Epitaxial Crystallization of Isotactic Poly(methyl methacrylate) from Different States on Highly Oriented Polyethylene Thin Film

Through fixing the orientation of oriented polyethylene (PE) thin film during melt-recrystallization with the help of a vacuum evaporated thin carbon layer, the isothermal melt- and cold-crystallization of isotactic poly(methyl methacrylate) (iPMMA) on oriented PE substrate was studied. The results show that same parallel chain epitaxy of iPMMA on the oriented PE substrate takes place in both cold- and melt-crystallization processes based on a two-dimensional lattice matching. However, the crystallization kinetics in the two processes is quite different. The induction time of iPMMA during melt-crystallization is significantly longer than during cold crystallization (11 h vs 2.5 h). This is related to the different nucleation mechanism for cold- and melt-crystallization processes. On the other hand, the crystal growth rate of iPMMA from melt is much higher than from glassy solid state. This is associated with a higher molecular chain mobility of iPMMA in supercooled melt than in the frozen amorphous solid film.