Crosslink distribution of epoxy networks studied by small-angle neutron scattering

Crosslink distribution of epoxy networks of diglycidyl ether of bisphenol A (DGEBA) cured with stoichiometric amounts of meta-phenylene diamine (mPDA) was examined by small-angle neutron scattering (SANS). A monodisperse DGEBA resin with the smallest molecular weight was used to enhance the crosslink density and to simplify the network structure for deuterium-labelling. Meta-phenylene-d₄ diamine (mPDAd₄) was applied to label definitively the crosslinks. SANS measurements covered a reciprocal space range from 0.016 to 0.220 Å^?1 or, equivalently, real-space distances from 400 to 30 Å. Application of SANS on the deuterium-labelled epoxy networks consistently produces a constant excess intensity over the unlabelled epoxy networks. Since the scattering intensity from total correlation of the network was negligible, as evident from measurements of SANS on the unlabelled epoxy networks and small-angle X-ray scattering on the epoxy networks, the constant excess SANS intensity can only be attributed to a uniform spatial distribution of the amine curing agent. In other words, the crosslinks are distributed uniformly throughout the epoxy network.     

Influence of external environments on fracture toughness of epoxy resin

Crack propagation in an epoxy resin in the presence of organic solvents was investigated. Fracture toughness (K_IC, a critical stress intensity factor) of the epoxy resin in various external environments was measured using a double cantilever beam specimen. Fracture toughness for initiation (K_ICi) of the resin in the presence of organic solvents was larger than that in the absence of solvents, and the epoxy resin showed a minimum value of K_ICi in the presence of the organic solvent whose solubility parameter was about 11 (cal/cm³)^1/2. This was due to large plastic deformation at a crack tip and the yield strength was lowered by exposure to organic solvents. The former increases K_IC, while the latter decreases K_IC. Fracture surfaces of the resin fractured in solvents suggest that a crack grew slightly when accompanied by a large plastic deformation, and then propagated at high speed.     

Improvement of fracture toughness and glass transition temperature of DGEBA‐based epoxy systems using toughening and crosslinking modifiers

Several toughening and crosslinking modifiers were tested in two epoxy resin systems based on the diglycidyl ether of bisphenol A (DGEBA) with the objective to improve the critical stress intensity factor K_IC and the glass transition temperature (T_g) simultaneously. An amine hardener (isophorone diamine (IPD)) and a homopolymerization initiator (1‐ethyl‐3‐methylimidazolium acetate (EMIM Ac)) were used as curing agents. The highest effect on the K_IC value of the resin system DGEBA/IPD (K_IC = 0.72 MPa^1/2; T_g = 164°C) was achieved with the dendric polymer Boltorn P501 (10 wt%), but it decreased the T_g (K_IC = 1.39 MPa^1/2; T_g = 136°C). A high toughening effect with a low decrease of T_g was achieved with a combination of a self‐organized block copolymer (Nanostrength M22N) and silica nanoparticles (Nanopox F400) (K_IC =1.15 MPa^1/2; T_g =157°C). The K_IC value of the resin system DGEBA/EMIM Ac was improved from 0.44 to 0.66 MPa^1/2. An improvement of both, the thermal and mechanical properties was established for a combination of a poly(tetrahydrofuran) as toughening modifier (PolyTHF2000) with the post‐crosslinking modifier diethylphosphite (DEP) in the resin system DGEBA/IPD (K_IC = 0.86 MPa^1/2; T_g = 180°C). A system with chemical linkages between both modifiers was investigated for comparison but yielded inferior results. POLYM. ENG. SCI., 59:86–95, 2019. © 2018 Society of Plastics Engineers     

Synthesis and architecture study of a reactive polybutadiene polyamine as a toughening agent for epoxy resin

In this study, a novel reactive toughener for the epoxy resin was developed and compared with traditional hydroxyl‐terminated polybutadiene (HTPB). For this purpose, the highly reactive aliphatic amine‐terminated polybutadiene (ATPB) was synthesized at ambient conditions by nucleophilic substitution amination. The characterizations of the product were provided by Fourier transform infrared and ¹H NMR spectroscopy. According to the mechanical test results, incorporation of ATPB into epoxy networks can significantly toughen the epoxy matrix. The addition of 10 phr ATPB increased the critical stress intensity factor (K_IC) and critical strain energy release rate (G_IC) of the epoxy from 0.85 to 2.16 MPa m^1/2 and from 0.38 to 3.02 kJ m^?2, respectively. Furthermore, unlike HTPB, the presence of the ATPB did not deteriorate the tensile strength of the matrix. The toughening and failure mechanisms were discussed based on the epoxy network morphological characteristics. The reduction in cross‐linking density and glass transition temperature of the epoxy system upon modification with liquid rubbers was confirmed by dynamic mechanical analysis. This article opens up the possibility of utilizing reactive flexible diamines with polybutadiene backbone as effective toughening agents for thermoset polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44061.     

The effect molecular weight of polyol components on shape memory effect of epoxy-polyurethane composites

This paper describes the experimental findings of the study of a series of PU/epoxy composites, which formed interpenetrating networks and have shape-memory properties. The morphological variation for different chemical compositions and the influences of morphology on mechanical performance and shape-memory behavior are discussed. Length and mass fraction of polyethylene glycol (PEG) units are chosen as the key parameters in this study. The molecular weight of PEG was varied from 400 (as such PEG units are unable to crystallize) to 1500, 4000, and 6000, which are crystallizable. It was shown that the crystallization of PEG units is the key parameter, which determines the mechanical performance and shape-memory behavior of PU/epoxy composites in this study. DMTA results show the linear dependence of glass transition temperature and tensile strength, elongation, and other mechanical parameters on the amount of PEG in PU/epoxy composites independently of the amount of PEG unit lengths. The maximal value of shape fixation rate was achieved for 30–40 mass percentage of PEG 4000 (4.5 × 10⁻² s⁻¹ at T_g + 20°C) or PEG 6000(4.1 × 10⁻² s⁻¹ at T_g + 20°C) in PU/epoxy composites.     

Silarylene-containing poly(ether-amide)s obtained by Yamazaki–Higashi phosphorylation technique: use of bis(4-(4-aminophenoxy)phenyl)ethylmethyl silane

Aromatic poly(ether-amide)s (PEAs) based on -(R₁,R₂)diphenylsilane- and oxyether units were synthesized by direct polycondensation of a diamine and two dicarboxylic acids. For this, the diamine bis(4-(4-aminophenoxy)phenyl)ethylmethylsilane was obtained by reduction of the respective dinitro compound, which was synthesized by nucleophilic aromatic halogen displacement from 1-fluoro-4-nitrobenzene with bis(4-hydroxyphenyl)ethylmethylsilane in basic medium. New silicon-containing aromatic diamine and the PEAs were characterized by elemental analysis, FT-IR, ¹H, ¹³C and ²⁹Si NMR spectroscopy and the results were in agreement with the proposed structures. The incorporation of aliphatic units such as methyl and/or ethyl groups on the silicon atoms affected positively the solubility of the PEAs in organic polar solvents. When their thermal and optical properties were compared with two PEAs of similar structure, containing phenyl groups bonded to the silicon atoms, it was observed a decrease of the glass transition temperature and transmittance values, maintaining a high thermal resistance.     

Synthesis and coating characteristics of novel calcium‐containing poly(urethane ethers)

Calcium salt of mono(hydroxypentyl)phthalate [Ca(HPP)₂] was synthesized by the reaction of 1,5‐pentanediol, phthalic anhydride, and calcium acetate. Calcium‐containing poly(urethane ethers) (PUEs) were synthesized by the reaction of hexamethylene diisocyanate (HMDI) or toluylene 2,4‐diisocyanate (TDI) with a mixture of Ca(HPP)₂ and poly(ethylene glycol) (PEG₃₀₀ or PEG₄₀₀) with di‐n‐butyltin dilaurate as a catalyst. We synthesized a series of calcium‐containing PUEs with different compositions by taking the molar ratio of Ca(HPP)₂ : PEG₃₀₀ or PEG₄₀₀ : diisocyanate (HMDI or TDI) as 2 : 2 : 4, 3 : 1 : 4, and 1 : 3 : 4 to study the coating properties of the PUEs. Blank PUEs without a calcium‐containing ionic diol were also prepared by the reaction of PEG₃₀₀ or PEG₄₀₀ with HMDI or TDI. The PUEs were well characterized by fourier transform infrared spectroscopy, ¹HNMR, ^?13C‐NMR, solid‐state cross‐polarity/magic‐angle spinning ¹³C‐NMR, viscosity, solubility, and X‐ray diffraction studies. The thermal properties of the polymers were also studied with thermogravimetric analysis and differential scanning calorimetry. The PUEs were applied as a top coat on acrylic‐coated leather, and their physicomechanical properties were also studied. The coating properties of PUEs, including tensile strength, elongation at break, tear strength, water vapor permeability, flexing endurance, cold crack resistance, abrasion resistance, color fastness, and adhesive strength, were better than the standard values. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 710–721, 2004     

Mechanical properties of epoxy networks based on DGEBA and aliphatic amines

The mechanical properties of epoxy networks based on diglycidyl ether of bisphenol A epoxy resin cured with various linear aliphatic amines, such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and cyclic amines such as 1‐(2‐aminoethyl)piperazine and isophorone diamine, were studied. General characteristics such as T_g, density, and packing density, were determined and related to the structure and funcionality of the curing agent. Dynamic mechanical spectra were used to study both the α and β relaxations. Tensile and the flexural tests were used to determine the Young's and flexural modulus, and fracture strength all in the glassy state. Furthermore, linear elastic fracture mechanics was used to determine K_IC. As a rule, isophorone diamine network presented the higher tensile and flexure modulus while 1‐(2‐aminoethyl)piperazine gave the highest toughness properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and characterization of epoxy resins containing bismuth

The synthesis of epoxy resins in the presence of Bi as bismuth acrylate (BiA₃) showed that the properties such as epoxide equivalent weight (eq/100 g), molecular weight, and viscosity (η_sp) increased; whereas hydrolyzable chlorine content, hydroxyl content, and refractive index decreased in the presence of BiA₃. The metal forms a complex with ether linkage of epoxy resins, as evidenced from infrared spectroscopy. The presence of Bi in epoxy resins has been confirmed by scanning electron microscopy (SEM) and qualitative analysis. The glass transition temperature (T_g) of epoxy resins containing 1.18 × 10⁻⁵ and 2.8 × 10⁻⁵ molar equivalent of BiA₃ is 131.58 and 190°C, respectively, and is greater than that of blank (130°C). The heat of reactions for epoxy resins containing 1.18 × 10⁻⁵ molar equivalent of BiA₃, calculated by differential scanning calorimetry, is 4.75 J g. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1359–1365, 1997     

Development and characterization of novel DOPO based phosphorus tetraglycidyl epoxy nanocomposites for aerospace applications

A study was made in the present investigation on the development and characterization of 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) based phosphorus tetraglycidyl epoxy nanocomposites and to find its suitability for use in aerospace and high performance applications. Phosphorus-containing diamine (DOPO-NH₂) was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 4,4′-diaminobenzophenone (DABP), and this is utilized for the preparation of DOPO based phosphorus containing tetraglycidyl epoxy denoted as ‘D’. The synthesized resin was characterized by Fourier transform infrared spectra (FT-IR) and ¹H, ¹³C nuclear magnetic resonance (NMR) spectra. Nanoclay and polyhedral oligomeric silsesquioxane (POSS)-amine nano-reinforcements denoted as N1 and N2 were incorporated into the synthesized epoxy resin. Curing was done with diaminodiphenylmethane (DDM) and bis(3-aminophenyl) phenylphosphine oxide (BAPPO) curing agents denoted as X and Y respectively. Mechanical, thermal, flame retardant, water absorption behaviour and electrical properties of the epoxy nanocomposites were studied and the results are discussed.     

Study of impact properties and morphology of 4,4′‐diaminodiphenyl methane cured epoxy resin toughened with acrylate‐based liquid rubbers

Randomized carboxyl poly(2‐ethylhexyl acrylate) (A‐1) and randomized epoxy poly(2‐ethylhexyl acrylate) (B‐1) rubbers were synthesized in the form of liquid rubber by a solution polymerization technique. The liquid rubbers A‐1 and B‐1 were characterized by ¹H NMR and IR spectroscopic analysis, non‐aqueous titration, viscosity measurements and gel permeation chromatography. The liquid rubbers A‐1 (M?_n = 3900 g mol^?1), B‐1 (M?_n = 4100 g mol^?1) and a (1:1) mixture of A‐1 and B‐1 were pre‐reacted with epoxy resin separately and the modified epoxy networks were made by curing with high temperature curing agent. The modified epoxy networks were evaluated by unnotched Izod impact testing. The morphology and toughening behaviour were analysed by scanning electron microscopy. Optimum properties were obtained with the mixture of A‐1 and B‐1. Copyright © 2003 Society of Chemical Industry     

Synthesis and characterization of chlorinated soy oil based epoxy resin/glass fiber composites

Composites with good toughness properties were prepared from chemically modified soy epoxy resin and glass fiber without additional petroleum based toughening agent. Chlorinated soy epoxy (CSE) resin was prepared from soybean oil. The CSE was characterised by spectral, and titration method. The prepared CSE was blended with commercial epoxy resin in different ratios and cured at 85°C for 3 h, and post cured at 225°C for 2 h using m‐phenylene diamine (MPDA) as curing agent. The cure temperatures of epoxy/CSE/MPDA with different compositions were found to be in the range of (151.2–187.5°C). The composite laminates were fabricated using epoxy /CSE/MPDA‐glass fiber at different compositions. The mechanical properties such as tensile strength (248–299 MPa), tensile modulus (2.4–3.4 GPa), flexural strength (346–379 MPa), flexural modulus (6.3–7.8 GPa) and impact strength (29.7–34.2) were determined. The impact strength increased with the increase in the CSE content. The interlaminor fracture toughness (G_IC) values also increased from 0.6953 KJ/m² for neat epoxy resin to 0.9514 KJ/m² for 15%CSE epoxy‐modified system. Thermogravimetric studies reveal that the thermal stability of the neat epoxy resin was decreased by incorporation of CSE. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Blends of epoxy resin with amine‐terminated polyoxypropylene elastomer: Morphology and properties

A liquid diglycidyl ether of bisphenol A (DGEBA) epoxy resin is blended in various proportions with amine‐terminated polyoxypropylene (POPTA) and cured using an aliphatic diamine hardener. The degree of crosslinking is varied by altering the ratio of diamine to epoxy molecules in the blend. The mixture undergoes almost complete phase separation during cure, forming spherical elastomer particles at POPTA concentrations up to 20 wt %, and a more co‐continuous morphology at 25 wt %. In particulate blends, the highest toughness is achieved with nonstoichiometric amine‐to‐epoxy ratios, which produce low degrees of crosslinking in the resin phase. In these blends, the correlation between G_IC and plateau modulus (above the resin T_g), over a wide range of amine‐to‐epoxy ratios, confirms the importance of resin ductility in determining the fracture resistance of rubber‐modified thermosets. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 427–434, 1999     

Synthesis and characterization of a new family of cationic amino acid‐based poly(ester amide)s and their biological properties

A new family of positively charged and water soluble amino acid‐based poly(ester amide)s (PEAs) consisting of nontoxic L ‐arginine, diols, and aliphatic dicarboxylic acids building blocks was synthesized and characterized. The L ‐arginine based PEAs (Arg‐PEAs) were prepared by a solution polycondensation of two monomers: tetra‐p‐toluenesulfonic acids salts or hydrochloride acid salts of bis‐(L ‐arginine) α, ω‐alkylene diesters (monomer II ), and di‐p‐nitrophenyl esters of saturated or unsaturated dicarboxylic acids (monomer I ). Optimal reaction conditions were studied as functions of type of solvents and acid acceptors, concentrations of reactants. The molecular weights (M_n and M_w) of Arg‐PEAs measured by GPC ranged from 20,000 to 60,000 g mol^?1 with a rather narrow molecular weight distribution below 1.5. The chemical structures were confirmed by IR and NMR spectra. Arg‐PEAs obtained were all amorphous materials with T_g from 33 to 125°C, depending on the number and the type (saturated vs. unsaturated) of methylene groups in diols or diacids, and the type of counter‐ions attached to the guanidine group of the Arg‐based PEAs. The Arg‐PEAs had a high solubility in all polar solvents, including water. Preliminary studies of cell morphology and DNA capture capability of Arg‐PEAs indicated that this new family of cationic PEAs was nontoxic and more biocompatible than a commercial transfection agent (Superfect®), and can successfully capture plasma DNA. The strong positive charge of Arg‐PEAs as well as their good water solubility could provide unique characteristics for potential gene transfection or other charge preferred biomedical applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thiocyanate Ion Promoted E ⇌ Z Isomerization of a-Bromo-β,β-Diactivated Electrophilic Olefins: An Apparent High Nucleofugality of NCS−

(E)-β-Chloro-α-phenylcinnamaldehyde and (E)- and (Z)-methyl α-tert-butoxycarbonyl-p-nitro-β-bromocinnamates in the presence of NCS⁻ ion in acetonitrile undergo an (E) ⇌ (Z) isomerization which is faster than the vinylic substitution. (E)- and (Z)-methyl α-cyano-β-mesyloxy- (and β-chloro-) p-nitrocinnamates undergo substitution under similar conditions without preceding isomerization. MO calculations gave the energy differences between the eclipsed and the perpendicular conformers of carbanions ⁻CH₂CH₂X and (NC)₂ČH₂X (X = Cl, NCS). These rotational barriers denote the hyperconjugation stabilization energy resulting from interaction of the C-X bond and the 2p(C⁻) orbital. Both HCA values are high, those for X = Cl being 15–20% higher than for X = NCS. The limited literature data on the nucleofugality of NCS⁻ suggests that it can have a nucleofugality which is not much lower than that of Cl⁻ or Br⁻. Consequently, NCS⁻-catalyzed isomerizations of electrophilic vinyl chlorides and bromides, which involve a 180° internal rotation followed by a faster expulsion of NCS⁻ than of Cl⁻ from the initially formed intermediate carbanion Y'Y⁻C-C(R)(Cl)SCN, are not unreasonable, especially if solvation, which was not included in the calculations, plays an important role in the nucleofuge expulsion process.     

Preparation of poly(1,4‐cyclohexylenedimethylene phthalate)s and their use as modifiers for aromatic diamine‐cured epoxy resin

Poly(1,4‐cyclohexylenedimethylene phthalate) s, prepared by the reaction of phthalic anhydride and 1,4‐cyclohexane dimethanol (35/65 or 73/27 mol % cis/trans or trans alone), have been used to improve the toughness of bisphenol‐A diglycidyl ether epoxy resin cured with 4,4′‐diaminodiphenyl sulfone. The aromatic polyesters include poly(cis/trans‐1,4‐cyclohexylenedimethylene phthalate) (PCP) based on a commercial cyclohexanedimethanol, poly(trans‐1,4‐cyclohexylenedimethylene phthalate) (trans‐PCP) and poly(cis/trans‐1,4‐cyclohexylenedimethylene phthalate) (cis‐rich PCP) prepared from a cis‐rich diol. The polyesters used were soluble in the epoxy resin without solvents and were effective as modifiers for toughening the cured epoxy resin. For example, the inclusion of 20 wt% of PCP (MW 6400 g mol⁻¹) led to an 80% increase in the fracture toughness (K_IC) of the cured resin with no loss of mechanical and thermal properties. The toughening mechanism is discussed in terms of morphological and dynamic viscoelastic behaviours of the modified epoxy resin system. © 2000 Society of Chemical Industry     

The influence of matrix chemical structure on the mode I and II interlaminar fracture toughness of glass‐fiber/epoxy composites

The present paper is concerned with Mode I and Mode II delamination tests performed on three different glass fiber reinforced epoxy composites, chosen to obtain different final structures. The effect of crosshead speed on the fracture resistance of the composites was also analyzed. It was found that Mode I propagation values (G_IC) increase as the crosshead speed decreases, probably because of the increase of brittleness in the studied range. An Arrhenius type relation between G_IC and the glass transition temperature of the epoxy resin/amine system (T_g) was found. Mode II initiation values (G_IIC^init) and apparent shear strength (S_H) were found to increase with the decrease of T_g. The relation between matrix toughness and composite interlaminar fracture toughness was also considered. Finally, the G_IC propagation values were compared to the data available in literature for similar materials.     

Electrostatic dissipation and flexibility of poly(oxyalkylene)amine segmented epoxy derivatives

A family of hydrophilic and flexible epoxy polymers was prepared from the reaction of poly(oxyalkylene)amines and diglycidyl ether of bisphenol‐A (DGEBA) at 1:1 molar ratio of N H to epoxide. The use of a high molecular weight (M_W = 1000–6000) poly(oxyethylene–oxypropylene)amine and a low M_W amine as curing agents provided epoxy materials with good properties in toughness and hydrophilicity. The hydrophilicity, probed by surface resistivity of these cured materials, was found to be affected by the nature and weight content of poly(oxyethylene) segment in the polymer backbone, and also by the degree of crystallinity. Specifically, in the presence of a water‐soluble poly(oxyethylene–oxypropylene)diamine of M_W 2000 the cured epoxies can reach surface resistivity as low as 10^8.6–9.6 Ω/□. In comparison, the water‐insoluble poly(oxypropylene)diamine of M_W 2000 afforded a higher surface resistivity of 10^10.5 Ω/□ because of the difference in hydrophilicity between oxyethylene and oxypropylene functionalities. Poly(oxypropylene)diamine of M_W 230 as the sole curing agent generated an epoxy with even higher surface resistivity of 10¹³ Ω/□ due to a highly crosslinking structure. With proper selection of mixed poly(oxyethylene–oxypropylene)diamine (25 wt%) and 2‐aminoethanol (9 wt%), the DGEBA cured polymer had an appropriate surface resistivity of 10^9.8 Ω/□ for antistatics. Moreover, this material was extremely ductile in appearance and showed over 500 % elongation at break during mechanical tests. The high flexibility is rationalized by the balanced chemical structure of poly(oxyalkylene) segments and bisphenol‐A distributed in a slightly crosslinked system. © 2000 Society of Chemical Industry     

Tetraglycidyl epoxy resins and graphite fiber composites cured with flexibilized aromatic diamines

Studies were performed to synthesize new ether modified, flexibilized aromatic diamine hardeners for curing epoxy resins. The effect of moisture absorption on the glass transition temperatures of a tetraglycidyl epoxy, MY 720, cured with flexibilized hardeners and a conventional aromatic diamine was studied. Unidirectional composites, using epoxy-sized Celion 6000 graphite fiber as the reinforcement, were fabricated. The room temperature and 300°F mechanical properties of the composites, before and after moisture exposure, were determined. The Mode I interlaminar fracture toughness of the composites was characterized, using a double cantilever beam technique to calculate the critical strain energy release rate, G_IC.     

Reactions of Photoexcited Triplet States of Zinc Porphyrin with Transient Radicals in Aqueous Solutions

The technique of simultaneous pulse radiolysis and photolysis, PRAP, has been utilized to study the reactions of various radicals with ground state ZnTPPS and the triplet state ZnTPPS^T in aqueous solutions. The radicals H and OH add to both states with k ∼ 1 × 10¹⁰ M⁻¹ s⁻¹. The CH₂C(CH₃)₂OH radical from t-BuOH is relatively inert toward ZnTPPS but reacts rapidly (k = 1.8 × 10⁹ M⁻¹ s⁻¹) with ZnTPPS^T to form an adduct. Electron transfer reactions are found to be about an order of magnitude faster with the triplet than with the ground state. The (CH₃)₂COH radical reduces both ZnTPPS (k = 1 × 10⁸ M⁻¹ s⁻¹) and ZnTPPS^T (k = 3 × 10⁹ M⁻¹ s⁻¹) to the anion radical (ZnTPPS)⁻. The radical Br⁻₂ oxidizes both states to the cation radical (ZnTPPS)⁺ with k = 8 × 10⁸ M⁻¹ s⁻¹ for the ground state and 5 × 10⁹ M⁻¹ s⁻¹ for the triplet. The transient cation Cd⁺ reduces both states with a diffusion-controlled rate (k = 1 × 10¹⁰ M⁻¹ s⁻¹) to produce the anion radical. The above mechanisms of radical addition and electron transfer are also supported by the product spectra.