Synthesis and properties of a novel bio‐based benzoxazine resin with excellent low‐temperature curing ability

A novel bio‐based benzoxazine resin (diphenolic acid/furfurylamine benzoxazine resin, PDPA‐F‐Boz) was prepared by using bio‐based diphenolic acid, furfurylamine and paraformaldehyde as raw materials. The structure of DPA‐F‐Boz monomer was characterized by Fourier transform infrared spectroscopy, ¹H NMR and ¹³C NMR, and then its curing reaction and the thermal stability of the cured PDPA‐F‐Boz were analyzed. Compared with the traditional fossil‐based benzoxazine (bisphenol A/aniline benzoxazine, BPA‐A‐Boz) and the bio‐based benzoxazine (diphenolic acid/aniline benzoxazine, DPA‐A‐Boz), DPA‐F‐Boz monomer showed the lowest curing temperature, and PDPA‐F‐Boz had the highest residual char ratio at 800 °C and the lowest degradation rate at the peak temperature. Meanwhile, the total heat release, peak heat release rate and heat release capacity of PDPA‐F‐Boz were much lower than those of PBPA‐A‐Boz and PDPA‐A‐Boz. Thus, PDPA‐F‐Boz showed excellent low‐temperature curing ability and thermal stability. © 2019 Society of Chemical Industry     

Improving the curing process and thermal stability of phthalonitrile resin via novel mixed curing agents

High curing temperature (including post‐curing temperature) and long curing time of phthalonitrile resins make them thermally stable but difficult to process. In this paper, novel mixed curing agents (CuCl/4,4′‐diaminodiphenylsulfone (DDS) and ZnCl₂/DDS) were firstly designed for solving these problems. Bisphenol‐based phthalonitrile monomer (BP‐Ph; melting point: 228–235 °C) was synthesized and used as the curing precursor. Differential scanning calorimetry results indicated that BP‐Ph cured with CuCl/DDS and ZnCl₂/DDS exhibited curing temperatures close to the melting point of BP‐Ph with curing ending temperatures of 225.4 and 287.1 °C, respectively. Rheologic investigations demonstrated obvious curing reactions of BP‐Ph occurred with the mixed curing agents at 220 °C. Thermogravimetric analysis showed that BP‐Ph cured by CuCl/DDS or ZnCl₂/DDS maintained 95% mass at 573 or 546 °C, respectively, at a post‐curing temperature of 350 °C for 2 h. Reasonable long‐term thermo‐oxidative stability was also demonstrated. When the post‐curing temperature decreased to 290 °C, char yield at 800 °C of BP‐Ph cured by CuCl/DDS was 77.0%, suggesting the curing procedure can be milder when using mixed curing agents. © 2017 Society of Chemical Industry     

Research progress on bio‐based thermosetting resins

Compared with the rapid progress on bio‐based thermoplastics, research on bio‐based thermosetting resins should have attracted much more attention, considering that they will have a bright future. In this paper, the current research progress on bio‐based thermosetting resins is reviewed. We pay special attention to the synthesis and investigation of properties of epoxies and unsaturated polyesters derived from renewable plant oil, cardanol, rosin acid, lignin, glycerol, gallic acid, furan, isosorbide, itaconic acid, etc. This mini review gives an overall perspective for bio‐based thermosets.© 2015 Society of Chemical Industry     

Synthesis and curing behavior of a novel benzoxazine‐based bisphthalonitrile monomer

A novel bisphthalonitrile containing benzoxazine units (BZ‐BPH) was synthesized via a solventless method from 4,4′‐dihydroxybiphenyl, paraformaldehyde, and 4‐aminophenoxylphthalonitrile. The chemical structure of BZ‐BPH was confirmed by ¹H‐NMR and ¹³C‐NMR analyses. The curing behavior was investigated with DSC, FTIR, TGA, and rheology techniques. The monomer manifested a two‐stage thermal polymerization pattern. The first stage was attributed to the ring‐opening polymerization of benzoxazine moiety, and the second to the polymerization of phthalonitriles. Study about the effect of the catalysts including 4,4′‐diaminodiphenylsulfone and FeCl₃ on the polymerization of BZ‐BPH was performed, and the result indicated that the addition of these agents could increase the curing rate and lower the curing temperature. Additionally, the cured product showed excellent thermal and thermo‐oxidative stability, the high char yield was 76.0% by weight at 800°C in nitrogen atmosphere and 81.2% by weight at 600°C in air, and temperature at 5% weight loss (T_5%) in nitrogen and air was 477.9°C and 481.7°C, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Single component self‐curable aqueous‐based PU system with new aziridinyl curing agent

The self‐emulsified aqueous‐based polyurethane (PU) consists of carboxyl group, which is an ionic center not only stabilizing the aqueous polymer dispersion but also serving as the curing site toward aziridinyl curing agent. Two new aziridinyl curing agents, HDI‐AZ and ADA‐AZ, are prepared from an addition reaction of aziridine to hexamethylene diisocyanate (HDI) and adipic acyl chloride (ADA), respectively. These curing agents are added separately into NCO‐terminated PU prepolymer before or after the water dispersion process. The resulting PU dispersion becomes a single component self‐curable aqueous‐based PU system. The cured PU is obtained from this single component PU dispersion on drying at ambient temperature. The improved PU properties demonstrate the feasibility of this convenient single component self‐curable aqueous‐based PU system. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91:1997–2007, 2004     

Copolymerization modification: improving the processability and thermal properties of phthalonitrile resins with novel comonomers

Two novel tetrahydrophthalic anhydride end‐capped imide compounds (THAN and THBN) with high thermal stability were synthesized to promote the curing reaction of 1,3‐bis(3,4‐dicyanophenoxy)benzene (3BOCN), and to study the effects of comonomer structure on the curing behavior and thermal performance of phthalonitrile resins. The curing behaviors of THAN/3BOCN and THBN/3BOCN blends with various molar ratios were investigated using rheological analysis and differential scanning calorimetry, suggesting a wide processing window. Dynamic mechanical analysis and thermogravimetric analysis showed that the cured resins possessed high glass transition temperatures (> 500 °C), and superior thermal and long‐term thermo‐oxidative stabilities with weight retention of 95% ranging from about 544 to 558 °C in both nitrogen and air. All these results indicated that the processability and thermal properties of phthalonitrile resins could be improved further by modifying the structure of comonomer in this kind of curing system. © 2018 Society of Chemical Industry     

Thiourethane thermoset coatings from bio‐based thiols

Three bio‐based thiols were synthesized via the thermal thiol‐ene reactions between sucrose soya ester (SSE) and multifunctional thiols; then, thiourethane coatings were produced from these thiols and their coating properties were studied. A series of high bio‐renewable content thiol oligomers were synthesized according to the previously reported thermal thiol‐ene reaction. Fourier transform infrared spectra (FTIR) confirmed the complete consumption of the double bonds in SSE, and gel permeation chromatography confirmed the formation of high‐molecular‐weight oligomers. The viscosity of these oligomers remained low due to their compact and branched structures. Thermoset thiourethane coatings were prepared from these thiol oligomers and polyisocyanate trimer resins with dibutyltin diacetate as the catalyst. FTIR spectra confirmed the formation of the thiourethane group. However, coatings based on isophorone diisocyanate (IPDI) polyisocyanate resin showed a lower degree of cure because of the decreased resin mobility due to the rigid cyclohexane ring. Generally, all the coatings showed good adhesion to aluminum panels, and had high gloss. However, they exhibited low tensile strength, modulus and chemical resistance due to the flexibility of the fatty acid chain. Coatings based on more rigid IPDI‐based polyisocyanate showed higher T_g, hardness and direct impact resistance compared with the hexamethylene‐diisocyanate (HDI) based polyisocyanate counterparts. Thermogravimetric analysis results showed that coatings based on mercaptanized soybean oil have better thermal stability than those from di‐pentene dimercaptan or glycol di‐3‐mercaptopropionate. Two T_g values were found by both differential scanning calorimetry and dynamic mechanical thermal analysis of thiourethanes from HDI‐based polyisocyanate and di‐pentene dimercaptan or glycol di‐3‐mercaptopropionate based oligomers due to phase separation resulting from the poor compatibility between HDI‐based polyisocyanate and the respective oligomers. Copyright © 2011 Society of Chemical Industry     

Synthesis of rosin‐based imidoamine‐type curing agents and curing behavior with epoxy resin

Rosin is an abundantly available natural product. The characteristic fused ring structure of rosin acids is analogous to that of some aromatic compounds in rigidity, and makes rosin and its derivatives potential substitutes for those aromatic compounds. In the study reported, the synthesis of biobased curing agents containing imide structure using rosin and the cure reaction were investigated. Rosin‐based imidoamine‐type curing agents were synthesized, and the chemical structure was confirmed using ¹H NMR, Fourier transform infrared and electrospray ionization spectroscopy. The curing behavior with diglycidyl ether of bisphenol A epoxy was studied using differential scanning calorimetry. The thermal mechanical properties and thermal stability of the cured epoxy resins were evaluated using dynamic mechanical analysis and thermogravimetry, respectively. The results indicate that the curing behavior of the rosin‐based curing agents is similar to that of curing agents with analogous structures. Cured products have good thermal stability due to the presence of the imide group and the bulky hydrogenated phenanthrene ring structure. Rosin acids have a great potential in the synthesis of epoxy curing agents as replacements for some of the current commercial aromatic or cycloaliphatic analogues. Copyright © 2010 Society of Chemical Industry     

Preparation and properties of soybean oil–based curing agents for epoxy resin

In order to improve the flexibility properties of conventional epoxy resin, two novel soybean oil–based curing agents were synthesized. The curing agent obtained from the reaction between epoxy soybean oil and ethylene diamine was named EEDA, and another curing agent derived from epoxy soybean oil and isophorone diamine was named EIPDA. Several techniques were used to systematically investigate the effects of the structure and content of the two curing agents on the properties of the cured products. The Fourier transform infrared analysis demonstrated that epoxy resin reacted with soybean oil–based curing agents. The differential scanning calorimetry analysis showed that the curing process between diglycidyl ether of bisphenol‐A (DGEBA) and soybean oil–based curing agents only had an exothermic peak. Thermogravimetric analysis indicated that the cured DGEBA/EIPDA system was more stable than the DGEBA/EEDA system below 300 °C. Mechanical tests and Shore D hardness tests suggested that excessive EEDA greatly enhanced the toughness of cured products because of the introduction of aliphatic chains.© 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44754.     

Thermal study on the copolymers of phthalonitrile and phenylnitrile‐functional benzoxazines

Ortho‐, meta‐, and para‐phenylnitrile–functional benzoxazines are polymerized at different compositions with phthalonitrile‐functional monomers providing copolybenzoxazines of high thermal stability and easy processability. The most positive effect on these properties is obtained on copolymerizing phthalonitrile‐ and ortho‐phenylnitrile–functional benzoxazines. Thermal decomposition of these polybenzoxazines is studied by thermogravimetry (TGA). It is demonstrated that only 30 mol % of phthalonitrile‐functional benzoxazine added to the ortho‐phenylnitrile–substituted monomer improves char yield significantly from 59 to 77 wt %, which is the value of neat phthalonitrile‐based polybenzoxazine. Glass transition temperature (T_g) also dramatically increases from 180°C for neat ortho‐phenylnitrile polymer to 294°C for the copolymer with 30 mol % of phthalonitrile‐functional monomer. Additionally, the high melt viscosity of phthalonitrile‐functional benzoxazines is dramatically decreased upon blending with phenylnitrile‐functional monomer. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2937–2949, 1999     

Synthesis of rosin‐based flexible anhydride‐type curing agents and properties of the cured epoxy

BACKGROUND: Although rosin acid derivatives have received attention in polymer synthesis in recent years, to the best of our knowledge, they have rarely been employed as epoxy curing agents. The objective of the study reported here was to synthesize rosin‐based flexible anhydride‐type curing agents and demonstrate that the flexibility of a cured epoxy resin can be manipulated by selection of rosin‐based anhydride‐type curing agents with appropriate molecular rigidity/flexibility. RESULTS: Maleopimarate‐terminated low molecular weight polycaprolactones (PCLs) were synthesized and studied as anhydride‐type curing agents for epoxy curing. The chemical structures of the products were confirmed using ¹H NMR spectroscopy and Fourier transform infrared spectroscopy. Mechanical and thermal properties of the cured epoxy resins were studied. The results indicate that both the epoxy/anhydride equivalent ratio and the molecular weight of PCL diol play important roles in the properties of cured resins. CONCLUSION: Rosin‐based anhydride‐terminated polyesters could be used as bio‐based epoxy curing agents. A broad spectrum of mechanical and thermal properties of the cured epoxy resins can be obtained by varying the molecular length of the polyester segment and the epoxy/curing agent ratio. Copyright © 2009 Society of Chemical Industry     

A new tri‐functional azetidine compound for self‐curing aqueous‐based PU system

A mono‐azetidine compound had been demonstrating a ring opening reaction with carboxylic acid (e.g., trimethylacetic acid, TMAA) and that resulted in an amino ester bond formation at ambient temperature. A triazetidine compound (trimethylolpropane tris(1‐azetidinyl)propionate, TMPTA‐AZT) was obtained via Michael addition of azetidine (AZT) to trimethylolpropane triacrylate (TMPTA). The carboxylic groups of anionic aqueous‐based polyurethanes (PU) served as internal emulsifier, which stabilized PU dispersion and also served as PU curing sites. The triazetidine compound (TMPTA‐AZT) was introduced into anionic aqueous‐based PU dispersion as a new latent curing agent and that mixture became a single‐component self‐curable aqueous PU system. A crosslinked PU film was obtained from this PU system on drying at ambient temperature. The final polymer performance properties demonstrated the crosslinking behaviors of this new curing agent, TMPTA‐AZT, with carboxylic ion‐containing aqueous‐based PU resins. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

New thermosetting resin from terpenediphenol‐based benzoxazine and epoxy resin

Terpenediphenol‐based benzoxazine was prepared from terpenediphenol, formaline, and aniline. Curing behavior of the benzoxazine with epoxy resin and the properties of the cured resin were investigated. Consequently, the curing reaction did not proceed at low temperatures, but it proceeded rapidly at higher temperatures without a curing accelerator. The properties of the cured resin both from neat resins and from reinforced resins with fused silica were evaluated, respectively. The cured resins showed good heat resistance, mechanical properties, electrical insulation, and especially water resistance, compared with the cured resin from bisphenol A type novolac and epoxy resin. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2266–2273, 1999     

Curing behavior and thermal property of epoxy resin with boron‐containing phenol‐formaldehyde resin

The curing reaction of bisphenol‐A epoxy resin (BPAER) with boron‐containing phenol–formaldehyde resin (BPFR) was studied by isothermal and dynamic differential scanning calorimetry (DSC). The kinetic reaction mechanism in the isothermal reaction of BPAER‐BPFR was shown to follow autocatalytic kinetics. The activation energy in the dynamic cure reaction was derived. The influence of the composition of BPAER and BPFR on the reaction was evaluated. In addition, the glass transition temperatures (T_gs) were measured for the BPAER‐BPFR samples cured partially at isothermal temperatures. With the curing conditions varying, different glass transition behaviors were observed. By monitoring the variation in these T_gs, the curing process and the thermal property of BPAER–BPFR are clearly illustrated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1054–1061, 2000     

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     

Structure and properties of bio‐based polyamide 109 treated with superheated water

The structure and properties of bio‐based polyamide 109 (PA109) after treatment with superheated water (140 °C ≤ T ≤ 280 °C) were investigated and characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, wide‐angle X‐ray diffraction, scanning electron microscopy and small‐angle X‐ray scattering. Below 170 °C, the hydrothermal treatment was considered to be a physical process, which exerted an annealing effect on PA109. It led to an increase in melting temperature, lamellar thickness and crystallinity, while the macromolecular structure, crystal structure and the order of crystalline regions were not affected. Above 170 °C, complete melting/dissolution of PA109 occurred with partial hydrolysis. Due to the high temperature and long reaction time, the hydrolysis reaction became more and more prominent, and the resin was completely hydrolyzed into oligomers at 280 °C. Also, above 170 °C, the hydrothermal treatment was accompanied by a chemical process and the melting temperature and molecular weight decreased progressively. Notably, the crystal structure was not altered, but the degree of perfection of crystals and the order of crystalline regions were broken, especially above 200 °C. The hydrolytic degradation reaction was significantly affected by temperature, while both time and the water to polyamide ratio were secondary factors which influenced it to a minor extent. The process could be considered as a typical nucleophilic substitution reaction which takes place step by step inducing the molecular weight to decrease gradually. Overall, this study provides a ‘green’ route for the processing, recycling and treatment of environmentally friendly polyamides based on hydrothermal treatment technology. © 2019 Society of Chemical Industry     

Sequential heat release: an innovative approach for the control of curing profiles during composite processing based on dual‐curing systems

The sequential heat release (SHR) taking place in dual‐curing systems can facilitate thermal management and control of conversion and temperature gradients during processing of thick composite parts, hence reducing the appearance of internal stresses that compromise the quality of processed parts. This concept is demonstrated in this work by means of numerical simulation of conversion and temperature profiles during processing of an off‐stoichiometric thiol–epoxy dual‐curable system. The simulated processing scenario is the curing stage during resin transfer moulding processing (i.e. after injection or infusion), assuming one‐dimensional heat transfer across the thickness of the composite part. The kinetics of both polymerization stages of the dual‐curing system and thermophysical properties needed for the simulations have been determined using thermal analysis techniques and suitable phenomenological models. The simulations show that SHR makes it possible to reach a stable and uniform intermediate material after completion of the first polymerization process, and enables a better control of the subsequent crosslinking taking place during the second polymerization process due to the lower remaining exothermicity. A simple optimization of curing cycles for composite parts of different thickness has been performed on the basis of quality–time criteria, producing results that are very close to the Pareto‐optimal front obtained by genetic algorithm optimization procedures. © 2018 Society of Chemical Industry     

Thermosetting foam with a high bio‐based content from acrylated epoxidized soybean oil and carbon dioxide

A resilient, thermosetting foam system with a bio‐based content of 96 wt % (resulting in 81% of C₁₄) was successfully developed. We implemented a pressurized carbon dioxide foaming process that produces polymeric foams from acrylated epoxidized soybean oil (AESO). A study of the cell dynamics of uncured CO₂/ AESO foams proved useful to optimize cure conditions. During collapse, the foam's bulk density increased linearly with time, and the cell size and cell density exhibited power‐law degradation rates. Also, low temperature foaming and cure (i.e. high viscosity) are desirable to minimize foam cell degradation. The AESO was cured with a free‐radical initiator (tert‐butyl peroxy‐2‐ethyl hexanoate, T_i ～ 60°C). Cobalt naphtenate was used as an accelerator to promote quick foam cure at lower temperature (40–50°C). The foam's density was controlled by the carbon dioxide pressure inside the reactor and by the vacuum applied during cure. The viscosity increased linearly during polymerization. The viscosity was proportional to the extent of reaction before gelation, and the cured foam's structure showed a dependence on the time of vacuum application. The average cell size increased and the cell density decreased with foam expansion at a low extent of cure; however, the foam expansion became limited and unhomogeneous with advanced reaction. When vacuum was applied at an intermediate viscosity, samples with densities ～ 0.25 g/cm³ were obtained with small (<1 mm) homogeneous cells. The mechanical properties were promising, with a compressive strength of ～ 1 MPa and a compressive modulus of ～ 20 MPa. The new foams are biocompatible. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007