Morphology of Polysiloxanes Crystallized from the Melt

Poly(tetramethyl-p-silphenylene siloxanes) fractions ranging in molecular weight from below 104 to above 106, have been crystallized isothermally from the melt. Samples have also been prepared under a wide range of annealing conditions varying from minutes to hundreds of hours. The morphology of these fractured specimens has been studied by electron microscopy. The ease of fracture increases as the molecular weight decreases. The dimension of the lamellar structures ascertained from Pt shadowing and Au decoration techniques increase as the annealing or crystallization temperature is raised. The values are consistent with the crystallite sizes estimated from small-angle x-ray measurements made on these same samples, and with the single crystal thickness obtained under comparable crystallization temperatures. The topography of the fracture surfaces depends on the molecular weight and on the annealing conditions. The lower molecular weight samples (below 40 000) exhibit a much higher degree of regularity than the fractions with longer chain lengths.