Synthesis and characterization of hetero three-arm star-branched polymers via macromonomers

The macromonomer method is generally acknowledged as one of the most powerful tools of macromolecular engineering, especially for the synthesis of graft copolymers. Much interest in multi-branched polymers comes from their unique three-dimensional structure which renders them more compact spatially and different in properties from the same molecular weight linear counterparts. Living anionic polymerization is one of the most versatile methods to prepare macromonomers with control of a number of structural parameters. The concept of preparing a graft copolymer with well-defined structure by using a non-homopolymerizable macromonomer was investigated by a model reaction which led to hetero, three-arm star-branched polymers. Hetero three-arm star branched polystyrene was made by stoichiometric coupling of a living polymer with a non-homopolymerizable macromonomer followed by monomer addition to complete the third arm. If not deliberately terminated, the above sequence could be repeated to generate a model graft copolymer with precise graft branches and graft distribution along the polymer backbone.; In the study described herein, a non-homopolymerizable macromonomer, namely polybutadiene bearing a 1,1-diphenylethylene chain-end, was prepared by the reaction of poly(butadienyl)lithium with 1,3-bis(1-phenylethenyl)benzene. The best results were obtained in a mixture of solvents at {dollar}-78spcirc{dollar}C. A series of polymers {dollar}rm (Msb{lcub}n{rcub}{dollar} = 4600-25000g/mol) having functionality of 98% as determined by UV spectroscopy was prepared. Both {dollar}sp1{dollar}H-NMR spectroscopy and SEC were used to characterize the macromonomers. The stoichiometric linking reaction of poly(butadienyl)lithium with the macromonomer was conducted in the presence of a small amount of Lewis base (10 x (PLi) of tetrahydrofuran) to overcome the unfavorable crossover reaction. Further addition of butadiene has been carried out at elevated temperature (70{dollar}spcirc{dollar}C) to obtain microstructure control. Both regular and heteroarm, star-branched polybutadienes {dollar}rm (Msb{lcub}n{rcub}{dollar} = 18000-21000g/mol) with narrow polydispersity were obtained after one fractionation step.; Star-branched polyethylene was prepared by hydrogenation of a polybutadiene star polymer with diimide generated in-situ. The major advantage of this hydrogenation method over others is that it circumvents the need for specialized hydrogenation apparatus and expensive transition metal catalysts. The star-branched diene polymers were readily reduced to high saturation levels as confirmed by {dollar}sp1{dollar}H-NMR and FTIR analyses.; The hydrodynamic properties of these star-polymer were investigated by measuring the solution viscosity and the branching factor, {dollar}rm gspprime{dollar}. In general, the {dollar}rm gspprime{dollar} values of regular star polymers were lower than those of heteroarm star polymers of similar molecular weights and the differences increased with increasing heterogeneity of the arm sizes.