Allyl ether‐modified unsaturated polyesters for UV/air dual‐curable coatings. II: UV and air‐curing behavior

The photoinduced and peroxide‐induced polymerization behavior of dual‐curable allyl ether‐modified unsaturated polyester (AUPE) and vinyl ether (VE) used as a reactive diluent for dual‐curable coating have been studied by infrared spectroscopy (IR). For UV curing systems in N₂ atmosphere, the maleate's conversion and total conversion decrease with the increasing of allyloxy content. However, the rate and of copolymerization and conversion of VE are independent of allyloxy concentration. The copolymerization of allyl ether (AE) and vinyl ether occurs in the presence of maleate (MA) under UV irradiation. For air curing, the rate of copolymerization increases with allyloxy content. The ultimate conversion is the same irrespective of the allyloxy concentration. Because the electron‐rich double bond of allyloxy would become an electron‐deficient one through oxidation, the conversion of maleate decreases with increasing of the allyloxy content due to the enhancement of copolymerization of AE with VE. The ATR‐IR showed that different curing mechanisms occur in AUPE/VE system during air‐curing process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2771–2776, 2004     

New thermosets obtained from bisphenol A diglycidyl ether and hydroxyl‐ended hyperbranched polymers partially blocked with benzoyl and trimethylsilyl groups

New epoxy thermosets with improved flexibility were prepared by chemical modification of bisphenol A diglycidyl ether (DGEBA) with hyperbranched polymers (HBPs). Hydroxyl‐ended hyperbranched polyesters were modified by blocking part of the hydroxyl groups with trimethylsilyl or benzoyl groups. The curing of mixtures of DGEBA with various proportions of two modified HBPs using ytterbium triflate as cationic initiator was investigated using differential scanning calorimetry and thermomechanical analysis. The characterization of these materials was performed using several thermal analysis techniques and their morphology was investigated using electron microscopy. High proportions of HBPs reduced the glass transition temperature and the relaxed storage modulus but barely affected gelation. The overall curing shrinkage was controlled by the content of hydroxyl groups and by the changes of HBP molecular interactions during curing. The results indicated that the relative proportion and type of terminal groups play a role in the evolution of the curing and the properties of the thermosets. Hydroxyl groups promoted the covalent incorporation of the HBP to the network via hydroxyl‐induced chain‐transfer reactions, whereas benzoyl groups promoted phase separation. Formulations containing HBP blocked with benzoyl groups showed two phases connected through covalent linkages between the HBP‐rich phase and the epoxy matrix. Copyright © 2010 Society of Chemical Industry     

New epoxy thermosets obtained from diglycidylether of bisphenol a and modified hyperbranched polyesters with long aliphatic chains cured by diisocyanates

Hyperbranched polyesters modified with long aliphatic chains with vinyl or epoxy groups as chain ends were synthesized and added as modifiers to diglycidyl ether of bisphenol A/toluene‐2,4‐diisocyanate mixtures in the presence of benzyldimethylamine as catalyst. The influence of the addition of these modifiers on the curing was investigated by thermal analysis and infrared spectroscopy. The materials obtained were investigated by electron microscopy and some mechanical characteristics were determined by nanoindentation tests. Epoxy terminated hyperbranched led to homogeneous materials with high crosslinking densities, whereas vinyl terminated hyperbranched produced phase separated morphologies. The materials showing phase separation presented a tough fracture, whereas the homogeneous materials obtained with epoxidated hyperbranched showed increased brittleness on increasing the proportion of modifier. On increasing the proportion of vinyl terminated hyperbranched in the thermosets, Young's modulus and hardness decreased but the addition of epoxy terminated hyperbranched did not influence these parameters. The addition of vinylic hyperbranched to the formulations produced a decrease in the curing shrinkage, whereas the epoxidic hyperbranched did not. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Ultraviolet‐curing behavior of an epoxy acrylate resin system

Ultraviolet (UV)‐curing behavior of an epoxy acrylate resin system comprising an epoxy acrylate oligomer, a reactive diluent, and a photoinitiator was investigated by Fourier transform infrared (FTIR) spectroscopy. The conversion changes of the resin system containing 20 phr of 1,6‐hexanediol diacrylate as a reactive diluent and 2‐hydroxy‐2‐methyl‐1‐phenyl‐propan‐1‐one as a photoinitiator were measured under different UV‐curing conditions. The fractional conversion was calculated from the area of the absorption peak for the vinyl group vibration occurring at 810 cm^?1. The effects of photoinitiator concentration, total UV dosage, one‐step or stepwise UV irradiation, UV intensity, atmosphere, and temperature on the curing behavior of the resin system were investigated. The conversion of the resin system increased rapidly at the initial stage of the UV‐curing process but increased very slowly after that. The final conversion of the resin system was mainly affected by total UV dosage. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1180–1185, 2005     

Hyperbranched polyesters with internal and exo‐presented hydrogen‐bond acidic sensor groups for surface acoustic wave sensors

Three hyperbranched aromatic polyesters carrying both internal and exo‐presented hydrogen‐bond acidic phenol, carboxylic acid, or mixed phenol/acetoxy groups were coated onto 500 MHz surface acoustic wave (SAW) sensor platforms, and sensor responses to the nerve agent simulant dimethyl methylphosphonate (DMMP) and the explosives simulant dinitrotoluene (DNT) were studied. All three hyperbranched polyesters gave strong responses to DMMP, and the hyperbranched polyester carrying carboxylic acid groups gave a particularly strong response. The hyperbranched polyester carrying phenol groups gave the best response to DNT of the three polymers studied. The DMMP and DNT responses of the three hyperbranched polyesters were also compared with hyperbranched SAW sensor polymers carrying exo‐presented phenolic sensor groups only, and also with linear SAW sensor polymers carrying phenolic sensor groups. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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     

Synthesis and ultraviolet‐curing behaviors of vinyl ether functionalized polyurethane oligomers

The vinyl ether functionalized oligomer is one of the most basic components of vinyl ether functionalized materials for cationic UV‐curable coatings. In this study, three types of vinyl ether functionalized polyurethane oligomers (i.e., polyether, polyester, and polydimethylsiloxane) were synthesized with diisocyanate, diol, and hydroxyethyl vinyl ether. These oligomers were characterized by IR, ¹H‐NMR, and ¹³C‐NMR spectroscopy. The effect of the raw material ratio on the oligomer, UV‐curing behaviors, and thermal properties of these oligomers were investigated. The UV‐curing behavior was analyzed by real‐time Fourier transform infrared spectroscopy. The vinyl ether terminated polyester urethane oligomer exhibited better UV curing, with a higher final conversion and maximum UV‐curing rates. In addition, the light intensity was enhanced for oligomers with better UV‐curing properties. Research on these vinyl ether functionalized oligomers is essential to the development and applications of cationic vinyl ethers systems. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40501.     

Cationic photopolymerization of oxetane‐functionalized hyperbranched polymers

An aliphatic–aromatic pehenolic hyperbranched starting material (HBP‐OH) with phenolic end groups was 85% functionalized by a Mitsunobu reaction with oxetane groups (OXT‐HBP). This new hyperbranched polyester was used, at a concentration of 5–20 wt %, as an additive for the cationic photopolymerization of a commercial oxetane‐based resin, 4,4′‐bis[(3‐ethyl‐3‐ethyl‐3‐oxetanyl) methoxymethyl]biphenyl (OXBP). HBP‐OXT acted as a multifunctional crosslinker, copolymerizing with the oxetane ring of the OXBP resin, reacting through chain transfer with the remaining phenolic OH groups, or doing both. The result was an increase in the glass‐transition temperature due to the increase in the crosslinking density. An increase in the weight residue at a high temperature was found in the presence of HBP‐OXT and was attributed to the presence of phenolic groups, which are commonly used as antioxidant additives. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 293–299, 2005     

Effect of solubility and miscibility on the adhesion behavior of polymer‐coated carbon fibers with vinyl ester resins

Interfacial shear strength (IFSS) of carbon fibers with vinyl ester resin was investigated as a function of the structure of the polymer coating on carbon fibers via microdroplet tests. For coating carbon fibers, high‐performance polymers such as poly(arylene ether phosphine oxide) (PEPO), Udel® P‐1700, and Ultem® 1000, water‐soluble poly(hydroxy ether ethanol amine) (PHEA), water‐dispersed carboxy‐modified poly(hydroxy ether) (C‐PHE), and water‐insoluble poly(hydroxy ether) (PHE) were utilized. Adhesion of polymers to carbon fibers was also evaluated and the failure surface of the fibers was analyzed by SEM to understand the adhesion mechanism. Diffusion between polymers and vinyl ester resins was investigated and the solubility parameters of the polymers were calculated, with the results being correlated to the IFSS. A highly enhanced IFSS was obtained with PEPO coating, while marginally improved IFSS resulted from PHE, Udel®, and C‐PHE coatings. However, PHEA and Ultem® coatings showed no improvement. Such results were attributed to the extent of solubility and/or miscibility of polymer coatings in vinyl ester resin, with better solubility and miscibility leading to a higher IFSS. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1042–1053, 2001     

Allyl ether‐modified unsaturated polyesters for UV/air dual‐curable coatings. I: Synthesis and characterization of the oligomers and their cured films

Allyl ether (AE)‐modified unsaturated polyester oligomers were synthesized from polyethylene glycol (PEG), maleic anhydride (MAH), and trimethylolpropane mono allyl ether (TMPAE), and characterized by Fourier transform infrared (FTIR) spectra. The UV/air dual‐curable coatings were prepared from the oligomers using vinyl ether (VE) as a reactive diluent. FTIR spectra showed that C?C bonds in the coating composition had polymerized partially after cured by UV or air. The investigation of rheological behavior of the dual curable composition suggested that all the systems belonged to pseudoplastic fluid, and the increasing allyloxy content in oligomer resulted in a higher viscosity. Differential scanning calorimetry (DSC) analysis showed that the increasing TMPAE‐PEG molar ratio resulted in lower T_g, and all samples had the same glass transition temperature irrespective of the type of curing. The results of TGA for cured films indicated that UV‐cured film had better thermal stability than the air‐cured one. The air‐cured film showed superior pencil hardness, impact strength, and flexibility to the UV‐cured counterpart. However, the air‐cured film had poor adhesion and electric resistance properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2765–2770, 2004     

An efficient fully bio‐based reactive diluent for epoxy thermosets: 2‐[(Oxiran‐2‐ylmethoxy) methyl] furan versus a petroleum‐based counterpart

Furfuryl alcohol and bio‐based epichlorohydrin were used to prepare a fully bio‐based reactive diluent, 2‐[(oxiran‐2‐ylmethoxy) methyl] furan (FOM). After spectral characterization, FOM was blended with epoxy resin, diglycidylether bisphenol A (DGEBA), at different ratios for reducing the viscosity. For a comparison, Cardura (one of the most common commercial reactive diluents), was separately incorporated to DGEBA. Amine‐curing process of the blends was recorded by FTIR and DSC. Similar trends of curing progression for DGEBA containing the reactive diluents were observed. Thermogravimetric analysis and dynamic mechanical thermal analysis, mechanical (hardness, adhesion, and stress–strain) and morphological properties were also investigated to study characteristics of the epoxy matrices formulated with FOM or Cardura. It was concluded that FOM could be considered as an efficient reactive diluent in formulations of polymer composites, structural adhesives and surface coatings based on epoxy resins. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44957.     

Phase separation in epoxy resin‐reactive dendritic hyperbranched polymer blends

Equilibrium phase diagrams in composition‐conversion space have been calculated for stoichiometric blends of an epoxy resin with a diamine hardener and dendritic hyperbranched polymers, to which various numbers of epoxy groups have been grafted. An attempt has been made to incorporate both the effects of the polydispersity of the resin and the reactivity of the functionalized hyperbranched polymers for any given value of the interaction parameter. However, if the reactivities of all the epoxy groups are comparable, the presence of a highly functionalized modifier is expected to lead to a reduction of the gel point conversion and a narrowing of the composition‐conversion window available for cure induced phase separation. The experimental cloud point data are consistent with the model, although they sugget that the functionalized hyperbranched polymers may be significantly less reactive than the resin. Moreover, in the present system, the influence of functionalization on the phase behavior is also strongly linked to the accompanying changes in the interaction parameter.     

Effect of hyperbranched acrylates on UV‐curable soy‐based biorenewable coatings

Utilization of biorenewable components in UV‐curable coating formulations is both economically and environmentally beneficial, particularly when compared to their petrochemical‐based counterparts. To produce UV‐curable coatings of high biorenewable content with enhanced performance, acrylated epoxidized soybean oil (ASBO) was combined with biorenewable reactive diluent tetrahydrofufuryl acrylate, adhesion promoters, photoinitiator and hyperbranched acrylates (HBAs) as synthetic tougheners. The HBAs were found to impart high functionality and low viscosity, thus increasing crosslinking in the coating network and improving mechanical and thermal properties such as film hardness, adhesion, solvent resistance, impact resistance, tensile modulus and toughness, glass transition temperature and thermal stability. Real‐time Fourier transform infrared spectroscopy showed decreased acrylate conversion when compared with a reference formulation without HBAs, which was attributed to earlier coating network vitrification during UV irradiation. ASBO‐based coatings were also thermally annealed to allow further reaction of unreacted components in the vitrified network. As a result, coating properties were further improved. Overall, the addition of HBAs as synthetic tougheners to UV‐curable ASBO‐based biorenewable coating systems was shown to greatly improve the corresponding coating properties. Copyright © 2010 Society of Chemical Industry     

Influence of a long‐side‐chain‐containing reactive diluent on the structure and mechanical properties of UV‐cured films

The dimethacrylate reactive diluent (HEMA‐DDSA), a long‐side‐chain‐containing reactive diluent, was prepared by reacting 2‐dodecen‐1‐ylsuccinic anhydride with two equivalents of hydroxyethyl methacrylate. Its structure was characterized by IR and ¹H NMR spectroscopy. This new diluent was added into the formulation of UV‐curable epoxy acrylate networks. Results show that the formulation with the addition of HEMA‐DDSA has massively reduced viscosity and shows several attractive properties of epoxy acrylate oligomers. The mechanical resistance of the films is dramatically enhanced with the incorporation of long alkyl groups derived from HEMA‐DDSA, the plastic deformation zone expands, thus decreasing the inner stress of the polymer structure. Moreover, the cured coatings have a higher glass transition temperature as the percentage of HEMA‐DDSA is increased up to 5 wt%. Due to the excellent integrated performance of the polymeric films, HEMA‐DDSA proved to be an effective reactive diluent, which is of potential interest for applications in high performance materials. © 2016 Society of Chemical Industry     

New aromatic–aliphatic hyperbranched polyesters with vinylic end groups of different length as modifiers of epoxy/anhydride thermosets

The synthesis and characterization of two new aromatic–aliphatic hyperbranched polyesters modified with long and short vinylic chains was reported. These hyperbranched polymers were used as toughening modifiers of epoxy/anhydride thermosets. The curing of mixtures of diglycidyl ether of bisphenol A and hexahydro-4-methylphtalic anhydride with different proportions of both hyperbranched polymers using N,N-benzyldimethylamine as catalyst was investigated by differential scanning calorimetry. The kinetic of curing process was established using an isoconversional integral procedure. The characterization of these materials was done by means of several thermal analysis techniques and their morphology was investigated by electron microscopy. The addition of highly branched structures led to homogeneous morphologies and a more toughening fracture of the thermosets in comparison to the neat epoxy/anhydride material. The modified thermosets presented slightly lower glass transition temperature than the unmodified one and the thermal stability barely changed by the addition of the modifiers.     

Synthesis and properties of photocross‐linked polymers of epoxidized linseed oil with different reactive diluents

Cross‐linked polymers were obtained by photopolymerization of epoxidized linseed oil with different reactive diluents (3,4‐epoxycyclohexylmethyl‐3,4‐epoxycyclohexane carboxylate, 1,4‐cyclohexane dimethanol diglycidyl ether, bisphenol A diglycidyl ether, trimethylolpropane triglycidyl ether, and bis[4‐(glycidyloxy)phenyl]methane) using the mixture of triarylsulfonium hexafluoroantimonates as photoinitiator. The kinetic of photocross‐linking reactions of compositions with different concentrations of reactive diluents was investigated. The 69%–91% conversion of epoxy groups of the compositions containing reactive diluents was reached. The mechanical properties, thermal stability, and swelling in polar and nonpolar solvents of the photocross‐linked polymers were studied. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Hydroxyl‐functional polyurethanes and polyesters: synthesis,properties and potential biomedical application

This mini review gives an overview of the synthesis of polyurethanes and polyesters with pendant hydroxyl groups performed mainly in our group. Significant for the synthesis of most of these polymers with hydroxyl‐functional side groups is that no protection groups are needed. This is realised either by generating the OH group during polymer synthesis—demonstrated by the preparation of hydroxyl‐functional polyurethanes from dicarbonate monomers and diamines—or by using catalysts which discriminate between primary and secondary OH groups—demonstrated by the synthesis of hydroxyl‐functional polyesters based on malic acid using scandium triflate as catalyst. In addition, the potential of carbonate couplers for the synthesis of multifunctional polyurethane is presented. The application of such multifunctional polyurethanes as antimicrobial polymers and coatings is briefly discussed. Copyright © 2012 Society of Chemical Industry     

Study of negative substitution and monomer self‐condensation effects on molar mass and structural characteristics of hyperbranched polyesters originating from a high‐functionality core

In order to provide more insight into the effect of core functionality on hyperbranched polymer characteristics, two series of hyperbranched polyesters (HBPEs) were synthesized by reacting 2,2‐bis(methylol)propionic acid (bis‐MPA) as AB₂ monomer with both dipentaerythritol (DPE) and pentaerythritol as six (B₆)‐ and four (B₄)‐functional core molecules. The molar mass, composition and structure of HBPEs were determined with respect to the negative substitution logic and monomer self‐condensation effect. The molar masses and structures of HBPEs containing DPE core were less influenced by the negative effect of a reacted hydroxyl group on the reactivity of other hydroxyl groups in the same monomer unit. Thus, the use of DPE core in copolymerization with bis‐MPA monomer could help slightly to increase the molar mass of HBPEs. Conversely, the effect of self‐condensation of bis‐MPA on the molar mass reduction was more pronounced in the case of DPE hyperbranched polymers due to the A–B negative substitution effect. These two effects become more significant with increasing pseudo‐generation numbers of the HBPEs. © 2014 Society of Chemical Industry     

Aliphatic hyperbranched polyesters based on 2,2-bis(methylol)propionic acid—Determination of structure, solution and bulk properties

Due to their highly branched structure and the large number of functional groups hyperbranched polymers possess unique properties that make them interesting for uses in a wide variety of applications. Some of the most widely investigated hyperbranched polymers are the polyesters based on 2,2-bis(methylol)propionic acid. In this paper we present the results of characterization studies of hyperbranched polyesters based on 2,2-bis(methylol)propionic acid which show that they are very complex products with a multidimensional distribution of various properties. The influence of the synthesis conditions on the structure and molar-mass characteristics of hyperbranched polyesters as well as the findings that allow a thorough understanding of the structure-property relationships are reviewed in detail.     

Development of epoxy/hyperbranched blends for resin transfer molding and vacuum assisted resin transfer molding applications: Effect of a reactive diluent

The rheological and thermomechanical properties of some epoxy blends modified with hyperbranched polymers are reported. The effects of different percentages of a multifunctional reactive diluent were investigated to develop formulations that could be processed by RTM (Resin Transfer Molding) and VARTM (Vacuum‐Assisted Resin Transfer Molding). The diluent chosen for the study was trimethylolpropane triglycidyl ether, which was added at three percentages: 10%, 20%, and 40%. The hyperbranched modifier used was aliphatic polyester of the fourth pseudo‐generation commercialized by Perstorp as Boltorn? H40. A cure cycle composed of a precure at 135°C followed by a postcure at 180°C was adopted. The blends were thoroughly characterized in both the unreacted and cured states. The unreacted blends were characterized by parallel plate rheometry, both in dynamic and isothermal mode. Analysis of the cured samples was carried out through dynamic mechanical tests after precuring and postcuring. The diluent had an impact, due to its peculiar structure, on both the uncured and cured properties. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers