A. Ratsimihety

Synthesis of photocrosslinkable fluorinated polydimethylsiloxanes: Direct introduction of acrylic pendant groups via hydrosilylation

The synthesis of photocrosslinkable fluorinated polydimethylsiloxanes was achieved through direct hydrosilylation with copoly(dimethyl)(methyl-hydrogen) siloxane. First, the hydrosilylation of a fluorinated olefin allowed the introduction of a fluorinated group onto the polysiloxane. Then, a second hydrosilylation of allyl methyl methacrylate led to the polysiloxane bearing both fluorinated and photocrosslinkable groups. This method, compared with a previous method of copolycondensation, is shown to be easier and more efficient. All the new products synthesized were characterized by IR, 1H NMR, 19F NMR, and 29Si NMR. A formulation containing the fluorosilicone was crosslinked after being coated on a mesoporous membrane and was evaluated as a vapor permeation membrane.

Hybrid fluorinated silicones, 2 Synthesis and thermal properties of homopolymers and copolymers

The syntheses of various random and alternating copolymers of a fluorosiloxane and a hybrid fluorocarbon-fluorosiloxane are described, and their thermal properties are compared. The parent hybrid homopolymer and the random copolymers were prepared by silanol-chlorosilane condensation, while the alternating copolymers were prepared by silanol/N-bis(acetamidosilane) condensation. The polymers were analysed by 1 H, 19 F and 29 Si NMR spectroscopies and SEC chromatography. The influence of the backbone architecture on their thermal properties was evaluated by DSC and TGA: the copolymers (random or alternating) showed little variation among themselves but slightly better thermal characteristics at low temperature (T g lowered by about 10 to 15°C) than the parent hybrid homopolymer, whereas the parent homopolymer exhibited higher (15 °C) stability at high temperature.

HYBRID SILALKYLENE POLYSILOXANES: SYNTHESIS AND THERMAL PROPERTIES

Abstract The three-step synthesis of polysilalkylene siloxanes or hybrid silicones HO—[Si(CH3)(R)C2H4R′C2H4Si(R)(CH3)O]n—H is presented. First, the hydrosilylation of α,ω-dienes H2C CH—R′—CH CH2 (where R′ = C6H12 and C2H4) with various chlorosilanes HSi(CH3)(R)Cl (where R = CH3, C8H17, C6H5) is reported. Then, the obtained bis-chlorosilanes are quantitatively hydrolyzed into the corresponding bis-silanols. Finally, the bis-silanols are polycondensed in the presence of tetramethylguanidine/trifluoroacetic acid to give the hybrid silicones. All the products were characterized by 1H and 29Si NMR spectroscopies and the silicones were analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The influence of R and R′ groups on the thermal properties of the silicones is studied. These properties are compared to those of a polydimethylsiloxane (PDMS), a polyphenylmethyl-p-siloxane (PPMS) and a poly(para-silphenylene siloxane) HO—[Si(CH3)2—p-C6H4—Si(CH3)2O]n—H prepared from commercial PDMS and PPMS oligomers and from 1,4-bis(hydroxydimethyl)benzene.

Side Group Modified Polysiloxanes

The chemistry and technology of siloxane-based polymers, or silicones, is a very broad and still growing research area owing to their many unique properties such as thermal and oxidative stability, low surface tension, gas permeability, excellent dielectric properties, physiological inertness and moisture resistance [1–3]. Because of these properties silicones find a tremendous number of applications. Modifications of polysiloxane side groups are extensively explored in order to obtain polymers with special properties or to make them chemically active, thus giving access to new industrial applications. Polysiloxanes may be silicon-functional, i.e. the functional group, X, is directly attached to the silicon atom (Si-X), or organofunctional, i.e. the functional group is fixed via a Si-C alkylene or arylene group (Si-R-X). The most important functional groups include hydrogen, vinyl, chloro, hydroxy, mercapto, alkoxy, cyano, methacryloxy and amino groups. There are three general routes to obtain side groups modified polysiloxanes: modification of polysiloxanes, polycondensation of bisilafunctional monomers and ring-opening polymerisation of functional cyclosiloxanes.

REDISTRIBUTION OF DICHLOROSILANES AND DIHYDRIDOSILANES. SYNTHESIS OF CHLORO HYDRIDOSILANES

Abstract The redistribution of dichlorosilanes RSi(CH3)Cl2 and dihydridosilanes RSi(CH3)H2, prepared by reduction of the homologues dichlorosilanes, in the presence of a quaternary ammonium salt is presented. The influence of the nature of R (fluoroalkyl chain RFCH2CH2 with RF = CF3, C4F17, alkyl chain R [dbnd] C6H13 or aromatic R [dbnd] C6H5) and of the temperature on the rate of the reaction is studied. The equilibrium constants and free enthalpies are calculated and discussed taking into account the nature of R. The new products described were characterized from I.R. 1H, 19F and 29Si NMR spectroscopies.

Study of the alkylation of chlorosilanes. Part IV. Influence of the introduction of branched chains on the synthesis and properties of tetra(fluoroalkyl)-silanes and α,ω-fluoroalkylene disilanes

Abstract The synthesis and structural characterization of new tetra(fluoroalkyl (silanes, R 1 R 2 R 3 R 4 Si [where R i = (CH 2 ) n R F , n = 2 or 3, R F is a perfluorinated chain, linear or branched], and α,ω-fluoroalkylene disilanes, R 1 R 2 R 3 SiR′SiR 1 R 2 R 3 [R i = Me, -(CH 2 ) n R F and R′= - (CH 2 ) n R F ′(CH 2 ) n - are reported. The thermal properties of these new compounds together with those of all the silanes and disilanes previously prepared have been investigated by DSC. Their refractive indexes are also given.

Use of Original Fluorinated Telomers in the Synthesis of Hybrid Silicones

The wide use of fluorosilicones is the result of their combination of excellent properties: good resistance to heat, solvents, acids, alkalies, and oxidizing media. Gaskets for connectics, hydraulic fluids, and heat-carrier fluids still account for the largest number of applications. After a first generation proposed by Dow-Corning, fluorinated hybrid silicones based on well-architectured fluorooligomers built by controlled stepwise telomerization of various fluoroolefins are presented. Such cotelomers are very interesting precursors of functional or telechelic derivatives (containing hydroxy, carboxy, amine or unsaturated groups).

Radical crosslinking during polyhydrosilylation between fluorinated and silicone molecules: a model study

Abstract The present study deals with an explanation for crosslinking reactions that occur during the polyhydrosilylation of telechelic Si-H silicones with divinylperfluoro molecules. For a better understanding of the chemical process, a model reaction was performed and characterized by a full battery of techniques, including the different nuclei NMR analyses. Even if hydrosilylation occurs, side methyl groups on the silicon atoms also react with tert-butoxy radicals. Abstraction of a hydrogen radical from the methyl side group of the silicone chains allows the vinyl fluorinated molecules to add on polydimethylsiloxane and to bridge chains together.