Compatibilizing block

Effects of addition of a compatibilizing block copolymer, poly(styrene-b-methyl methacrylate), P(S-b-MMA) on the rheological behavior of an immiscible blend of PS with SAN were studied by dynamic mechanical spectroscopy [Gleisner et al., 1994]. Upon addition of the compatibilizer, the average diameter of PS particles decreased from d = 400 to 120 nm. The data were analyzed using weighted relaxation-time spectra. A modified emulsion model, originally proposed by Choi and Schowalter [1975], made it possible to correlate the particle size and the interfacial tension coefficient with the compatibilizer concentration. It was reported that the particle size reduction and the reduction of occur at different block-copolymer concentrations. 

Compatibilizer, block copolymer Compatibilizer, copolymer Compatibilizer, co-solvent Compatibilizer, graft copolymer Compatibilizer, ionic/ionomeric... 

Figure 22.13 Experimental profiles of scattered intensity for blend of two immiscible polymers (PS/PMMA) with addition of a compatibilizing block copolymer. Total 30 intensity profiles with mutual time delay 90 s. Annealing temperatures 130, 160 and 180 1C (from top). The increasing temperature leads to enlargement of domains.

Compatibilization of PP blends is based on either copolymerization or grafting [3, 4]. In both cases, one part of the resulting compatibilizer should be miscible with the PP phase, the other with the second component. For example, EPR is used in PP/PE blends the propylene part of EPR provides miscibility with PP and the ethylene part does so with PE. For the purpose of compatibilization, the block-type EPR is more desirable than random. Acid or anhydride modified PP is used for blends with PA, PC or PEST. Here, the PP part provides miscibility with the PP phase, while the acidic or anhydride groups usually react with chain-end groups of the other poljmier to form a compatibilizing block copolymer. 

Incorporation of Copolymers (Nonreactive Compatibilization). Block or graft copolymers with segments that are miscible with their respective polymer components show a tendency to be localized at the interface between immiscible blend phases. The copolymers anchor their segments in the relevant polymer, reducing interfacial tension and stabilizing dispersion against coalescence (24-52). Random copolymers, sometimes also used as compatibilizers, reduce interfacial tension, but their ability to stabilize the phase structure is limited... 

Mixtures of two or more polymers in polymer blends are another combination of different macromolecules. The different polymer components are normally incompatible and thus show phase separation, with the minor component usually in the form of the dispersed phase and the major component as the matrix. Close to the composition of 50 50, interpenetrating structures or networks are formed. This phase separation corresponds to the microphase separation in block copolymers but-owing to the absence of covalent bonds between the components-with coarser structures. Several processes are used to enhance the compatibility between the polymer phases, including grafting, mixing with compatibilizers, or reactive blending. Compatibilizers (block copolymers, graft polymers) cause a reduction in particle size of the minor component in the matrix. Between the components, separate interfaces (only thin boundaries) and interphases (thicker layers with often an own structure) exist. 

Here, the compatibilizing block and/or graft copolymers are produced in situ. From the economic and the performance points of view, tlds method is more important than that by addition of a compatibilizer. 

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