Dimethylsiloxane Copolymer Research Articles

Preparation and characteristics of chitosan-g-PDMS copolymer

Chitosan-g-poly(dimethyl siloxane) (PDMS) copolymer was prepared by grafting PDMS prepolymer onto chitosan. PDMS prepolymer was prepared by ionic ring opening polymerization of octamethylcyclotrisiloxane (D 4 ) using n-buthyllithium (BuLi). The tensile strength and elongation of chitosan-g-PDMS copolymer were mostly constant regardless of PDMS prepolymer grafting %. While critical surface energy of chitosan is about 32 dyne/cm, that of chitosan-g-PDMS copolymer was a little decreased to 25∼29 dyne/cm by grafting PDMS onto chitosan.

N.m.r. analysis of poly(1,1,1-trifluoropropylmethylsiloxane- co-dimethylsiloxanes)

Oligomeric copolymers of dimethyl siloxane and 1,1,1-trifluoropropylmethyl sitoxane having functional amine groups at both ends were prepared and their microstructures were analysed by n.m.r. spectroscopic techniques. The compositions of these polymers were obtained by integration of the corresponding peaks of 1H n.m.r. spectra, while the monomer triad sequences were calculated from the SiC H 3 regions with the aid of curve fitting. Being oligomers, the polymers contain a significant amount of end groups, and the peak positions corresponding to the end SiC H 3 units that are contributing to the SiC H 3 regions were determined by two-dimensional 1H COSY spectroscopy. The compositions of the polymers were found to be almost equal to the feed ratios, and the monomer sequence distributions appeared to follow the Bernoullian statistics.

The thermogravimetric analysis of some polysiloxanes

Thermogravimetric (TG) and differential thermogravimetric analyses (DTG) of some homo- and copolymers of dimethylsiloxane have been performed. The effect of the presence of hydrido-substituents and/or vinyl end-groups on the thermal and thermo-oxidative stability of the examined polysiloxanes was determined. In all cases it was found that these polysiloxanes are thermally less stable than the parent all-methyl polysiloxane.

Quantitation in liquid chromatography of polymers: size-exclusion chromatography with dual detection

The problem of quantitation in size-exclusion chromatography (SEC) of polymers and oligomers is discussed, and a strategy for finding an appropriate combination of detectors and mobile phases for a given type of copolymer is described. This approach comprises the determination of response factors of different detectors for each homopolymer, and a simulation of dual detector SEC. The reliability of results is evaluated by analysis of homopolymers, polymer mixtures and copolymers of methyl methacrylate, ethylene oxide and dimethyl siloxane. Monodisperse fatty alcohol ethoxylates are used as models for block copolymers.

Optically active dimethylsiloxane copolymers with nucleophilic chiral sulfur groups pendant to the polysiloxane chain

Polydimethylsiloxanes with part of the siloxane units bearing an optically active sulfoxide group were synthesized. These copolymers had chiral sulfur centres connected to the siloxane chain by a dimethylene bridge. They were obtained mostly by the kinetically controlled anionic ring-opening polymerization of 1-(2-organothioethyl)1,3,3,5,5-pentamethylcyclotrisiloxanes, followed by stereoselective oxidation of prochiral groups to yield partially enantiomeric sulfoxide groups. Sulfoxides bearing cyclic monomers were also used. Polymers were characterized by spectroscopy and polarimetry. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 879–888, 1997

Optically active dimethylsiloxane copolymers with nucleophilic chiral sulfur groups pendant to the polysiloxane chain

Optically active dimethylsiloxane copolymers with nucleophilic chiral sulfur groups pendant to the polysiloxane chain

Optically active dimethylsiloxane copolymers with nucleophilic chiral sulfur groups pendant to the polysiloxane chain

Optically active dimethylsiloxane copolymers with nucleophilic chiral sulfur groups pendant to the polysiloxane chain

Hemocompatibility studies of surface-treated polyurethane-based chronic indwelling catheters

The objectives of this research were to evaluate and compare the interactions of several polyurethane-based central venous catheter materials with blood. Specifically, measurements of fibrinogen adsorption, platelet adhesion, kallikrein generation, and fibrinopeptide A (FPA) release were performed. The catheter materials examined in this study included: platinum-cured, 50 shore A durometer, barium sulfate-filled, silicone (SI); Tecoflex EG85A-B20 polyurethane (PU); PU catheters whose outer surface had been impregnated with ion beam-deposited silver atoms (AgI and AgII); PU catheters coated with a hydrophilic, polyacrylic acid polymer (UC); PU catheters coated with an air-cured PTFE emulsion (CS); and PU catheters coated with an aminofunctional dimethylsiloxane copolymer (JG). The time course of fibrinogen adsorption from plasma to the SI, JG, PU, and CS materials was similar, with CS exhibiting the least amount of adsorbed fibrinogen after 1 h (65±4.7 ng cm-2) and PU the greatest (144±16.5 ng cm-2). After 90 min of contact, AgI and AgII exhibited the greatest number of adherent platelets, levels that were approximately two to three times higher than those on the other catheter materials. With the exception of UC and PU, which caused kallikrein generation levels approximately half that of the positive (glass) control, little kallikrein formation was observed for any of the materials relative to the negative control. Finally, FPA generation was greatest using the SI, CS, and PU materials, with the latter causing the production of almost four times the amount of FPA as the negative control. This preliminary assessment of the hemocompatibility of the various catheters suggests that the surface treatments did not adversely affect their interactions with blood components; further investigations of these materials are therefore warranted in order to completely characterize their behavior prior to use in clinical situations.

Laser-Induced generation of thin silicone layers with high chemical and spectral purity

Excimer lasers (ArF, λ = 193 nm, and KrF, λ = 248 nm) were used to generate polymers free of additives such as catalysts, initiators, or sensitizers. The layers obtained are of potential interest for medical applications and future molecular electronics. Dimethylpolysiloxanes and dimethylsiloxane copolymers that contain phenyl-, n-hexyl- or 3.3.3-trifluoropropyl groups or silicon-bound hydrogen atoms were crosslinked in the liquid phase, whereby layer thicknesses in the range from 1–300 μm were obtained. Disiloxanes and alkoxysilanes were deposited from the gas phase (LCVD, laser chemical vapor deposition) resulting in layer thicknesses below 1 μm. In almost all cases, organic layers with a smooth surface, transparency, and good adhesion were obtained on silicon as well as quartz substrates. © 1994 John Wiley & Sons, Inc.

Influence of Isolated Chromophores on the Temperature Dependence of the Excimer Emission in Steady-State and Time-Resolved Fluorescence of Polysiloxanes

Steady-state fluorescence spectra and time-correlated emissions of a copolymer of dimethyl-siloxane and methylphenylsiloxane were measured, as a function of temperature, in the range -70 to 30°C. The stationary results indicate that the system is always, apparently, in the low-temperature limit, with a very low activation energy for excimer formation. Monomer decays are triexponential, and one of the components shows, at any temperature, a lifetime very similar to the monomeric analog. 29 Si NMR spectra demonstrate that the chromophore sequence distribution is very close to random and that about 79% of the phenyl units are isolated

Silicone acrylates through the hydrosilation of polyacryloyloxy functional monomers with copolymers of dimethyl and hydrogen methylsiloxanes

AbstractSilicone acrylates, as possible electron beam (EB) curable release coatings for paper, were prepared by the platinum‐catalyzed hydrosilation of polyacryloyloxy functional monomers with copolymers of dimethylsiloxane and hydrogen methylsiloxane (PDMHMS). The hydrosilation of either 1,6‐hexanediol diacrylate (HDDA) or trimethylolpropane triacrylate (TMPTA) with PDMHMS occurs to only one of the 2 or 3 available olefinic groups, respectively, as long as excess monomer is present. The amount of excess monomer needed to prevent gelation during hydrosilation or subsequent storage in excess of 1 month appears to be dependent on the hydrogen methylsiloxane content of the PDMHMS. A release coating having excellent cohesive and adhesive strength on paper was obtained by the EB curing of the product of hydrosilation of TMPTA with a PDMHMS containing 4 mol % hydrogen methylsiloxane at a dose‐to‐cure of 2 Mrad, but the aged release force was excessively high. The poor aged‐release performance was likely due to dilution of the dimethylsiloxane content of the coating with excess monomer required to stabilize the silicone acrylate. © 1993 John Wiley & Sons, Inc.

Fourier-transform infrared and electron spectroscopy for chemical analysis studies of block copolymers of styrene and dimethylsiloxane

The surface segregation of poly(dimethylsiloxane) (PDMS) in chloroform solution cast films of styrene and dimethylsiloxane block copolymers in AB diblock and ABA and BAB triblock types was investigated by ESCA and ATR-FTIR spectroscopy. The results show that the PDMS surface segregation is mainly dependent on the architectures of the block copolymers and the PDMS block length. AB-type diblock copolymers exhibit a relatively thicker pure PDMS surface layer and the PDMS surface segregation effects swere detected up to the ATR-FTIR sampling depth

Hydrosilylation crosslinking of silicone rubber catalyzed by bis (1,5‐cyclooctadiene) di‐μ,μ′‐chlorodirhodium

AbstractHydrosilylation vulcanization of addition silicone rubber catalyzed by bis (1,5‐cyclooctadiene) di‐μ,μ′‐chlorodirhodium at 150° was studied. The course of vulcanization, rubber network density, and mechanical properties of the vulcanizate are discussed with respect to the structure and molecular weight of the reactive groups of telechelic and internal vinylmethylpolysiloxanes and crosslinking methyl (hydrogen) dimethyl siloxane copolymers. Molecular weights of the polysiloxane components as well as the ration of unsaturated and Si—H groups were optimized. The results are in agreement with the theory of rubber elasticity of polymer networks and show wide application possibilities of the catalyst used.

Dipole Moment of Poly(methylphenylsiloxane) and Copolymers

The dielectric constant and the refractive index of several poly(methylphenylsiloxane) fractions (1.17×105≤Mw≤4.56×105) with well known tacticity and two copolymers of (dimethylsiloxane–methylphenylsiloxane) (4,200≤Mn≤6,400) were measured in cyclohexane solution, and in the case of the copolymers also in the bulk state. The copolymer compositions calculated by V-UV spectrometry were 54.3% and 9.5%, in (methylphenyl)siloxane content. A rotational isomeric state model was used to calculate the dipole moment ratio of the homopolymer. The theoretical value is in good agreement with the experimental one. A comparison of our results with those corresponding to other substituted polysiloxanes shows a very small variation of the dipole moment ratio with the nature of the substituent. The smaller values obtained for the dipole moment ratio of the copolymers in comparison with that of the homopolymer, could be attributed to the short chain length of the copolymers.

X‐ray investigations of liquid crystalline homo‐ and copolysiloxanes with paired mesogens

AbstractX‐ray scattering experiments on oriented polysiloxanes with paired mesogens and different distances between these swallow‐tailed side groups show a remarkable dependence of the smectic monolayer thickness on the degree of dilution, whereas the interplanar distance of the side groups remain nearly constant. Due to the dominating interaction of the mesogenic moieties, the flexible main chain is forced to take part in the layer formation. A packing model is proposed to explain the results of the X‐ray studies. For polymers with five or more dimethylsiloxane copolymer segments, a diffuse scattering appears in the smectic as well as in the isotropic phase. This scattering is independent of the orientation of the samples. It is probably caused by the main chain and has also been observed for the unsubstituted poly(hydrogenmethylsiloxane).

Preparation and properties of dimethyl phosphonomethyl methylsiloxane dimethylsiloxane copolymers

AbstractDimethyl phosphonomethylheptamethylcyclotetrasiloxane (II) and 1, 3‐bis(dimethyl phosphonomethyl)tetramethyldisiloxane (III) have been prepared by Arbuzov reaction of trimethyl phosphite with bromomethylheptamethylcyclotetrasiloxane (I) and 1, 3‐bis(bromomethyl)tetramethyldisiloxane, respectively. Dimethyl phosphonomethylmethylsiloxane dimethylsiloxane copolymers have been prepared by acid‐catalyzed ring‐opening polymerization of II with hexamethyldisiloxane (MM) as an end‐capping reagent and by reaction of II with III as an end‐capping reagent. Dimethylsiloxane polymers with dimethyl phosphonomethyldimethylsiloxy end groups have been prepared by acid‐catalyzed polymerization of octamethylcyclotetrasiloxane (D4) and III. Under these conditions hydrolysis of the dimethyl phosphonate ester groups was a problem. On the other hand Arbuzov reaction of trimethyl phosphite with bromomethylmethylsiloxane dimethylsiloxane copolymer gave a dimethyl phosphonomethylmethylsiloxane dimethylsiloxane copolymer with uniform properties. These polymers have been characterized by 1H‐, 13C‐, 29Si‐, and 31P‐NMR spectroscopy. Their molecular weight distributions have been determined by gel permeation chromatography (GPC) and their thermal stability measured by TGA.

Formula omitted] block and graft copolymers as selective permeable membranes

We synthesized tetramethyl-p- silphenylenesiloxane (TMPS) dimethylsiloxane (DMS) copolymers as selective permeable membranes for oxygen and nitrogen, and investigated the relation between their permeability and selectivity and microstructure after preparing some membranes by a solvent casting method. First, we examined the permeability of TMPS/DMS block and graft copolymers (DMS segment length 100) using measurements of dynamic viscoelasticity, crystallinity, melting temperature ( T m) and glass transition temperature ( T g). These measurements showed the permeability to increase by mixing the TMPS and DMS phases, thus disturbing the fold crystallinity of the TMPS phase. Accordingly we investigated the permeability of block copolymers having shorter DMS segment lengths (DMS segment length 40,20). The membranes with mixed microstructures with shorter DMS segment lengths were successfully synthesized and showed excellent permeability. The selectivity also increased by shortening the DMS segment length, the selectivity being affected considerably by the TMPS phase. In particular, one of the copolymers containing 19% DMS (segment length 20) showed high permeability ( P O 2 = 2.3 × 10 −8 cm 3 cm/s cm 2 cmHg) and high selectivity ( α = 3.0).

1,3‐Adamantanyl dimethylsiloxane copolymers. Preparation and properties

Abstract1,3‐bis(Dimethylhydroxysilyl)adamantane(I) has been prepared. Thermal condensation polymerization of this monomer yields poly‐1,3‐adamantyl‐1,1,3,3‐tetramethyldisiloxane. Condensation of I with bis(dimethylamino)dimethylsilane or 1,3‐bis(dimethylamino)‐1,1,3,3‐tetramethyldisiloxane gave the expected 1,3‐adamantyl dimethylsiloxane copolymers (II and III) respectively. These polymers have been characterized by 1H,13C, and 29SiNMR as well as GPC and TGA. They have unusually high thermal stability.

Thermal properties and relaxation transitions in copolymers of dimethylsiloxane with methyltrifluoropropylsiloxane

The linear thermal expansion coefficient, heat conductivity and dynamic and mechanical characteristics have been investigated for a number of copolymers of dimethylsiloxane with methyltrifluoropropyl in relation to the ratio of copolymer components over a wide range of temperatures. Relaxation transitions in these polymers have been examined by means of the radiothermoluminescence method. No effects related to processes of crystallization and melting were detected for the copolymers under study. The main β relaxation transition is displaced towards positive temperatures as the content of methyltrifluoropropyl units in the copolymer rises, besides which there is also a secondary γ transition that makes a major contribution to the glass transition process in the region of 150–160°K. A modified Simha-Boyer equation is presented to describe the multiple character of the glass transition process.

Thermal degradation of poly(tetramethyl‐p‐silphenylene) siloxane homopolymers and copolymers in nitrogen

AbstractThe thermogravimetry (TGA) in nitrogen was measured for poly(tetramethyl‐p‐silphenylene)‐siloxane (TMPS) fractions with narrow molecular weight distributions and for block copolymers of TMPS and dimethyl siloxane (DMS) with varying composition. The measurements were made with the Perkin‐Elmer DCS IB‐TGA attachment which consists of a Cahn electrobalance and a wire‐wound furnace with programmable temperature controls. The weight loss curves for heating rates of 10, 20, and 40°C/min were analyzed using the method of Flynn and Wall. The analysis indicates that thermal degradation proceeds primarily by scission of the siloxane bond with an activation energy of 44 ± 3 kcal/mole for the uncatalyzed reaction and 13 ± 2 kcal/mole for the reaction occurring in the presence of residual catalyst. The thermal stability of the TMPS–DMS copolymer is impaired through increasing the concentration of the DMS component. Cyclic DMS trimer and TMPS monomer and dimer were observed by mass spectrometry which gave results consistent with the proposed mechanism of degradation.