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

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 $T_m^0$, 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 ? CD₂? 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. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 771–779     

NMR Analysis and Regiochemical Structure of Some Selectively 13C‐Enriched Poly(propylene)s

Summary: The regiochemical structures of poly(propylene)s obtained in the presence of three single‐site catalysts, Cp*Ti(CH₃)₃ + B(C₆F₅)₃ (I + III), CpTi(CH₃)₃ + B(C₆F₅)₃ (II + III), and VCl₄ + anisole + Al(C₂H₅)₂Cl (V + A), are investigated by ¹³C NMR analysis. Polymer 1 , obtained in the presence of I + III is, seemingly, fully regioregular, while, surprisingly, polymer 2 , obtained in the presence of II + III, appears to be alternating sequence of primary and secondary regioblocks, very much like polymer 3 , obtained in the presence of V + A. The stereochemical structure of the polymer obtained in the presence of I + III is in excellent agreement with a Bernoullian statistical model of the stereoselective propagation, while those of the other two polymers possibly require a Coleman‐Fox model.

¹³C NMR spectra of 10%‐enriched poly[(2‐¹³C)propylene], 1′ and 2′ , prepared under the conditions reported in Table 1 for the corresponding poly(propylene)s, 1 and 2 . The resonances of the tertiary carbons are diagnostic of the regioblock structure of sample 2′ .