Isotope Effects on the Crystallization Kinetics of Selectively Deuterated Poly(ε‐Caprolactone)

Abstract

Deuterium labeling of semi-crystalline polymers can dramatically affect their crystallization behaviors. However, the influence of different labeled positions in a partially deuterated polymer on its crystallization is still far from understood. Here, we synthesized a series of selectively deuterated poly(ε-caprolactones) (PCLs) through ring-opening polymerization of ε-caprolactone with controlled deuteration sites, including fully protiated (D0), fully deuterated (D10), tetra deuteration at the 3-and 7-caprolactone ring positions (D4) and hexa deuteration at the 4-, 5-, and 6-caprolactone ring positions (D6). All the PCLs showed a similar lamellar structure and parameters. Differential scanning calorimetry (DSC) analysis revealed that the equilibrium melting temperature T 0 m , melting temperature T m , crystallization temperature T c , and crystallization kinetics changed systemically with the deuterium content except for D4, which indicates that the presence of CD 2 moieties on either side of ester group in the polymer chain combined with isotopic inhomogeneity could influence the chain packing. The nonmonotonic trend of T m as a function of deuterium content could be attributed to the difference in a hydrogen-bond like intermolecular interaction between different PCLs. Partially deuterated PCLs (D4 and D6) showed an Avrami index near 2. After analyzing the parameters at the same supercooling temperature ΔT c , the existence of two crystallization regimes of PCLs were detected.

Decoupling Poly(3-alkylthiophenes)’ Backbone and Side-Chain Conformation by Selective Deuteration and Neutron Scattering

“…For P3DT, clear proton peaks were found at the following locations: CDCl 3 , δ (ppm) = 2.81 (t, 2H), 1.71 (m, 2H), 1.43 (m, 2H), 1.37 (m, 2H), 1.29 (m, 10H), 0.88 (t, 3H). Also, as seen in the 13 C NMR spectra (Figure c), for P3DT-d21, a septet was observed for CD 3 , and the quintet was observed at all CD 2 unit positions due to the spin–spin couplings between 13 C and D atoms, rather than a single peak for all of the carbons in the side chains of P3DT . The degree of deuteration of each CD 2 and CD 3 unit is over 99% according to the integrated area of the peaks of fully deuterated CD 2 and CD 3 and partially deuterated CD 2 and CD 3 .…”

“…Also, as seen in the 13 C NMR spectra (Figure 2c), for P3DT-d21, a septet was observed for CD 3 , and the quintet was observed at all CD 2 unit positions due to the spin−spin couplings between 13 C and D atoms, rather than a single peak for all of the carbons in the side chains of P3DT. 59 The degree of deuteration of each CD 2 and CD 3 unit is over 99% according to the integrated area of the peaks of fully deuterated CD 2 and CD 3 and partially deuterated CD 2 and CD 3 . The degree of side-chain deuteriation could influence the contrast factors.…”

Regularity of Deuteration in Linear Polyethylene Prepared by Saturation of Polycyclopentene over Homogeneous Catalysts

“…Small-angle neutron scattering (SANS) allows measurement of the single-chain conformation − of polymers and thermodynamic interactions in polymer blends. − Scattering contrast is achieved by blending isotopically labeled and unlabeled polymers, exploiting the large difference in neutron scattering length between hydrogen (H) and deuterium (D) . Labeled polymers can be directly synthesized if the deuterated monomers are available, allowing for direct control over the deuterium level and the distribution of deuterium along the chain. − Alternatively, the double bonds in unsaturated polymers may be saturated with D 2 , over either heterogeneous or homogeneous catalysts, to prepare deuterated polymers. This approach is attractive as it allows the facile preparation of “matched pairs” of polymersidentical in all respects except for the D labelingby simply using either H 2 or D 2 as the reducing gas. ,,, While heterogeneous catalysts can achieve a higher level of deuteration, via H/D exchange between the polymer and D 2 in addition to the saturation of the double bonds, it has been repeatedly shown that the distribution of deuterium among the chains obtained with such catalysts is not uniform. − A uniformly deuterated polymer should not generate any coherent neutron scattering because there is no interchain contrast.…”

“…Quantitative 13 C NMR spectroscopy is used to assess the deuteration regularity at the monomer unit level as it enables a clear identification of CDH, CD 2 , and CH 2 methylenes via their characteristic isotope shifts and the multiplicity of C–D coupling . Recently, the isotope effect of deuterium in 13 C NMR has been employed to analyze deuterated poly­(ε-caprolactone) , and to determine the DL of methyl carbons in syndiotactic PP following H/D exchange . Any deviation from regular deuteration, that is, any CD 2 resonances, or any CDH resonances other than the vicinal −CDH–CDH– pair expected from regular deuteration, can be easily identified.…”

“…The present study aims to understand the mechanisms and extents of side reactions that accompany the deuteration of the unsaturated polymers over Wilkinson's and Ru−H catalysts, using polycyclopentene (PCP) as the precursor, which yields deuterated linear polyethylene (PE) upon saturation, as shown 39 Recently, the isotope effect of deuterium in 13 C NMR has been employed to analyze deuterated poly(ε-caprolactone) 15,40 and to determine the DL of methyl carbons in syndiotactic PP following H/D exchange. 41 Any deviation from regular deuteration, that is, any CD 2 resonances, or any CDH resonances other than the vicinal −CDH−CDH− pair expected from regular deuteration, can be easily identified.…”