Morphology, acrylonitrile copolymers

In addition to graft copolymer attached to the mbber particle surface, the formation of styrene—acrylonitrile copolymer occluded within the mbber particle may occur. The mechanism and extent of occluded polymer formation depends on the manufacturing process. The factors affecting occlusion formation in bulk (77) and emulsion processes (78) have been described. The use of block copolymers of styrene and butadiene in bulk systems can control particle size and give rise to unusual particle morphologies (eg, coil, rod, capsule, cellular) (77). 

Studies of the particle—epoxy interface and particle composition have been helphil in understanding the mbber-particle formation in epoxy resins (306). Based on extensive dynamic mechanical studies of epoxy resin cure, a mechanism was proposed for the development of a heterophase morphology in mbber-modifted epoxy resins (307). Other functionalized mbbers, such as amine-terminated butadiene—acrylonitrile copolymers (308) and -butyl acrylate—acryhc acid copolymers (309), have been used for toughening epoxy resins. 

The morphology of the fibrous cellulose graft copolymers depended on the method of initiation of free radical formation, experimental conditions during the copolymerization, chemical modification of the cellulose before reaction, and the type of monomer used (60). Variations in the shape of the fibrous cross section, in layering effects in the fiber, and in the location and distribution of the grafted copolymer in the fiber were observed by electron microscopy (61). Cotton cellulose—poly (acrylonitrile) copolymer was selected to show the possible variations in location and distribution of the grafted copolymer in the fiber. 

Composition (type of polymeric components). The base polymer (which is to be modified) may be an amorphous polymer [e.g., polystyrene (PS), styrene-acrylonitrile copolymer, polycarbonate, or poly(vinyl chloride)], a semicrystalline polymer [e.g., polyamide (PA) or polypropylene (PP)], or a thermoset resin (e.g., epoxy resin). The modifier may be a rubber-like elastomer (e.g., polybutadiene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, or ethylene-propylene-diene copolymer), a core-shell modifier, or another polymer. Even smaller amounts of a compatibilizer, such as a copolymer, are sometimes added as a third component to control the morphology. 

Using micro-Raman imaging three blends consisting of polypropene/polyethene/ethene-propene copolymer, PBTP/polycarbonate/LDPE, and styrene-acrylonitrile copolymer/styrene-maleic anhydride copolymer/ polydimethylphenylene oxide were studied with regard to compositional and morphological heterogeneities. The general structure of PE fibres in an epoxy resin matrix was also studied. 59 refs. 

Processing conditions or chemical reactions occurring in one or both phases of the blend can strongly affect the phase inversion. Of course, these two parameters have a direct effect on the viscosity ratio of the components. The same blend of polyamide/styrene-acrylonitrile copolymer developed phase morphology where PA6 is the matrix when processed using a single-screw extruder, whereas the inverse situahon occurred when the blend was mixed several times in a laboratory mixer. 

Choi, Y.S. Xu, M. Chung, I.J. Synthesis of exfoliated poly(styrene-co-acrylonitrile) copolymer/silicate nanocomposite by anulsion pol3miaization monomer composition effect on morphology. Polymer 2003, 44, 6989-6994. 

H. A. Stretz and D. R. Paul. Properties and morphology of nanocomposites based on styrenic polymers. Part I st5Tene-acrylonitrile copolymers. Polymer, 47 (2006), 8123-8136. 

The CN bond stretching frequency was shifted to a higher value with an increase in the methacrylonitrile (MAN) content in the copolymers. There was no linear relationship between the CN frequency and the diad fraction of MAN-MAN linkages in the copolymer chain, as reported previously for styrene-acrylonitrile copolymers. Different methods for the copolymer sample preparation can cause differences in the shifts in the CN frequency. This suggests that the polymer morphology plays an important role. A study of blends of polymethacrylonitrile (PMAN) with polystyrene has shown that the CN frequency is shifted to a higher value with an increase of the PMAN composition of the blends. 

Monomer compositional drifts may also occur due to preferential solution of the styrene in the mbber phase or solution of the acrylonitrile in the aqueous phase (72). In emulsion systems, mbber particle size may also influence graft stmcture so that the number of graft chains per unit of mbber particle surface area tends to remain constant (73). Factors affecting the distribution (eg, core-sheU vs "wart-like" morphologies) of the grafted copolymer on the mbber particle surface have been studied in emulsion systems (74). Effects due to preferential solvation of the initiator by the polybutadiene have been described (75,76). 

Fig. 10. Preparation and morphology of toughened PVC (a) secondary PVC grain (50—250 flm) (b) modified PVC with coherent primary grain (ca 1 -lm) (220). CPE = chlorinated polyethylene EVA = ethylene—vinyl acetate copolymers ABS = acrylonitrile—butadiene—styrene MBS = methyl...

Rubber-Modified Copolymers. Acrylonitrile—butadiene—styrene polymers have become important commercial products since the mid-1950s. The development and properties of ABS polymers have been discussed in detail (76) (see Acrylonitrile polymers). ABS polymers, like HIPS, are two-phase systems in which the elastomer component is dispersed in the rigid SAN copolymer matrix. The electron photomicrographs in Figure 6 show the difference in morphology of mass vs emulsion ABS polymers. The differences in stmcture of the dispersed phases are primarily a result of differences in production processes, types of mbber used, and variation in mbber concentrations. 

Y. Li and H. Shimizu, Improvement in toughness of poly(l-lactide) (PLLA) through reactive blending with acrylonitrile-butadiene-styrene copolymer (ABS) Morphology and properties, Eur. Polym. J., 45 (3) 738-746, March 2009. 

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