Multilayered thiol-ene network films with two and three different components were fabricated by spin coating and photopolymerization. The distinctive glass transition temperatures of each layer component were observed at corresponding glass transition regions of each bulk sample. Sub-Tg aging of 10-, 21-, and 32-layered thiol-ene films was investigated in terms of enthalpy relaxation. Enthalpy relaxation of each layer component occurred independently and presented the characteristic time and temperature dependency. Overlapped unsymmetrical bell-shaped enthalpy relaxation distribution having peak maximum at Tg-10°C of each layer component was observed, resulting in broad distribution of enthalpy relaxation over wide temperature range. In addition, enthalpy relaxation of each layer component in the multilayered thiol-ene films was significantly accelerated comparing to that of bulk thiol-ene samples. Dynamic mechanical thermal properties of multilayered thiol-ene films also showed two and three separated glass transition temperature. However, for 32-layered thiol-ene film consisting of three different layer components, glass transition and damping region are overlapped and the width is extended more than 100°C. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Thiol–alkyne ‘click’ chemistry is a modular, efficient mechanism to synthesize complex A2B 3-arm star polymers. This general motif is similar to a phospholipid where the A blocks correspond to lypophilic chains and the B block represents the polar head group. In this communication we employ thiol–yne chemistry to produce polypeptide-based A2B lipid mimetics. The utility of the thiol–yne reaction is demonstrated by using a divergent and a convergent approach in the synthesis. These polymers self-assemble in aqueous solution into spherical vesicles with a relatively narrow size distribution independent of block composition over the range studied. Using the thiol–yne convergent synthesis, we envision a modular approach to functionalize proteins or oligopeptides with lipophilic chains that can imbed seamlessly into a cell membrane.

UV-VIS spectral comparison with model compounds and isolation of the major product from preparative photolysis of one of the models has been used to show that the predominant photochemical reactions in the solid state of an aryl cinnamate polymer are 2+2 cycloaddition and photo-Fries rearrangement.

Following Sharpless' visionary characterization of several idealized reactions as click reactions, the materials science and synthetic chemistry communities have pursued numerous routes toward the identification and implementation of these click reactions. Herein, we review the radical-mediated thiol-ene reaction as one such click reaction. This reaction has all the desirable features of a click reaction, being highly efficient, simple to execute with no side products and proceeding rapidly to high yield. Further, the thiol-ene reaction is most frequently photoinitiated, particularly for photopolymerizations resulting in highly uniform polymer networks, promoting unique capabilities related to spatial and temporal control of the click reaction. The reaction mechanism and its implementation in various synthetic methodologies, biofunctionalization, surface and polymer modification, and polymerization are all reviewed.

Radical mediated thiol-yne polymerization reactions complement the more well-known thiol-ene radical polymerization processes, with the added advantage of increased functionality. In one system studied, the rate constant for the addition of the thiol to the vinyl sulfide created by the initial reaction of the thiol with the alkyne is three times faster than the initial reaction. When hydrocarbon based dialkynes and dithiols were copolymerized, the resulting thiol-alkyne networks containing only hydrocarbon and sulfide linking groups exhibited refractive index values tunable above 1.65, with the refractive index directly related to the sulfur content. The thiol-yne reaction was also found to be useful in functionalizing thiol-terminated polymer chain ends via sequential Michael thiol-ene addition followed by the thiol-yne reaction: the result is the dual functionalization of the polymer chain end. A thermally responsive polymer hydrogel network was formed when an yne terminated water-soluble homopolymer was polymerized with a tetrafunctional thiol.

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AbstractNach Sharpless’ visionärer Charakterisierung verschiedener idealisierter Reaktionen als Klick‐Reaktionen hat man innerhalb der Materialwissenschaften und Synthesechemie große Anstrengungen unternommen, um solche Reaktionen zu finden und zu implementieren. In diesem Aufsatz diskutieren wir die radikalvermittelte Thiol‐En‐Reaktion, die über all die Merkmale einer Klick‐Reaktion verfügt: hohe Effizienz, einfache Durchführung, keine Nebenprodukte, hohe Reaktionsgeschwindigkeiten, hohe Ausbeuten. Darüber hinaus besteht die Möglichkeit, die Thiol‐En‐Reaktion photoinitiiert auszuführen, was insbesondere für Photopolymerisationen zur Synthese extrem einheitlicher Polymernetzwerke genutzt wird. Der Reaktionsmechanismus wird nach dem aktuellen Kenntnisstand erläutert, und zentrale Anwendungen der Thiol‐En‐Reaktion in der Material‐ und Molekülsynthese, der Biofunktionalisierung, der Polymersynthese und der Oberflächen‐ und Polymermodifizierung werden zusammengefasst.

Multifunctional alkynes (2, 3, or 4 ynes per monomer) were prepared utilizing the nucleophile-catalyzed thio Michael addition reaction from commercially available multifunctional thiols (2, 3, or 4 thiols) and propargyl acrylate. Real-time FTIR (RTIR) and NMR spectroscopies indicate that the conjugate addition under these conditions proceeds to high conversions within seconds using the nucleophilic catalyst dimethylphenylphosphine, in the absence of solvent. at ambient temperature, and with no side products. A family of polymer networks was prepared by the photoinitiated thiol-yne reaction employing a 2:1 ratio of thiol to alkyne, which resulted in uniformly cross-linked materials of systematically increasing cross-link density. Photopolymerization kinetic profiles indicate that the thiol-yne reaction proceeded rapidly to high conversion with conversions decreasing with increasing functionality of the thiol and/or alkyne groups. Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) results clearly indicate that the glass transition temperature increases as the overall cross-link density increases (from -10 to 42 degrees C by DMTA). An increase in the rubbery modulus (from 6 to 23 MPa at 70 degrees C) results as the functionality increases, with a concomitant decrease in the molecular weight between cross-links.

The free volume, transport, and physical properties of a series of n-alkyl derivatized thiol-ene networks are reported. Derivatized thiol monomers were prepared via a nucleophile-catalyzed thio-Michael addition reaction of multifunctional thiols to n-alkyl acrylates ranging from n = 1 to n = 16 in length. Using UV-initiated photopolymerization, cross-linked networks were fabricated from these systematically modified thiol monomers. Each network consisted of the same molar concentration of alkyl chains. Both the thio-Michael reactions and the network photopolymerizations reached high conversion regardless of n-alkyl length, which is typical of the thiol-ene click reaction. The incorporation of alkyl chains led to the formation of new networks with markedly loose packing as probed by density measurements. The density decreased by 11% as n increased from 1 to 16. It is believed that the alkyl chains acted as spacers or pillars which expanded the cross-linked network scaffold increasing the free volume. The free volume behavior of these expanded networks was probed by positron annihilation lifetime spectroscopy (PALS). The hole volume size as measured by PALS doubled with an increase in alkyl chain length from 1 to 16. Oxygen transport measurements indicated an exponential increase in oxygen permeability across 2 orders of magnitude which was related to the increase in free volume. Glass transition temperatures were interestingly comparable for all derivatized networks regardless of n-alkyl length. Water contact angle was additionally evaluated for these derivatized networks. As expected, contact angle increased with increasing n-alkyl length, demonstrating that the surfaces were altered (becoming more hydrophobic) due to an increased concentration of methylene groups in the bulk.

Methacrylate monomers have been widely used in medical and dental applications such as bone cements, dental fillings, bioadhesives, and hydrogels. One major problem of these monomers resides in their low rates of polymerization leading to leaching problems that cause irritation of the surrounding tissues and even cell death. Here we describe the synthesis and polymerization of new mono-methacrylates containing multifunctional pyrrolidinone moieties. Such monomers possess stronger inherent hydrogen bonding potential susceptible to increase their reactivity and polymerization rates. These monomers were shown to homopolymerize rapidly leading to crosslinked polymers. The corresponding rates of polymerization were found to be comparable to difunctional methacrylates such as hexanediol dimethacrylate. Intermolecular hydrogen bonding interactions involving the pyrrolidinone unit leads these monomers to behave as “pseudo” difunctional monomers upon homopolymerization.

Submitted for the MAR10 Meeting of The American Physical Society Kinetics and physical properties of photolatent base catalyzed thiol-epoxy resins CHRISTOPHER COMER, OLIVIA MCNAIR, CHARLES HOYLE, DANIEL SAVIN, University of Southern Mississippi, School of Polymers and High Performance Materials — Typical epoxy resin systems based on multifunctional epoxides and multifunctional amines yield polymeric materials with unrivaled chemical resistance, toughness, and adhesion. Unfortunately amine cured epoxy resins must be mixed immediately prior to application because reactivity of the amine and epoxy is too high. Thiol-epoxy resins offer a less reactive alternative to these traditional epoxy resins and are catalyzed by the addition of a tertiary amine, such as DBN. In this study a combination of a diepoxide with multifunctional thiols based on mercaptoacetate (MA) and mercaptopropionate (MP) were polymerized using a photolatent base catalyst or DBN. The reactivity of the MA and MP based thiols were characterized using Real-time FT-IR. Mechanical and thermal properties of the resins were characterized using DMA, DSC, MTS, pencil hardness, and impact resistance. Thiol-cured epoxy systems have uniform network structures, as indicated by sharp tan δ peaks and distinct glass transition region shown by DMA and DSC respectively. Daniel Savin University of Southern Mississippi Date submitted: 19 Nov 2009 Electronic form version 1.4

A detailed evaluation of the kinetics of the thiol-Michael reaction between hexanethiol and hexyl acrylate is described. It is shown that primary amines are more effective catalysts than either secondary or tertiary amines with, for example, quantitative conversion being achieved within 500 s in the case of hexylamine with an apparent rate constant of 53.4 mol L-1 s(-1) at a catalyst loading of 0.057 mol %. Certain tertiary phosphines, and especially tri-n-propylphosphine and dimethylphenylphosphine, are shown to be even more effective species even at concentrations 2 orders of magnitude lower than employed for hexylamine and performed in solution with quantitative conversions reached within ca. 100 s for both species and apparent rate constants of 1810 and 431 mol L-1 s(-1), respectively. The nature of the thiol is also demonstrated to be an important consideration with mercaptoglycolate and mercaptopropionate esters being significantly more reactive than hexanethiol with reactivity mirroring the pK(a) of the thiols. Likewise, it is shown that the structure of the activated ene is also crucial with the degree of activation and ene-substitution pattern being important features in determining reactivity. In terms of reaction with hexanethiol in the presence of hexylamine as catalyst, it is shown that propylmaleimide > diethyl fumarate > diethyl maleate > dimethylacrylamide > acrylonitrile > ethyl crotonate > ethyl cinnamate > ethyl methacrylate.

Non-extractable photoinitiators could be advantageous for use in biological, electronic, and food packaging applications. Therefore, thioxanthone and benzophenone derivatives were synthesized from 1,6-hexane dithiol and chlorinated benzophenone or thioxanthone. The efficiency of thiol-functionalized photoinitiators in combination with amine co-initiators was compared to benzophenone and isopropylthioxanthone with amine co-initiators, and the cleavage of photoinitiator 2,2-dimethoxy-1,2-diphenylethan-1-one in acrylic resins. The reaction kinetics were analyzed using photo-differential scanning calorimetry and real-time FTIR. Coating physical properties were evaluated by pendulum and pencil hardness, steel–wool scratch and mandrel bend tests. The non-extractable photoinitiators had higher absorbance than their benzophenone or isopropylthioxanthone counterparts due to the sulfide substitution on the phenyl ring, and the free thiol groups reacted with the acrylate by either an amine catalyzed Michael addition or a free-radical chain process. The combination of thiol-functionalized photoinitiators with secondary amines provides an efficient photoinitiator system that is locked into the photopolymerized network and cannot be extracted with typical solvents.

Thiol-isocyanate-ene ternary networks with systematic variations (100/100/0, 100/80/20, 100/60/40, 100/40/60, 100/20/80, and 100/0/100) were prepared by sequential and simultaneous thiol-ene and thiol-isocyanate click reactions. The thiol-isocyanate coupling reaction was triggered thermally or photolytically to control the sequence with the thiol-ene photopolymerization. Triethyl amine (TEA) and 2,2-dimethoxy-2-phenyl acetophenone (DMPA) were used for the sequential thermally induced thiol-isocyanate coupling and photochemically initiated thiol-ene reaction, respectively. A thermally stable photolatent base catalyst (tributylamine.tetraphenylborate salt, TBA center dot HBPh4) capable of in situ generation of tributylamine by UV light was used with isopropylthioxanthone (ITX) for the simultaneous thiol-isocyanate/thiol-ene curing systems The kinetics of the hybrid networks investigated using real-time IR indicate that both thiol-isocyanate and thiol-ene reactions were quantitatively rapid and efficient (>90% of conversion in a matter of minutes and seconds, respectively) The T-g of the thiourethane/thiol-ene hybrid networks progressively increases (-5 to 35 degrees C by DSC) as a function of the thiourethane content due to the higher extent of hydrogen bonding, also resulting in enhanced mechanical properties. Highly uniform and dense network structures exhibiting narrow full width at half-maximum (similar to 10 degrees C) were obtained for both the sequential and the simultaneous thiol click reactions, resulting in identical thermal properties that are independent of the sequence of the curing processes

TheNovelPhotocurableNetwork： Urea-tetraaCrylate／thioISystem HironoriMatsushimaa，JunghwanShinb，JustinW．Chana，MasamitsuShiraiCandCharlesE．Hoylea α滋000材Pゆmer滋空eαα〃月鞄■カタeゆr∽α〃Ceル如er妨 徹的血相妙〆助〃伽r〃肋∫7∫∫讐-，助〟おろ〟移肋血妙jタ4略U朋 ∂αe∽血相頑〃eer-〃gα〃d肋′er-α由比綾乃Ce Uわルem砂q／腰刀〃e∫OJα，腑〃〃e(pOJれル伽〃e∫0才α55455，U鼠4 °か甲αrJme〃′〆4摺プアねdC e〝扉∫りGrαゐαe滋00村方〃g加er加島 0∫αbP頑cJ〟柁Uわgve相和ノーJGαん〟e〃-C転ぶd如才，0∫α玩5タクー∂JjtJ卸α〃 Keywords：urea-aCrylate，thiourethane-aCrylatethioIclickreaction，thiol-aCrylateMichaeladdition 1．Introduction Thiol-ene reaCtions，in both radical and base／nucleophilicreactions，havebeenintroduced as versatile synthetic tooIs，reCently being generalized as thioI click-tyPe reaCtions and demonstrated to be a powerfulmethodfor the fabrication of high perfomanCe POlymeric materials．1．4 The photopolymerizations of thiol-aCrylate SyStemS give networks with broader and indistinctglasstransitiontemperaturesduetothe largeextentofacrylatehomopolymerizationand resultantinhomogeneous morphology，While amine catalyzed thiol-aCrylate Michaeladdition reactionformsahomogeneousnetworkresulting inverynarrowglasstransitiontemperature・5 We reported that the thiol-isocyanate-aCrylate temary SyStem had higher glass transition temperature and refractiveindices than the thiol-ene-aCrylatesystemduetotheincorporation ofthiourethanelinkages6・ Urea derivatives formed by the amine-isocyanate click type reactionl have excellent physical／mechanical properties includinghigherthemalstability，hardness，and abrasion resistance due to stronger hydrogen bonding compared to polyurethanes or POlythiourethanes．However，urea-incorporated acrylateshavenotbeenreportedduetoprobably the extremely highviscosityand accompanying limitationinapplications

Thiol-ene click chemistry was adapted to easily and rapidly modify exo-olefin polyisobutylene with an array of thiol compounds bearing useful functionalities, including primary halogen, primary amine, primary hydroxyl, and carboxylic acid.

Thiol-isocyanate-acrylate ternary networks were formed by the combination of thiol-isocyanate coupling, thiol-acrylate Michael addition, and acrylate homopolymerization. This hybrid polymerization reaction sequence was preferentially controlled by using phosphine catalyst systems in combination with photolysis. The reaction kinetics of the phosphine/acrylate thiolisocyanate coupling reactions were systematically investigated by evaluating model, small molecule reactions. The thiol-isocyanate reaction was completed within 1 min while the thiol-acrylate Michael addition reaction required similar to 10 min. Both thiol-isocyanate coupling and thiol-acrylate Michael addition reactions involving two-step anionic processes were found to be both quantitative and efficient. However, the thiol-isocyanate coupling reaction was much more rapid than the thiol-acrylate Michael addition, promoting initial selectivity of the thiol-isocyanate reaction in a medium containing thiol, isocyanate, and acrylate functional groups. Films were prepared from thiol-isocyanate-acrylate ternary mixtures using 2-acryloyloxyethylisocyanate and di-, tri-, and tetra-functional thiols. The sequential thiol-isocyanate, thiol-acrylate, and acrylate homopolymerization reactions were monitored by infrared spectroscopy during film formation, whereas thermal and mechanical properties of the films were evaluated as a function of the chemical composition following polymerization. The results indicate that the network structures and material properties are tunable over a wide range of properties (T(g) similar to 14-100 degrees C, FWHM similar to 8-46 degrees C), while maintaining nearly quantitative reactions, simply by controlling the component compositions. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3255-3264, 2010