Kinetic modeling of the peroxide cross-linking of polymers: From a theoretical model framework to its application for a complex polymer system

Peroxides react with polymers in a variety of ways. The fundamental comprehension and prediction of pertinent kinetics of reactions is consequently indispensable. Based on the mechanisms of reactions of cross-linking process, a new theoretical kinetic model framework was developed. The kinetic model was then applied to the reactions of cross-linking process of various peroxides and a chosen complex polymer compound, namely partially hydrogenated poly(acrylonitrile-co-1,3-butadiene). Whereas the initial macromolecular backbone structure was determined utilizing attached proton test carbon nuclear magnetic resonance, the evolution of overall concentration of cross-links was monitored through viscoelastic characteristics of the system. The model demonstrated good agreement with experimentally measured data and, moreover; the evolution of concentrations of various crucial species inherent to the cross-linking process were predicted. The most significant advantage of the developed kinetic model is that it may be readily applied to an assortment of polymer/peroxide systems.     

Aryl acrylate porous functional polymer supports from water‐in‐oil‐in‐water multiple emulsions

Porous functional polymer supports are a class of material of wide interest due to the possibility of immobilising reactive species. A simplified procedure was applied for the preparation of porous polymer supports using a water‐in‐oil‐in‐water multiple emulsion. The primary emulsion was a high internal phase emulsion, having a volume fraction of water phase up to 95%. Two reactive acrylates, namely 4‐nitrophenyl acrylate and 2,4,6‐trichlorophenyl acrylate, were (separately) incorporated in the oil phase in order to obtain porous reactive polymer supports. Both acrylates were crosslinked with either divinylbenzene or ethylene glycol dimethacrylate, and beads of size ca 60 µm were obtained after the polymerisation of droplets suspended into the secondary aqueous phase. In the case of 4‐nitrophenyl acrylate and divinylbenzene as a crosslinker, particles with a star shape, the core being ca 60 µm in diameter and the arms ca 180 µm in length, were obtained. The polymers were functionalised with morpholine, tris(2‐aminoethyl)amine, piperidine or piperazine yielding supports with loadings of reactive groups of between 2.6 and 6.6 mmol g^?1. The results show that multiple emulsions can be precursors for porous polymer preparation. Copyright © 2007 Society of Chemical Industry     

Kinetics and modeling of diethylene glycol bisallyl carbonate bulk polymerization

The free‐radical polymerization kinetics of diethylene glycol bisallyl carbonate in bulk were investigated with Fourier transform infrared and Fourier transform Raman techniques in a wide temperature range of 50–140°C with four different peroxide initiators. In addition, the ratios of the degradative kinetic rate constant to the propagation rate constant under different reaction conditions were obtained from molecular weight measurements under various reaction conditions. The ratio of the chemically controlled termination and propagation rate constants of the polymerization system were obtained with the initial rates of polymerization and the number‐average molecular weight data, which were between 8.22 × 10^?5 and 1.47 × 10^?3 L mol^?1 s^?1. The initiator efficiencies were evaluated with special experiments at low initiator concentrations with the theory of dead‐end polymerization. The computed conversions from the developed kinetic model were in good agreement with the conversion and molecular weight measured data. The values of the diffusion‐controlled propagation and termination rate constants, with clear and physical meaning, were the only two parameters obtained from the developed kinetic model fitting the measured conversion points. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 345–357, 2005     

A modified element‐free Galerkin method with essential boundary conditions enforced by an extended partition of unity finite element weight function

In this work we propose a method which combines the element‐free Galerkin (EFG) with an extended partition of unity finite element method (PUFEM), that is able to enforce, in some limiting sense, the essential boundary conditions as done in the finite element method (FEM). The proposed extended PUFEM is based on the moving least square approximation (MLSA) and is capable of overcoming singularity problems, in the global shape functions, resulting from the consideration of linear and higher order base functions. With the objective of avoiding the presence of singular points, the extended PUFEM considers an extension of the support of the classical PUFE weight function. Since the extended PUFEM is closely related to the EFG method there is no need for special approximation functions with complex implementation procedures, and no use of the penalty and/or multiplier method is required in order to approximately impose the essential boundary condition. Thus, a relatively simple procedure is needed to combine both methods. In order to attest the performance of the method we consider the solution of an analytical elastic problem and also some coupled elastoplastic‐damage problems. Copyright © 2003 John Wiley & Sons, Ltd.     

Flavonoids and cell membrane fluidity

The membrane fluidity characteristics of multilamellar (MLV) and extruded liposomes prepared with kaempferol (K), kaempferol-3-glucoside (KG), (−)-epigallocatechin (EGC) or (−)-epigallocatechin-3-gallate (EGCG) are presented. Kaempferol caused the highest increase in fluorescence polarisation of DPH in both liposomes (other compounds had not) indicating that K with n_K/n_Lip below 0.2 or 0.1 decreased the membrane fluidity, while at higher molar ratios the membrane fluidity increased. EPR measurements with MLV and spin probes MeFASL(10,3) and MeFASL(2,11) showed a significant decrease in fluidity in the upper part of the membrane for all flavonoids measured, and in the core of the membrane an increase in fluidity for EGCG and EGC. Computer simulation of the EPR spectra showed that the membrane of the MLV used was composed of at least three coexisting domain types with different fluidity and that the order parameter of the most ordered domains is responsible for membrane fluidity alterations.     

Modeling of dynamic mechanical properties of vulcanized fluoroelastomer

The dynamic mechanical properties of a vulcanized fluoroelastomer (FKM) were studied over a range of temperatures and shear frequencies. Dynamic mechanical analysis and differential scanning calorimetry were used for the purpose of the study. A model was developed in order to describe FKM's viscoelastic behavior at various temperatures. The model was fitted to experimental data using an algorithm, which was developed for this purpose. As a result the FKM discrete relaxation spectrum at two reference temperatures was obtained, as well as the Williams‐Landel‐Ferry (WLF) equation parameters or the activation energy equivalent. Further on, the model was applied on storage modulus and loss tangent values obtained from the experiments, during which the temperature increased linearly. It was observed that the WLF equation fits well with the results during the glass transition, while the Arrhenius‐type relationship predicted too rapid decrease of the storage modulus during the glass transition. The master curves were constructed using the previously calculated WLF parameters and the activation energy equivalent. The developed model may be readily applied for the prediction of the numerous FKM compounds' frequency–temperature behavior using the dynamic mechanical properties obtained from either isothermal or low linear heating rate program measurements. POLYM. ENG. SCI., 47:2085–2094, 2007. © 2007 Society of Plastics Engineers     

An attempt to predict pork drip loss from pH and colour measurements or near infrared spectra using artificial neural networks

The ability to predict meat drip loss by using either near infrared spectra (SPECTRA) or different meat quality (MQ) measurements, such as pH₂₄, Minolta L^∗, a^∗, b^∗, along with different chemometric approach, was investigated. Back propagation (BP) and counter propagation (CP) artificial neural networks (ANN) were used and compared to PLS (partial least squares) regression. Prediction models were created either by using MQ measurements or by using NIR spectral data as independent predictive variables. The analysis consisted of 312 samples of longissimus dorsi muscle. Data were split into training and test set using 2D Kohonen map. The error of drip loss prediction was similar for ANN (2.2–2.6%) and PLS models (2.2–2.5%) and it was higher for SPECTRA (2.5–2.6%) than for MQ (2.2–2.3%) based models. Nevertheless, the SPECTRA based models gave reasonable prediction errors and due to their simplicity of data acquisition represent an acceptable alternative to classical meat quality based models.     

The influence of the polymerization on properties of an ethylacrylate/2-ethyl hexylacrylate pressure-sensitive adhesive suspension

In this paper, the batch suspension copolymerization process for production of microsphere acrylic pressure-sensitive adhesives (PSA) is presented. The effects of different process and chemical parameters on adhesion properties are discussed. The reaction was monitored in-line by using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Properties of the adhesive suspension (particle size), adhesive (gel phase, molecular weight, glass transition temperature (T_g)) and adhesion properties (tack, peel strength and shear) were determined. The results have shown that reaction kinetics strongly depends on polymerization temperature and initiator concentration. On the other hand, adhesion properties depend mainly on the T_g of the polymer and on the amount of insoluble gel fraction in the adhesive.     

Influence of Topology of Highly Porous Methacrylate Polymers on their Mechanical Properties

Porous polymer monoliths are prepared using glycidyl methacrylate and methyl methacrylate as monomers, in both cases crosslinked with ethylene glycol dimethacrylate. Up to 75% porous samples are produced using either emulsion templating or bulk polymerization with porogens. In the case of emulsion templating, a cellular topology with cavities between 3.1 and 5.5 µm is observed for both monomers, while a cauliflower‐like topology is formed in the case of bulk polymerization. The influence of topology features of monoliths on the mechanical properties is studied and for both polymers a dramatic influence, on both compressive moduli and compressive strength, is found. The mechanical parameters, namely elastic modulus and compressive strength are significantly higher for emulsion templated samples.