Synthesis And Characterization Of Polymers With Well-defined Non-linear Topological Structure By Living Anionic Polymerization

It is well known that the chain architectures of polymers have an important effect on their properties.The design of polymers is important for obtaining the polymer materials with predetermined properties.Polymers with well-defined architecture, homogeneous composition distribution and narrow molecular weight distribution are essential for establishing structure/properties relationship.Due to the synthetic difficulties of well-defined nonlinear polymeric materials with special architecture, such as graft polymers and hyperbranched polymers,however,very little is known about the influence of chain architectures on properties up to now.In order to study the relationship between the architecture and properties of polymers,and further designing the polymers with predetermined properties,it is necessary to apply known polymerization mechanism to synthesize polymers with special architecture.In present work,we took the advantages of anionic polymerizations in the design of polymers,and synthesized hyperbranched polystyrenes and come-on-comb graft (co)polymers,and studied their dilute solution properties.The main results obtained in this thesis are as follows:1) Synthesis of dendritic polystyrenes from an anionic inimer(a monomer with an initiating site).The anionic inimer(a monomer with an initiating site) is prepared by monoaddition of sec-butyllithium and 1,3-bis(1-phenylethenyl)benzene(MDDPE) in tetrahydrofuran(THF) at -78℃.The addition reaction is fast and the selectivity of monoaddition is high.HPLC and GC-MS both shows a high peak of monoadduct which constitutes 96%of the products,and the structure of the product is proven by ¹H NMR,¹³C NMR and GC-MS.After the preparation of the inimer,the solvent was switched from THF to cyclohexane,and the polymerization is conducted in cyclohexane.The resulting products are characterized by size exclusion chromatography equipped with a multi-angle light scattering detector and a viscometer.Smaller radius of gyration and intrinsic viscosity are measured for the hyperbranched products,demonstrating the successful synthesis of the hyperbranched polystyrene.2) The difference of polymerization behavior in THF and cyclohexane is a consequence of kinetically controlled reaction process.The mechanism of forming hyperbranched structure by the solvent-switching process is discussed according to M(u|¨)ller's theory and proven by the designed model reactions.3) Comb-on-comb graft copolymers are synthesized through two steps of "grafting-onto" reactions.The main chain is a random copolymer of styrene and p-chloromethylstyrene,coded PS-co-PCMS.The copolymer is then grafted with the first generation gratis through coupling of polyisoprenyllithium with the pendent benzyl chloride group.The graft copolymer is treated with HCO₃H to introduce epoxy group on PI segment,followed by grafting the second generation grafts,either polystyryllithium,polyisoprenyllithium or poly(α-methylstyryl)lithium,to form ABA-, ABB- and ABC-type comb-on-comb copolymers,respectively.The prepared comb-on-comb copolymers are characterized by gel permeation chromatography equipped with a multi-angle laser light scattering(MALLS) detector and a viscometer. The copolymers show symmetric monomodal distribution and smaller radius of gyration and intrinsic viscosity compared with the linear analogy.By changing the length ratio of the main chain to the branches,the comb-on-comb copolymers exhibit morphologies from hard sphere to cylindrical rod.