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We have investigated the effect of deuterium labeling on the thermodynamic interactions in blends of labeled and unlabeled saturated hydrocarbon polymers. Small-angle neutron scattering (SANS) was used to evaluate the Flory-Huggins interaction parameter at several temperatures and compositions.Light scattering was also used in several cases to confirm the location of phase boundaries. We find that deuterium labeling changes relative to the value for hydrogenous components and that the direction of the change depends on which of the two components is labeled. For blends of hydrogenated polybutadienes, always increases when the more branched component is labeled, a pattern first noted by Crist and Rhee and also consistent with the expectation that deuterium substitution reduces the cohesive energy density (solubility parameter) of hydrocarbon substances. A solubility parameter formalism is developed by which for hydrogenous components can be estimated with reasonable accuracy from SANS data obtained for the two combinations of singly-labeled components. It also provides a method for assigning relative values of the solubility parameter for a wide class of saturated hydrocarbon polymers.

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A symmetric diblock ethylene-propylene copolymer (DEP) was synthesized through hydrogenation of an anionically polymerized polybutadiene-poly(2-methyl-1,3-pentadiene) diblock copolymer (PBDb-PMPD). IR and NMR measurements showed the hydrogenation to be more than 98% complete. The resultant diblock copolymer consists of an atactic polypropylene block and a polyethylene block (b-PE) containing 3 mol % of ethyl branches. Differential scanning calorimetry (DSC) was carried out for three series of binary blends made from DEP (Mw = 113 x 103) and three atactic polypropylene (APP) samples with molecular weights of MW = 15,39, and 190 X 103. Blending did not affect the melting behavior of b-PE but drastically altered the crystallization behavior depending on the molecular weight and composition of the blend. Adding APP to DEP caused the primary crystallization peak to shift to lower temperature. In the composition range of more than 50 wt % of APP, another new crystallization peak appeared around 70 O C for all blends. This feature was especially pronounced for the blends with the lowest molecular weight APP. Isothermal crystallization studies were carried out for the blends and the data were analyzed by the Avrami theory. The analysis indicates that the dimensionality of the crystallization growth geometry was reduced by blending and each crystallization peak could be correlated with a different dimensionality in the growth geometry. These results are consistent with the framework of the currently accepted microphase separation model for homopolymerldiblock copolymer blends.