Polystyrene/polyethylene composites have been prepared by the heterogeneous radical polymerization of styrene within supercritical carbon dioxide−swollen high density polyethylene (HDPE) substrates. Composition of the composites can be controlled with reaction time and initial ratio of styrene to HDPE. The polystyrene produced within the substrate is of high molecular weight. Differential scanning calorimetry and wide-angle X-ray diffraction indicate that the crystalline portion of the HDPE substrate is unaffected by the procedure used in this investigation. Scanning electron microscopy indicates that the polystyrene resides in the noncrystalline domains and permeates throughout the spherulitic structure of the HDPE substrates. This morphology is very different from the morphology of polystyrene/polyethylene blends produced by conventional melt/mixing techniques. The strengthening of the spherulitic structure of HDPE produces an efficient enhancement in the modulus of the overall composite. The tensile strengths of the composites are dramatically enhanced over conventionally produced blends. The addition of brittle polystyrene to extremely tough HDPE substrates decreases the overall fracture toughnesses of the composites.

Activated carbonates facilitate the preparation of polycarbonates based on monomers that are unsuitable for traditional melt polymerization at high temperatures. Bis(methyl salicyl) carbonate (BMSC) clearly shows reactivity benefits over diphenyl carbonate in melt polymerization reactions, resulting in shorter reaction times and reduced heat exposure during polymerization. The increased reactivity enables the melt polymerization of a wide range of monomers, as demonstrated by two examples using volatile resorcinol and sterically hindered tert-butyl hydroquinone as monomers in the preparation of (co) polycarbonates.

Supercritical carbon dioxide (SC CO2) was used as an aid in fabricating polymer/polymer composites. Using a two-stage process, ethyl 2-cyanoacrylate (ECA) monomer was anionically polymerized within poly(tetrafluoroethylene-co-hexafluoropropylene) substrates. The composite fabrication process involved first infusing triphenylphosphine (the initiator) into the substrate using SC CO2. In the second step, monomer was introduced (again using SC CO2) to the substrate. As the monomer absorbed into the initiator-containing substrate, it polymerized. The composite surfaces were characterized using surfaceselective techniques. The mechanical performance of the composites was determined by measuring the adhesive fracture toughness of the composites. The locus of failure of fractured interfaces of composites with epoxy was determined by X-ray photoelectron spectroscopy.

This article presents the results of a combined experimental and analytical study of the fatigue and fracture behavior of a polymer/metal composite which was developed recently for self-lubricating applications in automotive engines that utilize liquefied natural gas as fuel. For comparison, the microstructure and the fatigue and fracture behavior of a nonpolymer-containing "matrix" material are also presented. Since the crack profiles observed in both systems under monotonic or cyclic loading reveal significant components of ligament bridging, micromechanics models are presented for the modeling of crack bridging. The resulting predictions of resistance-curve behavior are compared with measured resistance curves. The shielding effects of ligament bridging are also quantified under cyclic loading. The implications of the work are also discussed for the modeling of fatigue damage and fracture in polymer/metal coatings.

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Because of the recent emphasis on green chemistry, there has been interest in using supercritical carbon dioxide (sc CO2) as a solvent or swelling agent to aid in polymer processing and polymer chemistry (Adamsky and Beckman, 1994; DeSimone et al., 1992; Hayes and McCarthy, 1998; Kung et al., 1998; Mistele et al., 1996; Romack et al., 1995; Watkins and McCarthy, 1995). Supercritical CO2 is a very weak solvent for most polymers (some fluoropolymers and silicones are exceptions); however, it swells most polymers and dissolves many small molecules (Berens and Huvard, 1989). The density of a supercritical fluid (SCF), and thus its solvent strength, is continuously tunable as a function of temperature or pressure up to liquidlike values. This provides the ability to control the degree of swelling in a polymer as well as the partitioning of small-molecule penetrants between a swollen polymer phase and the fluid phase. The low viscosity and zero surface tension of SCFs allows for fast transfer of penetrants into swollen polymers. The lack of vapor/liquid coexistance in SCFs allows the sorption to proceed without the penetrant solution wetting the substrate surface. Since most of the common SCFs are gases at ambient conditions, the removal and recovery of the solvent from the final product is extremely facile. All of these factors aid in a new method we have developed for preparing polymer composites. This method involves the absorption of a supercritical solution of a monomer, initiator, and CO2 into a solid polymer substrate and subsequent thermal polymerization of the monomer to yield a composite system of the two polymers. We have focused on radical polymerization of styrene within various solid semicrystalline polymer substrates (Hayes and McCarthy, 1998; Kung et al., 1998; Watkins and McCarthy, 1995). Table 10.1 lists a number of systems that we have studied to make polymer–polystyrene composites. The method for preparing the polymer blends listed in Table 10.1 involves the soaking of the substrate polymer in a supercritical solution of styrene, a thermal radical initiator, and CO2 at a temperature where the initiator decomposes very slowly (half-lives of hundreds of hours).

The fatigue behavior of Fe-Ni-base metal/polymer composites is discussed in this paper. These are proposed as self lubricating surfaces with the potential to replace conventionally lubricated pistons in automotive engines. Following a description of composite microstructure and basic mechanical properties, the paper examines the effects of polymer volume fraction on long fatigue crack growth. The effects of temperature on fatigue crack growth are then elucidated before presenting some initial fracture mechanics concepts for the prediction of fatigue life. The implications of the results are assessed for the design of durable surfaces.