Effect of miscible polymer diluents on the development of lamellar morphology in poly(oxymethylene) blends

The development of lamellar morphology in poly(oxymethylene) (POM) and its miscible blends was studied by synchrotron time-resolved small-angle X-ray scattering (SAXS), during primary and secondary crystallization at temperat ures near 150 degrees C. The blends contained two different diluents: poly( vinyl 4-hydroxy styrene) [common name poly(vinyl phenol), (PVP)], which had a high glass temperature (T-g = 150 degrees C), and styrene-co-hydroxy sty rene oligomer (PhSO), which had a low glass temperature (T-g = -37 degrees C). The SAXS data were analyzed by correlation function analysis to extract several lamellar parameters: long period (L), lamellar crystalline thickne ss (Ic), amorphous layer thickness (la), and invariant (Q). The variation i n Q defined the region where spherulites quickly grew and filled the entire space, and was referred to as the primary crystallization dominant regime. A rapid drop in L and lc was observed at early times, and this can be expl ained by defective lamellar stacks filling in space between primary stacks, as secondary crystals form during the nominal primary crystallization domi nant regime. Lamellar thickening with time in the long-time secondary cryst allization region was observed in neat POM and the blend with 10% low T-g d iluent, while this process was inhibited with the high T-g diluent due to t he higher T-g of the interlamellar species. A decrease in la at long times confirmed the lamellar thickening. We refer to the lamellar thickening proc ess as a type of secondary crystallization. Interlamellar inclusion or trap ping was detected to different degrees with the high T-g diluent, while exc lusion was found for the low T-g diluent. (C) 1999 John Wiley & Sons, Inc.