M. Cochez

Thermal degradation of poly(methyl methacrylate) (PMMA): modelling of DTG and TG curves

The thermal behaviour of poly(methyl methacrylate) (PMMA) with average molecular weights of 996,000 and 350,000 g mol � 1 was investigated by thermogravimetric analysis in dynamic conditions at four different heating rates: 2, 5, 8 and 10 K min � 1 . In inert atmosphere, four degradation steps were found to be involved supporting the degradation behaviour previously investigated in the literature. Assuming four independent reactions, the apparent kinetic parameters were determined for each step using a non-linear fitting algorithm allowing us to simulate the overall weight loss of PMMA in any given experimental conditions. # 2002 Elsevier Science Ltd. All rights reserved.

Thermal degradation of methyl methacrylate polymers functionalized by phosphorus-containing molecules-II: initial flame retardance and mechanistic studies

Abstract The thermal behaviour of methyl methacrylate polymers functionalized by phosphorus-containing molecules was investigated by TGA/FT-IR and Py-GC–MS under air and argon atmosphere. Three homopolymers and four copolymers with methyl methacrylate (MMA) were prepared and studied. The gases emitted during the degradation of these materials were unambiguously identified, allowing us to suggest a degradation mechanism very different to that of PMMA. The measurement of the LOI values show that the polymers have potential flame retardant properties.

Thermal degradation of methyl methacrylate polymers functionalized by phosphorus-containing molecules I. TGA/FT–IR experiments on polymers with the monomeric formula CH2C(CH3)C(O)OCHRP(O)(OC2H5)2 (RH, (CH2)4CH3, C6H5Br, C10H7)

The thermal behaviour of methyl methacrylate polymers (PMMA) prepared from phosphorus-containing monomers: CH2C(CH3)C(O)OCHRP(O)(OC2H5)2 (RH, (CH2)4CH3, C6H5Br, C10H7) was investigated by thermal gravimetric analysis (TGA) coupled with on-line FT–IR analysis of evolved gases. Four homopolymers and two MMA/functionalized-MMA copolymers were studied. They exhibited a thermal behaviour largely different from that encountered for PMMA. Particularly, the results revealed a major and common degradation stage near 300°C leading to diethyl phosphite HPO(OC2H5)2 or diethyl phosphonate RPO(OC2H5)2, aldehyde RCHO, CO, CO2 and ethylene C2H4. Functionalization introduces high temperature degradation stages (above 750°C) and weak points in the polymeric chain leading to a complete cracking of the polymer as no monomer molecules were found during the degradation, in contrast to PMMA. A first evaluation of the fire retardation properties of the polymers was performed by determining the limiting oxygen index (LOI).

Influence of the dopant concentration on the OH− absorption band in Fe-doped LiNbO3 single-crystal fibers

Abstract The growth of iron-doped single-crystal fibers of lithium niobate was performed by the laser heated pedestal growth technique for different Fe2O3 contents in the feed rods. The infra-red optical absorption spectra (OH− band) were investigated by IR transmission microscopy. To explain the evolution of the OH− ions concentration in the crystals, a model is proposed involving the partial dissociation of LiNbO3 in the melt into Li2O and Nb2O5. The constitution of the OH− absorption band is also discussed on the basis of the Nb-vacancy structural model of lithium niobate.

Characterization of iron substitution process in Fe:LiNbO3 single crystal fibers by polaron measurements

Abstract The growth of iron-doped single-crystal fibers of lithium niobate was performed by the Laser Heated Pedestal Growth Technique for different Fe 2 O 3 contents in the feed rods. We used the polaron luminescence to explain the processes of iron substitution in iron-doped single-crystal fibers of lithium niobate. The interpretation of the polaron behavior as a function of iron concentration confirms several predicted effects as the decrease of the global amount of vacancies and the predominant role of the niobium in its polaronic or bipolaronic forms in the LN lattice.