Synthesis,Versatile Topological Transformation And Properties Of Multisite Polymers

Synthesis and properties of architecture-transformable polymers（ATPs）are important topics in polymer science.Starting from the same ATP,chemical reaction allows the formation of derivatives with one or a few kinds of connecting mode or molecular weight.This strategy can ensure similar compositions before and after topological transformation and favor to reveal the topology effect on physical properties.However,most of architecture-transformable polymers have relatively limited reactive sites and types of topological transformations,and it is difficult to reveal the unique structure-property correlations based on multiple architectures.Meanwhile,researches on rational design of macrocycles and macrocyclic derivatives（MCDs）have attracted increasing attention due to the potential to partly mimic structure and function of biomacromolecules.To address the problems on versatile topological transformations of macrocycle-bearing polymers,multisite polymers are designed in this thesis.By virtue of intra/inter-chain connection via anthracene dimerization and atom transfer radical coupling and thermo-induced cleavage of linking sites,versatile topological transformations among linear,tadpole-shaped,bicyclic,star,graft and single-chain folding polymers are achieved,and the influence of chemical composition and topology on physical properties are preliminarily investigated.Main contents are listed below.In part one,synthesis,versatile topological transformations and properties of multisite poly（ε-caprolactone）-b-polystyrene-b-poly（ε-caprolactone）were investigated.Using 2-（2-bromo）isobutyramide-3-hydroxypropyl anthracene-9-carboxylate（BHA）as an initiator,ring-opening polymerization（ROP）,atom transfer radical polymerization（ATRP）and radical trap-assisted atom transfer radical coupling（RTA-ATRC）strategies were combined to synthesize a multisite triblock copolymer PCL-b-PSt₂-b-PCL,in which PCL and PSt were poly（ε-caprolactone）and polystyrene,respectively.On this basis,anthracene dimerization,end group transformation and thermo-induced cleavage of anthracene dimer and alkoxyamine groups were combined to achieve topological transformations among linear,tadpole-shaped and bicyclic copolymers.Based on nuclear magnetic resonance diffusion order spectroscopy（DOSY NMR）analysis,the apparent diffusion coefficient（D）was liable to decrease in the order tadpole-shaped copolymer（c-PSt₂）（PCL-Ant）₂>linear triblock copolymer PCL-b-PSt₂-b-PCL>bicyclic copolymer（c-PSt₂）（c-PCL₂）>tadpole-shaped copolymer（c-PCL₂）（PSt）₂.As they were subjected to self-assembly in mixture of tetrahydrofuran and methanol,（c-PCL₂）（PSt）₂ could self-assemble into vesicles,while other copolymers could form spherical micelles of different sizes,as evidenced by transmission electron microscope（TEM）results.Based on differential scanning calorimetry（DSC）analysis,the topology could affect the crystallization and melting behaviors of PCL chains.In part two,synthesis,versatile topological transformations and properties of multisite poly（tert-butyl acrylate）-block-polystyrene-block-poly（tert-butyl acrylate）were investigated.Starting from a multifunctional initiator BHA,ATRP and RTA-ATRC were initially combined to generate a multisite triblock copolymer Pt BA-b-PSt’-b-Pt BA（where Pt BA was poly（tert-butyl acrylate））,followed by anthracene dimerization to synthesize tadpole-shaped copolymer（c-PSt’）（Pt BA）₂.On this basis,the combination of RTA-ATRC and thermo-induced cleavage of alkoxyamine group was used to achieve topological transformations among tadpole-shaped,graft,star and linear copolymers.Based on DOSY NMR analysis,the D values of various copolymer solutions were liable to decrease in the order star-shaped copolymer（PSt）₂（Pt BA）₂>tadpole-shaped copolymer（c-PSt’）（Pt BA）₂>linear triblock copolymer Pt BA-b-PSt’-b-Pt BA>graft copolymer Pt BA’-g-（c-PSt’）.DSC results indicated that the topology could partly affect the glass transition temperature of various copolymers.In part three,one-shot synthesis of multisite polystyrenes toward versatile topological transformations was investigated.Starting from a multifunctional initiator N,N-bis（2-（bromoisobutyryloxy）ethyl）-9-anthracenemethanamine（BAMA）,multisite multiblock PSt samples were synthesized by tandem ATRP and ATRC in one shot.The apparent weight-average anthracene functionality(F_w,Ant)of multisite PSt was further obtained by hydrolysis of ester groups lying in the backbone.For PSt samples with different F_w,Ant values,the topological transformation from linear to single-chain folding polymer was achieved by intrachain anthracene dimerization.By virtue of thermo-induced self-catalyzed cleavage of ester groups,the topological transformation from multi-segmented to one-segment PSt with reduced molecular weight was achieved.In addition,Diels-Alder addition reaction,quaternization and controlled polymerization were combined to achieve topological transformation from linear to graft copolymers with same or different side chains and enhanced molecular weight.DSC analysis showed that the crystallization and glass transition behaviors of various polymers were significantly dependent on the topology and chemical composition.In summary,this thesis aims at rational design of multisite polymers to achieve versatile topological transformations among linear,star and MCDs（e.g.,bicyclic,tadpole-shaped,linear-graft-cyclic and single-chain folding polymers）.Light-and thermo-induced topological reconstruction and molecular tailoring are adopted to obtain a diversity of polymers with different linking modes or molecular weight,and structure-property correlations are investigated.A general method toward synthesis and topological transformation of macrocycle-based polymers is efficiently developed,in which versatile topological transformations are achieved via photothermal stimulation.The progress of this study can enrich types of ATPs and underlie systematic researches on promising applications in materials science.