Entropically driven phase separation of highly branched linear polyolefin blends

Small-angle neutron scattering (SANS) was used to examine the melt phase be havior of a heavily branched comb PEE polymer blended separately with two l inear PEE copolymers. In this case, PEE refers to poly(ethylene-r-ethylethy lene) with 10% ethylene units; therefore, the molecular architecture was th e only difference between the two components of the blends. The molecular w eights of the two linear random copolymers were 60 and 220 kg/mol, respecti vely. The comb polymer contained an average of 54 long branches, with a mol ecular weight of 13.7 kg/mol, attached to a backbone with a molecular weigh t of 10 kg/mol. Three different Volume compositions (25/75, 50/50, and 75/2 5) were investigated for both types of blends. SANS results indicate that a ll the blends containing the lower molecular weight linear polymer formed s ingle-phase mixtures, whereas all the blends containing the high molecular weight linear polymer phase-separated, These results are discussed in the c ontext of current theories for: polymer blend miscibility. (C) 2000 John Wi ley & Sons, Inc.