Crystallization of the Growing Polyoxymethylenes

Lateral growth involves conventional propagation the growing species located at the surface of a side-wall react with monomer which, is incorporated into the 

The term insertion describes, in our understanding, the end result but not the actual process insertion does not have to proceed in one chemical step involving a four-center mechanism, but may occur stepwise by chain breaking, monomer addition, and recombination of the cation with a terminal hydroxyl group  

This process continues until the crystal reaches a thickness of several thousand A. Crystal growth does not stop even after equilibrium conversion (polymer-monomer equilibrium) is reached. This is explained in terms of the Ostwald ripening. Solubility of particles depends on their size thus smaller particles tend to redissolve (by depropagation) in favour of further growth of already larger ones. This is illustrated by the data shown in Table 7.7. 

As shown in the last column of Table 7.7, the degree of crystallinity increases from 79 % to almost 89 % with increasing crystal size. This is already close to 95 %, 

Time h Conversion % M 103 Crystal diameter pm Crystal thickness pm Crystallinity11 % 

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