A Deformation-Induced Phase Separation in the Solid State
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A DEFORMATION-INDUCED PHASE SEPARATION IN THE SOLID STATE J.M. LEFEBVRE*, R.S. PORTER* and G.D. WIGNALL** * Polymer Science of Engineering, University of Massachusetts Amherst MA 01003 ** National Center for Small Angle Scattering Research, Oak-Ridge National Laboratory, Oak-Ridge TN 37830. ABSTRACT Amorphous Polymethylmethacrylate/Polyethyleneoxide blends deformed by solid-state coextrusiza exhibit anomalous anisotropic Small Angle Neutron scattering patterns in the low q range. It is shown that upon drawing the samples have undergone phase separation to some extent. The resulting structure of the system is characterized by combining scattering techniques with Differential Scanning Calorimetry. INTRODUCTION In a recent paper Ill, we reported on a small angle neutron scattering (SANS) characterization of the drawing behavior of pure PMMA and compared it to that of an amorphous PMMA/PEO blend. While we were able in both cases to extract molecular parameters such as radius of gyration, Rg, molecular weight, Mw, and interaction parameter, X, for the isotropic undeformed systems, a strong anomalous scattering at low angle precluded any quantitative interpretation of the SANS data on drawn anisotropic PMMA/PEO blends. Preliminary differential scanning calorimetry (DSC) measurements indicated the presence of two transitions for the drawn blends, suggesting that phase separation has occured to some extent. Although the miscibility of PMMA with PEO in the melt has been predicted theoretically 121 and confirmed by various authors le.g. 3,41, vibrational spectroscopy studies concluded that the intermolecular interactions between PMMA and PEO molecules are very weak, of a Van der Waals type 151. Moreover the magnitude of the Flory-Huggins interaction parameter deduced from our SANS results Ill(X • 1.5 10-3) is close to the critical value, and in agreement with recent findings (-5 10-3 < X < 0) throughout the entire composition range 161. In order to investigate a potential effect of deformation on phase separation in these systems, DSC and scattering techniques have been used. RESULTS AND DISCUSSION Amorphous PMMA/PEO blends with composition 90/10 % by weight have been prepared by freeze drying from benzene solution and subsequent moulding under vacuum at 150'C. Both polymers have a molecular weight close to 105 g/mole. The blend exhibits a single glass transition temperature Tg = 88"C whereas that of the pure PMMA is Tg = 110°C. Both values are taken at the inflexion point of a DSC scan at a rate of 20°C/mm. Samples have been solid state coextruded in an Instron capillary rheometer using polyethylene billets at temperaturechosen between Tg + 10 and Tg + 30"C. Details of preparation and characterization have been given previously SANS experiments were performed at the National Center for Small Angle Scattering Research (NCSA5R) at Oak-Ridge on the 30 m facility with a neutron wavelength X = 4.75 A. For this purpose ternary mixtures of H-PMMA, D-PMMA and PEO have been prepared for which the global PMMA/PEO composition was kept
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