Thermodynamic and conformational properties of styrene-methyl methacrylate block copolymers in dilute solution II—Behaviour in theta solvents

Abstract

To find θ solvents for random and block copolymers of styrene and methyl methacrylate, various solvents were examined by the cloud point test. From among the solvents examined, cyclohexanol and 2-ethoxyethanol were chosen and the θ temperatures were determined by osmotic pressure measurement. In cyclohexanol two homopolymers have almost equal θ, to which the θs of the block copolymers are also quite close; while the θs of the random copolymers show a minimum at nearly equimolar composition.Intrinsic viscosities [η] of nearly equimolar block copolymers were examined in these two θ solvents. In contrast to random copolymers the [η]θ of the block copolymers are sensitive to the type of θ solvent employed. From [η]θ data in cyclohexanol the unperturbed mean square radius of gyration for the block copolymers was estimated as 1018〈s〉0M12w=6.35 (cm2) which is better approximated by the simple composition average of the parent homopolymers as previously suggested by Stockmayer. The behaviour of the block copolymers in a good solvent, toluene, was compared with that of the random copolymers and the homopolymers: the [η]s are smaller than those of the corresponding random copolymers but are about the average of the two homopolymers, An anomaly in [η] which was often suggested as that due to ‘intrachain phase separation’ in block copolymer chains was not observed.