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Polylactides (PLA) have been known for several decades and are recently of considerable commercial significance. However, the literature on basic chain properties and solution characterization is divided and inconsistent. In this study, a comprehensive and well‐controlled set of experiments is combined with rigorous quantitative analysis to resolve existing apparent contradictions. Homopolymers and copolymers spanning wide ranges of molecular weight and stereoisomer proportions were prepared by ring‐opening polymerizations of L‐ and D‐lactides using stannous octanoate as the catalyst. Samples were characterized by means of: (1) dilute‐solution viscometry in three different solvents; (2) size exclusion chromatography in tetrahydrofuran (THF) with light scattering detection; (3) static multiangle light scattering in a mixed acetonitrile–dichloromethane solvent; (4) variable‐angle spectroscopic ellipsometry; and (5) melt rheology. The data imply that PLA are typical linear flexible polymers; unperturbed PLA chain dimensions are describable in terms of a characteristic ratio of 6.5 ± 0.9, regardless of stereoisomer content. The Schulz‐Blaschke and Mark‐Houwink constants for dilute PLA solutions in chloroform and in THF are determined. For chloroform at 30°C, the correct values are kSB = 0.302, K = 0.0131 (mL/g), and a = 0.759, while for THF at 30°C, the correct values are kSB = 0.289, K = 0.0174 (mL/g), and a = 0.736. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3100–3111, 2005

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Fibers of poly(lactic acid) produced by twostep melt spinning have been studied. The morphology is elucidated with respect to the thermal and mechanical properties of fibers produced at cold-draw ratios of 1-8. With atomic force microscopy and small-angle X-ray scattering, a fibrillar morphology is found, with microfibril diameters ranging from 30 to 60 nm. Shrinkage properties indicate that, with increasing draw ratio, the fibers undergo a transition from class 2 to class 1 within the classification proposed by Keller. A supramolecular model for the morphology of the fibers is presented that entails a highly oriented skin with a core consisting of microfibrils. The orientation of the crystalline blocks within the microfibrils is similar to what has been reported for nylon fibers.