POLYETHYLENE DIBLOCK COPOLYMERS - DIRECT SYNTHESIS AND MORPHOLOGICAL ANALYSIS

A variety of diblock copolymers containing a high density polyethylene block were synthesized directly by a transformation reaction from an anionic to a Ziegler-Natta type polymerization. A wide range of reacti on parameters were investigated and optimized. Efficiencies of convers ion of the anionic first block to diblock were as high as 33% (100% no rmalized), consistent with the known 3/1 Li-R/Ti relationship in the a ctive catalyst species. The activity of the polymeric Li-R/Ti catalyst with regards to ethylene polymerization was as high as 40000 g of pol ymer per mole Ti. Molecular characterization of the resultant polymers is consistent with diblock copolymer structures, especially the chara cteristic microphase-separated structure exhibited in transmission ele ctron micrographs. Detailed microscopic and X-ray analyses show distin ct differences, however, between the morphological behaviour of these materials and the now well established morphological behaviour of amor phous-amorphous diblock copolymers. These differences are readily expl ained by consideration of the interactions between the competing therm odynamic processes of microphase separation and crystallization in the se copolymers.