Polydimethylsiloxane Rubber Research Articles

Fullerene C 60 as an antioxidant for polymers

The antioxidative activity of fullerene C 60 has been studied by model reaction of the initiated oxidation of cumene and also in accelerated tests of the mixtures with polystyrene and polydimethylsiloxane rubber. It was established that the initiation rate of the model oxidation is substantially reduced in the presence of C 60. The rate constant for the addition of cumyl radicals to C 60 was determined as k (333–353 K)=(2.0 ±0.8)·10 8 M −1 s −1. In accelerated tests fullerene showed a stabilizing effect comparable with the influence of the sterically-hindered phenol Irganox1076.

Composite material for medical application

AbstractComposite material for medical application on the basis of polydimethylsiloxane rubber (PDMS) and graphite was obtained. The physico‐chemical and mechanical properties of the material depending on the quantity, purity of the modifier and its preliminary treatment were studied. The established physico‐chemical properties of the material surface allow to make the preliminary prediction of its thromboresistance.

Reactive blending of ethylene-methylacrylate copolymer and poly-dimethyl siloxane rubber: kinetics studies from infrared spectroscopy

Reactive blending of ethylene-methylacrylate copolymer and poly-dimethyl siloxane rubber: kinetics studies from infrared spectroscopy

An investigation into the mechanical properties and curing kinetics of blends of low-density polyethylene and polydimethyl siloxane rubber

Curing reactions of low-density polyethylene (LDPE) and polydimethylsiloxane (PDMS) rubber blends have been investigated by Differential Scanning Calorimetry (DSC) and by Rheometry. From the DSC thermograms the kinetic parameters have been calculated. The order of the reaction has been found to be first order. The optimum level of peroxide was found to be 1.5 pbw. The activation energy of the blends was found to be higher than that calculated as per additivity rule which is indicative of an interaction of the blends constituents. Improved mechanical properties of the blends on curing is indicative of cure compatibility of the blends.

Sorption of low molar mass silicones in silicone elastomers

AbstractElastomers based on polydimethylsiloxane (PDMS) are used as insulating material in outdoor electrical power applications. It is believed that migration of small molecule PDMS species plays an important role in the recovery of hydrophobicity of oxidized or polluted PDMS elastomer surfaces. This paper reports data on diffusivity and solubility of low molar mass PDMS liquids in PDMS rubbers (8000 < Mc < 16,000 g/mol) obtained by sorption measurements. It was found that the diffusivity (D) of linear PDMS liquids was approximately independent of the concentration of penetrant and that in the molar mass range 400 < Mc < 18,000 g/mol it decreased with molar mass (Mc) of the diffusing liquid according to D α Mc−0.8. Theory and previous data for other oligomers and elastomers predict that D is proportional to M−1. Linear PDMS liquids of lower molar mass exhibited a stronger molar mass dependence. The diffusivity of a given PDMS liquid increased with increasing elastomer crosslink density. The activation energy of the diffusivity was constant at 15.5 ± 2 kJ/mol for linear PDMS liquids of Mc larger than 1000 g/mol−1 with only a negligible influence of network density and filler content. The activation energy of the lowest molar mass penetrant was considerably lower, 6 to 7 kJ/mol. The solubility increased markedly with decreasing molar mass of the penetrant and with decreasing elastomer crosslink density.

Kinetic investigation on the curing of ethylene methyl acrylate—Polydimethyl siloxane rubber blends by differential scanning calorimetry

Curing reactions of ethylene methyl acrylate (EMA) polydimethyl siloxane (PDMS) rubber blends have been investigated by differential scanning calorimetry (DSC) and by Rheometry. The curing exoterms obtained from DSC curves have been analysed to derive the kinetic parameters associated with the curing process. Crosslinking of EMA-PDMS rubber blends follow first order kinetics. The effect of blend ratio and peroxide concentration on the crosslinking characteristics of the blends have also been investigated.

Surface and blood‐contacting properties of alkylsiloxane monolayers supported on silicone rubber

Self-assembled monolayers of alkylsiloxanes supported on polydimethyl siloxane (PDMS) rubber were used as model systems to study the relation between blood compatibility and surface chemistry. The inner lumen of PDMS tubes was first treated with an oxygen plasma. The resultant oxidized surfaces were postderivatized by reacting them with alkyltrichlorosilanes to form the monolayer films. The chemical properties of the monolayers were controlled by varying the head-group chemical compositions. Surface derivatization was verified using variable-angle X-ray photoelectron spectroscopy (XPS or ESCA). Blood compatibility was evaluated using a canine ex vivo arteriovenous series shunt model. Surfaces grafted with hydrophobic head-groups as -CH3 and -CF3 had significantly lower platelet and fibrinogen deposition than the surfaces composed of hydrophilic groups such as -CO2CH3, -(CH2CH2O)3COCH3, and -(OCH2CH2)3OH.

In‐situ compatibilization of thermoplastic polyurethane and polydimethyl siloxane rubber by using ethylene methyl acrylate copolymer as a reactive polymeric compatibilizer

AbstractThe effect of Ethylene Methyl Acrylate (EMA) copolymer as a reactive polymeric compatibilizer in a blend of 50:50 Thermoplastic Polyurethane (TPU)‐Polydimethylsiloxane (PDMS) rubber has been studied. The compatibility was proved by mechanical property measurements and phase morphology studies. EMA reacted with PDMS rubber at 180°C at 100 rpm rotor speed during melt mixing to produce EMA‐g‐PDMS rubber in situ, which acted as the compatibilizer for the binary system of TPU and PDMS rubber. EMA‐g‐PDMS rubber is believed to undergo specific interaction via hydrogen bonding with the TPU matrix through the CO group of EMA and the unassociated NH group of TPU, whereas the PDMS rubber in the EMA‐g‐PDMS disperses well with the bulk PDMS matrix. The phase morphology studies showed a drastic reduction in the size of the dispersed phase at the optimum concentration of EMA. © 1995 John Wiley & Sons, Inc.

Studies on Reaction Mechanism Between Ethylene-Methyl Acrylate Copolymer and Poly Dimethyl Siloxane Rubber Processed Under High Shear and Temperature

Abstract Blending of ethylene–methyl acrylate (EMA) copolymer and polydimethyl siloxane (PDMS) rubber led to miscibility of the two components under the processing conditions of 180°C and 100 rpm rotor speed, and the miscibility was assumed to be due to reaction between EMA and PDMS rubber. A plausible mechanism has been suggested. The mechanism has been confirmed by infrared and solid-state MAS nuclear magnetic resonance spectroscopy, which show a reduction in the vinyl group concentration of PDMS rubber and an increase in the[sbnd]CH2[sbnd]bridge concentration of EMA in the vicinity of the α-carbon atom in the blend.

Studies on miscibility of blends of ethylene methyl acrylate and polydimethyl siloxane rubber

AbstractBlends of ethylene methyl acrylate (EMA) and poly(dimethylsiloxane) rubber (PDMS) are demonstrated to be miscible. The miscibility results in a single and composition‐dependent glass transition temperature. IR spectra of the blends provide direct evidence of chemical reaction between EMA and PDMS rubber.

In situ compatibilization of low‐density polyethylene and polydimethylsiloxane rubber blends using ethylene–methyl acrylate copolymer as a chemical compatibilizer

AbstractThe effect of the ethylene–methylacrylate copolymer as a chemical compatibilizer in the 50:50 blend of low‐density polyethylene (LDPE) and polydimethylsiloxane rubber (PDMS) has been studied in detail. Ethylene–methylacrylate (EMA) reacted with PDMS rubber during melt‐mixing at 180°C to form EMA‐grafted PDMS rubber (EMA‐g‐PDMS) in situ, which acted as a compatibilizer in the LDPE–PDMS rubber blend. An optimum proportion of the compatibilizer (EMA) was found to be 6 wt % based on results of dynamic mechanical analysis, adhesion studies, and phase morphology. Lap shear adhesion between the phases increased significantly on incorporation of 6 wt % of EMA. Dynamic mechanical analysis showed a single glass transition (Tg) peak at −119°C. This was further supported by X‐ray diffraction studies, which exhibited a remarkable increase in the degree of crystallinity and phase morphology and showed a drastic reduction in the size of the dispersed phase at the optimum concentration of EMA. © 1993 John Wiley & Sons, Inc.

Thermogravimetric studies on miscible blends of ethylene-methyl acrylate copolymer (EMA) and polydimethylsiloxane rubber (PDMS)

Thermogravimetric and derivative thermogravimetric analysis of blends of ethylenemethyl acrylate copolymer and polydimethylsiloxane of different compositions have been investigated. Curves of weight loss and derivative weight loss against temperature show that degradation takes place in two steps with peak maxima, at T 1max and T 2max, both proportional to the components in the blends. Kinetic studies show that the degradation of the blends and that of the single components follow first order reaction kinetics. Activation energies of the degradation have been determined using Freeman and Carroll's method and the thermal stability of the blends has been investigated.

Interfacial reactions and self-adhesion of polydimethylsiloxanes

Polydimethylsiloxane (PDMS) oil and crosslinked rubber react with hydroxylated surfaces, when heated at 250-300°C. PDMS is thus chemically bound to silicate glass sheets and to iron hydrous oxide particles. As a result, stable and adherent PDMS coatings may be obtained over glass, by heating silicone oil spread over glass sheets. Glass-PDMS-glass adhesive joints can also be obtained by heating preformed, crosslinked silicone sheets between glass parts. Also, PDMS rubber is heat-stabilized by in situ-generated iron hydrous oxide particles. These results are explained by considering that active Si-O chain ends, formed by chain scission, bind to surface hydroxyl groups, in a reaction competitive with the formation of cyclic oligomers. PDMS can thus be seen as a thermally-activated, reactive adhesive.

Water absorption, swelling, rupture and salt release in salt-silicone rubber compounds

Water vapour diffuses rapidly in silicone polydimethylsiloxane (PDMS) rubber. In a PDMS-salt compound surrounded by water, the water which has entered the rubber is absorbed by the salt particles, creating an osmotic pressure in the rubber. This pressure leads to internal cracks in the rubber, which eventually percolate and result in a salt exchange between the rubber-salt compound and the surrounding pure water. The absorption and rupture phenomena were derived, measured, and quantitatively analysed. Equations describing the onset and propagation of the microcracks in the silicone were derived as a function of rubber fracture toughness, tensile modulus and osmotic pressure of the salt. A single figure summarizes three possible situations: (1) the salt plus water pockets in the compound reach an equilibrium without cracking, (2) the salt pockets are fully dissolved, and cracking occurs, (3) the salt pockets generate microcracks before full dissolution of the salt. Finally, the salt release has been quantitatively related to the PDMS tensile modulus, fracture surface energy, and salt grain size.

Crosslinking of polydimethyl siloxane rubber filled with aerosil using oligoorganosilane with functional groups at the silicon atom

The action was studied of an oligoorganosilane modifying agent on properties of cross-linked compositions filled with Aerosil and based on SKTV-1 siloxane rubber. Higher strength and elastic modulus, improved heat-ageing coefficients and lower residual deformation when introducing a modifying agent are due to the formation of a three-dimensional network, based on chemical bonds between rubber, oligoorganosilane and a filler. It was found possible to prepare vulcanizates with reduced filler content, while retaining strength properties.

Post‐irradiation grafting of tetrafluoroethylene at low temperatures

AbstractLow‐temperature postirradiation grafting of tetrafluoroethylene (TFE) to polyolefines and silicone elastomers was the subject of study. After preliminary dissolution of TFE in the polymer at 273°K the system was slowly cooled to 77°K. In this process a certain part of TFE in polyolefines (ethylene‐propylene copolymer and polypropylene) is retained by the vitreous polymer matrix. When slowly heated after radiolysis at 77°K this system shows graft polymerization of dissolved TFE after Tg. The graft copolymer is soluble and its IR spectra contain absorption bands characteristic of polytetrafluoroethylene. In polydimethylsiloxane rubber (SKT) the dissolved TFE when frozen to 77°K remains sorbed between the SKT crystallites rather than in a separate phase. When these radiolyzed samples are heated the graft‐polymerization occurs primarily over the temperature range between the TFE and SKT melting points. The technique provedes for 100–150% grafting of TFE. This method also permits grafting to silicone rubbers and to several other polymers and elastomers.

Calorimetric study of entropy and energy effects in small deformations of elastomers

Deformation calorimetry was used to determine the energy and heat of uniaxial reversible elongation over the range of small deformation ( λ<1·8) for three natural rubber elastomers, a statistical copolymer of ethylene with propylene containing 45% propylene and polydimethylsiloxane rubber and in the approximation of a Gaussian chain network using the relations obtained a thermodynamic analysis was made of entropy and energy effects accompanying deformation. Overall changes of entropy and internal energy were classified as intra- or intermolecular components and it was shown that the proportion of intramolecular change in entropy and internal energy is independent of deformation and is determined by the molecular structure of the polymer. Intermolecular changes in entropy and internal energy show a marked dependence on deformation and these changes are due to volumetric variation in deformation and offset each other. Volumetric changes in deformation were calculated and thermoelastic inversion of heat and internal energy, analysed.

Investigation of molecular isomerism in polydimethylsiloxane by raman scattering

High optical quality samples of polydimethylsiloxane rubber have been prepared, crosslinked by γ radiation. The raman depolarization rations,ϱ, of two highly polarized bands, the CH 3 stretching at 2907 cm −1 and the Si — O skeletal mode at 491 cm −1, have been measured as a function of temperature and strain. The changes in ϱ are related to changes in the relative populations of trans and gauche isomer population, and a value for Δ E, the energy difference, is found to be 820 +50 −20 cal/mole. The proportionality constant in a theory connecting strain and isomer populations D 2 is measured to be 10 ± 2. Computer calculations based on statistical weight matrices yield Δ E = 875 cal/mole and D 2 = 1.18. Reasons for the discrepancy in the D 2 values are discussed.

Sustained release hormonal preparations: 6. Permeability constant of various steroids

Permeation of 6-methyl-17α-acetoxy-4,6-pregnadiene-3,20-dione through polydimethylsiloxane rubber film (PDS) was measured for several thicknesses and areas and was shown to follow Fick's law. The permeability constant for this steroid was 3.91 ± 0.25 × 10 −2cm 2/hr. From less extensive experimental data the permeability constant was calculated also for a number of other steroids. This constant can be used to estimate amounts of steroids diffusing from cylindrical implants. Relative diffusivity was measured for cylindrical implants filled with dry, crystalline steroids and with steroids suspended in oil or liquid polytrifluropropylmethylsiloxane; the rates were higher when no suspending media were used.

The sorption and diffusion of water in silicone rubbers: Part I. Unfilled rubbers

Abstract Equilibrium sorption, permeation, and sorption kinetic measurements have been made for water in polydimethylsiloxane rubbers containing various amounts of either sodium chloride or silica filler. In general the addition of filler leads to an increase in the uptake of water by the rubber. On the other hand, the permeability P which is independent of the relative humidity is not affected to the same extent suggesting that the water sorbed by the fillers does riot contribute significantly to the steady-state flux. For the salt-filled polymers the diffusion coefficient D is initially constant and then decreases with the concentration C of sorbed water. Compared with the unfilled rubbers the decrease in D can be orders of magnitude larger. The D vs. C curves for the silica-filled samples exhibit maxima. The results are interpreted in terms of a model in which a fraction of the water sorbed is immobilized by the filler or by the formation of pockets of salt solution.