Dyad 609, glass transition temperature

Firstly, some of the important characteristics of the performance properties of copolymers can be expressed through the fractions of these sequences. So, for example, dealing with copolymers they normally make extensive use of semiempiri-cal relationships relating the glass transition temperature, T , with the fractions of dyads in macromolecules [7]. The simplest of such relationships reads ... 

The data agree well with theoretical data obtained from the Barton equation (21). For copolymers and specifically for the styr-ene/AN system, the glass transition temperature is dependent on the amounts of the dyads SS,AS, AA occurring in the a copolymer, where S denotes a styrene monomer and A denotes a acrylonitrile monomer, as (22)... 

To predict the glass transition temperature of (styrene + methylacrylate + hep-tyl acrylate) terpolymerization products from Eq. (7.2) one should calculate the fractions of all dyads using reactivity ratios (7.4). Combining such calculations with experimental data on glass transition temperatures of homopolymers and alternating binary copolymers... 

In the early 1970s Barton [186] proposed an equation relating the glass transition temperature of copolymers to their molecular structure in terms of the mole fractions of the various dyad sequences of monomer units present in the copolymer chain, and temperature parameters (Ta) charactaistic of each type of sequence i j. The Tg of a copolymer chain then can be given by the following equation ... 

Copolymers of Methyl Methacrylate. The glass-transition temperatures of these copolymers exhibit a minimum of ca 87°C at ca 40 wt% acrylonitrile the Tg s of the homopolymers are ca 105°C. This unusnal behavior is explained by the interactions of the dyads and well predicted by the seqnence-distribntion equation (160). 

The copolsrmers have glass-transition temperatures in the range —20 to - -30°C. Above about 45 wt% (18 mol%) styrene content, the copolymer Tg increases with increasing st5nrene content. Satisfactory correlation between copolymer composition and Tg has been foimd by considering them either as random copolymers of ethylene and stsrrene or as random copolymers of ethylene and ES dyads. Thus, Tg data were shown by Chen and co-workers (46) to satisfactorily fit... 

Develop mathematical framework to predict two-glass transition temperatures Explore physical signihcance of entropic difference model Apply the quadratic expression for Tg to different systems Derive expression for change in change in entropy of mixing Cubic equation for prediction of glass transition temperature of blend Effect of chain sequence distribution of copolymer Entropy of copolymerization Dyads and triads... 

Johnston [7] took into account the chain sequence distribution of copolymers in the prediction of the glass transition temperatures. Sharma [8], and Sharms et al. [9] found that this model compared well with experimental data even for systems obtained from reversible copolymerization. Johnston s dyad model for prediction of copolymer glass transition temperature can be written as follows ... 

The dyad probabilities can be calculated as explained in Chapter 11. The glass transition temperature of polymer blends is discussed in Chapter 6. 

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