Thermal degradation behavior of a carboxylic acid-terminated amphiphilic block copolymer poly(ethylene)-b-poly(ethylene oxide)

The thermal degradation of an amphiphilic block copolymer poly(ethylene)-b-poly(ethylene oxide)-carboxylic acid terminated (PE-b-80%PEO–CH₂COOH) and its salt obtained as intermediary product from chemical oxidation of the end group of poly(ethylene)-b-poly(ethylene oxide) (PE-b-80%PEO) has been studied using a thermogravimetric mass spectrometry (TG/MS) coupled system. The isothermal fragmentation of PE-b-80%PEO–CH₂COOH showed a more complex fragmentation pattern than PE-b-80%PEO owing to the simultaneous occurrence of the polyether block and the carboxylic end group fragmentations. This led to the appearance of four overlapping ion current peaks of fragments with m/z 44 and two peaks relative to m/z 18 at different times by acid-terminated copolymer. For the PE-b-80%PEO copolymer, two ion current peaks associated to m/z 44 and one large peak relative to m/z 18 fragments were detected. The intermediary product (PE-b-80%PEO–CH₂COO⁻ K⁺) showed differences related to the fragmentation behavior. It has more defined ion current signals and presented characteristic peaks attributed to m/z 43 fragment at the very beginning of the thermal degradation process, which it not detected in the acid copolymer.     

“Best Match” Model and Effect of Na+/H+ Exchange on Anion Attachment to Peptides and Stability of Formed Adducts in Negative Ion Electrospray Mass Spectrometry

The “Best Match” model has been extended to account for the role that Na⁺/H⁺ exchange plays on anion attachment in negative ion electrospray. Without any Na⁺/H⁺ exchange on (Glu) fibrinopeptide B, the higher basicity anions F^? and CH₃COO^? can hardly form observable adducts; however, after multiple Na⁺/H⁺ exchanges, adduct formation is enabled. Moreover, dissociation pathways of CF₃COO^? adducts with singly deprotonated peptides that have undergone 0 to 3 Na⁺/H⁺ exchanges exhibit a shift in CID product ions from losing predominately CF₃COOH (case of 0 Na⁺/H⁺ exchanges) to losing predominately CF₃COO^? (case of 3 Na⁺/H⁺ exchanges). These phenomena can be rationalized by considering that Na⁺ cations exchange at, and serve to “block”, the most acidic sites, thereby forcing implicated anions to attach to lower acidity protons. In addition to forming ion pairs with carboxylate groups, Na⁺ also participates in formation of tri-atomic ions of the form ANaA^? during adduct dissociation. The fact that low gas-phase basicity (GB) anions preferentially form ANaA^? species, even though high GB anions form more stable tri-atomic species, indicates that the monatomic ions were not in close contact in the initial adduct. The propensity for formation of stable anionic adducts is dependent on the degree of matching between anion GBs and GB_app of deprotonated sites on the peptide. The GB_app is raised dramatically as the charge state of the peptide increases via a through-space effect. The presence of Na⁺ on carboxylate sites substantially decreases the GB_app by neutralizing these sites, while slightly increasing the intrinsic GBs by an inductive effect.

The anomeric effect: Ab-initio studies on molecules of the type X?CH2?O?CH3

The anomeric effect of the functional groups X = C?N, C?CH, COOH, COO^?, O? CH₃, NH₂, and NH⁺₃ has been studied with ab initio techniques. Geometry effects upon rotation around the central C? O bond in X? CH₂? O? CH₃ have been compared in the various compounds. The energy differences between the conformers with a gauche and trans (X? C? O? C) arrangement were calculated at the 6-31G* level in the fully optimized 4-21G geometries. Energy differences calculated at the 4-21G level appeared not to be reliable, especially for the groups X that contain non-sp³ hybridized atoms. The 6-31G* energy differences indicate a normal anomeric effect for X = COO^?, O? CH₃, and NH₂(g⁺) (ca. 13 kJ/mol) and a small anomeric effect for X = COOH, C?N, and C?CH (ca. 6 kJ/mol). For X = NH₂(t) and NH⁺₃ a reverse anomeric effect occurs. These observations are in line with experimental results and evidence is given for a competition among various stereoelectronic interactions that occur at the same anomeric center. Geometry variations can be understood in terms of simple rules associated with anomeric orbital interactions. Trends followed when the group X is varied cannot be related in a straightforward way to the energy differences between the trans and the gauche forms in these compounds. Only the variation in the gauche torsion angle X? C? O? C follows roughly the same trend.     

Effect of Partial Hydrolysis in Switching the Mode of Inter‐molecular Bonding between Metal Complexes

The assembly of [Cd(L¹)]^— {[L¹]^3— = N[CH₂CH₂N=C(CH₃)COO^—]₃} into the tetranuclear cluster {[Cd(L¹)]Na(H₂O)₂}₂ in the presence of Na⁺ is mediated by Na⁺‐carboxylate interactions; in contrast In³⁺ and Fe³⁺ induce the partial hydrolysis of [L¹]^3— to afford the complexes [In(L²)Cl] and {[Fe(L²)]₂O} {[L²]^2— = N[CH₂CH₂NH₂][CH₂CH₂N=C(CH₃)COO^—]₂} which aggregate via intermolecular H‐bonding.     

Syntheses and structures of Me3Sb+CH2COO−·H2O,the monohydrate of the antimony analogue of betaine,and related compounds

The syntheses of the antimony analogue of betaine, Me₃Sb⁺CH₂COO^? (1), of the precursor [Me₃SbCH₂COOH][Br] (2) and of [Me₃SbCH₂COOCH₂CH₃][Br] (3) are reported. A new method for the synthesis of solvent‐free Me₃Sb is described. The structures of 1·H₂O and 3 were determined by single crystal X‐ray diffractometry. Copyright © 2002 John Wiley & Sons, Ltd.     

pH‐Controlled Molecular Switches and the Substrate‐Directed Self‐Assembly of Molecular Capsules with a Calix[4]pyrrole Derivative

10α,20α‐Bis(4‐nitrophenyl)calix[4]pyrrole ( 1 ) forms 1:1 complexes with anions of selected aromatic hydroxy acids in which the host orientation within the guest is controlled by a change in the pH value. Some bis‐anionic guests, including those obtained from 4‐hydroxybenzoic acid, 1,4‐ and 1,3‐benzenedicarboxylic acids, induce the self‐assembly of molecular capsules involving two molecules of the receptor. ¹H NMR data and solid‐state structures of the 1:1 complex of 1 with p‐C₆H₄(COOH)(COO^?)⁺NMe₄ and the 2:1 capsule [( 1 )₂m‐C₆H₄(COO^?)₂(⁺NMe₄)₂] provide structural details in solution and in the solid state.     

Equilibrium,kinetics, and mechanism of the malonic acid–iodine reaction

The equilibrium constant for the reaction CH₂(COOH)₂ + I₃^? ? CHI(COOH)₂ + 2I^? + H⁺, measured spectrophotometrically at 25°C and ionic strength 1.00M (NaClO₄), is (2.79 ± 0.48) × 10^?4M². Stopped-flow kinetic measurements at 25°C and ionic strength 1.00M with [H⁺] = (2.09-95.0) × 10^?3M and [I^?] = (1.23-26.1) × 10^?3M indicate that the rate of the forward reaction is given by (k₁[I₂] + k₃[I₃^?]) [HOOCCH₂COO^?] + (k₂[I₂] + k₄[I₃^?]) [CH(COOH)₂] + k₅[H⁺] [I₃^?] [CH₂(COOH)₂]. The values of the rate constants k₁-k₅ are (1.21 ± 0.31) × 10², (2.41 ± 0.15) × 10¹, (1.16 ± 0.33) × 10¹, (8.7 ± 4.5) × 10^?1M^?1·sec^?1, and (3.20 ± 0.56) × 10¹M^?2·sec^?1, respectively. The rate of enolization of malonic acid, measured by the bromine scavenging technique, is given by k_en[CH₂(COOH)₂], with k_en = 2.0 × 10^?3 + 1.0 × 10^?2 [CH₂(COOH)₂]. An intramolecular mechanism, featuring a six-member cyclic transition state, is postulated to account for the results on the enolization of malonic acid. The reactions of the enol, enolate ion, and protonated enol with iodine and/or triodide ion are proposed to account for the various rate terms.     

Synthesis and Characterization of Polyvinylferrocene/Polypyrrole Composites

Conducting polymer composites of polyvinylferrocene and polypyrrole (PVF/PPy) were synthesized chemically by the in situ polymerization of pyrrole in the presence of PVF using FeCl₃ as oxidant. Acetic (CH₃COOH) and boric (H₃BO₃) acids were used as the synthesis medium. Effects of the synthesis medium on the properties of the PVF/PPy composite were investigated. The PVF/PPy composites and homopolymers were characterized by fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and magnetic susceptibility techniques. Conductivity measurements were performed using the four‐probe technique. We found that the conductivities of PVF/PPy‐H₃BO₃ (1.19 S cm^?1) and PVF/PPy‐CH₃COOH (4.5×10^?1 S cm^?1) increased relative to those of the homopolymers of PPy‐H₃BO₃ (2.1×10^?2 S cm^?1) and PPy‐CH₃COOH (1.2×10^?2 S cm^?1) due to the interaction of PVF with the pyrrole moiety. The stability of all homopolymers and composites were investigated by thermogravimetric analysis and by conductivity measurements during heating‐cooling cycles. There was a small drop in conductivity caused by the annealing of PVF/PPy composites at 70°C. The conductivity of all samples increased with temperature and exhibited stable electrical behavior with increasing temperature. TGA analysis of samples showed that the composites were more stable than the homopolymers or PVF separately. The magnetic susceptibility values of samples were negative, except for PVF/PPy‐H₃BO₃. Morphology changes of the composites investigated by scanning electron microscopy (SEM), attributed to synthesis conditions, have a significant effect on their conductivity.     

Selective complete decomposition of poly(n‐hexylisocyanate) and its use in a new molecular design method

Poly(n‐hexylisocyanate) (PHIC‐NH) as a rod‐like polymer having a ? NH group at one end of the polymer chain was found to instantly (less than a few seconds) be completely decomposed by CH₃O^?Na⁺ in tetrahydrofuran/CH₃OH under a mild experimental condition ([CH₃O^?Na⁺] < 1 mol L^?1 at room temperature).The mechanism of the decomposition for the PHIC‐NH consists of two steps: the first is abstraction of the proton for PHIC‐NH by Na⁺ with a slow reaction rate, and the second is the consequent depolymerization of PHIC‐N^? based on the equilibrium polymerization with a rapid depolymerization rate. The decomposition rate constants (k_d) depend on M_w of PHIC‐NH, namely k_d ～ M_w^?1.0. The decomposition of the PHIC‐NR having an end‐capped ? NR group was completely depressed. Using an “all or nothing” mechanism for the decomposition, the (PHIC)_3.43 comb‐shaped polymer and polystyrene (PSt)‐graft‐(PHIC‐NH)_4.28 graft copolymer were, respectively, decomposed to produce (PHIC‐NH)_3.43–1.03 and PSt‐graft‐(PHIC‐NH)_4.28–0 in a series with different numbers of PHIC‐NH combs and PHIC‐NH grafts by regulating the amount of CH₃O^?Na⁺ and the decomposition time. Molecular structure of (PHIC‐NH)_3.43–1.03 and PSt‐graft‐(PHIC‐NH)_4.28–0 was discussed from a viewpoint of PSt‐reduced chain dimension per molar mass. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Quantification of Ion‐Pairing Effects on the Nucleophilic Reactivities of Benzoyl‐ and Phenyl‐Substituted Carbanions in Dimethylsulfoxide

Second‐order rate constants for the reactions of acceptor‐substituted phenacyl (PhCO?CH^??Acc) and benzyl anions (Ph?CH^??Acc) with diarylcarbenium ions and quinone methides (reference electrophiles) have been determined in dimethylsulfoxide (DMSO) solution at 20 °C. By studying the kinetics in the presence of variable concentrations of potassium, sodium and lithium salts (up to 10^?2 mol L^?1), the influence of ion‐pairing on the reaction rates was examined. As the concentration of K⁺ did not have any influence on the rate constants at carbanion concentrations in the range of 10^?4–10^?3 mol L^?1, the acquired rate constants could be assigned to the reactivities of the free carbanions. The counter ion effects increase, however, in the series K⁺<Na⁺<Li⁺, and the sensitivity of the carbanion reactivities toward variation of the counter ion strongly depends on the structure of the carbanions. The reactivity parameters N and s_N of the free carbanions were derived from the linear plots of log k₂ against the electrophilicity parameters E of the reference electrophiles, according to the linear‐free energy relationship log k₂(20 °C)=s_N(N+E). These reactivity parameters can be used to predict absolute rate constants for the reactions of these carbanions with other electrophiles of known E parameters.     

Well‐defined polyolefin/poly(ε‐caprolactone) diblock copolymers: New synthetic strategy and application

A new synthetic strategy, the combination of living polymerization of ylides and ring‐opening polymerization (ROP), was successfully used to obtain well‐defined polymethylene‐b‐poly(ε‐caprolactone) (PM‐b‐PCL) diblock copolymers. Two hydroxyl‐terminated polymethylenes (PM‐OH, M_n= 1800 g mol^?1 (PDI = 1.18) and M_n = 6400 g mol^?1 (PDI = 1.14)) were prepared using living polymerization of dimethylsulfoxonium methylides. Then, such polymers were successfully transformed to PM‐b‐PCL diblock copolymers by using stannous octoate as a catalyst for ROP of ε‐caprolactone. The GPC traces and ¹H NMR of PM‐b‐PCL diblock copolymers indicated the successful extension of PCL segment (M_n of PM‐b‐PCL = 5200–10,300 g mol^?1; PDI = 1.06–1.13). The thermal properties of the double crystalline diblock copolymers were investigated by differential scanning calorimetry (DSC). The results indicated that the incorporation of crystalline segments of PCL chain effectively influence the crystalline process of PM segments. The low‐density polyethylene (LDPE)/PCL and LDPE/polycarbonate (PC) blends were prepared using PM‐b‐PCL as compatibilizer, respectively. The scanning electron microscopy (SEM) observation on the cryofractured surface of such blend polymers indicates that the PM‐b‐PCL diblock copolymers are effective compatibilizers for LDPE/PCL and LDPE/PC blends. Porous films were fabricated via the breath‐figure method using different concentration of PM‐b‐PCL diblock copolymers in CH₂Cl₂ under a static humid condition. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Extraktion von alkali- und erdalkalimetallionen mit (sym-dibenzo-14-krone-4-oxy)- und (sym-dibenzo-16-krone-5-oxy)-carbonsäuren

(Extraction of alkali on alkaline earth metal ions with (sym-dibenzo-14-crown-4-oxy)- and (sym-dibenzo-16-crown-5-oxy)-carboxylic acids.)The extraction of lithium, sodium, potassium, calcium and some other metal ions with dibenzo-4-crown-4-oxy- and dibenzo-16-crown-5-oxycarboxylic acids containing the groups -CH₂COOH, -(CH₂)₂COOH, -(CH₂)₃COOH, -CH(C₂H₅)COOH and -CH(C₄H₉)COOH was studied. The extraction increases as a function of the lipophilic character of the carboxylic acid group. Calcium, barium and strontium ions are better extracted than Li⁺, Na⁺ and K⁺; there are only small differences among the alkaline earth metal ions. Evaluated from the extraction data, the composition of the extracted species was 1:1 (metal/ligand) for Li⁺, and 1:2 for CaCa²⁺; Na⁺ and K⁺ favour the formation of 1:2 complexes with dibenzo-14-crown-4-derivatives bbut 1:1 complexes with dibenzo-16-crown-5-oxy-carboxylic acids. The dependence of the distribution ratio on pH does not provide unequivocal evidence for the composition of the extracted compounds.     

Unimolecular reactions of ionized methyl acetate and its hydrogen-rearranged isomers

The proposed formation of [CH₃C(OH)OCH₂]⁺˙ (b) as the intermediate in the isomerization [CH₂?C(OH)OCH₃]⁺˙ (c)?b?[CH₃COOCH₃]⁺˙ (c has been confirmed by preparation of b from CH₃COOCH₂OCH₃. For the three isomers a–c the dominant metastable ion (MI) dissociation, CH₃O˙ loss, involves identical kinetic energy release values. The kinetic barriers for a?b and b?c must be nearly as high as that for CH₃O˙ loss from c, as shown by the insensitivity of the mass spectra from collisionally activated dissociation (CAD) of a–c to ionizing electron energy. The H/D scrambling of metastable [CH₂?C(OD)OCH₃]⁺˙ and c–D₃ ions confirm this, indicating that the barrier for a?b is slightly below that for b?c. Minor low-energy dissociations include losses of CH₄ and CH₃OH from a and losses of ˙CHO and CH₂O from b. Comparison of MI and CAD spectra of a–c with those from [CH₃(OH)CH₂O]⁺˙ (d) and [CH₃COCH₂OH]⁺˙ (e) give no evidence for skeletal rearrangement of a–c to d or e.     

Thermal properties and ion mobility in complex antimony(III) fluorides with α-amino acids

Differential thermal analysis (DTA) and (¹⁹F, ¹H) NMR spectroscopy were used to study thermal properties and ion mobility in complex antimony(III) fluorides with amino acids of composition [(CH₃)₂CH(CH₂)CH(NH₃)COOH]SbF₄ (LeuHSbF₄), SbF₃[(CH₃)₂CH(CH₂)CH(⁺NH₃)COO^?] (SbF₃ · Leu), and SbF₃[(CH₃)₂CHCH(⁺NH₃)COO^?] (SbF₃ · Val). Ionic conductivity in L-leucinium tetrafluoroantimonate(III) was studied using impedance spectroscopy. LeuHSbF₄ was found to undergo a diffusion phase transition to a relatively highly conductive state in the range 385?C415 K with an attendant loss of thermal stability (softening) of the high-temperature phase.     

Synthesis and characterization of well‐defined ABC 3‐Miktoarm star‐shaped terpolymers based on poly(styrene), poly(ethylene oxide), and poly(ϵ‐caprolactone) by combination of the “living” anionic polymerization with the ring‐opening polymerization

A series of well‐defined ABC 3‐Miktoarm star‐shaped terpolymers [Poly(styrene)‐Poly(ethylene oxide)‐Poly(ε‐caprolactone)](PS‐PEO‐PCL) with different molecular weight was synthesized by combination of the “living” anionic polymerization with the ring‐opening polymerization (ROP) using macro‐initiator strategy. Firstly, the “living” poly(styryl)lithium (PS^?Li⁺) species were capped by 1‐ethoxyethyl glycidyl ether(EEGE) quantitatively and the PS‐EEGE with an active and an ethoxyethyl‐protected hydroxyl group at the same end was obtained. Then, using PS‐EEGE and diphenylmethylpotassium (DPMK) as coinitiator, the diblock copolymers of (PS‐b‐PEO)_p with the ethoxyethyl‐protected hydroxyl group at the junction point were achieved by the ROP of EO and the subsequent termination with bromoethane. The diblock copolymers of (PS‐b‐PEO)_d with the active hydroxyl group at the junction point were recovered via the cleavage of ethoxyethyl group on (PS‐b‐PEO)_p by acidolysis and saponification successively. Finally, the copolymers (PS‐b‐PEO)_d served as the macro‐initiator for ROP of ε‐CL in the presence of tin(II)‐bis(2‐ethylhexanoate)(Sn(Oct)₂) and the star(PS‐PEO‐PCL) terpolymers were obtained. The target terpolymers and the intermediates were well characterized by ¹H‐NMR, MALDI‐TOF MS, FTIR, and SEC. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1136–1150, 2008     

Anion Receptors Containing ‐NH Binding Sites: Hydrogen‐Bond Formation or Neat Proton Transfer?

When the amide‐containing receptor 1 ⁺ is in a solution of dimethyl sulfoxide (DMSO) in the presence of basic anions (CH₃COO^?, F^?, H₂PO₄^?), it undergoes deprotonation of the ‐NH fragment to give the corresponding zwitterion, which can be isolated as a crystalline solid. In the presence of less basic anions (Cl^?, Br^?, NO₃^?), 1 ⁺ establishes true hydrogen‐bond interactions of decreasing intensity. The less acidic receptor 2 ⁺ undergoes neat proton transfer with only the more basic anions CH₃COO^? and F^?, and establishes hydrogen‐bond interactions with H₂PO₄^?. An empirical criterion for discerning neutralisation and hydrogen bonding, based on UV/Vis and ¹H NMR spectra, is proposed.     

Vibrational analysis of l-alanine and deuterated analogs

Raman spectra of the polycrystalline l-alanine analogs CH₃CH(NH⁺₃)COO^?, CH₃CH(ND⁺₃)-COO^?, CD₃CD(NH⁺₃)COO^?, and CD₃CD(ND⁺₃)COO^? have been obtained. A normal coordinate analysis is carried out based on the experimental frequencies of the four isotopic analogs and a 34 parameter valence-type force field defined in terms of local symmetry coordinates. The final refinement, in which five stretching force constants are constrained to fixed values obtained from bond length data, results in an average error of 7 cm^?1 (0.9%) for the observed frequencies of the four isotopically substituted molecules. Band assignments are given in terms of the potential energy distribution for local symmetry coordinates. For non-deuterated l-alanine, the vibrations above 1420 cm^?1 and below 950 cm^?1 may be described as localized group vibrations. By contrast, the eight modes in the middle frequency range, viz. the three skeletal stretching, the COO^? symmetric stretching, one NH⁺₃ rocking, the symmetric CH₃ deformation, and the two methyne CH deformation vibrations, are very strongly coupled to one another. Some decoupling appears to take place in the perdeutero molecule, and all but five modes can be described as localized group vibrations.     

Polymerization and copolymerization of functionalized 2‐alkoxy‐1‐methylenecyclopropanes to form new polymers having alkoxy substituents

The polymers with functionalized alkoxy groups and with narrow molecular weight distribution (M_w/M_n < 1.12) are obtained from the living polymerization of 2‐alkoxy‐1‐methylenecyclopropanes using π‐allylpalladium complex, [(PhC₃H₄)Pd(μ‐Cl)]₂, as the initiator. The polymers with oligoethylene glycol groups in the alkoxy substituent are soluble in water, and hydroboration of the C?C double bond and ensuing addition of the OH groups to C?N bond of alkyl isocyanate produce the polymers with urethane pendant groups. The reaction decreases solubility of the polymer in water significantly. Di‐ and triblock copolymers of the 2‐alkoxy‐1‐methylenecyclopropanes are prepared by consecutive addition of the two or three 2‐alkoxy‐1‐methylenecyclopropane monomers to the Pd initiator. The polymers which contain both hydrophobic butoxy or tert‐butoxy group and hydrophilic oligoethylene glycol group dissolve in water and/or organic solvents, depending on the substituents. The ¹H NMR spectrum of poly( 1a ‐b‐ 1h ) (? (CH₂C(?CH₂)CHOBu)_n? (CH₂C(?CH₂)CH(OCH₂CH₂)₃OMe)_m? ) in D₂O solution exhibits peaks because of the butoxy and ?CH₂ hydrogen in decreased intensity, indicating that the polymer forms micelle particles containing the hydrophilic segments in their external parts. Aqueous solution of the polymer with a small amount of DPH (DPH = 1,6‐diphenyl‐1,3,5‐hexatriene) shows the absorbance due to DPH at concentration of the polymer higher than 5.82 × 10^?5 g mL^?1. Other block copolymers such as poly( 1b ‐b‐ 1h ) and poly( 1a ‐b‐ 1g ) also form the micelles that contain DPH in their core. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 959–972, 2009     

Electron Capture by the Thiyl Radical and Disulfide Bond: Ligand Effects on the Reduction Potential

The effect of non‐polar and polar ligands and of monovalent cations on the one‐electron reduction potential of the thiyl radical and the disulfide bond was evaluated. The reduction potentials E° for the CH₃S^.–n L/CH₃S^?–n L and CH₃SSCH₃–L/CH₃SSCH₃^.?–L redox couples were calculated at the B3LYP, M06‐2X and MP2 levels of theory, with n=1, 2 and L=CH₄, C₂H₄, H₂O, CH₃OH, NH₃, CH₃COOH, CH₃CONH₂, NH₄⁺, Na⁺, K⁺ and Li⁺. Non‐polar ligands decrease the E° value of the thiyl radical and disulfide bond, while neutral polar ligands favour electron uptake. Charged polar ligands and cations favour electron capture by the thiyl radical while disfavouring electron uptake by the disulfide bond. Thus, the same type of ligand can have a different effect on E° depending on the redox couple. Therefore, properties of an isolated ligand cannot uniquely determine E°. The ligand effects on E° are discussed in terms of the vertical electron affinity and reorganization energy, as well as molecular orbital theory. For a given redox couple, the ligand type influences the nature of the anion formed upon electron capture and the corresponding reorganization process towards the reduced geometry.     

Synthesis,characterization, and degradation of poly(ethylene‐b‐ε‐caprolactone) diblock copolymer

Poly(ethylene‐b‐ε‐caprolactone) (PE‐b‐PCL) diblock copolymers were synthesized by ring‐opening polymerization (ROP) of ε‐caprolactone (CL) with α‐hydroxyl‐ω‐methyl polyethylene (PE‐OH) as a macroinitiator and ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] as a catalyst. Polymerization was conducted in bulk (130–150°C) with high yield (87–97%). Block copolymers with different compositions were obtained and characterized by ¹H and ¹³C NMR, MALDI‐TOF, SAXS, and DSC. End‐group analysis by NMR and MALDI‐TOF indicates the formation of α‐hydroxyl‐ω‐methyl PE‐b‐PCL. The PE‐b‐PCL degradation was studied using thermogravimetric analysis (TGA) and alkaline hydrolysis. The PCL block was hydrolyzed by NaOH (4M), without any effect on the PE segment. Copyright © 2009 John Wiley & Sons, Ltd.