Crystal density and heat of fusion for a stereo‐complex of poly(L‐lactic acid) and poly(D‐lactic acid)

Abstract

Measured densities of films, consisting of only stereo‐complex (sc) crystals of poly(l‐lactic acid) (PLLA) and poly(d‐lactic acid) (PDLA), are sometimes significantly higher than the density of the sc‐crystal calculated on the basis of the previously proposed triclinic and trigonal unit cells. In this work, we reexamined the crystal density and determined the heat of fusion for the sc‐crystal. Twenty wide‐angle X‐ray reflections from a highly oriented sc‐film could be well indexed on the basis of a trigonal unit cell previously proposed by Cartier et al. The refined parameters of the trigonal cell are a = b = 1.50 nm, c = 0.823 nm, α = β = 90°, and γ = 120°. The c‐axis determined from the WAXD fiber pattern was significantly shorter than those (0.87–0.93 nm) previously reported. The crystal density of the modified cell was 1.342 ± 0.002 g/cm3, which was significantly higher than those previously reported (1.21–1.27 g/cm3). The heat of fusion for the sc‐crystal, extrapolated from the linear increase in the observed heat of fusion with decreasing the specific volume for the samples consisting of only sc‐crystals, was 155 ± 5 J/g. This value was significantly higher than those of α‐form and β‐form homo‐crystals of PLLA suggesting stronger interactions between the 32 helices of PLLA and 31 helices of PDLA in the sc‐crystal. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2632–2639, 2007

Computational investigation of spectroscopic parameters in putative secondary structure elements for polylactic acid and comparison with experiment

“…The equimolecular mixture of poly(L-lactic acid) (PLLA) and poly(Dlactic acid) (PDLA) enantiomers has another crystal modification known as the sc-form with 3 1 helices [13][14][15][16][17][18][19]. The crystal structures were also analyzed by computational chemistry.…”

Isothermal Crystallization Kinetics of Poly(lactic acid) Stereocomplex/Graphene Nanocomposites

“…It can be seen that both patterns show the same three peaks around 12, 21, and 24º which are related to the formation of PLA stereocomplexes crystallized in a triclinic unit cell. 21,23 The degree of crystallinity calculated for the stereocomplex PLA and scPLA/GNPO + nanocomposite was 36.4 and 41.3%, respectively. This increase in the degree of crystallinity suggests that the graphene acted as a nucleating agent.…”

Palladium-nanoparticles on end-functionalized poly(lactic acid)-based stereocomplexes for the chemoselective cinnamaldehyde hydrogenation: Effect of the end-group

“…Room temperature PXRD spectra of L R exhibited the characteristic Bragg reflexes of the PLA-stereocomplex L centered at 12.048°, 20.783°, 23.982°and 32.781°(2H) [27,28] regardless of the nature of terminal group present in the PLA backbone (Fig. 1, upper traces).…”