Unexpected end‐groups of poly(acrylic acid) prepared by RAFT polymerization

Low‐molecular‐weight poly(acrylic acid) (PAA) was synthesized by reversible addition fragmentation chain transfer polymerization with a trithiocarbonate as chain‐transfer agent (CTA). With a combination of NMR spectroscopy and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, the PAA end‐groups of the polymer were analyzed before and after neutralization by sodium hydroxide. The polymer prior to neutralization is made up of the expected trithiocarbonate chain‐ends and of the H‐terminated chains issued from a reaction of transfer to solvent. After neutralization, the trithiocarbonates are transformed into thiols, disulfides, thiolactones, and additional H‐terminated chains. By quantifying the different end‐groups, it was possible to demonstrate that fragmentation is the rate limiting step in the transfer reaction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5439–5462, 2004     

Ester interchange reactions catalyzed by tin compounds in reactive processing: NMR contribution via reactions with model compounds

Interchange reactions involving esters were used in reactive processing with a view to obtaining polymer blends with stabilized morphology. Dibutyltinoxide (DBTO) appeared to be an excellent catalyst for these reactions. In fact, it was shown that the true catalytic entity is a dimeric alkoxy, acyloxy distannoxane entity formed in situ, during processing, by the reaction of the DBTO with the polymer ester groups. This compound was first obtained with model esters and characterized by multinuclear NMR analysis (¹H, ¹³C, ¹¹⁹Sn). The catalytic efficiency of the in situ polymeric distannoxane was compared with other added parent distannoxanes. Later on – still with model compounds – ligand exchanges at the tin sites were investigated and it was shown that these exchanges are not essential to the catalyst activity, but when they take place it increases the catalytic efficiency. Then, this type of catalysis was successfully used for interchange reactions in reactive extrusion of different polymer blends, some applications are briefly presented. To cite this article: M.-F. Llauro and A. Michel, C. R. Chimie 9 (2006).     

Synergistic mechanisms of β-diketone derivatives and zinc-calcium soaps in PVC stabilisation

It has been possible to explain the mechanisms of stabilisation and of the synergistic effects of the β-diketone derivatives claimed in a patent as new stabilisers for improving the efficiency of those recipes based upon zinc and calcium soaps in the prevention of the initial discoloration of poly(vinyl chloride).Using chlorohexene as a model compound for allylic chloride structures and benzoylacetone as a model compound for enolised β-diketone derivatives, it has been shown that the benzoylacetone can substitute allylic chlorine atoms through a C-alkylation reaction which takes place only in the presence of ZnCl₂ as catalyst. This reaction drastically changes the percentage of the enol and causes the appearance of two bands at 1720 cm^?1 and 1680 cm^?1 in the infra-red spectrum due to the ketonic structures During the processing of the PVC on a rolling mill at 180°C in the presence of zinc and calcium stearates and benzoylacetone there is grafting of the ketone derivative through a C-alkylation reaction. There is a closed parallelism between the influence of the benzoylacetone on the dehydrochlorination of the chlorohexene and on the accumulation of chloride ions in the polymer matrix in the presence of zinc and calcium stearate. The synergistic effect of the benzoylacetone in the prevention of the initial discoloration is related to the substitution reaction through a C-alkylation which takes place only in the presence of zinc stearate which generates ZnCl₂ which, in turn, acts as a catalyst for both the C-alkylation and dehydrochlorination.     

Etude des copolymeres (ethylene-hexene-1) par resonance magnetique nucleaire du proton et du carbone 13

Ethylene 1-hexene copolymers obtained by catalytic polymerization have been examined by ¹H and ¹³C NMR. Copolymer compositions have been determined by ¹H NMR and i.r. and the sequence distributions for 1-hexene by ¹³C NMR. Variations of the copolymer microstructure have been related to the experimental conditions for copolymerization.     

Microstructure of vinyl acetate–butyl acrylate copolymers studied by 13C-NMR spectroscopy: Influence of emulsion polymerization process

The compositions and sequence distributions of vinyl acetate–butyl acrylate copolymers obtained with batch and semicontinuous emulsion polymerizations have been studied by ¹H and ¹³C NMR. The batch process gives heterogeneous copolymers while with the semicontinuous one the sequence distribution is statistical. These differences in sequence distributions have been related to the physical properties of the copolymers.     

Chloromethylation of polyphenylsiloxane prepolymers by silylation

Silylation of nonequilibrated phenyl-T-siloxane polycondensates by dimethylchloromethylchlorosilane involves only a small part of the silanol groups present in these prepolymers. At room temperature, silylation and condensation of the silanol groups occur at the same time. This condensation can be either intermolecular only or both intermolecular and intramolecular, depending on the initial condensation state of the prepolymer. It seems that no condensation reactions take place when the reaction is carried out with reflux. In any case, and even with strongly reactive disilazanes, no more than 35% of the silanol groups are consumed. The results give some information about a polymer, the structure of which is (after all) rather badly known.     

Condensation du cyanoacetate d'éthyle sodé sur les sels d'iminoethers cycliques synthese directe de dérivés d'oxazepine-1,4 one-7

Sodium ethylcyanoacetate was found to react exclusively at the 2-position of trifluoromethanesulfonate 2-alkyl(aryl) 1,3-oxazolinium salts 2. In most cases, the reaction leads specifically to a new series of 5-alkyl(aryl) 6-cyano 2,3-dihydro 1,4-oxazepine 7-ones 3. This efficient one-step ring-enlargement process occurs at the oxazolidine stage. Structural parameters affecting the scope and limitations of this condensation are discussed.     

Interfacial microgels formed by oppositely charged polyelectrolytes and surfactants. 1. Influence of polyelectrolyte molecular weight

The synergistic adsorption and complexation of polystyrene sulfonate, PSS (a highly charged anionic polyelectrolyte), and dodecyltrimethylammonium bromide, C12TAB (a cationic surfactant), at the air-water interface can lead to interfacial gels that strongly influence foam-film drainage and stability. The formation and characteristics of these gels have been studied as a function of PSS molecular weight by combining surface tension, ellipsometry, and foam-film drainage experiments. Simultaneously the solution electromotive force has been measured to track the polymer-surfactant interactions in the bulk solution. It has been found that there is a critical molecular weight for surface gelation as well as for bulk precipitation and aggregation. Furthermore, we show that for the lowest molecular weights, PSS adsorbs with C12TAB in compact layers at the air-water interface. In particular, for mixtures of C12TAB with the monomer compound of the PSS repeat unit (e.g. Mw = 208), interfacial complexation is found to be similar to that of catanionic mixtures (mixtures of surfactants of opposite charge).     

Determination of Compositional,Configurational Sequences in High Conversion Methyl Methacrylate-Methacrylic Acid Emulsion Copolymers Using a Rapid and Selective Counting Procedure

High conversion methyl methacrylate (MMA)-methacrylic acid (MA) copolymers prepared by two different emulsion polymerization processes were characterized in terms of composition and sequence distribution by ¹H- and ¹³C-NMR, taking into account the conversion effect. A rapid and selective counting procedure for calculating the compositional configurational pentads (512 values) in these copolymers is described. From this counting procedure and using the Klesper's assignment of the 18 peaks observed in the ¹³C-NMR carbonyl resonance spectrum of the copolymers, a relatively good agreement was found between the calculated and experimental fractions of each peak intensity. Moreover, this study allows differences in compositional homogeneity to be characterized as a function of the nature of the emulsion polymerization process.     

Microstructure and properties of poly(vinyl alcohol-co-vinyl acetate)-g-ε-caprolactone

Microstructural studies of Poly(vinyl alcohol-co-vinyl acetate)-g-polycaprolactone (PVA-Ac)-g-(PCL) were realized principally using NMR. Initial PVA-Ac has a rather blocky structure with an average sequence length of PVA units equal to 12.5. During the synthesis of the studied (PVA-Ac)-g-(PCL), alcoholysis and transesterification reactions led to PCL grafts with acetate end groups. These reactions typically concern 2-5.5% of the total acetate groups. The influence of the local tacticity on the alcohol triad reactivity was evidenced and explained the incomplete functionalization of the PVA-Ac hydroxyl groups. Alcoholysis reactions were also evidenced but with a very low rate in the tested conditions. Caprolactone homopolymerization was not observed. Other properties of the final synthesized copolymers were also presented. Crystallinity totally disappeared in the (PVA-Ac)-g-(PCL). The glass transition temperature was perfectly adjustable by the Fox law without significant modification of the viscoelastic properties characterized by dynamic rheology.