Epitaxy-Induced Crystallization of Olefin Block Copolymers

The epitaxy forced crystallization behavior of thin film olefin block copolymer (OBC) samples was investigated in the presence of benzoic acid (BA). The investigated OBC samples show apparent phase separation in the melt. However, their dissimilar comonomer difference between hard and soft segments (Delta C8) and block lengths results in different segregation strength, which controls their crystallization behavior. Independent of the crystallization conditions, for both OBCs the BA substrate induces highly oriented and epitaxially grown lamellar crystals. In case of the weakly melt segregated OBC, crystallization always breakout the melt separated phase domains, and crystals are homogeneously distributed in the entire sample. For strongly melt segregated OBC, on the other hand, phase separation is maintained when quenching the samples, and only isolated crystalline domains are formed. However, subsequent annealing of quenched samples, slow cooling from the melt, or isothermal crystallization at low supercoolings on the BA substrate forces crystals breakout the initial confinement. Such crystallization experiments help us better understanding the interplay between molecular architecture, segregation strength, and controlled crystallization conditions on the organization of OBCs.