The likely mechanism which allows the required migration of functional groups for solidstate polymerization (SSP) of polyamides and polyesters is shown to be interchange reactions. This "chemical diffusion" of functionality has exactly the same mathematical form as that of classical diffusion of small molecules. The consequent model for kinetics of SSP in fine geometries is seen to fit experimental data well. It yields an estimate of the critical distance over which the functionality jumps with each interchange reaction. The critical reaction distance thus obtained, ∼5 Å, is similar to those determined from diffusion-controlled reactions of small molecules. The profound changes that interchange reactions can produce during SSP in the topology of chain segments in the intercrystalline regions of flexible and semirigid polymers, especially in oriented structures, are revealed.
Interchange reactions during solid-state polymerization (SSP) can cause significant morphological changes in the intercrystalline regions. A coarse-grained model has been formulated for the effect of these reactions on the topological distribution of chains in the intercrystalline regions of oriented polymer morphologies. It includes a novel thermodynamic scheme, coupled with a Monte Carlo simulation, based on rotational isomeric states, of confined chains to determine the relative probabilities of topologically different reaction outcomes. The results show the role of intrinsic molecular rigidity on interchange-reaction dictated interconversions of bridges and loops during SSP of different polymers. The scheme presented here can serve to identify, via gedanken experiments, appropriate semirigid polymers for synthesis and processing to produce morphologies for high mechanical performance. It can also be used to determine the above-T g mechanical properties of noncrystalline domains, with a known initial topological distribution of chains, as well as the equilibrium distribution of these chains.
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