화학공학소재연구정보센터
Macromolecules, Vol.38, No.10, 4124-4132, 2005
Synthesis of arborescent isoprene homopolymers
A method was developed for the preparation of isoprene homopolymers with a dendritic architecture using an anionic "grafting onto" methodology. A linear polyisoprene substrate with a high (95%) 1,4-content was first epoxidized to introduce grafting sites randomly along the chain. Coupling of the epoxidized polyisoprene with polyisoprenyllithium yielded a comb-branched or generation GO arborescent polyisoprene. N,N,N',N'-Tetramethylethylenediamine, BF3, Me3Al, LiCl, and LiBr were investigated as promoters for the coupling reaction. Lithium salts were most effective, increasing the grafting yield from 78% to 92% for a linear substrate. Further epoxidation and grafting of the GO polyisoprene led to arborescent isoprene homopolymers of generations G1 and G2. The attempted synthesis of a G3 arborescent polyisoprene was unsuccessful. The graft polymers were purified by precipitation fractionation and characterized by size exclusion chromatography (SEC), light scattering, and NMR spectroscopy. The products have narrow molecular weight distributions (M-w/M-n ≤ 1.05) consistent with a uniform molecular size and display geometric increases in molecular weight and branching functionality for successive generations. The absolute weight-average molecular weight values determined from light scattering measurement are much higher than the apparent SEC values because of the highly branched structure of the molecules.