F. Guida-Pietrasanta

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.

Synthesis, characterization, and thermal properties of anhydride terminated and allyl terminated oligoimides

This study concerns the synthesis of anhydride terminated oligoimides (ANTOI) and allyl terminated oligoimides (ALTOI), in acetic acid medium, which allows a very fast reaction and an easy working out. For the preparation of ALTOIs, two methods are compared: the first one consists of adding the monofunctional compound (allyl amine) to the ANTOI already formed during a first step by reaction of a dianhydride (excess) and a diamine. The second method consists of a “one pot” reaction between the dianhydride, the diamine, and the monofunctional allyl–amine compounds, at the beginning of the reaction. The experimental results show that the best control of the molecular weights is obtained with the first method. If the amount of allyl amine is higher than the amount necessary to end cap the ANTOI, a transimidization reaction occurs. Thermal analyses of oligoimides terminated by anhydride or allyl groups have been performed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Transition and thermoresistance properties make ANTOI and ALTOI derivatives interesting as precursors for block polyimide copolymers.

Evaluation of photocrosslinkable fluorinated polydimethylsiloxanes as gas permeation membranes

Abstract Dense permselective membranes were prepared from two series of polydimethylsiloxanes (PDMS) bearing fluorinated groups and acrylic or vinyl ether type photocrosslinkable groups linked to the polysiloxane chain through urethane bridges. These dense permselective membranes were evaluated for their application as gas permeation membrane for the purification of natural gas. Permeabilities and selectivities towards the CO2/CH4 gas pair were measured. This study showed that the selectivity increased with the introduction of C8F17 fluorinated groups and/or acrylic groups.

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.

Synthesis and applications of polysiloxanes containing photocrosslinkable oxaalkylene styrenyl groups

Abstract The synthesis of photocrosslinkable polysiloxanes containing (or not) alkylfluorinated groups and oxaalkylene styrenyl groups was performed. It was carried out either by modification of commercially available polysiloxanes bearing Si-vinyl groups which were reacted with 2-mercaptoethanol followed by addition of p-(chloromethyl)styrene, or by copolycondensation of α,ω-dihydroxy polydimethylsiloxanes and dichlorosilanes bearing acetoxy groups and dichlorosilanes bearing fluorinated groups. The introduction of styrene groups was then achieved by hydrolysis of the acetoxy group into the corresponding alcohol followed by reaction with p-(chloromethyl)styrene. The structure of the final products was determined by IR, 1 H and 13 C NMR spectroscopies. These products have been crosslinked under UV, in the presence of a cationic photoinitiator, and showed very good release paper properties and a good thermal resistance. The properties are enhanced when the copolymers contain fluorinated groups.

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.

Study of photocrosslinkable polysiloxanes bearing gem di-styrenyl groups Synthesis and thermal properties

Abstract The synthesis of photocrosslinkable polysiloxanes containing gem di-oxaalkylene styrenyl groups and gem di-urethane-α-methyl styrenyl groups has been performed by copolycondensation of α,ω-dihydroxy polydimethyl siloxanes and dichlorosilanes bearing either cyclic acetal groups or Si–H groups (onto which the cyclic acetal groups are further added) and dichlorosilanes bearing alkyl groups. The introduction of styrenyl groups was then achieved by hydrolysis of the acetal groups into the corresponding alcohols followed by reaction with chloromethyl styrene or with 3-isopropenyl-α,α- dimethylbenzyl isocyanate. The structure of the different products synthesized was determined by IR, 1 H, 13 C and 29 Si NMR spectroscopies. The thermal properties of the polysiloxanes bearing gem di-styrenyl groups have been studied at low and high temperatures. These products have been crosslinked under UV, in the presence of a cationic photoinitiator, and showed very good release paper properties.