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The glass transition temperature of a copolymer depends not only on chemical composition but also on its comonomer sequences. This experimental fact is explained by Barton's and Johnston's equations. Their equations, though complicated, become simple, if a suitable parameter is used to describe the comonomer sequences. It is shown that with these new expressions, their equations can be used to understand glass transition temperatures of two additional types of copolymers, compatible multiblock copolymers and homopolymers with various tacticities treated as steric copolymers.
Abstract
A discussion on the influence of grafted polar groups (succinic anhydride and succinil-fluorescein) in glass transition behaviour of atactic polypropylene is shown in this work, on the basis of the reaction conditions used to obtain the modified polymers, kind and amount of grafted groups, and the degradation processes which may take place. The Box-Wilson experimental design methodology for two independent variables (reactant concentration to obtain the modified polymer) has been used to follow variations in glass transition temperatures. The existence of undesired degradation processes is considered as independent of the grafting reactions, and the model predictions seem to agree with this latter.
Abstract
Glass transition temperatures of polyurethane-urea elastomers (PU) based on two urea derivatives, have been investigated with differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) methods. The DMTA measurements have been proved as more useful to determine an optimal annealing time and to controlling polyurethane-urea synthesis then the DSC analysis.
state. Vitrification is the point at which the resin changes from the rubbery state to the solid glassy state. The TTT diagram may be augmented by adding iso-conversion, iso-glass transition temperature (iso- T g ), and iso-viscous contours as well as
) were added to carboxymethyl cellulose acetate butyrate (CMCAB), which acted as a plasticizer for CMCAB, leading to dramatic reduction of glass transition temperature of CMCAB, namely, Δ T g = −158 and −179 °C, respectively. The aim of this study is to
The purpose of this study was to measure the effect of co-lyophilized polymers on the crystallization of amorphous sucrose, and to test for a possible relationship between the ability of an additive to raise theT g of a sucrose-additive mixture, relative to theT g of pure sucrose, and its ability to inhibit crystallization. Differential scanning calorimetry was used to measure the glass transition temperature,T g, the non-isothermal crystallization temperature,T c, and the induction time for crystallization,Q, of sucrose in the presence of co-lyophilized Ficoll or poly(vinylpyrrolidone) (PVP). The effect of these polymers on the crystallization of sucrose was significant as demonstrated by a marked increase inT c, and in the induction time (Q) in the presence of relatively small amounts (1–10%) of additive. Surprisingly, small amounts of polymeric additive had no effect on theT g of sucrose, although at higher concentrations, theT g increased proportionally. Thus, it appears that the inhibition of sucrose crystallization by the additition of small amounts of a higher-T g component cannot be attributed solely to changes in molecular mobility associated with an increase inT g.
The glass transition temperature of polystyrene
Results of a round robin test
A round robin test was performed to determine the reliability of values for the glass transition temperatureT g as determined by DTA on polymers. Ten different instruments were involved. The test material was high molecular weight polystyrene. Values forT g (midpoint) were reported in the range 107°C±2 K. The respective heat flow curves differed considerably in shape. In the literature aT g of 100°C is often given for polystyrene. The discrepancy between this value and the value of 107°C found in the round robin test is due to three differences: the thermal history of the sample, the evaluation of the heat flow curves, and the effect of finite sample size.
Determination of the glass transition temperature
Methods correlation and structural heterogeneity
Abstract
The definition of the glass transition temperature, T g, is recalled and its experimental determination by various techniques is reviewed. The diversity of values of T g obtained by the different methods is discussed, with particular attention being paid to Differential Scanning Calorimetry (DSC) and to dynamic techniques such as Dynamic Mechanical Thermal Analysis (DMTA) and Temperature Modulated DSC (TMDSC). This last technique, TMDSC, in particular, is considered in respect of ways in which the heterogeneity of the glass transformation process can be quantified.
The glass transition temperatures of sorbitol and fructose were characterized by four points determined on DSC heating thermograms (onset, mid-point, peak and end-point), plus the limit fictive temperature. The variations of these temperature values, observed as functions of cooling and heating rates, were used to determine the fragility parameter, as defined by Angell [1] to characterize the temperature dependence of the dynamic behavior of glass-forming liquids in the temperature range above the glass transition.
Glass transition temperatures of polymer materials, measured by thermomechanical analysis
Influence of rates of heating and cooling
The linear expansions of two materials have been measured, a double-base propellant and a carboxyl-terminated polybutadiene. The glass transition temperature,T g and expansion coefficients below and aboveT g have been calculated. The influence of the heating and cooling rates and sample thickness has been investigated. The results show that the value ofT g is dependent on the rates of heating and cooling but not on the sample thickness. Extrapolating to zero rate gives the sameT g for both heating and cooling. The expansion coefficients are not influenced by the rates of heating and cooling or by the sample thickness.
