Isothermal Crystallization Kinetics of Poly(ε-caprolactone) Blocks Confined in Cylindrical Microdomain Structures as a Function of Confinement Size and Molecular Weight

The isothermal crystallization kinetics of poly­(ε-caprolactone) (PCL) blocks confined in cylindrical microdomain structures (nanocylinders) formed by the microphase separation of PCL-<i>block</i>-polystyrene (PCL-<i>b</i>-PS) copolymers were examined as a function of nanocylinder diameter <i>D</i> and molecular weight of PCL blocks <i>M</i>_n. Small amounts of polystyrene oligomers (PSO) were gradually added to PCL blocks in PCL-<i>b</i>-PS to achieve small and continuous decreases in <i>D</i>. The time evolution of PCL crystallinity during isothermal crystallization at −42 °C showed a first-order kinetic process with no induction time for all the samples investigated, indicating that homogeneous nucleation controlled the crystallization process of confined PCL blocks. The half-time of crystallization <i>t</i>_1/2 (inversely proportional to the crystallization rate) of PCL blocks with <i>M</i>_n ∼ 14 000 g/mol showed a 140-fold increase (from 0.48 to 69 min) by a 16% decrease in <i>D</i> (from 18.6 to 15.6 nm). Another set of PCL-<i>b</i>-PS/PSO blends involving slightly longer PCL blocks with <i>M</i>_n ∼ 15 800 g/mol showed a similar result. It was found by combining the results of two PCL-<i>b</i>-PS/PSO blends that the small increase in <i>M</i>_n (from 14 000 to 15 800 g/mol) yielded an approximately 90-fold increase in <i>t</i>_1/2 (from 0.76 to 67 min) for PCL blocks confined in the nanocylinder with <i>D</i> = 18.2 nm. It is possible from these experimental results to understand the individual contributions of <i>D</i> and <i>M</i>_n to the crystallization rate of block chains confined in nanocylinders

Quantitative Temperature Dependence of the Microscopic Hydration Structures Investigated by Ultraviolet Photodissociation Spectroscopy of Hydrated Phenol Cations

To discuss the temperature effect on microscopic hydration structures in clusters, relative populations of the isomers having different hydration structures at well-defined temperatures are quite important. In the present study, we measured ultraviolet photodissociation spectra of the temperature-controlled hydrated phenol cation [PhOH­(H₂O)₅]⁺ trapped in the 22-pole ion trap. Two isomers having a distinct hydration motif with each other are identified in the spectra, and a clear change in the relative populations is observed in the temperature range from 30 to 150 K. This behavior is quantitatively interpreted by statistical mechanical estimation based on density functional theory calculations. A ring with tail-type hydration motif is dominant in cold conditions, whereas a chain-like motif is dominant in hot conditions. The present study provides very quantitative information about the temperature effect on the microscopic hydration structures

One-Step Conversion of Potassium Organotrifluoroborates to Metal Organoborohydrides

This letter describes the one-step conversion of heteroatom-substituted potassium organotrifluoroborates (KRBF₃) to metal monoorgano­borohydrides (MRBH₃) using alkali metal aluminum hydrides. The method tolerates a variety of functional groups, expanding MRBH₃ diversity. Hydride removal with Me₃SiCl in the presence of dimethyl­aminopyridine (DMAP) affords the organoborane·DMAP (RBH₂·DMAP) adducts