MOLECULAR-WEIGHT DEPENDENCE OF POLYSTYRENE POLY(METHYL METHACRYLATE) INTERFACIAL-TENSION PROBED BY IMBEDDED-FIBER RETRACTION

Interfacial tensions between polystyrene (PS) and poly(methyl methacry late) (PMMA) were measured as a function of PS molecular weight at 190 -degrees-C via imbedded-fiber retraction (IFR). The dynamic experiment enabled studies of much higher molecular weight resins than probed to date with equilibrium experiments, and this ability was applied to co nfirm the presence of the high-molecular-weight limiting interfacial-t ension plateau for this system with direct measurements. Only narrow-p olydispersity (M(w)/M(n) < 1.3) samples were studied. The number-avera ge molecular weight (M(n)) for the set of 10 PS samples ranged from 2 to 200 kg/mol. The M(n) of the PMMA sample was 24.4 kg/mol. The interf acial tension (gamma12) followed a gamma12infinityM - C1M(n)-z depende nce at 190-degrees-C. For M(n) exceeding about 48 kg/mol, gamma12 was independent of M(n) with a mean value (gamma12infinityM) of 1.2 +/- 0. 1 dyn/cm. The scaling exponent (z), which summarizes the strong growth of gamma12 at lower M(n), was estimated to be 0.73 +/- 0.24. The resu lts are compared to gamma12 data from the pendant-drop technique and t o theoretical predictions.