A spectroscopic analysis of poly(lactic acid) structure

A vibrational analysis has been carried out to analyze the chain conformati on of poly(lactic acid) in the crystalline state. In conjunction with a nor mal-coordinate analysis, the Raman spectrum has yielded data regarding conf ormational distributions. Raman spectra of different helices were simulated using previously published structures, force constants, and intensity para meters. Some of the chain conformations predicted are inconsistent with the data. Only one of the four 3(1) helical structures predicted by conformati onal analysis agrees well with experiment. This analysis provides a new und erstanding regarding the relative probability of a 10(3) or 3(1) helix for poly(lactic acid).