HYPERBRANCHED POLYPHENYLENES

Highly branched polyphenylenes were synthesized from AB2 type Monomers, e.g., 3,5-dibromophenylboronic acid (1A) and 3,5-dihalophenyl Grignard reagents (IB and 2). Monomers 1 and 2 were polymerized by Pd(0) and Ni(II) catalyzed-aryl-aryl coupling reactions, respectively. Polymers obtained from 1 had molecular weights in the 5000-35 000 range with polydispersities less than 1.5. They are thermally stable to 550-degrees-C and soluble in many organic solvents. C-13 NMR indicates about 70% branching efficiency. A T(g) at 236-degrees-C was observed, but the polymer was brittle and did not form films. The melt viscosity of polystyrene was reduced, and the modulus was improved as a bromo functional hyperbranched polymer was added. The bromo polymer was metalated with butyllithium. The resulting lithio polymer reacted with various electrophiles to provide polymers with other end groups which control solubility as well as thermal properties. Some of these derivatives were used as multifunctional initiators to prepare star polymers, for example, via ring-opening polymerization of propiolactone and anionic polymerization of methyl methacrylate.