超分子模板法合成新型核交联星形聚合物及其自组装研究

This proposal aims to synthesize a new class of core-crosslinked star-shaped polymers using the supramolecular template strategy and study their self-assembly behavior in controlled binary mixture systems. First, a series of giant surfactants based on functionalized polyhedral oligomeric silsesquioxane (POSS) nanoparticles and polystyrene-b-poly(4-vinylbenzocyclobutene) (PS-b-PBCB) diblock copolymer chains will be synthesized by combining the controlled/“living” radical polymerization technique and the well-documented “sequential click” methodology. Molecular parameters of the resulting giant surfactants, XPOSS-PBCB-b-PS, including molecular weight, molecular weight distribution, and volume fractions of the PS and PBCB blocks, will be tuned to select samples that form highly ordered spherical phases in bulk by phase separation between the POSS heads and polymer tails. Second, using the self-assembled spherical motifs with POSS cores and polymer shells as the template, thermal-induced in situ dimerization of the benzocyclobutene groups in the PBCB block will be optimized to achieve core-crosslinking of individual supramolecular spheres in bulk. Chemical and topological structures of the resultant core-crosslinked star-shaped polymers will be thoroughly characterized. Importantly, by changing the molecular parameters of the giant surfactant precursors, core-crosslinked star-shaped polymers with different molecular weights, different number of shell polymer chains, narrow molecular weight distribution, and structural rigidity can be readily prepared. Third, using these core-crosslinked star-shaped polymers as spherical building blocks, self-assembled ordered structures in their controlled binary mixture systems will be systematically investigated to explore the formation of certain unconventional spherical phases. It is believed that this project will provide a novel supramolecular template synthesis route toward core-crosslinked star-shaped polymers with versatile compositions and parameters, which could serve as a powerful platform to further study unconventional spherical supramolecular assembly in polymeric materials.

本项目拟通过本体超分子模板法合成一类新型核交联星形聚合物，并研究其在可控二元混合体系中的自组装行为。计划开展以下三个方面的研究：(1) 合成含有苯并环丁烯可交联位点的基于多面体齐聚倍半硅氧烷的巨型表面活性剂分子，通过分子参数的调节使其在本体中自组装形成高度有序的体心立方球状相；(2) 以此球状有序结构为本体超分子模板，利用加热诱导的苯并环丁烯官能团的二聚反应，实现自组装球状结构单元的原位交联，制备尺寸可调、分子量分布可控的新型核交联星形聚合物；(3) 以此核交联星形聚合物作为球状高分子纳米粒子，研究其在可控的二元混合体系中的自组装行为，期望获得若干种非常规球状自组装相态并研究其形成机理。本项目将发展一种新颖的本体超分子模板合成路线，制备一类新型核交联星形聚合物，探究其二元混合体系中的非常规球状相结构的生成，为对该类材料的理论和应用研究奠定基础。

嵌段共聚物在本体中自组装形成的高度有序相结构是近年来研究的热点问题之一。特别是近年来在软物质体系中被陆续发现的类似金属合金体系中的一系列非常规球状相，引发了研究者们的极大兴趣。在本项目的研究中，我们计划从一种不同的策略出发，试图获得高分子体系中的非常规球状相并理解其形成的机理。为了实现这一点，我们计划通过模板法制备一类高接枝密度的核交联星形聚合物，其特点在于单个聚合物分子可被视为一个球状的“纳米原子”，并可被进一步用于在本体中直接进行排列和组装。为了实现这个目标，我们将具有苯并环丁烯官能团的单体与苯乙烯单体共聚，得到PS-b-PBCB嵌段共聚物，并基于此合成了一系列类似三嵌段共聚物的、含可交联PBCB嵌段的巨型表面活性剂分子XPOSS-PBCB-PS。通过调节分子参数，获得体心立方球状相，并以此有序结构为模板，在本体中通过苯并环丁烯的热致二聚反应实现原位交联，即可得到核交联星形聚合物。更加有趣的是，在对不含PBCB嵌段的对照组DPOSS-PS的研究中，我们意外的发现同样可通过高温处理实现对DPOSS头基的交联，推测其交联机理为脱水反应或倍半笼硅氧烷的开环重排反应。这种方法得到的样品具有更高的产率和更窄的尺寸分布，有望提供一种简单的策略制备核交联聚合物。此外，对巨型表面活性剂共混体系的初步研究也证明了可通过不同头基XPOSS-PS共混的方法得到不同的自组装结构；而对多头基巨型表面活性剂的研究进一步揭示了分子拓扑结构如何影响嵌段共聚物自组装行为。本项目的顺利开展验证了在本体中通过模板法合成核交联星形聚合物的可行性，并为系统研究其自组装行为提供了材料的平台。