In situ FTIR studies on the cold-crystallization process and multiple melting behavior of isotactic polystyrene

The structure evolution of iPS during isothermal cold-crystallization and subsequent melting processes is studied by in situ monitoring its FTIR spectra. Through following the intensity changes of the characteristic bands associated with its crystalline status and 31 helix conformation chains, the multiple melting behavior of iPS cold-crystallized at different temperatures has been discussed in detail. It is concluded that (i) the lowest-temperature annealing peak can be ascribed either to the relaxing of locally ordered long 3, helix chains in the amorphous phase or to the melting of some microcrystallites formed upon long-time annealing; (ii) the double melting behavior of iPS cold-crystallized at temperatures lower than 180 degreesC is mainly attributed to the model of melting, recrystallization, and remelting of the iPS crystals; and (iii) for the sample cold-crystallized at a temperature of 200 degreesC, the in situ IR experiments give strong evidence to support the existence of different kinds of crystals which show different thermodynamic stabilities.