A study of the phase behaviour of polyethylene blends using micro-Raman imaging

The origin of morphological phase structures in blends of a linear deuterated polyethylene and a hydrogenous branched polyethylene has been investigated using Raman imaging. Blends were crystallized to produce samples with large domains that are rich in linear material surrounded by a matrix that is rich in branched polymer. The samples were then remelted for a range of holding times and quenched to examine the remixing of the separated domains in the melt. The micro-Raman images show that the samples remixed to a homogeneous distribution by branch content within the expected time scale, as estimated from the diffusion constants. However, micro-Raman imaging was also used to detect crystallinity variations and it reveals a biphasic structure in quenched blends that display a morphological phase structure when examined in the transmission electron microscope. Raman images of the same samples are uniform when constructed by branch content. Possible causes for this phenomenon are briefly discussed.