Witold Fortuniak

Synthesis of a paraffin phase change material microencapsulated in a siloxane polymer

The coemulsification method suitable for the formulation of microcapsules of n-eicosane coated with a polysiloxane is developed. This method allows to synthesize core–shell microcapsules of paraffin which have the shape of spheres or distorted spheres and are designed for the use as phase change materials. The microcapsules are formed in aqueous phase by the precipitation of n-eicosane together with modified polyhydromethylsiloxane from a common solvent which is miscible with aqueous media. The polysiloxane is modified by the attachment of silylvinyl and alkoxy functions before coemulsification with the paraffin. It also contains the Pt(0) Karstedt catalyst. The microcapsules formed by coemulsification are stabilized by the in situ cross-linking of the polysiloxane shell. The shell is additionally modified by the in situ generation of silanol groups which provide colloidal stabilization of microspheres in aqueous phase. Microcapsules were studied by DSC, SEM, optical polarized microscope, and by thermooptical analysis (TOA).

Superhydrophobic properties of cotton woven fabrics with conducting 3D networks of multiwall carbon nanotubes, MWCNTs

This article presents the findings concerning the preparation and properties of cotton woven fabrics with a conductive network made of multiwall carbon nanotubes deposited on the fiber surface by the padding method. The next stage of treatment consisted of imparting superhydrophobic properties to the fabrics in solution with methyltrichlorosilane (MTCS) in a waterless medium. The tests performed show that the state of surface and water content in cotton fibers exerts a significant influence on the hydrophobic properties of the analyzed samples. In order to explain the differences in hydrophobic properties, the morphology of the cotton fabric surface was examined using samples with various water contents. The formation mechanism of MTCS coatings on cotton fabric has been proposed.

The mechanism of hydride transfer from silicon to a carbenium ion in a weakly nucleophilic medium

Abstract The reaction of hydrosilanes with triphenylmethylium hexafluoroantimonate in methylene chloride leads to the replacement by fluorine of hydrogen bound to silicon, and involves at least three steps. The first is hydride transfer leading to the formation of a positively-charged silicon intermediate. The second is the formation of an uncharged intermediate, which reacts in the third step to give the fluorosilane. Free carbenium ions and the corresponding ion pairs show similar reactivity towards hydrosilanes, indicating that the counter ion plays no role in hydride transfer. Effects of substituents at silicon on the reactivity are complex, and not those which might be expected if a simple trivalent silicenium ion were formed in the rate-determining step.

Polycondensation and disproportionation of an oligosiloxanol in the presence of a superbase

Abstract Kinetics of reactions of model oligosiloxanols, 1,1,3,3,3-pentamethyldisiloxane-1-ol (MDH) and 1,1,3,3,5,5,5-heptamethyltrisiloxane-1-ol (MD2H), which occur in the presence of phosphazenium superbase, hexapyrrolidine-diphosphazenium hydroxide, in an acid–base inert solvent, toluene, was studied using sampling and gas chromatographic analysis method. In addition, kinetics of reactions of MDH and MD2H with trimethylsilanol (MH) was studied. In the MDH and MD2H systems the oligosiloxanol condensation competes with the oligosiloxanol disproportionation, the latter being the dominating process. The disproportionation products, i.e. MDn+1H and MDn−1H, n=1, 2, … undergo analogous consecutive disproportionation and condensation reactions. The kinetic law was derived and rate parameters determined from initial rates and by computer simulation to the best agreement with experimental data. Both competing reactions, the disproportionation and the condensation, conform to the same general kinetic law being first internal order in substrate and first order in catalyst. Activation parameters of these reactions were determined. The results were interpreted in terms of a bimolecular mechanism in which nucleophilic attack of the silanolate anion directed to silicon of the silanol group causes the cleavage of one of its geminal bonds to oxygen, either the one to hydroxyl leading to condensation or the one to siloxane which leads to disproportionation. The latter is faster as the silanolate is a better leaving group compared with OH−. Moreover, in the pentacoordinate silicon transition state (or intermediate) the siloxane substituent preferentially enters the apical position, thus driving the OH substituent into the unreactive equatorial position.

Branched functionalised polysiloxane–silica hybrids for immobilisation of catalysts

Silica hybrids of functionalised polysiloxanes of well-defined structures, having various topologies (linear, comb-branched and dendritic-branched) and various densities of functional groups, were prepared. These hybrids were generated by the grafting of the polysiloxane to the prefunctionalised surface of porous silica particles. Polymers were obtained by living anionic ring opening polymerisation initiated by BuLi in THF of 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, V3, 2-(diphenylphosphino)ethyl-2,4,4,6,6-pentamethylcyclotrisiloxane, PD2, and by copolymerisations of V3 with hexamethylcyclotrisiloxane, D3 and with 2-vinyl-2,4,4,6,6-pentamethylcyclotrisiloxane, VD2. Living polysiloxanes were terminated on the –CH2CH2SiMe2Cl groups present on the modified silica surface. Vinyl groups, besides being the destination for the immobilisation of the metalloorganic catalyst, were also the precursors for the generation of –CH2CH2SiMe2Cl groups used for the grafting of living polysiloxanes to build comb-branched and dendritic-branched polymers on the hybrid structures. Dendritic and comb polysiloxanes were also synthesised separately and were then attached to the silica particle surface functionalised with –CH2CH2SiMe2OSiMe2H groups. A Pt(II) complex was attached to the vinyl groups of the hybrids. A high catalytic activity of this complex was found in the test reaction of hydrosilylation of 1-hexene by PhMe2SiH.

Synthesis and some properties of polyoxyhexakis (dimethylsilylene) and its copolymers with dimethylsiloxane

The synthesis of polyoxyhexakis(dimethylsilylene).1. by the hydrolytic polycondensation of α,ω-dichlorohexakisdimethylsilylene,2. and by cationic ring-opening polymerization of dodecamethyloxahexasilacycloheptane.6Dj, initiated with a protic acid is reported. The possibility of synthesis of alternative copolymers composed of oxyhexakis(dimethylsilylene) units and dimethylsiloxane or oligodimethylsiloxane units were also explored. Polymers are characterized by NMR spectroscopy. Their thermal behavior is discussed.

Controlled Synthesis of Siloxane Polymers and Siloxane-Siloxane Block Copolymers with 3-Chloropropyl Groups Pendant to the Siloxane Chain

Linear polysiloxanes bearing 3-chloropropyl groups pendant to the polymer chain and containing a vinyl functional group at one chain end were synthesized by anionic ring polymerizations of 2,4,6-tri(3-chloropropyl)-2,4,6-trimethylcyclotrisiloxane, 1, and 2-(3-chloropropyl)-2,4,4,6,6-pentamethylcyclotrisiloxane, 2, initiated with butyl lithium or lithium silanolate in tetrahydrofuran. The polymerizations led to high yields of polymers with narrow molecular weight distributions. The precise functionalizations of the polymers were performed by a termination method quenching the polymerization by dimethylvinylchlorosilane. Diblock copolymers AB of narrow molecular weight distribution and a high topological purity were obtained by the sequential anionic copolymerization of hexamethylcyclotrisiloxane, D 3 , with monomers 1 and 2.

Polysiloxane–silica hybrids from novel precursors by the sol–gel process

1,1,1,7-Tetramethoxy-3,3,5,5,7,7-hexamethyl-1,3,5,7-tetrasiloxane {TMOS-D3} and 1,1,1,7-tetramethoxy-3,5,7-trimethyl-3,5,7-trivinyl-1,3,5,7-tetrasiloxane {TMOS-V3} were made, respectively, by cationic telomerisation of hexamethylcyclotrisiloxane (D3) or 2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane (V3) with tetramethoxysilane (TMOS). These compounds were used as precursors of siloxane–silica materials. Their structure resulted in the generation of short trisiloxane segments which were well dispersed in the formed hybrid framework. These precursors or their mixtures with TMOS were subjected to sol–gel polycondensation in dispersions or in bulk catalysed by NaOH. Siloxane–silica hybrid materials were obtained either in the form of precipitated particles (1–80 µm) of various regular or irregular shapes or in the form of a monolithic material disintegrated on drying. In the sol–gel dispersion process, which was performed in the presence of a surfactant, cetyltrimethylammonium bromide, almost all methyl groups were converted to oxygen bridging two silicon atoms while in the bulk process a small fraction of unreacted alkoxyl and hydroxyl groups remained in the gel. Materials obtained from pure {TMOS-D3} and {TMOS-V3} showed a very low porosity and surface area. In contrast, particles having a high surface area can be obtained from mixtures of these new precursors and TMOS. Gels prepared from {TMOS-V3} and its mixture with TMOS were subjected to hydrosilylation with HMe2SiCl and the silylated particles were used for grafting of a living polysiloxane polymer.

Gamma Globulins Adsorption on Carbofunctional Polysiloxane Microspheres

Polysiloxane microspheres containing a large number of silanol groups were functionalized by reactions of these groups with organic alkoxy or chlorosilanes having chloro, amine or imidazole functions in their organic parts. The obtained imidazole groups on the microspheres were ionized by the reaction with n-octyl iodide and with methyl iodide while the chloro functions were used for quaternization of a tertiary amine. Adsorption of gamma globulins on these functionalized microspheres was studied in aqueous suspension at pH 5.2, 7.4 and 9.2. Hydrophilic–hydrophobic properties of these microspheres were examined by measuring adsorption of a hydrophobic dye, Rose Bengal. The functionalized microspheres showed higher adsorption of globulins and higher hydrophobicity than the not functionalized ones rich in silanol groups. In the case of microspheres with ionic functional groups the electrostatic forces also contribute to attractive interactions between proteins and microspheres.

Kinetics and mechanism of oligosiloxanol condensation and oligosiloxane rearrangement catalysed with model phosphonitrile chloride catalysts

Abstract The condensation kinetics of 1,1,3,3,3-pentamethyldisiloxanol (MDH) in n -heptane solution were compared for two types of phosphonitrilic catalyst, hexachloro-1 λ -diphosphaza-l-enium hexachloroantimonate salt, [Cl 3 PNPCl 3 ] + [SbCl 6 ] − , 1 , and P -trichloro- N -dichlorophosphoryle phosphazene, [Cl 3 PNP(O)Cl 2 ], 2 . The kinetic law of reaction is not changed when 1 is replaced by 2 . The process is selective leading to linear decamethyltetrasiloxane (MD 2 M, where D denotes the dimethylsiloxane unit, and M denotes the trimethylsiloxane unit) as almost the exclusive primary product. Other oligomers of the MD n M series are formed as a result of the MD 2 M rearrangement. The MD 2 M rearrangement was studied in separate experiments in the absence of the siloxanol and water. Both catalysts 1 and 2 gave similar rate—concentration behaviour. Some of the kinetic features of the process resemble those of chain reactions and mechanisms of the MDH condensation, and the MD 2 M rearrangement are discussed.