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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.

This work attempts to determine how percolation at an equilibrium state is correlated to percolation under experimental conditions. The dynamic process of forming conductive networks in carbon-black (CB)-filled poly(methyl methacrylate) composites was investigated by real-time tracing the time dependence of electrical resistivity during isothermal treatments. It was observed that the dynamic percolation curves maintains the same shape and shift to a shorter percolation time with increasing annealing temperature and filler concentration. An Arrhenius plot of the shift factor against the annealing temperature shows a linear relationship, irrespective of the filler concentration, and the activation energy of the percolation time is close to the activation energy of the zero-shear-rate viscosity of the polymer matrix. Furthermore, an increase in the thermodynamic interactions between CB and the polymer matrix causes a large reduction in polymer mobility, resulting in an increase in the percolation time. These results lead to the conclusion that percolation is delayed by the bulk mobility of polymer layers surrounding CB particles. An experimental approach for determination of the retardation time is proposed based on theoretical analysis of the dynamic movement of the carbon particles. It is suggested that the difference in the kinetic history with respect to percolation among different composite systems can be eliminated by normalizing the experimental conditions to the same value of retardation time.

This work attempts to clarify the influence of surface roughness on the thermodynamic interactions between carbon particles and polymer melts. The surface energy of carbon black (CB) and short carbon fibers (VGCF) having different surface roughnesses was estimated by inverse gas chromatography (IGC) and highly sensitive isothermal calorimeter (HS-ITC) measurements using lowmolecular-weight analogues of polymers as probes. We confirmed that the carbon surfaces possess energetic heterogeneity with the most active sites at the graphite crystalline edges, and the interactions in play are van der Waals in nature. Competitive adsorption of two chemically different polymers by incorporation of the carbon particles into the polymer blends was investigated based on SEM and TEM observations. We found that the selective location of CB in the polymer blends does not always depend on the surface tension of polymers but seems to be governed largely by the flexibility of the polymer chains. In VGCFfilled HDPE/PMMA composites, a self-assembled VGCF/HDPE network throughout the PMMA matrix was observed where the flexible HDPE chains are preferentially absorbed at the rough ends of the VGCF filaments. These experimental results lead to the conclusion that surface roughness strongly affects the carbon-polymer interactions, and the entropy penalty may play a main role in competitive adsorption of polymers on the rough carbon surfaces.

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A new technique for in situ studies on polymer dynamics in highly filled compositions was developed using carbon black (CB) as a self-diagnosing probe. It is based on the fact that CB particles dispersed in the polymer matrix are easy to aggregate and gradually form three-dimensional networks. Real-time monitoring of the dynamic process of the interparticle network formation was realized by tracing the time dependence of electrical resistivity during isothermal treatments. We investigated the influence of time, temperature, concentration, and the molecular weight of the polymer matrix on the dynamic percolation behavior and concluded that the percolation time when the electrical resistivity starts to decrease drastically is directly related to the zero-shear-rate viscosity of the polymer matrix. We also estimated the terminal relaxation time of polymer matrices from the dynamic percolation curves so as to eliminate the effect of CB concentrations. It is expected that the dynamic percolation measurements may provide an incisive method to study the influence of particle-polymer interactions on the relaxation and viscoelastic properties of a polymer matrix.