A series of novel thermoplastic elastomers based on ABA-type triblock prepolymers, poly[(propylene oxide)-(dimethylsiloxane)-(propylene oxide)] (PPO-PDMS-PPO), as the soft segments, and poly(butylene terephthalate) (PBT), as the hard segments, was synthesized by catalyzed two-step melt transesterification of dimethyl terephthalate (DMT) with 1,4-butanediol (BD) and α,ω-dihydroxy-(PPO-PDMS-PPO) (M n = 2930 g mol −1 ). Several copolymers with a content of hard PBT segments between 40 and 60 mass% and a constant length of the soft PPO-PDMS-PPO segments were prepared. The siloxane-containing triblock prepolymer with hydrophilic terminal PPO blocks was used to improve the compatibility between the polar comonomers, i.e. DMT and BD, and the non-polar PDMS segments. The structure and composition of the copolymers were examined using 1 H NMR spectroscopy, while the effectiveness of the incorporation of α,ω-dihydroxy-(PPO-PDMS-PPO) prepolymer into the copolyester chains was controlled by chloroform extraction. The effect of the structure and composition of the copolymers on the transition temperatures (T m and T g ) and the thermal and thermo-oxidative degradation stability, as well as on the degree of crystallinity, and some rheological properties, were studied.

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A series of thermoplastic elastomers based on ethylene oxide-poly(dimethylsiloxane)-ethylene oxide (EO-PDMS-EO), as the soft segment, and poly(butylene terephthalate) (PBT), as the hard segment, were synthesized by catalyzed two-step, melt transesterification reaction of dimethyl terephthalate (DMT) with 1,4-butanediol (BD) and a,x-dihydroxy-(EO-PDMS-EO). Copolymers with a content of hard PBT segments between 40 and 90 mass % and a constant length of the soft EO-PDMS-EO segments were prepared. The siloxane prepolymer with hydrophilic terminal EO units was used to improve the miscibility between the polar comonomers, DMT and BD, and the nonpolar PDMS. The molecular structure and composition of the copolymers were determined by 1 H-NMR spectroscopy, whereas the effectiveness of the incorporation of a,x-dihydroxy-(EO-PDMS-EO) into the copoly-mer chains was verified by chloroform extraction. The effects of the structure and composition of the copolymers on the melting temperatures and the degree of crystallinity, as well as on the thermal degradation stability and some rheological properties, were studied. It was demonstrated that the degree of crystallinity, the melting and crystallization temperatures of the copolymers increased with increasing mass fraction of the PBT segments. The thermal stability of the copolymers was lower than that of PBT homopolymer, because of the presence of thermoliable ether bonds in the soft segments.

The one-electron reduction of 2,4,6-tris(N-methylpyridinium-4-yl)pyridine trication, triparaquat, TPQ3`, synthesized in the form of the perchlorate salt, was studied by cyclic voltammetry on a platinum disc electrode. It was found that the reduction peak is centered at [880 mV (vs. SCE) at 500 mV s~1 scanning rate. The subsequent oxidation takes place at ]75 mV, indicating an irreversible process, but no changes in the solution content were found after the oxidation. The blue colored reduction product reacts anomalistically slowly with oxygen with a second-order rate constant of (0.65 ^0.01) mol~1 dm3 s~1. EPR experiments showed that the reduction product in ethanol solution does not possess an unpaired electron. A low temperature gamma radiolysis experiment revealed that the spectral peak maximum of the reduction product of TPQ3`solubilized in PVA Ðlm is shifted D200 nm with respect to that obtained in aqueous solution at room temperature. Pulse radiolysis experiments proved that this seemingly inconsistent set of data was a consequence of the very fast dimerisation process mol~1 dm3 s~1). Cyclic voltammetry 2TPQ2`~¢ (TPQ) 2 4`(k dim \ 1.4 ] 109 experiments on a mercury electrode revealed that the second reduction step corresponds to the dimer reduction. The third and fourth reduction steps were irreversible and initiated further chemical reactions of triparaquat, which was consistent with the data obtained by the prolonged steady state gamma radiolysis. Fig. 1 Structural formulae of triparaquat, TPQ3`, methyl viologen, MV2`and 1-ethylpyridinium, EP`.