Copolymer latex characteristics

Vinylidene Chloride Copolymer Latex. Vinyhdene chloride polymers are often made in emulsion, but usuaUy are isolated, dried, and used as conventional resins. Stable latices have been prepared and can be used direcdy for coatings (171—176). The principal apphcations for these materials are as barrier coatings on paper products and, more recently, on plastic films. The heat-seal characteristics of VDC copolymer coatings are equaUy valuable in many apphcations. They are also used as binders for paints and nonwoven fabrics (177). The use of special VDC copolymer latices for barrier laminating adhesives is growing, and the use of vinyhdene chloride copolymers in flame-resistant carpet backing is weU known (178—181). VDC latices can also be used to coat poly(ethylene terephthalate) (PET) bottles to retain carbon dioxide (182). 

Emulsion Polymerization. Poly(vinyl acetate) and poly(vinyl acetate) copolymer latexes prepared in the presence of PVA find wide appHcations in adhesives, paints, textile finishes, and coatings. The emulsions show exceUent stabiHty to mechanical shear as weU as to the addition of electrolytes, and possess exceUent machining characteristics. 

Abstract Emulsion homopolymers and copolymers (latexes) are widely used in architectural interior and exterior paints, adhesives, and textile industries. Colloidal stabihzators in the emulsion polymerization strongly affect not only the colloidal properties of latexes but also the fdm and mechanical properties, in general. Additionally, the properties of polymer/copolymer latexes depend on the copolymer composition, polymer morphology, initiator, polymerization medium and colloidal characteristics of copolymer particles. 

The surface characteristics of a two-stage polymer were compared against those of a corresponding blend and copolymer latex by minimum film temperature analysis (11) (Table XVI). 

A small-angle X-ray scattering(SAXS) study of a model copolymer latex, based on styrene and pentabromobenzyl acrylate(PBBA, 40 wt %), was conducted. The contrast variation method used was shown to be a sensitive probe for inhomogeneity in the particles. The separation of the homogeneous function allowed direct calculation of the size distribution of the spherical particles. The SAXS analysis revealed a particle s inner structure which was a continuous copolymer phase, the composition of which was slightly richer in PBBA, within which domains of PS were randomly distributed. The volume fraction of the PS domains was estimated as 11 vol % and their characteristic length as 5.1 nm. 24 refs. 

The emulsion polymerisation process strategy, can have a considerable effect on molecular structure and particle morphology. The intrinsic factors as well as the process conditions determine the colloidal aspects of the copolymer latex (particle diameter, surface charge density, colloidal stability etc.), the characteristics of the polymeric material in the particles and the structure of the particles (copolymer composition as a function of particle radius etc.). In turn, these factors determine the properties of the latex and the copolymer product. 

The latex stability characteristics related to surface chemistry were analyzed by Polatajko-Lobos and Xanthopoulo [47] by studying the relationships between the concentration of surface-bound functional groups on carboxylated styrene-butadiene copolymer latex particles and the mechanical and chemical stability of the latexes synthesized. 

AH-acryHc (100%) latex emulsions are commonly recognized as the most durable paints for exterior use. Exterior grades are usuaHy copolymers of methyl methacrylate with butyl acrylate or 2-ethyIhexyl acrylate (see Acrylic ester polymers). Interior grades are based on methyl methacrylate copolymerized with butyl acrylate or ethyl acrylate. AcryHc latex emulsions are not commonly used in interior flat paints because these paints typicaHy do not require the kind of performance characteristics that acryHcs offer. However, for interior semigloss or gloss paints, aH-acryHc polymers and acryHc copolymers are used almost exclusively due to their exceUent gloss potential, adhesion characteristics, as weU as block and print resistance. 

This paper presents the physical mechanism and the structure of a comprehensive dynamic Emulsion Polymerization Model (EPM). EPM combines the theory of coagulative nucleation of homogeneously nucleated precursors with detailed species material and energy balances to calculate the time evolution of the concentration, size, and colloidal characteristics of latex particles, the monomer conversions, the copolymer composition, and molecular weight in an emulsion system. The capabilities of EPM are demonstrated by comparisons of its predictions with experimental data from the literature covering styrene and styrene/methyl methacrylate polymerizations. EPM can successfully simulate continuous and batch reactors over a wide range of initiator and added surfactant concentrations. 

A quantitative method has been developed to separate free and graft copolymers in an ABS sample. The ABS powder is dispersed in MEK and then introduced into the cells of a preparative ultracentrifuge. After the reproducibility of the procedure was ascertained, the method was used to determine the grafting parameters of samples polymerized under specific conditions. This analytical technique is well suited to demonstrate how the grafting efficiency or grafting density is influenced by various polymerization conditions such as mercaptan content, monomer flow rate, emulsifier content, or polybutadiene content. The effects of other variables such as temperature, the initiator system, and characteristics of the polybutadiene latex can also be demonstrated. 

The last comprehensive review of the emulsion polymoization of vinyl acetate was published be El-Aasser and Vandeihoff in 1981[1]. Since this time improvements in processes, application characteristics and cost/pafcxmance of vinyl copolymers have made these latexes the largest selling class of binders for... 

The seed latexes used as the cores of the imprinted particles were prepared from hydrophilic or hydrophobic polymers. The hydrophilic seeds were prepared from methyl methacrylate and methyl methacrylate/ethyleneglycol dimethacrylate copolymers, while the hydrophobic seeds were composed of polystyrene or styre-ne/divinyl benzene copolymers. Hydrophilic- and hydrophobic-imprinted shells were then laid over these cores. It was found that the best cholesterol recognition was obtained with a hydrophilic-imprinted shell and a poly(methyl methacrylate) core. However, the performance deteriorated when the core was lightly cross-linked with ethyleneglycol dimethacrylate. In a second paper [10], imprinted polymers were prepared by the noncovalent approach with cholesterol rebinding relying upon hydrophobic interactions between cholesterol and the imprinted shell. To achieve this, the template was modified to give it the characteristics of a surfactant. The structure of the template surfactant is illustrated in Fig. 2. 

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