Superheated water (shH 2 O) is investigated as a process aid in conventional aliphatic polyamide (PA) systems. The polymers investigated include PA 6 (PA6), PA 6,6 (PA66), PA 6,12 (PA612), and PA 12 (PA12). It is shown that the PA melting and crystallization temperatures are significantly reduced when exposed to shH 2 O. For example, the melting temperature of PA6 is depressed from 206 to 153 8C in the presence of shH 2 O. A relationship between amide group density and thermal transition temperature reduction is observed. Processing these materials in shH 2 O has led to a variety of materials ranging from low-density foams to higher density locally anisotropic foamed morphologies. In situ observations of PAs melting in the presence of shH 2 O are performed using a specially designed reactor. Results from these experiments are used to estimate the diffusion coefficient of shH 2 O in PA6. Finally, lowtemperature extrusion is performed with PA6 and shH 2 O at temperatures as low as 180 8C and mixture viscosity is estimated. A 20-fold depression in the melt viscosity of PA6 is observed at 240 8C with shH 2 O.

A new approach to toughen anionically polymerized polyamide 6 (aPA6) is presented using an additive monomer that simultaneously polymerizes and undergoes reaction-induced phase separation (RIPS) during aPA6 polymerization. In this work, the selection of additive, concentration, and reaction conditions are controlled in such a way to produce rubbery domains of the proper size and interparticle distance necessary for effective toughening without the diminishment of other engineering properties. This method circumvents the issues of particle dispersion and mixture viscosity that are commonly associated with other conventional methods of impact modification thereby making it an ideal system for fiber-reinforced aPA6 reaction injection molding. Controlled phase separation, modulus retention, and increased crystallinity are achieved at low additive concentrations. The additive monomer used in this case is octamethylcyclotetrasiloxane (D 4 ). D 4 undergoes RIPS during aPA6 polymerization and simultaneously polymerizes to produce polydimethylsiloxane. Optimal properties to maximize fracture energy without reducing the modulus are achieved with 2 wt % D 4 . The fracture mechanisms are investigated and results show approximately a 3-fold increase in energy release rate and a twofold increase in Izod impact energy.The application of reaction injection molding (RIM) is of particular interest for aPA6 due to its rapid reaction rate, low monomer viscosity, and solid final form. RIM is commonly used in polyurethane and epoxy resin composite materials. aPA6 has potential as a new matrix material in high concentration fiber-based composites to compete with polyurethane and epoxy composites.Additional Supporting Information may be found in the online version of this article.

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