Styrene Polymer dispersions

Synthesis and Characterisation of Aqueous Hybrid Polyurethane-Urea-Acrylic/Styrene Polymer Dispersions... 

Hybrid polyurethane-urea-acrylic/styrene polymer dispersions were prepared according to methods la , lb , 2 and 3 described in Section 6.3.2. Dispersions designated as MDPUR-ASD were made by polymerisation of monomers in DPU according to the methods la, lb and 2 while dispersions designated as MDPUR were made by synthesis of DPUR in ASD according to method 3. In all syntheses the ratio of polyurethane-urea to acrylic/styrene polymer in the hybrid was 2 1. 

In this study, aqueous hybrid polyurethane-urea-acrylic/styrene polymer dispersions were obtained using four different methods. The dispersions are stable and their viscosity, and pH as well as average particle size and particle size distribution are similar to those observed for DPUR. Most of the hybrid dispersions formed transparent films of good mechanical properties, water resistance and organic solvent resistance. 

Table 6.31 Effect of various factors on the properties of hybrid polyurethane-urea-acrylic/styrene polymer dispersions synthesised in this study ... 

Silanated anionic acrylate-styrene polymer dispersions (60,62) Tronox 470 Tranox Ltd. 

Almost all synthetic binders are prepared by an emulsion polymerization process and are suppHed as latexes which consist of 48—52 wt % polymer dispersed in water (101). The largest-volume binder is styrene—butadiene copolymer [9003-55-8] (SBR) latex. Most SBRlatexes are carboxylated, ie, they contain copolymerized acidic monomers. Other latex binders are based on poly(vinyl acetate) [9003-20-7] and on polymers of acrylate esters. Poly(vinyl alcohol) is a water-soluble, synthetic biader which is prepared by the hydrolysis of poly(viayl acetate) (see Latex technology Vinyl polymers). 

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. 

An outstanding property of these polymers is their shear stability. The sonic shear stability testsfci indicate that these polymers are superior to some of the currently used polymers of ethylene-propylene or methacrylate type. The excellent stability of the hydrogenated diene-styrene polymers is attributed to their relatively low molecular weight and narrow distribution consistent with the established theory of shear degradation of polymers. The most recent developments in this field are block polymer VI improvers with dispersancy properties, built into the molecule by chemical modification of the rubber block. 2... 

The macromonomer system gives a polymer dispersion with larger particles (Dn mac=1860 nm, Dn PVp=980 nm, 3.1 wt% for styrene), narrower size distribu-... 

The colloidal stable polymer dispersions, the monodisperse polymer particles, and high conversions (85-100%) can be obtained with most of the other macromonomers (MAL,VB, and MA) of PEO (MW>PEO=2000)) [76]. Also, when macromonomers are used (3.1 wt% based on styrene), there is practically no coagulum produced. This is not the case in the presence of polymerizable PEO surfactants (surfmer I R1=CH3(CH2)11-, R2=H, n=34 and surfmer II R =CH3 (CH2)n-, R2=H, n=42) despite the higher amounts of stabilizer used (up to 60 wt% of coagulum). Furthermore, the particles are more monodisperse with PEO macromonomer (Dw/Dn=1.025 for PEO-MA and 1.13 for PVPo) compared to those with surfmer. Comparatively poorer results were obtained with conventional surfactants such as ethoxylated nonylphenol, even when used in large amounts. 

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. 

The colloidal stability of polymer dispersion prepared by the emulsion copolymerization of R-(EO)n-MA was observed to increase with increasing EO number in the macromonomer [42, 96]. Thus C12-(EO)9-MA did not produce stable polymer latexes, i.e., the coagulum was observed during polymerization. This monomer, however, was efficient in the emulsion copolymerization with BzMA (see below). The C12-(EO)20-MA, however, appears to have the most suitable hydrophilic-hydrophobic balance to make stable emulsions. The relative reactivity of macromonomer slightly decreases with increasing EO number in macromonomer. The most hydrophilic macromonomer with co-methyl terminal, Cr(EO)39-MA, could not disperse the monomer so that the styrene droplets coexisted during polymerization. The maximum rate of polymerization was observed at low conversions and decreased with increasing conversion. The decrease in the rate may be attributed to the decrease of monomer content in the particles (Table 2). In the Cr(EO)39-MA/St system the macromonomer is soluble in water and styrene is located in the monomer droplets. Under such conditions the polymerization in St monomer droplets may contribute to the increase in r2 values. 

Polymer colloids involve dispersions containing polymer particles having sizes greater than about 1 nm. If dispersed in aqueous solution, such a polymer dispersion is called a latex. These are usually synthetic polymer particles formed by free radical polymerization [784], Many kinds of polymerization systems exist, involving almost all of the possible kinds of colloidal dispersion, including emulsion polymerization, hence the more general term heterophase polymerization is sometimes used. Several reviews are available [785-789]. Emulsion polymerization provides a convenient means of controlling the polymerization of monomers and is used to make, for example, synthetic rubber which is mostly a co-polymer of butadiene and styrene. 

The consumption of polymer dispersions in 1997 was 10xl06 t. The market is divided among styrene-butadien dispersions (35 %), dispersions containing vinyl acetate (32 %), styrene and styrene-acrylate dispersions (25 %) and others in minor quantities. They have many applications coatings and paints, adhesives, textile finishing, paper coatings and others. When used as coatings the dispersions should be suitable for food contact. Many substances can be used as monomers ... 

Grafted Rubber Latex Particles as the Disperse Phase. ABS polymers or acrylonitrile-butadiene-styrene polymers, can be generally made by piggy-back grafting of a polybutadiene latex with styrene and... 

Figure 21.12 TEM of an SEBS polymer dispersed in a matrix of polycarbonate. The styrene domains and the polycarbonate matrix are stained dark with R11O4, making the rubber appear light...

Aqueous emulsions of styrene, methyl methacrylate, methyl acrylate, and ethyl acrylate were polymerized with y-radiation from a Co source in the presence of sodium dodecyl sulfate or sodium laurate. The continuous measurement of conversion and reaction rate was carried out dilato-metrically. The acrylates polymerized fastest and the over-all polymerization rate increased as follows styrene < methyl methacrylate < ethyl acrylate methyl acrylate. The effects of radiation dose, temperature, and original monomer and emulsifier concentrations were studied with respect to the following factors properties of polymer dispersions, number and size of polymer particles, viscometrically determined molecular weights, monomer-water ratio, and kinetic constants. 

A free-radical polymerization mechanism can be excluded on the basis of the polymer microstructure and experiments with radical inhibitors. Rhodium(I)-spe-cies, formed by reduction of Rh " salts used as catalyst precursors by butadiene monomer, have been suggested as the active species. The catalyst is stable during the aqueous polymerization for over 30 h [23]. Catalyst activities are moderate with up to ca. 2x10 TO h [24, 25]. By contrast to industrially important free-radical copolymerization, styrene is not incorporated in the rhodium-catalyzed butadiene polymerization [26]. Only scarce data is available regarding the stability and other properties of the polymer dispersions obtained. Precipitation of considerable portions of the polymer has been mentioned at high conversions in butadiene polymerization [23, 27]. 

Alkyl phenol ethoxylates can also react with P4O10 yielding alkyl phenol etherphosphates as a mixture of mono-/diesters or with maleic anhydride to yield maleic acid monoesters, which then react with NaHS03 to yield sulphosuccinate monoesters. Alkylphenolpolyglycolether sulphates, phosphates or sulphosuccinates are mainly used as primary anionic emulsifiers for the manufacturing of acrylic, styrene/acrylic or vinyl acetate co-polymer dispersions. Another type of non-ionic emulsifier is block copolymers of ethylene oxide with propylene oxide. 

The macromers used in the stabilisation of polymer dispersions are in fact polyether polyols with terminal double bonds, able to copolymerise with vinylic monomers (ACN, styrene) and to form graft species during the radical copolymerisation. The resulting graft polyether polyol, formed in situ by the copolymerisation process, is in fact a NAD ... 

MA can be used as comonomer together with the vinylic monomers (ternary copolymerisation ACN - styrene - MA) and the graft species is formed in situ by the reaction of the resulting copolymer ACN - styrene - MA with the polyether polyol, by its terminal hydroxyl groups. Another variant is to use a styrene - MA copolymer as NAD. This copolymer proved to be a very good NAD for high styrene content polymer dispersions in polyethers. Of course the real NAD is made by the reaction of a MA unit with the terminal hydroxyl group of the poly ether [57]. 

In a very elegant approach, Okamura et al. attached Cgo to a range of styrene polymers with different molecular weights (from 1000 to 10,000) [32]. The attachment was provided by 1,4-radical addition to Cgg, producing narrow-dispersity polystyryl adducts (Scheme 3). The electrochemical and ground state absorption properties of the polymers were identical to those of a low-mass, fully characterized model (Scheme 3). This indicates that the reported procedure is useful for the preparation of high-mass polymers, with retained fullerene properties. 

In conventional exterior-use paints SB dispersions have largely been replaced by styrene-acrylate dispersions, and their use is now restricted to special applications (corrosion protection primers, wood primers, mortar modification) where low film permeability to gases, water vapor, etc., and complete resistance of the polymer to hydrolysis are necessary. In order to achieve a uniform surface and thus improve printability, paper and card are coated with paper-coating colors. Carboxylated SB dispersions are used in these paints as binders. 

Polymer Dispersions (Emulsion Polymers). Waterborne paints based on polymer dispersions (usually referred to as emulsion paints) are not water soluble. They are water-thinnable systems composed of dispersions of polymer particles in water (see Section 3.5). The particles consist of high molecular mass polymers (e.g., of styrene, butadiene, acrylate, or vinyl monomers) and are produced by emulsion polymerization. These waterborne paints also contain small amounts of organic solvents (< 5 wt %) that serve as film-forming (coalescing) agents that partially evaporate on drying. 

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