Complex Crystal Formation of Poly(L-lactide) with Solvent Molecules

By screening examinations for a wide variety of organic solvents, we found that poly(L-lactide)(PLLA) forms the crystalline complex (epsilon-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 e-crystals. By fiber diagram analyses for the epsilon-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 alpha = beta = gamma = 90 degrees). 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 m the-unit cell.