Polymeric curing agent reinforced silicone rubber composites with low viscosity and low volume shrinkage

A new type of polymeric curing agent (PCA) was synthesized to improve processing property, increase mechanical properties, and decrease volume shrinkage of silicone rubber. The PCA was prepared by co‐hydrolysis condensation of dimethyldiethoxysilane (DDS) and polyethoxysiloxane, then modified by hexamethylcyclotrisilazane (D₃^N). Commercial silica and tetraethoxysilane (TEOS) were used as controls simultaneously. The properties of polydimethylsiloxane (PDMS) composites were characterized by shear viscosity measurements, room temperature mass loss, linear volume shrinkage, stress‐strain tests, swelling behaviors and thermogravimetric analysis (TGA). PDMS composites using PCA show lower shear viscosity than those using commercial silica. Compared with the traditional PDMS/TEOS curing systems, PDMS/PCA curing systems behave relatively lower volume shrinkage, better reinforcement and thermal properties. In short, PCA acts as a good compromise in providing the best balance of processing property, volume shrinkage, mechanical properties and thermal stability in silicone rubber composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of hydroxy‐terminated polyether‐polydimethylsiloxane‐polyether (PE‐PDMS‐PE) triblock oligomers and their use in the preparation of thermoplastic polyurethanes

A series of hydroxy‐terminated polyether‐polydimethylsiloxane‐polyether (α,ω‐dihydroxy‐(PE‐PDMS‐PE)) ABA triblock oligomers were synthesized from silanic fluids and methyl polyallyloxide polyethers. The reaction was a one‐step solventless hydrosilylation reaction with chloroplatinic acid (CPA) catalyst in the presence of heat. These ABA oligomers were characterized via ¹H‐NMR, ¹³C‐NMR, ²⁹Si‐NMR, FT‐IR, and GPC to demonstrate that they exhibit a 100% linear ABA structure with a siloxane Si? O chain in the center and polyether ethylene oxide (EO)/propylene oxide (PO) chains on the two sides terminated by hydroxy groups. The triblock oligomers were used to form thermoplastic polyurethanes (TPUs) using two‐step solventless bulk polymerization. The investigation of triblock oligomers impact on TPUs mechanical properties, thermal performance, surface water repellency, and morphology performance were analyzed by Instron material tester, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), water contact angles (WCA), scanning electron microscope (SEM), and transmission electron microscope (TEM). DSC and TGA indicated that PE‐PDMS‐PE modified TPUs had a clear lower T_g under ?120°C and the temperature of 50% weight loss was improved from 280 to 340°C. PE‐PDMS‐PE–modified TPU did not have the marked reduction on mechanical properties than pure polyether produced TPU. Tensile strength was maintained at 13 MPa and elongation was maintained at 300%. SEM and TEM were used to investigate the copolymers’ morphology performance and found that all PO PE‐PDMS‐PE had a pseudo‐three phase separation. WCA analysis confirmed that PE‐PDMS‐PE–modified TPU had significantly improved hydrophobic performance because the silicone structure linked into TPU copolymers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42521.     

Synthesis and characterization of polyurethane hybrids: Influence of the polydimethylsiloxane linear chain and silsesquioxane cubic structure on the thermal and mechanical properties of polyurethane hybrids

The structural effects of polydimethylsiloxane (PDMS) or polyhedral oligosilsesquioxanes (POSSs) on the thermomechanical properties of polyurethane (PU) networks were studied. An ester–amine‐functionalized silsesquioxane and a PDMS macromer were synthesized, and the macromer (10 wt %) was crosslinked with the PU prepolymer to obtain PU networks. The synthesized macromers and hybrids were characterized with Fourier transform infrared, ¹H‐NMR, ¹³C‐NMR, and ²⁹Si‐NMR spectroscopy techniques. The influence of POSS cubes on the thermal and mechanical properties of the polymer network films was studied comparatively with the similarly functionalized PDMS linear chain via thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) measurements. The degradation pattern of the POSS‐incorporated PU nanocomposites was almost the same as that of the PU network synthesized from the linear PDMS macromer. The differences in the char yields and activation energies of the hybrids reflected the enhancement of the thermal properties of the nanohybrids. The TGA and DSC curves of the macromers suggested that the thermal properties of the macromers not only depended on either the PDMS or POSS inorganic core but also depended on the organic peripheral attached to the inorganic core. The glass‐transition temperatures of the nanohybrids were higher than those of the linear‐PDMS‐incorporated hybrids. The storage modulus values increased 3‐fold upon the incorporation of POSS rigid groups into the PU hybrids in comparison with the flexible PDMS‐chain‐incorporated PU hybrids. The DMA measurements showed a long‐range rubbery plateau region for all the PU hybrids, with high storage modulus and tan δ values showing the structural homogeneity of the crosslinked networks. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A comparative study on the preparation and physical properties of environmental friendly PMMA‐silica nano/sub‐micron‐scale hybrid latexes controlled by chelating agent

In this article, a comparative study of the preparation and physical properties of as‐prepared PMMA‐silica nano‐hybrid (PSN) and sub‐micro‐hybrid (PSM) latexes is successfully presented. Vinyl‐modified silica spheres were prepared using the Stöber process with/without a chelating agent to control particle size. The as‐prepared vinyl‐modified silica spheres with different particle sizes were subsequently characterized by SEM, ¹³C‐solid‐state NMR, and ²⁹Si‐solid‐state NMR spectroscopy. A certain feeding amount of silica spheres was reacted with MMA monomers by emulsion polymerization to yield a series of PSN and corresponding PSM. Both as‐prepared nano/sub‐micronscale hybrid materials were further characterized by FTIR, SEM‐EDX mapping, and TEM studies. The comparative study on the physical properties of both as‐prepared nano/sub‐micron‐scale hybrid materials was done systematically based on a series of instrumentation evaluations performed using a dynamic mechanical analyzer, electrochemical corrosion measurements, salt spray test, and gas permeability analysis. Results indicated that PSN has more effectively enhanced mechanical properties, corrosion protection properties, as well as gas barrier compared to PSM. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Influence of the microstructure of gums on the mechanical properties of silicone high consistency rubbers

This paper is devoted to the characterization and processing of high molar mass vinyl‐bearing polysiloxanes in high consistency silicone rubber (HCR) formulations. The molar masses of five different polydimethylsiloxane gums, bearing vinyl groups at the ends and along their chains, were evaluated by size exclusion chromatography and rheometry. ²⁹Si and ¹H NMR spectroscopy allowed the precise determination of the vinyl content and of the distribution in the different polymers. Typical HCRs formulated from these gums were heat‐cured to process silicone rubber materials that were then tested mechanically. The macromolecular properties were correlated to the final material network structure. The amount of reactive vinyl moieties, rather than their distribution along or at the end of chains, is a key parameter to tailor the material mechanical properties. © 2016 Society of Chemical Industry     

Antireflective coatings using organically modified silica and polyimide via solution casting method

Antireflective (AR) coatings were prepared using a polyimide and two types of organically modified silica colloids via a solution casting method. The optically transparent polyimide was prepared from 2,2′‐Bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) and 4,4′‐oxydianiline (ODA). The silica colloids were driven to the coating‐air interface by either the fluorinated alkyl group or PDMS (Polydimethylsiloxane) segment tethered onto the silica colloids. The amount of fluorinated alkyl groups and the molecular weight of the siloxane grafted on the silica colloid were varied. The PDMS‐silica and fluorosilica colloids were characterized by TEM (Transmission Electron Microscopy), DLS (Dynamic Light Scattering), FTIR (Fourier Transform Infrared Spectroscopy), solid‐state ¹³C NMR (Nuclear Magnetic Resonance) and solid‐state ²⁹Si NMR. The AR coatings were characterized by UV–vis (Ultraviolet–Visible Spectroscopy) transmittance spectra, AFM (Atomic Force Microscope), and SEM (Scanning Electron Microscope). The effects of modified silica loading and type of solvent on AR properties were studied. An enhancement in AR activity was observed for 1 wt% PDMS‐modified (low molecular weight) silica coatings and 3 wt.% fluorosilica‐10 in dimethylacetamide (DMAc). In comparison with cyclopentanone (CPT), DMAc favors migration of silica particles toward coating‐air interface giving higher transmittance. The migration of particles to the surface and consequently increased surface roughness was observed by SEM. POLYM. ENG. SCI., 53:2228–2241, 2013. © 2013 Society of Plastics Engineers     

Polyhedral oligomeric silsesquioxane/silica/polydimethylsiloxane rubber composites with enhanced mechanical and thermal properties

Composites of polydimethylsiloxane (PDMS) rubber modified by three kinds of polyhedral oligomeric silsesquioxanes (POSSs) as well as fumed silica were prepared through solution blending and then open two‐roll mill blending with curing agent. Subsequently, the influences of POSS on mechanical and thermal properties of the resulting composites were investigated in detail. The addition of POSS significantly enhanced the tensile strength and elongation at break of the composite but lowered the tensile modulus, which could be ascribed to the interruption of silica–silica and silica–PDMS interactions. Octamethylsilsesquioxane (OMS)/silica/PDMS and octaphenylsilsesquioxane (OPS)/silica/PDMS composites did not show desirable mechanical and thermal properties. Nevertheless, heptaphenylvinylsilsesquioxane (VPS)/silica/PDMS composite with 5 wt % VPS exhibited enhanced glass transition temperature (T_g), mechanical properties, and thermal stability. Further studies revealed that more VPS unfavorably affected properties of the composite. Scanning electron microscope and X‐ray diffraction demonstrated that owing to the grafting reaction, 5 wt % VPS in the rubber matrix could form microcrystal domains the most effectively. Thus, the improved mechanical properties and thermal stability just resulted from the the formation of microcrystal domains and the increase in stiffness of PDMS chains because of the graft of VPS onto PDMS. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42173.     

Influence of clay modification on the reinforcement of vinyl‐terminated polydimethylsiloxane networks

A novel method was attempted to reinforce a vinyl‐terminated polydimethylsiloxane (PDMS) with two commercially available clays, sodium montmorillonite and Cloisite^® 25A. The two clays were functionalized with bis(3‐triethoxysilylpropyl)tetrasulfide (TESPT) to prepare Na⁺MMTS₄ and C25AS₄, respectively. Incorporation of the tetrasulfide group‐containing clays, especially Na⁺MMTS₄, was found to be effective for the enhancement of the interfacial interaction between PDMS and the clays by way of a plausible chemical reaction between the tetrasulfide groups (TSS) and the vinyl‐terminated PDMS. Compounding of PDMS with the TESPT‐modified clays improved the mechanical properties significantly. In particular, the elongation at break of PDMS/Na⁺MMTS₄ composite was almost twice as high as that of neat PDMS, even if the silicate layers were not fully exfoliated in the PDMS matrix. The tear strength of PDMS was also improved greatly as a result of the incorporation of Na⁺MMTS₄. According to toluene swelling test results, the crosslinking density of the composites was lower than that of neat PDMS, indicating that the improved mechanical properties of the composites arise from enhanced compatibility between the constituents and not from increased crosslinking density. Copyright © 2009 Society of Chemical Industry     

Method for preparing polyaluminocarbosilane

Polyaluminocarbosilane (PACS) was synthesized directly by the one‐pot reaction of polydimethylsilane (PDMS) with aluminum acetylacetonate [Al(acac)₃] in an autoclave. In this closed system, all the aluminum in Al(acac)₃ was converted into PACS. Therefore, the content of aluminum could be readily controlled quantitatively. On the basis of Fourier transform infrared, ¹H‐NMR, ¹³C‐NMR, ²⁹Si‐NMR, and ²⁷Al magic‐angle spinning NMR analysis, the reaction mechanism was proposed as follows: PDMS dissociated during pyrolysis to generate silicon free radicals, and then they reacted with Al(acac)₃ to yield PACS containing (Si? O)_nAl groups (n = 4, 5, or 6). Meanwhile, these reactions resulted in the cleavage of O? C and/or O?C bonds in Al(acac)₃. Some of the free‐radical fragments generated by this cleavage continued to react with the silicon free radicals and were incorporated into the structural units of PACS; the rest of them may have been converted into small oxygen‐containing compounds, which were removed in the subsequent processing after the reactions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and properties of polydimethylsiloxane/polyacrylate composite latex initiated by 60Co γ‐ray irradiation

In this study, polydimethylsiloxane (PDMS)/polyacrylate composite polymer latex was synthesized via polymerization of the acrylate monomer in the presence of vinyl‐containing PDMS seeded latex. The polymerization was initiated by ⁶⁰Co γ‐ray irradiation. The morphology of the PDMS/polyacrylate composite polymer latex was a core–shell structure with PDMS as the core and polyacrylate as the shell. There was an interpenetration layer between the PDMS core and the polyacrylate shell. The composition of the vinyl‐containing PDMS and the PDMS/polyacrylate composite latex were investigated with NMR and Fourier transform infrared spectroscopy, respectively. The effect of irradiation dose on the seeded emulsion polymerization conversion is discussed. Finally, the mechanical properties of latex film, such as water‐absorption ratio, tensile strength, pendulum hardness, and heat‐decomposed temperature, were tested. The results showed that the mechanical properties of the PDMS/polyacrylate film were remarkably improved when compared to the polyacrylate film. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2732–2736, 2003     

Synthesis of carbazole‐substituted poly(dimethylsiloxane) and its improved refractive index

A series of substituted 9‐vinylcarbazole polysiloxane was synthesized followed by room temperature vulcanization to afford a crosslink network via trimethoxysilane crosslinker. Structural confirmation was made using FTIR, one and two‐dimensional ¹H‐ and ²⁹Si‐NMR spectroscopy. Quantitative estimation of the amount of substituted carbazole was made based on NMR data. These were related to the refractive index whose values were in the range of 1.4370–1.4625 at increasing carbazole content. These values are higher than uncrosslink series, attributable to the tightness of the systems. They displayed an improved thermo‐optic coefficient compared to linear unsubstituted polydimethylsiloxane (PDMS). The synergistic effect of substituted carbazole unit with the crosslink network of PDMS presents a viable choice of encapsulant for opto‐electronic devices. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41654.     

聚硅氧烷交联剂与掺杂SiO2协同增强RTV硅橡胶的研究

研究了新型聚硅氧烷交联剂(PCA)与沉淀法SiO2协同增强室温硫化硅橡胶及其增强机理.发现PCA的引入可有效降低PCA/SiO2/PDMS硅橡胶的黏度,提高硫化胶的拉伸强度,保持良好的扯断伸长率,体系中原位生成的SiO2粒子和掺杂的SiO2粒子与PDMS聚合物之间有强烈的相互作用,协同补强效果好.     

Novel polymethoxylsiloxane‐based crosslinking reagent and its in‐situ improvement for thermal and mechanical properties of siloxane elastomer

Polymethoxylsiloxane (PMOS) with dense pendant silicone‐methoxy groups was synthesized from cyclosiloxane monomers by ring‐opening polymerization and dehydrocoupling reaction. Synthesis reactions were followed by IR spectroscopy and ²⁹Si NMR analyses. PMOS was used as crosslinking reagent for room temperature vulcanized polydimethylsiloxane (PDMS), and the apparent activation energy for crosslink reaction was 3.92 kJ/mol. TEM study shows that many dispersed high crosslink density PMOS phases were formed in siloxane elastomer as well as the PDMS networks, and the crosslink density increased from PDMS networks to PMOS phases gradually, without a clear interface. It was detected that these PMOS phases improved the thermal and mechanical properties of siloxane elastomer significantly because of their in‐situ microscale improvement effect. TG analysis demonstrated that thermal decomposition process of PMOS crosslinked siloxane elastomer was divided into three stages, the second one corresponding to a possible loss of some new structures, and the residual mass at 500°C was 66 wt %. The crosslink density went up as the loading of PMOS increased. Tensile stress and elastic module increased twice and three times, respectively, when the PMOS content increased from 15.1 to 41.6 wt %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Multifunctional Cu2+‐montmorillonite/epoxy resin nanocomposites with antibacterial activity

Multifunctional nanocomposites can be achieved by addition of modified layered nanoclays to impart to the final materials a designed set of properties. The easy reproducible preparation of copper modified montmorillonite has been reported here together with its spectroscopic characterization, including ²⁹Si NMR in the solid state. Epoxy‐nanocomposites and glass fiber reinforced laminates containing 1% wt and 3% wt of Cu²⁺‐MMT have been prepared and characterized. Thermal and mechanical properties have been evaluated. The experiments carried out to evaluate the antibacterial activity showed that the epoxy‐resin nanocomposites with 3% wt of Cu²⁺‐MMT exhibited an inhibition action higher than 96% against Escherichia coli and Staphylococcus aureus. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44733.     

Supramolecular association of acid terminated polydimethylsiloxanes

Summary. Benzoic acid terminated polydimethylsiloxanes (PDMS) have been synthesized by hydrosilylation of allyloxybenzylbenzoate with SiH terminated precursors followed by deprotection. These oligomers have been characterized by ¹H, ¹³C and ²⁹Si NMR, by FTIR and by SEC in tetrahydrofurane. Because of the flexibility and low polarity of the siloxane backbone, they are ideally suited to study the effect of hydrogen bonding on macromolecular properties. Received: 17 July 1997/Revised: 22 July 1997/Accepted: 6 August 1997     

Synthesis and characterization of maleinized‐silylated low molecular weight guayule rubber (MASiGR)

Maleinization followed by silylation of low molecular weight guayule rubber was accomplished for the first time via a two‐step process. Maleinization was first effected by grafting maleic anhydride onto guayule rubber under the influence of benzoyl peroxide catalyst to give maleinized guayule rubber (MAGR). The maleinized rubber was then further derivatized via hydrosilylation with dichloromethyl silane and chloroplatinic acid (Speier's catalyst) to give maleinized‐silylated guayule rubber (MASiGR). The silylated polymer (MASiGR) was further functionalized by reaction with ethanol or aqueous ammonia to produce ethoxysilane and silanol moieties, respectively. The products were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H‐, ¹³C‐, and ²⁹Si‐ nuclear magnetic resonance spectroscopy (NMR). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 754–761, 2001     

Dynamic properties of star‐shaped,solution‐polymerized styrene–butadiene rubber and its cocoagulated rubber‐filled with silica/carbon black

The dynamic properties, including the dynamic mechanical properties, flex fatigue properties, dynamic compression properties, and rolling loss properties, of star‐shaped solution‐polymerized styrene–butadiene rubber (SSBR) and organically modified nanosilica powder/star‐shaped styrene–butadiene rubber cocoagulated rubber (N‐SSBR), both filled with silica/carbon black (CB), were studied. N‐SSBR was characterized by ¹H‐NMR, gel permeation chromatography, energy dispersive spectrometry, and transmission electron microscopy. The results show that the silica particles were homogeneously dispersed in the N‐SSBR matrix. In addition, the N‐SSBR/SiO₂/CB–rubber compounds' high bound rubber contents implied good filler–polymer interactions. Compared with SSBR filled with silica/CB, the N‐SSBR filled with these fillers exhibited better flex fatigue resistance and a lower Payne effect, internal friction loss, compression permanent set, compression heat buildup, and power loss. The nanocomposites with excellent flex fatigue resistance showed several characteristics of branched, thick, rough, homogeneously distributed cross‐sectional cracks, tortuous flex crack paths, few stress concentration points, and obscure interfaces with the matrix. Accordingly, N‐SSBR would be an ideal matrix for applications in the tread of green tires. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40348.     

Purification,surface modification of coal ash silica and its potential application in rubber composites

This article reports the purification and surface modification of coal ash silica and afterwards its utilization as reinforcing filler in solution‐styrene‐butadiene rubber/butadiene rubber (S‐SBR/BR). The coal ash silica free of unwanted metal ions/mineral oxides was obtained using phosphoric acid. The chemical composition of the purified coal ash silica in comparison to impure coal ash indicates the presence of characteristic hydroxyl functional group at 3440 cm^?1 and an increase in the oxygen content as determined with the help of Fourier Transform Infrared and x‐ray photoelectron spectroscopy, respectively. The contact angle analysis shows that after purification the polar part of the surface energy increased to 17.5 from 12 m Jm^?2. While the surface area increased to an order of magnitude, i.e., 11.6 to 110.5 m² g^?1. The modification of purified silica particles with bis(3‐triethoxysilylpropyl) tetrasulfane reveal the functionalization of hydroxyl to ‐Si‐O‐R groups as detected at 1560 cm^?1. As a consequence, the modified silica based S‐SBR/BR composite resulted in improved mechanical properties due to enhanced silica‐rubber interaction. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical reinforcement in magadiite/styrene‐butadiene rubber composites

This work investigates mechanical properties of styrene‐butadiene rubber (SBR) composites incorporating magadiite (MGD), a synthetic layered silicate (Na₂Si₁₄O₂₉·9H₂O) with surface chemistry similar to precipitated silica used in tire tread formulations. Treatment with cetyltrimethylammonium (CTA⁺) expands the MGD layers and makes the interlayer face surfaces accessible to sulfur‐functional silane TESPT (Si69) and SBR, primarily during batch mixing. DMA and tensile testing of cured CMGD/SBR composites show that CTA‐treated MGD (CMGD) provides substantially higher levels of mechanical reinforcement than equivalent amounts of silica. However, CMGD/SBR composites exhibit larger loss tangent values above T_g, probably due to lower SBR‐SBR crosslink density resulting from interlayer trapping of sulfur released by Si69 during vulcanization. DMA and tensile testing also demonstrate Si69′s critical role in forming MGD‐SBR graft sites essential to mechanical reinforcement. Replacing silica with CMGD reduces composite weight without sacrificing tensile modulus, suggesting that use of CMGD in tire rubber formulations could improve vehicle energy efficiency. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44763.     

Synthesis, structure and morphology of poly(dimethylsiloxane) networks filled with in situ generated silica particles

The morphology of silica particles generated in situ in PDMS networks in the presence of two types of catalysts is evaluated by using different techniques including solid-state ²⁹Si MAS NMR, near-infrared spectroscopies and small-angle X-ray scattering. The interactions with the poly(dimethylsiloxane) chains are examined through the swelling properties and thermal characteristics (in particular crystallization process) of the composites. In addition, ¹H NMR is used to investigate the adsorption layer of reduced mobility on the particle surface.