THE EFFECTS OF SHORT-CHAIN BRANCHING AND COMONOMER TYPE ON THE INTERFACIAL-TENSION OF POLYPROPYLENE-POLYOLEFIN ELASTOMER BLENDS

The imbedded fiber retraction method was used to assess the effect of increasing octene content and comonomer type on the compatibility of p olypropylene-polyolefin elastomer (PP-POE) blends via direct measure o f the interfacial tension. The interfacial tension was found to decrea se monotonically with increasing octene content from a starting value of 1.5 +/- 0.16 dyn cm at an initial octene level of 9% down to 0.56 /- 0.07 dyn cm at an octene content of 24%. These effects can be inter preted in terms of the effective decrease in the molecular weight betw een chain ends for the branched POE materials. The experimental data w ere found to be described well by a modification of the empirical rela tionship used to describe the effect of molecular weight on the interf acial tension for linear materials. The power-law parameter was found to be numerically equivalent for that obtained for the molecular weigh t dependence of linear materials. The measured interfacial tension was also found to be dependent on the type of comonomer used in the PP-PO E systems. The interfacial tension ranged from 1.07 +/- 0.09 dyn cm fo r a PP-POE system made using ethylene-propylene down to 0.56 +/- 0.07 dyn cm for a PP-POE made using ethylene-octene (24% octene). (C) 1997 John Wiley & Sons, Inc.