Polysiloxane Chains Research Articles

Using structure biodegradability relationships for environmentally benign design of organosilicons – An experimental comparison of organosilicons and their carbon analogues

Organosilicon substances are ubiquitous in the environment due to their stability and numerous applications in consumer products. Therefore, it is desirable to reduce their environmental persistency. Our study aimed to better understand the impact of silicon atoms in organic compounds on their environmental biodegradability as a contribution to sustainable chemistry. Accordingly, we investigated the biodegradability of organosilicon compounds and their carbon analogues. OECD 301D test was used to assess ready biodegradability. In addition, GC-MS analyses were performed to study the fate of the compounds in the test. Three out of five carbon compounds and no organosilicon compound were found readily biodegradable. In all but one case, higher biodegradation degrees could be observed for the carbon compounds. Hydrolysis was identified as a mandatory step prior to the biodegradation of organosilicon substances. The silicon-free product of hydrolysis determined the rate of biodegradation. The silicon-containing reaction products of hydrolysis were not biodegradable. The high biodegradability of one organosilicon compound can be attributed to faster hydrolysis due to an easily hydrolysable Si–N bond and a high biodegradation rate of the resulting silicon-free hydrolysis product. Insertion of such heteroatoms or functional groups into polysiloxane chains may be a promising approach to benign organosilicon compounds.

Fast pyrolysis of silicones at low temperatures catalyzed by anatase titanium dioxide

Silicones are widely used in medical and engineering field for their remarkable properties. The resulting waste is an increasing economic and environmental problem. Pyrolysis can be a feasible way to recycle silicone waste. Since its high thermal stability, looking for an efficient catalyst becomes necessary. In this work, anatase titanium dioxide was found to be very efficient in catalyzing the pyrolysis of silicones even at extremely low temperatures. The pyrolysis rate, pyrolysis products, the catalytic mechanism of silicones and the reusability of catalyst were investigated in detail via thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), wide-angle X-ray diffractometer (wide angle XRD), thermogravimetric analysis-Fourier transform infrared spectroscopy (TG-FTIR), and pyrolysis-gas chromatography/mass spectroscopy (Py-GC/MS). During pyrolysis, polysiloxane chain undergoes catalyzed unzipping depolymerization. The catalytic mechanism is believed to be the nucleophilic attack of silicon in the main chain by the hydroxyl group on anatase titanium dioxide. This is the first report on pyrolysis of silicones catalyzed by anatase titanium dioxide. The blending of anatase titanium dioxide with polysiloxane may become a promising technology for inexpensive, high efficient and sustainable feature in feedstock recycling of silicones. In addition, this new discovery also offers guidance that fillers with such high active hydroxyl groups should be avoided in polysixoane composites.

Effect of surface morphology on the adhesion of silicone elastomers on AA6061 aluminum alloy

In this study, different primer formulations were used for enhancing the adhesion between a high consistency methyl phenyl vinyl silicone rubber (HCR) and AA6061 aluminum alloy. These formulations were selected on the basis of their different chemical composition. One contains only silanes and a titanate catalyst, a second contains only reactive macromolecular polysiloxane chains and a third contains both silanes and reactive macromolecular polysiloxane chains as the main components. The effect of the metal surface topography on the efficiency of the primers was investigated. The condensation reactions in the primers were followed by Fourier Transform Infrared Reflexion Absorption (FTIR-RA) spectroscopy and rheological measurements. 90° peel test was used to measure the adhesive strength of the silicone on metal and the fracture surfaces after peeling were analysed using SEM-EDS to determine the loci of failure. Cure monitoring of the silane based formulations showed that hydrolysis/condensation of silanes occur rapidly after their application on AA6061 surfaces and lead to a high degree of crosslinking even in the formulations with PDMS additives. The heat cure of the formulation based on a one-component addition curing system (SiH oligomer, vinylated-PDMS with a platinum catalyst) resulted in a film with a high cohesive strength. The primer formulation containing silanes and reactive PDMSs as the main components resulted in the best adhesion of the silicone elastomer with a dominant cohesive failure. However, a weaker adhesion was obtained at a high roughness of the substrate due to a weak adhesive strength at the metal/primer interface. A pretreatment composed of a first layer of activated silanes and a second layer of reactive silicone chains gave a good adhesion both at low and high roughness of the aluminum substrate.Roughening of the metal surface did not improve the adhesion of silicone elastomers on the primed metals in any of the studied treatments, indicating that mechanical interlocking and increase in contact area do not contribute to adhesion. The results were discussed based on the different chemical composition and rheological properties of the primer formulations.

Polycondensation of Water Glass Sodium Silicates in the Presence of [BnXn]2– (n = 10, 12; X = H, Cl) Boron Cluster Anions

It has been shown that two competing processes occur in a system of water glass (WG) silicates and [BnXn]2– (n = 10, 12; X = H, Cl) boron cluster anions (WG/[An]) in the range 100–200°C: the formation of a supramolecular structure due to cation–anion contacts of the silanol groups of the silicate with [An]'s at t ≤ 100°C and the condensation of the silanol groups of the silicate, resulting in the formation of polysiloxane chains (t ≥ 180°C). The difference in temperature conditions between these processes leads to inhibition of the silicate condensation process. The detailed structure of the silicate component of the WG/[An] systems has been studied as a function of [An] content.

Use of floating acylphosphine oxide-based photoinitiators to reduce surface oxygen inhibition of UV-LED photopolymerization

a series of acylphosphine oxide-based self-floating photoinitiators (PIs) of (TPO-F/Si/C12/C22) for improving the surface oxygen inhibition resistance are synthesized by following the modification of the traditional PI of ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate (TPO-L). The four self-floating PIs bear low surface free energy units of fluorine, polysiloxane, C12 and C22 long chain aliphatic alkane, respectively. The self-floating ability are assessed by UV absorption spectra and further confirmed by the X-ray photoelectron spectroscopy (XPS) and the water contact angle tests. The self-floating ability of the PIs can enable the UV-LED photopolymerization of the acrylic monomers to conquer the surface oxygen inhibition by increasing the local PI concentration, which is evidenced by ATR-IR, confocal Raman microscopy (CRM) and Photo-DSC. The self-floating ability enriches the PIs in the upper layers to consume the surface oxygen as well as to enable the fast cure of the resin surface to stop the further penetration of the oxygen into deeper sites.

Synthesis and Properties of Linear Polyether-Blocked Amino Silicone-Modified Cationic Waterborne Polyurethane

In this study, a waterborne polyurethane (WPU) is synthesized by using polytetramethylene ether glycol (PTMEG) to form the soft segment, 1,4-butanediol (BDO) as the chain extender, n-methyldiethanolamine (MDEA) as a hydrophilic chain extender, and isophorone diisocyanate (IPDI) to form the hard segment. Furthermore, the modified cationic WPU emulsion and its films are created through a reaction between the WPU and a linear polyether-blocked amino silicone (LEPS), which is an organosilicon compound that imparts flexibility. The properties of the structure and formed WPU films are then characterized by using Fourier transform infrared spectrometry, a thermogravimetric analysis, atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, as well as by measuring the water contact angle, testing the water absorption, etc. It is found that, with an increase in the LEPS content in the WPU, the particle size of the modified WPU emulsion is increased, the WPU films are more flexible, and the resistance of the modified WPU films to heat and water are increased, while the crystallinity is reduced. The polysiloxane chain segment, which is added to the LEPS-modified WPU emulsion, is significantly enriched on the surface of the modified WPU films, while there are no adverse effects of the LEPS-modified WPU emulsion on the adhesive force between the WPU and substrate. When the LEPS content of the WPU is 14.0 wt%, the modified WPU emulsion and film provide the best performance.

Dilution-Induced Physico-Chemical Changes of Metal Oxide Nanoparticles Due to Homeopathic Preparation Steps of Trituration and Succussion.

Although the presence of starting materials in extreme dilutions of homeopathic medicines has been established, the physico-chemical changes of these materials induced by the manufacturing steps-that is, solid-solid mixing involving grinding (trituration) and slurry mixing involving impact (succussion), followed by dilution-are still unknown. We subjected cupric oxide and zinc oxide nanoparticles (NPs) to the homeopathic processes of trituration and succussion, followed by dilution up to 6 cH. Particle image velocimetry was employed to analyze the fluid motion during succussion and its effect on the NPs. The resulting microstructural and chemical changes at different dilution steps were determined by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and transmission electron microscopy. The succussion triggered multi-sized bubble generation and turbulent fluid motion up to a duration of 400 ms, with maximum average velocity of 0.23 m/s. Due to 1% transfer of kinetic energy from a moving eddy with this velocity, upon collision, the rate of temperature change in a particle of size 1 µm and 1 nm was predicted to rise by approximately 102 K/s and 106 K/s respectively. During trituration, the oxide NPs reduced to metals and did not aggregate by remaining within lactose, but they converted to oxidized finer NPs after impact. Silicate chains leached from the vial cross-linked after third dilution, forming large macro-particles and encapsulating the NPs that were retained and carried at higher dilution steps. The results showed that the NPs sustained significant rate of temperature change due to energy transfer from moving eddies during succussion. Different physico-chemical changes, such as size reduction, successive reduction and oxidation of NPs, and morphological changes, were achieved through trituration and succussion. The retention of NPs within cross-linked poly-siloxane chains reveals the importance of both the borosilicate glass vial and the ethanol solution during preparation of homeopathic medicines.

High Fluorescent Hyperbranched Polysiloxane Containing β-Cyclodextrin for Cell Imaging and Drug Delivery.

Hyperbranched polysiloxane (HBPSi) is attracting increasing attention due to its intrinsic fluorescence and good biocompatibility. However, it is very challenging to explore its biological applications because of the low fluorescence intensity and quantum yield. Herein, we introduced rigid β-cyclodextrin to the end of flexible polysiloxane chain to synthesize a novel fluorescent polymer (HBPSi-CD) and explore its biological applications. Results showed that the fluorescence intensity and quantum yield of HBPSi-CD, compared with HBPSi, were significantly enhanced. Theoretical calculations and transmission electron microscopy demonstrated that the synergy effect of intra/intermolecular hydrogen bonds and hydrophobic effect promoted the formation of large supramolecular self-assemblies and space electron delocalization systems, leading to intense fluorescence. Notably, the biocompatible HBPSi-CD not only lighted up mouse fibroblast cells, but also possessed high ibuprofen loading capacity (160 mg g-1) and superior pH-responsive drug release performance. This work promoted the development of biological applications of HBPSi.

Load Transfer Behavior of 3D Aerogels Fabricated with Halloysite Nanotubes

AbstractNanofibrous network aerogels as an important class of porous material have received enormous attention in materials research. However, the fabrication of nanofibrous network aerogels with short fiber as building blocks is extremely challenging, since it is difficult for them to build 3D network structures spontaneously from the topological point of view. Here the synthesis and load transfer behavior of 3D aerogels composed of halloysite nanotube (HNT) short fibers are described. The resulting aerogels take inorganic materials as the skeleton, elastic organic materials as the connection point, and exhibit inorganic/organic phase interfaces. Confocal Raman microscopy system is utilized to investigate the structural‐dynamic profile of halloysite clay aerogels (HCAs) under applied load. The results indicate that the deformation mainly occurs in the polysiloxane (PSO) molecular chain connected with the HNT skeleton. HCAs have a certain load transfer capability, and the PSO chains between tubes are strong enough to support the HCA skeleton.

Functionalized graphene‐reinforced polysiloxane nanocomposite with improved mechanical performance and efficient healing properties

ABSTRACTIt is a challenge to design nanofiller reinforced self‐healing nanocomposites with both improved mechanical properties and highly efficient self‐healing properties. In this work, we report a self‐healing polysiloxane nanocomposite using furan‐functionalized graphene (G‐FA) as reinforcement based on Diels−Alder (DA) chemistry. The formed interactions between G‐FA and polysiloxane chains were reversible DA bonds, which negligibly affected the nanocomposites healing efficiency. The self‐healing polysiloxane nanocomposite with 6% G‐FA has a tensile strength of 0.25 MPa that was improved by 140% when compared to an elastomer without G‐FA. The healable polysiloxane nanocomposite recovered more than 90% of its tensile strength and 98% of its elongation‐at‐break, demonstrating that the nanocomposite exhibited highly efficient self‐healing properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47725.

How the Crosslinking Agent Influences the Thermal Stability of RTV Phenyl Silicone Rubber.

In this work, a thermal degradation mechanism of room temperature vulcanized (RTV) phenyl silicone rubber that was vulcanized by different crosslinking agents was discussed. Firstly, RTV phenyl silicone rubber samples were prepared by curing hydroxyl-terminated polymethyldiphenylsiloxane via three crosslinking agents, namely, tetraethoxysilane (TEOS), tetrapropoxysilane (TPOS), and polysilazane. Secondly, the ablation properties of RTV phenyl silicone rubber were studied by the muffle roaster test and FT-IR. Thirdly, thermal stability of the three samples was studied by thermogravimetric (TG) analysis. Finally, to explore the thermal degradation mechanism, the RTV phenyl silicone rubber vulcanized by different crosslinking agents were characterized by TG analysis-mass spectrum (TG-MS) and pyrolysis gas chromatogram-mass spectrum (pyGC-MS). Results showed that the thermal stability of RTV phenyl silicone rubber is related to the amount of residual Si–OH groups. The residual Si–OH groups initiated the polysiloxane chain degradation via an ‘unzipping’ mechanism.

Donor/Acceptor Segregated π-Stacking Arrays by Use of Shish-Kebab-Type Polymeric Backbones: Highly Conductive Discotic Blends of Phthalocyaninatopolysiloxanes and Perylenediimides

Construction of large-area electron donor–acceptor (D–A) interfaces and hole/electron pathways is important for photoconducting and photovoltaic functions. Although blends of D- and A-type discotic π-systems have a possibility to realize one-dimensional charge carrier pathways as well as heterointerfaces, D–A segregated structures are difficult to develop by self-assembly because they are entropically unfavored structures. Here we report the use of shish-kebab-type hole-transporting discotic columns fixed by a self-threading polysiloxane chain and approach to such segregated nanostructures. Electron-donor/acceptor blends of soluble phthalocyaninatopolysiloxanes (Poly-SiPcs) and perylenedicarboximides (PDIs) were prepared, and their photoconductive property was investigated. Although Poly-SiPc1 shows a photoinduced charge separation with PDI1 analogous to the corresponding monomeric phthalocyanines (SiPc1 and H2Pc1), the Poly-SiPc1/PDI1 system displays a remarkably larger photoconductivity than SiPc1/PDI1 ...

Synthesis and performances of polysiloxane-modified 5-arylthianthrenium salt cationic photoinitiators with self-floating capability

Currently cationic photoinitiators possess undesirable characteristics of poor solubility in epoxy resins and the release of odorous and toxic by-products. These shortcomings greatly limit the applications of the photoinitiators. Here, the synthesis and initiating cationic photopolymerization properties of three new polysiloxane-modified 5-arylthianthrenium salt cationic photoinitiators (1187-Si-A/B/C) whose polysiloxane-modified cations could be considered as environmentally friendly are reported. The photoinitiators are synthesized based on 9-(4-hydroxyethoxyphenyl) thianthrenium hexaflorophosphate (Esacure 1187) and polysiloxane. The cationic photoinitiators not only exhibit excellent solubility in epoxy resins, but also do not release odour and toxic by-products under UV irradiation, which is demonstrated by liquid chromatography-electrospray ionization-mass spectrometry [LC-ESI(+)-MS]. The photoinitiating activity of 1187-Si-A/B/C is investigated by real-time infrared spectroscopy (RTIR), and it is found that 1187-Si-A/B/C can effectively initiate cationic photopolymerization by the photosensitization of 9,10-dibutoxyanthracene (DBA). More importantly, the polysiloxane chains offer 1187-Si-A/B/C good self-floating capability, and thus the photoinitiators are promising for the preparation of gradient polymers by cationic photopolymerization.

Ordering minimalist bridged polysilsesquioxane films under visible LED light irradiation

ABSTRACTA visible light-mediated sol–gel process can promote the ordering of hexylene, octylene, and decylene-bridged polysilsesquioxane (SQ) with very simple organosilane building blocks having only a short alkylene bridging group: (CH3O)3SiCnH2nSi(OCH3)3 (n = 6, 8, 10). Photocondensation and self-assembly of films are promoted through exposure to a light-emitting diode (LED; 405 nm). The solvent-free synthesis involves very low light intensity (0.1 mW/cm2) and a minimum amount of photoacid generator (PAG; 0.5 wt%) acting as a photocatalyst. X-ray diffraction (XRD) and scanning electron microscopy (SEM) prove the high level of organization, while real-time Fourier transform infrared spectroscopy shows conformational ordering of alkylene chains throughout irradiation. Molecular modeling reveals a multilayer structure based on the stacking of a single polysiloxane chain, with organic groups attached to adjacent Si atoms showing up and down orientation.

Gradient polymer networks formed by photopolymerization with self‐floating polysiloxane‐containing nanogel

Polysiloxane‐containing nanogels can be used as a fast, convenient and environmentally friendly method to control gradient photopolymerization and to obtain gradient polymer network because of its self‐floating feature. The chain length of polysiloxane is a key factor that influences the self‐floating capability of the polysiloxane‐containing nanogel. This paper reports a series of nanogels compositions synthesized with methacrylate‐modified polysiloxanes with different chain lengths, urethane dimethacrylate (UDMA) and isobornyl methacrylate (IBMA) at a molar ratio of 10:20:70 in the presence of a thiol chain transfer agent. The effect of polysiloxane chain length on self‐floating capability of the nanogel and gradient polymer network was researched. The results show that polysiloxane chain length is the main driving force for the self‐floating capability of the nanogels. The nanogel with long polysiloxane chain length exhibits good self‐floating capability in the monomer–polymer matrix because of the lower surface tension of polysiloxane. Furthermore, the gradient polymer network containing the nanogel with long polysiloxane chain length presents lower dispersion surface energy and greater hardness and thermostability. Copyright © 2016 John Wiley & Sons, Ltd.

A study of nanogels with different polysiloxane chain lengths for photopolymerization stress reduction and modification of polymer network properties

Polysiloxane-based nanogels with different chain lengths can not only reduce polymerization stress, but also improve the flexibility, thermostability and hydrophobic properties of photopolymerization materials.

Brief overview on 2H NMR studies of polysiloxane-based side-chain nematic elastomers.

This is a brief overview on recent studies on liquid crystalline elastomers (LCEs) based on polysiloxane chain, in the form of monodomain films, selectively (2)H-labeled in different parts of the LCE samples, i.e. on the crosslinker or mesogenic units. (2)H NMR spectroscopic techniques were used to measure the temperature dependence of the quadrupolar splittings, line widths and relaxation times, T(1) and T(2). From these data, several information about the orientational order parameter, S, of various LCE fragments, thermodynamic features of the isotropic-nematic transition and main motional processes could be generalized for this type of elastomers.

Synthesis and characterization of new, liquid, branched poly(methylvinylborosiloxanes)

Abstract New liquid branched poly(methylvinylborosiloxanes) (br-PMVBS) of random structure were synthesized in three steps. By reacting boric acid with an excess of dimethyldichlorosilane (Me2SiCl2) in dry ether a “borosiloxane precursor”: tris(chlorodimethylsilyl) borate B(OSiMe2Cl)3 was prepared. In the second step of synthesis ether solution of B(OSiMe2Cl)3 was added to a mixture of appropriate organic chlorosilanes (Me2SiCl2, MeViSiCl2, MeSiCl3, and Me3SiCl) and all reagents were reacted with stoichiometric amounts of water, in the presence of pyridine (as an acceptor of HCl), in dry ether, at low temperature (usually at -10 to 0 C). In order to fully react (“to block”) trace silanol groups, reactions of intermediate PMVBS with additional batches of Me3SiCl were carried out in the third step, C5H5N·HCl was filtered off and washed with a dry ether. The solvent was distilled off from filtrates and low molecular weight siloxane oligomers were removed by a vacuum distillation at 130-150 C. Chemical structures of br-PMVBS were confirmed by elemental analysis and spectroscopic methods (FTIR, emission atomic spectroscopy ICP-AES, and NMR: 1H, 29Si and 11B). On the basis of analysis of their 29Si-NMR spectra the microstructure of polysiloxane chains was proposed. The prepared br-PMVBS had in their structures: triple branching borosiloxane units: BO1.5 and in some cases methylsiloxane moiety CH3SiO1.5 (T). They contained linkages: Si-O-Si, Si-O-B, vinyl(methyl)siloxane functional groups (CH2=CH)MeSiO (Dvi), dimethylsiloxane mers (CH3)2SiO (D), and non-reactive trimethylsiloxy terminal groups (CH3)3SiO0.5 (M), but they did not have: hydroxyl functional groups: Si-OH and B-OH, and sensitive to water B-O-B linkages. Molecular weights of br-PMVBS (Mn = 1500-3300 g/mol; Mw = 3800-7400 g/mol) and their polydispersity (Mw/Mn = 2.0-2.5) were determined by a size exclusion chromatography (SEC).

Controlled Thiol‐Ene Functionalization of Polyferrocenylsilane‐block‐Polyvinylsiloxane Copolymers

A general route for the controlled functionalization of polyferrocenylsilane‐block‐polyvinylsiloxane copolymers, which should be transferable to other silicone‐based materials, is developed utilizing the photoinitiated thiol‐ene reaction. Poly(ferrocenyldimethylsilane)54‐block‐poly(methylvinylsiloxane)510 (PFDMS54‐b‐PMVS510) is synthesized via sequential living anionic polymerization and quantitatively functionalized with a range of thiols, with the aim of tuning the solubility of the resulting materials for self‐assembly studies or incorporating more complex functionality for subsequent applications. When functionalization is attempted using a deficit of thiol, the photoinitiator 2,2‐dimethoxy‐2‐phenylacetophenone, used to accelerate the radical reaction, is found to cause significant cross‐linking of the polysiloxane chain. Reproducible percentage thiol‐ene functionalization of the polysiloxane block can be achieved by the use of PFDMS53‐b‐PMVS58/PDMS444 (PDMS = polydimethylsiloxane), prepared by the copolymerization of cyclic siloxane monomers, [Me(CHCH2)SiO]3 and [Me2SiO]3, to tune the vinyl group incorporation pre‐functionalization. image

Studying the rheology, optical clarity and surface tension of an acrylic/melamine automotive clearcoat loaded with different additives

Acrylic/melamine based automotive clearcoats were prepared by inclusion of functional and conventional additives. The conventional additives used were based on polysiloxane chains without any reactive groups. On the other hand, the functional additives were based on polyacrylate and polysiloxane backbones. The additives were added to the clearcoat formulations at different concentrations. Surface tension, optical properties and rheological behaviors of the clearcoats were studied by tensiometer, gonio-spectrophotometer, rheometric mechanical spectrometer (RMS) and Brookfield techniques. Results showed that addition of both conventional and functional additives reduced the surface tension of the clearcoat up to a certain value of the additive concentration. It was seen that functional additives could reduce surface tension much greater than the conventional ones. The coating clarity and transparency were not affected in presence of conventional additives. However, the functional additives, especially the one having higher molecular weight, reduced the coating transparency. The clearcoat viscosity was increased using functional additives. A shear thickening behavior of the clearcoats loaded with functional additives was seen. The conventional additives did not change the clearcoat viscosity. It was concluded that the additive functionality, molecular weight and chemical structure were influential parameters affecting the final properties.