Glass transition temperature effect dissolution

Summer MR Evener RP (1977) Effect of primidone concentration on glass transition temperature and dissolution of solid dispersion system containing of primidone and citric acid. J Pharm Sci 66 825-828... 

PVA Particles. Dispersions were prepared in order to examine stabilization for a core polymer having a glass transition temperature below the dispersion polymerization temperature. PVA particles prepared with a block copolymer having M PS) x 10000 showed a tendency to flocculate at ambient temperature during redispersion cycles to remove excess block copolymer, particularly if the dispersion polymerization had not proceeded to 100 conversion of monomer. It is well documented that on mixing solutions of polystyrene and poly(vinyl acetate) homopolymers phase separation tends to occur (10,11), and solubility studies (12) of PS in n-heptane suggest that PS blocks with Mn(PS) 10000 will be close to dissolution when dispersion polymerizations are performed at 3 +3 K. Consequently, we may postulate that for soft polymer particles the block copolymer is rejected from the particle because of an incompatibility effect and is adsorbed at the particle surface. If the block copolymer desorbs from the particle surface, then particle agglomeration will occur unless rapid adsorption of other copolymer molecules occurs from a reservoir of excess block copolymer. 

The dissolution of CO2 in polymeric carriers can cause important variations in their physical properties. Two properties of particular importance for precipitation and encapsulation processes are the glass transition temperature and the melting temperature. The dissolution of SC-CO2 in the polymer can reduce the glass transition temperature of amorphous polymers by as much as 4°C-30°C/MPa, an effect that has been related to the intermolecular interactions between dissolved CO2 and polymer. Significant reductions of melting temperature can be observed as well. As these effects are caused by the dissolved CO2, the trend of variation of these properties with pressure can be related to the trend of variation of solubility at... 

The reptation idea could account for the effect of polymer molecular weight and solvent concentration on the dissolution rate. However the key concentration identified in this approach [57,59] is one at the surface. This implies independence of the solvent concentration history. This may not be true as the disentanglement of polymer chains does not commence till the local solvent concentration is greater than a critical value at which the local glass transition temperature is lowered below the experimental temperature so that the glassy polymer changes into a gel. Also, all of the efforts discussed so far failed to take into account the effect of the viscoelastic properties of the polymer on the dissolution mechanism. 

Figure 14.17. Effect of carbon dioxide dissolution, facilitated by plasticizer, on glass transition temperature of plastificate. [Adapted from Yamaki H, Matsura Y, Kataoka H, US Patent 6,337,039, 2002.]...

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