Polyester from dimethylketene and acetaldehyde: Direct copolymerization and β‐lactone ring‐opening polymerization

Two ways to obtain aliphatic polyesters (PEs) from dimethylketene and acetaldehyde were investigated. On the one hand, a direct anionic copolymerization was carried out in toluene at ?60 °C. The resulting polymer was mainly composed of PE units. On the other hand, a two‐step process involving the synthesis of 3,3,4‐trimethyl‐2‐oxetanone by [2+2] cycloaddition, followed by its ring‐opening polymerization, with various initiators and solvents, led to the expected PE. Molecular weights up to 9000 g mol^?1 (measured by nuclear magnetic resonance (NMR)), with narrow polydispersity around 1.2, were obtained. These polymers were found stable up to 274 °C under nitrogen and a broad and complex endothermic peak attributed to crystallinity was observed near 139 °C by differential scanning calorimetry (DSC). The crystallinity, measured by X‐ray diffraction, was close to 0.45. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Palladium-catalyzed alpha-vinylation of carbonyl compounds

A mild, general, catalytic system for the alpha-vinylation of carbonyl compounds has been developed. By employing [Pd(P(t)Bu(3))Br](2) as catalyst and LHMDS as base, vinyl bromides, vinyl triflates, and vinyl tosylates couple with 3-methyloxindole in satisfactory yields. The same catalytic system is extended to the alpha-vinylation of ketones and esters.     

Photocrosslinking of a novel α,ω‐unsaturated copolyamide: mass spectrometric study on model compounds with benzophenone as photoinitiator

The aim of this work was to understand the reactions involved in the photocrosslinking processes of a α,ω‐unsaturated copolyamide foreseen as a new UV‐curable powder coating. The crosslinking reaction was photoinitiated with benzophenone. In this paper, the photochemical reaction between benzophenone and several model compounds was investigated. The model compounds contained functional groups which could be present in copolyamide. The products resulting from UV curing were identified using a combination of high‐resolution mass spectrometry and MSⁿ experiments. The characterization of the products allowed localization of the hydrogen abstraction by the type II photoinitiator during UV curing and, consequently, the determination of the reactive sites of the unsaturated polyamide chain which were involved in the photochemical reaction. Copyright © 2009 John Wiley & Sons, Ltd.     

Transfer constants relative to the cationic polymerization of 1- and 2-vinyl naphthalenes and 3-vinyl phenanthrene

Transfer and termination constants have been determined for the cationic polymerization of 1- and 2-vinyl naphthalenes and 3-vinyl phenanthrene. They have been compared with the values obtained for styrene under the same experimental conditions. Experimental values are in good agreement with theoretical determinations.     

Thermal Characterization of Polyurethane Acrylate Resins

Polyurethane acrylate resins cured by two different ways, a thermal way and a photochemical way, are investigated by means of differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). Even if both curing methods lead to the same material from a chemical point of view, we show that important differences exist between the thermocured resin and the photocured resin in terms of molecular relaxation behaviour.This revised version was published online in November 2005 with corrections to the Cover Date.     

The ionic polymerizations of methyl glyoxylate

Methyl glyoxylate has been polymerized in CH₂Cl₂ solution either cationically or anionically to give the corresponding polyacetal. Thermodynamic and kinetic results of the polymerizations initiated by CF₃SO₃H, BF₃OEt₂, and NEt₃ are reported here. Monomer conversion was followed by UV and active centers concentrations were determined through phosphorus end-capping. A ceiling temperature of 26°C was observed for M_eq=l mol.H (T_c = 109°C for bulk) with ΔH°=−29.5 kJ.mo⁻¹ and ΔS°=−99 J.mo⁻¹.K⁻¹. Both initiations were found instantaneous and quantitative, and no termination was observable within the time scale of the reaction (second to hour). Cationic propagation appears to take place essentially on free ions (k_p+ ≈ 60 l.moH.s⁻¹ at −20°C) in equilibrium with a larger amount (K_d ≈ 6.7.10⁻⁶ mol.⁻¹) of much less reactive ion-pairs (k_p± ≈ 0.16 ± 0.03 1.mo⁻¹.s⁻¹). A stopped-flow device was used to follow the much more rapid anionic polymerization (k_p,app ≈ 8 ± 2.10³ 1.mo⁻¹.s⁻¹ at −20°C).     

Enzymatic release of drug from polymer matrices: Diffusion and activity of lysozyme within ophtalmic hydrogels

Diffusional behaviour of lysozyme into a high-hydrated hydrogel, used as precursor of contact lenses, is reported. The gel is a swollen statistical copolymer of methyl methacrylate and N-vinyl-2-pyrrolidone (≁ 70% water), and the penetration of the enzyme, labeled with 8-anilinonaphthalene-1-sulfonate, was followed by fluorescence microscopy. Mathematical analysis of the profiles led to the diffusion parameters (D ≁ (2–6) · 10⁻⁸ cm² · s⁻¹). It is shown that the enzymatic activity persists when the lysozyme and the cleavable substrate are trapped in the matrix.     

Enthalpy relaxation in polymethyl(α-n-alkyl)acrylates: Effect of length of alkyl chain

In this work, we have investigated by DSC the structural relaxation of amorphous polymethyl(α-n-alkyl)acrylates in which it is possible to change the length of the alkyl chain. We have evaluated the Narayanaswamy parameter, x, which controls the relative contribution of temperature and of structure to the relaxation time, the apparent activation energy, Δh*, and the nonexponentiality parameter, β, of the stretched exponential response function. The results suggest that x increases while Δh* decreases and β remains constant as the length of the side chain increases. This allows us to comment on the effect of chemical modification on the relaxation kinetics. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 583–593, 1998