SOLID-STATE STRUCTURES, PHASE-TRANSITIONS, AND THERMOCHROMISM IN POLYSILYLENE COPOLYMERS

Building upon our previous results on silicon-based homopolymers, we have now synthesized and characterized copolymers of these novel materials. The copolymers poly(di-n-butylsilylene-co-di-n-pentylsilylene) (PB-co-PS) and poly(di-n-pentylsilylene-co-di-n-hexylsilylene) (PP-co-HS) were synthesized from solutions containing equal molar concentrations of the two respective monomers. The materials were examined by solution- and solid-state NMR, X-ray diffraction, DSC, and UV spectroscopy to obtain a description of the solid-state structures, phase transitions, and thermochromism of these copolymers. The conformational properties, crystal packing, and UV absorption characteristics of PB-co-PS are found to be the same as those of the two corresponding homopolymers poly(di-n-butylsilylene) (PDBS) and poly(di-n-pentylsilylene) (PDPS). In contrast, we find that while the silicon chain conformation of PP-co-HS (either a 7/3 or 9/4 helix) appears similar to that of the PDPS homopolymer, the UV absorption characteristics and the crystal packing differ from those of either of the corresponding homopolymers, PDPS and poly(di-n-hexylsilylene) (PDHS). The results of this study demonstrate that the properties of the polysilylene copolymers are complex and not directly predictable solely on the basis of the corresponding homopolymers.