One- and Two-Dimensional Solid-State ¹³C NMR Analyses of the Solid Structure and Molecular Motion of Poly(ε-caprolactone) Isothermally Crystallized from the Melt

Abstract

The crystalline-noncrystalline structure and molecular motion of poly( -caprolactone) (PCL) isothermally crystallized from the melt have been investigated by one-and two-dimensional solid-state 13 C NMR spectroscopy. The 13 C spin-lattice relaxation time (T1C) analysis reveals that the PCL sample contains three components with different T1C values, which are assignable to the crystalline, mobile crystalline, and noncrystalline components. By the 13 C spin-spin relaxation time (T2C) analysis, it is found that the noncrystalline component can be further resolved into the crystalline-amorphous interfacial, and amorphous components. The mass fractions of the crystalline, interfacial, and amorphous components are finally determined to be 0.42, 0.30, and 0.28, respectively. In the crystalline region, different molecular mobilities along the methylene sequence are suggested through the difference in T1C value for the constituting carbons. More detailed molecular motion in the crystalline region has been characterized by the analysis of the 13 C chemical shift anisotropy (CSA) in terms of the two-site exchange model. 13 C CSA spectra of the individual carbons are successfully recorded by using the two-dimensional switching angle sample spinning technique. The CSA spectrum of the carbonyl carbon exhibit that the carbonyl carbon is almost in the rigid state or undergoes the jump motion around the molecular chain axis with a jump angle less than 30°. In contrast, methylene carbons exhibit almost axially symmetric CSA spectra, suggesting the rapid jump motions around the molecular chain axis with a jump angle of 60-90°. Further narrowed CSA spectra, which are still axially symmetric, are observed for the methylene carbons not directly attached to the ester group, suggesting the existence of additional enhanced jump motion around the C-C bonds. Such enhanced molecular motions of the methylene sequence may be due to the distorted nonplanar zigzag chain conformation of PCL in the crystalline region.

Biofunctionalization of electrospun PCL-based scaffolds with perlecan domain IV peptide to create a 3-D pharmacokinetic cancer model

“…The crystallinity of the PCL sample used in the same study determined by DSC was ~ 50.2% [33]. The crystallinity of PCL has been reported by others to be 42% by small angle X-ray scattering [50] and NMR [51], and 60% by the density method [52]. This suggests that the crystallinity of electrospun PCL fibers determined in this study by Raman spectroscopy is comparable with values determined by other conventional techniques.…”

Novel FTIR method for determining the crystallinity of poly(?-caprolactone)

“…The crystallinity of PCL has also been reported by others to be 42 % by smallangle X-ray scattering (SAXS) 11 and NMR, 12 and 60 % by the density method. 13 This suggests that the crystallinity of PCL determined in this study by FTIR is comparable with values determined by other conventional techniques.…”

Thermal properties and crystallization behaviour of blends of poly(ε‐caprolactone) with chitin and chitosan

“…Since the T g value of PCL is about −50 °C, it is reasonable to consider that the resonances of PCL observed in this study arise mainly from its crystalline region. But the α, ε and CO resonances of pure PCL consist of at least two components, ie one attributed to the crystalline region and the other to the amorphous region 23. Since the rigid molecular chains can make the efficiency of CP sufficiently high, even in the amorphous state, it is thought that a somewhat rigid portion exists in the amorphous region of highly crystalline PCL samples at room temperature.…”