ABA-type block copolymers containing poly(dimethylsiloxane) and ketonic resins

Block copolymer containing segments of poly(dimethylsiloxane) (PDMS) and ketonic resins were synthesized. Dihydroxy-terminated PDMS were reacted with the isophorone diisocyanate (IPDI) to obtain the diisocyanate-terminated PDMSs (urethane). These urethanes were reacted with reactive hydroxyl groups in the cyclohexanone–formaldehyde, acetophenone–formaldehyde, and in situ melamine-modified cyclohexanone–formaldehyde resins. Formation of block copolymers was illustrated by several characterization methods, such as chemical and spectroscopic analysis and gel permeation chromatography. The solubilities of the block copolymers were determined, and their surface properties were investigated by contact angle measurements. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 643–648, 1998     

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。     

Some dynamic mechanical properties of unimodal and bimodal networks of poly(dimethylsiloxane)

Summary Elastomeric networks of polydimethylsiloxane prepared by end-linking chains having molecular weights in the range 18,500 to 220 g mol^-1 were studied from -128 to 50°C using a Rheovibron DDV III Viscoelastometer. In the case of the unimodal networks, the glass transition temperature T_g was generally insensitive to degree of cross-linking. The intensity of the tan δ relaxation, however, increased by over an order of magnitude over the range of cross-link densities investigated. Bimodal networks prepared from mixtures of relatively long and very short PDMS chains also had values of T_g which were insensitive to degree of cross-linking. Finally, as expected, the intensities of the tan δ peak for the bimodal networks could not be explained on the basis of simple additivity of contributions from the relatively long and the very short network chains.     

Interpenetrating polymer networks of poly(dimethylsiloxane): 1. Preparation and characterization

Model networks of ,ω-dihydroxy-poly(dimethylsiloxane) (PDMS) were prepared by tetrafunctional crosslinking agent tetraethyl orthosilicate (TEOS) and the catalyst stannous 2-ethylhexanoate. Hydroxylterminated chains of PDMS having molecular weights 15 × 10³ and 75 × 10³ g mol⁻¹ were used in the crosslinking reaction. Bimodal networks were obtained from a 50% (w/w) mixture of PDMS chains with M_n = 15 × 10³ and 75 × 10³ g mol⁻¹. A sequential interpenetrating network of these PDMS chains was also prepared. Physical properties of the elastomers were determined by stress-strain tests, swelling and extraction experiments, and differential scanning calorimetry measurements.     

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.     

Synthesis and characterization of five-block copolymers prepared by vinyl pyrrolidinone and a macro initiator with poly(dimethylsiloxane) and polycaprolactone

A new generation of a series of five-block copolymers of poly(dimethylsiloxane) (PDMS), polycaprolactone (PCL), and polyvinyl pyrrolidinone (PVP), (PVP-PCL-PDMS-PCL-PVP), are synthesized to obtain new polymeric systems containing PDMS with improved compatibilities. For this, a commercial reactive triblock copolymer of PCL and PDMS, namely (PCL-PMDS-PCL), was used as the starting material from which the peroxidic macroinitiator was prepared. By use of physicochemical methods, a five-block copolymer structure was confirmed, and its characterization was accomplished. Mechanical and thermal test results showed higher thermal resistances and increased toughness characteristics of the copolymer as compared with that of the component homopolymers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1961–1969, 1997     

Viscosity–molecular weight relationship for aminopropyl‐terminated poly(dimethylsiloxane)

Aminopropyl‐terminated poly(dimethylsiloxane) (ATPS) with different molecular weights was prepared by base‐catalyzed equilibration of octamethylcyclotetrasiloxane and 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetramethyldisiloxane with different ratios. Their number‐average molecular weights (M_n) were determined by end–group analysis, and intrinsic viscosity ([η]) in toluene was measured with a Ubbelohde viscometer. A relationship between M_n and [η] was obtained for ATPS. For 1.0 × 10⁴ < M_n < 6.0 × 10⁴, it was in accord with [η]_{toluene,25°C} = 5.26 × 10^?2 M_n^0.587. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 975–978, 2001     

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     

Structure-property behavior of poly(dimethylsiloxane) based segmented polyurea copolymers modified with poly(propylene oxide)

Poly(propylene oxide) (PPO) was incorporated in a controlled manner between poly(dimethylsiloxane) (PDMS) and urea segments in segmented polyurea copolymers and their solid state structure-property behavior was investigated. The copolymers contained PDMS segments of MW 3200 or 7000 g/mol and an overall hard segment content of 10-35 wt%. PPO segments of MW 450 or 2000 g/mol were utilized. Equivalent polyurea copolymers based on only PDMS as the soft segment (SS) component were used as controls. The materials (with or without PPO) utilized in this study were able to develop microphase morphology as determined from dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS). DMA and SAXS results suggested that the ability of the PPO segments to hydrogen bond with the urea segments results in a limited inter-segmental mixing which leads to the formation of a gradient interphase, especially in the PPO-2000 co-SS containing copolymers. DMA also demonstrated that the polyureas based on only PDMS as the SS possessed remarkably broad and nearly temperature insensitive rubbery plateaus that extended up to ca. 175 °C, the upper temperature limit depending upon the PDMS MW. However, the incorporation of PPO resulted in more temperature sensitive rubbery plateaus. A distinct improvement in the Young's modulus, tensile strength, and elongation at break in the PPO-2000 and PDMS-7000 containing copolymers was observed due to inter-segmental hydrogen bonding and the formation of a gradient interphase. However, when PPO was incorporated as the co-SS, the extent of stress relaxation and mechanical hysteresis of the copolymers increased relative to the segmented polyureas based on the utilization of only PDMS as the soft segment component.     

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.     

Surface properties of poly(dimethylsiloxane)-based inorganic/organic hybrid materials

Poly(dimethylsiloxane) (PDMS)-based hybrid materials were prepared by the sol-gel method on Si wafers, Al and polystyrene (PS) substrates. The reaction was monitored by attenuated total reflectance-infrared (ATR-IR) spectroscopy. The hybrid materials have always one surface made in contact with air and one with a substrate. These surfaces were investigated by using tapping mode atomic force microscopy (AFM), X-ray photo-electron spectroscopy (XPS), low-energy ion scattering (LEIS) and dynamic contact angle (DCA) analysis. The hybrid sample surfaces made in contact with air and substrates appeared to have different structures. The former have a silica-free PDMS top layer of ∼2 nm thick; while in the latter cases, SiO₂ are located at or just beneath the outermost atomic layer. In air and at room temperature, SiO₂ are likely beneath the outermost atomic layer. In contact with water, polar -OH groups at the surface of SiO₂ can easily stretch out to the outermost atomic layer. No correlation was found between the roughness of the surfaces and the amount of in situ formed SiO₂ present in the materials.     

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     

Cyclic poly(dimethylsiloxane) from kinetically controlled cyclodepolymerization of linear precursors in dilute solution

Cyclic poly(dimethylsiloxane) (PDMS), [(CH₃)₂SiO]_x or D_x, was prepared in high yield (>70% for x > 12) from commercially available linear α,ω-dihydroxy-PDMS by base-catalyzed unimolecular ring closure in dilute solution. Cyclization, which occurs with formation of charged linear byproducts, was confirmed by GPC, FTIR, MALDI-ToF and NMR spectroscopy. Product mixtures were analyzed with a newly developed dual-detector GPC method in which the linear byproducts were end-labeled with a UV-absorbing group and separately detectable with a UV detector. Alternatively, charged linear byproducts were removed with anion-exchange resin. Yields and molecular weight distributions of the cyclic products are consistent with Monte Carlo simulations of kinetically controlled cyclodepolymerization. Large cycles from this cyclodepolymerization route are obtained in much higher yields (>70% for x > 12) than those reported for the traditional base-catalyzed ring-chain equilibration of D₄ and D₅ (∼13% for x > 6) [1].     

Manufacturing and characterizations of flexible poly(dimethylsiloxane)/poly(vinyl acetate)/polythiophene ternary composite films

ABSTRACT

In this study, polythiophene and poly(dimethylsiloxane)/poly(vinyl acetate)/polythiophene ternary composites were synthesized. The new ternary composites obtained in powder and film forms were characterized using various techniques. Magnetic properties of all the materials were analyzed by Gouy balance measurements, and it was found that their conductivity mechanism is of polaron nature. The surface structure, surface roughness, and thermal properties of the prepared samples were identified by Scanning Electron Microscopy, Atomic Force Microscopy, and Thermogravimetric Analysis, respectively. The tensile-tension test studies were performed for mechanical properties. The PDMS/PVAc/PT (6%) composite demonstrated about 50% of the maximum strain value (%) of vulcanized natural rubber.     

An investigation of the interaction of potassium ions with poly(dimethylsiloxane)

The interactions of potassium ions with , -hydroxy-terminated and , -trimethylsilyl-terminated poly(dimethylsiloxanes) (PDMS) have been investigated. After mixing with potassium hydroxide followed by partial extraction, the , -hydroxy-terminated PDMS samples gave elastomeric materials which are thought to result from aggregation of terminal potassium silanolate ion pairs. Uniaxial tensile testing of these materials was carried out at 298 K. The , -trimethylsilyl-terminated PDMS, when mixed with potassium hydroxide, however, gave completely soluble material following identical solvent extraction procedures.     

Synthesis and physicochemical characterization of a well-defined poly(butadiene 1,3)-block-poly(dimethylsiloxane) copolymer

For the first time, order-order and order-disorder transitions were detected and characterized in a model diblock copolymer of poly(butadiene-1,3) and poly(dimethylsiloxane) (PB-b-PDMS). This model PB-b-PDMS copolymer was synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene 1,3 (B) and hexamethylciclotrisiloxane (D₃), and subsequently characterized by nuclear magnetic resonance (¹H and ¹³C NMR), size exclusion chromatography (SEC), Fourier Transform infrared spectroscopy (FTIR), Small-Angle X-ray scattering (SAXS) and rheology. SAXS combined with rheological experiments shows that the order-order and order-disorder transitions are thermoreversible. This fact indicates that the copolymer has sufficient mobility at the timescale and at the temperatures of interest to reach their equilibrium morphologies.     

Effect of filler amount on thermoelastic properties of poly(dimethylsiloxane) networks

End-linked poly(dimethylsiloxane) (PDMS) networks were prepared in the presence of fumed silica particles with hydroxyl groups at their surfaces. The silica particles were introduced into the polymer solution prior to end-linking. Hydroxyl ended PDMS chains were end-linked via the tetra functional crosslinker, tetraethoxysilane. The filler content varied in the range 0-5 wt%. Atomic Force Microscopy was used to image and characterize the silica particles. Swelling, stress-strain and thermoelasticity experiments were performed. The temperature coefficient and the energetic part of the force in uniaxial extension are found to increase with increasing silica amount. This observation is ascribed to effects contributed possibly by the adsorption layer around the silica particles.     

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     

Combination of polymer ions. Formation of copolymer containing polytetrahydrofuran and poly(dimethylsiloxane) blocks

The polymerization of tetrahydrofuran initiated by a silenium (silyl-enium) initiator with perchlorate counterions proceeds without transfer and termination i.e. via a ‘living mechanism. However, the degree of polymerization of the product is lower. This was explained by the ability of the ester form of an active centre to form macrocycles. The combination of living dianionic poly(dimethylsiloxane) with silenium dicationic initiator increases the molecular weight of the initial poly(dimethylsiloxane) by an order of magnitude. The A(BA)_nB type block copolymer was prepared from dianionic poly(dimethylsiloxane) and dicationic polytetrahydrofuran by an analogous reaction. TheSiOCH₂bond is relatively stable towards hydrolysis.     

Microscopic surface and bulk morphology of semicrystalline poly(dimethylsiloxane)–polyester copolymers

In this study, two series of semicrystalline poly(dimethylsiloxane) (PDMS)–polyester segmented copolymers with various PDMS contents were synthesized. One series was based on polybutylene adipate (PBA) as the polyester segment and the other was based on a polybutylene cyclohexanedicarboxylate ester (PBCH) segment. The copolymers were characterized using ¹H‐nuclear magnetic resonance, size exclusion chromatography, dynamic mechanical analyses, differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD). The microscopic surface morphology and the microscopic bulk morphology were investigated using atomic force microscopy (AFM) and transmission electron microscopy, respectively. The effects of the polyester type and the PDMS content on the crystallinity degree as well as the copolymer surface and bulk morphology at room temperature were investigated for each series. DSC and WAXD results showed the ability of the copolymers to crystallize, to various degrees, depending on the polyester type and the PDMS content. The results showed that the PDMS content had a greater influence on the crystallinity degree in the PDMS‐s‐PBCH (cycloaliphatic) copolymer series than in the PDMS‐s‐PBA (aliphatic) copolymer series. In the copolymers with a low PDMS content, the AFM images showed spherulitic crystal morphology and evidence of PDMS nanodomains in between the crystal lamellae of the ester phase on the copolymer surface. A heterogeneous distribution of the PDMS domains was also observed for these copolymers in the bulk morphology as a result of this segregation between the polyester lamellae. All the copolymers, in both series, showed microphase separation as a result of the incompatibility between the PDMS segment and the polyester segment. Three types of surfaces and bulk morphologies were observed: spherical microdomains of PDMS in a matrix of polyester, bicontinuous double‐diamond type morphology, and spherical microdomains of polyester in a matrix of PDMS as the PDMS content increases. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010