含支化核的星形和树枝状聚合物的快速合成、结构转换及性能研究

This project aims at rapid synthesis, topology transformation and properties of star and dendritic copolymers bearing cleavable bonds and reactive functionalities. These polymers bearing a hyperbranched polymer in inner layer and polymer "arms" involving linear, V- and Y-shaped copolymers in outer layer are synthesized by 2-4 step reactions, in which self-condensing vinyl copolymerization, controlled polymerization techniques, and highly efficient linking reactions are combined, and the "as-prepared" hyperbranched polymers, block copolymers and heteroarm star polymers are used as building modules. The target star and dendritic copolymers with controlled molecular weight and low polydispersity are achieved under optimized conditions, and their properties and potential applications are investigated. Moreover, three types of topology transformations are performed via cleavage reaction and followed by a second coupling reaction, namely, (a) the structural conversions to form star and dendritic copolymers with similar chemical components and different linkage sequences of polymer segments, (b) reversible structural conversions between star / dendritic copolymers and their building modules comprised of hyperbranched core and polymer "arms", and (c) irreversible topology transformations among dendritic, star, comblike (graft) and linear polymers via stimuli-triggered bond cleavage reactions. Effects of chemical components, linkage sequence and types of macromolecular architectures on physicochemical properties of various polymers are investigated, the structure-property relationships are better understood, and their potentials as stimuli-responsive materials are explored. The efficient implementation of this project can not only significantly accelerate the development of methodology for polymer synthesis but further promote the development of polymer physics and materials science.

本项目将结合自缩合乙烯基共聚合、控制聚合和高效连接反应，以支化聚合物、嵌段共聚物和星形聚合物等为构筑单元，采用两至四步反应快速合成含可断裂键和反应性官能团、内层为支化核、外层为线型、V型和Y型聚合物"臂"的星形和树枝状聚合物。通过反应条件的优化，实现目标聚合物的准控制合成，研究它们的功能性和潜在应用。然后通过化学键断裂和二次偶联反应，实现三类结构转变：（1）化学组成类似、链段键接方式不同聚合物之间的结构转变；（2）星形、树枝状聚合物和它们的构筑单元之间的可逆结构转变；（3）光照、酸碱度和温度等外界刺激驱动的树枝状、星形、梳形、线型聚合物之间的不可逆结构转变。研究化学组成、键接方式和拓扑结构种类等因素对聚合物物理化学性能的影响，掌握其内在变化规律，并探索它们在环境响应材料等方面的应用。本项目的顺利开展能有力促进高分子合成方法学的发展，同时也可望能推动高分子物理和材料学等相关学科的深入发展。

本项目结合可控聚合和点击化学，快速合成了一系列多组分星、支化星和树枝状聚合物，实现了聚合物和基本构筑基元之间的可逆或不可逆结构转变，并探索了它们的功能和潜在应用。采用先核后臂、先臂后核、偶联反应等策略，结合二次点击、分级沉淀等纯化手段，获得了目标聚合物，主要包括含断裂键或功能端基的ABC、AB2C2、ABCD和ABCDE等杂臂星，A(BC)m、A(BC)mD和A2mB2nC2等星形或嵌段接枝共聚物，(A-b-B)m、AmBm等支化星和(A-BC)m、(A-BCD)m、(A-BCDE)m等树枝状聚合物。结合端基转换、化学键断裂和二次偶联技术，成功实现了树枝状、星形、接枝和线型聚合物之间的拓扑结构转变反应。譬如，采用氧化-还原实现了AmBnC（杂臂星）和(AmBnC)o（嵌段接枝）之间的可逆转变；结合端基转换和叠氮-炔点击，实现了A(BC)mD、(A(BC)mD)o（线型或支化接枝）之间的不可逆结构转变；结合DA和逆DA反应，实现了支化星、树枝状聚合物和它们的构筑基元之间的可逆结构转变；采用逆DA和点击反应，实现了组成和分子量类似、键接方式不同的拓扑转变，如(A-b-B)m、(B-b-A)n和AoBo（m ≈ n ≈ o）之间的转变、(A-BC)m和(C-AB)n（m ≈ n）之间的转变；从含有单一或双重断裂键的聚合物出发，施加外界刺激诱导支化核解体和链段解离，实现了多种降解型结构转变。测试了结构转变过程中材料性能（如玻璃化转变、熔融、结晶、粘度、聚集行为、药物负载及释放、表面浸润性能）的变化，发现聚合物的性能主要依赖于分子参数、可裁剪位点和链段键接顺序等因素，所合成聚合物在纳米载体、表界面材料、无机盐生物矿化等方面具有一定的应用前景。本项目为星形和树枝状聚合物提供了一些普适性较强的合成方法，刺激断裂位点的引入能赋予聚合物多样化的分子裁剪能力，采用化学键断裂和偶联反应能带来多类结构转变。本项目的开展有力促进了非线型结构聚合物合成化学的发展，丰富了拓扑聚合物和智能材料的种类，为深入研究拓扑结构、化学组成、键接方式等因素对材料性能及应用的影响奠定了坚实的基础，并适当促进了高分子物理、功能材料、生物医用材料等学科的发展。