Polysiloxane Backbone Research Articles

Free-radical synthesis of new phosphorus-containing silane monomers and polysiloxanes

This paper deals with the synthesis of silane monomers and polysiloxanes bearing phosphorus compounds. Two reactive schemes were used. The first one was a direct hydrosilylation of unsaturated phosphonate on triethoxy silane. This reaction was too low and conversion rate was weak. Inversely, hydrosulfidation was very effective either with mercapto silane or mercapto polysiloxane. Thus, allyl and vinyl phosphonates were immobilized quantitatively on triethoxy mercaptopropyl silane monomer and on poly (dimethyl-co-mercapto propyl) siloxane. All the compounds were characterized by FTIR, 1H and 31P NMR. Thermogravimetric analysis of modified compounds shows clearly that the presence of phosphonic acid functions onto polysiloxane backbone decreases drastically the thermal stability.

Extraction resistant polymer stabilizers

AbstractA new generation of polysiloxane based polymer stabilizers is examined. The flexibility and versatility of polysiloxane backbones have allowed the development of a family of products that provide outstanding radical trapping efficiency, an unexpected resistance to extraction, and a high degree of compatibility in certain polymeric systems. Functionalization with graftable moieties results in a product that can be chemically bound to the polymer itself. The key to success in this work was optimizing the balance of graft linkages and mobility of the stabilizer chain.

Increasing the performance and permanence of polymer stabilizers

AbstractA new generation of polysiloxane based polymer stabilizers is examined. The flexibility and versatility of polysiloxane backbones have allowed the development of a family of products which provide outstanding radical trapping efficiency, an unexpected resistance to extraction, and a high degree of compatibility in certain polymeric systems. Functionalization with graftable moieties results in a product which can be chemically bound to the polymer itself. The key to success in this work was optimizing the balance of graft linkages and mobility of the stabilizer chain.

Thermally stimulated current and DSC studies of the dual glass transitions in side-chain liquid crystalline copolysiloxanes containing 4-[(S)-2-methylbutoxy]phenyl 3-chloro-4-alkenyloxybenzoate side groups

SUMMARY The synthesis of side-chain liquid crystalline copolysiloxanes containing 0-[4-[4-[(S2-methylbutoxy]phenoxycarbonyl]-2-chlorophenoxy]alkyl side groups is presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffractometry reveal smectic mesomorphism for most of the obtained polymers. The copolysiloxane with three methylene units in the spacer is the only one showing no mesomorphic property. The other four copolysiloxanes, containing four, five, six or eleven methylene units in the spacer, display a smectic A phase. All of the obtained polymers present dual glass transition behavior by both DSC and thermally stimulated current (TSC) techniques. The first glass transition (Tgl) at lower temperature is due to the segmental motions of the polysiloxane backbone, while the second glass transition (Tg2) is due to the cooperative relaxation motions of spacers and mesogenic units.

Laterally Aromatic Branched Two-Ring Mesogens Connected to Polysiloxane Backbone

Surprisingly, two-ring mesogens with a phenyl ring containing lateral segment can show liquid-crystalline behaviour. Linking to a polysiloxane backbone can be realized via three different para positions of the mesogens. Polymorphism and mesophase stabilization depend strongly on the position and type of substituents as well as on the length and position of the spacer.

Time-Resolved Fourier-Transform Infrared Spectroscopy on the Inter- and Intramolecular Orientational Dynamics in Ferroelectric Liquid Crystalline Dimers

On a base of time-resolved step-scan IR-spectroscopy data, we present a detailed model of the segmental reorientation during the ferroelectric and electroclinic switching of a chiral liquid crystalline dimer. We detected that the magnitude of the motion of the molecular segments differ from each other: The tilt angle is maximal for the mesogens and minimal for the ``virtual polysiloxane backbone.'' In contrast to a recently published conjecture, we prove that in the \ensuremath{\mu}s scale the responses of different molecular segments are unambiguously synchronous with each other.

Dicyanobiphenyl polysioloxane stationary phases for capillary column gas chromatography

The chromatographic performance of newly developed dicyanobiphenyl polysiloxane stationary phases were evaluated and compared with the performance of other polar stationary phases, including the previously reported monocyanobiphenyl polysiloxanes. Due to the unique combination of polarizable biphenyl and polar cyano functionalities in the side chains of the flexible polysiloxane backbone, and by virtue of their mild liquid crystalline properties, the new stationary phases provide excellent resolution of a wide variety of analytes, both polar and nonpolar, in both GC and SFC. They can be easily coated and cross-linked in open tubular columns, and the resultant columns demonstrate excellent efficiency and performance at temperatures up to 280–300°C. The new stationary phases exhibit enhanced selectivities for various types of isomeric compounds.

Synthesis, Characterization, and Properties of Stars Consisting of Many Polyisobutylene Arms Radiating from a Core of Condensed Cyclosiloxanes

Novel stars of many polyisobutylene(PIB) arms radiating from a core of condensed methylcyclosiloxanes are described. The synthesis involves hydrosilation of allyl-terminated PIB prearms by small methylcyclosiloxanes (e.g., D4H, D6H) and competitive moisture-mediated core−core coupling. The effect of conditions (e.g., time, temperature, stoichiometry, nature and molecular weight of prearms, and size of methylcyclosiloxane) on synthesis was investigated. The processes can be controlled and well-defined 21−28 arm stars have been perpared. Microstructures were characterized by various techniques. The intrinsic viscosities of stars are much lower than those of linear PIBs of the same molecular weight over the 30−100 °C range. Branching coefficients depend on the number of arms. Hydrodynamic volumes of stars and combs (polysiloxane backbone carrying PIB branches) are similar, indicating that both assume radial conformations. The stars are resistant to strong acids and bases indicating that resistant PIB coronas protect acid- and base-vulnerable cores. The temperature resistance of stars is similar to that of PIB.

Unusual behaviour of a new kind of side chain crown ether polysiloxanes used in capillary gas chromatography

A new side chain crown ether polysiloxane (PSCP-3-15C5) has been prepared and characterized in chromatography. Its chromatographic behaviour was compared with that of the other side chain crown ether polysiloxane (PSCP-11-15-C5), which has a longer spacer. The unusual effects caused by the length of the spacer on the polysiloxane backbone are described. An interesting phenomenon, liquid-liquid transition occurring in the measurement of phase transition on PSCP-3-15-C5, is discussed.

Synthesis and solid-state NMR structural characterization of some functionalized polysiloxanes

Polysiloxane-immobilized propylamine, diethylpropylamine and trimethylpropylammonium systems, and some other types of ligand systems, have been prepared. Polysiloxane-immobilized amine and trimethylpropylammonium chloride materials were made through hydrolytic condensation of Si(OEt)4 and (EtO)3Si(CH2)3X, with X = −NH2 or −N+ (CH3)3Cl−. The polysiloxane-immobilized diethylpropylamine ligand system was prepared by the reaction between the polysiloxane-immobilized 3-chloropropyl system and diethylamine. Polysiloxanes carrying the −CH2CO2Me group were made by the reaction of methylchloroacetate with polysiloxane-immobilized amine or thiol ligand systems, S−(CH2)3X (where X=−NH2 or −SH, and S represents the polysiloxane backbone). Polysiloxane-immobilized glycinate and iminodi-acetate systems were made by the reactions of sodium glycinate or disodium iminodiacetate with the polysiloxane-immobilized 3-chloropropyl system. Solid-state 13C and 29Si NMR spectroscopy, based on cross polarization (CP) and magic-angle spinning (MAS) techniques, were employed. 13C NMR results determined that, in the above-mentioned glycinate and iminodiacetate substitution reactions, the acetate groups of glycinate and iminodiacetate systems serve as the reaction site for displacement of the chloride in the polysiloxane-immobilized 3-chloropropyl system.

Polysiloxane-based photorefractive polymers for digital holographic data storage

A photorefractive polymer system based on a substituted polysiloxane backbone is described. In addition to high holographic diffraction efficiency and reasonable writing speed, the material reported exhibits excellent optical clarity and low optical scattering characteristics. These latter optical properties are necessary in high density holographic digital data storage applications. The utility of the polysiloxane based photorefractive polymers for storage applications is demonstrated by recording digital data at a density of 0.52 Mbit/cm2 and reading it back without error.

Stilbene-Containing Liquid Crystalline Side Chain Homo- and Copolysiloxanes: Microphase Separation and Chemical Modification to Electroconducting Materials

The phase behaviour of two classes of side chain polysiloxanes, containing respectively 4-cyano- and 4-alkoxy-4′-stilbene-ether mesogens, was studied over a wide temperature range by differential scanning calorimetry and wide angle X-ray diffraction, with special attention devoted to the characterisation of the microdomain phase morphology. Room temperature X-ray diffraction studies suggest for certain polymers with cyanostilbene mesogens the occurrence of microphase separation; this effect becomes significant as the amount of polysiloxane backbone versus the side chains increases. The onset of electrical conductivity was followed upon exposure of the polymeric films to various doping agents; conductivities up to 2 × 10−1 S cm−1 were measured when cyanostilbene-containing polymers were exposed to strong Lewis acids such as SO3 or SbF5. However, occurrence of some chemical degradation upon heavy doping and of electrode polarisation during DC conductivity measurements indicate that the observed electroconductivity is not purely electronic.

High pyroelectric sensitivity in alternate layer Langmuir-Blodgett superlattices

A family of polysiloxanes which have been designed for the purpose of achieving high pyroelectric activity in Langmuir-Blodgett (LB) film form is reported. The alternate layer LB deposition process has been used in which each siloxane monolayer (S) is co-deposited with a monomeric eicosylamine monolayer (E) to form alternate layer multilayer assemblies of the form SESESE… This approach ensures a macroscopic polarization within the LB film, which is an essential criterion for observation of the pyroelectric effect. Pyroelectric devices have been fabricated using aluminium electrodes and their pyroelectric sensitivity has been measured using a quasi-static technique. This collaborative study has involved investigating the effect on the pyroelectric response of (i) varying the degree of substitution on the polysiloxane backbone with aliphatic pendant side-chains, (ii) varying the length of the aliphatic pendant side-chains and (iii) incorporating polar aromatic pendant side-chains. This iterative strategy has led to an improvement in the pyroelectric coefficient from around 0.8 μC m −2 K −1 for an aliphatic substituted homopolymer to 4.6 μC m −2 K −1 for a copolysiloxane substituted with an aromatic pendant side-chain. The effects of LB film thickness (number of deposited monolayers) and the electrode overlap area have also been investigated and have brought about a further dramatic increase in activity to around 13 μC m −2 K −1. This is the highest pyroelectric coefficient ever reported for an alternate layer LB film assembly. It is believed that the activity of these thin films arises predominantly from the primary pyroelectric effect since an investigation into the response from two substrates possessing very different thermal expansion coefficients yielded almost identical behaviour, suggesting that the secondary piezoelectric component is small.

Polysiloxane-based biomembranes

Natural phosphatidylcholine was attached to a polysiloxane backbone. The Langmuir film, Langmuir-Blodgett deposition and Montal-Mueller properties were studied. The material forms exceptionally stable Langmuir films. Montal-Mueller bilayers have a resistance of about 2 × 10 4 Ω cm −2 and a breakdown voltage of about 350 mV. Langmuir-Blodgett bilayer films have a low-voltage resistance of about 2 × 10 5 Ω cm −2, a transition to a square-law dependence at around 0.1 V, and a breakdown voltage greater than 1 V. There is evidence that bacteriorhodopsin in readily incorporated into such films.

A convenient synthesis of a permethyl‐substituted β‐cyclodextrin‐containing polysiloxane stationary phase using an amide linking group

AbstractA novel amide‐linked permethyl‐substituted β‐cyclodextrin‐bound polysiloxane stationary phase was prepared in only four steps. First, mono(6‐O‐toluenesulfonyl)‐β‐cyclodextrin was treated with sodium azide. Second, the resulting azide derivative was treated with methyl iodide and base followed by reduction with hydrogen to give amine‐substituted permethylcyclodextrin 3. Third, cyclodextrin 3 was treated with p‐(allyloxy)benzoyl chloride to form 6A‐(p‐allyloxybenzamido)‐substituted permethyl‐β‐cyclodextrin 4. Lastly, β‐cyclodextrin 4 was hydrosilylated onto a polysiloxane backbone containing hydrogen, methyl, and p‐tolyl substituents. This new phase separated the enantiomers of certain chiral lactones and alcohols in capillary supercritical fluid chromatography.

Preparation and thermal characterisation of some new liquid crystalline copolymers involving a spacer unit based on vinylacetic acid

Three series of new liquid crystalline (LC) copolymers having a polysiloxane backbone and two different mesogenic pendant groups, one involving a vinylacetic acid moiety in the spacer, have been synthesised. Thermal characterisation of these polymeers has allowed comparison of behaviour between a number of different copolymer systems. It was found that increasing amounts of the vinylacetic acid moiety lowered the clearing points (Ti) of the copolymers in an almost linear fashion whilst also inhibiting crystallinity in these polymers.

Enhanced selectivity in the analysis of chlorobiphenyls on a carborane phenylmethylsiloxane copolymer gas chromatography phase (HT-8)

The congener specific analysis of polychlorinated biphenyls (PCBs) on a new chemically bonded stationary GC phase, HT-8 (1,7-dicarba-closo-dodecarborane phenylmethyl siloxane) is investigated. The incorporation of carborane in the polysiloxane backbone enhances selectivity and temperature stability of the phase. On a 60 m × 0.25 mm I.D. fused-silica column coated with 0.25 μm HT-8, a total of 106 congeners in Aroclor mixtures elute as separated peaks. By the use of mass spectrometric detection 138 congeners can be analysed without interference from coeluting PCBs. In literature, no other GC phase has been reported with such a high PCB selectivity. An interesting feature of HT-8 is its near-baseline separation of the critical pair CB138/CB163. Separations for these congeners on other GC phases are reviewed. The performance of a thin film (0.15 μm) version of the HT-8 column with fast temperature programming is tested. It is concluded that congener-specific, rapid screening of seven indicator PCBs (CB28, CB52, CB101, CB118, CB138, CB153 and CB180) with a total GC run-time of 13 min is feasible with an accuracy sufficient for most purposes.

Piezoelectric and pyroelectric properties of new polysiloxane smectic C ∗ elastomers

We investigated the pyroelectric and piezoelectric effects of new smectic C ∗ liquid crystalline elastomers. The materials are made up of a flexible polysiloxane backbone bearing chiral mesogenic side groups and are cross-linked via alkylene chains. The polar structure of the mesophase is evidenced by the observation of piezoelectric and pyroelectric effects. Integration of the pyroelectric coefficient over the whole smectic C ∗ stability range allows the determination of the spontaneous polarization ( P S = 3–6 nC/cm 2). Due to the rubber elasticity, these materials exhibit a high piezoelectric response. The piezosignal at room temperature does not vanish after annealing at temperatures even much higher than the Curie point. The piezoelectric coefficient d 31 ranges from 0.5 pC/N for non-poled samples to 2.5 pC/N after application of a poling field.

Backbone modification of Chirasil-Val: Effect of nonpolar side chains on enantiomer separation in gas chromatography

The polysiloxane backbone of the gas chromatography phase Chirasil-Val has been modified by replacing one methyl group per dialkylsiloxy unit by pentyl and hexyl groups, respectively. The new phases offer the advantage of reduced polarities and softening points, while the separation factors (α) of enantiomeric pairs of N,O-trifluoroacetyl amino acid propyl esters show small but intriguing deviations from those determined on Chirasil-Val.

Backbone modification of Chirasil-Val I. Effect of loading on the separation of enantiomers by gas chromatography

Abstract For the gas chromatographic phase Chirasil-Val, the effect of loading of the polysiloxane backbone with l -valine tert.-butylamide units on the chromatographic properties is described. For three enantiomeric pairs of N-trifluoroacetyl amino acid n-propyl esters, a maximum separation factor (α) was observed when the ratio x:y of x dimethylsiloxane units per y chirally modified dialkyl siloxane units was adjusted to the range of x:y = 5.6−5.9; whereas a ratio x:y = 7 has proven more suitable for the complete separation of all 39 components present in a mixture of the 20 proteinogenic amino acids.