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     

UV‐curable methacrylic epoxy dispersions for cationic electrodeposition coating

UV‐curable epoxy dispersions were prepared for cationic electrodeposition coating. Sequential reactions were used to introduce methacrylate groups to the epoxy‐amine polymer as coupling agents to the multifunctional acrylates. The molecular weight values of the prepared epoxy‐amine polymer were M_n = 2800 and M_w = 4300. The neutralized epoxy‐amine polymer containing photoinitiator with or without multifunctional acrylate (pentaerythritol triacrylate, PETA) could be dispersed into a stable dispersion without any phase separation. The size of the particles in these epoxy dispersions was approximately 77.7 nm, and increased with the incorporation of PETA. The electrodeposition process was introduced to the prepared epoxy dispersions, and the electrodeposited films were cured by UV irradiation after a 10‐min flash off at 80°C. Studies of the kinetics using photo‐DSC revealed that the crosslinked films containing PETA gave a higher conversion rate than those without PETA, resulting in better resistance to methyl ethyl ketone. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5566–5570, 2006     

Fluorinated epoxides as surface modifying agents of UV‐curable systems

Two commercially available epoxy‐fluorinated monomers, 3‐(perfluorooctyl)‐1,2‐propenoxide and 3‐(1H, 1H, 9H‐hexadecafluorononyloxyl)‐1,2 propenoxide, were used as modifying additives for UV curable systems. These two fluorinated monomers were mixed, in small amounts (less than 1% w/w) with a hydrogenated epoxy monomer 1,4‐cyclohexanedimethanol‐diglycidyl ether. The mixtures were coated on glass substrate and UV‐cured, giving rise to transparent films. Notwithstanding their very low concentrations, the fluorinated monomers caused a change in the surface properties of the films, without changing their curing conditions and their bulk properties. The air side of the coatings became highly hydrophobic, while the substrate side was unmodified. As shown by XPS measurements, the fluorinated monomers were able to concentrate selectively on the air side of the films, forming a fluorinated layer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1524–1529, 2003     

Preparation and characterization of UV‐curable MPS‐modified silica nanocomposite coats

A series of UV‐curable nanocomposites were prepared with 3‐(trimethoxysilyl) propyl methacrylate (MPS) modified nanosilica under the initiation of 2,2‐dimethoxy‐1,2‐diphenylethan‐1‐one. It was found that MPS‐modified nanosilica together with free MPS could form transparent nanocomposite coats. As the particle size of nanosilica increased, the photopolymerization rate, final double bond conversion, and tack‐free time of nanocomposites increased while the surface roughness, glass‐transition temperature, and UV absorbance of nanocomposites decreased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2274–2281, 2005     

Preparation and evaluation of epoxy methacrylate UV‐curable coatings containing phthalazinone

Epoxy methacrylate resin (EMA) UV‐curable coatings exhibit high reactivity, low viscosity and excellent chemical resistance in environmentally friendly coatings. A novel EMA containing phthalazinone moieties for high temperature resistant UV‐curable coatings was synthesized. The formulations were cured with hexanediol diacrylate (HDDA) and trimethylol propane triacrylate (TMPTA) as reactive diluents promoted by a photoinitiator, and then interpenetrating polymer networks were generated. The mechanical, chemical and thermal properties of the clear coatings were characterized using Chinese National Standard methods (GB). EMA was used with UV radiation curing in combination with 6.7 wt% of HDDA and 13.4 wt% of TMPTA, and the properties of the cured films were as follows: pencil hardness of 5 H, 30% NaOH resistance for 30 days, 15% HCl resistance for 10 days, 3% NaCl resistance for 30 days and 5% weight loss temperature of 300.5 °C. EMA UV‐curable coatings containing phthalazinone exhibit excellent chemical and thermal stability, and could be potential candidates for UV‐curable zero volatile organic compound coatings applied in the fields of salt spray corrosion, strong radiation and high‐temperature resistance. Copyright © 2009 Society of Chemical Industry     

An UV‐curable epoxy acrylate oligomer with high refractive index containing fluorene: Preparation,characterization, and application

In this article, a novel UV‐curable epoxy acrylate oligomer (BPEFPGMA) with high refractive index is successfully prepared through semi‐esterification reaction of 9,9‐bis[4‐(2‐hydroxyethoxy)phenyl]fluorene and phthalic anhydride, followed by end‐caping of glycidyl methacrylate. After 15 times’ repetitions, the process and properties of this oligomer are stable and reliable. The resulting BPEFPGMA exhibited low solvent content (≤1600 ppm), low viscosity (1900–2500 mPa s at 60°C), high refractive index (1.587 ± 0.003 at 20°C), and normal M_w (2550–3536 g/mol). The coating formulations of 1.57 UV‐curable glue are mixed with BPEFPGMA as reactive oligomer. Through the technology of UV‐curing forming, the corresponding brightness enhancement films are obtained. The resulting films exhibit normal structure, excellent adhesion (5B), good scratch resistance (50 g), and good abrasion resistance (50 g). They show excellent performance, and have reached the quality standard for use in liquid crystal display industry. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42386.     

Investigation on the effect of the presence of hyperbranched polymers on thermal and mechanical properties of an epoxy UV‐cured system

The use of hydroxyl‐functionalized hyperbranched polymers (HBPs) (Boltorn^® H20, H30 and H40) was investigated with respect to a UV‐cured epoxy system. Their presence induced an increase of the final epoxy conversion, which was interpreted on the basis of a chain‐transfer reaction. A decrease of the T_g values in the photocured films was observed when the amount of HBP additive in the photocurable formulation was increased. When the amount of HBP in the photocurable resin was increased, the density of photocured films increased, indicating a decrease on the free volume. Moreover, a clear increase in toughness was observed and attributed to the plasticization effect induced by the presence of HBP. This effect is particularly interesting for epoxy thermosets, which are characterized by good mechanical properties, although they are brittle and fragile. By increasing the toughness properties of these photocured resins it may be possible to broad their applications. Copyright © 2005 Society of Chemical Industry     

Improvement of epoxy thermosets using a thiol‐ene based polyester hyperbranched polymer as modifier

The anionic curing initiated by 1‐methyl imidazole of diglycidyl ether of bisphenol A with a hyperbranched polymer (HBP) containing long aliphatic chains in the structure were studied. The hydroxyl groups present as chain ends in the HBP structure played an important role in the curing kinetics, as demonstrated by differential scanning calorimetry, Fourier transform infrared spectroscopy and rheological studies. Properties such as shrinkage on curing and thermomechanical characteristics were also investigated. The structure of the HBP, which contains long aliphatic chains and reactive hydroxyl groups as chain ends, flexibilizes the network significantly, improving the impact resistance without notably affecting either the glass transition temperature or the microhardness of the modified thermosets. Copyright © 2012 Society of Chemical Industry     

Modification of UV‐cured epoxy resins with fluorescent sensors through photopolymerization and click chemistry reactions and preparation of polarity‐sensitive films

In this work, functionalization of epoxy films with dansyl and naphthalimide fluorophores is described. The procedure involves UV‐photopolymerization of an epoxy formulation that includes bromomethyl reactive groups, and their post‐functionalization modification through a click strategy. Quantitative click reaction within the bulk of the film allows one to obtain films in which the fluorophore is uniformly and covalently linked throughout the epoxy network. Depending on the chromophore bounded, the films are sensitive to different stimuli. Evaluation of the fluorescence emission of the films shows a linear response towards changes in polarity but less sensitivity than that of the low‐molecular‐weight chromophore. © 2013 Society of Chemical Industry     

Novel moisture‐curable epoxy resins and their characterization

The shelf‐life stability and curability of a moisture‐curable epoxy resin system were evaluated with ketimines, which were used as moisture‐latent hardeners and were derived from different kinds of ketones as protective groups. Both the shelf‐life stability and curability of the compounds were mainly influenced by the steric hindrance of the ketimines. The theoretical results calculated by MOPAC showed good agreement with the experimental results. Methyl i‐propyl ketone and methyl t‐butyl ketone, having a narrow space (<4.2 Å) around ketimine N and a wide space (>3.7 Å) around ketimine C, were demonstrated to be the optimum ketones for the ketimines. The lap shear strength, with respect to the adhesive properties of the ketimines, was higher with a large‐volume ketone than with a small‐volume ketone as the protective group. This was due to the higher reaction conversion of the epoxide for the system. In addition, the large plasticizing effect of the large ketone volume could lead to a large relaxation of the stress generated at the bonding interface. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 91–95, 2003     

Phosphorus‐containing epoxy resins: Thermal characterization

Three novel aromatic phosphorylated diamines, i.e., bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl} pyromellitamic acid (AP), 4,4′‐oxo bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AB) and 4,4′‐hexafluoroisopropylidene‐bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AF) were synthesized and characterized. These amines were prepared by solution condensation reaction of bis(3‐aminophenyl)methyl phosphine oxide (BAP) with 1,2,4,5‐benzenetetracarboxylic acid anhydride (P)/3,3′,4,4′‐benzophenonetetracarboxylic acid dianhydride (B)/4,4′‐(hexafluoroisopropylidene)diphthalic acid anhydride (F), respectively. The structural characterization of amines was done by elemental analysis, DSC, TGA, ¹H‐NMR, ¹³C‐NMR and FTIR. Amine equivalent weight was determined by the acetylation method. Curing of DGEBA in the presence of phosphorylated amines was studied by DSC and curing exotherm was in the temperature range of 195–267°C, whereas with conventional amine 4,4′‐diamino diphenyl sulphone (D) a broad exotherm in temperature range of 180–310°C was observed. Curing of DGEBA with a mixture of phosphorylated amines and D, resulted in a decrease in characteristic curing temperatures. The effect of phosphorus content on the char residue and thermal stability of epoxy resin cured isothermally in the presence of these amines was evaluated in nitrogen atmosphere. Char residue increased significantly with an increase in the phosphorus content of epoxy network. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2235–2242, 2002     

A novel hybrid linear–hyperbranched poly(butylene adipate) copolymer as an epoxy resin modifier with toughening effect

A study was carried out on the effect of a hybrid linear–hyperbranched poly(butylene adipate) copolymer on the properties of a commercial epoxy resin. First, the synthesis of the hyperbranched systems was optimized. These systems were obtained by reacting linear oligomers with 1,1,1‐tris(hydroxymethyl)propane used as branching agent and varying the reaction times from 16 to 44 h. The synthesized samples were characterized through matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry, differential scanning calorimetry and thermogravimetric analysis. Results showed that for reaction times of 30 h a highly branched system, namely 5HB30, was obtained. This system was chosen as toughening agent for a commercial high‐performance epoxy resin. A kinetics analysis of epoxy/5HB30 blends indicated that the hyperbranched system had no accelerator or catalytic effect on the crosslinking reaction in the resin. Furthermore, it was demonstrated that 5HB30 acted as an excellent toughening agent, increasing significantly impact resistance up to 90% with respect to neat epoxy resin. The toughness behaviours of epoxy‐based blends were explained by investigating the fracture surface after impact tests through scanning electron microscopy before and after solvent etching. It was observed that the globular‐like hyperbranch‐rich domains, dispersed throughout the continuous epoxy resin, were able to absorb the impact energy without affecting thermal stability. © 2015 Society of Chemical Industry     

Properties of nanocomposites based on maleate‐vinyl ether donor—acceptor UV‐curable systems

UV‐curable nanocomposites based on donor–acceptor crosslinking chemistry were prepared containing organically modified montmorillonites. The coatings were characterized for thermal, mechanical, and morphological properties. X‐ray diffraction and transmission electron microscopy showed that nanocomposites were formed in all samples. Results showed that an increase in the percentage of clay caused an increased modulus and glass‐transition temperature. It was also seen that tensile modulus showed dramatic improvement when compared with the unmodified polyester sample. Real time IR kinetic data showed that higher conversions were obtained at higher clay loadings. Pendulum hardness values and tensile modulus values showed different trends in properties depending on the combination of polymer matrix and organomodification. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Photorheology of Fast UV‐Curing Multifunctional Acrylates

Summary: The fast photopolymerization of different multifunctional acrylates was analyzed by means of photorheology. The materials studied included a penta/hexaacrylate monomer and two different acrylated hyperbranched polymers. The sensitivity of the commercial rheometer was improved several‐fold, by a combination of an adaptive filter algorithm and improved data treatment, using powerful oversampling acquisition hardware. The novel set‐up was capable of monitoring up to a five orders of magnitude increase in shear modulus within short experiment timescales (about 10 s). The improvement in sensitivity and acquisition rate enabled the induction time, gelation, and vitrification of the multifunctional acrylates to be determined. In addition, the influence of UV intensity on stiffness build‐up within these materials was studied. In the case of the penta/hexaacrylate system, gelation and vitrification were detected as distinct events, in contrast to the second‐generation hyperbranched polyester, for which vitrification could not be identified. These findings are related to the difference in the glass transition temperature of the cured networks.

Absolute value of the complex shear modulus as a function of time for different acrylate monomers during UV curing.     

Effects of preparation method on microstructure and properties of UV‐curable nanocomposite coatings containing silica

UV‐curable nanocomposites were prepared by the blending method or the in situ method with nanosilica obtained from a sol–gel process. The microstructure and properties of the nanocomposite coatings were investigated using ²⁹Si‐NMR cross‐polarization/magic‐angle spinning, transmission electron microscopy (TEM), Fourier transform IR (FTIR), differential scanning calorimetry (DSC), and UV–visible (UV–vis) spectra, respectively. The NMR and TEM showed that during the blending method, tetraethyl orthosilicate (TEOS) completely hydrolyzed to form nanosilica particles, which were evenly dispersed in the polymer matrix. However, for the in situ method, TEOS partially hydrolyzed to form some kind of microstructure and morphology of inorganic phases intertwisted with organic molecules. FTIR analysis indicated that the nanocomposites prepared from the in situ method had much higher curing rates than those from the blending method. DSC and UV–vis measurements showed that the blending method caused higher glass‐transition temperatures and UV absorbance than the in situ method. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1119–1124, 2005     

Rheological and mechanical properties of DGEBA‐S epoxy copolymer initiated by N‐benzylquinoxalinium hexafluoroantimonate

The rheological and mechanical properties of the DGEBA‐S epoxy copolymer initiated by N‐benzylquinoxalinium hexafluoroantimonate (BQH) as a cationic latent thermal catalyst were investigated. The rheological properties of the DGEBA‐S/BQH system were investigated using a rheometer under isothermal conditions, and the mechanical properties of the casting specimens, involving flexure and impact tests, were also performed. The crosslinking activation energy and mechanical properties of the DGEBA‐S/BQH system were higher than those of the DGEBA/BQH system. This could be attributed to the introduction of sulfone groups with a polar nature to the main chain of the epoxy resins which led to a decrease of molecular motion and an improvement in the toughness of the cured epoxy copolymers. Copyright © 2005 Society of Chemical Industry     

Processing and chemorheology of epoxy resins and their blends with dendritic hyperbranched polymers

Toughened epoxy systems have found increasing applications in automotive, aerospace, and electronic packaging industries. The present article reported work done for elucidation of gelation and vitrification for various epoxy systems and their blends with dendritic hyperbranched polymers (HBPs) having epoxy and hydroxyl functionality. Gel time was found to increase with increasing functionality from diglycidyl ether of bisphenol A (DGEBA) to tetraglycidyl diaminodiphenyl methane (TGDDM). The vitrification point was clearly identified from rheological experiments for triglycidyl p‐amino phenol (TGAP) and TGDDM. In the case of DGEBA a clear display of vitrification was not observed. TGDDM underwent vitrification sooner than did TGAP. Hydroxyl‐functionalized HBP reduced the gel time of the blends because of the accelerating effect of –OH groups to the epoxy curing reaction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1604–1610, 2004     

An epoxy‐ended hyperbranched polymer as a new modifier for toughening and reinforcing in epoxy resin

A new epoxy‐ended hyperbranched polyether (HBPEE) with aromatic skeletons was synthesized through one‐step proton transfer polymerization. The structure of HBPEE was confirmed by Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR) measurements. It was proved to be one high efficient modifier in toughening and reinforcing epoxy matrix. In particular, unlike most other hyperbranched modifiers, the glass transition temperature (T_g) was also increased. Compared with the neat DGEBA, the hybrid curing systems showed excellent balanced mechanical properties at 5 wt % HBPEE loading. The great improvements were attributed to the increased cross‐linking density, rigid skeletons, and the molecule‐scale cavities brought by the reactive HBPEE, which were confirmed by dynamical mechanical analysis (DMA) and thermal mechanical analysis (TMA). Furthermore, because of the reactivity of HBPEE, the hybrids inclined to form a homogenous system after the curing. DMA and scanning electron microscopy (SEM) results revealed that no phase separation occurred in the DGEBA/HBPEE hybrids after the introduction of reactive HBPEE. SEM also confirmed that the addition of HBPEE could enhance the toughness of epoxy materials as evident from fibril formation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1064‐1073, 2013     

Synthesis of polysiloxane‐type multifunctional flame retardant and its application in epoxy systems

Polymethyl(3‐glycidyloxypropyl)siloxane (PMGS) was synthesized as a flame‐retardant additive, which were cocured with diglycidyl ether of bisphenol‐A (DGEBA) using 4,4′‐diaminodiphenylsulfone as a curing agent. The structure of PMGS was confirmed through Fourier transform infrared and ¹H‐NMR spectra. The cured products were characterized with dynamic mechanical thermal analysis, thermogravimetric analysis, and oxygen index analyzer. With PMGS incorporated, the cured epoxy resin showed better thermal stability, higher limited oxygen index, and higher char yield. At moderate loading of PMGS, the storage modulus and glass transition temperature of the cured epoxy resin based on neat DGEBA were obviously improved. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and UV curing kinetics of rapidly UV‐curable hyperbranched polycarbosiloxanes

Hyperbranched polycarbosiloxanes with peripheral photo‐crosslinkable groups were synthesized through controllable hydrosilylation reaction from A₂‐type and CB₃‐type monomers. The polymerization of the monomer pairs was monitored using Fourier transform infrared spectroscopy, from which it was found that vinyl silane and methacrylate groups reacted with hydride silane from the beginning of the reaction. The results thus suggest a step‐by‐step polymerization rather than a two‐step process for this system. The polycarbosiloxanes could be cured rapidly in either nitrogen or air atmosphere, this feature making them attractive for potential application as precursors of advanced ceramic devices with complex structures. The effects of light intensity, reaction temperature and atmosphere on the UV curing rate (R_p) and conversion (α) of the photo‐crosslinkable groups were characterized carefully, and the curing kinetics was also investigated systematically. The results show that R_p and α increased with an increase of light intensity or temperature, and that the inhibiting effect of oxygen in air could be suppressed by enhancing the irradiation intensity. Copyright © 2010 Society of Chemical Industry