Marc J.M. Abadie

Superabsorbant hydrogels based on xanthan and poly(vinyl alcohol): 1. The study of the swelling properties

The swelling properties of some superabsorbant composite hydrogels, based on xanthan and poly(vinyl alcohol) and crosslinked with epichlorohydrin, were studied. The maximum swelling degree of the hydrogels and the swelling rate constant were determined as a function of the hydrogels composition (the % of poly(vinyl alcohol) in the polymer mixture and the amount of crosslinking agent), the crosslinking reaction conditions (the time and the temperature of the crosslinking reaction), and the composition of the swelling solutions (the glycerin/water ratio and the concentration of the electrolyte).

An in vivo recording of variations in oral temperature during meals: a pilot study.

Thermocycling is often used in the in vitro evaluation of marginal leakage of dental restorations. The in vivo temperatures occurring during meals were recorded at different surfaces of restored teeth, to compare the variations in temperature with laboratory thermocycling. Temperatures were recorded with thermocouples at three different sites: (1) on the facial surface of a silver amalgam restoration, (2) at the base of a silver amalgam restoration and (3) within the root canal. The maximal temperature differences between upper and lower extremes were 29.6 degrees C at the base of a coronal restoration, 27.1 degrees C at the facial surface, and 11.8 degrees C within the root canal. A practical regimen for these experiments is suggested in the light of these ranges because many thermocycling regimens in in vitro studies appear extreme or unrealistic.

Proton-Conducting Polymers and Membranes Carrying Phosphonic Acid Groups

The results of the research of novel proton-conducting membranes carrying phosphonic acid groups have been analyzed and summarized with respect to their application in fuel cells. General approaches to the preparation of heterochain and heterocyclic polymers carrying phosphonic acid groups have been considered, including polycondensation of phosphonic acid functionalized monomers and phosphorylation of existing polymers. The bibliography includes 85 references.

Photopolymerization of glycidyl acrylate and glycidyl methacrylate investigated by differential photocalorimetry and FT-I.R.

Abstract The kinetics of photopolymerization of glycidyl acrylate (GA) and glycidyl methacrylate (GMA) sensitized by radical and cationic initiators have been studied using a combination of photodifferential scanning calorimetry (PDSC) and Fourier Transform i.r. spectroscopy (FT-i.r.). PDSC analysis shows that GA has much higher reactivity than GMA when a typical radical photoinitiator, 2,2-dimethoxy-2-phenylacetophenone (DMPA), was used. No great difference in rate constants and activation energies between the two monomers, except the higher conversion of GA, was found for the cationic polymerization initiated by sulphonium salts. The results of FT-i.r. show that both double bond and epoxy ring are polymerized at the same time. For both radical and cationic initiating systems, photopolymerization kinetics are also studied as a function of initiator concentration.

New catalysts for linear polydicyclopentadiene synthesis

Abstract The ring-opening polymerization of dicyclopentadiene (DCPD) may occur in two ways: in the first way the reaction occurs by opening of the norbornene ring, in the second one both rings, norbornene and cyclopentene are involved. The polymerization of DCPD via opening of norbornene moiety implies the utilization of very selective catalytic systems. In our work, several new catalytic systems for synthesis of linear polydicyclopentadiene, derived from WCl 6 and WOCl 4 and organosilicon compounds have been employed. The microstructure of the linear polydicyclopentadiene (prepared from endo -DCPD) was evaluated from IR, and 13 C -NMR spectroscopy, showing that the polymer has prevailingly “ cis ” double bond configuration. The thermal behavior has been followed by differential scanning calorimetry. The linear polydicyclopentadiene obtained under these conditions has a glass-transition temperature of 53°C.

Synthesis and photocrosslinking of benzyl acrylate substituted polydimethylsiloxanes

This article deals with the synthesis of polydimethylsiloxanes (PDMSs) substituted with chain or end benzyl acrylate groups by the hydrosilation of appropriate hydro-siloxanes, followed by phase transfer catalysed reaction of chloromethylated aromatic groups with the sodium salt of acrylic acid. Differential scanning photocalorimetry (DPC) was used to study the crosslinking behaviour of the mentioned functional PDMSs in the presence of different photoinitiators. The reaction rate, the final conversion and the inhibition period characterizing the crosslinking were found to be dependent on reaction atmosphere, light intensity, nature and concentration of photoinitiator and on polymer functional groups content.

Study of crosslinking AMS/DGEBA system by FTIR

Fourier transform infrared spectroscopy (FTIR) was used to follow the curing of the diglycidylether of bisphenol A (DGEBA) typical epoxide resin by poly(styrene-alt-maleic anhydride) (AMS), the reaction being accelerated by triethylamine (TEA) in the presence of methanol. The study was done in an isothermal mode for four temperatures: 85, 82, 80, and 75°C. We followed, for each temperature, the variation of the area of the epoxy band (916 cm−1) versus time. After 200 min of reaction, the degree of conversion of epoxy is 0.5 at 85°C. A postcure at 100°C during 96 h allows one to reach a total conversion of epoxy. The reaction mechanism involves three steps to form the tridimensional network.

An evaluation of the bactericidal effect of the Nd: YAP laser

The aim of this in vitro study was to compare the efficacy of a classical irrigant with that of a laser in disinfecting a contaminated root canal. Thirty canals of extracted single-root teeth were prepared with files to size #20. The teeth were sterilized with Germispad (Spad, France) for 30 min and then inoculated with Streptococcus mitis ATCC 33399. By randomization, the teeth were divided into six groups of five teeth each. In the first group, teeth were neither inoculated nor prepared. This was the sterility control group (1). In the second group (2) teeth were inoculated without any preparation: as positive controls. The third group was inoculated and then hand-instrumented with files to size #30 with 5.25% NaOCl as irrigant. This was the hand instrumentation group. The other groups were prepared with hand instrumentation with files to size #30, using sterile water as an irrigant, and the canal was then lased with different frequencies as follows: group 4, frequency of 5 Hz and power of 260 mJ; group 5, frequency of 10 Hz and power of 310 mJ; and group 6, frequency of 30 Hz and power of 300 mJ. After experimentation, the residual colonies were counted. The results indicated that (i) the treatment with NaOCl and manual instrumentation effectively inhibited the growth of Streptococcus mitis ATCC 33399; and (ii) the antibacterial effect of the Nd:YAP laser depended on the frequency. Only a frequency of 30 Hz of the Nd:YAP laser inhibited the growth of Streptococcus mitis ATCC 333999.

Study of the Nd: YAP laser. Effect on canal cleanliness

The aim of this study was to evaluate the canal cleanliness achieved by five different preparation techniques, including use of the laser. By randomization, the palatal roots of 50 maxillary molars were assigned to one of five groups. During all preparations, a sodium hypochlorite irrigant was used. The following techniques were studied: (A) manual instrumentation (serial preparation), (B) laser preparation (Nd:YAP laser), (C) manual preparation with laser as adjunct, (D) manual preparation with a subsonic device as adjunct (MM 3000 with shapers), and (E) manual instrumentation with a subsonic device and laser as adjuncts (MM 3000 with shapers, Nd:YAP laser). The canal wall surfaces were examined under a scanning electron microscope at all levels with a new method using grid incrustation on the microscope screen. Techniques A and C differed from each other only by the size of the debris particles, which were smaller for the C preparation. For laser preparation (B) there was little increase in canal diameter increase, and a substantial amount of debris was present. The differences between techniques A, C, and D were not significant. The use of the subsonic device and laser together as adjuncts (E) showed the cleanest preparation with very little debris, opened tubules, and very small particle size. This result suggests that the laser has a potential in ensuring optimal canal cleanliness.

Étude par DSC de la reticulation de systèmes DGEBA/polyacides

Abstract Crosslinking reactions between epoxy and carboxylic groups in the presence of an activator (triethylamine, TEA) have been studied. The epoxy compound was diglycidylether Bisphenol A (DGEBA) and hardeners were either random poly(styrene-co-acrylic) copolymers, polyacrylic acid (PAA) or an alternating maleic anhydride/styrene copolymer. Reactions were followed using a DSC technique in a dynamic mode between 25 and 250 °C at different heating rates (2.5, 5, 7.5, 10, 15 and 20 °C/min). Crosslinking reactions followed second order kinetics. Arrhenius parameters were determined.