In situ SAXS investigations of isothermal crystallization in poly(TMPS) fractions

Abstract

Abstract:The isothermal crystallization kinetics of poly(TMPS) has been measured by ISSAXS and results obtained for a molecular weight fraction (21,000) below the critical entanglement molecular weight (25,000) and another one above it (371,000). The SAXS intensity vs. time curves suggest that a single transformation mechanism exists. The SAXS long period is independent of crystallization time for both poly(TMPS) fractions. However the interlamellar thickness contribution to the long period is dependent upon molecular weight and crystallization temperature, increasing with temperature and molecular weight. The crystallite contribution also increases over the range studied. Both fractions exhibit a significant, but reversible decrease in thickness on cooling the sample from the crystallization temperature to room temperature and recyling again. The change is more pronounced for 371,000 specimen in keeping with its lower crystallinity. The path dependence of lamellar dimensions has significant implications in the morphological characterization of polymers annealed or crystallized at one temperature and then measured at another one.

Self-Generated Fields and Polymer Crystallization

“…Robelin-Souffaché and Rault find a significant increase with molecular weight of the thickness l a of the amorphous layer separating lamellar crystals within spherulites of polyethylene formed at the same undercooling, as shown in Figure . Magill et al have shown, using poly­(tetramethyl- p -silphenylene siloxane), that the effect of this molecular weight effect on l a persists over a wide range of crystallization temperature . Both sets of authors have attributed this effect to stresses associated with chain entanglements trapped between adjacent lamellae.…”

“…Magill et al have shown, using poly(tetramethyl-p-silphenylene siloxane), that the effect of this molecular weight effect on l a persists over a wide range of crystallization temperature. 140 Both sets of authors have attributed this effect to stresses associated with chain entanglements trapped between adjacent lamellae. Robelin-Souffachéand Rault (R-S-R) write, "The balance between the enthalpy of crystallization and the energy of deformation of the amorphous layers explains the correlation law L ∼ l a ∼ r [L is the long period and r the end-to-end distance of the chain], the variation of L with supercooling, and the order of magnitude of the crystallinity for high molecular weight materials ...." In other words, R-S-R associate the thickness of the amorphous layer with an equilibrium between the driving force for crystallization and the creation of stress in the amorphous layer.…”