Polymer glass, solvent-induced crystallization

The experimental results indicate that in solvent induced crystallization there is an interplay between the conventional Avrami type kinetics and the diffusion of the solvent through the polymer sample. There are many different factors involved. These include the type of diffusion, whether or not Pick s law is obeyed, the geometry and dimensions of the sample and the role of the solvent in reducing the glass and equilibrium melting temperature, and the solubility parameter among others. (104a) Complete analysis of this crystallization process is obviously... 

A crystalline or semicrystalline state in polymers can be induced by thermal changes from a melt or from a glass, by strain, by organic vapors, or by Hquid solvents (40). Polymer crystallization can also be induced by compressed (or supercritical) gases, such as CO2 (41). The plasticization of a polymer by CO2 can increase the polymer segmental motions so that crystallization is kinetically possible. Because the amount of gas (or fluid) sorbed into the polymer is a dkect function of the pressure, the rate and extent of crystallization may be controUed by controlling the supercritical fluid pressure. As a result of this abiHty to induce crystallization, a history effect may be introduced into polymers. This can be an important consideration for polymer processing and gas permeation membranes. 

Fourier transform infrared (FTIR) studies of the poly(bis-phenol A-carbonate) (PC) - poly(e-caprolactone) (PCL) blend system are presented. This is a complex blend system containing two crystallizable polymers, with large differences in crystalline melting points and glass transition temperatures (Tg), which are compatible in the amorphous state. FTIR spectroscopy has proven to be an excellent technique with which to study these blends. Evidence for the presence of specific chemical interactions between the two polymers in the amorphous state, which infers compatibility, has been obtained. Furthermore, the crystallization of the components of this blend system are readily followed at room and elevated temperatures. Solvent and polymer induced crystallization and the role of the effective Tg of the amorphous phase of the blends in the crystallization of PC is discussed. 

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