NMR investigations of reactively extruded PVC/PMMA and PVC/PS blends

Abstract

AbstractReactively extruded PVC/PMMA and PVC/PS polymer blends were investigated by 1H and 13C high‐resolution and 13C MAS NMR spectroscopy. To obtain blends, liquid solutions of monomer, initiator, and cross‐linking agent were absorbed into porous polyvinyl chloride (PVC) particles, forming dry blends; subsequently, the dry blends were fed into a twin‐screw extruder at 180°C activating in situ polymerization within the PVC matrix. Polymer and monomer fractions of resultant extruded blends were identified and characterized at the molecular level by nuclear magnetic resonance (NMR) spectroscopy, providing important insights into the microscopic details of the blends. NMR characterization includes: residual monomer content and its dispersion and site heterogeneity within the PVC matrix; effect of initial concentrations of monomer, initiator, and cross‐linker on the final products; and possible occurrences of copolymer grafting. NMR spectroscopy reveals efficient polymerization of methyl methacrylate (MMA) (ca 90% polymethyl methacrylate (PMMA)) and inefficient polymerization of styrene (less than 10% polystyrene (PS) with a significant fraction of unreacted monomer remaining entrapped in the PVC matrix) under the reactive extrusion of PVC/monomer (15 phr monomer) dry blends. Morphologically, the reactively extruded PVC/PMMA forms a single‐phase blend. In contrast, the PVC/PS forms a phase separated blend. Both the in situ polymerization efficiency and the phase behavior of the resulting blends are rationalized in terms of the affinity of the monomers in the initial dry blends, and of the resulting polymers in the final reactively extruded blends, to the PVC. This understanding can guide the design and control of properties of blends obtained through the reactive extrusion process and other in situ polymerization techniques. Copyright © 2007 John Wiley & Sons, Ltd.