Crystalline structure and molecular dynamics in α and α′ crystals of poly(L-lactide) (PLLA) and PLLA/poly(Dlactide) (PDLA) stereocomplex (sc) crystals have been investigated by the temperature-variable FTIR and solid-state 13 C CP-MAS NMR spectroscopy. The crystal forms of polylactide (PLA) have different band frequencies, correlation field splittings in FTIR spectra and different line shapes, and resonance splittings in solid-state NMR spectra, which become more distinct with cooling to the cryogenic conditions. The well-resolved splittings in NMR resonances of α crystals, attributable to the crystallographically inequivalent sites within crystal unit cell, are considered to be due to the dipolar interactions related to the carbonyl, methyl, and methine groups. The splittings in FTIR bands and NMR resonances are absent in α′ crystals, indicating the disordered conformation and loose molecular lateral packing within their crystal lattices. The significant FTIR frequency shifts of ν(CO), ν(CH 3 ), and ν(CH) modes during stereocomplex crystallization of PLLA/PDLA blend and the appearance of spectral splittings at cryogenic conditions suggest the coexistence of weak C−H···OC hydrogen bonds and dipolar interactions between PLLA and PDLA chains in the sc crystals of PLA. Below the glass transition temperature (T g ), the spin−lattice relaxation times of PLA with different crystalline structures increase in the order of amorphous ≈ α′ < α < sc.

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The effects of poly(vinylidene fluoride) (PVDF) component on the crystallization kinetics, crystalline structure, phase transition, and morphology of polymorphic poly(butylene adipate) (PBA) in their miscible PVDF/PBA binary blends have been investigated. The polymorphism of PBA can be regulated upon blending with PVDF. The incorporated PVDF faciliates the formation of PBA α-crystal, which is probably attributed to the thermodynamic and kinetic contributions. From the crystallization kinetics, it was found that a small amount of PVDF acts as a nucleating agent and can accelerate the crystallization of PBA, while a large amount of PVDF hinders the crystallization of PBA due to the confinement effect. In addition, the addition of PVDF greatly accelerates the β- to α-form phase transition of PBA upon annealing the PBA β-form at higher tmeperataure (48 °C). However, the large amount of PVDF decelerates the phase transition to a certain extent. The possible reasons for these phenomena were also proposed.