Siloxane Chain Research Articles

Poly(silyl ether)s by Ruthenium-Catalyzed Hydrosilylation Polymerization of Aliphatic ω-Dimethylsilyloxy Ketones and Copolymerization of Aliphatic α,ω-Diketones with α,ω-Dihydridooligodimethylsiloxanes

The hydrosilylation polymerization of aliphatic ω-dimethylsilyloxy ketones is catalyzed by activated dihydridocarbonyltris(triphenylphosphine)ruthenium (Ru) to yield unsymmetrical poly(silyl ether)s. Likewise, Ru catalyzes the copolymerization of aliphatic α,ω-diketones with α,ω-dihydridooligodimethylsiloxanes to yield symmetrical poly(silyl ether)s. These polymers have been characterized by 1H, 13C, and 29Si NMR as well as IR spectroscopy. Their molecular weight distributions (Mw/Mn) have been determined by GPC. End group analysis by 1H NMR provides an independent measure of Mn. Their thermal stability was measured by TGA, and their glass transition temperatures (Tg's) were determined by DSC. Chiral centers affect the NMR spectra of these poly(silyl ether)s. The effect of siloxane chain length on copolymer Tg has been evaluated.

Oligodimethylsiloxane Linked Cyanate Ester Resins

A series of dimethylsiloxane linked cyanate ester monomers (NCOC6H4(CH2)3(Si(CH3)2O)nSi(CH2)3C6H4OCN, n = 1, 2, 3) have been synthesized and characterized. Monomer melting points range from 5 to −12 °C, and characterization includes 1H, 13C NMR, and IR spectroscopies and DSC. Thermoset formation occurs by a cyclotrimerization of the cyanate group to a cyanurate structure. Cured resins are homogeneous rubbery castings with Tg ranging from 15 to −43 °C. Dielectric constants display little dependence on siloxane chain length but a strong dependence on frequency (2.5/15 GHz; 2.85/1 GHz). The corresponding loss tangent increases with siloxane chain length and displays a small frequency dependence.

Low‐modulus siloxane‐based polyurethanes. I. Effect of the chain extender 1,3‐bis(4‐hydroxybutyl)1,1,3,3‐tetramethyldisiloxane (BHTD) on properties and morphology

AbstractA series of eight polyurethane elastomers was prepared using a two‐step bulk polymerization procedure to investigate the effect of the siloxane chain extender 1,3‐bis(4‐hydroxybutyl)1,1,3,3‐tetramethyldisiloxane (BHTD) on polyurethane properties and morphology. All polyurethanes were based on 40 wt % hard segment derived from 4,4′‐methylenediphenyl diisocyanate (MDI) and a mixture of 1,4‐butanediol (BDO) and BHTD in varying molar ratios. The soft segment was based on an 80 : 20 (w/w) mixture of the macrodiols α,ω‐bis(6‐hydroxyethoxypropyl)polydimethylsiloxane (PDMS, MW 965) and poly(hexamethylene oxide) (PHMO, MW 714). Polyurethanes were characterized by size‐exclusion chromatography, tensile testing, differential scanning calorimetry, dynamic mechanical thermal analysis, and FTIR spectroscopy. Clear and transparent polymers were produced in all cases with number‐average molecular weights in the range of 90,000 to 111,000. The ultimate tensile strength decreased only slightly (15%), but Young's modulus and flexural modulus decreased by 76 and 72%, respectively, compared with that of the pure BDO extended polyurethanes as the amount of BHTD was increased to 40 mol %. This change resulted in “softer” and more elastic polyurethanes. Polyurethanes with BHTD contents above 40 mol % were more elastic but had poor tensile and tear strengths. A 60 : 40 molar ratio of BDO : BHTD produced a “soft” polyurethane, which combined good tensile strength and flexibility. The DSC and DMTA results confirmed that the incorporation of BHTD as part of the hard segment yielded polyurethanes with improved compatibility between hard and soft segments. IR data indicated that the amount of hard segments soluble in the soft‐segment phase increased with increasing BHTD, contributing to the improved phase mixing. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 736–746, 2002

29Si NMR and Si2p XPS correlation in polysiloxane membranes prepared by plasma enhanced chemical vapor deposition

Abstract Thin a-SiO x C y H z membranes were deposited from two different organosilicon precursors, a linear one the octamethyltrisiloxane (MDM) and a cyclic one the hexamethylcyclotrisiloxane (D3), in a low-frequency plasma polymerization process. The chemical structure of polysiloxane plasma materials was characterized using two different spectroscopic analyses: the X-ray Photoelectron Spectroscopy (XPS) and the 29 Si solid-state Nuclear Magnetic Resonance (NMR). Both techniques show that it is possible to synthesize a wide range of materials, more or less organic and close to silicone-type conventional polymers, depending on whether the energetic character of the plasma is low or high. The structural differences between plasma films synthesized from MDM (PP-MDM films) and plasma materials deposited from D3 (PP-D3 films) are all the more pronounced that the plasma conditions are soft due to the better preservation of the monomer chemical structure. The NMR analysis allows to display the presence of cyclic siloxane chains in PP-D3 layers whereas PP-MDM materials are exclusively composed of linear siloxane chains.

Synthesis of Copoly[arylene-1,2-dioxy/oligodimethylsiloxanylene]s by Ruthenium-Catalyzed Dehydrogenative Silylation Copolymerization of o-Quinones with α,ω-Dihydridooligodimethylsiloxanes

Activated dihydridocarbonyltris(triphenylphosphine)ruthenium (Ru) catalyzes the dehydrogenative silylation condensation copolymerization of o-quinones with α,ω-dihydridooligodimethylsiloxanes to give high molecular weight copoly(arylene-1,2-dioxy/oligodimethylsiloxanylene)s in good chemical yield. These copolymers have been characterized by 1H, 13C, and 29Si NMR as well as IR and UV. Their molecular weight distributions (Mw/Mn) have been determined by GPC. Their thermal stability was measured by TGA, and their glass transition temperatures (Tgs) were determined by DSC. The photoluminescence properties of the copolymers were studied along with those of two model compounds. The decrease in Tgs with increase in siloxane chain length as well as fluorescence spectra will be discussed. A mechanism of the copolymerization is proposed, in which, for these substrates, β-hydride elimination is favored over reductive elimination.

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, D3, with monomers 1 and 2.

Synthesis and Solid-State NMR Investigations of Radiation-Immobilized Polysiloxanes on Bare, Titanium-Grafted, and Zirconium-Grafted Silicas

Three different reversed-phase materials for high-performance liquid chromatography, obtained by sorption of poly(methyloctylsiloxane) (PMOS) onto bare silica, titanized silica, and zirconized silica pores, followed by immobilization with γ-radiation, were characterized by means of solid-state NMR spectroscopy. The surface properties of these stationary phases were investigated by 29 Si CP/MAS and 13 C CP/MAS NMR spectroscopy. γ-Radiation causes the formation of new bonds, either between PMOS and the different supports or between different siloxane chains, which leads, in either case, to a higher amount of polysiloxane immobilized onto the silica support material.

Metal Containing New Inorganic Ring Systems Based on Siloxane and Phosphazane Frameworks

High-field 31P NMR spectroscopy and single crystal X-ray diffraction studies have been used to study the ring opening and nucleophilic substitution reactions of the λ3-cyclotriphosphazane [EtNPCl]3. The synthesis of the ring opened silicophosphonate [RSi(OH){OP(O)(H)(OH)}]2O (R = (2,6-iPr2C6H3)NSiMe3) (1) represents the first ever molecular silicophosphonate to be isolated bearing free reactive hydroxyl groups. The structure and conformation of the bulky aryloxide substituted λ3-cyclotriphosphazane derivative [EtNP(OAr)]3 (Ar = 2,6-iPr2C6H3) (2) has also been investigated. Interaction of 2 with transition metal precursor complexes leads to the isolation of phosphazane metal complexes with different mode of co-ordination of 2. Further, the reaction of Cp ★Ti(OAr)Cl2 (Ar = 2,6-(CH3)2C6H3OH) with O{SiPh2(OH)}2 gave the eight-membered trititanosiloxane [Cp ★Ti(Cl) (O(SiPh2O)2SiPh2O) (3). Siloxane chain expansion effects, presumed to be a consequence of ring strain, have been observed in the product. The presence of reactive Ti-Cl bond in 3 offers opportunities for its reaction chemistry to be explored.

Photo-probe study of siloxane polymers: low-temperature structural relaxation in siloxane polymers probed by persistent spectral hole burning

We have investigated low-temperature structural relaxation in polysiloxane matrices by using persistent spectral hole burning (PSHB). The irreversible increase in hole width and the irreversible decrease in hole area were evaluated in terms of PSHB temperature-cycling experiments starting at 4 or 20 K. MQ-type silicone resins containing cross-linked nanoparticles (an uncured prepolymer mixture and cured MQ resins) and poly(methylphenylsiloxane) (PMPS) were used. The increase in hole width was observed at 15–20 K for all measured polysiloxanes. The increase is attributed to the local relaxation originating from the siloxane chains. The local structural relaxation of siloxane chains in this temperature range is confirmed for the first time. The local structural relaxation observed in the PSHB can be related to the rapid decrease in the final cis fraction between 4 and 20 K observed in the previous azobenzene photo-isomerization study. The curing effects of the MQ resin on the local relaxation are also discussed.

Investigations of morphology of moisture‐cured silicone–urethanes

Results of studies on synthesis and properties of siloxane–urethane prepolymers as well as on selected properties of moisture-cured silicone–urethanes have already been published. In this paper, some results of investigations of the effect of chemical structure of such silicone–urethane polymers on their phase seggregation investigated using mainly (TEM) transmission electron microscopy and small-angle x-ray scattering (SAXS) techniques are presented. It was found in TEM studies that in silicone-urethanes obtained by moisture-curing of NCO-terminated prepolymers prepared from siloxane oligomer diols (SOD) and isophoronediisocyanate (IPDI), two factors determine the morphology of samples: length of siloxane chain and NCO/OH ratio. SAXS investigations showed that these silicone–urethanes had a lamellar structure. It was found that the long period of this structure changed from 4 to 9 nanometers as the siloxane chain length increased nine times. The increase of the long period correlated with the decrease of Young's modulus of the corresponding samples. TEM investigations of silicone–urethanes obtained by moisture-curing of NCO-terminated prepolymers prepared from the blends of SOD and polyoxypropylenediol (PPG) revealed complex morphology which depended on the SOD/PPG ratio. Copyright © 2000 John Wiley & Sons, Ltd.

Synthesis and properties of polyurethane modified with an aminoethylaminopropyl-substituted polydimethylsiloxane. II. Waterborne polyurethanes

A series of polyurethane (PU) emulsions modified with aminosilicone were synthesized, based on 2,4-toluene diisocyanate (TDI), poly(tetramethylene oxide) (PTMO), and dimethylolpropionic acid (DMPA) as a prepolymer which was chain-extended with aminoethylaminopropyl polydimethylsiloxane (AEAPS) in an aqueous emulsion. Their chemical compositions, structures, bulk and surface properties, and emulsion morphologies were investigated using Fourier transform infrared spectrum analysis (FTIR), tensile and surface contact angle measurements, electron spectroscopy for chemical analysis (ESCA), water swellablity, an emulsion stability test, and transmission electron microscopy (TEM). It was shown that the PU emulsions were stable and the siloxane chains were enriched on the PU surface. The water resistance of the PU film increased but the bulk tensile properties of the PU film were not changed significantly with a small amount siloxane modification up to 6 wt %. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 295–301, 2001

Thermal Destruction of Polydimethyl-Siloxane on a Phosphorus-containing Silica Surface

Thermogravimetry, differential thermal analysis, and IR spectroscopy were used to investigate the process of thermal destruction of adsorbed polydimethylsiloxane (PDMS) in air. The disperse adsorbents were pristine fumed silica and modified fumed silica whose surface contained oxygen compounds of phosphorus. It was shown that under the given experimental conditions the thermal destruction of PDMS on the fumed silica surface was accompanied by the complete transformation of the adsorbed PDMS to SiO2. In the case of phosphorus-containing silica, the thermal destruction proceeded in a different way. It was found that at 140–300°C depolymerization of the siloxane chains of a certain part of the adsorbed polymer took place with the concurrent removal of volatile products of the reaction. However, the remaining part of the adsorbed PDMS interacted with the modified silica surface to form chemisorbed dimethylsilyl structures. The thermal destruction of the chemisorbed fragments of PDMS in air was initiated at 400°C or above for both types of silica investigated.

Hybrid plasma polymerized membranes from organosilicon precursors for gas separation

Thin a-SiO x C y H z films were deposited from different cyclic and linear organosilicon precursors in a radio-frequency plasma polymerization process. The plasma deposition and the film properties were characterized with respect to the deposition rate, the layers density and the chemical structure determined by FTIR and 29 Si NMR analysis. The qualification of the films for gas-selective membranes was tested on ester of cellulose substrates using N 2 , H 2 , O 2 , CO 2 and CH 4 . We are able to correlate both physico-chemical properties and permeation performances of the synthesized polymers with the composite parameter V/F.M (V: input voltage. F: monomer flow rate. M: monomer molecular weight) which describes the energetic character of the plasma. At low V/F.M ratios, the thin layers extremely preserve the monomeric structure and get close to polydimethylsiloxane; this resemblance is all the more considerable that the precursor siloxane chain is longer, and particularly pronounced using cyclic monomers. As V/F.M increases, the plasma polymers have a more inorganic structure and higher density: the materials tend towards a silica-like structure. Concurrently, the synthesized membranes exhibit solution-diffusion controlled or Knudsen-like separation factors depending on whether plasma conditions are soft (low V/F.M ratios) or drastic (high V/F.M ratios).

Manufacture and Physical Properties of Silicon-Organic Films for LC Alignment

Preparation of silicon-organic films for LC alignment is described. Effect of the molecular structure of organic substituents in siloxane chains on type of LC the alignment (homeotropic, tilted, planar) is considered. Contribution of polar and dispersion parts of the surface energy of siloxane films is discussed.

Dynamics of siloxane chains bearing phenyl chromophores

Dynamics of siloxane chains bearing phenyl chromophores

Dynamics of siloxane chains bearing phenyl chromophores

Molecular dynamics simulations are used to model the conformational motions associated with transitions between rotational states which may be responsible for the coupling between chromophores (excimer forming states) in the chains of poly(methylphenylsiloxane). Analysis of the trajectories show that the rotations around backbone bonds occur much faster than the coupling-uncoupling between the lateral chromophores. Although fast, the rotations around backbone bonds are strongly coordinated, each pair of Si-O-Si bonds rotating in a concerted fashion, such that the lateral phenyl groups (attached to the Si atoms) remain coupled over long times (many backbone rotations). The quantitative assessment of these results is established by calculating the correlation times for the backbone rotational angles (Si-O), for the distance separating chromophores (Ph…Ph), and for the lateral Si-Ph bonds. The relevance for the kinetics of excimer emission is discussed.

Photo-probe study of siloxane polymers. I. Local free volume of an MQ-type silicone resin containing crosslinked nanoparticles probed by photoisomerization of azobenzene

We have investigated the local free volume of an MQ-type silicone resin consisting only of M (R 3SiO 1/2) and Q (SiO 4/2) units by using photoisomerization of azobenzene molecularly dispersed in the matrices. Photoisomerization profiles in the uncured and cured MQ resin over a wide temperature range (4–300 K) are discussed based on three parameters: first-order plots, final cis fraction and quantum yields for trans-to-cis photoisomerization of azobenzene. For uncured MQ resins or prepolymers, for which the structure was proposed to be an assembly of crosslinked nanoparticles, a large fluctuation of local free volume was observed between room temperature and 20 K. At 4 K, a drastic decrease in the final cis fraction was observed in both the uncured prepolymer mixture and the cured MQ resin, implying the complete suppression of the free-volume fluctuation at 4 K. The formation of heterogeneous sites after curing is shown by the deviation from first-order kinetics for the cured MQ resins. Data for the cured MQ resin are analyzed quantitatively with the three-component approximation and the validity of a free-volume fluctuation model is verified. Comparison of the results for linear polysiloxanes with those for poly(methyl methacrylate) shows that siloxane chains are very flexible at low temperatures down to 20 K.

Preparation and Properties of Inorganic-Organic Hybrids From Vinyland 3-Methacryloxypropyltrimethoxysilane

ABSTRACTThe organic-inorganic polymer hybrids consisting of carbon-carbon and siloxane chains were prepared by radical polymerization of vinyltrimethoxysilane (VTS) and 3-methacryloxypropyltrimethoxysilane (MAS) followed by hydrolytic polycondensation. Polyvinyltrimethoxysilane (PVTS) and poly(3-methacryloxypropyltrimethoxysilane) (S-PMA) with various molecular weights Mw=3900–64800 were prepared by polyaddition of VTS and MAS, respectively. PVTS and S-PMA provided transparent and flexible free-standing films and coating films. With increasing carbon-carbon chain length, the elasticity of the films increased, while the tensile strength and Young's modulus decreased. The adhesive strength of the coating films on organic substrates was particularly dependent on the solubility parameter, polarity and crystallinity of each substrate. The pencil-hardness of coating films was clearly increased with increasing degree of condensation of sila-functional group in PVTS and S-PMA.

Preparation and properties of silicon-containing polymer hybrids from 3-methacryloxypropyltrimethoxysilane

The preparation of organic‐inorganic polymer hybrids consisting of carbon‐carbon and siloxane chains was investigated by radical polymerization of 3-methacryloxypropyltrimethoxysilane (MAS) followed by acid-catalyzed hydrolytic polycondensation. The condensation of poly(3-methacryloxypropyltrimethoxysilane) (S-PMA) of various molecular weights Mn = 830‐12000 prepared by polyaddition provided transparent and flexible free-standing hybrid gel films. The mechanical properties of these films were highly dependent on the carbon‐carbon chain length: with an increase in the carbon‐ carbon chain length, the elasticity of gel films increased, while the tensile strength and Young’s modulus decreased. Hydrolyzability of S-PMA decreased with an increase in the carbon‐carbon chain length, resulting in the formation of rubber-like films with flexibility. # 1998 John Wiley & Sons, Ltd.

Effect of permeation temperature on permeation and separation of a benzene/cyclohexane mixture through liquid‐crystalline polymer membranes

When a benzene/cyclohexane mixture of 10 wt % benzene was permeated through side-chain liquid-crystalline polymer (LCP) membranes by pervaporation at various temperatures, the permeation rate increased with increasing permeation temperature. The LCP membranes also exhibited a benzene permselectivity. The permselectivity for the benzene/cyclohexane mixture through the LCP membrane was different in the glassy, liquid-crystalline, and isotropic states. The LCP membrane had different apparent activation energies for permeation at each state. LCP membrane in the liquid-crystalline state had the highest apparent activation energy of the three states. Results suggest that the benzene permselectivity was influenced by changes in the LCP membrane structure, i.e., a state-transformation. It was found that a balance of the orientation of mesogenic groups and the flexibility of the siloxane chains was very important for benzene permselectivity. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 281–288, 1998