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

Building upon our previous results on silicon-based homopolymers, we h ave now synthesized and characterized copolymers of these novel materi als. The copolymers poly(di-n-butylsilylene-co-di-n-pentylsilylene) (P B-co-PS) and poly(di-n-pentylsilylene-co-di-n-hexylsilylene) (PP-co-HS ) were synthesized from solutions containing equal molar concentration s of the two respective monomers. The materials were examined by solut ion- and solid-state NMR, X-ray diffraction, DSC, and UV spectroscopy to obtain a description of the solid-state structures, phase transitio ns, and thermochromism of these copolymers. The conformational propert ies, crystal packing, and UV absorption characteristics of PB-co-PS ar e 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-c o-HS (either a 7/3 or 9/4 helix) appears similar to that of the PDPS h omopolymer, the UV absorption characteristics and the crystal packing differ from those of either of the corresponding homopolymers, PDPS an d poly(di-n-hexylsilylene) (PDHS). The results of this study demonstra te that the properties of the polysilylene copolymers are complex and not directly predictable solely on the basis of the corresponding homo polymers.