Solubilization of regioregular and regioirregular poly(p-phenylene)s via CF3 and OCF3 substituents to generate a model for rigid-rod polymers

Regioirregular poly(p-phenylene)s (PPPs) with OCF3, CF3 or OCH3 substituents (16a, 16b, or 16c, respectively) were synthesized via Ni(0)-catalyzed polymerization of 2-substituted-1,4-bis[[(trifluoromethyl)sulfonyl]oxy]benzenes (5, 8, or 10, respectively). Regioregular head-to-head PPPs with OCF3 or CF3 substituents (17a or 17b) were prepared from 2,2'-disubstituted-4,4'-bis[[(trifluoromethyl)sulfonyl]oxy]biphenyls 14a, 14b and 2,2'-disubstituted-4,4'-bis[methylsulfonyl)oxy]biphenyls 15a, 15b. Regioregular head-to-head statistical copolymers with combinations of OCF3 or CF3 substituents with OCF3, CF3, CO(p-FC6H5), CH3, or H substituents (17xy) were synthesized by the copolymerization of 15a or 15b with 2,2'-disubstituted-4,4'-bis[(methylsulfonyl)oxy]biphenyls 15a-15e. Regioirregular and regioregular PPPs with OCF3 or CF3 substituents were soluble (THF, CHCl3, dipolar aprotic solvents). The highest molecular weight PPPs were obtained from OCF3-substituted monomers. Regioirregular PPP (16a) with M(n) = 35 200 (corresponding to 220 phenylene groups relative to polystyrene standards) was obtained from 5. Regioregular PPP (17a) with M(n) = 54 500 (340 phenylene units) was obtained from 14a. Regioregular PPP copolymers (17ab) with M(n) = 55 200 (363 phenylene units) were obtained from copolymerization of 15a and 15b. The lambda(max) values of OCF3- and CF3-substituted PPPs were 302-307 and 273-271, respectively. A 10% weight loss occurs in the range of 550-575 degrees C for PPPs with OCF3 substituents and 580-615 degrees C for those with CR substituents. Polymers 17a, 17b, and 17ab exhibit enantiotropic nematic and lyotropic mesophases. The thermotropic nematic phase of 17a, 17b, and 17ab is stable up to the decomposition temperature. Most probably, 17a and 17b also exhibit a second mesophase which is monotropic and becomes enantiotropic in 17ab. The rigid-rod character of these polymers was demonstrated by the Mark-Houwink coefficient alpha = 1.58-1.60. Phosphorus was not detected (MALDI and P-31 NMR) in the structure of these homopolymers and copolymers.