Release mechanisms of semipolar solutes from poly(dimethylsiloxane) elastomers: Effect of a hydrophilic additive

The release profiles of three xanthine derivatives from matrices of pure poly(dimethylsiloxane) (PDMS), and the effect of incorporating 10% w/w polyethylene glycol (PEG)?3000 in the matrix are presented. Theobromine (TBR), theophylline (TPL), and caffeine (CAF), although structurally very similar, are characterized by different physicochemical properties. In addition, differential scanning calorimetry and scanning electron microscopy measurements indicate different physical interactions with the polymeric matrices. The observed rates of release from pure PDMS matrices loaded at 0.065 g/g with each one of the drugs increase in the order TBR < TPL < CAF. The same order holds for the corresponding permeabilities derived from the release kinetic data. The slopes of the release curves versus the square root of time were linearly correlated to the square root of calculated solubilities in the polymer, as expected by the Higuchi equation for diffusive transport of solutes of the same diffusivity. The incorporation of 10% w/w PEG in the PDMS matrix accelerates the release rate of each drug, because of the concurrent water uptake induced by the hydrophilic additive. The extent of the corresponding permeability enhancement for theophylline was close to that predicted by the Maxwell equation for a composite two‐phase system, consisting of a PDMS continuous phase characterized by a much lower permeability than that of the fully swollen PEG dispersed phase. The corresponding enhancement of permeability was higher for TBR and lower for CAF. Possible reasons for these differences are discussed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40782.     

Crystalline morphology of poly(dimethylsiloxane)

The crystalline morphology of poly(dimethylsiloxane) was studied using a scanning electron microscope equipped with a cold stage. Samples of two different molecular weights were used. In both cases, spherulitic morphology is seen, from −70 °C, with spherulites of about 100 μ in size. Small single crystals of about a micron in size are also seen, and these are attributed to the presence of cyclics.     

Poly(dimethylsiloxane)/poly(hexamethylene oxide) mixed macrodiol based polyurethane elastomers. I. Synthesis and properties

The compatibilizing effect of poly(hexamethylene oxide) (PHMO) on the synthesis of polyurethanes based on α,ω‐bis(6‐hydroxyethoxypropyl) poly(dimethylsiloxane) (PDMS) was investigated. The hard segments of the polyurethanes were based on 4,4′‐methylenediphenyl diisocyanate (MDI) and 1,4‐butanediol. The effects of the PDMS/PHMO composition, method of polyurethane synthesis, hard segment weight percentage, catalyst, and molecular weight of the PDMS on polyurethane synthesis, properties, and morphology were investigated using size exclusion chromatography, tensile testing, and differential scanning calorimetry (DSC). The large difference in the solubility parameters between PDMS and conventional reagents used in polyurethane synthesis was found to be the main problem associated with preparing PDMS‐based polyurethanes with good mechanical properties. Incorporation of a polyether macrodiol such as PHMO improved the compatibility and yielded polyurethanes with significantly improved mechanical properties and processability. The optimum PDMS/PHMO composition was 80 : 20 (w/w), which yielded a polyurethane with properties comparable to those of the commercial material Pellethane™ 2363‐80A. The one‐step polymerization was sensitive to the hard segment weight percentage of the polyurethane and was limited to materials with about a 40 wt % hard segment; higher concentrations yielded materials with poor mechanical properties. A catalyst was essential for the one‐step process and tetracoordinated tin catalysts (e.g., dibutyltin dilaurate) were the most effective. Two‐step bulk polymerization overcame most of the problems associated with reactant immiscibility by the end capping of the macrodiol and required no catalysts. The DSC results demonstrated that in cases where poor properties were observed, the corresponding polyurethanes were highly phase separated and the hard segments formed were generally longer than the average expected length based on the reactant stoichiometry. Based on these results, we postulated that at low levels (∼ 20 wt %) the soft segment component derived from PHMO macrodiol was concentrated mainly in the interfacial regions, strengthening the adhesion between hard and soft domains of PDMS‐based polyurethanes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2026–2040, 2000     

Inorganic particle coating with poly(dimethylsiloxane)

Stable, thick poly(dimethylsiloxane) (PDMS) coatings are formed on iron(III) and aluminum oxide and calcium carbonate particles by impregnating the particles with dimethylsilicone oil and heating at 250–280°C. These coatings are strongly resistant to solvent extraction and to exposure in a water-saturated atmosphere. Coated particles are strongly hydrophobic, as evidenced by their greater stability in apolar solvents. Silicone coating formation on oxide particles is interpreted as a result of two reactions: siloxane chain opening at higher temperatures, followed by the reaction of active chain end-groups with hydroxo groups at the metal oxide or carbonate surfaces and silicone cross-linking by methylene or siloxane bridges. The procedures described in this paper differ from usual silanization or siliconization procedures because it uses stable PDMS and yields thicker coatings. © 1996 John Wiley & Sons, Inc.     

Reinforcement of siloxane elastomers by silica. Interactions between an oligomer of poly(dimethylsiloxane) and a fumed silica

The study of the adsorption of an organosiloxane onto a fumed silica was undertaken in order to improve our knowledge of the reinforcement of silicon rubbers by silica. IR and gas-phase chromatography techniques were used to characterize the adsorption of octamethyltetracyclosiloxane. At room temperature, the occurrence of hydrogen bonding between the solute and the adsorbent was shown. The amount of material adsorbed according to this mechanism was shown to be strongly dependent on temperature. The heats of adsorption at various covering ratios were calculated from the isotherms measured at temperatures close to 150°C.     

Reactivity of poly(dimethylsiloxane) toward acidic permanganate

Poly(dimethylsiloxane) (PDMS) has been widely used in various microfluidic devices because it is considered to be one of the most inert materials available. A PDMS-based microfluidic system for the synthesis of manganese oxide (MO) nanoparticles is developed and tested. However, synthesis of MO nanoparticles in the PDMS-based microfluidic system is unsuccessful due to an unexpected reaction between acidic permanganate and PDMS. PDMS is pitted and coated with MnO₂ and opalized silica, which are confirmed by SEM and EDX. The products of the reaction between PDMS and acidic permanganate are mainly MnO₂, Cl₂, SiO₂ and CO₂, respectively. Here we report for the first time the reactivity of PDMS toward acidic permangante resulting in a new process to coat the channel walls with MnO₂.     

Properties of poly(alkylene oxide) elastomers

The catalyst comprised of triisobutylaluminum, zinc acetylacetonate, and water was used to prepare homopolymer of epichlorohydrin; copolymers of epichlorohydrin with propylene oxide, ethylene oxide, and allyl glycidyl ether; and terpolymers of epichlorohydrin, propylene oxide, and allyl glycidyl ether and of epichlorohydrin, ethylene oxide, and allyl glycidyl ether. The vulcanizates of these rubbers provide variations of stressstrain and dynamic properties, freeze point, hardness, and solvent resistance depending on the type and amount of comonomer. In general, these rubbers have excellent heat, ozone, and oxidation resistance as well as oil and solvent resistance.     

聚醚酯弹性体的微相分离

聚醚酯弹性体是一类重要的热塑性弹性体，研究它的微相分离对提高其性能有重要的意义。笔者介绍了聚醚酯弹性体微相分离的热力学和动力学因素、微区形态与尺寸和微相分离程度的袁征．讨论了聚酯硬段、聚醚软段以及加工方法对聚醚酯弹性体微相分离的影响。     

Fracture and fatigue response of a self-healing epoxy adhesive

A self-healing epoxy adhesive for bonding steel substrates is demonstrated using encapsulated dicyclopentadiene (DCPD) monomer and bis(tricyclohexylphosphine)benzylidine ruthenium (IV) dichloride (Grubbs’ first generation) catalyst particles dispersed in a thin epoxy matrix. Both quasi-static fracture and fatigue performance are evaluated using the width-tapered-double-cantilever-beam specimen geometry. Recovery of 56% of the original fracture toughness under quasi-static fracture conditions occurs after 24 h healing at room temperature conditions. Complete crack arrest is demonstrated for fatigue test conditions that render neat resin and control samples failed. Inspection of fracture surfaces by electron microscopy reveals evidence of polymerized DCPD after healing. These results are the first mechanical assessment of self-healing for thin (ca. 360 μm) films typical of adhesives applications.     

Reinforcement of siloxane elastomers by silica. Chemical interactions between an oligomer of poly(dimethylsiloxane) and a fumed silica

The study of the interactions between an organosiloxane and a fumed silica was undertaken in order to improve our knowledge of the reinforcement of silicon rubbers by silica. IR spectroscopy, gravimetry, and chromatography techniques were used to characterize the chemical interactions taking place above 150°C between octamethylcyclotetrasiloxane and a fumed silica which yield silicas modified by grafted siloxanes. Reaction mechanisms were proposed for the interpretation of the grafting processes. They were checked by the study of the reaction of water with octamethylcyclotetrasiloxane. The results obtained suggest that the reactions proceed through an attack of the siloxane by the surface free silanol groups of silica, causing an opening of the siloxane cycle and the grafting of the subsequent material on the surface of the filler. It was shown that the siloxane-modified silicas exhibit a high thermal stability.     

Small-angle neutron scattering from symmetric blends of poly(dimethylsiloxane) and poly(ethylmethylsiloxane)

We present results of a small-angle neutron scattering (SANS) study of the structure and thermodynamic properties of symmetric blends of deuterated poly(dimethylsiloxane) (d-PDMS) and poly(ethylmethylsiloxane) (PEMS) as a function of temperature (T) (40≤T≤300 °C) and the molecular weight (M_w) (4700≤M_w≤23,200). The radius of gyration (R_g) of d-PDMS was measured using the high-concentration labeling method and revealed unperturbed chain dimensions at all temperatures regardless of the polymer M_w. The random phase approximation (RPA) fits the data for low M_w blends, however it fails to describe the SANS data for M_w>10,000 g/mol. This observation is explained by the fact that for high M_w blends the correlation length of the concentration fluctuations ξ is always large (ξ>R_g), implying that these blends remain microscopically inhomogeneous at all temperatures studied in this work. At the same time, the low M_w blends are randomly mixed (ξ<R_g) at all T and can reach the ‘ideal mixing’ or Θ condition (χ=0).     

Block copolymers of acrylonitrile and poly(dimethylsiloxane)s

The chemical redox system of ceric ammonium nitrate(Ce⁴⁺) and poly(dimethylsiloxane)s (PDMS) with monohydroxy (MH), dihydroxy (DH), and diamine(DA) chain ends was used to polymerize acrylonitrile (AN) to produce monohydroxy poly(dimethylsiloxane)s‐b‐polyacrylonitrile (MH.PDMS‐b‐PAN), dihydroxy poly(dimethylsiloxane)s‐b‐polyacrylonitrile (DH.PDMS‐b‐PAN), and α, ω‐diamine poly(dimethylsiloxane)s‐b‐polyacrylonitrile (DA.PDMS‐b‐PAN) block copolymers. The concentration, reaction time, and the type of poly(dimethylsiloxane) affect the yield and the molecular weight of the copolymers. The ratio of AN/ceric salt/PDMS has remarkably affects the properties of formed copolymers. DH.PDMS‐b‐PAN copolymers were also prepared by electroinduced polymerization in the presence of catalytic amount of Ce⁴⁺ in a divided electrochemical cell where Ce³⁺ is readily oxidized into Ce⁴⁺ at the anode. The products were characterized by Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, DSC, and their surface properties were investigated through contact‐angle measurements. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Reinforcement of poly(dimethylsiloxane) networks by montmorillonite platelets

A PDMS network, synthesized from a vinyl‐terminated precursor, was reinforced by plate‐like montmorillonite (volclay) particles with different surface cations. The optimal ratio of crosslinker‐to‐PDMS precursor was ascertained from the mechanical properties of networks prepared with different crosslinker concentrations. The elastic modulus of the polymer was enhanced by the montmorillonite particles. The increase in modulus was higher in the Li– than in the Na–volclay composites. The ultimate strength of the composites was also strongly enhanced by the small platelets, especially in presence of surface Li⁺. The stronger influence of Li–volclay on the mechanical properties of the composites can be attributed to the partial formation of an intercalated structure, which leads to thinner particles with a high aspect ratio. Both composite strength and modulus were proportional to the filler‐volume‐fraction, but the increase in strength was limited by rising particle agglomeration at high loading. In contrast to organic‐modified montmorillonite, the inorganic surface of volclay catalyzed the thermal degradation of PDMS. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2175–2183, 2002     

Surface immobilization of star‐shaped poly(ethylene oxide) on poly(dimethylsiloxane)

A thin layer of star‐shaped poly(ethylene oxide) (PEO) (starPEO), on the polydimethylsiloxane (PDMS) membrane was prepared by a simple immobilization procedure. Photoreactive molecules were introduced on the surface of the polymeric support to achieve the formation of thin starPEO film from the materials having no functional groups. This novel technique enabled us to immobilize any kind of chemical, especially one that had no functional groups, and readily to control the amount of immobilization. The gas permeation properties of the starPEO‐immobilized PDMS membranes were investigated for pure propane and propylene. The permeance of gases were found to decrease in the starPEO‐immobilized PDMS membranes, although the ideal separation factors for propylene/propane were increased with the loading amount of silver ions, because of the facilitation action of silver ions in the immobilized PEO unit on the PDMS membranes, as propylene carriers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2369–2373, 2002     

Casting poly(urethane-imide) elastomers with improved thermoviscoelasticity

Polyurethane (PU) is a versatile material that can be customized to meet specific commercial requirements in different industries because of its favorable mechanical properties. However, it is not resistant to high temperatures, and it requires structural modifications before it can be used in high-temperature structural materials. In this study, isocyanates and anhydrides are copolymerized at high temperatures to obtain a solvent-free oligomer, thus eliminating the risks associated with highly polar aprotic solvents. A casting technique is used to synthesize a solid poly(urethane-imide) (PUI) elastomer. According to the results, casting PUI (CPUI) exhibits optimal physical properties at a hard segment content of 30.5%. Incorporating an ether, symmetric, or imide structure into CPUI may reduce its hysteresis and improve its thermal creep performance. Compared with PU, CPUI exhibits considerably higher creep aging resistance. In dynamic load application tests, CPUI wheels take a substantially longer time to reach failure compared with PU wheels. Overall, CPUI is an environmentally friendly material with high elasticity, low creep, and high heat aging resistance and is suitable for static and dynamic manufacturing applications.     

Preparation and characterization of poly(trifluoropropylmethyl)siloxane-block-polyurethane-urea elastomers

A series of poly(trifluoropropylmethyl)-siloxane-block-polyurethane-urea (FSPUU) films is prepared through moisture curing based on a three-step process. First, prepolymers are produced from poly(tetramethylene oxide) and toluenediisocyanate. Second, the prepolymers are chain-extended by α,ω-bis(3-aminopropyldiethoxylsilane) poly(trifluoropropylmethyl)siloxane (APFS). Third, another chain extension is performed using 3,3′-dichliride-4,4′-diaminodiphenylmethane (DDDPM). The FSPUU films are characterized by Fourier transform IR spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, scanning electron microscopy, and mechanical testing. The effects of the APFS amount on the microstructure of the materials are also investigated. The results show that the material with approximately 15 wt% APFS exhibits high phase mixing. The materials display strong phase separations and weak tensile strengths when the APFS amounts range from 21.6 to 26.8 wt%. In particular, due to the incorporation of DDDPM in FSPUU, this segment increases the bonding of the different phases when the APFS amount is in the range of 35.6–44.5 wt%. The APFS segment is involved in compatibilizing the different phases in the materials. The tensile strength of the FSPUU films containing DDDPM can reach or surpass that of polyurethane. The copolymers may also have a functional application in coatings and adhesives.     

Damping modulus studies of poly(dimethylsiloxane)-bisphenol-a-polycarbonate block copolymers

Random multiblock copolymers of bisphenol-A-polycarbonate and poly(dimethylsiloxane) were hot-pressed or solvent cast into films which were studied by dynamic mechanical methods over the range 11 to 110 hertz (Hz) and 100 to more than 2200 Hz, respectively. The samples were studied also by differential-scanning calorimetry. The two phases are separated well in spite of the low-molecular weights of the blocks. This separation is altered by thermal history and by the solvent medium when solvent casting is used to prepare the films. The damping properties do not vary greatly with frequency. Damping is greatest near the glass-transition temperatures of the two components. The expansion of the block copolymer with heat appears to be retarded by the polycarbonate phase until the glass transition of that phase is approached.     

丙烯酸酯接枝硅油消泡剂的制备与性能

分别以丙烯酸甲酯接枝硅油(MA-g-PHMS)、丙烯酸乙酯接枝硅油(EA-g-PHMS)和丙烯酸丁酯接枝硅油(BA-g-PHMS)为原料,制得了3种有机硅乳液消泡剂;并用正交试验优化了工艺条件,优化后的条件分别为:MA-g-PHMS硅膏质量分数为24%,乳化剂质量分数为4%,于70℃反应5 h;EA-g-PHMS硅膏质量分数为24%,乳化剂质量分数为3%,于70℃反应4 h;BA-g-PHMS硅膏质量分数为24%,乳化剂质量分数为3%,于75℃反应6 h。3种消泡剂都具有高效的消泡性能,其中EA-g-PHMS消泡剂性能极佳,其消泡时间为10.1 s,抑泡时间为21.6 min。     

聚二甲基硅氧烷表面亲水改性的研究进展

聚二甲基硅氧烷（PDMS）广泛地用作制造生物医疗器械和微流控装置材料,但其具有高疏水性,且在表面亲水化处理后容易发生疏水复原,对其应用产生了不利影响。综述了PDMS表面亲水改性的各种方法,如基于等离子体表面处理、静电自组装法、紫外光辐照接枝聚合及表面活性剂动态改性等,并对PDMS表面改性的各种方法进行了评价,指出了PDMS表面改性的发展前景。