Synthesis and thermal behavior of phenylethynyl-terminated linear and hyperbranched polyphenylquinoxalines

Abstract

A phenylquinoxaline (PQ) AB monomer mixture was treated with mono-functional and difunctional end-capping agents and with and without a coupling agent to afford phenylethynyl-terminated linear PQ oligomers. The resulting PQ oligomers were soluble in common organic solvents and had intrinsic viscosities (IVs) of 0.21-0.30 dL/g. The glass-transition temperature (T g) of the diphenylethynyl-end-capped PQ oligomer on both sides increased the most, from 215°C (before curing) to 251°C (after curing). The PQ AB 2 monomer, which acted as both a coupling agent and a monomer for the hyperbranched polymer, was treated with an AB monomer and end-capping agents to afford phenylethynyl-terminated hyperbranched polyphenylquinoxalines (PPQs). They were also soluble in common organic solvents, had IVs of 1.00-1.65 dL/g and T g's of 251-253°C, and underwent exothermic cure with maxima around 412-442°C. The T g's of the cured hyperbranched PPQs ranged from 258 to 261deg;C, depending on the number of phenylethynyl groups on the surface. After further curing, they displayed a T g of 316°C in one sample and turned into a fully crosslinked network. The dynamic melt viscosities of a linear oligomer (IV = 0.21 dL/g), a hyperbranched sample (IV = 1.00 dL/g), and a linear reference PPQ (IV = 1.29 dL/g) were compared with respect to the processing temperature. The PQ oligomer and hyperbranched PPQ had low melt viscosities.