Chain Conformation of Poly(d-lactide) in Tetrahydrofuran by Static Light Scattering, Small-Angle X-ray Scattering, and Intrinsic Viscosity

2020 
The dimensional features of an isotactic poly(lactic acid), poly(d-lactide) (PDLA), chain with a weight-averaged molar mass (Mw) ranging from 9.84 × 102 to 4.44 × 105 g mol–1 are studied in tetrahydrofuran (THF) at 25 °C using static light and small-angle X-ray scattering and the intrinsic viscosity ([η]). Sixteen PDLA samples with polydispersity indices (Mw/Mn) ranging from 1.04 to 1.15 are prepared by ring-opening polymerization of d-lactide, followed by fractionation using recycling preparative size-exclusion chromatography. The Mw dependence of the z-averaged root-mean-square radius of gyration (⟨S2⟩z1/2) and [η] is tabulated and compared with that of atactic poly(lactic acid) (PDL50, a random copolymer with a 1:1 molar ratio of d-lactide to l-lactide). The Mw dependence of ⟨S2⟩z1/2 and [η] and the scattering form factor [P(q)] for the PDLA chain are consistently and quantitatively described by a cylindrical wormlike model with a stiffness parameter (λ–1 = 6.5 nm), molar mass per unit contour length (...
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