Julian Chojnowski

Biocidal polymers active by contact. V. Synthesis of polysiloxanes with biocidal activity

Polysiloxanes with 3-(alkyldimethylammonio)propyl pendant groups were synthesized by quaternization of n-octyldimethylamine or n-dodecyldimethylamine with linear polysiloxanes containing 3-chloropropyl groups and/or 3-bromopropyl groups attached to silicon atoms. The precursor polysiloxanes, poly[(3-chloropropyl)methylsiloxane] homopolymer and various copolymers containing (3-halogenopropyl)methylsiloxane and dimethylsiloxane units, were obtained by equilibrium cationic polymerization of linear and cyclic siloxanes with (3-halogenopropyl)methylsiloxane units. The polysiloxanes bearing quaternary ammonium salts (QAS) showed bactericidal activity against bacteria such as Escherichia coli and Aeromonas hydrophila when incorporated in a polysiloxane network. The activity was retained after 66 days of immersion in water. The QAS-containing polysiloxanes are also active in aqueous solution.

Synthetic and mechanistic aspects of the reaction of trialkylsilyl halides with thio and seleno esters of phosphorus

Abstract A study is described of the reaction of trimethylbromosilane and trimethyliodosilane with various esters of phosphorothioic and phosphoroselenoic acids of general structures (RO) 2 (RY)P=O (I) and (RO) 3 P=Y (II) (Y = S or Se, R = alkyl). The reaction results in replacement of the R groups by trimethylsilyl groups. No S -trimethylsilyl and Se -trimethylsilyl substituted esters were found among the products. Thus the displacement of the O -R group in II as well as the replacement of S -organyl or Se -organyl groups in I both lead to the corresponding O -trimethylsilyl isomer containing thiophosphoryl or selenophosphoryl groups. The following sequence of reactivity of the ester groups was observed: Download full-size image The process involves initially the reversible formation of a phosphonium salt intermediate in a fast step, followed by slow dealkylation. It was shown by low temperature 31 P FT-NMR studies that in the reaction of trimethyliodosilane with an ester bearing a P=O phosphoryl group, the equilibrium for the phosphonium salt formation lies well over towards the intermediate and so the intermediate can be observed directly. These mechanistic proposals were confirmed by conductance studies on the reaction system and by investigation of the stereochemical course of the corresponding reaction of an optically-active model thiophosphonate. In some cases the reaction of the halosilanes with the phosphates takes a selective course which allows the reaction to be used as a convenient route to O -silyl substituted esters of phosphorothioic or phosphoroselenoic acids.

Modification of polysiloxanes by free-radical addition of pyridylthiols to the vinyl groups of the polymer

Abstract Polysiloxanes containing pyridyl groups were prepared by thiol-ene addition to vinyl side groups of polysiloxanes. Apart from polymethylvinylsiloxane, poly(methylvinylsiloxane-co-dimethylsiloxane)s synthesized by three different methods were used: (1) equilibrium copolymerization of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (V4) with hexamethylcyclotrisiloxane (D3); (2) kinetically controlled homopolymerization of 1-vinyl-1,3,3,5,5-pentamethylcyclotrisiloxane; and (3) kinetically controlled copolymerization of V4 and D3, which permitted us to obtain siloxane copolymers with different arrangements of the pyridyl groups along the chain. Addition of 2-(4-pyridyl)ethanethiol (PET) to the vinyl groups of these polymers proceeded with high yields, leading preferentially to β-addition products. The addition of 4-pyridylthiol (PT) proceeded much less readily. Polymers were characterized by FT-IR, 1H and 13C NMR, and by thermal analytical methods.

Condensation of model linear siloxane oligomers possessing silanol and silyl chloride end groups: the mechanism of silanol silylation by a chlorosilane in the presence of neutral nucleophiles

Abstract The condensation of pentamethyldisiloxane-1-ol (1) with 1-chloro-1-isopropyltetramethyldisiloxane (2) in methylene chloride solution has been studied as model of the polyheterocondensation of functional oligosiloxanes. The process catalysed by triethylamine, hexamethylphosphoroamide (HMPA) or some nitrogen heterocycles showed a high selectivity towards heterocondensation. Triethylamine promotes the reaction by acting as the base bonding to the incipient proton on the silanol group entering into the condensation. This mechanism of the catalysis by Et3N was demonstrated by kinetic studies involving use of gas-liquid chromatography in conjunction with study of the hydrogen bonding by IR spectroscopy. In contrast, the kinetic data and the reactivity pattern indicate that N-heterocycles and HMPA catalyse the reaction by functioning as nucleophiles to form a transient complex with the chloride substrate. A mixture containing a highly nucleophilic N-heterocycle, triethylamine has no effect on the rate of the reaction, acting only as a HCl acceptor.

Kinetically controlled siloxane ring-opening polymerization

Some basic aspects of the kinetics and mechanisms of anionic and cationic ring-opening polymerization of cyclic siloxanes are discussed in connection with their use in polymer synthesis. The emphasis is put on the polymerization of strained ring monomers, such as cyclic trisiloxanes, since these provide the possibility of tailoring the polymer structure. Much attention is devoted to association phenomena and to oligomer formation processes.

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).

Organic polysilanes interrupted by heteroatoms

Abstract This review article covers the synthesis and properties of organic polysilanes having SiSi sequences interrupted by heteroatoms. Thus, as a rule, silicon based polymers which have ∼SiSiX∼ fragments in the skeleton are regarded, where X are atoms of Groups VIA, VA, IVA (excluding carbon), IIIA, as well as atoms of metals. X may be also a characteristic group of atoms, such as silole or metallocene. Particular attention is paid to polysilanes interrupted by oxygen in a regular way, as these polymers can be considered as silicon analogues of polyethers. Since their structure is a hybrid of those of polysilane and polysiloxane, the knowledge of the behavior of these polymers permits a deeper understanding of the chemistry of polysiloxanes and polysilanes. This is the reason why oxygen interrupted polysilanes have been studied more extensively than the polysilanes interrupted by other heteroatoms. Methods of the synthesis of these polymers, including mechanism and equilibria of the ring-opening polymerization of (SiMe 2 O) 2 , are discussed. Some attention is also devoted to thermal properties and morphology. The article is concluded by a section in which prospective practical uses of polysilanes interrupted by heteroatoms are discussed.

The reactivity of monomeric silanol intermediates in the hydrolytic polycondensation of tetraethoxysilane in acidic media

Abstract Trimethylsilylation-gas-liquid chromatography techniques combined with computer simulation were used to study the acid catalyzed hydrolytic polycondensation of tetraethoxysilane (TEOS) in dioxane solution. The kinetics of the initial period of this process, in which the reactions of Q 0 species, i.e. monomer and hydroxysilanes derived from the monomer, predominate, were investigated. Rate constants of some individual component reactions of the Q 0 intermediates were estimated. The reactivity in all three reactions of compounds of (EtO) 4 − n Si(OH) n series, i.e. hydrolysis ethanolysis and condensation, strongly increases with the number of hydroxyl groups n . It was also demonstrated that the ethanolysis reactions play an important role in the overall process since they control concentration of hydroxyl-substituted silane intermediates.

Thermal decomposition of poly(tetramethyloxydisilaethylene)

Thermal decomposition of poly[oxybis(dimethylsilylene)] having chains terminated with trimethylsiloxy groups was studied by thermogravimetry, pyrolysis-mass spectrometry, and infrared spectroscopy. The polymer is thermally less stable than poly(dimethylsiloxane). Depolymerization occurs at temperatures of 250–350°C, although this process also takes place at lower temperatures. The depolymerization produces cyclic oligomers of general formula [(Me2Si)2O]n, with predominant formation of the oligomern=2. The depolymerization is accompanied by processes which are referred to as restructurization because they change the structure of the polymer backbone. Decomposition may lead also to the formation of branching points. The shape of the thermograms taken under isothermal conditions is in agreement with an unzipping mechanism for depolymerization involving random initiation. Excluding the short initial period of the process, the unzipping is terminated at a restructurization point. A low activation energy points to initiation induced by electron transfer, presumably involving traces of contaminant. At higher temperatures, 350–600°C, loss of organic parts of the polymer takes place along with further restructurization. At higher temperatures the polymer was also found to undergo easily oxygenation of its backbone with atmospheric oxygen, which leads to the formation of siloxane groups.

The nature of the interaction between hexamethyl-phosphortriamide and trimethylhalosilanes; cations containing tetracovalent silicon as possible intermediates in nucleophile-induced substitution of silicon halides

Stable ionic 11 adducts, thought to be of the type [(Me2N)3POSiMe3]+X− have been isolated from the interaction of HMPT with the halides Me3SiX (X  Br or I). Conductometric studies show that the equilibrium for formation of these adducts in CH2Cl2 lies well over to the products for X  Br or I, but for X  Cl the equilibrium lies close to the reactants. The known kinetic characteristics of reaction involving HMPT-catalysed racemisations or substitutions of silicon halides can be interpreted in terms of the formation of such phosphonium intermediates.