Through detailed analysis of the temperature dependence of the infrared spectra, the structural change occurring in the cocrystallization and phase segregation processes has been investigated for polyethylene (PE) blends between the deuterated and hydrogeneous species with various degrees of branching. In the blend of deuterated high-density PE (DHDPE) with linear low-density PE (LLDPE(2), 17 ethyl branches/1000 carbons), almost perfect cocrystallization occurs, during which the D and H chains are distributed statistically randomly in crystalline lamellae at a probability determined by the relative content of the D and H species. In the blend of DHDPE with LLDPE (3) (41 ethyl branches/1000 carbons), basically the phase segregation occurs but some portion of the H species cocrystallizes with the D chains. In this case the H chain stems are isolated from each other by the neighboring D chain stems as clarified from the analysis of the infrared band splitting width as a function of temperature.