Effects of chemical variations on the mesophase behavior of new fluorinated poly(vinylcyclopropane)s

Several new structures of fluorinated polymers poly(1)-poly(9) were prepared by free radical ring opening polymerization of vinylcyclopropane monomers 1-9 containing different fluorinated side groups of the type (CH₂)_n(CF₂)_pF. While in poly(1)-poly(3) p varied from 6 to 10 for a fixed n=2, in poly(4)-poly(6) n increased from 3 to 5 at the given p=8. In poly(7) and poly(8) a phenyl ring was incorporated to elongate the mesogenic side group (n=2; p=6 and 8, respectively), that was further separated from the polymer backbone by a methylene spacer (m=11) in poly(9). Therefore, the effects of various chemical variations of the polymer structure on the mesophase behavior could be assessed. The polymers were in fact co-polymers comprising both 1,5-linear and cyclobutane-ring isomer units. In any case they formed smectic mesophase(s) owing to the special character of the perfluorinated chains. The order and the isotropization temperature (T_i) of the mesophase were enhanced by increasing p, but T_i lowered with increasing n. Extension of the side group by insertion of a phenyl ring improved T_i. Wide angle X-ray diffraction studies clarified the nature of the different smectic phases, the occurrence of which was discussed in terms of the ability of the fluorinated side groups to pack antiparallel in either a partly or fully interdigitated structure. Co-polymers of 3 with a non-mesogenic, not fluorinated co-monomer 10 were also prepared with different chemical compositions. Co-polymerization was found to be another effective means of modifying the mesophase behavior of the poly(vinylcyclopropane)s.