High-Tg latex

Table 4.3 Percolation thresholds, ultimate conductivities, and critical exponent values determined for high-Tg latex S5rstems processed in three different ways...

High Tg monomers, for latex acrylic polymers, 22 41-42 High-throughput characterization, 7 419-120... 

In ncmnar FTIR die polymer is either ground into a powdo widi KBr and pressed into a disc (high-Tg polymers) or dissolved in a suitable solvent (not water), and applied on to a KBr or NaCl plate, which after evaporation of the solvent leads to a thin polymer film, Wang and Poehlein [55] used FTIR in combination with carbon Nh to analyse the composition of oligomers in latexes formed from styrene (S)-(meth)aciylic acid and S-methyl methacrylate (MMA) cmnonomer mixtures. 

Practical methods can be used to ensure that the required particle morphology is obtained. A high Tg or molar mass for the hrst-formed polymer forces the second-formed polymer to reside on its surface due to kinetic effects. The use of an inherently more water-soluble second polymer as compared to the first will also contribute to obtaining the desired morphology. Inverted core-shell latexes are most readily obtained when a more hydrophobic monomer for the second-formed polymer is polymerized in the presence of a less hydrophobic polymer latex. An alternative is to render the second monomer coUmdaUy unstable ufien polymerized, forcing it to reside in the core of the first formed polymer. 

Virtually all end-use formulations of latex polymers of MFT much above 5 °C (40 °F) contain a moderately low volatility solvent for the polymer. These act as temporary plasticizers to ensure low MFT and enhance polymer interdiffusion. The solvent should diffuse and evaporate as quickly as possible for film hardness development, but not at the expense of completeness of film strength development A complication is that compositions of high Tg which contain solvent... 

Table 6.4 presents a typical formulation for emulsion polymerization. The principal monomers present low water solubihty and the ratio between hard (leading to high Tg polymers) and soft (leading to low Tg polymers) monomers is chosen to achieve the Tg required for the application. Minor functional monomers provide some special characteristics, such as improved latex stability and adhesion. Crosslinking agents and chain transfer agents (CTAs) are used to control the chain architecture and the MWD of the polymer. 

Changes in the percolation threshold and critical exponent for composites prepared via a latex-based route using different processing techniques have been observed. Composites prepared with both a latex of high-Tg [PS) and low-Tg [poly[methyl acrylate) [PMA)) polymer, and SWCNTs and MWCNTs were compared, and the results are presented in the following sections. 

A copolymer of ethyl acrylate with 5% chloroethyl vinyl ether has been marketed as an oil-resistant, high-temperature-stable, specialty elastomer. The pendant chlorine group gives a preferred cross-linking site with polyfunctional amines. The relatively high Tg of the rubber (about 28°C) can be lowered by plasticization, but this can be temporary if oils or solvents are in contact with the product and leach out the plasticizer. Interpolymers of ethyl acrylate with methyl methacrylate and with higher acrylates and methacrylates are widely used as latex paints and as additives for paper and textiles. The Tg of an interpolymer can be tailored for a particular application by varying the ratio of acrylate to methacrylate monomers. 

Figure 7.23 Applications of the NMR-MOUSE to elastomer materials (a) T2 values for a curing series of carbon-black filled NR. Comparison of values obtained at high homogeneous field (DMX 300) and with the NMR-MOUSE, (b) cross-link series of unfilled SBR with different sulfur content, (c) T2 versus glass-transition temperature Tg of unfilled SBR by the CPMG and the steady-state CPMG methods, (d) normalized Hahn-echo decay curves for poly(butadiene) latex samples. Different decay rates are obtained for small medium and large cross-link densities...

Series I Acrylic Latex Emulsions. A series of four acrylic latex emulsions varying in glass transition temperature (Tg) (3) were applied first. Tg is the temperature at which the resin changes from a relatively flexible to a relatively stiff material. The acrylic latexes are made from water-insoluble monomers such as acrylates and alkyl acrylates polymerized in emulsion form to produce an aqueous dispersion or latex of the polymer. Upon drying, the emulsion is irreversibly broken so that the applied material becomes wash-fast. The application requires no catalyst or high temperature heating. 

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