Copolymer latex behavior

Recent investigations have shown that the behavior and interactions of surfactants in a polyvinyl acetate latex are quite different and complex compared to that in a polystyrene latex (1, 2). Surfactant adsorption at the fairly polar vinyl acetate latex surface is generally weak (3,4) and at times shows a complex adsorption isotherm (2). Earlier work (5,6) has also shown that anionic surfactants adsorb on polyvinyl acetate, then slowly penetrate into the particle leading to the formation of a poly-electroyte type solubilized polymer-surfactant complex. Such a solubilization process is generally accompanied by an increase in viscosity. The first objective of this work is to better under-stand the effects of type and structure of surfactants on the solubilization phenomena in vinyl acetate and vinyl acetate-butyl acrylate copolymer latexes. 

Figure 14. Schematic explanation of alkali-swelling and/or dissolving behaviors of carboxylated MMA-MAA copolymer latexes...

The object of this study was to clarify some aspects of the mechanism of shear-induced flocculation in colloidal dispersions. Vinyl chloride homopolymer and copolymer latices were prepared by emulsion polymerization using sodium dodecyl sulphate as emulsifier. Agglomeration behavior in these latices was studied by measuring the mechanical stability using a high speed stirring test. The latex particle size was measured by an analytical centrifuge. Molecular areas of emulsifier in the saturated adsorption layer at the surface of homopolymer and copolymer latex particles were estimated from adsorption titration data. 

A study [17] has been made of the effect of a dialyzed styrene-acrylate copolymer latex on the foam and the resistance to antifoam of three different surfactants—SDS, aerosol OT (sodium bis-diethylhexyl sulfosucdnate), and Triton X-100 (OP.EOjq)— all at a nominal concentration of 0.03 M. The polymer particles were dispersed in the surfactant solutions at a proportion of 25.5 wt.%. Adsorption of the surfactant onto the polymer particles significantly reduced the concentration of free surfactant in solution. A comparison was therefore made between the foam and resistance to antifoam behavior of the latex polymer-containing surfactant solution and a surfactant solution at the same depleted surfactant concentration, but containing no polymer. These depleted solutions were all submicellar—from about 80% to 99.9% of the surfactant (depending on the surfactant) was lost by adsorption onto the polymer-water surface. 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Salt effects in polyelectrolyte block copolymer micelles are particularly pronounced because the polyelectrolyte chains are closely assembled in the micellar shell [217]. The situation is quite reminiscent of tethered polymer brushes, to which polyelectrolyte block copolymer micelles have been compared, as summarized in the review of Forster [15]. The analogy to polyelectrolyte brushes was investigated by Guenoun in the study of the behavior of a free-standing film drawn from a PtBS-PSSNa-solution [218] and by Hari-haran et al., who studied the absorbed layer thickness of PtBS-PSSNa block copolymers onto latex particles [219,220]. When the salt concentration exceeded a certain limit, a weak decrease in the layer thickness with increasing salt concentration was observed. Similar results have been obtained by Tauer et al. on electrosterically stabilized latex particles [221]. 

This microscopic difference in the copolymer composition could influence the particle morphology, especially the distribution of the carboxyl groups within the latex particle, which in turn could be expected to influence the alkali-swelling behavior. 

Although MAA monomer possesses a larger reactivity ratio than MMA monomer, more MAA was found to exist in the outer side of the particle in the batch latex, as shown in Figures 5 and 6. This behavior could be explained if one can accept the fact that the MAA-rich polymers, which are formed early on during the polymerization, can migrate to the surface of the particle due to their higher hydrophilicity and plasticization of the polymer with the monomer. In the semi-continuous process, it could be expected that copolymer with the same composition as the comonomer feed is formed, and the particle contains a uniform distribution of carboxyl groups. 

In the industrial production of structured AN-Bu-St (ABS) latex particles, the grafting copolymerization of AN and St on crossUnked polybutadiene (PB) seed latex is carried out in emulsion polymerization. Therefore, information on the effect of PB crosslinking density on the swelling of PB latex particles by a St-AN monomer mixture is very important for the production of ABS copolymers with desired properties. Mathew et al. [177] studied the effect of several thermodynamic parameters, such as the crosslinking density, particle size and monomer mixture composition on the swelling behavior of PB latex particles by pure St and AN, and St-AN mixtures of various compositions. They reported... 

Witt [1959] studied under vacuum gamma-radi-ation-induced crosslinking in butadiene-styrene copolymers, homopolymers and mixtures of these homopolymers, (Table 11.9). The behavior of the styrene units in the copolymers and in the physical mixtures, was different. Gel fraction measurements showed that in the copolymer, the styrene units did inhibit the crosslinking of the polybutadiene. However, there was no evidence of such inhibition in the mill- and latex-prepared physical mixtures of the two homopolymers. 

These materials also serve as models of the block-copolymer thermoplastic elastomers. In this case, post-curing of the continuous elastomer phase was required to attain normal rubber behavior. However, the polybutadiene portion is not covalently bonded to the polystyrene latex spheres. 

The present communication is confined to a report on the behavior of a copolymer of acrylonitrile and acrylic acid regulated with n-octyl mercaptan. The alkali salt of this copolymer is water soluble and shows considerable stabilizing power in latex, but it is without the foaming tendencies which are produced in latex by conventional emulsifiers. 

The agglomerating methods described above are economical, reliable, and effective and have been used in the production of impact-resistant resins. But the mechanism and the characteristics of these agglomerating processes have not been reported in the literature therefore, in this chapter, the behavior and the mechanism of agglomeration was studied using poly(n-butyl acrylate) as the agglomerated latex A, and n-butylacrylate-acrylic acid copolymer as the agglomerating latex B, based on the interaction between hydrophilic free polymer and polymer latex. 

In continuous operation mode, both feed and effluent streams flow continuously. The main characteristic of a continuous stirred tank reactor (CSTR) is the broad residence time distribution (RTD), which is characterized by a decreasing exponential function. The same behavior describes the age of the particles in the reactor and hence the particle size distribution (PSD) at the exit. Therefore, it is not possible to obtain narrow monodisperse latexes using a single CSTR. In addition, CSTRs are hable to suffer intermittent nucleations [89, 90) that lead to multimodal PSDs. This may be alleviated by using a tubular reactor before the CSTR, in which polymer particles are formed in a smooth way [91]. On the other hand, the copolymer composition is quite constant, even though it is different from that of the feed. 

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