Viscometric behaviour of polystyrene in tetralin/cyclohexane mixtures

Abstract

For solutions of polystyrene ( M=10 5–10 6 g mol −1), intrinsic viscosities [η] have been measured at 34.5°C, which is the θ temperature for the polymer in cyclohexane. The solvents comprised cyclohexane in admixture with a thermodynamically good solvent, 1,2,3,4-tetrahydronaphthalene (tetralin, TET) over the whole range of solvent composition. From an assessment of several extrapolation procedures, a value of 85 × 10 −3 (±1 × 10 −3) cm 3 g −3 2 mol 1 2 was obtained for K θ (in the relationship [η] = K θM 1 2 α 3 , where α is the expansion factor), thus yielding 0.681 A ̊ g −1 2 mol 1 2 , 2.25 and 10.2 for the unperturbed dimensions, steric factor σ and characteristic ratio C ∞ respectively. The value of K θ was independent of solvent composition despite the finite excess free energy of mixing for the solvent components alone, which has been asserted elsewhere to affect K θ . The present results, in conjunction with previous ones relating to 98.4°C, indicate a value of −0.89 × 10 −3 deg −1 for the temperature coefficient of the unperturbed dimensions.