Nicolas Desilles

Gradient structure materials from homogeneous system induced by UV photopolymerization

Abstract This work deals with the synthesis of a gradient structure material from a homogeneous system of monomers. This new synthesis involved hydroxyethylmethacrylate, a hydroxytelechelic polybutadiene, and 4,4′-methylene-bis(cyclohexylisocyanate). These materials were made in two steps. The first one consisted in creating a photopolymerization gradient in methacrylic double bonds under UV exposure thanks to the decay of UV light intensity through the sample thickness. The second one involved a thermal crosslinking reaction leading to the formation of a polyurethane network in order to set the obtained gradient. Using FTIR and UV spectroscopies, the required experimental conditions to obtain and keep the gradient were investigated. Thus, these parameters enabled us to obtain a 20% hydroxyethylmethacrylate double bonds conversion gradient in the ultimate 5 mm thick material. Further DMA analysis well revealed a difference of structures between the two sides of the material.

Aliphatic polyketone obtained by cationic polymerization of ethylketene

For the first time, ethylketene, synthesized by thermolysis of butyric anhydride, was polymerized cationically in order to obtain a novel aliphatic polyketone. Initiated by Lewis acid initiator AlBr3, this polymerization was undertaken in different solvents and at −78 °C (top polymerization yield of 57% in toluene). 1H-13C HSQC NMR experiments clearly demonstrated the polyketonic microstructure. The thermal properties of this new polymer were analyzed by DSC, TGA and X-ray diffraction: with a glass transition temperature around 70 °C and an average crystallinity of 0.34, this polymer showed a starting degradation temperature near 210 °C.

Tandem mass spectrometry of low solubility polyamides.

The structural characterization of polyamides (PA) was achieved by tandem mass spectrometry (MS/MS) with a laser induced dissociation (LID) strategy. Because of interferences for precursor ions selection, two chemical modifications of the polymer end groups were proposed as derivatization strategies. The first approach, based on the addition of a trifluoroacetic acid (TFA) molecule, yields principally to complementary bn and yn product ions. This fragmentation types, analogous to those obtained with peptides or other PA, give only poor characterization of polymer end-groups [1]. A second approach, based on the addition of a basic diethylamine (DEA), permits to fix the charge and favorably direct the fragmentation. In this case, bn ions were not observed. The full characterization of ω end group structure was obtained, in addition to the expected yn and consecutive fragment ions.

Exploration of polyamide structure–property relationships by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

RATIONALE Polyamides (PA) are among the most used classes of polymers because of their attractive properties. Depending on the nature and proportion of the co-monomers used for their synthesis, they can exhibit a very large range of melting temperatures (Tm ). This study aims at the correlation of data from mass spectrometry (MS) with differential scanning calorimetry (DSC) and X-ray diffraction analyses to relate molecular structure to physical properties such as melting temperature, enthalpy change and crystallinity rate. METHODS Six different PA copolymers with molecular weights around 3500 g mol(-1) were synthesized with varying proportions of different co-monomers (amino-acid AB/di-amine AA/di-acid BB). Their melting temperature, enthalpy change and crystallinity rate were measured by DSC and X-ray diffraction. Their structural characterization was carried out by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Because of the poor solubility of PA, a solvent-free sample preparation strategy was used with 2,5-dihydroxybenzoic acid (2,5-DHB) as the matrix and sodium iodide as the cationizing agent. RESULTS The different proportions of the repeating unit types led to the formation of PA with melting temperatures ranging from 115°C to 185°C. The structural characterization of these samples by MALDI-TOF-MS revealed a collection of different ion distributions with different sequences of repeating units (AA, BB; AB/AA, BB and AB) in different proportions according to the mixture of monomers used in the synthesis. The relative intensities of these ion distributions were related to sample complexity and structure. They were correlated to DSC and X-ray results, to explain the observed physical properties. CONCLUSIONS The structural information obtained by MALDI-TOF-MS provided a better understanding of the variation of the PA melting temperature and established a structure-properties relationship. This work will allow future PA designs to be monitored.