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By screening examinations for a wide variety of organic solvents, we found that poly(L-lactide) (PLLA) forms the crystalline complex (ε-form) with the specific organic solvents such as tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) below room temperature. It was revealed that PLLA has high selectivity for low molecular weight compounds to form the ε-crystals. By fiber diagram analyses for the ε-forms, it was found that PLLA chains take the 10 7 (left-handed 10 3 ) helical conformation and are packed in the orthorhombic lattice (a = 1.5−1.6 nm, b = 1.2−1.3 nm, c = 2.8−2.9 nm, and α = β = γ = 90°). Based on R-factor and packing energy calculations, the plausible crystal structure of PLLA−DMF complex was proposed, in which four PLLA chains and eight guest solvents are packed in the unit cell. ■ INTRODUCTIONThe complexation of macromolecules with low molecular weight compounds via nonbonded interactions is categorized as the supramolecular chemistry composed of macromolecules and low molecular weight compounds. There have been many studies on crystalline complexes and clathrates composed of macromolecules and low molecular weight compounds: amylose/iodine, 1 poly(vinyl alcohol)/iodine, 2 cellulose/low molecular weight compounds, 3 polymer/urea, 4 polymer/cyclodextrins, 5 poly(ethylene oxide) (PEO)/inorganic compounds, 6 syndiotactic polystyrene (sPS) /solvents, 7,8 polyethylenimine (PEI)/low molecular weight compounds, 9 syndiotactic poly-(methyl methacrylate) (st-PMMA)/solvents, 10 st-PMMA/fullerenes, 11 chitosan/low molecular weight compounds, 12 etc. In particular, the complexation of amylose with iodine 1 is wellknown phenomenon as the "iodo-starch reaction". The complexation of PEO with metallic salts 6 has a great effect on the ionic conductivity, which is of great importance in use of solid electrolytes. Petraccone et al. reported the nanoporous polymer crystals with pores or channels using sPS/solvents clathrates (δ-and ε-forms), which are suitable for applications such as chemical separation. 8 Kawauchi et al. found that in aromatic solvents such as toluene st-PMMA encapsulates C 60 molecules in its helical cavity to form a supramolecular inclusion complex. 11 Uda et al. prepared the sPS clathrate containing organic dye (azulene) by the guest-exchange procedure and controlled the orientation of organic dye encapsulated in the sPS crystal. 13 In addition, coordination polymers, which are constructed from transition metal ions and bridging organic ligands, attract much attention because these polymers can adsorb gases to a remarkable extent. 14 Thus, studies on the complexation of macromolecules with low molecular weight compounds are of great importance in terms of both basic and applied researches.Poly(L-lactide) (PLLA), one of the enantiomers of polylactide, can be synthesized from the plant-derived materials. PLLA shows the crystal polymorphism: the α-, 15,16 α′ (δ)-, 17,18 α″-, 19 β-, 20 and γ-21 forms. Sasaki et al. clearly showed that PLLA helices in the α-form (orthorhombic unit cell of paramet...

Crystalline structure and morphology of poly(L-lactide) (PLLA) formed under high-pressure CO 2 were studied by comparing the CO 2 -treated PLLA and the annealed one in terms of the crystallization behavior, crystalline forms, and crystalline superstructures. The crystallization temperature dependence of the diffraction peak position (2θ ≈ 16°) and crystallinity for the CO 2 -treated PLLA indicates that the crystal modification changes continuously from the disorder R (R′′) to R forms not through the R′ one with increasing temperature. By using light scattering technique, we clarified that the morphological transition from spherulites on a micrometer scale to rodlike crystalline superstructures on a nanometer scale occurs around 15 °C under 7-15 MPa CO 2 and around 30 °C under 3 MPa CO 2 . By introducing the parameters η and ∆ in the theoretical calculation for Vv light scattering from spherulites, it is indicated that there is a distinct difference in the arrangement of crystalline lamellae within spherulite between the CO 2 -treated PLLA and the annealed one.