How Do Subchain Distribution And Solvent Quality Affect The Chain Conformation Of Hyperbranched Polymers

Hyperbranched polymer is an important type of branched topological polymers.Because of the advantages given by the random branched structure,such as low viscosity,weak entanglement,high terminal function and so on,it has attracted extensive attention in the areas of high performance coatings,biological adhesives,novel gene carriers,etc.For polymer system,the chain conformation is the most unique characteristic that is different from small molecule system,and this is because the macroscopic properties of polymeric materials are the average reflection of all possible microcosmic conformations.For hyperbranched polymers,the introduction of random branched structure decorates the chain with dual structural parameters:whole chain and branched chain,consequently,results in more complicated dependence relationship between conformation and chain structure.However,the experimental research on the conformation of hyperbranched polymers has been far behind the theoretical research for a long time.In this Ph.D.thesis,we have prepared a series of "perfect" hyperbranched model samples with uniform subchain length,and then studied the influence of subchain distribution and solvent quality on the chain conformation of flexible hyperbranched polymers in dilute solution by a combination of laser light scattering technique and triple-detection size exclusion chromatography.The main achievements are as listed as follows:1.Clarified the influence of subchain length and distribution on the conformational properties of hyperbranched polymers.For a long time,V-type and Y-type AB2 macromonomer strategies are the most commonly used strategies to prepare the long-subchain hyperbranched polymers.However,different strategies may lead to significant difference in branching patterns and structures.The influence of subchain length and distribution on the conformation properties of hyperbranched polymers is still unclear.In this chapter,V-type(B??A??B)and Y-type(A????B2)polystyrene macromonomers were prepared by combining atomic transfer radical polymerization(ATRP)and azide-alkyne click reaction,where"??"represents long chains,and A,B represent azide and alkyne group respectively.The effects of macromonomer structure on the kinetics of click polymerization,branching structure of hyperbranched polymer and conformation properties of polymer solution were studied.The results show that:i)Due to the difference in topological structure,V-type macromonomers have stronger steric hindrance shielding effect,which makes intrachain cyclization more likely to occur during polymerization process than Y-type macromonomers.This trend suggesting that the steric hindrance might be the determinant of relative rates of intrachain cyclization and interchain coupling.?)By measuring the intrinsic viscosity([?])and mean square radius of gyration(<Rg>)of hyperbranched polymer in dilute solution,the scaling relationship between conformational properties and molecular weight of whole chain(Mt)and macromonomer(Mm)was established:[?]=K?,V/YMt0.40Mm0.25,...