Synthesis of unsaturated polyester resins for large sized composites

A series of unsaturated polyesters based on phthalic anhydride (PHA), maleic anhydride (MA), ethylene glycol (EG), diethylene glycol (DG), triethylene glycol (TG), propylene glycol (PG), styrene (Sty) and acrylonitrile (AN) were prepared. The molecular weights of the prepared polyesters were determined by end-group analysis. The effect of the structure of the resin on its curing behavior has been investigated. On the basis of the experimental study, the following were concluded: (1) The maximum curing temperature (T_max) is related to the molecular weight of the glycol incorporated in these castings. In this context the T_max was found to decrease with increasing the molecular weight. Meanwhile the time to peak temperature t_max was increasing. (2) The higher the percentage of AN in the crosslinking monomer system, the slower a resin cures. (3) The values of T_max were found to be influenced to a large extent by the percentage of AN.     

Composite cure kinetic analysis of unsaturated polyester free radical polymerization

Curing kinetics of unsaturated polyester resin system exhibiting apparent induction periods was investigated by modeling free radical initiation and propagation processes. The isothermal curing induction time as well as the maximum-rate time provided the same activation energy in the Arrhenius relation, and therefore, the isothermal curing master curve was constructed by using the reduced time method. Two model elementary rate equations for radical and monomer were proposed to describe the free radical polymerization of unsaturated polyester resin systems. The power law was adopted to express the conversion dependence function of the initiation efficiency and the monomer reaction rate. Demonstrating the capability of the developed model, the agreement between experimental and predicted data was excellent in both isothermal and dynamic-heating conditions, even with the same model parameters in different thermal conditions. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2447–2456, 1997     

Fracture behavior–morphology relationships in an unsaturated polyester resin modified with a liquid oligomer

An unsaturated polyester (UP) resin modified with a liquid polymer, polyoxypropylenetriamine (POPTA), at a concentration of 10 wt% has been precured at several temperatures. Phase separation takes place before gelation at all precure temperatures used. The glass‐transition region has been analyzed by dynamic mechanical analysis. Mechanical properties have been related to microstructural features. With a precure temperature fixed, the unsaturated polyester (UP) resin has also been modified with different contents of POPTA. Fracture toughness of the mixtures has also been analyzed and results are compared to those for the unmodified mixture. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1677–1685, 1999     

A facile strategy for enhancing the fire safety of unsaturated polyester resins through introducing an efficient mono‐component intumescent flame retardant

Unsaturated polyester resins (UPRs) are usually used in the field of automotive and electronic appliances, but their natural flammability severely constrain their wide application. In this research, a mono‐component intumescent flame retardant piperazine pyrophosphate (PPAP) was incorporated into the UPR matrix and the fire retardancy, thermal properties, combustion performance, and flame‐retarded mechanisms of UPR/PPAP were comprehensively investigated. With as low as 18 wt% PPAP introduced, UPR/18 wt% PPAP thermosets fulfilled UL‐94 V‐0 grade during vertical burning tests and the limiting oxygen index value reached 29.8%. Cone calorimeter tests shown that the peak of heat release and CO production were prominently declined with the decrease of 60.9% and 70.2% compared with those of UPR. The incorporation of PPAP efficaciously enhanced the fire safety of UPR thermosets. The investigation of flame‐retarded mechanisms for UPR/PPAP thermosets indicated that PPAP stimulated UPR thermosets to form sufficient, compact, partially graphitized, and expanded char layer on thermosets surface in advance and the char layer effectively exerted shielding effect in condensed phase. Thus, the total amount of heat of UPR/PPAP was suppressed with the reduction of 42.5% compared with that of UPR. Overall, the excellent fire safety performance promised the flame‐retardant UPR/PPAP thermosets crucial application values in some key areas.     

Synthesis and characterization of high bio-based content unsaturated polyester resin for wood coating from itaconic acid: Effect of various reactive diluents as an alternative to styrene

The present work focuses on the ability of 2-hydroxyethyl methacrylate (HEMA), isobornyl methacrylate (IBOMA) and methyl methacrylate (MMA) as reactive diluents to replace styrene in unsaturated polyester resin based on itaconic acid, sebacic acid, 1,4-Butanediol, 1,6-Hexanediol and glycerol. The structural analysis confirmed the presence of itaconate linkages in the UPs. The synthesized resins were characterized by infrared spectroscopy and their physiochemical properties such as appearance, viscosity, acid value, %volatile content, curing characteristics like gel time, peak exotherm temperature and total cure time. Among all the resins formed; the resin based on 1,6-Hexanediol showed optimum molecular weight and viscosity needed for final application. The cured resins were investigated for their thermal stability by thermo-gravimetric analysis which revealed that all the diluted resins had good thermal stability. From the results it could be concluded that styrene-free bio-based unsaturated polyester resin can be synthesized having properties equivalent to the commercial styrene based resin.GRAPHICAL ABSTRACT     

Low viscous unsaturated polyester resin for monomer free UP-resins

It was possible to develop comonomer free unsaturated polyester resins for the application in electrical industry. By testing model compounds and mixtures of model compounds it was possible to find the optimised structure of the resin molecule with respect to the position of the copolymerizable double bonds. By choosing the proper composition of the other components of the resin, e.g. the glycols and modifying dicarboxylic acids, it was also possible to manufacture low viscous resins.     

Relaxations during the postcure of unsaturated polyester networks by ultrasonic wave propagation,dynamic mechanical analysis,and dielectric analysis

Ultrasonic wave propagation, dynamic mechanical analysis, and dielectric analysis were used to monitor relaxation phenomena during the nonisothermal postcure of unsaturated polyester networks. The measurements covered 6 decades of frequency. As a result, the residual reactive groups, immobilized in the glassy state by vitrification during an isothermal cure step, gained molecular mobility, which promoted the formation of additional crosslinks. After the postcure, the reaction was complete, and the maximum achievable glass‐transition temperature was reached. Moreover, the frequency and temperature dependence of the two relaxations, one related to the glass‐transition temperature of the partially cured sample and the other to the glass transition of the fully cured sample, was evaluated. The Williams–Landel–Ferry equation was used to model the frequency dependence of the main α‐relaxation data obtained with the different techniques. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 596–602, 2005     

Renewable benzoxazine monomers from “lignin‐like” naturally occurring phenolic derivatives

The benzoxazines of three naturally occurring phenylpropanoid phenols: ferulic, coumaric, and phloretic acids, and their esters are described. Benzoxazines with conjugated unsaturated chains exhibit unusual poor thermal stability and degrade partially at the polymerization temperature making necessary the use of a catalyst (BF₃.Et₂O) to low the polymerization temperature and prevent degradation. Polybenzoxazines are prepared thermally and characterized by DSC and TGA techniques. The resulting materials have superior Tgs when compared with those prepared from an unsubstituted monofuctional benzoxazine due to the additional crosslinking through the ester and carboxylic moieties. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4894–4903     

Mechanical properties of unsaturated polyester resins in relation to their chemical structure. I. Secondary relaxations and local motions

Dynamic mechanical spectroscopy has been combined with high-resolution solid-state ¹³C NMR to characterize the molecular motions responsible for the γ and β secondary relaxations in unsaturated polyester networks. In DEG networks the 7γ transition is assigned to restricted phenyl group rotation in the styrene cross-links whereas the motion of molecular groups in the vicinity of the residual maleic double bonds account for the β transition. © 1994 John Wiley & Sons, Inc.     

Novel quaternary ammonium borates as latent catalysts for epoxy–phenolic resins

Novel tetrabutylammonium tetrakis(substituted benzoyloxy)borate salts ( 1a – 1d ) were synthesized by the reaction of tetrabutylammonium tetraphenylborate and corresponding substituted benzoic acids. Polyaddition reactions of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐bisphenol F (44BPF) or bisphenol F (BPF‐D) with the ammonium borates were investigated as model reactions of epoxy/phenol–novolac resin systems with respect to the thermal latency and storage stability of the catalyst. The polyaddition of DGEBA/44BPF with the ammonium borates in diglyme at 150 °C for 6 h proceeded up to 84–94% conversions and gave polymers with number‐average molecular weights of 3750–5750, whereas the polyaddition at 80 °C for 6 h gave less than 9% conversions. The catalytic activity of ammonium borates 1a – 1d depended on the substituent of the phenyl group of the borates, and the order of activity was 1b (p‐OMe) > 1a (? H) > 1c (p‐NO₂) > 1d [3,5‐(NO₂)₂]. The ammonium borate catalyst with the substituent that yielded lower acidity of the corresponding substituted benzoic acid tended to reveal higher activity. In comparison with tetrabutylammonium bromide (TBAB) as a conventional ammonium salt, 1a – 1d revealed better thermal latency. The storage stability of DGEBA/BPF‐D with the ammonium borate catalysts in bulk at 40 °C was better than that with TBAB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2689–2701, 2002     

Preparation and thermomechanical properties of epoxy resins modified by octafunctional cubic silsesquioxane epoxides

The thermomechanical properties of octafunctional cubic silsesquioxane‐modified epoxy resins associated with dicycloaliphatic hardener (4,4′‐dimethyldiaminodicyclo hexyl methane) were studied using thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. The structures of epoxy resin containing cubic silsesquioxane epoxides were characterized by Fourier transform infrared spectroscopy and wide‐angle X‐ray scattering techniques. In this work, octa(dimethylsiloxybutylepoxide) octasilsesquioxane (OB), and octa(glycidyldimethyl‐siloxyepoxide) octasilsesquioxane (OG), were synthesized and used as additives to improve the properties of a commercial epoxy resin by exploring the effects of varying the ratio of OB or OG. The commercial Ciba epoxy resin (Araldite LY5210/HY2954) was used as a standard. It was found, by thermogravimetric analysis and dynamic mechanical analysis, that the highest thermal stability was observed at N = 0.5 (N = number of amine groups/number of epoxy rings). No glass transition temperature was observed by adding 20 mol % OB to the Ciba epoxy resin, indicating the reduction of chain motion in the presence of octafunctional cubic silsesquioxane epoxide. The storage modulus of the OB‐modified epoxy resin also increased, especially at higher temperatures, compared with the Ciba epoxy resin under identical curing conditions. Fourier transform infrared data elucidated the preservation of cubic silsesquioxane structure after curing at high temperature. In contrast, the OG/Araldite LY5210/HY2954 systems gave poorer thermomechanical properties. The low viscosity of OB at room temperature (～ 350 cPs) makes it suitable for composite processing and, when used in conjunction with the Ciba epoxy, lowers the viscosity of this system as well. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3490–3503, 2004     

Thermal latency of novel chelating borate catalysts as latent catalysts for epoxy–phenolic resins

Novel quaternary ammonium bis(2‐oxybenzoyloxy)borate salts ( 1a – 1c ) or quaternary ammonium bis(1,2‐benzenedioxy)borate salts ( 2a and 2b ) with tetra‐n‐butylammonium (TBA⁺), tetra‐n‐octylammonium (TOA⁺), or bis(triphenylphosphoranylidene)ammonium (PNP⁺) cations were synthesized as latent catalysts of epoxy/phenol–novolac resins by the complexation between boric acid and salicylic acid or catechol, followed by neutralization with quaternary ammonium hydroxide. Polyaddition reactions of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐bisphenol F (44BPF) or bisphenol F (BPF‐D) with the ammonium borates were investigated as model reactions of epoxy/phenol–novolac resin systems with respect to the thermal latency and storage stability of the catalyst. The polyaddition of DGEBA/44BPF with 1a – 1c in diglyme at 150 °C for 6 h proceeded up to 85–96% conversions and gave polymers with number‐average molecular weights of 4180–10,500, whereas the polyaddition at 80 °C for 6 h gave less than 8% conversions. However, the polyaddition with 2a containing TBA⁺ cation proceeded to only a 32% conversion at 150 °C for 6 h in diglyme and to a 64% conversion even at 180 °C for 6 h in triglyme and only gave low molecular weight oligomers, and no reaction proceeded in the polyaddition at 80 °C. However, polyaddition with 2b containing PNP⁺ cation proceeded up to a 96% conversion at 150 °C for 6 h in diglyme and gave a higher molecular weight polymer with a number‐average molecular weight of 8050, whereas the polyaddition at 80 °C for 6 h gave only a 5% conversion. The catalytic activity of ammonium borates 1a – 1c and 2a and 2b depended on the borate anion structure: 1a and 1c with bis(2‐oxybenzoyloxy)borate anion revealed higher activity than 2a and 2b with bis(1,2‐benzenedioxy)borate anion, respectively. In comparison with tetra‐n‐butylammonium bromide (TBAB) as a conventional ammonium salt or tetra‐n‐butylammonium tetrakis(benzoyloxy)borate (TBA‐TBB), 1a – 1c and 2b revealed better thermal latency. The catalytic activity of ammonium borates also depended on the bulkiness of the ammonium cation, and the order of activity was 1c (PNP⁺) > 1b (TOA⁺) ≧ 1a (TBA⁺) and 2b (PNP⁺) > 2a (TBA⁺). The storage stability of DGEBA/BPF‐D with the ammonium borate catalysts 1a – 1c and 2a and 2b in bulk at 40 °C was much better than that with TBAB and TBA‐TBB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2702–2716, 2002     

Influence of glass transition temperature of crosslinked unsaturated polyester resin/styrene formulations on the final conversion after an isothermal curing at 100°C

SMC (sheet molding compound) is a composite based on fibers‐reinforced unsaturated polyester (UP) resin molded usually at 140°C to 170°C under a pressure of 60 to 100 bars. In order to develop new SMC formulations that can be molded at lower temperature (100°C) for economic and environmental reasons, the formulation of the composite had to be completely modified, both to allow a rapid reaction at 100°C, but also to avoid a vitrification phenomenon due to the fact that the glass transition temperature (Tg) of the SMC parts becomes, during the molding process, higher than the mold temperature. In this paper, the relation between the molding temperature, the glass transition temperature, and the final conversion of UP resin/styrene formulations has been underlined. The Tg of the cured resin was decreased by two different ways. The first way involved the reduction of the crosslinking density of the UP resin by using a blend of two resins, a pure maleic and a more flexible one. This blend allows to adjust the Tg over a temperature range from 197°C (Tg of the pure UP resin) to 75°C (Tg of the pure flexible resin). The second way consisted in the addition of butyl methacrylate (BuMA), a reactive plasticizer, to the formulation, allowing a decrease of the final material's Tg from 197°C to 130°C by replacing 35 wt% of styrene by BuMA. These two methods allow to obtain a final conversion of 99% after 8 minutes of molding at 100°C.     

Monomers,polymers, copolymers,resins, and coated silicas containing benzylamine residues planned as artificial substrates of benzylamine oxidase

The new monomers 3-(3-methacryloxypropoxy)benzylamine and 4-(3-methacryloxypropoxy)benzylamine in the form of hydrochlorides have been synthesized and radically copolymerized under various conditions with comonomers of different hydrophilicity, including N-acryloylmorpholine, N-acryloylpyrrolidine, N,N-dimethylacrylamide, and N-vinylbenzoylmorpholine, to obtain linear soluble, granular crosslinked, and silica-based macromolecular systems designed for investigating the action mechanism of benzylamine oxidase. Some characteristics of the prepared materials, including scanning electron microscopy photographs, are reported. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3109–3118, 1999     

Injection molded hybrid composites based on corn fibers and poly(vinyl alcohol)

Ongoing research cooperation between USDA and the University of Pisa, Italy has yielded several composite blends of poly(vinyl alcohol) (PVA) and corn fibers (CF). The USA is the largest producer of ethanol from cereal grains. Composites based on natural fibers alone are extremely sensitive to water. Their mechanical properties deteriorated upon the absorption of water, thus suggesting a limited usefulness of such formulations in practical applications. In this study, corn-fibers produced during the wet milling process of corn for fuel ethanol were used to prepare composites. CF and PVA were processed in variable amounts in the presence of both dry/fluid plasticizers, such as glycerol and pentaerythritol. Composites prepared from CF in combination with PVA showed little change in their mechanical properties even after conditioning at variable relative humidities, as well as complete soaking in water. Composites tested after storage for one year under 50% relative humidity and 23°C exhibited mechanical properties similar to those of freshly prepared composites. Cornstarch was introduced in the formulation for the purpose of reducing the cost of the final product and to further increase the composition of natural components in the composites. Addition of starch moderately reduced the mechanical properties of the composites.     

Vinylcarbonates and vinylcarbamates: Biocompatible monomers for radical photopolymerization

The last decade has seen a remarkable interest in the use of biocompatible and biodegradable polymers as scaffolds for tissue engineering. The fabrication of 3D scaffolds by lithography‐based additive manufacturing technology (AMT) represents an appealing approach. As poly(lactic acid), the state of the art biocompatible and biodegradable material, cannot be processed by these photopolymerization‐based techniques, it has so far been necessary to use selected (meth)acrylates. By developing new photopolymers based on vinyl carbonates and vinyl carbamates as a reactive group we have been able to avoid most of the disadvantages of classical (meth)acrylate‐based photopolymers. The new generation of biocompatible monomers show low cytotoxicity, have good storage stability, and are sufficiently photoreactive to be structured by lithography based AMT. The mechanical properties and rates of degradation of the polymers can be easily tuned over a broad range. Degradation results in the formation of nonacidic and nontoxic degradation products of low molecular weight that can be easily transported within the human body. Initial in vivo tests showed significant osseointegration of the 3D cellular scaffolds and no signs of implant rejection. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

New powder coatings with low curing temperature and enhanced mechanical properties obtained from DGEBA epoxy resins and Meldrum acid using erbium triflate as curing agent

New low curing temperature powder coatings obtained by copolymerization of epoxy resins with Meldrum acid (MA) initiated by erbium (III) trifluoromethanesulfonate have been formulated. Their mechanical and thermomechanical properties have been studied and compared with a commonly used industrial system (o-tolylbiguanide/epoxy resin) and with an already formulated epoxy powder coating homopolymerized by erbium trifluoromethanesulfonate. Systems containing low proportions of MA and initiated by erbium trifluoromethanesulfonate lead to a great reduction of curing conditions (temperature/time). Moreover, the new formulated systems present very good mechanical properties, adhesion, and impact resistance. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2316–2327, 2007     

Reactive rubbers as toughening agents for thermoset polyester resins. Molecular analysis by FTIR and fracture behavior of the resulting blends

A reactive rubber obtained by isocyanation of hydroxyl-terminated polybutadiene was used as toughening agent for an unsaturated polyester resin. Both the isocyanation and the successive reaction between the modified rubber and the polyester were investigated by Fourier-transform infrared spectroscopy (FTIR). Fracture measurements at high and low strain rate were carried out on the cured materials to test their toughness. The failure mechanisms were established by morphological analysis of fractured surfaces, performed by scanning electron microscopy. © 1993 John Wiley & Sons, Inc.     

Application of Modified Natural Oils as Reactive Diluents for Epoxy Resins

Bisphenol A based low-molecular-weight epoxy resin was modified with epoxidized soybean oil, which exhibit viscosity reducing ability comparable to commercial grade active diluents. The studied compositions showed a non-Newtonian rheological behavior, typical for Bingham liquids. The values of the flow index (n) and the consistency index (k) for the compositions tested in the temperature range 25–65 °C were calculated from the Ostwald-de Waele rheological model and were used to calculate the flow-activation energy (E_a) using the Arhenius equation. Studies of co-crosslinking of mixed oil-resin compositions using isophorone diamine showed essential decrease of the reaction heat and peak maximum temperature. Mechanical properties, thermal stability, water absorption and chemical resistance of the epoxy resin modified with natural oil, were also investigated. Compositions of epoxy resin Ruetapox 0162, modified with the oil diluent, preserved very good mechanical properties of the epoxy resins and demonstrated relatively low water absorption as well as high chemical resistance. The compositions displayed even higher impact strength than pure epoxy resin due to plasticizing effect of the built-in oil. Compositions with the high contents (up to 60 weight %) of the oil were flexible materials with fast elastic recovery.