スチレン―ブタジエンブロック共重合体/メタクリル酸メチル―スチレン共重合体ブレンドの構造と機械的性質I..構造と機械的性質の関係
Morphology and Mechanical Properties of Blends of Styrene-butadiene Block Copolymer with Methyl Methacrylate-styrene CopolymerI. Structure-property Relationships
山岡育郎・木村正生
Yamaoka, lkuro / Kimura, Masao
Polymer blends of a styrene-butadiene block copolymer (SBS) with a methyl methacrylate-styrene copolymer (MS) were prepared by extrusion and the morphology of the extrudates was observed. These extrudates were injection and compression molded, and the resultant morphology and mechanical properties of the moldings were also examined. In all cases the SBS phase of SBS/MS blends formed lamellar structure in which the polybutadiene (PB) phase and the polystyrene (PS) phase showed alternate layers with thicknesses of 150〜200_ and 200〜250_, respectively. Such lamellae strictly consisted of quasi-layers in which the PB dispersed phase in large aspect ratio was surrounded by the PS matrix. Compression molded blends showed higher order than injection molded blends, which suggests that lamellae in the former were relaxed on slow cooling to neat stratification. The MS particles in extrudates were highly oriented because of the extensional flow field which occurred in the melt strands after exiting from the die on extrusion. Such flow-induced orientation was well relaxed after compression molding. Compression molded blends including 10 to 40wt.% MS , showed excellent notched Izod impact strength, but were inferior to the corresponding injection molded blends in tensile and flexural properties and deflection temperature under flexural load. Compression molded blends showed good impact energy dissipation, since the highly ordered lamellae were deformed with extensive shear yielding development and the neat MS particles were debonded from the SBS matrix on fracture. The improved tensile and flexural properties of the injection molded blends would be due to the smaller aspect ratio of the PB dispersed phase leading to a closer network of the rigid PS phase in the quasi-layers of the SBS lamellae.
Key words: Styrene-butadiene Block Copolymer / Methyl Methacrylate-styrene Copolymer / Polymer Blend / Shear Yielding / Debonding