Structure-photooxidative stability relationship of amine-crosslinked epoxies (original) (raw)
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Epoxy-amine Macromolecules 2007
Fundamental understanding of mechanisms of the epoxy-amine curing reaction is crucial for developing new polymer materials. Nearly all experimental studies, to date for elucidating its mechanisms are based on thermometric measurements and thus cannot provide the molecular level details. This study used density functional theory (DFT) methods to examine the mechanism of epoxy-amine poly addition reactions at the molecular level. Different reaction pathways involving both acyclic and cyclic transition state structures were examined for different reaction conditions, namely isolated, self-promoted by amine, catalyzed by alcohol, and in different solvents. The results indicate that the reactions catalyzed by an alcohol dominate the rate over the self-promoted reaction by other amine species and the isolated one in early stages of the conversion. The concerted pathways involving cyclic transition-state complexes are not significant due to their high activation energies. Calculated activation energies are within the experimental uncertainty. In addition, solvent, not steric and electronic effects as suggested earlier, are shown to be responsible for secondary amines to react slower than primary amines.
A perspective approach on the amine reactivity and the hydrogen bonds effect on epoxy-amine systems
European Polymer Journal
Abbreviations: 3-cyclohexanedimethanamine (1,3-BAC), 2,5-bis[(2-oxiranylmethoxy)methyl]-benzene (BOB), 2,5-bis[(2-oxiranylmethoxy)-methyl]-furan (BOF), bisphenol A (BPA), 1,3-cyclohexanediamine (1,3-CHDA), carcinogenic, mutagenic and reprotoxic (CMR), 4,4'-diaminodiphenylmethane (DDM), density functional theory (DFT), diglycidyl ether of bisphenol A (DGEBA), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), high performance liquid chromatography (HPLC), isophoronediamine (IPDA), kinetic substitution effect (KSE), m-phenylenediamine (mPDA), m-xylylenediamine (MXDA), non-isocyanate polyurethane (NIPU), nuclear magnetic resonance (NMR), polyamide (PA), poly(εcaprolactone) (PCL), poly(diglycidyl ether of bisphenol A) (poly(DGEBA)), poly(ethylene oxide) (PEO), poly(methyl methacrylate) (PMMA), polyurethane (PU) size-exclusion (SEC), tetrafurane (THF), volatile organic compound (VOC).
Polymer Degradation and Stability, 2001
A number of dialkyl and heterocyclic amine-terminated diacrylate resins were prepared by a Michael addition reaction of the appropriate secondary amine with a triacrylate diluent monomer. Photocuring rates are found to be dependent upon the extent of UV absorption of the photoinitiator used with ITX in this case exhibiting the most rapid cure. There is no consistency in cure rate with amine structure. Transient absorption spectra on conventional microsecond flash photolysis are assigned to the formation of free radical intermediates by electron transfer. Photoinduced polymerisation activities of the resins measured by real-time infrared spectroscopy appear to be closely related to the formation of such transient species. The initiator structure is the more determining factor. Their photo-oxidative stability and photoyellowing (by UV derivative absorption) are studied after UV and electron-beam curing through Fourier transform infra-red (FTIR) and second derivative UV spectroscopic methods and hydroperoxide analysis. On photo-oxidation UV cured diluent monomer undergoes oxidation at a higher rate than EB cured systems. Initial photo-oxidation of the coatings as measured by hydroperoxide analysis and hydroxyl index via FTIR analysis exhibited similar changes. Again the oxidation profiles are dependent upon the terminal amine structure with 1-methylpiperazine exhibiting the strongest oxidation. Hydroxyl index showed generally an initial rise followed by a sharp decline and then a slow increase over much longer irradiation periods. The presence of the amine functionality is found to be an effective scavenger of oxygen and hydroperoxide formation in EB cured coatings. In the UV cured coatings the hydroperoxide levels are found generally to be significantly higher than in EB systems due to the photosensitising effect of the residual photoinitiator. Diluent monomer terminated with dialkylamine groups are found to be more prone to oxidation and UV absorption increase than alkanolamines, cycloaliphatic amines and heterocyclic amines. UV cured resins exhibit a more facile transient photoyellowing than the same electron-beam cured systems, and this is associated with hydrogen-atom abstraction and oxidation of the alkylamine group by the residual photoinitiator enhancing the rate of hydroperoxidation of the amine group. #
The Effect of Amines on the UV-curing of Epoxy Resins
Iranian Polymer Journal, 2006
E poxies are generally cross-linked by the addition of a hardener, most of the time a diamine such as diamine diphenyl sulphone, oxydianiline or methylene diamine, and then thermocured. These formulations are quite often used, particularly in the aerospace industry for making structural materials, prepregs or composites. In this paper we have investigated the cross-linking reactions of a difunctional cycloaliphatic epoxide monomer 3,4-epoxycyclohexylmethyl-3', 4'-epoxycyclohexane carboxylate initiated by UV-irradiation and compared the kinetics with N,N-diglycidyl-4-glycidyloxyaniline (a nitrogen-containing monomer with a functionality of three) and 4,4'-methylenebis (N,N-diglycidylaniline) (another nitrogen-containing monomer with a functionality of four). Kinetics is followed using a differential photocalorimetry (DPC) technique. Upon UV irradiation in the presence of cationic photoinitiator, the difunctional cycloaliphatic epoxide monomer shows an exotherm peak whereas for the latter two monomers, no exotherm peaks were observed from the sample as a result of exposure to the UV source. To explain the phenomenon observed, the effect of addition of two amines with wide difference in the basicity of p-nitroaniline and pyridine, has been studied on the UV-curing of epoxy resins. It has been found that the presence of amines does retard the rate of photopolymerization and the extent of retardation is dependent on the basicity of the amine. Of the two amines used, pyridine and p-nitroaniline, the former is a stronger inhibitor, because of the ready availability of the lone pair of electrons. The results explain the non-reactivity of nitrogencontaining epoxy monomers N,N-diglycidyl-4-glycidyloxyaniline and 4,4'-methylenebis (N,N-diglycidylaniline) to cationic polymerization upon exposure to UV-radiation.
Journal of Applied Polymer Science, 1992
SYNOPSIS l-Acryloyl-4-acryloyloxy-2,2,6,6-tetramethylpiperidine (AATP) has been covalently attached to polypropylene under conditions of reactive processing to give substantial concentrations of essentially 100% grafted antioxidant (AATP-B). Solution of the concentrates showed that at high concentration of grafted antioxidant some homopolymerized AATP was present and the polymer undergoes transient cross-linking during processing. Concentrates of bound AATP (AATB-B) when used as conventional additives for polypropylene are very effective photoantioxidants due to conversion to the related polymer-bound nitroxyl radicals by photosensitized oxidation. A typical commercial hindered phenol, Irganox 1076, when used at low concentration in combination with AATP-B also acts as a photosensitizer for nitroxyl formation. Unlike low molar mass-hindered piperidinoxyl, polymer-bound nitroxyls are effective thermal antioxidants that synergize very effectively with low concentrations of Irganox 1076.
Macro 2007 40 4370 epoxy-amine mech.pdf
Fundamental understanding of mechanisms of the epoxy-amine curing reaction is crucial for developing new polymer materials. Nearly all experimental studies, to date for elucidating its mechanisms are based on thermometric measurements and thus cannot provide the molecular level details. This study used density functional theory (DFT) methods to examine the mechanism of epoxy-amine poly addition reactions at the molecular level. Different reaction pathways involving both acyclic and cyclic transition state structures were examined for different reaction conditions, namely isolated, self-promoted by amine, catalyzed by alcohol, and in different solvents. The results indicate that the reactions catalyzed by an alcohol dominate the rate over the self-promoted reaction by other amine species and the isolated one in early stages of the conversion. The concerted pathways involving cyclic transition-state complexes are not significant due to their high activation energies. Calculated activation energies are within the experimental uncertainty. In addition, solvent, not steric and electronic effects as suggested earlier, are shown to be responsible for secondary amines to react slower than primary amines.
Journal of the American Chemical Society, 2012
an AMPERE event Symposium and School are supported by: • Ministry of Education and Science of Russian Federation • Russian Foundation for Basic Research • Bruker-BioSpin Organising Committee: Co-Chairmen: • R. Z. Sagdeev (Novosibirsk) • V. I. Chizhik (Saint Petersburg) Vice-chairmen: • V. S. Kasperovich (Saint Petersburg) • A. V. Komolkin (Saint Petersburg) Members: • V. V. Frolov (Saint Petersburg) • A. V. Gribanov (Saint Petersburg) • N. A. Grigorieva (Saint Petersburg) • S. Jurga (Poznan) • S. A. Lavrov (Saint Petersburg) • V. V. Matveev (Saint Petersburg) • D. Michel (Leipzig) • Yu. S. Tchernyshev (Saint Petersburg) • K. V. Tyutyukin (Saint Petersburg)
Macromolecules, 1994
Peroxy radicals, when generated in the presence of hindered-amine light stabilizers (HALS), oxidized HALS to produce nitroxides. This reaction, in addition to the scavenging of alkyl radicals by nitroxides, forms a cycle describing HALS as a class of excellent polymer stabilizers. As model systems for the mechanism of the oxidation of HALS, both alkyl peroxy and acyl peroxy radicals were produced by photolyzing the photoinitiators, ketones 2,4-diphenylpentan-3-one and 1-benzoyl-1-hydroxycyclohexane, in oxygen-saturated hexane in the presence of HALS amine I and amino ethers 11-V. Significant yields of the nitroxide VI were observed in these reactions. Product analysis shows that the chemical yields of nitroxide VI are dependent on the HALS structure and on the electronic properties of peroxy radicals, being substantially higher for acylperoxy radicals than for alkyl peroxy radicals. ESR analysis shows that the oxidation of HALS amine I to VI was much less temperature dependent than the oxidation of the HALS amino ether 111. A
Polymer Degradation and Stability, 2011
Understanding processes resulting in heterogeneous degradation in polymers is of extreme importance for improving their stabilization and minimizing negative impact of photooxidation on the material properties. We adopted modern physical techniques for studies of spatial distribution of intermediates and products of photodegradation during accelerated ageing of four commodity polymers, polypropylene (PP), polyethylene (PE), polystyrene (PS) and poly(ethylene-co-norbornene) (Topas Ò , TP) stabilized with hindered amine stabilizer (HAS). Concentration profiles of nitroxides inside polymer plaques along the direction perpendicular to their surface were determined by electron spin resonance imaging (ESRI) as a function of the duration of the accelerated photooxidation. We present data characterizing stabilization activity of three alkoxyamine derivatives of HAS (Tinuvin Ò NOR 123, Tinuvin Ò NOR 371, Flamestab Ò NOR 116), Chimasorb Ò 119 structurally similar to Flamestab Ò NOR 116, and nitroxide-based HAS Dastib Ò 1045 and compare them with the data characterizing stabilization activity of the secondary HAS (>NH) Tinuvin Ò 770. ESRI data are complemented by ATR FTIR spectroscopic detection of oxidation products on the surface and inside the plaques and by data characterizing diffusive optical transmittance of the polymer plaques in the spectral region 280e400 nm (terrestrial range of the solar UV radiation).