engleski

Modification of Morphology and Properties of PS/PB Blends with Styrene-butadiene Multiblock Copolymers

The mechanical properties of the blends of immiscible polymers can be improved by addition of compatibilizers such as block copolymers (BC) having their blocks compatible with the pertinent polymers. These copolymers are localized at the polymer interface, reduce the interfacial tension and so provide a finer morphology of the blend. The copolymers, anchored through their blocks in polymers, suppress their separation and improve interphase adhesion. Strength of these crossings depends on the structure of the copolymer, above all on the length and number of blocks. Meanwhile the role of block length follows from its ability to entanglement formation [1, 2], opinions on effect of the number of blocks differentiates [3, 4]. A theory of interfacial crossings formed by copolymers with various numbers of blocks has been formulated [5, 6]. The theory predicts the multiblocks are more efficient than diblocks. Nevertheless, clear experimental evidence of the theory has not been brought up to now. Therefore an attempt has been made to compare morphology and selected properties of the polymer blends compatibilized with the copolymers of different block number and the same block length. According to compatibilization efficiency of various copolymers the different character of crossings has been judged. Because besides influence of molecular characteristics of a compatibilizer the effect of mixing condition as well as structure and ratio of the components play important role, we tried to limit interference factors followed these facts. A set of the model of linear styrene-butadiene (S-B) block copolymers – S-B, S-B-S and S-B-S-B-S were prepared by anionic polymerization [3] and then blended with polystyrene (PS) and polybutadiene (PB) in an extruder. Weight ratio of PS/PB in all blends was 4/1 and amount of the copolymer was 5wt %. Scanning electron microscopy (SEM) with image analysis (IM) and small-angle X-ray scattering (SAXS) were used for determination of the blend structure, the mechanical properties were measured by standardized methods using Instron, Zwick and Charpy Testers. Morphology (the size of dispersed particles, particle size distribution and phase structure regularity) and stress-transfer induced characteristics (tensile strength, elongation, tensile impact strength and notch impact strength) were chosen as criteria of the compatibilization efficiency of the BCs used. The authors appreciate the financial support of the Grant Agency of the Czech Republic.

Block Copolymers; Morphology; Mechanical Properties

nije evidentirano