Factors Influencing Properties of San/Pmma Blends
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FACTORS INFLUENCING PROPERTIES OF SAN/PMMA BLENDS R. SUBRAMANIAN, Y. S. HUANG, J. F. ROACH AND 0. R. NIFF GenCorp Research, 2990 Gilchrist Road, Akron, Ohio 44305 ABSTRACT The versatility of polymeric blends is reflected in the range of usable end properties that can be achieved through alterations in the composition and/or effective control of the morphologies of the mixtures. Solvent cast and melt mixed blends of SAN and PMMA have been studied to understand the Influence of PMMA tacticity and the acrylonitrile content of the SAN copolymer on their phase behavior. The results show a shifting of the cloud point curves and the miscibility windows for the blends of SAN with different stereo-regular PMMAs. This is interpreted as being due to specific interactions between the acrylonitrile and methacrylate groups. The 'goodness' of mixing in the melt mixed blends were determined by FTIR ATR spectroscopy. The effects of the processing conditions on the mixing characteristics and subsequent improvement in mechanical properties are discussed. The limits of mixing that can be achieved using standard mixing procedures and their role in affecting the end use properties such as the flexural strength will also be discussed. INTRODUCTION Miscibility in multicomponent polymeric systems is not always desirable; but gross phase separation invariably leads to inferior properties. As in block copolymers, controlled chemical structure and microphase heterogeneity in polyblends often lead to superior mechanical Such intricate phase properties and improved processability [1-7]. morphology can be obtained upon phase demixing (separation) of a homogeneous blend via a spinodal mechanism, Which would result in phase domains approaching molecular dimensions (- 101A*) and the phase separated blend would behave like a self-assembled composite [8]. It has been known for quite sometime now that polymethylmethacrylate (PMMA) forms miscible blends with the copolymer, styrene acrylonitrile (SAN) over a limited range of acrylonitrile (AN) content [9]. This 'miscibility window' has been explained by Paul and Barlow [10] and others [11,12] as resulting from a dilution of the unfavorable interactions among the various segments, leading to a net negative contribution to the free energy of mixing, AGM. The SAN/PMMA system has been widely studied for phase behaviour by many researchers [9-12]. However, the investigations have been limited to blending SAN (with varying amounts of AN) with commercial, heterotactic PM4A (h-PMMA) and other higher order methacrylates [13). The influence of PMMA tacticity on the phase behavior of this system has not been investigated. Isotactic, syndiotactic and heterotactic forms of PMMA exhibit large differences in T and other physical properties [14,15). Thus, it Is reasonable to epect these different PMMAs to behave differently when blended with SAN. Based on this consideration, a systematic study of the effects of PMMAtacticity on phase behavior, processing and mechanical properties of the blends was undertaken.
Mat. Res
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