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Chemistry in supercritical fluid-swollen polymers: Direct synthesis of polymer/polymer and polymer/metal composites

James Joseph Watkins, University of Massachusetts Amherst


A simple and versatile method for the preparation of polymer composites in supercritical fluids (SCFs) is proposed and demonstrated by experiment. Reagents are infused into solid polymers as SCF solutions and converted to the desired product by inducing a reaction to occur in the presence of the SCF solution or subsequent to its removal by depressurization. The product of the reaction, which may or may not be soluble in the SCF solution, constitutes the second phase of the composite. The process is effective for modifying virtually all polymers including those such as poly(chlorotrifluoroethylene) (PCTFE), polytetrafluoroethylene (PTFE) and ultra-high molecular weight polyethylene that are solvent resistant or otherwise difficult to process. Polymer/polymer composites are prepared by the sequential infusion and free radical polymerization of vinyl monomers within carbon dioxide-swollen substrates. Experiments involving combinations of eight polymer substrates and five monomers demonstrate the utility of the method and control over the severity of substrate modification. A study of styrene polymerization within CO$\sb2$-swollen PCTFE indicates composite composition and structure is dictated by system variables including temperature, pressure and monomer concentration. The control imparted is consistent with the underlying phase behavior and absorption kinetics of the CO$\sb2$/polymer/monomer system. Diffusion rates within the matrix are sufficiently rapid to yield high molecular weight polystyrene (PS) (M$\rm\sb{w}>200,000$ g/mol). The resulting PCTFE/PS composites exhibit unique, co-continuous morphologies. Polymer/metal composites are produced by the sequential SCF-assisted infusion and reduction of organometallic compounds within solid polymers. The hydrogenolysis of dimethylcycloocatadiene platinum (II) (CODPtMe$\sb2)$ in poly(4-methyl-1-pentene) (PMP) and PTFE yields isolated Pt nanoclusters distributed throughout the substrates. The reduction is autocatalytic and is shown to be mass transfer limited in PMP. Cluster size is controlled by adjusting diffusion rates in the substrate during CODPtMe$\sb2$ reduction. The discovery that the reduction of organometallic compounds proceeds cleanly in CO$\sb2$ is the basis for Chemical Fluid Deposition (CFD), a new, generally useful metal deposition scheme. CFD is demonstrated by the low temperature (80$\sp\circ$C) deposition of platinum and palladium films onto silicon wafers and polymer substrates. X-ray photoelectron spectroscopy indicates the films are continuous and free of ligand-derived contamination.

Subject Area

Polymers|Chemical engineering

Recommended Citation

Watkins, James Joseph, "Chemistry in supercritical fluid-swollen polymers: Direct synthesis of polymer/polymer and polymer/metal composites" (1997). Doctoral Dissertations Available from Proquest. AAI9721497.