Cyclic PDMS Research Articles

Studies of cyclic and linear poly(dimethyl siloxanes): 8. Light scattering measurements in good and poor solvents

Weight average molar masses ( M w ) and second virial coefficients ( A 2) have been measured for linear and cyclic poly(dimethyl siloxane) (PDMS) fractions in toluene at 298K and for linear PDMS in bromocyclohexane at 301K. The values of M w are compared with those deduced previously using gel permeation chromatography, broadly confirming the values already assigned to the fractions. The values of A 2 for linear PDMS in toluene are shown to be consistent with previously published values for oligomeric linear PDMS. The values of A 2 for cyclic PDMS approach those of linear PDMS for M w <∼1000 g mol −1 and decrease more rapidly as M w increases in approximate agreement with theoretical predictions. In addition, the conventional relations between A 2 and the expansion factor α s are shown to be inapplicable at low molar mass.