Synthesis of novel polymeric HALS stabilizers and chain transfer effect of hindered amine norbornene derivatives on ring-opening metathesis polymerization

Cyclooctadiene (COD) was polymerized via ring-opening metathesis polymerization (ROMP) in the presence of 5-norbornene-exo, endo-2-carboxylic acid 2,2,6,6-tetramethyl-4-piperidinyl ester (PN) or 5-norbornene-2-exo-3-endo-dicarboxylic acid bis(2,2,6,6-tetramethyl-4-piperidinyl) ester (2,3-PN) to prepare a new kind of polymeric hindered amine (HALS) stabilizers. Unexpectedly, hindered amine norbornene derivatives PN and 2,3-PN did not act as comonomer but acted as chain transfer agent (CTA). The resulting polymers were characterized by gel permeation chromatography (GPC) and ¹H-NMR. Investigation of polymerization behavior showed that hindered amine groups were introduced into polymer chain by virtue of chain degradation resulted from chain transfer. The molecular weight (M _n) and HALS content of the resulting polymeric HALS stabilizer could be regulated by varying molar ratio of initial monomer to catalyst.     

Interactions between basecoats and clearcoats in car refinish systems

The introduction of VOC compliant waterborne basecoats and solventborne basecoats on one hand and the introduction of VOC compliant clearcoats on the other hand forces to look to the interactions between the two systems. As well known from studies in the automotive OEM area small molecules like HALS and UV-absorbers additives diffuse from the clearcoat into the basecoat. This influences the durability performance of the system.The main question addressed in this paper is the interaction of the binder system of the basecoat and clearcoat. In general crosslinkers (e.g. poly-urethane coatings) are rather low molecular weight materials which may diffuse between layers as well. Also the lower molecular weight functional resins of the binder may move throughout the system.The interactions of basecoat/clearcoat combinations were investigated by means of chemical and physical techniques. The effect of a medium solid clearcoat, a VOC compliant p-urethane clearcoat and UV-clearcoat on interpenetration, physical and paint properties were studied.Also some attention is paid to the diffusion of HALS and UV-absorbers from the clearcoat into the basecoat.     

Effect of penta- and tetramethyl HALS on the radiation resistance of polypropylene

2,2,6,6-Tetramethyl-4-piperidinyl methacrylate (TMPM), a new pentamethyl HALS 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate (PMPM), their homopolymers (PTMPM and PPMPM), and their copolymers, [i.e., TMPM or PMPM copolymerized with monomers methyl methacrylate (MMA), methacrylic acid (MAA), acrylic acid (AA), and styrene (St) separately] were synthesized. PMPM shows an extremely excellent stabilizing effectiveness on improving the radiation resistance of polypropylene (PP) in comparison with other low molecular weight (LMW) HALS or polymeric HALS. Polymeric HALS shows a much higher thermal stability and better extraction resistance than that of LMW HALS. It is found that the Eb values of the PP-added pentamethyl HALS series are higher than those of PP with the corresponding tetramethyl HALS series at a given irradiation dose. A conclusion can be drawn that the pentamethyl HALS series has a higher stabilizing effectiveness than that of the tetramethyl HALS series. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2649–2656, 1998     

催化合成受阻胺光稳定剂UV-292

以石油醚为溶剂,颗粒状活性炭负载四丁基钛酸酯为催化剂,-定比例的癸二酸二甲酯和1．2．2．6,6-五甲基-4-羟基哌啶在110～120qC下缩合反应2～5h。然后水洗、活性炭脱色、脱溶齐4等后处理操作。-步合成了产物受阻胺光稳定剂（HALS）UV-292,其中1-甲基-8-（1,2,2,6．6-五甲基-4-哌啶）癸二酸酯（单酯）质量分数为15％～30％和双（1,2,2,6,6-五甲基-4-哌啶基1癸二酸酯（双酯1质量分数为65％～80％）,收率超过97％．纯度不低于96％。得到了优化的工艺条件：反应时间为2．5h,在癸二酸二甲酯为0．1IYIOl的情况下,n（癸二酸二甲酯）：n（1。2,2,6,6-五甲基-4-羟基哌啶）为0．1：0．165,催化剂用量为1．0g、溶剂的用量为40g。催化剂不经处理可循环使用多次,     

Synthesis and characterization of silicone-modified polyester as a clearcoat for automotive pre-coated metals

Four types of silicone-modified polyester resins were synthesized for cleanable characteristics with silicone intermediate, which has a long chain, to extend the polymer chains of the resins. These resins were formulated to make polyester/melamine heat-cured coatings to control the formability. The characteristics, viscoelastic behavior and flexibility of the resins were measured by DMA and tensile test. The contact angle measurement can be measured by the water repellence of the coating surface, which is a standard method to evaluate cleanable characteristics. The surface free energy was calculated by the contact angle measurement, and the surface analysis of each cured coating was evaluated using an XPS. Silicone-modified polyester coatings were coated on the cold rolled steel sheets to verify their formability, using a deep drawing test. Results showed that the storage modulus decreased, and the glass transition temperature shifted to a lower temperature with increasing contents of silicone intermediate. So, silicone intermediate provides lower stiffness and higher softness to polyester coating. To analyze the formability, we calculated F_U (the forming coefficient based on strain energy) and F_? (the forming coefficient based on strain). When F_U and F_? are both larger than 1, the polyester coatings have good formability. CSiPE-3 and CSiPE-5 had good formability. Also, CSiPE-5, which had the highest amount of silicone intermediate, had 93.5° of water contact angle, and had 26.5 mN/m of surface free energy and had 5.5 N/25 mm of the peel strength. So, it is implied that silicone intermediate can give a low surface energy and peel strength to polyester coatings. From those tests, the polyester/melamine coating of CSiPE-5 that had 0.5 mol of silicone intermediate had good formability and low peel strength, which are semi-removable characteristics. So, it would be an appropriate coating as a clearcoat for automotive pre-coated metals.     

Long-term weathering behavior of UV-curable clearcoats: Depth profiling of photooxidation,UVA, and HALS distributions

The long-term weathering performance of two UV-curable clearcoat systems was studied using in-plane microtomy in combination with infrared spectroscopy, UV spectroscopy, and ESR spectroscopy. Oxygen transport characteristics were also studied using the half-time method. The photooxidation versus depth profile was highly dependant on the presence of hindered amine light stabilizers (HALS) for both coating systems. Ultraviolet light absorbers (UVA) had little effect on the photooxidation profile. A photooxidation gradient was formed in both clearcoats due to a reduction in oxygen solubility when compared to standard thermoset clearcoats. This gradient was only seen in formulations not containing HALS. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.     

Synthesis and characterization of hindered amine light stabilizers based on end functionalization of polypropylene

A polymeric hindered amine light stabilizer (HALS), where HALS moiety was attached at the terminal end of the polypropylene chain via end‐functionalized vinylidine PP through simple organic reactions, was synthesized. It comprises the synthesis of vinylidine‐terminated polypropylene by using Cp₂ZrCl₂/MAO as catalyst system and epoxidation of vinylidene polypropylene. The final product was synthesized by carrying out the reaction between epoxy end functionalized polypropylene and 4‐amino‐2,2,6,6‐tetrametyl piperidine. The final product was characterized by using ¹H NMR, ¹³C NMR, and FT‐IR spectra. Functionality was calculated by using vapor phase osmometry and ¹H NMR. The solubility and diffusion coefficient of the product were calculated and also its stabilization performance was checked. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1596–1602, 2007     

Water absorption of water-based anticorrosive coatings and its effect on mechanical property and adhesive performance

We focused on the water absorption of newly developed water-based anticorrosive coatings, which contain low volatile organic compounds. We investigated (1) the water absorption behavior of the coatings, (2) the effect of water absorption on the mechanical property of the coatings, and (3) the relationship between the water-absorbing properties and adhesive performance under accelerated aging conditions. It was found that the water absorption of the coatings indicated Fickian diffusion, and the saturated water content M _∞ and diffusion coefficient D of the coatings were quantitatively determined. The storage modulus E′ of the coatings decreased due to water absorption. However, in the coating that exhibited higher crosslink density, the effect of water absorption on the decrease in E′ was relatively small in spite of its higher M _∞ . The lower M _∞ and higher D coating resulted in better adhesive performance than the higher M _∞ and lower D coating. Thus, M _∞ value affected adhesive performance under accelerated aging conditions much more than D value.     

Ultraviolet light absorber mobility in crosslinked coatings: Experiments and modeling

The diffusion of an ultraviolet absorber (UVA) across a concentration step change in an acrylic melamine clearcoat was measured via micro-ultraviolet spectroscopy. Concentration profiles were obtained after diffusion times of 4–200 h at steady temperatures of 70, 80, and 90 °C. The glass transition temperature of the coating was measured via dynamic mechanical analysis for each time–temperature pair, and T_g was observed to increase with thermal aging, with a faster rate of increase at higher aging temperatures. The change in T_g was modeled using a first-order dependence on the deviation from a long-time T_g asymptote. The diffusion coefficient was then represented by a free volume expression, and the combination provided an accurate model of the measured concentration profiles. The time-dependent increases in glass transition temperature helped to explain why UVA diffusion does not alleviate concentration gradients created by photooxidation under natural weathering conditions.     

On the combined use of UVA, HALS, photooxidation, and fracture energy measurements to anticipate the long-term weathering performance of clearcoat/basecoat automotive paint systems

Transmission UV spectroscopy measurements of clearcoat ul traviol et light absorber (UVA) disposition, electronspin resonance (ESR) spectroscopy measurements of clearcoat and basecoat Active hindered amine light stabilizer (HALS) disposition, and transmission Fourier transform infrared (FTIR) measurements of photooxidation have been carried out on 5 μm thickslioes of clearcoat/basecoat/primer/e-coatpaint systems on steel panels as a function of outdoor exposure. These analysis results are combined with clearcoat fracture energy measurements to assess the possibility that a clearcoat/basecoat paint system will resistcatastrophic cracking/peeling failure at long times. Taken together, all results indicate that these nontraditional paint weathering performance metrics should be added to the existing repertoire of paint weathering performancemetrics to ensure that inferior clearcoat/basecoat automotive paint systems are not introduced into service. Ford Research Laboratory, MD 3182SRL, P.O. Box 2053. Dearborn, MI 48124     

Approaches for multicopper oxidases in the design of electrochemical sensors for analytical applications

We report an effective approach for the construction of a biomimetic sensor of multicopper oxidases by immobilizing a cyclic-tetrameric copper(II) species, containing the ligand (4-imidazolyl)ethylene-2-amino-1-ethylpyridine (apyhist), in the Nafion^® membrane on a vitreous carbon electrode surface. This complex provides a tetranuclear arrangement of copper ions that allows an effective reduction of oxygen to water, in a catalytic cycle involving four electrons. The electrochemical reduction of oxygen was studied at pH 9.0 buffer solution by using cyclic voltammetry, chronoamperometry, rotating disk electrode voltammetry and scanning electrochemical microscopy techniques. The mediator shows good electrocatalytic ability for the reduction of O₂ at pH 9.0, with reduction of overpotential (350 mV) and increased current response in comparison with results obtained with a bare glassy carbon electrode. The heterogeneous rate constant (k^′ME) for the reduction of O₂ at the modified electrode was determined by using a Koutecky-Levich plot. In addition, the charge transport rate through the coating and the apparent diffusion coefficient of O₂ into the modifier film were also evaluated. The overall process was found to be governed by the charge transport through the coating, occurring at the interface or at a finite layer at the electrode/coating interface. The proposed study opens up the way for the development of bioelectronic devices based on molecular recognition and self-organization.     

Apparent diffusion coefficient of intercalated species measured with PITT: A simple formulation

Apparent values (D_ap) of chemical diffusion coefficients (D) of intercalated species are measured with the potentiostatic intermittent titration technique (PITT) due to the usual approximations of infinitely fast charge-transfer kinetics at the electroactive interface and negligible Ohmic drop effects. A simple expression is derived in this work that enables one to predict the parametric dependence of the diffusion coefficient ratio (D_ap/D) on the ‘key-factor’ (Λ) for insertion/extraction processes. The parameter Λ can be either experimentally determined from electrochemical impedance spectra, or predicted from theoretical expressions of insertion/extraction reaction rate. The measurement error of diffusion coefficient is predicted theoretically due to slow charge-transfer kinetics at the interface, Ohmic drop effects and bulk interactions in the host material. The influence of electrode or particle geometry is also analyzed. In most cases, but not in all cases, a minimum value of apparent diffusion coefficient is observed near the standard potential of insertion material. The measurement error of D becomes very important in the presence of attractive interactions in host materials, together with slow charge-transfer kinetics at the electroactive interface. Finally, the superposition between spurious behavior of the chemical diffusion coefficient and its dependence on the guest ions interactions is investigated within the framework of Frumkin insertion isotherm.     

Test of ‘scaling laws’ describing the concentration dependence of osmotic pressure,diffusion and sedimentation in semidilute macromolecular solutions

Data of osmotic pressure, diffusion and sedimentation in semidilute macromolecular solutions are systematized with regard to scaling laws. The observed main features are: (a) the concentration dependence of the osmotic pressure both at good and theta solvent conditions is in excellent agreement with that predicted by the scaling laws. (b) The concentration dependence of the mutual diffusion coefficient D_m could not uniquely be described by a simple scaling law. A difference in concentration dependence between D_m and the cooperative diffusion coefficient was observed for polystyrene under good solvent conditions. (c) The concentration dependence of the permeability coefficient (related to sedimentation) and the sedimentation coefficient were for most of the systems in close agreement with that predicted by the scaling laws.     

Determination of adsorption and diffusion parameters in zeolites through a structured approach

Temporal analysis of products (TAP) is a transient pulse-response technique that allows to extract kinetic information from reacting and adsorbing systems. In a previous work (Chem Eng Sci 57(2002) 1835), a detailed-transport model for the Multitrack set-up, a TAP-like system, was developed, which allows studying systems with a low bed resistance. The use of structured beds, having both a low bed resistance and small sorbent particles, is required to determine adsorption and diffusion parameters when strong adsorption and slow diffusion occurs. A method is presented to extend the range of measurable adsorption and diffusion parameters in zeolitic sorbents in the TAP technique by a structured approach. Small zeolite crystals are coated on larger non-porous glass beads. Adsorption and diffusion parameters for n-butane, SF₆ and 3-methylpentane have been determined in MFI-type zeolites. Absolute diffusivity values in the zeolite coating are estimated by using a well-defined silicalite sample as a reference to determine the effective diffusion length in the coating.Two criteria have been derived, one for the characteristic time for transport through the bed, , and one for the ratio of the latter and the characteristic diffusion time in the zeolite crystal, 0.01<α<200t_bed/(1+t_bed), which should be satisfied both to be able to determine values of the zeolite diffusivity.     

Optimization of C/TiCx duplex diffusion barrier coatings for SiCf/Ti composites based on interfacial structure evolution exploration

Introducing a carbon single coating is a popular method used to protect SiC_f/Ti composites from severe interface reactions. However, carbon coatings lose their protective effect on SiC fibres at high temperature, even after a short period time. As such, given the strong demand for high temperature applications in aeronautics and astronautics a more coating which is more effective at high temperatures is desirable. In order to improve the high temperature interfacial stability of SiC_f/Ti composites, a C/TiC_x duplex coating system with different C contents in TiC_x was introduced to explore the protection of fibres at 1200?°C for 1?h. The results show that the C/quasi-stoichiometric TiC coating system protects the SiC fibres most effectively. Based on insights from the evolution of the interface structure, TiC_x has been identified as an interfacial reaction product from the C single coating, exhibiting a gradient in C content and grain size, which is different from a deposited TiC layer with a well-distributed composition and structure. The different coating structure gives rise to different ability to resist C diffusion at high temperatures, in which poor resistance ability appears in TiC_x interfacial reaction layer coming from C single coating due to short-circuit diffusion in C-rich fine-grained TiC layer and fast intracrystalline diffusion trigged by amounts of vacancies in sub-stoichiometric coarse-grained TiC layer. Therefore, C/quasi-stoichiometric TiC duplex coatings with a thick, coarse-grained quasi-stoichiometric TiC layer could effectively inhibit C diffusion by comparison to C single coatings, and is more effective than C/rich-carbon TiC duplex coatings due to the existence of short-circuit diffusion in the latter. As such, C/quasi-stoichiometric TiC duplex coatings appear to be an optimal diffusion barrier for SiC_f/Ti composites at high temperature.     

High-entropy thermal barrier coating of rare-earth zirconate: A case study on (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 prepared by atmospheric plasma spraying

We report a double-ceramic-layer (DCL) thermal barrier coating (TBC) with high-entropy rare-earth zirconate (HE-REZ) as the top layer and yttria stabilized zirconia (YSZ) as the inner layer sprayed on Ni-based superalloy by atmospheric plasma spraying. La₂Zr₂O₇ (LZ) was selected as a reference for the HE-REZ. Thermal cycling test results demonstrate that the HE-REZ/YSZ DCL coating exhibited obviously improved thermal stability when compared to the LZ/YSZ DCL coating. The reasons for the improvement of the thermal shock resistance are considered to be the anti-sinterability of the HE-REZ ceramics during the thermal cycling test attributed to the sluggish diffusion effect and as well as the better match in the coefficient of thermal expansion of HE-REZ coating with the YSZ inner layer. In addition, the HE-REZ coating maintains fluorite structure after thermal cycling test. This study makes one step forward in the development and application of high-entropy rare-earth zirconate ceramic thermal barrier coatings.     

Enhancement of UV-aging resistance of UV-curable polyurethane acrylate coatings via incorporation of hindered amine light stabilizers-functionalized TiO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> nanoparticles

In this study, polymeric hindered amine light stabilizers (HALS)-functionalized silica coated rutile titanium dioxide (TiO₂-SiO₂) nanoparticles were prepared by encapsulating commercially available TiO₂-SiO₂ nanoparticles with methyl methacrylate (MMA) and 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate (PMPM) copolymers via miniemulsion polymerization. The obtained functional (TiO₂-SiO₂/P(MMA-co-PMPM)) fillers have been added to polyurethane acrylate (PUA) oligomers to get UV-curable nanocomposite coatings. The functionalization of the TiO₂-SiO₂ nanoparticles with polymeric HALS has been confirmed by infrared spectra (IR), thermogravimetric (TG), and X-ray photoelectron spectroscopy (XPS) analyses. The scanning electron microscope (SEM) micrographs indicated that homogeneous dispersion of TiO₂-SiO₂/P(MMA-co-PMPM) composite nanoparticles resulted in improved transparency and mechanical properties of the UV-curable PUA coatings. Rhodamine B (Rh.B) photodegradation measurement confirmed the excellent UV-shielding performance of PUA nanocomposite coatings containing TiO₂-SiO₂/P(MMA-co-PMPM). The addition of TiO₂-SiO₂/P(MMA-co-PMPM) composite nanoparticles reduced the UV-curable PUA coatings degradation rate dramatically. The UV-aging resistance of PUA coatings was improved significantly. Over all, the combination of TiO₂-SiO₂ nanoparticles and polymeric HALS offers an attractive way to fabricate the multi-functional fillers, which can be used to improve the mechanical properties and UV-aging resistance of PUA coatings simultaneously.     

Redox and transport behaviors of Cu(I) ions in TMHA-Tf<Subscript>2</Subscript>N ionic liquid solution

The redox and transport behavior of monovalent copper species in an ammonium imide-type ionic liquid, trimethyl-n-hexylammonium bis((trifluoromethyl)sulfonyl)amide (TMHA-Tf₂N) were examined with a micro-disc electrode to clarify its applicability to, for example, electroplating. It was found that the diffusion coefficient of Cu(I) ions in TMHA-Tf₂N containing 12 mmol dm⁻³ Cu(I) ions was 1.2 × 10⁻⁶ cm² s⁻¹ and the redox potential of Cu(I)/Cu was in the potential range 0.1–0.2 V vs. I ⁻/I ₃⁻ at 50 °C. The diffusion coefficient was one order smaller than that of Cu(II) ions in aqueous solution due to the high viscosity of the ionic liquid. The diffusion coefficient of Cu(I) ion increased with rising temperature and was 1.0 × 10⁻⁵ cm² s⁻¹ at 112 °C, which was comparable to that of Cu(II) ions in aqueous CuSO₄ solutions at ambient temperature. This is accounted for by the drastic decrease in the viscosity of the ionic liquid solution with increasing temperature. The activation energy of diffusion was estimated to be 39 kJ mol⁻¹ in the ionic liquid solution.     

Combined analysis of self-diffusion, conductivity, and viscosity data on room temperature ionic liquids

The self-diffusion coefficient of anions and cations, the ionic conductivity and the viscosity of four room-temperature ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF₄), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI), 1-butylpyridinium tetrafluoroborate (BPBF₄), and 1-butylpyridinium bis(trifluoromethylsulfonyl)imide (BPTFSI) were analysed within a comprehensive ionic transport model. The experimental data, covering wide temperature ranges, were taken from the work of Noda et al. [J. Phys. Chem. B, 105, 2001]. To compare the dc conductivity with the self-diffusion coefficients, the former quantity was converted into a charge diffusivity D_σ using the Nernst-Einstein equation. In a similar way, we calculated a viscosity-related diffusivity D_η with the aid of the Stokes-Einstein equation. Taking three mobile species into account, i.e., single cations, single anions and neutral ion pairs, our model yields their individual diffusivities that obey a uniform Vogel-Tammann-Fulcher-like temperature dependence described by common values of the parameters B and T₀. Evaluating simultaneously all experimental data within this model yields the contribution of ion pairs to the self-diffusion coefficient of cations and anions separately. We further obtain the temperature-independent cation transference number and the effective hydrodynamic radius, which are important characteristics of charge and mass transport in these ionic liquids.     

Inter-tablet coating variability: Tablet residence time variability

This paper investigates inter-tablet coating variability, specifically, the variability of tablet residence times within the spray zone of a horizontal coating pan. Results from experiments, discrete element method (DEM) computer simulations, and an analytical model developed to describe the coating mass distribution are presented.The simulations indicate that the coefficient of variation of tablet residence times, and subsequently, of coating mass, decreases with time following a power law relation. The theoretical model demonstrates that the coefficient of variation of residence time for a randomly mixed tablet bed is inversely proportional to the square root of the number of coating “trials”. DEM simulations show that during each pan revolution, tablets in the spray zone remain in a quasi-segregated state from tablets located outside the spray zone for some time period termed Δt_seg. Increasing the pan's Froude number, the spray zone aspect ratio, and the tablet-tablet and tablet-pan friction coefficient all act to decrease Δt_seg, leading to more uniform residence times and less inter-tablet coating variability for a given operating time. The relationship between Δt_seg and tablet load is more complex due changes in bed dynamics. In addition to the variability studies, a model is developed that relates coating fraction, effective mass flow rate, Δt_seg, and the desired coating mass to the allowable fraction of tablets with a coating mass lying outside of a specified range of coating masses.