Studies On Pmma/Montmorillonite Nanocomposites

Polymer/montmorillonite (MMT) nanocomposites is a kind of novel composites and arouses great interest due to its excellent synthetical properties. In this paper, different polymerization methods are used to prepare PMMA/MMT nanocomposites, whose thermal property and mechanical properties are obviously improved. The effects of MMT and Organo-MMT (OMMT) on the bulk polymerization mechanisms of methyl methacrylate and terminal polymer structure are also studied.First, the preparation process of OMMT is optimized via the modification of sodium silicate. Then, by suspension, emulsion and bulk polymerization, PMMA/MMT (OMMT) nanocomposites is prepared. XRD and TEM characterizations show that the spacings of OMMT are expanded and exfoliated in PMMA/OMMT nanocomposites by suspension and emulsion methods, while PMMA/MMT and PMMA/OMMT nanocomposites by bulk polymerization belong to intercalated and exfoliated type, respectively. In the nanocomposites mentioned above, part of PMMA can't be dissolved by acetone, which is fine solvent of PMMA. This means that there are strong interactions between PMMA and MMT (OMMT).The studies of the effect of MMT (OMMT) on the bulk polymerization of methyl methacrylate show that MMT acts as a retarder, while OMMT influences the polymerization rate and induction period as well, which is dependent on its dosage.The effects of MMT (OMMT) on the terminal polymer structure are also studied by viscosity method, FT-IR and XRD. Compared with pure PMMA, the PMMA molecular weight ( Mn), termination method and macromolecular arranging regularity are changed in the nanocomposites. At the OMMT content of 2~4wt% in emulsion system, Mr/ increases with OMMT content, above 4wt%, M^ decreases. In the range of 0~ 1 .Owt% for MMT or OMMT in bulk system, A/,7 of PMMA increases with the content. In these composites, the coupling termination content of PMMA decreases while disproportionation content increases. The macromolecular ranging regularity of PMMA also increases.Compared with pure PMMA, the thermal and mechanical properties of the nanocomposites are obviously improved at a very small amount of MMT(OMMT) loading. The Tgs of the composites via different methods are improved by 10 ~ 26 癈 , the decomposition temperatures at weight loss of 5wt% are increased by 42~99癈. In the bulk system, tensile strength, tensile modulus and impact strength are improved by 32.2%, 60.3% and 68.6%, respectively, without the loss of light transmittance.The thermal decomposition kinetics of nanocomposites is studied by Freeman-Carroll method. The reaction order and apparent activation energy of nanocomposites by emulsion and bulk methods are obviously increased. This also shows that the thermal stability of nanocomposites is much better than pure PMMA, which is also confirmed by Doyle method.