Unperturbed chain dimensions of isotactic polypropylene in theta solvents

The unperturbed mean‐square end‐to‐end distance 〈R02〉 and its temperature variation d In 〈R02〉/dT for isotactic polypropylene have been estimated from intrinsic viscosity data in three theta solvents, i.e., diphenyl, diphenyl ether, and dibenzyl ether, measured at their θ temperatures as determined by precipitation temperature measurements. The characteristic ratios, 〈R02〉/nl2, where n is the number of bonds of length l in the main chain, evaluated by assuming Φ = 2.87 × 1021, are 5.80 in diphenyl (at θ = 125.1°C.), 5.41 in diphenyl ether (at θ = 142.8°C.), and 4.56 in dibenzyl ether (at θ = 183.2°C.). These values lead to the temperature coefficient d In 〈R02〉/dT = −4.09 × 10−3 deg.−1 Results are compared with the data previously reported on polyethylene.