Effects of the presence of water on ultrasonic devulcanization of polydimethylsiloxane

The effects of the presence of water on ultrasonic devulcanization of 30 phr silica‐filled polydimethylsiloxane (PMDS) were investigated at increasing feed rates and different die gap sizes. The results showed that the initial die entrance pressure without ultrasound for wet rubber was higher than in the case without water and then it decreased monotonously with applying ultrasound. The die pressure for wet rubber decreased significantly even at low ultrasonic amplitude, while that for dry rubber changed little at low amplitude. The power consumption at an amplitude of 10 μm, where devulcanization was most effectively achieved, was lower for wet rubber even though the pressure was lower. The crosslink density and gel fraction after the devulcanization of wet rubber were lower than those of dry rubber, indicating that the presence of water facilitates the devulcanization process under the same devulcanization conditions. The good mechanical properties of recycled silica‐filled PDMS were obtained at higher feed rates and at lower ultrasound amplitudes, which are directly related to the economics of a recycling process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2630–2638, 2003     

Physical,mechanical, and biocompatibility evaluation of three different types of silicone rubber

Silicone rubber as a valuable biomaterial is widely used in medical applications, but its surface properties and low wettability make serious problems in long‐term implants. This work was undertaken to evaluate the biocompatibility of modified silicone rubber using two different techniques. A blend of poly(acrylamide) and silicone rubber was compared with virgin silicone surfaces as well as with those modified by laser treatment. Physical and mechanical properties of the samples were examined using different techniques. The hydrophilicity of the silicone rubber increased with increasing hydrogel content and decreased as a result of laser treatment. Both fibroblast cell (L929) and platelet behavior in contact with these surfaces were evaluated in vitro. The morphology of fibroblast cells that adhered to the blends was similar to the control. In contrast, on the laser‐treated surfaces fibroblast cells showed different proliferation. On the other hand, fewer platelets adhered to the laser‐treated surface than adhered to the blend and the unmodified PDMS surfaces. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2522–2529, 2003     

Effect of filament temperature on the chemical vapor deposition of fluorocarbon–organosilicon copolymers

The effect of filament temperature on the hot‐filament chemical vapor deposition (HFCVD) of fluorocarbon–organosilicon copolymer thin films from 1,3,5‐trivinyl‐1,3,5‐trimethylcyclotrisiloxane (V₃D₃) and perfluorooctane sulfonyl fluoride (PFOSF) was examined. Significant changes in chemical structure occur as the filament temperature is varied, and these changes give rise to differences in thermal and mechanical properties. When the filament temperature is low, the films consist primarily of carbon‐backbone polymer chains with siloxane ring pendant groups. When higher filament temperatures are used, the film structure consists of siloxane‐backbone chains with some degree of crosslinking. Films produced with low filament temperatures have a greater degree of thermal stability and flexibility than those produced with high filament temperatures. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2176–2185, 2004     

Effects of blend ratio and vulcanizate powders on the processability of silicone rubber/fluororubber blends

While silicone rubber has a much lower shear viscosity than that of fluororubber, the viscosity of silicone rubber/fluororubber blends is closer to that of silicone rubber. All rubber compositions show pseudoplastic behavior. While the viscosity of a 50/50 silicone rubber/fluororubber blend increases on replacement of the silicone rubber by silicone rubber vulcanizate powder (SVP), the effect of fluororubber replacement by the corresponding fluororubber vulcanizate powder (FVP) on the shear viscosity is less pronounced. The difference in viscosity between SVP‐replaced silicone rubber and FVP‐replaced fluororubber becomes less prominent at higher shear rates. Fluororubber exhibits a higher extrudate die swell than that of silicone rubber. The die swell of the silicone rubber/fluororubber blends is higher than are the figures obtained by the additivity rule. Replacement of constituent rubbers in the blend by the corresponding vulcanizate powders causes an increase in the die swell. While the silicone rubber extrudate surface is smooth, the fluororubber extrudate shows melt fracture. The extrudate surfaces of the silicone rubber/fluororubber blends are similar to that of the silicone rubber extrudate. Replacement of constituent rubbers by the corresponding vulcanizate powders increases the roughness of the extrudate surface, which is more prominent in the case of silicone rubber replacement by SVP. SVP can replace 50% of silicone rubber and FVP can replace 75% of fluororubber in the 50/50 silicone rubber/fluororubber blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2377–2387, 2003     

Rheological properties of silicon polymer networks: The influence of the crosslink density

This study was focused on the influence of the microstructural properties of a silicon polymer network on its rheological properties. Two commercial silicon oils were mixed in different ratios to form, by hydrosilylation, networks with different crosslink densities. The chemical compositions of the oils were determined by NMR, whereas their molecular weights and viscosities were studied with gel permeation chromatography and viscosimetry, respectively. The different networks were characterized through their crosslink densities. Afterward, the rheological properties were studied. The formulation notably influenced some characteristic values of the rheological behavior: the α‐transition temperature and the onset temperature of the caoutchoutic plateau shifted toward higher temperatures as the crosslink density increased, the storage modulus at the onset temperature of the caoutchoutic plateau increased with the crosslink density, and the amplitude of the peak associated with the α‐transition temperature decreased. These behaviors were explained as follows: as the crosslink density increased, a drastic decrease in the amount of free chains in the network occurred, and both phenomena induced a large decrease in the chain mobility, which might explain the aforementioned behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1152–1160, 2003     

Preparation,morphology, and physical properties of transparent PSt hybrid materials containing silicone macromonomer

The aim of this study was to prepare transparent polystyrene (PSt) hybrid materials containing silicone macromonomer. Silicone urethane methacrylate (SiUMA) was synthesized by the reaction between the hydroxyl end groups of a silicone macromonomer and the isocyanate group of 2‐methacryloyloxyethyl isocyanate (MOI), and copolymers with different weight proportions were prepared by copolymerization of styrene (St), SiUMA and ethyleneglycol dimethacrylate (EGDMA). Though the prepared P(St‐co‐SiUMA) copolymers which had not introduced EGDMA were opaque, the prepared P(St‐co‐SiUMA‐co‐EGDMA) copolymers were transparent, similarly to pure PSt. DSC and ¹H‐NMR measurements were carried out to investigate the factors in this transparency in detail. From these measurement results, it was confirmed that the reactivity of the copolymerization had a significant influence on the transparency of the product. In addition, the contact angle of P(St‐co‐SiUMA‐co‐EGDMA) with 10 wt % SiUMA was greater than 90°, which was a 10° improvement compared to pure PSt. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Novel fluorescence method for cure monitoring of hydrosilation‐curable silicones

This study aimed to evaluate a reactive fluorescent probe, 9,10‐bis‐(phenylethynyl) anthracene (BPEA), for cure monitoring of hydrosilation‐curable silicones. The hydrosilation‐curable silicones consisted of a vinyl‐terminated polydimethylsiloxane prepolymer, a methylhydrosiloxane‐dimethylsiloxane copolymer, and an inhibitor, 1,3‐divinyltetramethyldisiloxane. The hydrosilation reaction was catalyzed with the solution of a platinum catalyst in the prepolymer. The catalyst solution also contained a trace amount of the reactive fluorescent probe. Three hydrosilation‐curable silicones, with the prepolymer of varying molar mass, were investigated. Each of the hydrosilation‐curable silicones was mixed with the catalyst solution at the mass ratio of 1 : 1 to initiate the cure. During the cure of each mixture at 22°C, the elastic modulus of the mixture and the fluorescence spectrum of the probe at the excitation wavelength of 360 nm were measured. Initially, the elastic modulus changed slowly, but then increased rapidly as a result of the increase in molar mass. The elastic modulus leveled off and reached a plateau value at the setting time. The ratio of the fluorescence intensities at 422 and 466 nm increased steadily, and then leveled off and reached a plateau value at the setting time, in agreement with the setting time determined from the change in elastic modulus. The reactive fluorescent probe, BPEA, can therefore be used for nondestructive fluorescence monitoring of hydrosilation‐curable silicones. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and properties of styrene–butylacrylate emulsion copolymers modified by silane compounds

Styrene (St)/butyl acrylate (BA) copolymers were prepared by adding triethoxyvinylsilane (TEVS), trimethoxyvinylsilane (TMVS), and triphenylvinylsilane (TPVS), each one through emulsion copolymerization. The polymerization was performed with methacrylic acid and auxiliary agents at 80°C in the presence of potassium peroxodisulfate as the initiator. Nonylphenol ethylene oxide‐40 units (NP‐40) and sodium lauryl sulfoacetate were used as nonionic and anionic emulsifiers, respectively. The resulting copolymers were characterized by using Fourier transform infrared spectroscopy. Thermal properties of the copolymers were studied by using thermogravimetric analysis and differential scanning calorimetry. The morphology of copolymers was also investigated by optical microscopy, and then the effects of silicone kinds and concentrations on the properties of the St/BA emulsion copolymers were discussed. The obtained copolymers have high solid content (50 %) and can be used in emulsion paints as a binder. The comparison of three different vinyl silanes indicates that the TEVS influences on the copolymer properties more than the others. The calculations of monomer conversion and monomer conversion versus time histories indicate that by increasing the silicone concentration, the polymerization rate decreases. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hydrophobic,amorphous metal–organic network readily prepared by complexing the aluminum ion with a siloxane spaced dicarboxylic acid in aqueous medium

A less common dicarboxylic acid with siloxane spacer, 1,3-bis(carboxypropyl)tetramethyldisiloxane, whose structure is for the first time determined crystallographically, is used to coordinate aluminum through an environment-friendly preparation process, resulting in a polymeric structure of amorphous metal–organic framework (aMOF) type. The high flexibility of the spacer induced by the siloxane bond gives the polymeric product a glass transition slightly below room temperature, while the long length of the former creates the premises for collapse of the network and consequently reduced porosity. At the same time, the high hydrophobicity of the tetramethyldisiloxane fragment and its low surface energy, which causes it to migrate to the air interface, gives the network low moisture sorption capacity guaranteeing the stability of its properties in a wet environment. The particulate complex, of the order of 1–200 nm, as generated by the synthesis, proves to be suitable as filler for silicone with outstanding reinforcement effect, without significantly affecting their transparency. The presence of the dimethylsiloxane units in the structure of both the matrix and the filler ensures good incorporation of the latter without the need for special compatibility treatments. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47144.     

A New Method for Producing High Melt Strength Poly(propylene) with a Reactive Extrusion

Summary: A new class of melt blend material was prepared by extruding a mixture of 3‐aminopropyltriethoxysilane (APTES), maleic anhydride‐grafted poly(propylene) (PP‐g‐MA) with different molecular weight and MA content and poly(propylene) powder produced with a TiCl₃‐based catalyst (PP‐A). A suitable selection of PP‐g‐MA provided extremely high melt strength (MS) of resultant blend materials. Such a superior melt property was caused by the synergy between the present melt reaction and the higher molecular weight portion containing PP‐A. The gel content measurements of typical blend materials and PP‐g‐MA/APTES blends indicated that an excessive amount of inert PP suppresses the formation of gels. The reaction between PP‐g‐MA and APTES was then investigated by analyzing crystalline polymer fractions separated from the atactic PP/PP‐g‐MA/APTES and atactic PP/PP‐g‐MA blends. The FT‐IR analysis of the fractions revealed that the NH₂ group in APTES readily reacts with MA grafted on PP and the reaction leads to the formation of imide linkage. Moreover, the GPC analysis of the fraction showed that higher molecular weight polymers were formed in the presence of APTES. Since a trace amount of water surely produces in the vicinity of active silyltriethoxy groups during the reactive extrusion, such polymers were formed by the condensation between hydrolyzed APTES‐grafted polymer chains. These results led us to the conclusion that long‐chain‐branched PP (LCB‐PP) was certainly produced and its formation is essential for the increase in MS of the present blend materials.

Relationship between log(MS) and log(MFR) for PP/PP‐g‐MA/APTES and commercial PP resins.