Alain Fradet

Structural analysis of alfa grass (Stipa tenacissima L.) lignin obtained by acetic acid/formic acid delignification.

Alfa grass lignin obtained by the acetic acid/formic acid/water CIMV pulping process was characterized by FTIR and (1)H, (13)C-(1)H 2D HSQC, and (31)P NMR spectroscopies. Lignin samples purified by further dissolution/precipitation or basic hydrolysis steps were also analyzed. The CIMV alfa lignin is a mixture of low molar mass compounds (M(n) = 1500 g/mol) of SGH type with β-O-4 ether bonds as the major interunit linkage. The crude lignin contains fatty acids and residual polysaccharides. It also contains large amounts of acetate and hydroxycinnamates, mostly in the γ-position of β-O-4 interunit linkages. Although partial acetylation induced by the process cannot be excluded, the absence of aromatic acetates and acetylated polysaccharides in crude lignin demonstrates the mildness of the process. By combining smooth alkaline hydrolysis and dissolution/precipitation steps to the CIMV pulping, it is possible to produce a purified lignin with a composition and a structure quite analogous to that of the native polymer in the plant.

Poly(phenylene sulfide)/liquid crystalline polymer blends: 1. Non-isothermal crystallization kinetics

Abstract The non-isothermal crystallization behaviour of poly(phenylene sulfide) (PPS) in blends with thermotropic liquid crystalline polymer (TLCP) was studied by means of differential scanning calorimetry. The TLCP chosen for the investigation was poly(oxybenzoate-co-ethylene terephthalate). It was observed that the Ozawa equation is valid not only for neat PPS, but also for the blends. The PPS crystallization temperature was found to increase markedly upon addition of the TLCP. A notable reduction in Avrami exponents for the PPS/LCP blend systems suggests that the nucleated process leads to rod-shaped growth with thermal nucleation. The cooling crystallization function, which represents the rate of non-isothermal crystallization, was found to decrease with decreasing temperature and/or increase in LCP content. It has been concluded that the non-isothermal crystallization of PPS is strongly accelerated by the presence of TLCP.

Kinetics and mechanisms of polyesterifications

In this article we critically review most of the literature concerning non-catalyzed, proton-catalyzed and metal-catalyzed polyesterifications. Kinetic data relate both to model esterifications and polyesterifications. Using our own results we analyze the experimental studies, kinetic results and mechanisms which have been reported until now. In the case of Ti(O Bu)4-catalyzed reactions we show that most results were obtained under experimental conditions which modify the nature of the catalyst. In fact, the true nature of active sites in the case of metal catalysts remains largely unknown.

In situ compatibilisation of poly(phenylene sulphide)/wholly aromatic thermotropic liquid crystalline polymer blends by reactive extrusion : Morphology, thermal and mechanical properties

Abstract Compatibilisation of immiscible poly(phenylene sulphide) (PPS)/wholly aromatic thermotropic liquid crystalline polymer (TLCP) blends is reported. In situ compatibilised PPS/TLCP blends were prepared in a twin-screw extruder by reactive blending of PPS and TLCP in presence of dicarboxyl-terminated poly(phenylene sulphide) (DCTPPS). The block copolymer formed during reactive blending, by transesterification reaction between carboxyl groups of DCTPPS and ester linkages of TLCP, is tested for its role as the compatibiliser by studying the morphology, mechanical and thermal properties of the compatibilised PPS/TLCP blends over a wide range of composition. The heat of melting ( Δ H m ), crystallisation temperature ( T c ) and heat of crystallisation ( Δ H c ) of PPS phase are observed to decrease marginally as a result of improvement in the interfacial adhesion between the two phases on compatibilisation. The tensile properties and impact strength of PPS/TLCP blends are seen to improved on compatibilisation. This observation is further supported by morphological features of the blend.

Influence of Brønsted acid ionic liquid structure on hydroxyacid polyesterification

Bronsted acid ionic liquids (BAILs) based on the 4-(3′-butyl-1′-imidazolio)-1-butanesulfonic acid cation were found to be very efficient polyesterification solvents and catalysts. Only 5–30 min at 90–110 °C was required to obtain high molar mass poly(12-hydroxydodecanoic acid) (Mw up to 40000 g mol−1). The polyesterification was faster in BAILs with the bis(trifluoromethylsulfonyl)imidide anion (Tf2N), but small amounts of ethers and double bonds arising from side reactions were detected in the final polymer. On the other hand, no side reactions took place in the BAIL with the hydrogen sulfate anion, except for the formation of a sulfonate ester intermediate that can further react with carboxylic acid groups to yield the expected ester. This intermediate, not observed in Tf2N-based BAILs, might be involved in the protection of hydroxy end groups from etherification side reactions in HSO4−-based BAILs. To explain the different behaviors of these BAILs, and since the acidity of H2SO4 is much higher than that of Tf2NH, it is suggested that the structure of these BAILs could be different: alkylsulfonic acid-substituted imidazolium for the former, while the latter could be just a mixture of imidazolium–sulfonate zwitterion and Tf2NH. The influence of reaction temperature, water elimination method and BAIL concentration on polyesterification are also discussed.

Purification, structural characterization, and modification of organosolv wheat straw lignin.

Biolignin, a wheat straw lignin produced by acetic acid/formic acid/water hydrolysis, was characterized by (31)P and (13)C-(1)H 2D NMR spectroscopy and by size-exclusion chromatography. Biolignin is a mixture of low molar mass compounds (Mn = 1660 g/mol) made up of S, G, and H units and of coumaric and ferulic acid units. β-5 and β-O-4 interunit linkages are partially acylated in the γ-position by acetate and p-coumarate groups. Deacylated samples with a low content of contaminants were obtained by combining alkaline hydrolysis and solvent extraction. The high phenolic OH content found by (31)P NMR reflects the presence of condensed aromatic units, such as 5-5 units. Reaction of purified lignin with ethanol and ethane-1,2-diol yielded esterified lignins much more soluble than Biolignin in common organic solvents. During this reaction, the secondary OH of β-O-4 linkages was simultaneously etherified. Phenol hydroxyethylation by 2-chloroethanol yielded samples containing only aliphatic hydroxyl groups.

Study of bulk chain-coupling reactions

SummaryBlock copolymers containing polyester and polyamide blocks have been prepared by the bulk reaction of the corresponding carboxy-terminated polymers with 2,2′-bis(2-oxazoline) or 2,2′-bis(5,6-dihydro-(4H)-1,3-oxazine) as chain-coupling reagents (CC). A two-step reaction has been used, involving (i) the reaction of polyamide with CC excess, and (ii) the addition of polyester, leading to a random distribution of blocks in the final block-copolymer. 1H and 13C NMR studies show that the coupling reaction takes place in the expected way. The stability of the resulting polymers is higher than that of the starting oligomers, and DSC indicates a phase separation between polyester and polyamide phases.

Determination of the degree of randomness in condensation copolymers containing both symmetrical and unsymmetrical monomer units: a theoretical study

Abstract Expressions for the degree of randomness, B, and for the number- and weight-average block lengths of condensation copolymers containing both symmetrical (AA + BB) and unsymmetrical (AB) monomer units are established through an approach based on functional group probabilities. Several parameters introduced in literature to characterize randomness in AA + BB condensation copolymers are also calculated using this approach and compared to B, showing that they are simple linear or rational functions of B. A method for calculating functional group probabilities from the dyad and triad number-fractions determined by NMR spectroscopy is described for poly(ethylene terephthalate)-poly(ε-caprolactone) copolyesters. This method obviously applies to any AA + BB + AB polycondensation and is easily generalizable to other types of condensation copolymers.

Investigation of anisotropic epoxy–amine thermosets synthesised in a magnetic field

Bis{4‐[2‐(2,3‐epoxypropyl)ethoxy]benzoate}‐1,4‐phenylene and bis[4‐(2,3‐epoxypropoxy)benzoate]‐methyl‐1,4‐phenylene liquid crystalline diepoxy monomers were crosslinked with various diamines in a magnetic field. X‐ray scattering was used for mesophase identification and to determine the nematic order parameter of the resulting thermosets, which were cured under various temperature and magnetic field strength conditions. All thermosets exhibited nematic or smectic A (SmA) mesophases. The thermosets obtained from aliphatic diamines exhibited a very low degree of orientation. This phenomenon was assigned to their high reactivity, inducing a very fast crosslinking reaction that prevents the alignment of the mesogens. On the other hand, very high degrees of orientation along the magnetic field axis were observed for the SmA thermosets. In this case, the smectic period was smaller than the length of the epoxy monomer unit, which might be due to a staggered packing of the mesogenic cores. Negative longitudinal thermal expansion coefficients were measured below and above the glass transition temperature for the materials cured in a magnetic field.

Bis[4-monosubstituted-5(4H)oxazolinones] as coupling agents for block copolymer synthesis: Reaction with amine-terminated oligomers and with hydroxy-terminated/amine-terminated oligomer mixtures

Block copolymers were prepared by the bulk reaction of mixtures of amine-terminated aliphatic polyamides and polyethers with bis[4-monosubstituted 5(4H)-oxazolinones] as the coupling agents. The simultaneous chain-coupling reaction of amine-terminated polyethers and hydroxy-terminated polyesters with these coupling agents also was investigated. As indicated by NMR and size exclusion chromatography studies, block copolymers of Mn ≥ 10,000 were obtained without side reactions in a much shorter reaction time than required when the conventional reaction was used between oligomers bearing mutually reactive end-groups. The block copolymers behaved as thermoplastic elastomers. Their thermal and thermomechanical properties were evaluated by differential scanning calorimetry and dynamic mechanical thermal analysis and compared to the block copolymers synthesized in the conventional way. When low molar mass oligomers were used (Mn ≤ 1000), copolymers of low crystallinity or amorphous copolymers were obtained. This was assigned to the disruption of chain regularity induced by the presence of the chain-coupling-agent moieties. However, properties comparable to those of copolymers obtained by using the conventional method were obtained by reacting oligomers of Mn ≥ 2000.