A vibrational analysis has been carried out to analyze the chain conformation of poly(lactic acid) in the crystalline state. In conjunction with a normal-coordinate analysis, the Raman spectrum has yielded data regarding conformational distributions. Raman spectra of different helices were simulated using previously published structures, force constants, and intensity parameters. Some of the chain conformations predicted are inconsistent with the data. Only one of the four 3 1 helical structures predicted by conformational analysis agrees well with experiment. This analysis provides a new understanding regarding the relative probability of a 103 or 31 helix for poly(lactic acid).

Vibrational assignments for α-syndiotactic polystyrene are made with the use of parallel and perpendicular polarization of uniaxially oriented film, and by comparison of vibrational data and assignments for toluene and atactic and isotactic polystyrene. Vibrational assignments are given for a cast film of β-syndiotactic polystyrene. These assignments are made by comparison with assignments for toluene and isotactic and atactic polystyrene and partial assignments for α- and β-syndiotactic polystyrene. Some of our assignments suggest that the crystal structure of α-SPS may not be isomorphous with C2 r symmetry.

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The crystallinity of syndiotactic polystyrene (sPS) is studied by hyperspectral Raman line imaging. Images of a 140 × 1200 μm region of an sPS test piece containing 39 200 pixels/image were generated from spectra taken over the wavenumber interval between 300 and 875 cm−1. The spectral region includes the moderate-intensity crystallinity-sensitive bands in the 770 800 cm−1 region, as well as other useful but weaker marker bands. Factor analysis was used to extract structure information from the set of spectra. Four non-noise factors were extracted; two were assigned to crystalline and amorphous sPS and the other two to background. Score images of the crystalline and amorphous sPS factors were used to visualize distribution of those species. The results were compared to the integrated Raman intensity image for the 773 cm−1 band of crystalline sPS.

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28) Carter, C. A,; Harris, J. M. Appl. Opt. 1984, 23, 476-481. (29) Gordon, J. P.; Leite, R. C. C.; Moore, R. S.; Porto, S. P. S.; Whinnery, (30) Carter, C. A.; Harris, J. M. Appl. Spechosc. 1983, 37, 166-172. (31) Brannon, J. H.; Magde, D.A technlque based on photoacoustlc spectroscopy and utillzlng pulsed laser excltatlon has been developed for quantitatlvely detecting acetaldehyde In purlfled air at total pressures of 1 atm. Results are reported which demonstrate a llmltlng sensltlvlty of 25 ppbv for acetaldehyde and a llnearlty of photoacoustic signal wlth acetaldehyde partlal pressures over 6 orders of magnltude. The lowest acetaldehyde concentratlon detected corresponds to the observatlon of an absorptlon coefflclent of 9 X lo-@ cm-'. The methods for