Photocuring of a thiol‐ene system based on an unsaturated polyester

To produce a photocurable thiol‐ene system, unsaturated polyester was prepared from the condensation reaction of ethylene glycol, diethylene glycol, and fumaric acid. Diallyl groups were introduced into the ends of the unsaturated polyester by a sequential condensation reaction. The coating formulation studied contained an equimolar ratio of thiol and vinyl groups of the prepared unsaturated polyester, including 1 wt % Irgacure 184. The curing behaviors of the unsaturated polyester with multifunctional thiols were investigated using real‐time FTIR spectroscopy. The rates of disappearance of thiol and vinyl groups of the unsaturated polyester were similar, demonstrating that there was little free‐radical homopolymerization of the internal fumaric group or the end‐capped vinyl ether group during the photocuring process and that the thiol‐ene reaction is the dominant process. The kinetics of the model compounds demonstrated that the reaction of the terminal allyl double bond with the thiyl radical is faster than that of the internal fumaric double bond in the UV curing of the unsaturated polyester. The storage stability of the thiol‐ene system based on unsaturated polyester was effectively increased by the addition of N‐PAL. The Raman spectra revealed that the presence of a multifunctional thiol (penta 3‐MP4) in the coating formulation increased the degree of surface curing due to the chain‐transfer ability of the thiyl radical. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 342–350, 2005     

Novel modification of polybut‐1‐ene using auto‐oxidation controlled by addition of limonene monomer

Free radical graft polymerization has been used as a modification method to incorporate functional groups into polyolefins using a melt‐mixing process. The presence of oxygen simultaneously brings about auto‐oxidation during the polymerization. Although functional groups such as ketones are easily incorporated into polyolefin chains by auto‐oxidation, the method is rarely employed because of the difficulty of handling. In the study reported here, a novel modification of polybut‐1‐ene (PB) was performed using auto‐oxidation controlled by the addition of limonene monomer. The modified PB samples were prepared using 2,2′‐azobis(2‐methylpropionitrile), benzyl peroxide, tert‐butyl peroxide (TBPO) and Nd₂O₃/dicumyl peroxide (DCP) radical initiators in air. It was found that excessive auto‐oxidation was suppressed by the presence of the limonene, and that the greatest numbers of grafted groups were contained in the modified PB samples prepared using TBPO and Nd₂O₃/DCP. The samples obtained showed slower crystallization behavior and slower crystal–crystal transformation rates, respectively. In addition, the modified PB sample prepared using Nd₂O₃/DCP showed less ductile behavior than that prepared using TBPO because of a much slower transformation rate. Copyright © 2009 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     

Preparation and characterization of hybrid thiol‐ene/epoxy UV–thermal dual‐cured systems

Hybrid thiol‐ene/epoxy coatings were prepared by combining thiol‐ene photo‐curable formulations with epoxy monomers, through a dual UV–thermal curing process. An increase in glass transition temperature and in storage modulus was observed for the hybrid thiol‐ene/epoxy coatings when compared with the pristine thiol‐ene UV‐cured system. Also, the bisphenol A moieties introduced into the hybrid networks during the dual‐curing process induced an increase in thermal stability of the cured materials. It has been demonstrated that the addition of epoxy monomer to the thiol‐ene photo‐curable system is a good strategy to follow in order to improve the final properties of thiol‐ene‐based coatings leading to a wide range of possible applications for the hybrid materials. Copyright © 2010 Society of Chemical Industry     

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.     

Formation of a tunable starch‐based network by in situ incorporation of mercapto groups and a subsequent thiol‐ene click reaction

A tunable starch‐based hydrogel was prepared by crosslinking unsaturated macromonomers in the presence of H₂S. First, well‐defined poly(vinyl alcohol) (PVA) was prepared by alcoholysis of poly(vinyl acetate) obtained by reversible addition‐fragmentation chain transfer (RAFT) polymerization of vinyl acetate. Subsequently, carbon‐carbon double bonds were incorporated onto PVA through esterification with maleic anhydride. Finally, the hydrogel was formed via concurrent electrophilic addition and thiol‐ene reaction between starch maleic half‐ester, unsaturated PVA and H₂S using potassium persulfate as initiator at 60 °C. Elemental analysis showed the percentage of sulfur in the gel ranged from 0.86% to 1.73%, depending on the chain length of PVA. The storage modulus, loss modulus and glass transition temperature of the networks varied from 12.7 to 50.9 MPa, from 3.7 to 15.7 MPa and from 57.0 to 71.8 °C, respectively. Both the swelling and release behavior of the gels were also modulated by changing the unsaturated PVA component. © 2012 Society of Chemical Industry     

Fabrication of polymer‐dispersed liquid crystals with low driving voltage based on the thiol‐ene click reaction

Polymer‐dispersed liquid crystals (PDLCs ) with a well‐defined polymer matrix were successfully fabricated by the thiol‐ene click reaction based on poly(ethylene glycol) diacrylate (PEGDA ) and trimethylolpropanetris‐(3‐mercaptopropionate) (TMTP ). UV ?visible spectrophotometry, Fourier transform IR spectroscopy, SEM and polarized optical microscopy were employed to explore the PDLC films obtained. Electro‐optical properties were studied with a UV ?visible spectrophotometer. It was found that the PDLC films with optimal thiol content fabricated by the thiol‐ene click reaction showed high transmittance, low driving voltage and a low memory effect. It was concluded that the driving voltage change of PDLCs with different thiol concentrations was caused by the polymerization rate and the structure of the polymer matrix. © 2017 Society of Chemical Industry     

UV curable soybean‐oil hybrid systems based on thiol‐acrylate and thiol‐ene‐acrylate chemistry

In this study, epoxidized soybean oil was modified to prepare acrylated epoxidized soybean oil (AESO) and vinyl/acrylate ended soybean oil (VASO), which were blended with mercaptopropyl polyhedral oligomericsilsequioxane (POSS‐SH) to prepare UV curable thiol‐acrylate and thiol‐ene‐acrylate hybrid coatings. Photopolymerization processes of the coatings were measured and the results showed that addition of POSS‐SH obviously increased the conversion of double bond. The physical and mechanical properties of all cured samples were investigated, which indicated that the pencil hardness, tensile strength, and fracture toughness were significantly improved by POSS‐SH. Moreover, with increasing POSS‐SH content, the water contact angles of cured samples were increased, and the water resistance was greatly improved. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42095.     

Synthesis and photoinitiating activity study of polymeric photoinitiators bearing BP moiety based on hyperbranched poly(ester‐amine) via thiol‐ene click reaction

A series of polymeric photoinitiators (BP‐HPEAs) bearing BP moiety based on hyperbranched poly(ester‐amine) were synthesized via the thiol‐ene click reaction of 3‐(4‐benzoylphenoxy)propyl 2‐mercaptoacetate (BPPM) with acrylated HPEA. BPPM was obtained by the esterification of (4‐(3‐hydroxypropoxy) phenyl) phenyl methanone (HPPM) with mercaptoacetic acid in the presence of p‐toluene sulphonic acid as a catalyst. HPEA was prepared through Michael addition of piperazine with tri(hydroxymethyl)propane triacrylate. Their molecular structures were confirmed by the ¹H NMR, ¹³C NMR, and FTIR analysis. The UV–vis spectrum analysis results showed that BP‐HPEAs exhibit the stronger n–π* absorption at ～ 340 nm with over two times higher molar extinction coefficients than BP at the concentration of 1.00 × 10^?3M. The photoinitiating activity study showed that the maximum photopolymerization rates of 1,6‐hexanediol diacrylate initiated by BP‐HPEAs in the absence of coinitiator were obtained by two times higher than that by BP in the presence of triethylamine as a coinitiator. Moreover, the excellent miscibility of BP‐HPEAs with the commercial bisphenol A epoxy diacrylate was achieved according to the T_s/T_g ratios of over 9.0 from DMTA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Synthesis and post‐polymerization modification of maleimide‐containing polymers by ‘thiol‐ene’ click and Diels–Alder chemistries

This mini‐review provides an introduction to the key work in the area of synthesis and post‐polymerization functionalization of maleimide‐functional polymers. The versatility and utility of the maleimide group in the efficient functionalization of polymers by both ‘thiol‐ene’ Michael addition and Diels–Alder cycloaddition chemistries are highlighted. Copyright © 2011 Society of Chemical Industry     

Preparation and characterization of photocured thiol‐ene hydrogel: Adsorption of Au(III) ions from aqueous solutions

In this study, photocured a novel thiol‐ene hydrogels based on P(Penta3MP4/PEG‐DA/HEMA) were investigated for adsorption of Au(III) ions from aqueous solutions purposes. The photopolymerization kinetics of thiol‐ene‐based formulations was investigated by real‐time infrared spectroscopy. The chemical composition and surface morphology of hydrogels were also characterized. The effect of different parameters on Au(III) adsorption efficiency was examined in detail. Better adsorption behavior was achieved for Au(III) by P(Penta3MP4/PEG‐DA/HEMA) F1 hydrogels. The maximum uptake for Au(III) was at pH 0.5. Both Langmuir and Freundlich adsorption isotherm models were applied and the reusability of thiol‐ene hydrogels investigated. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Covalent Bonding of an Electroconductive Hydrogel to Gold‐Coated Titanium Surfaces via Thiol‐ene Click Chemistry

In the present study, the covalent bonding of electroconductive cross‐linked hydrogel networks with both electro‐properties and hydrogel characteristics to titanium surfaces via a UV‐initiated radical thiol‐ene click reaction is investigated. The electroconductive hydrogel layers are formed by the electropolymerization of pyrrole within the titanium implant‐supported gelatin methacrylate hydrogel. Characterization of the surface morphology of the layers reveals a unique rough macroporous structure. The hydrogel coating layer on the titanium surfaces possesses the desired characteristics of high electrochemical activity and high mechanical stability due to the effects of the chemical functionalization. Bone mesenchymal stem cells cultured on the hydrogel substrates exhibit high cell viability. This study is the first to demonstrate the potential of an electroconductive hydrogel as a surface coating on titanium implants for cell growth and provides a foundation for the development of new implantable bioelectronic devices.

     

Thiol‐ene/clay nanocomposite thin film as novel transparent barrier

Thiol‐ene/clay (TE/clay) nanocomposite thin films were prepared by a simple photocuring process for use as transparent barrier films. In this work, tetrafunctional thiol and triene monomer were employed and organic clay surface modified with octadecylamine was mixed by sonication and a mechanical method as a reinforcing filler. The successful formation of the TE structure was confirmed by differential scanning calorimetry and X‐ray diffraction. The homogeneous dispersion (intercalation and exfoliation) of clay into the TE polymer matrix was observed with transmission electron microscopy. Atomic force microscopy images displayed the surface properties of the TE/clay nanocomposite thin films. The thermal expansion behavior of the resulting hybrid film was monitored by thermomechanical analysis. In addition, gas permeation properties as well as light transmittance of the TE/clay films were measured for potential applications in various fields as dimensionally stable films under heating and as a transparent barrier. Copyright © 2012 Society of Chemical Industry     

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     

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     

Addition‐cure‐type phenolic resin based on alder‐ene reaction: Synthesis and laminate composite properties

A maleimide‐functional phenolic resin was reactively blended with an allyl‐functional novolac in varying proportions. The two polymers were coreacted by an addition mechanism through Alder‐ene and Wagner–Jauregg reactions to form a crosslinked network system. The cure characterization was done by differential scanning calorimetry and dynamic mechanical analysis. The system underwent a multistep curing process over a temperature range of 110–270°C. Although the cure profiles were independent of the composition, the presence of maleimide led to a reduced isothermal gel time of the blend. Increasing the allylphenol content decreased the crosslinking in the cured matrix, leading to enhanced toughness and improved resin‐dominant mechanical properties of the resultant silica laminate composites. Changing the reinforcement from silica to glass resulted in further amelioration of the resin‐reinforcement interaction, but the resin‐dominant properties of the composite remained unaltered. Increasing the maleimide content resulted in enhanced thermal stability. Integrating both the reactive groups in a single polymer and its curing led to enhanced thermal stability and T_g, but to decreased mechanical properties of the laminate composites. This can be attributed to a brittle matrix resulting from enhanced crosslinking facilitated by interaction of the reactive groups located on the polymer of an identical backbone structure. The cured polymers showed a T_g in the range of 170–190°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 737–749, 2001     

Free‐radical terpolymerization of n‐butyl acrylate/butyl methacrylate/d‐limonene

d ‐Limonene (Lim) is a renewable monoterpene derived from citrus fruit peels. We investigated it for use as part of a more sustainable polymer formulation. The bulk free‐radical terpolymerization of n‐butyl acrylate (BA)/butyl methacrylate (BMA)/Lim was carried out at 80°C with benzoyl peroxide as the initiator. The terpolymerization was studied at various initial BA/BMA/Lim molar ratios, and the products were characterized for conversion, terpolymer composition, molecular weight, and glass‐transition temperature. Lim was observed to undergo a significant degradative chain‐transfer reaction, which greatly influenced the polymerization kinetics. The rate of polymerization, final conversion, and polymer molecular weight were all significantly reduced because of the presence of Lim. Nonetheless, polymers with relatively high weight‐average molecular weights (20,000–120,000 Da) were produced. The terpolymer composition was well predicted with the reactivity ratios estimated for each of the three copolymer subsystems. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42821.     

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