Mechanism of Step-Growth Thermal Polymerization of Arylacetylene

Abstract

The reaction mechanism of arylacetylene thermal polymerization has been studied on 4-(1-hexyloxy)-phenylacetylene 1, used as a monofunctional model compound. Its linear dimers 2-5 [a diyne and 3 enyne isomers] were also synthetized and their thermal behavior investigated. Reaction products were analyzed by chromatography (HPLC, SEC), spectroscopy ( 1 H and 13 C NMR) and spectrometry (SIMS) techniques. The lowest molecular weight components were isolated and their structure established. There are naphthalenic dimers (2 isomers) and benzenic trimers (3 isomers) and they represented 30% in weight of the overall thermal reaction product of 1. We have shown that linear dimers 2-5 are not reaction intermediates of the thermal polymerization of 1. Moreover, under prolonged curing, a depolymerization process was pointed out, indicating that the highest polymerization steps could give termination by intramolecular reactions inducing chain cleavage leading to lower molecular weight entities. A bimolecular reaction mechanism generating diradical intermediate species is proposed and its implications are discussed.Many acetylene terminated resins have been described (1,2). Although some α,ω-diethynylimide oligomers were commercialized in the seventies, the reaction mechanism of the thermal polymerization of the arylacetylene group is not yet well established. The polymerization takes place above 130°C, without catalyst (1,2). The properties of the resulting networks are dependent on the length and the nature of the aromatic or heterocyclic moieties, as well as on polymerization and post-cure conditions. Different assumptions concerning the polymerization mechanism were based on kinetic data, electron spin resonance (ESR) analyses, structures determination of low molecular weight species and nuclear magnetic resonance (NMR) studies of the oligomeric products.

Polyarylene Networks via Bergman Cyclopolymerization of Bis‐ortho‐diynyl Arenes

“…300°C and their resulting structures, although thermally robust, are not well-defined. [47][48][49] Radical polymerization of 1,2-dialkynyl arenes below 100°C (depending on substitution) yields what are often called "polynaphthalene" structures that have recently been shown to have a more complicated polymer backbone. [37] Tetraphenyl pendant substitution in BODA monomers provides large melt processing windows ranging from 4-5 h at 210°C as found by dynamic mechanical spectroscopy.…”