Styrene copolymers particle size

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). 

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). 

Almog et al. [80] studied the dispersion polymerization of styrene in different alcohols as the continuous medium by using AIBN and vinyl alcohol-vinyl acetate copolymer as the initiator and the stabilizer, respectively. Their results showed that the final particle size decreased with the alcohol type according to the following order ... 

Figure 2 Influence of added styrene-butadiene block copolymer (BCP) on the particle size.

Vaterite is thermodynamically most unstable in the three crystal structures. Vaterite, however, is expected to be used in various purposes, because it has some features such as high specific surface area, high solubility, high dispersion, and small specific gravity compared with the other two crystal systems. Spherical vaterite crystals have already been reported in the presence of divalent cations [33], a surfactant [bis(2-ethylhexyl)sodium sulfate (AOT)] [32], poly(styrene-sulfonate) [34], poly(vinylalcohol) [13], and double-hydrophilic block copolymers [31]. The control of the particle size of spherical vaterite should be important for application as pigments, fillers and dentifrice. 

Styrene as matrix and polybutadiene as dispersed phase. During this phase inversion the above-mentioned graft copolymers act as polymeric emulsifiers and determine, inter alia, the particle size and particle size distribution of the dispersed polybutadiene phase. This morphology is fixed through another chemical reaction, that is the crosslinking of the polybutadiene phase. Therefore, the reaction mixture at the end of the prepolymerization period (at 30% conversion) does scarcely alter its morphology when it is polymerized to complete conversion, which is done without stirring mostly in bulk in a separate vessel. 

Most ABS is made by emulsion polymerization. A polybutadiene or nitrile rubber latex is prepared, and styrene plus acrylonitrile are grafted upon the elastomer in emulsion. The effect of rubber particle size in ABS graft copolymer on physical properties is the subject Chapter 22 by C. F. Parsons and E. L. Suck. Methyl methacrylate was substituted for acrylonitrile in ABS by R. D. Deanin and co-workers. They found a better thermoprocessability, lighter color, and better ultraviolet light stability. 

The morphology of these two systems is shown in Figures 1 and 2, respectively. Figure 1 shows electron photomicrographs of fracture replicas of SBR vulcanizates containing polystyrene fillers of two different particles sizes, and the existence of the individual polystyrene particles is easily confirmed. Figure 2 shows a schematic of the morphology of a styrene-diene-styrene block copolymers, in which the formation of a... 

The stable polymer dispersions with small-sized polymer particles of diameter >60 nm were prepared by dispersion copolymerization of PEO-MA macromonomer with styrene, 2-ethylhexyl acrylate, acrylic and methacrylic acids, and butadiene at 60 °C [79]. The particle size was reported to decrease with increasing macromonomer fraction in the comonomer feed. Besides, it varied with the type of the classical monomer as a comonomer. Tg of polymer product was found to be a function of the copolymer composition, the weight ratio macromonomer/monomer, and monomer type and varied from 50.6 to 220.4 °C. 

It was previously reported that the homopolymer surfactant PFOA successfully stabilized poly(methyl methacrylate) (PMMA) dispersion polymerizations (DeSimone et al., 1994 Hsiao et ah, 1995), but was not successful for styrene dispersion polymerizations (Canelas et al., 1996). In these styrene polymerizations, the C02 pressure used was 204 bar. However, later studies showed that both PFOA and poly(l,l-dihydroper-fluorooctyl methacrylate) (PFOMA) could stabilize polystyrene (PS) particles (Shiho and DeSimone, 1999) when a higher pressure was used. These polymerizations were conducted at 370 bar, 65 °C, and the particle size could be varied from 3 to 10 pm by varying the concentration of stabilizer. These homopolymer surfactants are less expensive and easier to synthesize than block copolymer surfactants and provide access to a large range of particle sizes. 

Figures 4A and 4B are the ultra-thin cross-sections of OsOi+-stained two-stage (styrene//styrene-butadiene) and (styrene-butadiene/ /styrene) latex particles at the stage ratio of 50/50 (LS-10 and LS-11), respectively. Latex samples were mixed with a polymerizable monomer mix of butyl and methyl methacrylates, cured, and microtomed for examination. Figure 4A shows particle cross-sections much smaller than the actual particle size of LS-10. It appears that since the embedding monomer solution was a solvent for polystyrene, the continuous polystyrene phase was dissolved and small S/B copolymer microdomains were left behind. This is further evidence that the second-stage S-B copolymers phase-separated as microdomains within the first-stage polystyrene phase, as shown in Figures 1A and 1A. Figure 4B shows somewhat swollen and deformed particle cross-sections, suggesting that the first-stage cross-linked S-B copolymers were a continuous phase. Indeed, the former (LS-10) behaved like a hard latex, but the latter (LS-11) behaved like a soft latex.

We will describe its use for controlling the styrene-acrylonitrile emulsion copolymerization system. Results concerning copolymer compositions, molecular characteristics and particle sizes will be compared to the corresponding ones from batch or semi-continuous processes. 

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