Study Of The Chain Conformation Of Hyperbranched Polymers In Dilute Solutions

Via combining experimental and theoretical approaches,this Ph.D thesis has investigated the static average conformation and dynamic conformational relaxation of ABn-type hyperbranched polymers in dilute solutions.In terms of the average conformation,a few universal scalings between average conformation and characteristic structural parameters have been established.In addition,the physical mechanism by which the synergistic effects of "segment back-folding" and "segment interpenetration" dominate the average conformation has been revealed.In terms of conformational relaxation,direct experimental evidence has been obtained for the deviation of the spring vibrational coupling mode from the linear mode due to random branch bonding,revealing the behavior of ultrafast spring resonance relaxation due to random branching.Specifically,this Ph.D thesis has comprehensively answered several important scientific questions on the chain conformation of hyperbranched polymers in dilute solutions,which helped to test and refine the theoretical framework of polymer solutions.The main contributions are as follows:1."Defect-free" ABn-type long-chain hyperbranched model polymers were prepared.By drawing on the design concept of "defect-free" AB2 long-chain hyperbranched model chains,this work carefully designed star-shaped AB3 and AB4 polystyrene macromonomers.The "defect-free" AB2,AB3 and AB4 long-chain hyperbranched polystyrene model polymers with different branched patterns were prepared by using interchain click reactions.The effect of macromonomer branching on interchain polymerisation was investigated.The experimental results showed that in the click coupling reaction,the increase of the branching effect of macromonomers inhibited the interchain coupling reaction,and reduced the coupling efficiency,which promoted the occurrence of intrachain self-cyclization reaction.2.The physical mechanism by which the synergistic effects of "segment backfolding" and"segment interpenetration" dominate the average conformation was revealed.The structure and conformation of ABn-type hyperbranched model chains were characterized by triple-detection size exclusion chromatography.The scaling relations between properties(intrinsic viscosity([?])and radius of gyration(Rg))and structural parameters(total molar mass(Mhyper)and macromonomer molar mass(Mmacro))were established.Moreover,the draining factor as well as the segment-segment interpenetration factor were calculated.The experimental results and Langevin kinetic simulations showed that:i)the fractal properties of hyperbranched polymer were almost independent of the local segment density at the branching point,i.e.independent of the n-value;ii)the AB3 hyperbranched system differed from the AB2 and AB4 systems in that its average conformation showed a much weaker dependence on Macro.The experimental results pointed to the unique synergistic effect of segment back-folding and segment interpenetration in the AB3 system.3.The behavior of ultrafast spring resonance relaxation induced by random branching was revealed.The conformational relaxation behavior of model samples(<Rg>>200 nm)with a narrow distribution(Mw/Mn<1.40)and oversized hyperbranched chains was investigated.The number and intensity of the characteristic line widths(?n)of relaxation within the chains were measured using light scattering techniques,and information on the number,relaxation time and intensity of conformational relaxation modes,were analyzed.The results showed that:i)for different scattering vector(q)regimes(1<qRg<5),the hyperbranched chains exhibited two to three internal relaxation modes,unlike the single relaxation mode of linear chains,and the characteristic linewidth values were significantly smaller than those of linear chains;?)the experimentally measured relaxation time(?1)of the first internal relaxation mode was about one order of magnitude smaller than the theoretically calculated value,revealing the behavior of ultrafast spring resonance relaxation due to random branching;(?)the increased density of local branching significantly reduced the relaxation strength of the whole chain conformation.