Polymer-diluent mixtures melting temperatures

One of the thermodynamic methods involves the adaptation of the classical freezing point-composition relation to the melting of polymer-diluent mixtures. The most common situation encountered when a low molecular weight diluent is admixed with a polymer, is that the crystalline phase remains pure. Under these conditions, for polymers of high molecular weight, the melting temperature of a polymer-diluent mixture, T, can be expressed as [7,21]... 

The analysis of dependence of melting temperature on plasticizer content in the range in which PLA and acetyl tri-n-hutyl citrate (ATBC) are miscible gives indications of polymer-plasticizer interactions (Baiardo et al, 2003). The Flory (1953) equation fits well for miscible polymer-diluent mixtures ... 

The enthalpy change can be estimated by adding varying quantities of a diluent to the polymer, which serves to depress the observed melting temperature, and measuring for each polymer and diluent mixture. The results are then plotted according to the Flory equation ... 

According to Eq. (3.2) the depression of the melting temperature depends on the volume fraction of diluent in the mixture, its molar volume and the thermodynamic interaction between polymer and diluent. The melting point depression is a colligative property. Therefore, as Eq. (3.2) indicates the depression will be larger with diluents of smaller molar volume. It is also expected that the larger the value... 

For mixtures that display a continuous depression of the melting temperature with decreasing polymer concentration, a direct comparison with Eq. (3.2) can be made. Establishing the validity of Eq. (3.2) is important since it is a potential method for determining AH. According to this equation, the initial slope of the plot of 1/Tra against the diluent concentration, (1 — V2), should be inversely proportional to AHu. A quantitative analysis of experimental data by means of Eq. (3.2) requires... 

In analyzing polyethylene-diluent mixtures it was noted that for certain diluents and concentrations the melting temperature remained invariant with composition. This is not an isolated observation. Besides linear polyethylene, this phenomenon has also been observed in long chain branched polyethylene,(21) poly(chlorotrifluoroethylene),(22) poly(N,N -sebacoyl piperazene),(23) isotactic poly(propylene),(24) and poly (acrylonitrile) (25) when the polymers are admixed... 

Typical phase diagrams that illustrate these principles are presented in Fig. 3.8 for isotactic poly(propylene)-alky phenol mixtures (24) and in Fig. 3.9 for poly (N,N -sebacoyl piperazine) (23) with various diluents. At the higher isotactic poly (propylene) compositions only liquid-solid curves are observed that result in typical melting temperature depression. Although at lower polymer concentrations... 

Fig. 3.9 Plot of melting temperatures against volume fractions of polymers for mixtures of poly(N,N sebacoyl piperazine) with different diluents. Diphenyl ether O < -nitrotoluene...

We expected that this mixture would not crystallize and could be used as a reactive diluent of our polymers. The resulting isomer mixture, however, is solid at room temperature and the three dimer isomers presumably cocrystallize. Furthermore, it thermally cures at a temperature below melting. It, therefore, can not be used as a reactive diluent. We are exploring several other possibilities in this direction. 

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