Synthesis of hyperbranched polymers by anionic self-condensing vinyl polymerization

Abstract

Anionic self-condensing vinyl polymerization is achieved from an situ creation of a vinyl monomer bearing an active anion by the reaction of equimolar amount of 1,3-diisopropenylbenzene (DIPB) and butyllithium in THF at 30°C. Onset of the intermolecular-equilibrium between isopropenyl groups (α-methylstyrene) and isopropenyl-α-methylstyryllithium sites of the oligomer restricts the growth of hyperbranched poly-(DIPB) in THF at -40°C. Addition of a small amount of styrene interrupts this equilibrium. Conversion of isopropenyl-α-methylstyryllithium into styryllithium sites Quickly directs the consumption of styrene and concurrent intermolecular-condensation into remaining α-methylstyrene groups of the oligomers. Thus, the equilibrium is reestablished and it has been shifted to the right by one or more α-methylstyrene units that increase the molecular weight of the hyperbranched living polymer. Repeated small additions of styrene are attended by impressive multiplications of molecular weights. Up to seven generations of hyperbranched polymers have been synthesized as reported in this paper; the polymers exhibit high molecular weight and broad molecular weight distributions (1.8 <4). the Mark-Houwink exponent, α, is found to be 0.38 indicating a densely packed three-dimensional structure resulting from the hyperbranched topology.