Unsaturated polyester resin: kinetics of the cross-linking reaction by pulsed NMR

Summary Pulsed NMR at 20 MHz has been used to monitor the time course of the intermediate-final stage of the radical crosslinking reaction (cure of unsaturated polyester-styrene resins.) The measurement of Spin lattice relaxation time T₁ allowed us to follow the hardening process having as a parameter the loss of general mobility of the system at the molecular level.The degree of cure as a function of time, the kinetic constant as well as the activation energy for the crosslinking reaction in isothermal conditions has been evaluated using the semiempirical kinetic equation proposed by Kamal and coworkers. The activation energy was estimated to be 13.6 Kcal per mole of double bonds in the components.     

Unsaturated polyester resins for thermoset applications using renewable isosorbide as a component for property improvement

Unsaturated polyester (UPE) resins are used in a variety of thermosetting applications due to the reduced cost when compared to epoxy resins; however, UPE resins also have reduced thermomechanical performance. Investigating avenues to improve the performance of UPEs has led to the use of bio‐based starting materials as structural components of the synthesized prepolymers as a result of their advantageous structural features. Isosorbide, a compound derived from renewable feedstocks, has been utilized to provide additional stiffness from the diol component for novel unsaturated polyesters resins. These resins have been shown to possess T_g's (32?72°C) and storage moduli (540?2200 MPa) that are in the desired range for composite materials with viscosities (1.2?25 Pa s) amenable to a variety of liquid molding techniques. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42315.     

Solid-state NMR characterization of unsaturated polyester thermoset blends containing PEO-PPO-PEO block copolymers

First, the NMR method proposed in our previous work was improved to provide more accurate measurement of interphase thickness in multiphase polymers. Then the improved method, in combination with other techniques, was applied to elucidate the phase behavior, miscibility, heterogeneous dynamics and microdomain structure in thermoset blends of unsaturated polyester resin (UPR) and amphiphilic poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer. The experimental results were compared with those of epoxy resin (ER)/PEO-PPO-PEO blends to systematically elucidate the influence of binary polymer-polymer interaction on the phase behavior, domain size and especially the interphase thickness in thermoset blends of UPR and ER, respectively, with the same PEO-PPO-PEO triblock copolymer. It was found that UPR/PEO-PPO-PEO exhibits strong phase separation with considerably small interphase, and only a small fraction of PEO is mixed with UPR. Whereas ER/PEO-PPO-PEO exhibits weak phase separation with thick interphase, and a large amount of PEO is intimately mixed with ER. It was suggested that the thermodynamic interaction between the block copolymer and cross-linked thermoset resin is one of the key factors in controlling the phase behavior, domain size and interphase thickness in these blends. These NMR results are qualitatively in good agreement with the previous theoretical prediction of interphase properties between two immiscible polymers. Our NMR works on different thermoset blend systems with weak and strong microphase separations clearly demonstrate that the improved NMR method is a general and useful method for measuring the interphase thickness and elucidating the phase behavior and subtle microdomain structure in multiphase polymers with detectable heterogeneous dynamics.     

聚酯预缩聚反应动力学研究

从工程应用出发简化反应 ,建立主要可测变量的动力学关系式 ,通过实验和数据处理求出了模型参数。如特性粘度变化的模型参数 ,计算值与实验值对比 ,平均相对误差为 3 6 %。在 2 80℃时 ,各压力下特性粘度和端羧基值的计算值与实验值吻合较好 ,有了这些参数 ,根据反应器的类型和操作条件进行模拟计算就比较容易     

An essential work of fracture study of the toughness of thermoset polyester coatings

The fracture toughness of a range of thermoset polyester paints with different cross-link densities has been studied, using the essential work of fracture (EWF) method. The glass transition temperature, T_g, of each of the materials was measured using differential scanning calorimetry, and found to lie between 8 and 46 °C. EWF tests were performed on the paint films at a range of temperatures around the measured glass transition temperature of each material. The essential work of fracture, w_e, at T_g was found to decrease with increasing cross-link density from around 20 kJ/m² at a cross-link density of 0.4 × 10⁻³ mol/cm³ to around 5 kJ/m² for cross-link densities of approximately 1 × 10⁻³ mol/cm³ or higher. A maximum in the essential work of fracture was observed at around T_g when w_e was plotted versus temperature, which could be attributed to the effect of an α-relaxation at a molecular level. The polyesters were found to be visco-elastic, and the applicability of the EWF test to the study of these visco-elastic thermoset materials is discussed.     

Synthesis of polylactide‐based thermoset resin and its curing kinetics

A new class of biobased thermoset resins, methacrylated four‐armed star‐shaped polylactides (M4sPLAs), was prepared. The effect of star architecture, e.g. varying arm length, on the properties of the cured products was examined. Based on differential scanning calorimetry, the non‐isothermal and isothermal curing behaviors of these M4sPLAs were investigated. Various curing kinetic parameters were obtained and elucidated using autocatalytic reaction models. Experimental results indicate that the oligomers can be crosslinked into a rigid network within a curing time varying from several minutes to more than an hour upon thermal initiation. The curing processes of M4sPLAs with varying arm length are different and complex, as indicated by the change of various kinetic parameters, reaction orders and evolutions of activation energy under the test reaction conditions. High crosslinking density is especially effective for improving the thermal stability of polylactide, but also leads to slower degradation rate and deterioration of its impact properties. Copyright © 2012 Society of Chemical Industry     

不饱和聚酯封端反应

介绍了不饱和聚酯封端反应的原理、配方及工艺操作。其中包括丁醇、环己醇、双环戊二烯等一元醇,松香酸、酸酐等一元酸的封端反应。通过封端反应可改进不饱和聚酯的耐腐蚀性、气干性、电绝缘性和与苯乙烯的混溶性等性能。     

Curing reaction of saturated aliphatic polyester modified unsaturated polyester resins

Two series of unsaturated polyesters (UPE from isophthalic acid, fumaric acid, and propylene glycol) were prepared. In series-A resins, UPEs wee thickened with isocyanate-terminated saturated aliphatic polyestes, i.e., an isocyanate-terminated polycaprolactone diol (PE-di-OL), through reaction of the isocyanate group with the hydroxyl group of the UPE. In series-B resins, the UPEs were mixed with saturated aliphatic polyesters i.e., PE-di-OL. The curing reaction of these two series of UPEs with styrene was studied by using differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The DSC data show that for a fixed PE-di-OL molecular weight, the curing reaction rate of series-A UPE is faster than that of series-B UPE. The variation of microgel size during curing ws studied by GPC. These results revealed that microgel formation has a great effect on the kinetics of cure for the unsaturated polyester-styrene system. The curing of these two series of UPEs is found to strongly depend on the compatibility of the components in the curing system.     

Photopolymerization kinetics of hyperbranched acrylated aromatic polyester

The influences of the irradiation temperature, comonomer content, sample thickness, and photoinitiator concentration on the polymerization kinetics of hyperbranched acrylated aromatic polyester (HAAPE) were investigated with photo‐differential scanning calorimetry and IR measurements. The maximum photopolymerization rate increased with the temperature rising up to 110°C but decreased beyond 110°C. An activation energy of 16 kJ mol^?1 for the photopolymerization was obtained below 110°C from an Arrhenius plot, but it was negative beyond 120°C. A remarkable synergistic effect between HAAPE and the comonomer trimethylolpropane triacrylate with a molar fraction of around 0.4 was observed from a photopolymerization kinetic study of the resins. The final unsaturation conversion in an ultraviolet‐cured film decreased with the sample thickness, and this became more remarkable as the photoinitiator concentration increased. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1500–1504, 2003     

Adsorption kinetics and isotherms of a pesticide on polyester fibers by carrier finishing

The effective management and control of mosquitoes in human living environments are crucial to minimize vector‐borne diseases in homes. Pesticides, such as pyrethroids, are considered powerful tools in the control of mosquitoes and are intended to be incorporated into textiles. The adsorptive behavior of the pesticide ZX‐1 [the main component is 1,1,1‐trichloro‐2,2‐bis(p‐chlorophenyl) ethane] in aqueous solution on polyesters fibers at different treatment times, temperatures, and concentrations are discussed in this article. The second‐order model was found to be the most suitable for describing the kinetic diffusion process, and the intraparticle diffusion was the rate‐controlling process. The Langmuir, Freundlich, and Dubinin–Radushkevich adsorption models were applied to these approaches. The results show that the Langmuir model appeared to fit the adsorption of ZX‐1 on the polyester fibers better than other adsorption models. In addition, thermodynamic parameters, such as the free energy of adsorption (ΔG⁰), enthalpy (ΔH⁰), and entropy, were calculated. Positive values of ΔH⁰ and ΔG⁰ indicated the endothermic and nonspontaneous nature of ZX‐1 adsorption on the polyester fibers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of plasma treatment on the release kinetics of a chemotherapy drug from biodegradable polyester films and polyester urethane films

Investigation was made into the effect of plasma treatment on the release kinetics of the drug Temozolomide (TMZ) from thin, biodegradable polyester films, comprising polylactic acid (PLA) and polyester urethane. The authors utilized two systems to achieve this, the first being diffuse coplanar surface barrier discharge, applying air as the gaseous medium, while the other involved capacitively coupled radio frequency discharge plasma under an argon atmosphere with hexamethyldisiloxane. Results showed that both forms of plasma treatment positively reduced the undesirable burst effect and benefited the release rate of TMZ. The hydrolytic degradability of the materials was slightly enhanced following hydrophilization, whereas the same diminished after hydrophobization had taken place. This was especially true for PLA due to modification of its wettability.     

Differential scanning calorimetry analysis of thermoset cure kinetics: Phenolic resole resin

The Differential Scanning Calorimetry (DSC) trace for a commercial phenolic resole resin shows two distinct peaks. Assuming that these represent two independent cure reactions results in a kinetic model of the form: with κ_i = κ_io exp(-B_i/T). The Arrhenius parameters were estimated from a plot of ln(β/T) versus 1/T_p. The parameters, p, n₁, and n₂ were obtained by writing the DSC response predicted by the equation above in terms of a function which contains temperature as the only variable. with $ \theta _i = \left({1/\beta} \right)\int_{T_0}^T {\kappa _i dT \le r_i} $ dT ? r_i and r_i = 1/(1-n_i). Fitting this equation to the DSC response measured at a scan rate of 4°C/min obtains p ≈ 0.66; n₁ ≈ 0.55; n₂ ≈ 2.2; B₁ ≈ 8285; B₂ ≈ 7480; κ₁ ≈ 1. 12 × 10⁸ s^?1; κ₂ ≈ 0.99 × 10⁶ S^?1.     

Modeling the curing kinetics of two thermoset adhesives under varying temperature conditions

This paper presents detailed curing kinetics models for two thermoset adhesives. The cure kinetics were characterized using differential scanning calorimetry in both anisothermal and isothermal modes. The Sestak–Berggren autocatalytic model was applied to describe the anisothermal cure kinetics of the two adhesives with the Malek and undetermined coefficients methods determining their kinetic parameters. The Kamal autocatalytic model was adopted for the isothermal curing processes with the Kenny analytical-graphical method determining the kinetic parameters. A modified Kamal model was developed by introducing a concept of the maximum degree of cure (DOC) and temperature-depended kinetic parameters to describe the isothermal cure kinetics of the adhesive with a typical exothermic peak, and an extended Kamal model was further proposed by adding an initial-phase-control term to the modified Kamal model to describe the isothermal cure kinetics of the adhesive with two exothermic peaks. The results showed that the presented curing kinetics models with the determined parameters can precisely predict the evolutions of the DOC of the two thermoset adhesives in both anisothermal and isothermal modes.     

Experimental characterization of a curing thermoset epoxy‐anhydride system—Isothermal and nonisothermal cure kinetics

This work describes in detail the kinetic model for the cure of an epoxy‐anhydride thermoset matrix resin system. The cure kinetics in both nonisothermal and isothermal modes has been characterized using differential scanning calorimetry. The Sestak–Berggren two‐parameter autocatalytic model was used to describe the nonisothermal cure behavior of the resin satisfactorily. The isothermal cure data was fitted with Kamal's four‐parameter autocatalytic model, coupled with a diffusion factor. These characterization data will form material property inputs for a multiscale modeling framework for the estimation of cure‐induced residual stresses in thick thermoset matrix composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of crosslinker reaction rate on film properties for thermoset coatings

With thermoset coatings that employ room temperature crosslinkers, there is often a competition between film formation and crosslinking. In order to meet the early use/handling requirements for the coated substrate, formulators sometimes need to use crosslinkers with very fast room temperature reaction rates. However, when the coatings are based on aqueous latex resins, sufficient time must be allowed for latex particle coalescence to occur prior to crosslinking, or the resulting films will be partially or completely precross-linked, which is detrimental to many coatings properties. In this paper the effect of the crosslinker reaction rate on various film properties of coatings based on acrylic and acrylic/styrene latex resins will be investigated using several model carbodiimide-functional crosslinkers which have different reaction rates. Presented at the 76th Annual Meeting of the Fedeation of Societies for Coatings Technology on October 14–16, 1998, in New Orleans, LA. 727 Norristown Rd., Spring House, PA 19477, E-mail: RSCWTB@rohmhaas.com.     

聚酯反应催化剂的研究

阐述了锑系、锗系、钛系催化剂的特点和在聚酯生产中的应用情况,介绍了聚酯催化剂的现状,并指出聚酯催化剂的发展方向。     

Cure kinetics of T700/BMI prepreg used for advanced thermoset composite

A new isothermally based, cure kinetic model for the prepreg was presented using an industrially supplied prepreg rather than pure resin. The matrix resin was bismaleimide (BMI) resins, and the reinforcement was carbon fiber T700–12S. The BMI prepreg was measured from 170 to 220°C by isothermal DSC. The isothermal cure reaction heat increases with the increment of cure temperature. The DSC data were analyzed by the proposed nth‐order reaction model. An increase in reaction rate was observed at higher temperature in both neat and prepreg. After reaching the peak value, the reaction rate dropped off faster in prepreg, resulting in a lower average value of the ultimate heat of reaction. It was suggested the presence of carbon fiber had an effect on the cure kinetics as a heat sink. The carbon fibers imposed restrictions on the molecular mobility of the reactive species and did not change the cure mechanism. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2238–2241, 2005     

The steady-state kinetics of a catalytic reaction sequence

With the growth in the use of DFT for predicting elementary catalytic reaction step kinetics, it is desirable to develop approaches that provide the overall reaction (OR) rate in terms of these. Deriving an explicit rate expression for a sequence with three or more steps by solving the quasi-steady-state (QSS) equations, however, is tedious, or infeasible, and the resulting expressions are often unwieldy and difficult to interpret. As a result, the microkinetics approach is favored, providing, however, only numerical results.Here, we provide an alternate approach to obtain the QSS rate expression for a reaction sequence in analogy to an electrical circuit, i.e., OR rate = driving force/overall resistance, where the overall resistance may be obtained in terms of the individual step resistance following the electrical analogy. The individual step resistances, in turn, can be derived readily based on the traditional Langmuir-Hinshelwood-Hougen-Watson (LHHW) approach, by assuming each step in turn to be rate-limiting, combined with the notion of “intermediate reactions” for the formation of the intermediate species. This provides exact expressions for mechanisms with linear (first-order in intermediates) step kinetics in linear sequences, and approximate but accurate expressions in others. Further, it allows insightful conclusions to be drawn about one or more rate-limiting steps in a sequence, and the resulting simplifications. The approach is illustrated with the help of catalytic N₂O decomposition (linear kinetics), and the hydrogenation of isobutene (nonlinear kinetics).     

Phase‐separation mechanism and corresponding final morphologies of thermoset blends based on unsaturated polyester and low‐molar‐weight saturated polyester

The final morphology of cured blends based on unsaturated polyester, styrene, and low‐molar‐weight saturated polyester as a low profile additive (LPA) was investigated with atomic force microscopy and scanning electron microscopy. The observed structure was compared to those obtained with widely used poly(vinyl acetate) (PVAc). On the surface and in the bulk, a network of particles, ranging in size from 50 to 60 nm, was observed with saturated polyester as an LPA. The influence of the molar weight and LPA content was investigated. To determine the mechanism of formation of such a morphology, in situ experiments were carried out to elucidate the phase‐separation mechanism. Small‐angle laser light scattering and small‐angle neutron scattering experiments were performed on ternary blends containing PVAc and saturated polyester, respectively. The first stage of spinodal decomposition was observed in both cases. Within our experimental conditions, gelation froze further evolution and led to a two‐phase cocontinuous structure that imposed the final morphology characteristics. In particular, the period and amplitude of the concentration fluctuations generated during the phase separation played essential roles. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1459–1472, 2005     

不饱和聚酯树脂固化动力学研究进展

介绍了不饱和聚酯树脂(UPR)固化反应动力学的n级反应模型和自催化模型,指前因子(A)和表观活化能(E)的求解方法:Kissinger法,Ozawa法和Friedman法以及由Crane方程或形状指数Si求解反应级数(n)的方法,综述了目前国内外DSC法研究UPR固化动力学的进展。