AbstractThe actual viscosity η of six fractions of poly(2,4,5‐trichlorophenyl methacrylate) (PTCPh) with weight‐average molecular weightM̄w, ranging from 9,11 · 104to 94,8 · 104, was determined in benzene at a number of temperatures from 22 to 60°C. The variation of the pre‐exponential termAand the apparent activation energy of viscous flowQ, with molecular weight and concentration was studied. Moore's equations are valid for PTCPh. The temperature coefficient of the unperturbed dimensions dln 〈r20〉/dTestimated from the intrinsic viscosity data by using the Burchard‐Stockmayer‐Fixman relation, is −3 . 10‐3(from 22 to 40°C) and −0,87 . 10‐3(from 40 to 60°C). These negative values indicate that extended configurations of PTCPh in benzene must be as