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).     

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。     

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.     

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.     

Synthesis and properties of poly(amide-imide-urethane) thermoplastic elastomers

A new class of poly(amide-imide-urethane) thermoplastic elastomers based on two-step synthesis of 4,4′-methylene bis(4-phenylisocyanate) with different polyols (PPG and PTMG) and trimellitic anhydride was synthesized. Both resulting polymers showed semicrystalline structures and were readily soluble in polar solvents such as N-methyl-2-pyrrolidone and dimethyl formamide. The soluble poly(amide-imide-urethane)s afforded transparent, flexible, and tough films. Both new copolymers were then characterized by FTIR spectroscopy, universal tensile tester, simultaneous DTA/TGA (SDT), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction studies, to determine their morphological structures, thermal stability, and mechanical properties. Compared to typical polyurethanes, these polymers exhibited better thermal stabilities due to the presence of imide groups. DSC and X-ray diffraction studies showed semicrystalline patterns for these polymers. Stress–strain properties revealed that these polymers have good extensibility like typical polyurethanes. © 1998 SCI.     

Some evidence on pore sizes in poly(dimethylsiloxane) elastomers having unimodal,bimodal, or trimodal distributions of network chain lengths

Summary Unimodal, bimodal, and trimodal networks were prepared by end linking functionally-terminated chains of poly(dimethylsiloxane). The resulting materials were characterized using a thermoporometric technique in which freezing points or melting points are determined for solvent absorbed into the network stuctures. The extent to which the normal melting point is suppressed depends on how much the solvent is constrained within the network pores. Several well-defined melting points were observed for some of the multimodal networks, which is consistent with their unusual distributions of network chain lengths.     

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     

Reinforcement of siloxane elastomers by silicas. Comparison between fumed and precipitated silicas in their interactions with an oligomer of poly(dimethylsiloxane)

Comparison between fumed and precipitated silicas in their interactions with an oligomer of poly(dimethylsiloxane) showed both materials to exhibit general identical behavior depending on the experimental temperature range. However, the results obtained suggest on the one hand that these interactions are directed more by morphological and structural characteristics than by chemical properties and on the other hand that the distribution of surface silanol groups on precipitated silicas is not the same as on fumed silicas. Both siloxane-modified fillers exhibit high thermal stability.     

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.