Living polymerization techniques can be used to achieve a high degree of control over polymer chain architecture. Examples of the type of polymers that can be synthesized include block copolymers, comb-shaped polymers, multiarmed polymers, ladder polymers, and cyclic polymers. This control of structure, in turn, results in polymers with widely diverse physical properties, even though they are made from readily available low-cost monomers.

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Highly branched polyphenylenes were synthesized from AB2 type monomers, e.g., 3,5dibromophenylboronic 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 aC and soluble in many organic solvents. 13C NMR indicates about 70% branching efficiency. A Tt at 236 °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.

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