When two polymers are brought into intimate contact, the interface is not perfectly sharp. Instead, localized molecular mixing produces an interphase with thickness on the order of 10 nm. Forced assembly by layer multiplying coextrusion makes it possible to create films that are entirely interphase. The new interphase materials can be characterized using conventional tools of polymer analysis. In this study we vary the ratio of poly(methyl methacrylate) (PMMA) to polycarbonate (PC) in the coextrusion process in order to obtain very thin PMMA nanolayers sandwiched between thicker (∼50 nm) PC layers. We use oxygen permeability to probe the nature of the interphase as the PMMA layer thickness is reduced below the interphase thickness to the limit of layer stability. If the PMMA nanolayers are made thinner than the 12 nm interphase dimension, they more closely resemble a thin interphase region sandwiched between thicker PC layers than they do discrete PMMA layers. The interphase region becomes progressively thinner with decreasing PMMA layer thickness until the limit in melt stability of the PMMA layer is reached. Efforts to obtain PMMA nanolayers thinner than 5 nm resulted in layer instability and breakup. Oxygen permeability suggested that the nanolayer fragments had a very high aspect ratio.

In this work, we have shown for the first time that assemblies of up to 64 alternating foam and film layers can be successfully made via the microlayer coextrusion technology. We have investigated the effect of some important processing variables on the foam-film structure, and have demonstrated how they can be optimized. With the optimum concentration of the right type of chemical blowing agent, the cell size can be significantly reduced for the polypropylene foam-film systems by increasing the number of layers. The foam layer density does not change significantly with increasing number of layers. Measurements of the cell density and cell volume indicate that enhanced nucleation and/or reduced coalescence is responsible for the reduction in cell size with an increasing number of layers. Constrained cell growth comes into play when a single cell/layer morphology is observed. Different types of polymers can be used as the film layer to alter the flexibility of the foam/film composite. The compressive behavior of the hard/hard polypropylene foam/polypropylene film system is similar to that of cork in terms of the compressive modulus, collapse stress, and densification strain. The tensile and compressive moduli increase with the increasing number of layers and this could be explained on the basis of an increase in the fraction of material in the cell walls, using the conventional Gibson-Ashby model. The soft/soft polyethylene foam/ethylene-styrene copolymer film system exhibits enhanced toughness in tension. The effect of the foam/film composition on the tensile and compressive moduli can be explained using the composite series and parallel models.

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The blends of a nonlinear optical dye with polycarbonate are described and comparisons are made with solutions of the dye in chloroform. Absorption spectra of blends with up to 1 wt % lead tetracumylphenoxy phthalocyanine showed the dye to be primarily in the monomer form. The monomer absorption spectrum and the measured extinction coefficient replicated those in chloroform solution. As the dye concentration increased to 20 wt %, the monomer intensity decreased and new spectral features characteristic of the dimer appeared. The spectra were resolved into contributions of monomer and dimer, and the concentration effect was analyzed according to the monomer/dimer equilibrium. Much higher monomer concentrations were achieved in polycarbonate blends compared to chloroform solutions. It was concluded that when the blends were quenched from the melt, the equilibrium established at the melt temperature was preserved in the solid state glass. Quenching the blend from different melt temperatures confirmed this interpretation. Extrapolation of the temperature dependent equilibrium constant to 25°C yielded a value close to that reported for chloroform solution at 25°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 104: 464–469, 2007

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