Elongational viscosity for miscible and immiscible polymer blends. I. PMMAand AS with similar elongational viscosity

The effects of miscibility and blend ratio on uniaxial elongational viscosi ty of polymer blends were studied by preparing miscible and immiscible samp les at the same composition by using poly(methyl methacrylate) (PMMA) and p oly(acrylonitrile-co-styrene) (AS). Miscible polymer blend samples for the elongational viscosity measurement were prepared by using three steps: solv ent blends, cast film, and hot press. A phase diagram of blend samples was made by visual observation of cloudiness. Immiscible blend samples were pre pared by maintaining the prepared miscible samples at 200 degrees C, which is higher than cloud points using a LCST (lower critical solution temperatu re) phase diagram. The phase structure of immiscible blends was observed by an optical microscope. The elongational viscosity of all samples was measu red at 145 degrees C, which is lower than the cloud-point temperature at al l blend ratios. The elongational viscosity of PMMA and AS was similar to ea ch other. The strain-hardening property of miscible blends in the elongatio nal viscosity was only slightly influenced by the blend ratio, and this was also the case with immiscible blends. The strain-hardening property was on ly slightly influenced, whether it was miscible or immiscible at each blend ratio. Polydispersity in molecular weight for blend samples was not change d by GPC (gel permeation chromatography) analysis. Almost no change in the polydispersity of the molecular weight for blends and the similarity of elo ngational viscosity between PMMA and AS resulted in little influence of the blend ratio and miscibility on the strain-hardening property. (C) 1999 Joh n Wiley & Sons, Inc.