Glass and melting transitions of copolymers of tetrafluoroethylene with propylene and isobutylene

Copolymers of tetrafluoroethylene and propylene were prepared that contained 30–65 mole-% of the former. Reactivity ratios of tetrafluoroethylene- and propylene-ended radicals are 0.008 and 0.06, respectively, resulting in formation of highly alternating copolymers. The glass temperatures, T_g, were determined using a differential scanning calorimeter. Values ranged from 260 to 275°K. A plot of T_g versus composition has a low maximum centered about the equimolar composition. Copolymers of tetrafluoroethylene and isobutylene were prepared that contained 30–56 mole-% of the former. Reactivity ratios of tetrafluoroethylene- and isobutylene-ended radicals are 0.005 and 0.021, respectively. The glass temperatures of these copolymers range from 257 to 313°K. A higher maximum at the equimolar composition is obtained when T_g is plotted versus composition. Isobutylene-containing copolymers having 45–54 mole-% tetrafluoroethylene are crystalline. Melting temperatures range from 416 to 476°K and have their maximum value at the equimolar composition. It is thought that long sequences of alternating units behave as a third entity in these copolymers, the other two being nonalternating units of the two monomers. Unless inhibited, ionic homopolymerization of isobutylene can be appreciable, sometimes resulting in the polymer having two T_g.