Synthesis of Substituted Poly(p-phenylenevinylene) Copolymers by the Heck Method for Luminescence Studies

Heck carbon−carbon bond-forming polymerization was used to make segmented copolymers based on poly[1,8-octanedioxy-1,4-phenylene-1,2-ethenylene-1,4-phenylene-1,2-ethenylene-1,4-phenylene]. The Heck methodology yielded copolymers with molecular weights, polydispersities, and optical properties that are comparable to or better than those previously obtained for the same or very closely related polymers obtained by Wittig methodology. However, it proved important to have methoxy groups incorporated into the chromophore of the copolymers to get high yields of material with good degrees of polymerization. The obtained yields and purities for the Heck-derived polymers are better, in part due to the direct formation of desirable trans olefin linkages in the polyphenylenevinylene type chromophore units. Differential scanning calorimetric measurements show that placement of isopropyl groups on the central ring of the chromophoric fragment does not alter the polymer glass transition temperature relative to an unsubstituted copolymer but that placement of n-hexyl groups lowers the glass transition substantially. The decrease in Tg is attributable to copolymer self-plasticization by the n-hexyl groups.