Phase diagram molecular weight dispersity

In addition to the molecular weight of the free polymer, there axe other variables, such as the nature of the solvent, particle size, temperature, and thickness of adsorbed layer which have a major influence on the amount of polymer required to cause destabilization in mixtures of sterically stabilized dispersions and free polymer in solution. Using the second-order perturbation theory and a simple model for the pair potential, phase diagrams relat mg the compositions of the disordered (dilute) and ordered (concentrated) phases to the concentration of the free polymer in solution have been presented which can be used for dilute as well as concentrated dispersions. Qualitative arguments show that, if the adsorbed and free polymer are chemically different, it is advisable to have a solvent which is good for the adsorbed polymer but is poor for the free polymer, for increased stability of such dispersions. Larger particles, higher temperatures, thinner steric layers and better solvents for the free polymer are shown to lead to decreased stability, i.e. require smaller amounts of free polymer for the onset of phase separation. These trends are in accordance with the experimental observations. 

In the previous section we have described the three types of phase behavior observed in the low-molecular-weight PMMA/PS system and reviewed the four types observed in the low-molecular-weight PS/PMMA system. These various phase relationships have been studied in terms of their dependence on the molecular weight (Mn) and weight percent (W) of the initial polymer present. Further, we have presented quantitative data concerning the sizes of the dispersed particles, again correlated to variations in Mn and W. In this section we will discuss the results in terms of the poly (methyl methacrylate )/polystyrene/styrene and poly-styrene/poly( methyl methacrylate)/methyl methacrylate ternary phase diagrams, whichever is appropriate. 

Figure 26. PMMA/PS/S phase diagram indicating various relationships between molecular weight and composition of PMMA and the dispersed particle size...

Blanazs A, Ryan AJ, Armes SP (2012) Predictive phase diagrams for RAFT aqueous dispersion polymerization effect of block copolymer composition, molecular weight, and copolymer concentration. Macromolecules 45 5099-5107... 

Four types of phase behavior characteristic of the PS/P(MMA-S) system have been described and illustrated in some detail in the previous section and further, the average particle sizes have been tabulated as a function of molecular weight and weight percent of PS initially present in the PS/MMA-S mixture and of the composition of the final P(MMA-S) copolymer resulting after polymerization. In the section we will discuss these results in terms of the ternary polystyrene/poly(methyl methacrylate-styrene)/methyl methacrylate-styrene phase diagram, dealing with (1) the four types of phase relationships, (2) particle size, and lastly (3) multiple emulsions or subinclusions within the dispersed phase. 

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