No abstract

Impact modifiers with grafted PMMA shell are used to modify polymethylmethacrylate matrix. The composition of the shell is chosen to enhance the interactions at the modifier/matrix interface and to obtain good dispersion of the impact modifier in order to optimize impact strength of the blend. The degree of interactions at the interface is characterized by the interfacial region where the chains of the matrix mix with those of the shell of the modifier. The deviation of the measured viscoelastic behavior of these blends from that predicted by the emulsion models has been attributed to the formation of the network structure due to the association of matrix chains with the shell of the modifier. It is expected that the network structure will decrease with increasing frequency and, as such, the effective volume of the particle is frequency dependent. This study uses the emulsion models to estimate the larger effective volume of the particle and, therefore, the extent of interaction at the interface. In the blends of this study it can be shown that at low modifier levels the solvent swelling of the modifier shell results in stronger interactions with the matrix; this effect is negated by the aggregation of particles at higher modifier loadings. The interaction of core modifier with the PMMA matrix seems to be similar to that of the core‐shell modifier. This would not be expected from the calculated interfacial thickness of approximately 4 nm. It is, therefore, proposed that during melt‐processing the core modifier surface was altered due to grafting of the matrix PMMA chains during melt‐blending to (BA/St) copolymer of the core modifier thus reducing the interfacial tension. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2623–2634, 1998

SYNOPSISSeveral different polymer modifications are currently used to produce commercial plastic materials, especially engineering resins, that have significantly improved melt strength. However, these modifications rarely produce materials that can be formed into very large parts. This study shows that the melt strength of engineering resins can be enhanced by rubber particles having grafted shells that are compatible with the resin. The melt strength of the engineering resin can be further improved by the incorporation of compatible highmolecular-weight polymers. The melt strength improvements thus obtained facilitate the formation of very large parts requiring 8-10 ft long parisons. The effects of shear rate on complex viscosity indicate that the extent of interaction between the polycarbonate matrix and the core-shell impact modifier decreases with increasing shear rate. Therefore, the impact strength of the part molded from a matrix modified with a core-shell rubber may depend on the process history. Dynamic mechanical measurements may provide a means to evaluate the interaction between the matrix and a core-shell modifier in an actual blend.

SynopsisThe synthesis of block copolymers and the study of their morphology were undertaken to find improved thermoplastic rubbers for service at elevated temperatures. The basis was the extraordinary properties possessed by ABA-type block copolymers in which the terminal blocks are polystyrene and the central block is either polyisoprene or polybutadiene. In these systems it has been well established that the unusual properties are a result of domain formation in which the hard and the soft blocks aggregate separately into distinct phases. The hard segment is thought to act both as a crosslink and as a filler. Block copolymers were synthesized with different soft and hard segments. The effects of these segments and of their properties on the morphology and the stress-strain properties of the block copolymers were measured and evaluated. Electron microscopy and birefringence were used to determine the morphology. It was found that the glass transition temperatures of the segments, the bulk of the monomer unit in the glassy segment, and the morphology determined the strength of the material. Some of the materials prepared have tensile strengths of 0.1 kg/cmZ or more at temperatures in excess of 180°C and therefore appear promising as elastomers for service at elevated temperatures.