C. Sanglar

Propargylic and Chromene Terminated Prepolymers. 3. Study of Homopolymerization and the Effect of the Chromene Content on Reaction Kinetics

We have chemically synthesized CTR (chromene terminated resin) prepolymers in order to more specifically study the homopolymerization reaction of chromene. Physicochemical data were used to show the value of working with dichromene prepolymers instead of propargylic monomers. In particular, the homopolymerization reaction is less exothermic than the thermally induced ring formation. So, when the homopolymerization reaction is predominant, the processability of the final thermoset material will be easier. Besides, the rate constant of the homopolymerization reaction is higher than that measured for dipropargylic monomers. This explains the interest in overcoming β stage formation which is the kinetically rate limiting step. On the other end, the presence of residual propargylic functions in dichromene prepolymers after synthesis has no considerable effect on reaction temperature or advancement of reaction.

Propargylic Terminated Prepolymers. 2. Molten State Mechanisms and Kinetics of Difunctional Systems

We have synthesized five dipropargylic compounds containing electron donor and acceptor substituents between the two phenyl groups. Based on physicochemical data obtained it is shown that heat-induced polymerization depends on the nature of the substituent. Thus, reaction kinetics are modified while molten state mechanisms involved remain identical (principal reaction: intramolecular ring formation; secondary reaction: formation of phenolic entities). The physicochemical techniques used to obtain these results were Fourier transform infrared spectroscopy (FT-IR) and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, correlated with chromatographic separation.

Propargylic- and Chromene-Terminated Prepolymers. 4. Influence of the Type of Catalyst on Reaction Mechanisms and Kinetics

The addition of catalyst to polymerize the propargylic function causes a decrease in the reaction onset temperature T 0. Depending on the nature of the catalyst we demonstrate different reaction mechanisms involving the formation of the chromene group (as in the case of non-catalysed systems), of the Sabourin dimer, or the cyclooctatetraene structure in the molten state. We thus show that the catalytic effect is more determinant towards the propargylic function than towards the chromene group.

Propargylic-Terminated Prepolymers. 5. Mechanistic and Kinetic Studies of the Polymerization Reaction of Compounds with an Imide Group meta to the Propargylic Function

We have synthesized two functionalized prepolymers with an imide group meta to the propargylic function in their central skeleton. Based on data obtained by a variety of solid and liquid state physicochemical techniques, we show that meta substitution modifies the reaction path and leads to the formation of two chromenes, α and β. In addition, the reaction kinetics and thermal stability of the final system are affected by the presence of an imide group in the structure of the propargylic prepolymer.

Phenolic resins (III) - Solid state structures and thermal properties of cross-linked phenolic resins

Non-destructive, solid state physicochemical techniques were used to analyze the structure of phenolic resins prepared with precise syntheses and thermal parameters. The results obtained with solid state 13C NMR (CP/MAS) and FTIR were analyzed and related to the thermal characteristics of the networks (DSC and TGA/FTIR). The data were correlated with parameters and conditions of syntheses of resols and of the initial prepolymers.

Phenolic resins - Characterizations and kinetic studies of different resols prepared with different catalysts and formaldehyde/phenol ratios (I)

The physicochemical and kinetic properties of resols prepared with different catalysts (NaOH, LiOH and Ba(OH)2) and variable formaldehyde/phenol ratios (2.5 £ R £ 3.5) were followed to determine their effects on the mechanisms and reaction products at a fixed pH and temperature. Kinetic monitoring and quantification of residual monomers were carried out by liquid chromatography coupled with mass spectrometry (LC/UV/MS), by 13C nuclear magnetic resonance (NMR) and by chemical assay for formaldehyde. Oligomer formation (n ≥ 2) was determined by LC/UV/MS, size exclusion chromatography (SEC) and 13C NMR. It was found that minor compounds form during syntheses (phenol methanol hemiacetals, hemiacetals of phenol and of oligomers…) and that the ratio R affects primarily the kinetics of formation of monomers and oligomers, in contrast to the catalysts that modify reaction mechanisms. The understanding of the structure of the resols was an important step for the determination of the final properties of the material.

Synthesis, mechanisms and kinetics of formation of bi-component polyurethanes

In order to understand the single-step molten state reactivities of a diaromatic isocyanate (4,4’ dPDhenylmethane diisocyanate MDI), the mechanisms and reaction kinetics were modelled using a monofunctional aromatic isocyanate (para-tolyisocyanate p-TI) and hydroxytelechelic polyols (polyethylene glycol PEG) (polypropylene glycol PPG) with variable macromolecular chains and structure (from 200 to 2000 g.mol-1). The molar ratio of reactive functions NCO/OH was set at 1.1. We were able to characterise the bi-component polyurethanes synthesised and identify side products formed (urea, trimer, allophanate…). The results were obtained by the use of a panoply of classical analytical techniques (NMR, FTIR, HPLC/UV/MS, ESI/MS, DSC) or those more recent in the field of synthetic polymers (MALDI-TOF). This work shows the necessity of using several efficient and complementary techniques in order to understand the molten state reaction mechanisms and kinetics of these complex PU systems.

Phenolic resins (IV). Thermal degradation of crosslinked resins in controlled atmospheres

The study involved the thermal degradation of phenolic resins in controlled atmospheres (inert and oxidizing). Its aim was to characterize volatile organic compounds (VOC) and inorganic compounds released during heat treatment. The methods used were thermogravimetry coupled with thermodesorption/gas chromatography/mass spectrometry (TG/TCT/GC/MS) and thermogravimetric analysis coupled with infrared (TGA/IR). At the end of the heat cycle, residues were characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (solid state 13C NMR (CP/MAS)). The data show that the synthesis conditions of the crosslinked resins, the controlled environment and the temperature of the degradation heat cycle, all affect the composition of volatile compounds and residues at the end of the cycle. The data have enabled us to propose decomposition reaction mechanisms for these resins in oxidizing and inert environments.

Heat stability and degradation of thermally stable prepolymers in a controlled atmosphere. III. Thermal homopolymerization cycle of dicyanate monomers and physicochemical characterization of the crosslinked system

Monitoring the homopolymerization of cyanate monomers during heat treatment shows that triazine rings formed during the 180°C step. Oligomers were composed of 1 to 15 triazine rings. Analysis of compounds formed before the gel point revealed the presence of side products containing terminal phenolic functions: the phenol-cyanate (M0-OH) and oligomers with one or two hydroxyl functions (M1,2,…-OH). Kinetic and mechanistic monitoring during treatment at 210°C in the solid state allowed the determination of the structure of the final system and the detection and quantification of unreacted cyanate functions. Kinetic and thermal studies in the temperature range of 100 to 220°C showed that the homopolymerization of hexafluorobisphenol A dicyanate starts at a lower temperature and is slower than that of bisphenol A dicyanate. Thermogravimetric data showed that residual monomers volatilized between 150 and 300°C, while the degradation of crosslinked products occurred between 400 and 600°C and involved two distinct steps.

Thermal degradation of polyurethane bicomponent systems in controlled atmospheres

Although the thermal degradation of polyurethanes has been extensively studied in the past, the use of a panoply of recent analytical techniques has provided more detailed data and enabled us to confirm prior findings on the thermal degradation of bicomponent polyurethanes. The thermal behaviour of bicomponent polyurethanes in conditions of controlled atmosphere and temperature was characterized by determining their heat stability by on-line TGA/FT-IR coupling and off-line TGA/TCT/GC/MS coupling in order to identify the volatile compounds released. Degradation residues were analyzed by FT-IR and MALDI-TOF (matrix assisted laser desorption/ionization coupled with time-of-flight) mass spectrometry. A major drawback of these thermoplastic elastomers is that one of the components, isocyanate, is toxic. Based on the data obtained with model urethane compounds (p-TI-based) and bicomponent polyurethane polymer (MDI- and PEG-based), we show that the thermal degradations are different. The widespread application of these materials exposes them to extreme working conditions, which is why we propose reaction mechanisms for their degradation.