T.C. Chang

Effect of phenolic phosphite antioxidant on the thermo-oxidative degradation of PMMA

Abstract A novel high molar mass phenolic phosphite antioxidant, tetrakis-(2,5-di- tert -butyl-4-hydroxyphenyl)-2,5-di- tert -butyl-hydroquinonediyl diphosphite (2P5B), was prepared and characterized by IR, 31 P NMR, FAB-MS and thermogravimetric analysis (TGA). The effect of 2P5B content on the thermal properties of poly(methyl methacrylate) (PMMA) was studied by TGA, differential scanning calorimetry (DSC), and oxidative induction time (OIT). 0.5 wt.% of the novel phenolic phosphite antioxidant retarded the 10% weight loss temperature and reduced the maximum rate of weight loss. The stabilized-PMMA showed a clear OIT onset that increased with increasing 2P5B content. The apparent activation energies for initial thermo-oxidative degradation, evaluated by van Krevelen method, of the stabilized-PMMA were less than that of antioxidant free PMMA. Hence, it seems reasonable that the PMMA was degraded easily as the 2P5B antioxidant was consumed.

Organic–inorganic hybrid materials XI. Characterization and degradation of hydrogen-bonded acidic fluorinated poly(siloxane-amideimide-silica) hybrids

Abstract Hydrogen-bonded acidic fluorinated poly(siloxane-amideimide-silica) hybrid materials (FPSAI–SiO 2 ) were obtained using the sol-gel technique by polycondensation of tetramethoxysilane (TMOS) in diethoxysilane-terminated amic acid solution. IR, 29 Si- and 13 C-NMR spectroscopy and thermogravimetric analysis (TGA) were used to study hybrids containing various proportions of TMOS. The abundant Q 4 structures implied that in the absence of HCl the degree of condensation of TMOS was enhanced by hydrogen-bonded acidic fluorinated poly(siloxane amideimide). The microstructure and chain mobility of the hybrids were investigated by measurements of the spin-lattice relaxation time in the rotating frame ( T H 1ρ ) and the time constant for energy exchange between 1 H and 29 Si spin systems ( T SiH ). The results suggested that the rate of polarization transfer in FPSAI–SiO 2 hybrids was dependent on the local motion. On the other hand, the spin-diffusion path length ( L ) in FPSAI–SiO 2 hybrids was around 3.6 nm. The apparent activation energy ( E a ) for degradation of the hybrids was studied by the van Krevelen method. The E a values of the FPSAI–SiO 2 hybrids in thermal degradation decreased with increasing silica content, whereas those for thermo-oxidative degradation were almost unchanged.

Characterization and degradation of hydrogen-bonded acidic polyamideimides linked by disiloxanes

Hydrogen-bonded acidic poly(siloxane amideimide)s (PSAIs) were synthesized by partial imidization of 3,3′,4,4′-benzophenone- tetracarboxylic dianhydride (BTDA) with 2,2′,bis(3-amino-4-hydroxyphenyl) hexafluoropropane (AHHFP) and 1,3-bis(3-aminopropyl)tetramethyldisiloxane (APrTMDS). Infrared (IR) and 13C nuclear magnetic resonance (NMR) spectroscopies characterized the structure of PSAI copolymers. The apparent activation energy Ea of degradation of PSAI copolymers in air was studied by thermogravimetry and compared with unmodified polyamideimide (PAI). The higher Ea of the PSAIs in air than that of the PAI suggests that the disiloxane enhanced the stability of the polyamideimide, and the smaller spin–spin relaxation time T2 of the PSAI copolymers than that of the PAI reveals that the PSAI had more closely packed structure with increasing APrTMDS.

Chain dynamics and thermal stability of trifluoroacetylated ethyl cellulose

Abstract Trifluoroacetyl ethyl cellulose (TFAEC) was prepared by reaction of ethyl cellulose (EC) with trifluoroacetic anhydride. The effect of the trifluoroacetylation on the chain dynamics and thermal stability of the ethyl cellulose was investigated. Chain dynamics of TFAEC were investigated using the 1 H spin-lattice relaxation time in the rotating frame ( T H 1ρ ). The trifluoroacetylation reduced the mobility of the polymeric glucose chain. The apparent activation energies ( E a ) of degradation under nitrogen and air were evaluated by differential and integral methods. The value of E a of TFAEC under nitrogen was affected by the equivalent ratio of trifluoroacetic anhydride to EC, while that under air was less affected.