Investigation of poly(arylene vinylene)s, 41. Synthesis of soluble dialkoxy-substituted poly(phenylene alkenylidene)s by applying the Horner-reaction for condensation polymerization

Soluble poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-1,2-ethenylene] (MEH-PPV) and its alternating copolymer poly[2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-1,2-ethenylene] (M3EH-PPV) were successfully synthesized by condensation polymerization of substituted terephthalaldehydes with substituted xylylene bisphosphonates via the Horner reaction. This polycondensation method was also applied to the synthesis of the analogous poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-1,3-butadiene-1,4-diyl] (MEH-PPB), which contains a 1,3-butadiene instead of a vinylene unit. The optical data of MEH-PPV and M3EH-PPV (solid film, abs. λ_max 484 nm, em. λ_max 589 nm) are consistent with those previously reported for MEH-PPV from the dehydrohalogenation route. In comparison to MEH-PPV, the longer alkenylene sequence of MEH-PPB exhibits a slight red shift in its absorption and fluorescence spectra (abs. λ_max 502 nm, em. λ_max 604 nm). All three polyphenylene alkenylidenes (MEH-PPV, M3EH-PPV, and MEH-PPB) are completely soluble in common solvents. They are well-defined conjugated polymers of high molecular weight (M_w > 20 000) and possess all-trans structure. Optical quality solid films are easily prepared from these polymers by solution processing. Blends with phenyl-substituted PPV derivatives can also be prepared in this way. This combination of properties is highly desirable for many light-emitting, nonlinear optical, and photoelectrical applications.