Solution copolymerizations glass transition temperatures

The glass-transition temperature in amorphous polymers is also sensitive to copolymerization. Generally, T of a random copolymer falls between the glass-transition temperatures of the respective homopolymers. For example, T for solution-polymerized polybutadiene is —that for solution-polymerized polystyrene is -HlOO°C. A commercial solution random copolymer of butadiene and styrene (Firestone s Stereon) shows an intermediate T of —(48). The glass-transition temperature of the random copolymer can sometimes be related simply as follows ... 

SBR is produced by addition copolymerization of styrene and butadiene monomers in either emulsion or solution process. The styrene/butadiene ratio controls the glass transition temperature (To) of the copolymer and thus its stiffness. T ... 

Different materials for the hydrophobic membrane in which the receptor is incorporated, have been investigated. Polysiloxanes that have the required glass transition temperature and dielectric constant provide a stable chemical system that transduces the complexation of cationic species into electronic signals. The material properties can be optimized by copolymerization of three building blocks viz. dimethyl-, (3-cyanopropyl)methyl-, and methacryloxypropylmethyl siloxane. CHEMFETs made with this terpolymer have fast response times (<. 1 sec.). With valinomycin and hemispherands (2) and (3) linear responses to changing K+ concentrations are obtained in the range 10"5 - 1.0M (55-58 mV/decade) in a solution of 0.1M NaCl. Similar devices specific for Na+ and Ca2+ have been obtained with other ionophores. 

Poly(vinyl acetate) is used for adhesives and as a wood glue (40% solution), as a raw material in lacquers and varnishes (dispersions), and as a concrete additive (in the form of a fine, dispersible powder obtained by spray drying). Poly(vinyl acetate) grades that are more resistant to hydrolysis are obtained by copolymerization with vinyl stearate or vinyl pivalate, since the saponification rate is reduced by the bulkier side groups. Pure poly(vinyl pivalate) has too high a glass transition temperature, 78 C, for most poly(vinyl ester) applications. Other copolymers of vinyl acetate are produced with ethylene (see Section 25.2.1) or vinyl chloride (see Section 25.7.5.3). 

SBRs are produced by addition copolymerization of styrene and butadiene monomers in either an emulsion or a solution polymerization process. The ratio of styrene to butadiene controls the glass transition temperature (Tg) of the copolymer and thus the stiffness of the elastomer. The higher the styrene content, the higher the Tg and stiffness. Polymers can be made over the whole range of Tg from about — SO C for polybutadiene to about H-100°C for polystyrene. 

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