The effect of separation of blocks on the crystallization kinetics and phase composition of poly(butylene adipate) in multi-block thermoplastic polyurethanes.

The influence of the hard segment nature on the crystallization kinetics of multi-block thermoplastic polyurethanes containing poly(butylene adipate) (PBA) as a soft segment was investigated. Using a combination of FTIR spectroscopy, time-domain 1H nuclear magnetic resonance (TD-NMR), differential scanning calorimetry (DSC), fast-scanning calorimetry (FSC) and wide-angle X-ray diffraction (WAXS), it was shown that aliphatic, cycloaliphatic and aromatic diisocyanates affect the phase separation efficiency of soft and hard segments. The best phase separation efficiency was observed for a sample containing aliphatic diisocyanate due to the development of a hydrogen bond network. The thermal history, phase separation and the degree of ordering of the polyurethane determine the polymorphic behavior of melt-crystallized PBA. The formation of a partially-ordered mesophase of linear aliphatic polyurethane leads to an increase in the crystallization rate of PBA at room temperature and the formation of thermodynamically stable α-crystals. The presence of bulk cycloaliphatic and aromatic diol-urethane fragments prevents the phase separation of PBA, which crystallizes after slow cooling in a mixture of α- and ß-crystalline forms. The new nanocalorimetry technique allows the identification of a direct correlation between the phase separation and crystallization kinetics of the melt-crystallized PBA in a wide range of cooling rates - from 2 to 30 000 K s-1. Particularly, ultra-fast cooling suppresses the nucleation of the ß-phase of PBA resulting in slow crystallization of only α-modification at room temperature. The role of the polyurethane mesophase in the crystallization of the soft segment was discussed for the first time.

Features of the Gas-Permeable Crystalline Phase of Poly-2,6-dimethylphenylene Oxide.

Poly-2,6-dimethylphenylene oxide (PPO) film samples with varying degrees of crystallinity (from 0 to 69%) were obtained by means of different techniques. The films were studied by various physicochemical methods (Fourier-transform infrared spectroscopy, positron annihilation lifetime spectroscopy, X-ray diffraction, and 1H nuclear magnetic resonance relaxation). Solubility coefficients of gases in the PPO samples were measured via sorption isotherms of gases by volumetric technique with chromatographic detection. The apparent activation energy of permeation and the activation energy of diffusion of all gases were estimated based on temperature dependences of gas permeability and diffusivity for amorphous and semi-crystalline PPO in the range of 20-50 °C. The peculiarities of free volume, density, and thermal properties of gas transport confirm the nanoporosity of the gas-permeable crystalline phase of PPO. So, the PPO can be included in the group of organic molecular sieves.