The isothermal crystallization behavior of poly( l -lactide) (PLLA) at 150 °C from the melt was monitored by infrared (IR) spectroscopy. The two-dimensional (2D) correlation analysis of time-dependent IR spectra collected during the melt crystallization process revealed details about the intermolecular interaction of the CH 3 and C O groups and the conformational changes in the C−O−C backbone that are not easily detected by conventional one-dimensional spectra. It was found that the intermolecular interaction of the CH 3 group appears during both the induction period and the growth period of PLLA melt crystallization, while the intermolecular coupling of the C O group can only be observed during the crystallization period. The order formation of C−O−C backbone during the induction period of PLLA melt crystallization can also be clearly observed in the 2D synchronous spectra. These observations not only provide direct evidence that the distorted 10 3 helix conformation of PLLA chain in α crystals is due to the interchain interactions between CH 3 groups, but also show that the weak interchain interactions play an important role in controlling the nucleation and growth of polymer crystallization.
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Zhang et al. (2004) studied this question.
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