HIGH-TEMPERATURE METATHESIS POLYMERS - STRUCTURE-PROPERTY RELATIONSHIPS

This paper describes the synthesis of N-phenylnorbornene-5,6-dicarboxi mides (NDIs) with substituents at different positions in the aromatic ring and their polymerization by ring-opening metathesis polymerizatio n (ROMP) leading to high-temperature polymers. A structure-property re lationship study showed that the polymer properties are significantly influenced by the size and position of the substituent groups on the r ing. Substitution at the ortho position leads to an increase in the gl ass transition temperature (T(g)) of the polymer, where as metasubstit ution has the opposite effect. An increase in the size of the substitu ent for ortho-substituted polymers is found to further increase the T( g). Polymers with T(g)s up to 270-degrees-C are prepared by choosing a n appropriate substituent at the ortho position. It is proposed that c hanges in the polymer properties, observed when the size and/or positi on of the substituent is changed, are due to the differences in the re lative ease of segmental motion of the polymer backbone. Molecular mod eling studies suggest that the barrier to rotation of the phenyl group is at a maximum when the substituent is at the ortho position. In add ition, resistance to rotation increases with the increase in the size of the substituent. Phenyl rotation is not significantly affected when the substituent is at the meta or the para position. Blends of poly(N -phenylnorbornenedicarboximide) with ortho and meta substituents are f ound to immiscible, giving two distinct T(g)s corresponding to the T(g )s of the homopolymers. Copolymerization of the ortho- and meta-substi tuted NDIs results in a homogeneous random copolymer with one glass tr ansition temperature. The glass transition temperature increases linea rly as the amount of ortho-substituted phenyl content in the copolymer increases.