Rheological properties of RAFT-mediated poly(styrene-co-butyl acrylate)-clay nanocomposites [P(S-co-BA)-PCNs]: Emphasis on the effect of structural parameters on thermo-mechanical and melt flow behaviors

RAFT-mediated random poly(styrene-co-butyl acryl ate)-[N-(4-((((dodecylthio)-carhonothioyl)thio)methyl)benzyl)-N,N-dimethylethanammonium]-clay nanocomposites (P(S-co-BA)-DCTBAB-PCNs) and poly(styrene-co-butyl acrylate)-[N,N-dimethyl-N-(4-(((phenylcarbonothioyl)thio)-methyl)benzyl)ethanammonium]-clay nanocomposites (P(S-co-BA)-PCDBAB-PCNs) were prepared by miniemulsion free-radical polymerization. The RAFT agents (i.e. DCTBAB and PCDBAB) were anchored onto the clay layers prior to polymerization, and were able to control the polymerization process, as evident from the decreasing molar mass and polydispersity index (PDI) values as the concentration of the RAFT agent in the system increased. The efficiency of the anchored RAFT agents increased as the RAFT agent concentration in the system increased, i.e. as the clay loading increased. The nanocomposites that were prepared were found to have a partially exfoliated morphology at low clay loadings, as determined by SAXS and TEM, whereas, at high clay loadings the morphology changed to become predominantly intercalated. The thermo-mechanical properties of the nanocomposites were found to be a function of the molar mass, PDI, PCN morphology, and clay loading. In the glassy state, the storage modulus was seen to effectively decrease as clay loading increased, whereas the opposite was true for the loss modulus and tan delta. At low clay loadings the melt theological properties were dominated by the matrix effects, whereas at high clay loadings the effect of the clay filler dominated, resulting in pseudo solid-liquid-like behavior. (C) 2008 Elsevier Ltd. All rights reserved.