The mechanism of solid state polycondensation has been subjected to a fundamental analysis. Equations were formulated for combined diffusion and chemical reaction for two separate situations. One was for solid state polycondensation in polymer flakes or chips. The other dealt with polymer powders. The resultant solutions related molecular weight changes to rate functions. A technique for deriving the rate functions from experimental data is described.
Solid state polycondensations were then studied for nylon 66, nylon 6-10, and polyethylene terephthalate. These data which ranged from 120 to 200°C. were tested with various mechanisms. The most appropriate one was found to be that developed in the present work. Chemical reaction was found to be the rate controlling step in solid state polycondensation in nylon 66, polyethylene terephthalate, powders of nylon 6-10 and larger particles of nylon 6-10 at and above 160°C. Diffusion of byproduct through the solid was the rate controlling step for larger particles of nylon 6-10 at temperatures below 160°C. Thermograms of nylon 6-10 indicated morphological changes which possibly influenced the behavior of the larger nylon 6-10 particles. The Arrhenius relation was fitted to the situations where chemical reaction controlled.