Preparation of ultra-thin elastomeric films.

When polydimethylsiloxane elastomers are produced, in the absence of great care, chains remain that are unbound to the cross-linked matrix. Due to the unbound chains swelling the crosslinked matrix, these materials are gels. We have developed a simple process to prepare well-controlled elastomeric thin films which do not rely on unknown commercial formulations.

High Refractive Index, Enantiopure Silicones Based on BINOL.

The high refractive index aromatic compound, binaphthol (BINOL), is readily incorporated into silicone polymer chains using the Piers-Rubinsztajn (PR) reaction; alternating and random linear copolymers, and elastomers are available. The highest refractive index (RI) materials are BINOL rich. It is not possible to directly make high refractive index linear polymers with very short HSi-capped, telechelic silicone chains, as they do not react cleanly. However, chain extending short vinyl-capped BINOL macromers with simple arylsilanes using hydrosilylation leads to polymers with a molar mass of up to 8000 and refractive indices of up to 1.58. Elastomers are prepared using similar processes. The reactions are facile to practice and suggest BINOL can be harnessed in these and other processes to augment RI.

Chelating Silicone Dendrons: Trying to Impact Organisms by Disrupting Ions at Interfaces.

The viability of pathogens at interfaces can be disrupted by the presence of (cationic) charge and chelating groups. We report on the synthesis of silicone dendrimers and linear polymers based on a motif of hexadentate ligands with the ability to capture and deliver metal ions. Mono-, di- or trialkoxysilanes are converted in G1 to analogous vinylsilicones and then, iteratively using the Piers-Rubinsztajn reaction and hydrosilylation, each vinyl group is transformed into a trivinyl cluster at G2. The thiol-ene reaction with cysteamine or 3-mercaptopropionic acid and the trivinyl cluster leads to hexadentate ligands 3 × N-S or 3 × HOOC-S. The compounds were shown to effectively capture a variety of metals ions. Copper ion chelation was pursued in more detail, because of its toxicity. On average, metal ions form chelates with 2.4 of the three ligands in a cluster. Upon chelation, viscous oils are converted to (very) soft elastomers. Most of the ions could be stripped from the elastomers using aqueous EDTA solutions, demonstrating the ability of the silicones to both sequester and deliver ions. However, complete ion removal is not observed; at equilibrium, the silicones remain ionically crosslinked.

Reversible Redox Crosslinking of Thiopropylsilicones.

Most silicone elastomers are thermosets. As a response to the new paradigm of polymer recyclability, the development of silicone elastomers that can be reversibly and repeatedly cured and uncrosslinked using redox conditions is reported. Thiopropyl-modified silicones are oxidized to elastomers with disulfide crosslinks using the organosoluble oxidant PhI(OAc)2 . As with any elastomer, mechanical properties can be tuned by varying crosslink density. Thermal stabilities in air show that the products are comparable to traditional silicone thermosets, with degradation only starting over 300 °C. Uncrosslinking back to the same thiopropyl-modified silicones involves reductive S-S bridge cleavage using a Piers-Rubinsztajn reaction with hydrosilanes catalyzed by B(C6 F5 )3 ; HSiMe2 OSiMe3 is identified as a convenient reducing agent. The initially formed silicone-(CH2 )3 S-SiMe2 OSiMe3 products need deprotection with water in isopropanol/water to completely regenerate the thiopropylsilicones. This oxidation/reduction crosslinking/uncrosslinking cycle is practiced thrice, with a yield of 89% per cycle, with essentially no change in the Young's moduli of the elastomers, or 1 H NMR spectra of the uncrosslinked fluids after reduction. Further oxidation of disulfide groups on the elastomer surface permanently and significantly improved water wettability.

Naturally Derived Silicone Surfactants Based on Saccharides and Cysteamine.

Silicone surfactants are widely used in many industries and mostly rely on poly(ethylene glycol) (PEG) as the hydrophile. This can be disadvantageous because commercial PEG examples vary significantly in polydispersity-constraining control over surface activity of the surfactant-and there are environmental concerns associated with PEG. Herein, we report a three-step synthetic method for the preparation of saccharide-silicone surfactants using the natural linker, cysteamine, and saccharide lactones. The Piers-Rubinsztajn plus thiol-ene plus amidation process is attractive for several reasons: if employed in the correct synthetic order, it allows for precise tailoring of both hydrophobe and hydrophile; it permits the ready utilization of natural hydrophiles cysteamine and saccharides in combination with silicones, which have significantly better environmental profiles than PEG; and the products exhibit interesting surface activities.

When Attempting Chain Extension, Even Without Solvent, It Is Not Possible to Avoid Chojnowski Metathesis Giving D3.

A simple, mild and efficient method to prepare HSi- or HOSi-telechelic, high-molecular-weight polydimethylsiloxane polymers (to 41,600 g·mol-1) using the one-shot hydrolysis of MHMH is reported; titration of the water allowed for higher molecular weights (to 153,900 g·mol-1). The "living" character of the chain extension processes was demonstrated by adding a small portion of MHMH and B(C6F5)3 (BCF) to a first formed polymer, which led to a ~2-fold, second growth in molecular weight. The heterogeneous reaction reached completion in less than 30 min, much less in some cases, regardless of whether it was performed neat or 50 wt% in dry toluene; homogeneous reactions in toluene were much slower. The process does not involve traditional redistribution, as judged by the low quantities (<3%) of D4 produced. However, it is not possible to avoid Chojnowski metathesis from MHDDMH giving D3, which occurs competitively with chain extension.

Psychopathy is associated with fear-specific reductions in neural activity during affective perspective-taking.

Psychopathic individuals are notorious for their callous disregard for others' emotions. Prior research has linked psychopathy to deficits in affective mechanisms underlying empathy (e.g., affective sharing), yet research relating psychopathy to cognitive mechanisms underlying empathy (e.g., affective perspective-taking and Theory of Mind) requires further clarification. To elucidate the neurobiology of cognitive mechanisms of empathy in psychopathy, we administered an fMRI task and tested for global as well as emotion-specific deficits in affective perspective-taking. Adult male incarcerated offenders (N = 94) viewed images of two people interacting, with one individual's face obscured by a shape. Participants were cued to either identify the emotion of the obscured individual or identify the shape from one of two emotion or shape choices presented on each trial. Target emotions included anger, fear, happiness, sadness, and neutral. Contrary to predictions, psychopathy was unrelated to neural activity in the Affective Perspective-taking > Shape contrast. In line with predictions, psychopathy was negatively related to task accuracy during affective perspective-taking for fear, happiness, and sadness. Psychopathy was related to reduced hemodynamic activity exclusively during fear perspective-taking in several areas: left anterior insula extending into posterior orbitofrontal cortex, right precuneus, left superior parietal lobule, and left superior occipital cortex. Although much prior research has emphasized psychopathy-related abnormalities in affective mechanisms mediating empathy, current results add to growing evidence of psychopathy-related abnormalities in a cognitive mechanism related to empathy. These findings highlight brain regions that are hypoactive in psychopathy when explicitly processing another's fear.

Energy-Dissipating Polymeric Silicone Surfactants.

Materials that are able to withstand impact loadings by dissipating energy are crucial for a broad range of different applications, including personal protective applications. Shear-thickening fluids (STFs) are often used for this purpose, but their preparation is still limited, in part, to high production costs. It is demonstrated that polymeric surfactants comprised of linear telechelic sugar-modified silicones-with neither additives nor particles-generate transient polymer networks (TPNs) that represent a promising alternative to STFs. The reported polymers have distinct viscoelastic properties and can turn from a liquid into a rubbery network when force is applied. Saccharide-modified silicones with short chains (degree of polymerization (DP) ≈ 34, 68) are solids, but become energy-absorbing viscoelastic fluids when diluted in low-viscosity silicone oils; longer silicones (DP ≈ 338, 675) with low saccharide contents are viscoelastic fluids at room temperature. Excellent damping properties are found for the reported silicone surfactants, even those containing only 0.1% saccharides. The degree of energy absorption can be tailored simply by controlling the sugar/silicone ratio.

Reliable Condensation Curing Silicone Elastomers with Tailorable Properties.

The long-term stability of condensation curing silicone elastomers can be affected by many factors such as curing environment, cross-linker type and concentration, and catalyst concentration. Mechanically unstable silicone elastomers may lead to undesirable application failure or reduced lifetime. This study investigates the stability of different condensation curing silicone elastomer compositions. Elastomers are prepared via the reaction of telechelic silanol-terminated polydimethylsiloxane (HO-PDMS-OH) with trimethoxysilane-terminated polysiloxane ((MeO)3Si-PDMS-Si(OMe)3) and ethoxy-terminated octakis(dimethylsiloxy)-T8-silsesquioxane ((QMOEt)8), respectively. Two post-curing reactions are found to significantly affect both the stability of mechanical properties over time and final properties of the resulting elastomers: Namely, the condensation of dangling and/or unreacted polymer chains, and the reaction between cross-linker molecules. Findings from the stability study are then used to prepare reliable silicone elastomer coatings. Coating properties are tailored by varying the cross-linker molecular weight, type, and concentration. Finally, it is shown that, by proper choice of all three parameters, a coating with excellent scratch resistance and electrical breakdown strength can be produced even without an addition of fillers.

High-Throughput Synthesis and Characterization of Aryl Silicones by Using the Piers-Rubinsztajn Reaction.

Arylsilicones are widely exploited for their thermal and optical properties. The creation of phenylsilicone elastomers with specific physical properties is typically done by a "one-off" formulation and test process. Herein, it is demonstrated that high-throughput synthesis methods can be used to rapidly prepare a series of arylsilicone elastomers and then the relative impact of different aryl groups on their physical properties is assessed. Aromatic groups were incorporated into polydimethylsiloxane (PDMS) elastomers by exploiting the relative reactivity of different functional groups in the Piers-Rubinsztajn reaction. To analyze trends in the silicone mechanical properties as a function of increasing aryl concentration-structure/property relationships-libraries of elastomers were both quickly synthesized and characterized by using high-throughput suites starting from low viscosity silicone oils/monomers in 96-well plates. Liquid handling parameters were optimized to effectively work with the silicones. Incorporating aryl instead of alkyl crosslinkers into the PDMS backbone increased the silicone elastomer modulus by approximately 50 % (at a crosslink density of 6 %); elastomers prepared with an aromatic crosslinker with three contact points led to much higher moduli compared with those with one contact point at the same crosslink density. When located at precise rather than random points on the silicone chains, diphenylsilicones had lower moduli than analogous monophenylsilicones.

Evaluation of a cognitive-behavioral intervention for high- and medium-risk probationers.

Reducing recidivism is a central goal of treatment programs for offenders. Preliminary evidence suggests that cognitive-behavioral group interventions based on the National Institute of Corrections curriculum (Bush, Glick, & Taymans, 1997) may be effective in reducing recidivism rates among adult probationers. We evaluated the effectiveness of a program based on this curriculum among 167 high- and medium-risk probationers assigned to this program and a comparison group of 120 high- and medium-risk probationers matched on age and number of prior criminal charges. Improvements over prior studies included use of survival analytic methods and propensity score matching, a longer follow-up interval, and examination of treatment effectiveness within ethnic groups. Relative to the comparison group, treatment group probationers were more likely to complete probation satisfactorily and survive longer before rearrest. Moreover, supplementary analyses suggested that ethnicity was associated with differences in intervention effectiveness. Treatment was predictive of lower recidivism rates among European Americans and African Americans but was less effective among Latino American probationers.

Hyperbranched Silicone MDTQ Tack Promoters.

Low molecular weight, highly crosslinked silicone resins are widely used as reinforcing agents for highly transparent elastomers and adhesion/tack promoters in gels. The resins are complex mixtures and their structure / property relationships are ill defined. We report the synthesis of a library of 2, 3 and 4-fold hyperbranched polymeric oils that are comprised of linear, lightly branched or highly branched dendronic structures. Rheological examination of the fluids and tack measurements of gels filled with 10, 25 or 50% dendronic oils were made. Viscosity of the hyperbranched oils themselves was related to molecular weight, but more significantly to branch density. The properties are driven by chain entanglement. When cured into a silicone gel, less densely branched materials were more effective in improving tack than either linear oils or Me3SiO-rich, very highly branched oils of comparable molecular weight, because the latter oils underwent phase separation.

New Control Over Silicone Synthesis using SiH Chemistry: The Piers-Rubinsztajn Reaction.

There is a strong imperative to synthesize polymers with highly controlled structures and narrow property ranges. Silicone polymers do not lend themselves to this paradigm because acids or bases lead to siloxane equilibration and loss of structure. By contrast, elegant levels of control are possible when using the Piers-Rubinsztajn reaction and analogues, in which the hydrophobic, strong Lewis acid B(C6 F5 )3 activates SiH groups, permitting the synthesis of precise siloxanes under mild conditions in high yield; siloxane decomposition processes are slow under these conditions. A broad range of oxygen nucleophiles including alkoxysilanes, silanols, phenols, and aryl alkyl ethers participate in the reaction to create elastomers, foams and green composites, for example, derived from lignin. In addition, the process permits the synthesis of monofunctional dendrons that can be assembled into larger entities including highly branched silicones and dendrimers either using the Piers-Rubinsztajn process alone, or in combination with hydrosilylation or other orthogonal reactions.

Silicone Microemulsion Structures Are Maintained During Polymerization with Reactive Surfactants.

Bicontinuous microemulsions exhibit domain structures on the nanoscale (<20 nm). Normally, such fine details are lost during the conversion from a fluid microemulsion to solid elastomeric materials, as a consequence of interfacial destabilization via polymerization of either the oil phase or monomers in the aqueous phase. Very little is known about the polymerization of silicone microemulsions and the morphological changes that occur upon transition from a nanostructured liquid to a solid matrix. Silicone microemulsions polymerized by free radical (aqueous phase) and condensation (silicone phase) processes, respectively, were characterized by small-angle X-ray scattering and transmission electron microscopy. It was found that cross-linking of the silicone phase alone led, over time, to large increase of the size of the microemulsion nanodomains. By contrast, photoinduced polymerization of a reactive surfactant and acrylic monomers in the aqueous phase was effective at retaining bicontinuous nanomorphology, irrespective of the degree of cross-linking of the silicone phase.

Glycerol-Silicone Elastomers as Active Matrices with Controllable Release Profiles.

Drug release regimes must be controlled for the optimal therapeutic effect. Although it is relatively straightforward to create first-order release matrices, it can be challenging to avoid an initial burst. Matrices with zero-order profiles are perceived to be beneficial in many cases but are even more difficult to formulate. We describe the straightforward synthesis of elastomeric composites prepared from silicone in which the active substance is dispersed in glycerol. The release of glycerol-soluble actives from the films of these materials was shown to be tunable with respect to the order of release (zero- or first-order) simply by changing the glycerol content. Importantly, release from the elastomers showed no burst effect. The discrete glycerol domains embedded within a silicone matrix act as reservoirs for active substances. Upon contact with aqueous media, the active substances are released from the matrices exhibiting zero-order, near zero-order, or first-order release kinetics. Various parameters that could influence the release process, including glycerol content, glycerol domain size, or membrane thickness, are thoroughly investigated, elucidating guidelines for creating matrices capable of delivering the active substances at desired rates. Additionally, the composites proved to absorb significant amounts of liquid water (up to 1850% of sample mass), a feature that can be tuned by the manipulation of the composite structure.

Murder and psychosis: Neuropsychological profiles of homicide offenders with schizophrenia.

BACKGROUND: Neurocognitive dysfunction, a core feature of schizophrenia, is thought to contribute to the impulsive violent aggression manifested by some individuals with schizophrenia, but not enough is known about how homicidal individuals with schizophrenia perform on neuropsychological measures. AIMS: The primary aim of our study was to describe the neuropsychological profiles of homicide offenders with schizophrenia. Supplementary analyses compared the criminal, psychiatric and neuropsychological features of schizophrenic homicide offenders with and without God/Satan/demon-themed psychotic symptoms. METHODS: Twenty-five men and women diagnosed with schizophrenia who had killed another person - 21 convicted of first-degree murder and 4 found not guilty by reason of insanity - completed neuropsychological testing during forensic evaluations. RESULTS: The sample was characterised by extensive neurocognitive impairments, involving executive dysfunction (60%), memory dysfunction (68%) and attentional dysfunction (50%), although those with God/Satan/demon-themed psychotic symptoms performed better than those with nonreligious psychotic content. CONCLUSIONS: Our findings indicate that impaired cognition may play an important role in the commission of homicide by individuals with schizophrenia. A subgroup with God/Satan/demon delusions seem sufficiently less impaired that they might be able to engage in metacognitive treatment approaches, aimed at changing their relationship to their psychotic symptoms, thus reducing the perception of power and omnipotence of hallucinated voices and increasing their safety. Copyright © 2016 John Wiley & Sons, Ltd.

Surface Behavior of Boronic Acid-Terminated Silicones.

Silicone polymers, with their high flexibility, lie in a monolayer at the air-water interface as they are compressed until a critical pressure is reached, at which point multilayers are formed. Surface pressure measurements demonstrate that, in contrast, silicones that are end-modified with polar groups take up lower surface areas under compression because the polar groups submerge into the water phase. Boronic acids have the ability to undergo coordination with Lewis bases. As part of a program to examine the surface properties of boronic acids, we have prepared boronic acid-modified silicones (SiBAs) and examined them at the air-water interface to better understand if they behave like other end-functional silicones. Monolayers of silicones, aminopropylsilicones, and SiBAs were characterized at the air-water interface as a function of end functionalization and silicone chain length. Brewster angle and atomic force microscopies confirm domain formation and similar film morphologies for both functionalized and non-functionalized silicone chains. There is a critical surface pressure (10 mN m(-1)) independent of chain length that corresponds to a first-order phase transition. Below this transition, the film appears to be a homogeneous monolayer, whose thickness is independent of the chain length. Ellipsometry at the air-water interface indicates that the boronic acid functionality leads to a significant increase of film thickness at low molecular areas that is not seen for non-functionalized silicone chains. What differentiates the boronic acids from simple silicones or other end-functionalized silicones, in particular, is the larger area occupied by the headgroup when under compression compared to other or non-end-functionalized silicones, which suggests an in-plane rather than submerged orientation that may be driven by boronic acid self-complexation.

Silicone boronates reversibly crosslink using Lewis acid-Lewis base amine complexes.

Silicone elastomers are normally thermosets, which are not readily recycled or repurposed. The few examples of thermoplastic silicone elastomers depend on reversible covalent and non-covalent molecular interactions. It is demonstrated that amine-boronate complex formation provides a simple and flexible route to reversible crosslinked silicones. A variety of network structures were prepared by use of terminal and pendantly functionalised silicone boronates and amines. The crosslink density was quantified using a combination of Shore-hardness measurements, swelling, and rheological analyses. Stress induced by compressive force could be relieved through dynamic B-N bond reformation at 60 °C. Materials could be fully disassembled through introduction of n-butylamine and successfully reformed upon removal of the monofunctional amine by evaporation.

Printing silicone-based hydrophobic barriers on paper for microfluidic assays using low-cost ink jet printers.

Paper-based microfluidic devices exhibit many advantages for biological assays. Normally, the assays are restricted to certain areas of the paper by hydrophobic barriers comprised of wax or alkyl ketene dimers (AKD). Neither hydrophobic barrier is able to constrain aqueous solutions of surfactants, which are frequently used in biological assays. We demonstrate that rapidly curing silicone resins can be inkjet printed onto pure cellulose paper using inexpensive thermal ink-jet printers. The Piers-Rubinsztajn (PR) reaction dominates the cure chemistry leading to cellulose fibers that are surface coated with a silicone resin. The resulting barriers are able to resist penetration by surfactant solutions and even by the lower surface energy solvents DMF and DMSO. The utility of the barrier was demonstrated using a coliform assay based on detection of ß-galactosidase.