Irregular cyclization reactions in titanocenes bearing pendant double bonds

Reduction of methyl-substituted titanocene dichlorides bearing pendant double bonds [TiCl₂{η⁵-C₅Me₄(CH₂CMeCH₂)}₂] (1) and [TiCl₂{η⁵-C₅Me₄(SiMe₂(CH₂)₂CHCH₂)}₂] (2) with magnesium yielded diamagnetic Ti(IV) compound [Ti{η¹:η¹:η⁵-C₅Me₃(CH₂)(CH₂CH(Me)CH₂)}{η⁵-C₅Me₄(CH₂C(Me)CH₂)}] (4) and paramagnetic Ti(III) compound [Ti{η⁵-C₅Me₄(SiMe₂CH₂CHCHMe)}(μ-η³,η¹:η⁵,η¹(Ti:Mg){C₅Me₃(CH₂)(SiMe₂CHCHCMe)})Mg(OC₄H₈)₂] (6), respectively. The reluctance of titanocene intermediates to undergo intramolecular cyclization to cyclopentadienyl-ring-tethered titanacycles (as typically observed) can be explained by a shortness of the 2-methylallyl group and steric hindrance of its double bond in the former case and, in the latter case, by an attack of magnesium on the titanocene intermediate, faster than cyclization reactions. The crystal structures of 4 and 6 were determined by single-crystal X-ray diffraction.     

Miscibility of methacrylic polymers with different pendant groups

Miscibility is not always common in blends of homologous polymers that differ in structure but possess the same functional groups. In this study, two methacrylate polymers, which differ by a methylene unit, were found to be miscible in accordance with morphology and thermal transition criteria of polymer miscibility. Miscibility of the pair poly(phenyl methacrylate) and poly‐(benzyl methacrylate) is quite unusual. Interactions between carbonyl units and phenyl rings of these two polymers are discussed. FT‐IR results indicate an intimate mixing state between these two polymers leading to mutual influence in the absorbance wavenumbers for C=O, ether groups and, possibly, phenyl rings.     

Synthesis of vinyl polymers with pendant phenoxazinyl group

Vinyl monomers bearing phenoxazine units, were synthesized: 2-vinyl-phenoxazine starting with phenoxazine in a five-step synthesis; 3-acrylamido- or 3-methacrylamido-phenoxazines with or without 10-PhCH₂ or 10-Me-substituent starting with o-benzylideneaminophenol or o-anisidine via 3-aminophenoxazines; and 3-(p-styrenesulfonamido)phenoxazines with or without 10-PhCH₂- or 10-Me-substituent, also via 3-aminophenoxazines. Polymerizations of these noval monomers proceeded smoothly, except those having no 10-substituent. Changes of the visible absorption spectrum of iodine in THF with addition of the polymers and oligomers thus prepared were considerable, with the appearance of new absorption peaks for polymers with 10-Me-substituent.     

Complexation behaviour of polymers with pendant cyclodextrin side groups

The influence of the chain conformation on the formation of polymeric supramolecular complexes as well as the influence of the complexation on the conformation of the polymer chain has been studied. The complexation of pyrene into the cavity of β-cyclodextrin (β-CD) was investigated in aqueous solutions of β-CD substituted poly(allylamine) (PAA) under variation of external parameters, i.e. temperature, pH, ionic strength and addition of urea. The observed changes of the complexation constant K for the formation of the 2:1 β-CD/pyrene complex can be explained by a change of the chain flexibility which leads to a variation of the mean distance between neighbouring β-CD-moieties along the polymer chain. The intra-chain association of the decyl group with β-CD in PAA with co-pendant decyl and β-CD is disrupted by the addition of 1-adamantanamine HCl resulting in a more extended structure of the polymer. The β-CD moiety in PAA-CD shows one order of magnitude greater affinity to 2-(p-toluidyl)naphthalene-6-sulfonate than the native β-CD and the affinity increases further by the presence of decyl side groups.     

Photoinitiators with double and triple bonds

In continuation of our research on new chromophores for photoinitiators (PIs) we investigated a series of double and triple bond containing PIs based on benzophenone (BP), thioxanthone, benzil (BZ), benzildimethylketal (BDK), and hydroxyalkylphenone. UV‐Vis spectroscopy revealed an absorption shifted up to 50 nm to the visible range of the spectrum. With steady state photolysis experiments, the rates of decomposition (R_d) were determined. Compared to the commercially available reference PIs the R_d of the new PIs were nearly identical. By quenching reactions with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO), α‐cleavage was identified for Type I initiators. Generally, all new compounds are suitable as PI especially for longer wavelengths. Nevertheless it has to be noted that the PI concentration has to be selected carefully to achieve optimum reactivity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 289–301, 2008     

Reactions of diazomethane with sulfonyl-activated double bonds

The cyclo-addition reaction of diazomethane with α,β-unsaturated sulfones is described. Divinyl sulfone and phenyl vinyl sulfone give 1- or 2-pyrazolines depending on the reaction conditions. cis- and trans-1,2-Bis(methylsulfonyl)ethene form pyrazolines, which on reaction with either triethylamine or excess of diazomethane lead to substituted pyrazoles.     

Chemiluminescence of hydrocarbon polymers

The thermal oxidation of some hydrecarbon polymers differing by their degree of branching was studied simultaneously by chemiluminescence and infrared spectrophotometry. In the case of isotactic polypropylene, measurements were made at various temperatures ranging from 140 to 180°C. The other polymers—ethylene–propylene copolymer, low and high density polyethylene—were studied only at 160°C. In all cases, the induction times of chemiluminescence coincide with those of carbonyl growth. The previously proposed mechanisms of light emission are not consistent with the kinetic data or with the structure effects on luminescence, which seems directly related with the presence of tertiary hydrogens. A hypothetical mechanism based on the β scission of tertiary alkoxyls is proposed.     

Synthesis and properties of carbon-chain polymers with pendant 1,3,4-oxadiazole rings

Carbon-chain polymers with 1,3,4-oxadiazole rings were prepared by radical polymerization and polymer-analogous transformations. The kinetic relationships of the polymerization of vinyl-1,3,4-oxadiazole monomers and some properties of the resulting polymers were studied. The thermodynamics of interaction of poly-2-vinyl-5-methyl-1,3,4-oxadiazole, a nonionic water-soluble polymer, with water was examined.     

Dielectric absorption in hydrocarbon polymers with non-polar additives

Polypropylene films containing various non-polar additives including CCl₄, tetramethylsilane and CS₂ (99.9 or 99.8%) exhibit weak dielectric absorption at the temperatures where molecular tumbling motions are expected on the relevant timescale. The absorption possibly corresponds to rotational jumps of up to 90° between inequivalent orientations of the additive molecules as has been suggested for ammonium in alums.     

Synthesis and photophysical properties of conjugated polymers with pendant 9,10-anthraquinone units

We have synthesized and investigated the photophysical properties of a series of electron-donor conjugated copolymers with pendant electron-acceptor units. The copolymers consist of diethynyl-1,4-phenylene, fluorene, or phenylene rings alternating with a phenylene unit bearing a pendant 9,10-anthraquinone moiety. The pendant donor-acceptor polymers were designed to have different optical pi-pi* band gaps, while the oxidation potential of the polymer backbone remains approximately constant in the series. The reduction potential of the donor-acceptor polymers is associated with the pendant acceptor units. This leads to the special situation that the electrochemical gap between oxidation and reduction potentials is constant, while the optical band gap decreases, going from PPP, via PPF, to PPE. This design is used to study the effect of the optical gap on the photoinduced electron-transfer reaction that occurs between the main chain electron donor and the pendant acceptor, while the same polymer architecture and energy of the charge separated state are maintained. Fluorescence and photoinduced absorption spectroscopy are used to study the electron transfer following photoexcitation in relation to solvent polarity and in thin solid films. For the fluorene-phenylene alternating copolymer, intramolecular photoinduced electron transfer occurs in the Marcus optimal region.     

Synthesis and characterization of styrenic polymers with pendant pyrazole groups. II

The synthesis of styrenic monomers that have pyrazolic or bipyrazolic pendant groups is described. Their homopolymerization and their copolymerization with maleic anhydride (MA) and N-(3-acetoxy propyl) maleimide is reported. The monomers were prepared from the Williamson reaction between 2-pyridine carbinol, hydroxy monopyrazole, hydroxy bipyrazole, and chloromethyl styrene. The homopolymerizations of such styrenic monomers were tried under different conditions, which led to low molecular weight polymers with a high polydispersity. However, alternating copolymers were obtained using maleic anhydride or N-(3-acetoxy propyl) maleimide as comonomers, as shown by ¹H-NMR, elemental analysis, and reactivity ratios r₁ and r₂. Furthermore, the hydrolysis of the acetate function of different copolymers was performed quantitatively. Unlike the acetoxy copolymers, such products do not have any glass transition temperature. Thermogravimetric investigations have shown that these copolymers exhibit good thermostability. © 1994 John Wiley & Sons, Inc.     

A Schiff-base porphyrin complex with double intramolecular hydrogen bonds

We have designed a porphyrin with a Schiff-base substituent as a model to study intramolecular hydrogen-bonding. The corresponding complex [Zn(SATPP)(CH₃OH)] has been synthesized and characterized by X-ray crystallography, ¹H NMR, and UV-Vis spectroscopy. The structure shows that there are three phenyl groups and one salicylideneaminophenyl group at the meso positions of the porphyrin, and the phenol oxygen is involved in double hydrogen bonds, one within the salicylideneaminophenyl and the other between coordinated methanol and phenol oxygen. ¹H NMR spectra suggest that the binding of methanol to zinc is an equilibrium process in solution and the equilibrium constant has been determined by UV-Vis measurements. The intramolecular hydrogen bond stabilizes the structure, and the binding affinity increases 10 times over the corresponding TPP (TPP, dianion of meso-5,10,15,20-tetraphenylporphyrin).     

Synthesis of functional polymers bearing pendant mono-and oligo-saccharide residues

The present paper focuses on (i) a new synthetic methodology to prepare vinyl ether-based synthetic glycoconjugates (glycopolymers) with well-controlled structure, and on (ii) the application of glycopolymers bearing modified disaccharide residue as thermotropic liquid crystalline (LC) materials. Two vinyl ethers (VEs) having pendant glucose residues with their hydroxyl functions protected by acetyl and isopropylidene groups, respectively, were found to undergo living cationic polymerization initiated by a HI/ZnI2-initiating system. Deprotection of the resultant monodisperse polymers led to water-soluble polymers bearing a pendant glucose residue. Sequential living block copolymerization of glucose-containing VE and alkyl VE, and subsequent deprotection afforded an amphiphilic block copolymer of well-controlled structure. Transmission electron microscopic observation of its cast thin film revealed microphase-separated surface morphologies that varied with varying segment composition ratio. A VE substituted with a heptadecanoated cellobiose pendant was independently prepared, and was cationically polymerized to give a thermotropic LC polymer. From X-ray analysis, the mesophase was assigned to a discotic columnar in type, in which each main chain, extended due to the steric repulsion between the neighboring bulky pendants, was surrounded by three discotic columns.