Solution properties of polyurethane

Polyurethane was fractionated and the fractions were characterized by gel permeation chromatography (GPC) and viscometry. The intrinsic viscosities of polyurethane in ten solvents varying in their polarity were determined and are in the order of mineral spirit < acetone < cyclohexane < cyclohexanone < xylene < ethyl benzene < toluene < benzene < methyl ethyl ketone < tetrahydrofuran. The Mark-Houwink relations suggested that solvent blend MEK: n-heptane (1:3) is a poor solvent with an a value of 0·52 and tetrahydrofuran is a good solvent with an a value of 0·78. The weight average molecular weight has been estimated by an extrapolation technique based on a linear relationship between the viscosity average molecular weight Mv and the Mark-Houwink constant. The weight average molecular weights obtained from viscosity studies were used to evaluate the unpertureb dimension of the chain.