Miscibility of polymer

The understanding of the formation of miscible and immiscible polymer blends requires the application of the principles of phase chemistry. A miscible blend may be regarded as a solution of one polymer in the other. The thermodynamic criteria for the miscibility of liquids are well known and may be applied to polymers as a first approximation. The added complexity comes from the long-chain nature of polymers. In addition to the entropic factors there are kinetic factors to be considered. Since in reactive processing the reactions are occurring within a short time, they will very often be a long way from equilibrium. 

Liquid-liquid, liquid-polymer and polymer-polymer miscibility 

This figure clearly shows the temperature and composition windows where it is either a two-phase system or a single-phase system. The characteristic features of an upper critical solution temperature (UCST) and a lower critical solution temperature (LCST) corresponding to the phase transition are identified. For a particular composition of two immiscible polymers, if the temperature is increased, the UCST is the highest temperature at which two phases may co-exist in the blend. There is then a window of miscibility as the temperature is increased further, followed by phase separation again at the LCST. This type of diagram is often seen for polymer solutions, e.g. polystyrene in cyclohexane. Often polymer blends show 

This combinatorial entropy of mixing for low-molar-mass species is given by 

In a real solution, the interaction between the mixing species is considered (i.e. 0) 

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Coleman, M.M., Graf, J.F., and Painter, P.C., Specific Interactions and the Miscibility of Polymer Blends, Technomic Publishing, Lancaster, 1991. 

How do entropic and enthalpic effects determine the miscibility of polymers in blends Which term dominates the formation of a miscible blend ... 

Freed, K. F. and Dudowicz, J. Influence of Monomer Molecular Structure on the Miscibility of Polymer Blends. Vol. 183, pp. 63-126. 

In the laboratory simple tests for the miscibility of polymer melts can be carried out, in which the turbidity of the system is an indicator for the immiscibility. 

Coleman MM, Graf JF, Painter PC. Specific interactions and the miscibility of polymer blends. Lancaster (PA) Technomic 1991. 

Coleman, M. M., J. F. Graf, and P. C. Painter. ISKplecific Interactions and the Miscibility of Polymer Blends. Lancaster Technomic Publishing Company. 

M.M. Coleman, J.F. Graf and P.C. Painter, Specific Interactions and Miscibility of Polymer Blends, Technomic Publishing Company, Lancaster, PA, 1991. 

Hence, both UCST and LCST shift to higher temperatures with increasing pressure. However, if AVM > 0 in the gap between UCST and LCST then the gap diminishes with increasing pressure. As a rule, taken from the theory, positive volumes of mixing are likely when the gap between LCST and UCST is sufficiently small. In other words, an increasingly positive volume of mixing is unfavorable for miscibility of polymers and leads ultimately to phase instability. 

Paxton, T. R., "The Miscibility of Polymers Interaction Parameter for Polybutadiene with Polystyrene," J. Appl. Polym. Sci., 7, 1499 (1963). 

We have already described how the heats of mixing dominate the miscibility of polymers and so it was obvious to examine the heats of mixing of the above acrylates with PVC in order to understand the reasons for their miscibility or immisdbility. Fig. 19 shows the heats of mixing of various oligomeric polyacrylates and polymethacrylates with a chlorinated hydrocarbon which was used as an analogue for PVC. One can see... 

The term compatibility is often assumed to mean the miscibility of polymers with other polymers, plasticizers, or diluents. Decisions as to whether a mixture is compatible are not always clear-cut, however, and may depend in part on the particular method of examination and the intended use of the mixture. 

Studies continue on the effects of a polymer host matrix on the excited-state properties of guest molecules. For example, the lifetime of excited singlet-state species may be greatly prolonged through restrictions of molecular motions (Gusten and Meisner, inter alia). Accurate information on the blend miscibility of polymers is provided by studies of excimer emission (Mikes et al.), and George et al. claim that the service life of many polymers can be predicted from their luminescence properties see also Martin. 

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