Behavior of nonazeotropic compositions of a styrene–unsaturated polyester resin analyzed through FTIR spectroscopy and dynamic mechanical thermal analysis

Styrene is one of the comonomers most frequently used in the curing of unsaturated polyester resins. The use of nonazeotropic compositions leads to the formation of networks, in which the styrene–polyester ratio varies significantly during curing, as shown through FTIR spectroscopy. Dynamic mechanical thermal analysis (DMTA) showed how the variation in the styrene content affects the network structure that is formed. The results showed a decrease in network density in the systems in which the azeotropic composition was not used. The styrene content is therefore a factor that governs the curing process, in addition to the ultimate properties of the cured resins. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3618–3625, 2003     

Peroxide crosslinking of a styrene‐free unsaturated polyester

Thermoset unsaturated polyesters are usually obtained by the crosslinking of unsaturated polyester chains dissolved in an unsaturated, reactive, monomeric diluent, which is usually styrene. This article describes a new approach in which styrene‐free unsaturated polyester chains are intrinsically cured into a crosslinked matrix. The gel time, gel content, swelling degree, glass‐transition temperature, dynamic mechanical properties, tensile properties, and molecular weight between crosslinks (calculated according to both the Flory–Rehner equation and the theory of rubber elasticity) of the crosslinked polymer are studied as a function of the peroxide concentration. All properties change considerably upon the addition of small amounts of peroxide (between 1 and 2 wt %) and change to a lesser extent with higher peroxide concentrations (up to 6 wt %). The thermal properties of the isolated gel fraction are studied as a function of the peroxide concentration. The sol fraction demonstrates a plasticizing effect on the crosslinked network, affecting the glass‐transition temperature and stress–strain behavior of the crosslinked polymer. In light of the crosslink densities derived from swelling experiments, a molecular structure and crosslinking mechanism are suggested for the gel fractions of 1 and 6 wt % peroxide crosslinked unsaturated polyester chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Curing kinetics of medium reactive unsaturated polyester resin used for liquid composite molding process

The cure kinetics of medium reactivity unsaturated polyester resin formulated for Liquid Composite Molding process simulation was studied by Differential Scanning Calorimetry (DSC) under isothermal conditions over a specific range of temperature. For isothermal curing reactions performed at 100, 110, and 120°C, several influencing factors were evaluated using the heat evolution behavior of curing process. We propose two‐ and three‐parameter kinetic models to describe the cure kinetics of thermoset resins. Comparisons of the model solutions with our experimental data showed that the three‐parameter model was the lowest parameter model capable of capturing both the degree of cure and the curing rate qualitatively and quantitatively. The model parameters were evaluated by a non‐linear multiple regression method and the temperature dependence of the kinetic rate constants thus obtained has been determined by fitting to the Arrhenius equation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Ionomeric blends of poly(ethylene oxide) with poly(styrene‐co‐maleic anhydride) ionomer: Miscibility,crystallization, and melting behavior

The miscibility and crystallization behavior of poly(ethylene oxide) (PEO) and poly(styrene‐co‐maleic anhydride) ionomer (SMAI) blends were studied by the dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). This study has demonstrated that the presence of ion–dipole interactions enhances the miscibility of otherwise immiscible polymers in the PEO and high molecular weight poly(styrene‐co‐maleic anhydride) (SMA). The effect of ion–dipole interactions on enhancing miscibility is confirmed by the presence of a single glass transition temperature (T_g) and a depression of the equilibrium melting temperature of the PEO component. The equilibrium melting temperature of PEO in the blends are obtained using Hoffman‐Weeks plots. The interaction energy density, β, is calculated from these data using the Nishi‐Wang equation. The results suggest that PEO and SMAI blends are thermodynamically miscible in the melt. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1–7, 2000     

Preparation,characterization, and properties of crosslinked hydroxylated poly(styrene‐b‐butadiene‐b‐styrene) triblock copolymer

Acrylic acid was crosslinked with N,N′‐methylenebisacrylamide and converted to bioactive hydrogels by neutralization with different amino containing compounds. Several amino containing compounds were used such as 2‐aminopyridine, triethanol amine, hexamethylenetetramine (HMTA), pyridine, and imidazole. The best crosslinker ratio was determined in addition to the maximum absorbed water in different mediums. The antibacterial activity of the prepared gels were examined against examples of Gram‐positive (Staphylococcus aureus) and Gram‐negative bacteria (Escherichia coli) using agar plate method. The study was extended by evaluating one of prepared gels in columns as models for water filters. All prepared gels showed antibacterial action in agar plate method against both bacterium and the column method using one of the prepared gels showed excellent filtration and biocidal action. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Photo‐fabricated unsaturated polyester resin composites reinforced by kenaf fibers,synthesis and characterization

New bio‐fiber composites (UPRC) cured by ultraviolet radiation were produced using kenaf fiber as reinforcing agent and unsaturated polyester resins as matrix in the presence of styrene and IRGACURE 1800 as photoinitiator. Unsaturated polyester resins based on palm oil were prepared from various ratios of monoglyceride (MG)/maleic anhydride (MA) by the interaction of the corresponding MG monomer, with different equivalents of MA, in the presence of 2‐methylimidazole as catalyst. The various characteristics of the obtained bio‐fiber composites, including mechanical, gel content, water absorption and thickness swelling test, thermal analysis, were determined and the data were discussed. Bio‐fiber composite with MG: MA ratio (1 : 4 eq./eq.) showed better mechanical properties (tensile, flexural, and impact strength) than other formulations. Gel content increased as the amount of MA was increased up to the MG: MA ratio was 1 : 4 (eq./eq.) then slightly decreased at the higher ratio formulation. Bio‐fiber composite (UPRC_c) was considered the best prepared bio‐fiber composite which contained higher degree double bond, cross‐linking and thermal stability. Moreover, morphological study of selected examples of the formed bio‐fiber composites was also carried out and showed the evidence of the enhancement of the compatibility between fiber and polymer matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Phase separation of unsaturated polyester resin blended with poly(vinyl acetate)

The behavior of phase separation during the curing reaction of unsaturated polyester (UPE) resin in the presence of low profile additive, that is, poly(vinyl acetate) (PVAc), was studied by low-angle laser light scattering (LALS) and scanning electron microscopy (SEM). The experimental results revealed that the PVAc-rich phase was regularly dispersed in the cured styrene–UPE matrix for styrene–UPE resin blended with 5 wt % of PVAc. As the PVAc content was increased higher than 10 wt %, a cocontinuous PVAc and cured styrene–UPE phase was observed for the cured systems. The LALS observations were carried out in situ at a curing temperature of 100°C; thus, the effect of the rate of exothermic heat released from curing reaction on the morphology of curing system was investigated and reported in this work. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2413–2428, 1999     

New aspects of unsaturated polyester resin synthesis. Part I: modelling and simulation of reactant sequence length distributions in stepwise polymerization

The quantification of the relationship between physical properties of polymeric products and the sequence distribution of comonomer units in a polymer chain is not an easy task. In this work, detailed consideration is given to the sequence lengths and sequence length distributions to be expected in unsaturated polyesters formed by the reaction of maleic anhydride, phthalic anhydride and a diol, a reaction which gives rise to the low molecular weight precursors used in unsaturated polyester resins. Monte Carlo methods are used to explore the effects of rate constants, reactant stoichiometry and extent of reaction on the microstructure of the chain. Attention is also given to structural asymmetry of the diol component and the influence of the dynamics of the ring opening of the anhydride coreactants on the products. The approach is generic and can be readily adapted for any copolymerization which proceeds by a stepwise kinetic mechanism. © 2003 Society of Chemical Industry     

Microgelation of unsaturated polyester resins in the presence of poly(vinyl acetate) by static and dynamic light scattering

The partially cured unsaturated polyester (UPE)/styrene resins with various degrees of conversion lower than gel conversion blended with PVAc and 2‐fluorotoluene solvent were investigated using both static and dynamic light scattering (SLS and DLS). The solvent (i.e., 2‐fluorotoluene) is isorefractive with PVAc; thus, one sees only primary and partially cured UPEs in light‐scattering experiments. DLS was used to follow the variations of primary UPE and UPE microgel particle sizes, and SLS was used to follow the variations of UPE molecular weight, second virial coefficient (A₂), anisosymmetry (ρ_v), and differential index refraction (dn/dC) with degree of UPE conversion and PVAc concentration. The experimental data showed that, at a fixed degree of UPE/styrene conversion, increasing PVAc concentration in the UPE/styrene system caused decreases in dn/dC, A₂, ρ_v, and particle sizes of UPE microgels. These results suggest that mixing PVAc into UPE/styrene resins causes an increase in the compactness of UPE coils and favors intramolecular UPE/styrene cyclization in the early stage of curing. Thus A₂, ρ_v, and particle sizes of microgels decreased with increasing PVAc concentration. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1439–1449, 2001     

Polymer microgels prepared by emulsifier‐free emulsion polymerization of unsaturated polyesters and styrene

In the present work polymer microgels were prepared by emulsifier‐free emulsion copolymerization of unsaturated polyesters (UPs) with end carboxyl groups and styrene (St). The nucleation mechanism of UP‐St emulsifier‐free emulsion polymerization was proposed. The effects of the ratio of the monomers to water, pH, and the ratio of UP to St on the stability of polymerization and the yield of microgels were studied. It was found that the polymer microgels can be used to markedly improve the impact strength of UP. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3049–3053, 2000     

The effect of nanoclay and MWNT on fire‐retardency and mechanical properties of unsaturated polyester resins

The influence of nanomaterials such as Multi‐Walled Carbon NanoTubes (MWNT) and organoclay (Cloisite 30B) on the physical and mechanical properties of thermoset matrix such as Unsaturated Polyester (UP) resins is investigated. Although styrene containing UP resins have a wide spread application in industry, lack of information exists regarding the behavior of MWNT/organoclay/polyester ternary nanocomposite systems. The main aim of this research was first to evaluate the effect of nanofiller on the flammability of UP resins and, second, to characterize their mechanical properties such as toughness and their tensile strength. The rheological studies showed shear thinning for samples of UP resins containing MWNT and Cloisite 30B. The cone calorimetry measurement was used to evaluate the flame‐retardency, the gas emission of the nanocomposite and whether or not this system can be designated as a nanocomposite. This was understood in the test by the peak heat release rate being lowered and shifted to shorter times. Furthermore, the tensile and impact properties of samples were evaluated. The obtained results indicated that nanofiller particles caused both increase and decrease in the impact and tensile strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Model‐free kinetics: Curing behavior of phenol formaldehyde resins by differential scanning calorimetry

Isoconversional analysis was used to treat nonisothermal DSC data and yield the dependence of activation energy on conversion during the curing process of PF resins. The shape of the dependence revealed that the curing process of PF resins displayed a change in the reaction mechanism from a kinetic to a diffusion regime. In the kinetic regime a comparative DSC experimental analysis between monomer mixtures and PF resins showed that the addition reactions between phenol and formaldehyde had been mostly completed during the synthesis of PF resins and that the main kinetic reactions contained parallel condensations in the curing process. For the diffusion regime a modified equation for the diffusion rate constant, k_D = D₀ exp(?E_D /RT + K₁α + K₂α²), is proposed. This equation is in good agreement with the experimental dependence of E_α on α in the diffusion regime, which shows the effect of both temperature and conversion on diffusion. A prediction of the conversion advancement with the reaction time under isothermal condition for PF resin has been made. This prediction can be useful in practical applications for evaluating isothermal behavior of thermosetting systems from nonisothermal experimental data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 433–440, 2003     

Viscosity modeling of a medium reactive unsaturated polyester resin used for liquid composite molding process

The development of new composite product for an application through liquid composite molding (LCM) process simulation requires submodels describing the raw material characteristics. The viscosity during resin cure is the major submodel required for the effective simulation of mold-filling phase of LCM process. The viscosity of the resin system during mold filling changes as the cure reaction progresses. Applied process temperature also affects the viscosity of the resin system. Hence, a submodel describing the resin viscosity as a function of extent of cure and process temperature is required for the LCM process simulation. In this study, a correlation for viscosity during curing of medium reactive unsaturated polyester resin, which is mostly used for the LCM process, has been proposed as a function of temperature and degree of cure. The viscosity and the degree of cure of reacting resin system at different temperatures were measured by performing isothermal rheological and isothermal differential scanning calorimetry experiments, respectively. A nonlinear-regression analysis of viscosity and degree of cure data were performed to quantify the dependence of viscosity on temperature and extent of cure reaction. Comparisons of model solutions with our experimental data showed that the proposed empirical model is capable of capturing resin viscosity as a function of extent of cure and temperature qualitatively as well as quantitatively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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

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

New aspects of unsaturated polyester resin synthesis. Part 2. Reactant sequence distribution and its effect on cure kinetics

The distribution of unsaturations in the prepolymer of a typical unsaturated polyester (UP) resin (maleic anhydride, phthalic anhydride and 1,2‐propylene glycol) has been shown to influence the kinetics of the cure process with styrene monomer. Segments containing double bonds in close proximity appear to lower the reactivity of the resin due to steric hindrance, as indicated by the fact that the rate of cure and the final degree of cure, measured by differential scanning calorimetry (DSC), increase as the average sequence length (SL) of maleic units decreases. This implies that the reactivity of UP resins may be improved by synthesis of prepolymers with certain reactant sequence‐length distributions. The copolymer formed by the melt condensation process of maleic anhydride, phthalic anhydride and 1,2‐propylene glycol in the absence of a transesterification catalyst has a non‐random structure with a tendency towards blockiness. This was established using ¹H NMR analysis in tandem with deterministic and Monte Carlo modelling techniques. Copyright © 2003 Society of Chemical Industry     

Hemp‐fiber‐reinforced unsaturated polyester composites: Optimization of processing and improvement of interfacial adhesion

The processing variables for making hemp‐fiber‐reinforced unsaturated polyester (UPE) composites were optimized through orthogonal experiments. It was found that the usage of initiator, methyl ethyl ketone peroxide, had the most significant effect on the tensile strength of the composites. The treatment of hemp fibers with a combination of 1,6‐diisocyanatohexane (DIH) and 2‐hydroxyethyl acrylate (HEA) significantly increased tensile strength, flexural modulus of rupture, and flexural modulus of elasticity, and water resistance of the resulting hemp‐UPE composites. FTIR spectra revealed that DIH and HEA were covalently bonded to hemp fibers. Scanning electron microscopy graphs of the fractured hemp‐UPE composites demonstrated that treatment of hemp fibers with a combination of DIH and HEA greatly improved the interfacial adhesion between hemp fibers and UPE. The mechanism of improving the interfacial adhesion is proposed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis,characterization, and curing of {2,6–bis‐[2‐(bis‐oxiranylmethyl‐amino)‐methylbenzyl]‐phenyl}‐bis‐oxiranylmethylamine (BPBOMA)

The curing behavior of epoxy resin prepared by reacting epichlorohydrin with amine functional aniline acetaldehyde condensate (AFAAC) was investigated using AFAAC as a curing agent. The epoxy resin, {2,6‐bis‐[2‐(bis‐oxiranylmethyl‐amino)‐methylbenzyl]‐phenyl}‐bis‐oxiranylmethylamine (BPBOMA), was characterized by FTIR and ¹H‐NMR spectroscopy, viscosity measurement, and determination of epoxy content. Analysis of the curing reaction was followed by differential scanning calorimetry (DSC) analysis. To investigate the curing kinetic with AFAAC, dynamic DSC scans were made at heating rates of 5, 10, 15, and 20°C/min. The activation energy and frequency factor of the AFAAC formulation were evaluated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3168–3174, 2006     

Curing kinetics of a “green” thiol‐containing resin: Oligo(ethylene‐2‐mercaptosuccinate)

This work focuses on examining the curing process of neat oligo(ethylene‐2‐mercaptosuccinate) using differential scanning calorimetry (DSC), rheology, and Fourier transform infrared (FTIR) spectroscopy. The thiol‐containing resin offers much promise as a bioabsorbable polymer in medical field and as a reusable thermoset in sustainable applications. Although curing between thiol groups has been investigated in solutions, studies of neat materials without solvent are rare. Here, the evolution of glass transition temperature (T_g), complex shear modulus (G*), gelation, and chemical structure are monitored as a function of isothermal curing time and temperature. Both T_g and G* increase with curing, indicating the formation of polymer networks. The conversion of the cure is determined from the DiBenedetto equation and is found to follow a second‐order plus second‐order autocatalytic reaction model. Importantly, the intensity of the S–H bond absorption decreases with the extent of curing, which confirms the curing mechanism, i.e., disulfide formation between the thiol groups. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43205.     

Resin‐transfer molding of natural fiber–reinforced plastic. I. Kinetic study of an unsaturated polyester resin containing an inhibitor and various promoters

In this study an autocatalytic model was used to describe the cure of a polyester system containing various promoters and an inhibitor. The effect of the initiator concentration was investigated. Isothermal DSC measurements were used to determine the kinetic parameters for the curing reaction. The rate of curing increased with increasing initiator concentration. The parameters were found to be temperature dependent. The nonlinear regression analysis showed that by fixing one parameter at a constant value the temperature dependency of the other parameters was described by simple relationships. The model was then compared to the experimental data. The reaction rate could be predicted fairly well in a wide range of temperatures. These results will be used to model the cure of this resin in a resin transfer‐molding (RTM) process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2553–2561, 2003     

Structural characterization of alpha methyl styrene‐butyl acrylate‐grafted polyetheretherketone films

Radiation‐induced graft copolymerization of alpha methyl styrene (AMS)‐butyl acrylate (BA) mixture onto poly(etheretherketone) (PEEK) was carried out to develop films of varying copolymer compositions. The characterization of films was carried out with fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The presence of AMS and BA units within the film matrix was confirmed by FTIR. The intensity of the characteristic peaks for AMS and BA increased with the increasing grafted component in the films. The crystallinity of the films as observed from DSC and XRD decreased with the increasing graft levels. On the other hand, the melting temperature of the base polymer was almost unaffected by irradiation and the grafting process. The glass transition temperature (T_g) of the grafted film increased as compared to the virgin PEEK. Ungrafted film showed a stable thermogram up to ～500°C. However, the grafting introduced a new decomposition range in the copolymer, due to the presence of the AMS/BA. AFM images showed the formation of domains on the grafted PEEK film surface. The SEM also showed domain formation of the grafted component within the PEEK matrix. However, the fracture analysis did not show any prominent phase separation. Mechanical characterization of films in terms of tensile strength, elongation, and modulus was also carried out. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013