Synthesis of 1,4-Polybutadiene Dendrimer-Arborescent Polymer Hybrids

A divergent synthetic scheme was developed for the preparation of high branching functionality hybrid polymers from carbosilane dendrimer substrates and polybutadiene side chains. Carbosilane dendrimers with 32, 64, or 128 peripheral Si-Cl functional groups were first coupled with 1,2-polybutadienyllithium chains having a number-average molecular weight M(n) approximate to 1000. The polybutadiene-grafted substrates were then hydrosilylated with dichloromethylsilane and reacted with high 1,4-microstructure content polybutadienyllithium chains to generate high branching functionality dendrimer arborescent hybrids. Three series of hybrid polymers were synthesized containing 1,4-polybutadiene side chains with M(n) approximate to 1500, 5000, or 30000. Size exclusion chromatography analysis of the polymers confirmed that a narrow molecular weight distribution was maintained (M(w)/M(n) <= 1.14). The branching functionality of the arborescent hybrids varied from 140-335, 160-1110, and 360-2830 for the 32-, 64-, and 128-site coupling precursors, respectively. The experimental branching functionalities attained were lower than the theoretical values due to decreased coupling efficiency within each series, in particular for polymers with longer polybutadiene side chains, apparently due to steric limitations in the grafting reaction.