Polymer conditioned nonequilibrium

When monomers with dependent groups are involved in a polycondensation, the sequence distribution in the macromolecules can differ under equilibrium and nonequilibrium regimes of the process performance. This important peculiarity, due to the violation in these nonideal systems of the Flory principle, is absent in polymers which are synthesized under the conditions of the ideal polycondensation model. Just this circumstance deems it necessary for a separate theoretical consideration of equilibrium and nonequilibrium polycondensation. 

No thermodynamic signature at Tg is evident in specific heat data at equilibrium, but a peak is observed under nonequilibrium conditions and is often taken as the definition of the glass transition. Unfortunately, this nonequilibrium peak cannot be addressed within the LCT of glass formation. We strictly avoid a discussion of the specific heat, given the complications of interpreting these data for polymer materials and the omission of the important vibrational component in the LCT treatment. 

Assume as a model for a Ziegler-Natta system the diffusion of monomer to a site of catalytic activity—presumably one of a number of sites on a solid particle—where it is inserted into a growing polymer chain. For the bulk polymerization of a monomer such as 4-methylpentene-l where polymer is insoluble in monomer, the solid catalyst particle becomes the center of an expanding sphere of precipitated polymer chain (s) growing from the inside. On this molecular level, the rate of chain growth will be directly proportional to the monomer activity at the individual sites. At equilibrium the monomer activity at each site encapsulated in precipitated polymer will equal that of the surrounding bulk monomer, [Mo]. Under nonequilibrium conditions, where the rate of diffusion of monomer from the bulk monomer thru the precipitated polymer to the polymerization site becomes comparable to the rate of polymerization at that site, the localized activity will be lower, and the rate of polymerization will be correspondingly lower. 

At point B, corresponding to the glass transition, penetration of the solute into the bulk of the polymer begins, causing an inaease of retention volume with temperature. Due to an initially slow rate of diffusion of the solute into and out of the stationary phase, nonequilibrium conditions prevail. As the temperature is increased in region BC the diffusion coefficient rises sharply, leading to equilibrium conditions at point C. 

As discussed earlier, polydichlorophosphazene depolymerizes to a spectrum of cyclic oligomers when heated at 250-350°C jn helium flow-tube apparatus at 400°C, species (NPCl2)3 g are identified, with the cyclic hexamer predominating. It should be noted that these results are for nonequilibrium reaction conditions under which all or most of the polymer is converted to oligomers. 

A series of non-equilibrium Tm-values were measured on samples recrystallised from the melt under standard conditions (the so-called Tm2-values, see 1.1.4) and a number of nonequilibrium literature values were used to look for an improved correlation between Tm/Tg relations. We tried to improve the results of such a relation by distinguishing different groups of polymers instead of looking for one relation for all types of polymers. Three groups of polymers offering the best fitting correlations, were selected finally ... 

Generally, a decrease in the thermodynamic affinity of the solvent (X-induced syneresis) during cooling would have to result in decreasing copolymer swelling. However, if much solvent has to be removed from the beads, it first separates as droplets inside the gel, because the network relaxation is fairly slow [266]. Excess solvent is then slowly pushed out of the beads having a rather flexible gel-type matrix that is homogeneous under equilibrium conditions. Consequently, the microsyneresis is a nonequilibrium state of the particular gel-type polymer-solvent system. 

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