Isochiral form II of syndiotactic polypropylene produced by epitaxial crystallization

Epitaxial crystallization of syndiotactic polypropylene (sPP) on 2-quinoxal inol (2-Quin) yields, in the lower part of the crystallization range, the l ess common and metastable form II based on the packing of isochiral helices , rather than the stable antichiral form I. The contact plane is (110)(II). Form II exits only as a thin layer (< 50 nm) near the substrate surface. D uring further growth away from the surface, a transition takes place to the disordered form I, observed in "conventional" thin film growth. The epitax ial relationship rests only partly on dimensional matching with the chain a xis repeat distance (which would be valid for both forms I and II) and on i nterchain distances. Whereas a better dimensional match would be achieved w ith form I, selection of the isochiral form II results from better correspo ndence of the surface topographies of the deposit (110)(II) sPP and substra te 2-Quin (001) contact faces.