、熔体的性能密切相关。在聚乙烯醇主链中引入支化结构，可有效调控其溶液、熔体性能，拓展聚乙烯醇的应用范围，发展新材料。在国家自然科学基金的资助下，本项目系统开展了支化聚乙烯醇制备方法学、聚乙烯醇近程结构与性能关系及聚乙烯醇基功能材料的研究工作，具体内容包括：.（1）设计合成出由酰胺键桥接可聚合基团（双键）及链转移基团（黄原酸酯基团）的支化单体 — N-烯丙基-（2-乙基黄原酸基）-丙酰胺（NAPA）和由羧酸酯键桥接的支化单体 — 2-（2-乙基黄原酸基）丙酰氧基丙烯酸乙酯（ETcPE）；通过对支化单体在醇解条件下稳定性的研究，掌握并建立了保持醇解过程中支化点稳定的关键技术。.（2）结合“活性”/可控自由基聚合物法与自缩合乙烯基共聚合法，以NAPA或ETcPE为支化单体与乙烯酯类单体共聚合成出具有支化结构的前驱体；建立了通过线性链转移剂与支化单体复配，同步调控聚合物支化结构和分子量的方案；揭示了聚合过程中支化结构的演化和发展规律；建立了通过选择性醇解制备支化聚乙烯醇的方案。.（3）探索、发展了基于氧化-还原引发型自缩合乙烯基共聚合制备支化聚乙酸乙烯酯及支化聚乙烯醇的方案，揭示了聚合过程中支化结构的演化与发展规律；建立了基于已商业化支化单体（DMAEMA）和氧化-还原引发的常规自由基聚合、快速、高效合成高分子量支化聚合物的方案，丰富了乙烯基单体支化聚合方法学。.（4）系统研究了聚乙烯醇近程结构（支化结构、共聚单体含量、乙酰氧酯基序列分布等）对聚乙烯醇聚集态结构及性能的影响规律。进一步发展出表面活性剂用聚乙烯醇基功能材料及面向环境净化用聚乙烯醇多孔材料。.本项目发表学术论文6篇，会议论文4篇，获准中国发明专利1项，申请中国发明专利1项，圆满王城项目计划研究内容，达到了预期目标。相关研究成果为设计、发展新型聚乙酸乙烯酯材料、聚乙烯醇材料积累了实验数据，提供了基础研究理论和方法。.