An alternative method for the determination of siloxane activities toward basic equilibration catalysts

The method used is based on the well-known fact that siloxane equilibrates, once formed, do not change their compositions unless some siloxane compound is added, in which case new equilibrium compositions appear. As these composition changes, as well as their dynamics, are caused solely because of the addition of a particular siloxane compound, they are expected to be specific, and should contain information about the siloxane activities toward the applied equilibration catalyst. It was shown that the viscosities of such systems, measured as a function of reaction times, could be used for the determination of the relative activities of siloxanes. Proceeding from this basic assumption, some commonly used siloxanes were tested in equilibrations catalysed with tetramethylammonium hydroxide, TMAH. The siloxanes were: hexamathylcyclotrisiloxane, D3, octamethylcyclotetrasiloxane, D4, tetravinyltetramethylcyclotetrasiloxane, D4Vinyl, hexamethyldisiloxane, MM, and a linear all-methyl oligosiloxane of number average molecular weight of approximately 800. MD8,5M. The following decreasing order of activities toward the TMAH-catalyst was obtained: D3>MD8,5M>D4>D4Vinyl>MM

JSCS–3384 Original scientific paper

An alternative method for the determination of siloxane activities toward basic equilibration catalyst

The effect of segment length on some properties of thermoplastic poly(ester-siloxane)s

A series of novel thermoplastic elastomers, based on poly(dimethylsiloxane) (PDMS) as the soft segment and poly(butylene terephthalate) (PBT) as the hard segment, were synthesized by catalyzed two-step, melt transesterification reactions of dimethyl terephthalate and methyl esters of carboxypropyl-terminated poly(dimethylsiloxane)s (M̄ n = 550-2170 g mol -1 ) with 1,4-butanediol. The lengths of both the hard and soft segments were varied while the weight ratio of the hard to soft segments in the reaction mixture was maintained constant (57/43). The molecular structure, composition and molecular weights of the poly(ester-siloxane)s were examined by 1 H NMR spectroscopy. The effectiveness of the incorporation of the methyl-ester-terminated poly(dimethylsiloxane)s into the copolymer chains was verified by chloroform extraction. The effect of the segment length on the transition temperatures (T m and T g ) and the thermal and thermo-oxidative degradation stability, as well as the degree of crystallinity and hardness properties of the synthesized TPESs, were studied

The effect of the mass ratio of hard and soft segments on some properties of thermoplastic poly(ester-siloxane)s

A series of thermoplastic elastomers based on soft polydimethylsiloxane (PDMS) and hard poly(butylene terephthalate) (PBT) segments was synthesized using a two-step transesterification reaction in the melt. The molar mass of the soft PDMS component was constant (M̄ n P DMS = 1056 g mol -1 ) while the starting reaction mixture compositions were varied to obtained copolymers with a mass ratio of hard to soft segments in the range from 70/30 to 40/60. The structure and composition of the copolymers was verified by 1 H NMR spectroscopy. It appeared that there was a pronounced molar mass maximum when the PBT content of the copolymers was approximately 60 mass%, whereas all samples were considerably inhomogeneous with respect to the distribution of the lengths of the hard segments. Differential scanning calorimetry-(DSC) thermograms showed that the melting and crystallization temperature increased with increasing PBT content, as did the total degree of crystallinity, which was confirmed by wide-angle X-ray scattering (WAXS) analysis. Thermogravimetric analysis (TGA) performed in nitrogen gave subtle differences for samples of different composition, including that of the PBT homopolymer, whereas in oxygen these differences were more pronounced in the way the thermo-oxidative stability of the obtained copolymers decreased with decreasing PBT content. Finally, it was shown that the hardness depended directly on the PBT content, ie the higher the PBT content, the greater the hardness of the corresponding copolymer

Kinetics of the Formation of Poly(methyldecylsiloxane) by Hydrosilylation of Poly(methylhydrosiloxane) and 1-Decene

Poly(methylhydrosiloxane) [PMHS], prepared by siloxane equilibration reaction, was used for the hydrosilylation with 1-decene to obtain poly(methyldecylsiloxane) [PMDS]. Pt(0)-1,3-divinyltetramethyldisiloxane complex was used as a catalyst for hydrosilylation reaction. In order to investigate the kinetics of the formation of PMDS, a series of experiments was performed at different reaction temperatures (from 48 to 64 degrees C) with catalyst concentrations of 7.0 center dot 10(-7) Mol Of Pt per mol of CH=CH2. All reactions were carried out in bulk, with equimolar amounts of the reacting Si-H and CH=CH2 groups. The course of the reactions was monitored by following the disappearance of the Si-H bands by quantitative infrared spectroscopy. The obtained results show that an induction period occurs at lower reaction temperatures and that the rate of Si-H conversion follows the first-order kinetics

Synthesis and Characterization of Novel Urethane-Siloxane Copolymers with a High Content of PCL-PDMS-PCL Segments

Novel polyurethane copolymers derived from 4,4'-methylenediphenyl diisocyanate (MDI), 1,4-butanediol (BD) and alpha, omega-dihydroxy-[poly(caprolactone)-poly (dimethylsiloxane)-poly(caprolactone)] (a, x-dihydroxy( PCL-PDMS-PCL); (M) over bar (n) 6100 g mol(-1)) were synthesized by a two-step polyaddition reaction in solution. In the synthesis of the polyurethanes, the PCL blocks served as a compatibilizer between the nonpolar PDMS blocks and the polar comonomers, MDI and BD. The synthesis of thermoplastic polyurethanes (TPU) with high soft segment contents was optimized in terms of the concentrations of the reactants, the molar ratio of the NCO/OH groups, and the time and temperature of the polyaddition reaction. The structure, composition, and hard MDI/BD segment length of the synthesized polyurethane copolymers were determined by H-1, C-13-NMR, and two-dimensional correlation (COSY, HSQC, and HMBC) spectroscopy, while the hydrogen bonding interactions in the copolymers were analyzed by FT-IR spectroscopy. The influence of the reaction conditions on the structure, molecular weight, thermal, and some physical properties was studied at constant composition of the reaction mixture. A change in the molar ratio of the NCO/OH groups and the reaction conditions modified not only the molecular weight of the synthesized polyurethanes, but also the microstructure and therefore the thermal and physical properties of the copolymers. It was demonstrated that only PCL segments with high soft segment contents crystallize, thereby showing spherulitic morphology

Synthesis and characterization of poly(ester ether siloxane)s

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) (M̄ 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

About the mode of incorporation of silanol-terminated polysiloxanes into butylene terephthalate-b-dimethylsiloxane copolymers

The modality of the incorporation of silanol-terminated siloxanes into copolymers with butylene terephthalate were investigated and determined. Besides siloxanes, the other participants in this well-known copolymerization, called the catalyzed two-step transesterification/polycondensation reaction, are dimethyl terephthalate and 1,4-butanediol. The employed approach to this problem was to exactly examine all the possibilities of the reactions between particular pairs of reactants, as well as of single reactants. The final results were, firstly, that reactions between siloxanes and dimethyl terephthalate did not occur and, secondly, that the only possibility for silanol-terminated siloxanes to be incorporated into the copolymers was by means of their condensation with 1,4-butanediol. This means that siloxanes are incorporated into the copolymer by ether and not by ester linkages