Hydride-terminated Polydimethylsiloxane Research Articles

Preparation of liquid polysiloxane-based anti-misting agents for application in release coatings

Liquid polysiloxanes are prone to misting in coating processes performed at high roller speeds, and the addition of anti-misting agents is a cost-effective method to address this issue. In this work, a series of mildly cross-linked fluorinated polysiloxane-based viscoelastic fluids were synthetized via the successive hydrosilylation of (perfluorohexyl) ethylene (PFHE) and vinyl-terminated polydimethylsiloxane (PDMS-Vi) with hydride-terminated polydimethylsiloxane (PMHS). As anti-misting agents for high-speed coating process of silicone release agents, their inhibition efficiency can reach 92.1 % with a dosage of 4 wt%. It was also found that the physical properties, rheology, and molecular structure of the agents have various influences on inhibition efficiency depending on the anti-misting mechanisms. Additionally, the agents could significantly reduce the negative impact of coatings, and have no obvious adverse effect on the heat curing process or the transparency. The transparency of the films on the surface of the underlying polyethylene terephthalate (PET) substrate is still in excess of 95 %. Finally, the agents are conducive to improving the thermal stability of the films, and the results show that this type of viscoelastic fluids has the potential to be used in the industrial production of silicone release coatings.

Preparation of siloxymethyl-modified silicone acrylate prepolymers with UV/moisture dual curability for applications in anti-smudge and anti-fingerprint coatings

UV-curing technology is an efficient, energy-saving and eco-friendly technology, which has been widely used in industrial production and daily life. However, UV curing is difficult to achieve with thick coatings, coloured coatings, and shadowed regions of coatings, which greatly limits the applicability of this process. As reported herein, UV/moisture dual curable siloxymethyl-modified silicone acrylate (SMSA) prepolymers were synthesized through the two-step sequential hydrosilylation of pentaerythritol tetraacrylate (PETTA), hydride-terminated polydimethylsiloxane (H-PDMS) and trimethoxysilane (TMOS). The prepolymer contains UV-curable acrylate groups and moisture-curable siloxymethyl groups, and thus it can be readily cured via exposure to UV light, moisture, or a combination of UV light and moisture. Combining the advantages of UV and moisture curing, the prepolymer is capable of curing rapidly and overcomes the problem of UV curing about shadowed areas and thick coatings. This combined UV/moisture dual curing process also solves the problem of oxygen inhibition and poor adhesion of conventional UV-curable silicone materials. The properties of UV/moisture dual cured coatings were characterized and found to exhibit excellent transparency, heat resistance, as well as hydrophobicity. The transparencies of these coatings are over 93% even the thicknesses are up to 100 µm. The coatings remain stable when temperatures reach up to 296.5 and 317.2 °C. The water contact angles of coatings are between 97° and 103°, and surface energies of the coatings vary from 25.43 to 21.27 mN/m. The UV/moisture dual cured coatings also have excellent resistance to smudge and fingerprints. Therefore, they will be suitable for the preparation of anti-smudge and anti-fingerprint coatings.

Synthesis of PDMS-grafted-polyether and its application to polymer electrolyte

A terpolymer, poly(ethylene oxide-co-propylene oxide-co-allyl glycidyl ether) (P(EO/PO/AGE)), was reacted with linear mono-functional hydride-terminated polydimethylsiloxane (PDMS-SiH) to obtain PDMS-grafted-polyether (PDMS-g-P(EO/PO/AGE)) by hydrosilylation. Three polyelectrolytes were prepared based on PDMS-g-P(EO/PO/AGE). Best result was obtained when 8wt% of PDMS was introduced onto polyether. Cyclic voltammetry measurement of the PDMS-g-P(EO/PO/AGE polyelectrolytes showed improvement of oxidative stability.

Preparation of multifunctional silicone acrylate prepolymers with anti-oxygen inhibition ability for application in UV-curable anti-smudge coatings

UV curing technology is a new green technology developed in the 21st century, and has been widely used in daily life and industrial production. However, a major drawback encountered with UV curing is oxygen inhibition, especially in free radical photopolymerization. As reported herein, three multifunctional silicone acrylate prepolymers were obtained via the one-step hydrosilylation of dipentaerythritol hexaacrylate (DPHA) and hydride-terminated polydimethylsiloxane (H-PDMS). These prepolymers contain five acrylate groups at each end of the polysiloxane chain, and also has a high viscosity, all of which contribute to overcome oxygen inhibition, and thus they have efficient anti-oxygen inhibition abilities. After the addition of a few photoinitiators, each of the prepolymers could be rapidly cured in air to yield a transparent film. The transparency of these cured films is over 95% on the surface of an underlying polyethylene terephthalate (PET) substrate. They remain stable at temperatures reaching up to 352.2 to 364.8 °C, thus demonstrating that they have excellent heat resistance. Water droplets exhibit water contact angles between 103° and 105° on these films, and surface energies of the cured films are from 24.58 to 20.69 mN/m. Finally, the coatings have good anti-smudge and anti-fingerprint properties, and the overall results show that these films have potential applications as UV-curable anti-smudge coatings.

One-step synthesis of novel multifunctional silicone acrylate prepolymers for use in UV-curable coatings

As reported herein, three multifunctional silicone acrylate prepolymers were obtained via the one-step hydrosilylation of pentaerythritol tetraacrylate (PETTA) and hydride-terminated polydimethylsiloxane (H-PDMS). The structures of these prepolymers were subsequently characterized by FT-IR and 1H NMR spectroscopy techniques, which confirmed the successful synthesis of the target products. These prepolymers contain three acrylate groups at each end of the polysiloxane chain, which can participate in the UV curing process, and thus they have high UV curing activities. After the addition of a little photoinitiator, each of the prepolymers could be rapidly cured to yield a transparent film. The transparency of these cured films is over 95% on the surface of an underlying polyethylene terephthalate (PET) substrate. Water droplets exhibit water contact angles between 100° and 105° on this film, these films remain stable at temperatures reaching up to 356.0 to 386.8 °C, thus demonstrating that these films are hydrophobic and have excellent heat resistance. Finally, the coatings have good anti-smudge properties, and the overall results show that these films have potential applications as UV-curable anti-smudge coatings.

Cellulose-based hybrid glycosilicones via grafted-to metal-catalyzed hydrosilylation: “When opposites unite”

Hydrosilylation catalyzed by the rhodium(I) complex [Rh(acac)(CO)2] or platinum(0)-based Karstedt’s catalyst was employed to combine hydrophilic propargylated hydroxyethyl cellulose and hydrophobic hydride-terminated polydimethylsiloxane to give polymer hybrid structures. The final polymers were characterized by FTIR, solid state 1H, 13C and 29Si NMR, contact angle, microcalorimetry and thermogravimetry measurements. The grafting degree was controlled by the catalyst choice and by the reagent load variations; an increase of the polysiloxane load and a change from Karstedt’s to the rhodium catalyst led to a higher (from 2 to 7%) silicon content in the glycosilicones. The glycosilicones were insoluble in water, but swelled in organic solvents (DMSO, DMF, and chloroform). The hydrophilicity of the glycosilicones decreased with incrementing silicon content: the contact angles increased from 30 (cellulose) to 103–131° in the hybrids. The glycosilicones obtained via the hydrosilylation are less toxic toward algae Chlorella vulgaris and infusoria Paramecium caudatum than those obtained with CuAAC.

Hydrosilylation of Reactive Quantum Dots and Siloxanes for Stable Quantum Dot Films.

The reactive acrylate-terminated CdZnSeS/ZnS quantum dots (QDs) were designed and prepared by the effective synthetic route to bond with a siloxane matrix via hydrosilylation. The conventional QD with oleic acid ligands does not have any reactivity, so the QDs were functionalized to assign reactivity for the QDs by the ligand modification of two step reactions. The oleic acid of the QDs was exchanged for hydroxyl-terminated ligands as an intermediate product by one-pot reaction. The hydroxyl-terminated QDs and acrylate-containing isocyanates were combined by nucleophilic addition reaction with forming urethane bonds and terminal acrylate groups. No degradation in quantum yield was observed after ligand exchange, nor following the nucleophilic addition reaction. The modification reactions of ligands were quantitatively controlled and their molecular structures were precisely confirmed by FT-IR and 1H-NMR. The QDs with acrylate ligands were then reacted with hydride-terminated polydimethylsiloxane (H-PDMS) to form a QD-siloxane matrix by thermal curing via hydro-silylation for the first time. The covalent bonding between the QDs and the siloxane matrix led to improvements in the stability against oxygen and moisture. Stability at 85 °C and 85% relative humidity (RH) were both improved by 22% for the QD-connected siloxane QD films compared with the corresponding values for conventional QD-embedded poly(methylmethacrylate) (PMMA) films. The photo-stability of the QD film after 26 h under a blue light-emitting diode (LED) was also improved by 45% in comparison with those of conventional QD-embedded PMMA films.

Synthesis and characterization of poly(siloxane–ether–urethane) copolymers

Poly(siloxane–ether–urethane) (PSEU) copolymer materials were successfully synthesized from 4,4-diphenylmethane diisocyanate (MDI), 2,2-dimethylol propionic acid (DMPA) chain extender, and poly(siloxane–ether) copolymer (PSE) soft segments formed by hydrosilation of hydride-terminated polydimethylsiloxane (PDMS) and polyalkyl glycol allyl epoxyl ethers (PAGAEEs). The morphology, structure, and surface wettability of PSEU copolymer materials were characterized by FT-IR, XPS, TG, SEM, GPC, and contact angle measurements. It was demonstrated that the introduction of hard (urethane) segments can improve the thermal stability of PSEU materials. Moreover, due to the existence of strong polar groups originating from MDI segment, PSEU copolymer materials was superhydrophilic with water contact angle of 2.1°, which was possibly useful for surfactants and coatings applications.

Siloxane-based thin films for biomimetic low-voltage dielectric actuators

Molecular beam deposition of siloxane-based polymer thin films was employed to realize single-layer dielectric elastomer actuators. With molecular weights of 6000 and 28,000g/mol, vinyl-terminated polydimethylsiloxane (PDMS) was evaporated under high-vacuum conditions at crucible temperatures between 100 and 180°C. Both deposition rate and realizable film thickness showed linear dependency with respect to the crucible temperature and were significantly higher for PDMS with lower molecular weight. Optimized growth conditions for 6000g/mol were obtained at 180°C with a deposition rate of (130±5)nm per hour and a maximal film thickness of (530±1)nm. Thermally induced polymerization was observed to limit the maximum accessible evaporation temperature for hydride-terminated PDMS above 180°C and for vinyl-terminated PDMS above 230°C. Ultraviolet (UV) light induced polymerization of vinyl-terminated PDMS was successfully established via radicalization at the functional vinyl end groups of the chains. Atomic force microscopy nanoindentation of the UV-polymerized network reveals that the oligomer chain length determines the elastic modulus of the polymer layer. Manufactured as asymmetric cantilever structures, the bending characteristic gave evidence that a 200nm-thin film, activated in the voltage range between 1 and 12V, maintains the actuation compared to a 4μm-thick, spin-coated film, operated between 100 and 800V. The force of the presented 200nm-thin film cantilever actuator was about 10−4N. This means that a multilayer actuator with more than 104 layers would reach forces comparable to natural muscles. Therefore, such nanostructures can qualify for medical applications for example to treat severe incontinence.

Covalent Grafting of Polydimethylsiloxane over Surface-Modified Alumina Nanoparticles

The synthesis of ``smart structured'' conducting polymers and the fabrication of devices using them are important areas of research. However, conducting polymeric materials that are used in devices are susceptible to degradation due to oxygen and moisture. Thus, protection of such devices to ensure long-term stability is always desirable. Polymer nanocomposites are promising materials for the encapsulation of such devices. Therefore, it is important to develop suitable polymer nanocomposites as encapsulation materials to protect such devices. This work presents a technique based on grafting between surface-decorated gamma-alumina nanoparticles and polymer to make nanocomposites that can be used for the encapsulation of devices. Alumina was functionalized with allyltrimethoxysilane and used to conjugate polymer molecules (hydride-terminated polydimethylsiloxane) through a platinum-catalyzed hydrosilylation reaction. Fourier transform infrared spectroscopy, X-ray-photoelectron spectroscopy, and Raman spectroscopy were used to characterize the surface chemistry of the nanoparticles after surface modification. The grafting density of alkene groups on the surface of the modified nanoparticles was calculated using CHN and thermogravimetric analyses. The thermal stability of the composites was also evaluated using thermogravimetric analysis. The nanoindentation technique was used to analyze the mechanical characteristics of the composites. The densities of the composites were evaluated using a density gradient column, and the morphology of the composites was evaluated by scanning electron microscopy. All of our studies reveal that the composites have good thermal stability and mechanical flexibility and, thus, can potentially be used for the encapsulation of organic photovoltaic devices.

Hydrosilylation of Impact Polypropylene Co-polymer in a Twin-screw Extruder

The production of hydrosilylated impact polypropylene (PP) copolymer has been demonstrated in a co-rotating twin-screw extruder. This has been accomplished through a two-step reactive extrusion process that involves: (i) the formation of terminal double bonds on a commodity PP copolymer through peroxide initiated degradation reactions, and (ii) the melt-phase functionalization of these double bonds with hydride-terminated polydimethylsiloxane (PDMS). Spectroscopic analysis of the peroxide degraded PP and the purified hydrosilylated PP has been performed to confirm the attachment of PDMS onto the PP chains. In addition, the hydrosilylated PP has been characterized in terms of molecular, rheological, surface, and mechanical properties. It has been found that the two-step hydrosilylation reaction decreases molecular weight, imparts formation of branching/chain extension, decreases impact strength, and improves surface hydrophobicity. Finally, oscillatory shear measurements exhibit an unusual up-turn in the viscosity curve at low frequencies.