Morphological structure of crystalline polymer blend involving hydrogen bonding: Polycaprolactone/poly(4-vinylphenol) system

The importance of crystal growth rate in the morphological formation of strongly interacting crystalline/amorphous polymer blends has been assessed by considering polycaprolactone (PCL)/poly(4-vinylphenol) (PVPh) systems. The effects of composition and molecular weight (MW) on the morphological structure were investigated by small-angle X-ray scattering (SAXS). Blending with PVPh increased the long period associated with the alternating crystalline-amorphous layers. The long period increase was characterized by the thickening of PCL crystals upon blending instead of the swelling of amorphous layers, The extent of extralamellar segregation of PVPh was revealed from the volume fraction of lamellar stacks. Despite the relatively high T-g of PVPh, significant extralamellar segregation of PVPh was observed. The extent of extralamellar segregation increased with PVPh composition for a given molecular weight combination of PCL and PVPh. For a given composition, the blends with PCL molecular weight (M-PCL) of 15 800 exhibited a higher extent of extralamellar segregation than the systems with M-PCL = 2600 and 3800. The extent of segregation was relatively unaffected by the MW of PVPh (M-PVPh) for the two molecular weight fractions investigated (M-PVPh = 4000 and 30 000). Good correlations were found between the extent of extralamellar segregation and crystal growth rate, where slower growth rate led to higher extent of extralamellar segregation. The crystal growth rate of PCL in the blends thus played the dominant role in the morphological formation of PCL/PVPh system.