Novel hydrogels based on a high‐molar‐mass water‐soluble dimethacrylate monomer

This report describes the preparation and swelling behaviour of novel hydrogels based on a water‐soluble dimethacrylate monomer (EBisEMA), which is characterized by a relatively high molar mass (M_n ～ 1700 g mol^?1) and contains a high proportion of aliphatic ether bonds in its structure. This feature results in moderately crosslinked and flexible polymer networks. Significant differences were observed in degree of swelling, depending on the synthesis method employed to obtain the hydrogels. The equilibrium water sorption of EBisEMA photopolymerized in bulk was 68 wt% while that of EBisEMA photopolymerized in aqueous solution (0.5 g mL^?1) was 104 wt%. Thiol–methacrylate hydrogels were prepared by visible light photopolymerization of EBisEMA with a tetrafunctional thiol (PETMP) at various EBisEMA‐to‐PETMP molar ratios. These hydrogels contained unreacted thiol groups because of a faster homopolymerization reaction of EBisEMA. Hydrogels were also prepared in bulk by propylamine‐catalysed Michael addition reaction. No significant differences in swelling were observed between EBisEMA homopolymer and photocured EBisEMA–PETMP copolymer. Conversely, a marked increase in water uptake (110 wt%) was observed in the EBisEMA–PETMP hydrogels prepared by the Michael addition reaction catalysed by propylamine. These trends are explained in terms of a balance between the mass fraction of hydrophilic groups and the crosslinking density of the network. EBisEMA–PETMP hydrogels formulated with thiol in excess showed a noticeable tendency to adhere to diverse substrates, including paper, metals, glass and skin. This feature makes them especially attractive in applications for which adhesion is particularly critical such as dermatological patches. © 2018 Society of Chemical Industry     

Novel thermal curing of cycloaliphatic resins by thiol–epoxy click process with several multifunctional thiols

Novel thermosets were prepared by the base‐catalysed reaction between a cycloaliphatic resin (ECC) and various thiol crosslinkers. 4‐(N,N‐Dimethylaminopyridine) (DMAP) was used as base catalyst for the thiol–epoxy reaction. A commercial tetrathiol (PETMP) and three different thiols synthesized by us, 6SH‐SQ, 3SH‐EU and 3SH‐ISO, were tested. 6SH‐SQ and 3SH‐EU were prepared from vinyl or allyl compounds from renewable resources such as squalene and eugenol, respectively. Thiol 3SH‐ISO was prepared starting from commercially available triallyl isocyanurate. A kinetic study of the mixtures was performed using differential scanning calorimetry. Stoichiometric ECC/thiol/DMAP formulations were cured at 120 °C for 1 h, at 150 °C for 1 h and post‐cured for 30 min at 200 °C. The materials were characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis and dynamic mechanical thermal analysis. The results revealed that the materials obtained from the synthesized thiols had higher thermal stability and glass transition temperatures than those obtained from the commercial PETMP. In addition, all the materials obtained exhibited very good transparency. This study proves the ability of multifunctional thiols to crosslink cycloaliphatic epoxy resins, leading to more flexible materials than those obtained by cationic homopolymerization of ECC or base‐catalysed ECC–anhydride copolymerization. © 2017 Society of Chemical Industry     

Thiol–ene addition enables tailored synthesis of poly(2‐oxazoline)‐graft‐poly(vinyl pyrrolidone) copolymers for binder jetting 3D printing

The continued interest in graft copolymer architectures arises from their unique solution properties and potential for a myriad of applications ranging from drug delivery to adhesives. Poly(vinyl pyrrolidone) (PVP) represents a popular amorphous, water‐soluble polymer used as a polymeric binder in binder jetting additive manufacturing, as fillers in cosmetic products, and for subcutaneous drug delivery systems. This report describes the synthesis of poly(2‐oxazoline) and PVP graft copolymers using a ‘grafting to’ methodology with an efficient thiol–ene ‘click’ reaction. Copolymerization of 2‐methyl‐2‐oxazoline and 2‐(3‐butenyl)‐2‐oxazoline introduced pendent vinyl grafting sites with a predictable absolute number‐average molecular weight. In parallel, reversible addition‐fragmentation chain‐transfer polymerization and subsequent aminolysis yielded well‐defined, oligomeric, thiol‐terminated PVP. Thiol–ene click chemistry enabled the formation of poly(2‐oxazoline)‐graft‐poly(vinyl pyrrolidone) (PMeOx‐g‐PVP) copolymers with varying mole percent grafting sites and PVP graft length. ¹H NMR spectroscopy, aqueous SEC with multiangle light scattering (SEC‐MALS), and bromine titrations confirmed chemical structure, and DSC with TGA elucidated thermal transitions. Aqueous SEC‐MALS and ¹H NMR spectroscopy also determined absolute number‐ and weight‐average molecular weights and average grafting levels, which revealed optimal reaction conditions. Zero‐shear viscosities of 5 and 10 wt% solutions in deionized water for each graft copolymer compared to their linear analogs demonstrated a significant (ca 31%) decrease in viscosity at the same number‐average molecular weight. This decrease in solution viscosity suggested PMeOx‐g‐PVP copolymers as exceptional alternatives to linear analogs for aqueous‐based, binder jetting additive manufacturing.     

Correlating structure with ionic conductivity in bis(phosphonium)‐containing [NTf2] thiol–ene networks

Thiol–ene photopolymerization was employed in order to prepare a series of covalently crosslinked bis(phosphonium)‐containing poly(ionic liquid) (PIL) networks. While the counteranion was held constant (NTf₂), the structure of the bis(phosphonium)‐containing ‘ene’ monomer was varied in order to explore the breadth of thermal, mechanical and conductive properties available for this system. Towards this end, it was determined that more flexible spacers within the cationic monomer led to PIL networks with lower T_g values and higher conductivities. Most notable was a two‐ to three‐orders‐of‐magnitude increase in ionic conductivity (from 10^?9 to 10^?6 S cm^?1 at 30 °C, 30% relative humidity) when the R group on phosphonium was changed from phenyl to isopropyl. Changing the functional group ratio to off‐stoichiometry also led to a slight increase in conductivity. Although the thermal stability (T_d5%) of the phosphonium ionic liquid monomers was found to be significantly higher (>400 °C) than that of analogous imidazolium monomers, this improvement was not observed to directly transfer over to the polymer where a two‐step decomposition pathway was observed. The first step is attributed to the thiol monomer backbone while the second step correlates well with decomposition of the phosphonium portion of the PIL. © 2019 Society of Chemical Industry     

Hyperbranched polyesters based on hydroxyalkyl‐lactones via thiol‐ene click reaction

The preparation of AB₂ monomers via thiol‐ene click reaction from six‐ and seven‐membered unsaturated lactones is described. The hydroxyl‐functionalized valerolactone was prepared by use of Michael thiol‐ene‐addition reaction starting from 2‐mercaptoethanol and 3‐methylenetetrahydro‐2H‐pyran‐2‐on. The hydroxyl‐functionalized caprolactone was prepared radically from 2‐mercaptoethanol and 7‐allyloxepan‐2‐one. Both AB₂ monomers were polymerized via ring opening in the presence of tin(II)‐2‐ethylhexanoate (Sn(Oct)₂) as a catalyst yielding the hyperbranched polyesters. The new hyperbranched polyesters were analyzed by ¹³C NMR spectra to determine the degree of branching. © 2014 Society of Chemical Industry     

Evaluation of new 3‐mercaptopropionate thiols for thiol‐ene photopolymerization coatings using experimental design

Three 3‐mercaptopropionate thiols, 1,6‐Hexane bis(3‐mercaptopropionate) (HD‐SH), trans‐1,4‐Cyclohexanedimethyl bis(3‐mercaptopropionate) (CHDM‐SH), and 4,4′‐Isopropylidenedicyclohexane bis(3‐mercaptopropionate) (HBPA‐SH) were formulated with 1,3,5‐triallyl‐1,3,5‐triazine‐2,4,6(1H,3H,5H)‐trione (TATATO) and photoinitiator. The formulations were photopolymerized via thiol‐ene photopolymerization. A ternary experimental design was employed to elucidate the influence the three thiols on the thermomechanical and coatings properties of thiol‐ene photopolymerizable materials. Tensile strength, tensile modulus, elongation‐to‐break, glass transition temperature (T_g), and crosslink density (XLD) were investigated. Coating properties including pencil hardness, pull‐off adhesion, MEK double rubs, and gloss were also investigated. Relative reaction conversion was determined by photo differential scanning calorimeter (PDSC). Thiol‐ene photopolymerizable materials containing HBPA‐SH resulted in improving tensile strength, tensile modulus, T_g, and pencil hardness but lowering of crosslink density and relative conversion. This was attributed to steric and rigidity of the double cycloaliphatic structure. The inclusion of CHDM‐SH into the systems resulted in the synergistic effect on elongation‐to‐break and pull‐off adhesion. The HD‐SH generally resulted in a diminution of thermomechanical and coating properties, but improved the crosslink density. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal polymerization of thiol–ene network‐forming systems

The thermal polymerization of a tetrafunctional thiol (PETMP) and divinyl ether (TEGDVE) was monitored by temperature‐ramping differential scanning calorimetry (DSC) and the effects of inhibitor type and concentration, oxygen inhibition and initiator type were studied. The incorporation of inhibitors was required to produce a stable system at room temperature. Butylated hydroxytoluene (BHT) inhibited polymerization at low temperatures, but was inefficient at high temperatures and polymerization rates, and hence BHT is an ideal stabilizer. In contrast, a nitroxide inhibitor (NO‐67) was a very effective inhibitor and no polymerization occurred until all of the nitroxide was depleted. The presence of oxygen retarded the onset of polymerization but did not change the final conversion significantly. Polymerization with initiators having higher half‐life temperatures shifted the DSC peak to higher temperature because the rate of initiator decomposition and thus initiation was slower. Rheological investigations of the cure at different temperatures revealed that the gel time decreased significantly with increasing cure temperature, and the calculated apparent activation energy for PETMP/TEGDVE was 54 kJ mol^?1. Dynamical mechanical thermal analysis of the cured material was undertaken and frequency‐superposed results revealed that the glass transition region of PETMP/TEGDVE/azobisisobutyronitrile was much narrower than that of free‐radically cured dimethacrylate, but was similar to that of an epoxy resin cured with an aromatic diamine. This behaviour could be attributed to PETMP/TEGDVE network homogeneity, or to the less constrained crosslinks in the PETMP/TEGDVE network. Copyright © 2007 Society of Chemical Industry     

3D‐Printing of High‐κ Thiol‐Ene Resins with Spiro‐Orthoesters as Anti‐Shrinkage Additive

Tri(ethylene glycol) divinyl ether and the spiro‐orthoester 2‐((allyloxy)methy)‐1,4,6‐trioxospiro[4.4]nonane can be formulated in different ratios and crosslinked by thiol‐ene reactions. The spiro‐orthoester is used as anti‐shrinkage additive, enabling shrinkage reduction of up to 39%. Addition of a radical photoinitiator for the thiol‐ene reaction and a cationic photoinitiator for the double ring‐opening of the spiro‐orthoester enables dual‐curing for application in 3D‐printing. The formulation free of the spiro‐orthoester shows gelation during the printing process and, correspondingly, low resolution. The formulations containing the spiro‐orthoester exhibit higher resolutions in the range of 50 µm. The resins containing mixtures of tri(ethylene glycol) divinyl ether and the spiro‐orthoester show permittivities as high as 10⁴. The dielectric loss factor of the resins is in the range of 0.5–7.6, and the conductivity in the range of 1.3?10^?11 to 2.0?10^?11 S cm^?1. These high‐κ materials can be 3D‐printed by digital light processing for the next generation of electronic materials.     

Synthesis and thermomechanical properties of allyl‐functionalized polycaprolactone urethane‐co‐2‐hydroxylethyl methacrylate networks

PCL‐segmented multiallyl‐functionalized poly (ester urethane) prepolymers (PEUs) were prepared in a two‐step process. First, hydroxyl‐terminated PCL and glycerol simultaneously reacted with an excess of a diisocyanate, the obtained isocyanate functionalized prepolymers then reacts with allyl amine. PEUs structure choice mainly focused on two aspects: the PCL segments concentration and the allyl functionality that, respectively, affects the biodegradability and the density of the issued networks. The concentrations of the different reactants were fixed, taking into account the desired mean structure and also to prevent crosslinking during the synthesis of the prepolymers. FTIR was principally used to monitor the synthesis of allyl functionalized PEUs. The carbonyl absorption of PCL, initially located at 1720 cm^?1, reaction of the PCL and shifted toward 1730 cm^?1, due to a decrease in crystallinity as confirmed by DSC. The structure of allyl‐functionalized PCL‐segmented PEU analyzed by ¹H NMR, double bond content was between 0.2 and 1.2 mmol g^?1. Networks were obtained by UV‐initiated radical copolymerization of allyl‐functionalized PEUs and HEMA. The effects of PCL concentration and molar mass on their thermomechanical and thermal properties were analyzed. Particular damping properties were obtained. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41295.     

Preparation of multifunctional thiol‐ and acrylate‐terminated polyurethane: A comparative study on their properties in UV curable coatings

The multifunctional thiol‐ and acrylate‐terminated polyurethane (PU) has been successfully prepared for using as the main resin in the UV curable coatings. The structure and molecule weight of prepared PUs were analyzed by fourier transformed infrared spectroscopy (FTIR) and gel permeation chromatography, respectively. The results showed that the different terminal multifunctional groups have been grafted onto the PU and their difference in molecule weight was significant. Used as the main resin in coatings, the curing kinetic and percentage conversion of the different UV curing coatings system were investigated by real‐time FTIR method, and the effects of terminal functional groups and photoinitiator on the final conversion percentage and conversion rate were also compared. It is observed that the thiol‐terminated PU had higher conversion speed and final conversion percentage due to the remarkable effect of mercapto groups on reducing oxygen inhibition during UV curing process. The shrinkage, viscosity, and adhesion of UV curable coatings with thiol‐ and acrylate‐terminated PUs were also investigated and compared, and the results indicated that the former exhibited lower shrinkage and higher adhesion performances than the latter, along with the lower viscosity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40740.     

A new atom transfer radical polymerization initiator based on phenolphthalein for the synthesis of bis‐allyloxy functionalized polystyrene macromonomers

A new atom transfer radical polymerization (ATRP) initiator, namely 2‐(1,1‐bis(4‐(allyloxy)phenyl)‐3‐oxoisoindolin‐2‐yl)ethyl 2‐bromo‐2‐methylpropanoate, was synthesized starting from phenolphthalein, a commercially available and an inexpensive chemical. Well‐ defined bis‐allyloxy functionalized polystyrene macromonomers (M_n,GPC 4800–11 700 g mol^?1) with controlled molecular weight and narrow molecular weight distribution (1.05–1.09) were synthesized using ATRP by varying the monomer to initiator feed ratio. The presence of allyloxy functionality on polystyrene was confirmed by Fourier transform infrared and ¹H NMR spectroscopy. A kinetic study of polymerization revealed pseudo‐first‐order kinetics with respect to monomer consumption. Initiator efficiency was found to be in the range 0.80–0.95. Matrix‐assisted laser desorption ionization time of flight spectra showed a narrow molecular weight distribution with control over the molecular weight. The reactivity of the allyloxy groups on polystyrene was successfully demonstrated by quantitative photochemical thiol‐ene click reaction with benzyl mercaptan as the model thiol reagent. Furthermore, the thiol‐ene click reaction was exploited to introduce other reactive functional groups such as hydroxyl and carboxyl by reaction of α,α′‐bis‐allyloxy functionalized polystyrene with 2‐mercaptoethanol and 3‐mercaptopropionic acid, respectively. © 2014 Society of Chemical Industry     

Photopolymerization kinetics,photorheology and photoplasticity of thiol–ene–allylic sulfide networks

BACKGROUND: Thiol–ene networks are of interest due to their facile photopolymerization and their open network structure. In this work, an allylic disulphide divinyl ether monomer is reacted with tetrathiol and divinyl ether monomers, which allows the network structure to permanently change in shape if stressed while under irradiation. We also study the photo‐differential scanning calorimetry (DSC) kinetics and photorheology during cure and the dynamic mechanical properties after cure. RESULTS: The heat of polymerization is similar for the thiol–ene systems and suggests ca 80% conversion of the vinyl ether groups. An increase in the initiator concentration increases the photocure rate as expected. The activation energy for photopolymerization is 7.6 kJ mol^?1. DSC and rheometry studies show that the polymerization kinetics is slowed by the addition of the allylic disulfide divinyl possibly due to the formation of less reactive radicals. However, as shown by dynamic mechanical thermal analysis, the network structure is not changed very much by addition of this monomer. If radicals are generated by irradiation of a photoinitiator in the network while a stress is being applied, the polymer will permanently deform depending on the fraction of 2‐methylenepropane‐1,3‐di(thioethyl vinyl ether) in the network, due to a bond interchange reaction. CONCLUSION: The rate of thiol–ene reaction is slowed by the addition of the allylic disulfide divinyl ether. Photoplasticity is observed in the networks containing the allylic disulfide groups. Further work is required to optimize the extent of photoplasticity in these systems. Copyright © 2007 Society of Chemical Industry     

Properties of polythiourethanes prepared by thiol–isocyanate click reaction

Polythiourethane networks with systematic compositional variations of thiol [ethoxylated trimethylol‐propane tri(3‐mercapto‐propionate), ETTMP1300 and pentaerythritol tetra(3‐mercapto‐propionate), PETMP] and isophorone diisocyanate (IPDI), i.e., IPDI/ETTMP1300/PETMP = 100/100/0, 100/80/20, 100/60/40, 100/40/60, 100/20/80, and 100/0/100, were prepared by base catalyzed thiol–isocyanate click type reaction where the base catalyst (tributylamine, TBA) was photolytically generated using photolatent amine (TBA·tetraphenylborate salt, TBA·HBPh₄). The kinetics of the polythiourethane network formation investigated using real‐time infrared indicates that the thiol–isocyanate coupling reaction was successfully triggered photolytically and the conversion of both thiol and isocyanate reached near 100% in a matter of minutes. The T_g of the polythiourethane networks progressively increases (–8 to 143 °C by DMTA) as a function of the PETMP content due to the higher extent of crosslinks, also resulting in enhanced rubbery modulus. Very narrow full width at half maximum (15–28 °C) of tan δ peak was obtained for all six sets of polythiourethane networks, which is induced by the highly uniform and dense structures of thiol‐based polymeric network. Energy damping performance of polythiourethane networks measured by nondestructive impact testing exhibited remarkably high (～95%) and the relationship with temperature was in accordance with tan δ peak. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46070.     

Design of S‐Allylcysteine in Situ Production and Incorporation Based on a Novel Pyrrolysyl‐tRNA Synthetase Variant

The noncanonical amino acid S‐allyl cysteine (Sac) is one of the major compounds of garlic extract and exhibits a range of biological activities. It is also a small bioorthogonal alkene tag capable of undergoing controlled chemical modifications, such as photoinduced thiol‐ene coupling or Pd‐mediated deprotection. Its small size guarantees minimal interference with protein structure and function. Here, we report a simple protocol efficiently to couple in‐situ semisynthetic biosynthesis of Sac and its incorporation into proteins in response to amber (UAG) stop codons. We exploited the exceptional malleability of pyrrolysyl‐tRNA synthetase (PylRS) and evolved an S‐allylcysteinyl‐tRNA synthetase (SacRS) capable of specifically accepting the small, polar amino acid instead of its long and bulky aliphatic natural substrate. We succeeded in generating a novel and inexpensive strategy for the incorporation of a functionally versatile amino acid. This will help in the conversion of orthogonal translation from a standard technique in academic research to industrial biotechnology.     

Preparation of epoxy‐ended hyperbranched polymers with precisely controllable degree of branching by thiol‐ene Michael addition

Epoxy‐ended hyperbranched polymers (EHPs) have a wide range of applications due to their outstanding performances. Because their microstructures are not positively identified, it is very difficult to ascertain the reinforcing and toughening mechanisms of EHPs and their interface interaction with other matrixes. Controllable synthesis of EHPs with precise degree of branching (DB) remains to be a major challenge. Here, a method for preparing novel nitrogen‐phosphor skeleton epoxy‐ended hyperbranched polymers (NPEHP) with controllable DB by a thiol‐ene Michael addition between thiol‐ended hyperbranched polymers (NPHSH) and glycidyl methacrylate have been firstly reported. NPHSH is synthesized by an esterification between hydroxyl‐ended hyperbranched polymers (NPHOH) and 3‐mercaptopropionic acid. NPHOH is prepared by a thiol‐ene Michael addition between methacrylate group of a monomer and thiol group of linear monomer (AB) and/or branched monomer (AB₂). The molar ratio between the AB and AB₂ monomers controls the DB of the products. The ¹H NMR spectra analysis of NPHOH shows that their experimentally determined DBs are very close to their theoretical values, indicating good controllability of their DBs. The narrow molecular weight distributions of NPHOH, NPHSH, and NPEHP suggest high efficiency of the thiol‐ene Michael addition. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44277.     

Synthesis of PS‐g‐POSS hybrid graft copolymer by click coupling via ”graft onto” strategy

Polystyrene (PS)‐incorporated polyhedral oligomeric silsesquioxanes (POSS) organic–inorganic hybrid graft copolymer could be achieved by click coupling reaction between alkyne groups in POSS and azido groups in PS via “graft onto” strategy. Alkyne‐functionalized POSS was synthesized via thiol‐ene facile click reaction and subsequent amidation reaction with very high yield. Azido‐multifunctionalized PS could be synthesized by chloromethylation and subsequent azido reaction. The chemical structures of PS‐(CH₂Cl)_m, PS‐(CH₂N₃)_m, and PS‐g‐POSS were determined by Fourier transform infrared and ¹H NMR characterization. PS‐g‐POSS presented a better hydrophobic property with contact angle of 113° than that of PS (85°). And PS‐g‐POSS with ≤5% of grafting degree had lower glass transition temperature (T_g) than that of PS and then it increased up to 112°C with grafting degree. An obvious aggregation of POSS phase with 10–80 nm in size was formed in PS‐g‐POSS matrix. In addition, 5 wt % of PS‐g‐POSS was added to general purpose polystyrene (GPPS) to remarkably improve its tensile strength from 45 to 57 MPa. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dual‐Cure Coatings: Spiroorthoesters as Volume‐Controlling Additives in Thiol–Ene Reactions

Most thiol–ene systems exhibit shrinkage during cross‐linking, potentially resulting in micro‐cracks and delamination. Oligocyclic monomers like spiroorthoesters (SOEs), on the contrary, show expansion during the ring‐opening polymerization. In this communication, a photocurable thiol–ene system composed of a trifunctional thiol, a bisfunctional allyl‐bisphenol A compound, and an SOE compound bearing one olefin function shows expansion in the range from ?3.07 to +1.70 vol% if the SOE content is increased from 0–30 wt%. Network formation can be accomplished under visible light if a radical as well as a cationic photoinitiator (dual‐cure mechanism) and a sensitizer are used. The elasticity of the cured resin increases upon the addition of the SOE; correspondingly, the glass‐transition temperature shows a (minor) decrease from 16 to 3 °C. A tailor‐made combination of the allyl‐bisphenol A compound (90 wt%) and the SOE (10 wt%) yields networks that are volume‐neutral during curing.     

Synthesis and properties of ultraviolet‐curable resins via a thio–ene (thiol and allyl) addition reaction

Benzophenone diallyl ester (I) and benzophenone tetraallyl ester (II) based on 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) with allyl alcohol (AAL) were synthesized. Glycidyl methacrylate (GMA) was added to I and formed diallyl diglycidyl methacrylate (III). These BTDA‐based allyl‐containing compounds (II and III) reacted with 1,4‐butanedithiol and 4,4′‐thiol‐bisbenzene‐thiol to produce ultraviolet (UV)‐curable resins via a thio–ene addition reaction. The ester (III) was cured easily when exposed to UV or sunlight radiation without any photoinitiator and only required a lower thermal curing temperature. The diallyl ester (I) and tetraallyl ester (II) required the addition of benzophenone to increase the photosensitivity, which reduced the exposition time. These resins used AAL as a monomer to successfully reduce the oxygen effect of the photocuring. The resin BTDA–2Allyl–2GMA had a glass‐transition temperature of 166°C and a hardness of 6H. The resultant UV‐curable coatings had excellent hardness, chemical resistance, adhesion, and tensile properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1878–1885, 2002     

Thiol‐ene photofunctionalization of 1,4‐polymyrcene

1,4‐Polymyrcene was synthesized by anionic polymerization of β‐myrcene and was subjected to photochemical functionalization with various thiols (i.e. methyl thioglycolate, methyl 3‐mercaptopropionate, butyl 3‐mercaptopropionate, ethyl 2‐mercaptopropionate and 2‐methyl‐2‐propanethiol) using benzophenone/UV light as the radical source. The yield of thiol addition to the trisubstituted double bonds of 1,4‐polymyrcene decreased in the order 1° thiol (ca 95%) > 2° thiol (ca 80%) > 3° thiol (<5%), due to the reversibility of the thiol‐ene reaction. Remarkably, thiol addition to the side‐chain double bonds was 8 ? 10 times (1° thiol) or 24 times (2° thiol) faster than to the main‐chain double bonds, which can be explained by the different accessibility of the double bonds and steric hindrance. Despite the use of a 10‐fold excess of thiol with respect to myrcene units, the thiol‐ene addition was accompanied by chain coupling reactions, which in the extreme case of 3° thiol (or in the absence of thiol) resulted in the formation of insoluble crosslinked material. As an example, a methyl‐thioglycolate‐functionalized 1,4‐polymyrcene was saponified/crosslinked to give submicron polyelectrolyte particles in dilute alkaline solution. © 2018 Society of Chemical Industry     

Influence of the Thiol Structure on the Kinetics of Thiol‐ene Photopolymerization with Time‐Resolved Infrared Spectroscopy

Photopolymerization kinetics of difunctional thiols with alkenes were studied. Two of the thiols, trans‐1,4‐bis(mercaptomethyl)cyclohexane (CHDMT) and 1,4‐bis(mercaptomethyl)benzene (BDMT) were synthesized. The CHDMT was synthesized via a two step process using potassium thioacetate and hydrochloric acid as reagents. The BDMT was synthesized by a one step process using 1,4‐benzenedimethanebromine with thiourea and potassium hydroxide as reagents. Three types of alkenes (divinyl ether, diallyl ether, and dimethacrylate) were reacted with CHDMT, BDMT or 1,8‐octanedithiol (ODT). The photopolymerization was investigated with and without a photoinitiator. The kinetics of the thiol‐ene photopolymerization was investigated by time‐resolved infrared spectroscopy. It was proposed that the steric hindrance of the cyclohexane (CHDMT) resulted in a lower rate of photopolymerization compared to BDMT and ODT. The vinyl ether (alkene) exhibited the highest activity compared to allyl ether and acrylate which was attributed to a high electron density of the alkene. Incorporation of photoinitiator increased the reaction rate and final conversion of the system, particularly in the ODT system.