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.     

Dependence of interaction parameter on molecular weight and concentration for solutions of poly(dimethylsiloxane) in methylethylketone

The polymer-solvent interaction parameter x for solutions of poly(dimethylsiloxane) (PDMS) of different molecular weights (4600–220000) in methylethylketone (MEK) at segment fractions of PDMS ø2 ranging from 0.3 to 0.7 was measured by means of the vapour pressure method at 30°C, (20°C higher than the θ temperature for the PDMS-MEK system). The x values obtained experimentally were found to be almost independent of the molecular weight of PDMS. The observed x values were reproduced by applying Flory's new theory with evaluated values of three quantities: (1) the ratio of the surface area per segment for the polymer to that for the solvent $\text{s}{}_2\text{s}{}_1$; (2) the enthalpy exchange parameter X₁₂ and (3) the entropy exchange parameter Q₁₂.     

Durability of poly(dimethylsiloxane) when exposed to chlorine gas

Highly crosslinked poly(dimethylsiloxane) (PDMS) is discussed as an alternative membrane material for the gas separation of highly concentrated chlorine gas (90–95 vol %) and oxygen, due to an initial high permeation for Cl₂ and a high selectivity of Cl₂/O₂. It was found that the separation properties of the PDMS membrane change over time upon exposure to aggressive chlorine gas; the flux will go down, and the material may even degrade if not appropriately prepared and protected. The PDMS was exposed to chlorine gas over 4 weeks in a glass chamber at both 30 and 60°C and analysed by (FTIR). The membranes were exposed to chlorine gas in a permeation cell with measurements of the permeability of N₂, O₂, and Cl₂ at regular intervals. The temperature range for the permeation measurements was 30–100°C, and the pressure difference over the membrane was ca. 2 bar. The time of exposure in the permeation cell was several weeks. The absorption of N₂, O₂, and Cl₂ in the PDMS at temperatures in the same range was also measured. This article discusses the durability of the highly crosslinked PDMS membrane following chlorine exposure. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2458–2470, 2002     

Characterization of hydrogels based on chitosan and copolymer of poly(dimethylsiloxane) and poly(vinyl alcohol)

Copolymers composed of poly(vinyl alcohol) (PVA) and poly(dimethylsiloxane) (PDMS) were crosslinked with chitosan to prepare semi‐interpenetrating polymer network (IPN) hydrogels by an ultraviolet (UV) irradiation method for application as potential biomedical materials. PVA/PDMS copolymer and chitosan was cast to prepare hydrogel films, followed by a subsequent crosslinking with 2,2‐dimethoxy‐2‐phenylacetophenone as a nontoxic photoinitiator by UV irradiation. Various semi‐interpenetrating polymer networks (semi‐IPNs) were prepared from different weight ratios of chitosan and the copolymer of PVA/PDMS. Photocrosslinked hydrogels exhibited an equilibrium water content (EWC) in the range of 65–95%. Swelling behaviors of these hydrogels were studied by immersion of the gels in various buffer solutions. Particularly, the PCN13 as the highest chitosan weight ratio in semi‐IPN hydrogels showed the highest EWC in time‐dependent and pH‐dependent swelling. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2591–2596, 2002     

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.     

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.     

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     

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).     

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     

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。     

Effects of dimethylsiloxane diluents on the optical properties of poly(dimethylsilmethylene) networks

Summary Low molecular weight cyclic and linear molecules of highly flexible dimethylsiloxane (DMS) units [-Si(CH₃)₂O-] were used to swell elastomeric networks of poly(dimethylsilmethylene) [-Si(CH₃)₂CH₂-]. Strain birefringence measurements in elongation at 10°C showed the birefringence to decrease regularly with increase in degree of polymerization of the DMS diluent, with three of the four diluents having the unusual effect of increasing the birefringence. Therefore, if correlative effects are the origin of the increase, they do not seem to require high geometric asymmetry in the diluent molecules.     

Synthesis and characterization of semi‐interpenetrating networks based on poly(dimethylsiloxane) and poly(vinyl alcohol)

Semi‐interpenetrating networks (Semi‐IPNs) with different compositions were prepared from poly(dimethylsiloxane) (PDMS), tetraethylorthosilicate (TEOS), and poly(vinyl alcohol) (PVA) by the sol‐gel process in this study. The characterization of the PDMS/PVA semi‐IPN was carried out using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and swelling measurements. The presence of PVA domains dispersed in the PDMS network disrupted the network and allowed PDMS to crystallize, as observed by the crystallization and melting peaks in the DSC analyses. Because of the presence of hydrophilic (? OH) and hydrophobic (Si? (CH₃)₂) domains, there was an appropriate hydrophylic/hydrophobic balance in the semi‐IPNs prepared, which led to a maximum equilibrium water content of ～ 14 wt % without a loss in the ability to swell less polar solvents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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 and electrical characteristics of poly(amide imide)–poly(dimethylsiloxane) nanocomposites

A series of poly(amide imide)–poly(dimethylsiloxane) (PDMS) nanocomposites were fabricated through the reaction of poly(amide imide), epoxysilane (coupling agent), and diethoxydimethylsilane (DEDMS) via a sol–gel process. Nanocomposite films were obtained through the hydrolysis and condensation of DEDMS in poly(amide imide) solutions. The existence of the condensation product of DEDMS in the poly(amide imide) matrix was confirmed with Fourier transform infrared (FTIR). The concentration of PDMS on the surface of the poly(amide imide) matrix was observed through a comparison of FTIR and attenuated total reflection spectra. The contact angle of the poly(amide imide)–PDMS composites increased more than 40° with respect to that of pure poly(amide imide). The alternating‐current (ac) breakdown strength was obtained through the measurement of the ac breakdown voltage at the temperature of liquid nitrogen. As the PDMS concentration in poly(amide imide) increased, the characteristics of the insulation breakdown improved greatly. The best ac breakdown strength was observed in a poly(amide imide)–epoxysilane (30 wt %) nanocomposite with 30 wt % PDMS. The samples at the temperature of liquid nitrogen were brittle, as in a glassy state. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 342–347, 2004     

Torsion fatigue response of self-healing poly(dimethylsiloxane) elastomers

Incorporating self-healing functionality in a polysiloxane elastomer successfully retards the growth of fatigue cracks under torsional fatigue loading. The fully in situ self-healing material consists of a microencapsulated vinyl-terminated poly(dimethylsiloxane) resin containing platinum catalyst compounds and a microencapsulated initiator (methylhydrosiloxane), embedded in a poly(dimethylsiloxane) elastomer matrix. A torsion fatigue test protocol is adopted to assess the self-healing performance of two different elastomeric matrices. Significant recovery of torsional stiffness occurs after approximately 5 h, the time required to achieve a measurable degree of cure of the healing agents. Total fatigue crack growth in a self-healing specimen is reduced by 24% in comparison to relevant controls. The retardation of growing fatigue cracks is attributed, in part, to a sliding-crack-closure mechanism, where polymerized healing agent shields the crack tip from the applied far-field stress.     

Determination of the number of degrees of freedom for chemical-engineering objects: Distillation column

Various methods of calculation of the number of independent variables (degrees of freedom) are analyzed for chemical-engineering objects, including continuous distillation columns with different organizations of external flows and auxiliary equipments. The number of degrees of freedom is demonstrated to be invariant with respect to the type of calculation for the distillation process (design, confirmatory, or designconfirmatory calculation).     

Synthesis of ABA block Co-Oligomers of polymethylmethacrylate and poly (dimethylsiloxane)

A methoxysilyl macromonomer containing an acrylic chain is obtained by telomerization of methyl methacrylate with mercaptopropylmethyldimethoxysilane. This macromonomer is then reacted with a polydimethylsiloxane hydroxytelechelic leading to new block Co-Oligomers with acrylic and siloxane moieties.     

Miscibility,phase separation,and volumetric properties in solutions of poly(dimethylsiloxane) in supercritical carbon dioxide

Miscibility conditions and volumetric properties of solutions of poly(dimethylsiloxane) in supercritical carbon dioxide have been determined as a function of polymer molecular weight, polymer concentration, temperature, and pressure. Measurements have been conducted in a variable volume view cell equipped with an LVDT sensor to identify the position of a movable piston and thus the internal volume of the cell and consequently the density of the solution at a given pressure and temperature. The demixing data (in the form of P‐T curves for a given concentration, or as P‐x diagrams at a given T) and the density isotherms are presented for solutions of two polymer samples with different molecular weights (M_w = 38,600; M_w/M_n = 2.84 and M_w = 94,300; M_w/M_n = 3.01) at several concentrations in the range from 0.05 to 10 mass % over a temperature range from 302–425 K. Solution densities corresponding to the demixing points also have been identified. Representation of the demixing densities on the density isotherms, i.e., pressure‐density plots is a new methodology that gives a direct assessment of the volumetric expansion the solution must undergo before phase separation. The temperature–composition diagrams generated at selected pressures show that the poly(dimethylsiloxane) + CO₂ solutions display both lower critical solution and upper critical solution type behavior. The lower critical solution temperature moves to lower temperatures and the upper critical solution temperature moves to higher temperatures with decreasing pressure and they eventually merge together at lower pressures forming an hourglass‐shaped region of immiscibility. This behavior is linked to the solvent quality of supercritical carbon dioxide that changes with pressure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1397–1403, 2000