M. Rama Rao

Synthesis and characterization of poly(ether sulfone) copolymers

Poly(ether sulfone) copolymers I–V were synthesized by the nucleophilic substitution reaction of 4,4-dichlorodiphenyl sulfone with varying mole proportions of 4,4-isopropylidene diphenol (bisphenol A) and 4,4-dihydroxydiphenyl sulfone (bisphenol S) using sulfolane as the solvent in the presence of anhydrous K2CO3. The polymers were characterized by different physicochemical techniques. The glass transition temperature was found to decrease with increase in the concentration of bisphenol A units in the polymers. All polymers were found to be amorphous. Thermogravimetric studies showed that all the polymers were stable up to 400°C with a char yield of about 36% at 900°C in a nitrogen atmosphere. 13C-NMR spectral analysis reveals that bisphenol S-based triads are preferentially formed compared to bisphenol-A triads, indicating greater reactivity of bisphenol S toward dichlorodiphenyl sulfone. The overall activation energy for the thermal decomposition of bisphenol A-based polymer (1) is much higher than that of bisphenol S-based polymer (II). This was attributed to the modification of the backbone of polymer I during the initial cleavage of the C—CH3 bond of the isopropyledene group. Polymer II decomposes by cleavage of the C—SO2 bond.

Microstructure and thermal degradation of poly(ether ketone sulfone) copolymers: 13C NMR and thermogravimetry studies

Microstructure of poly(ether ketone sulfone) copolymers I–V, derived from varying mol proportions of dihydroxy diphenyl sulfone (DHDPS, A) and dihydroxybenzophenone (DHBP, C) with stochiometric amounts of difluorobenzophenone (DFBP, B) was studied by 13C nuclear magnetic resonance spectroscopy. The results were interpreted in terms of the compositional triads BBB, BBA, ABA, BAB, and AAB because B and C moieties become indistinguishable in the copolymers. Feed ratios calculated from the triad intensities agree well with experimental values, validating the chemical shift assignments. The presence of AAB and BBA triads in polymer II (A : C = 1 : 0) indicates the occurrence of transetherification reaction during its synthesis. Thermal decomposition characteristics of the copolymers were studied by thermogravimetry. Activation energies for thermal degradation were calculated using Coats-Redferns method assuming the order of the reaction is 1 and was found to vary from 281 to 193 kJ mol−1. A good linear correlation was obtained between activation energy values and BBB triad intensities. These observations were rationalized by consideration of their decomposition mechanisms.

Spectroscopic studies on the oligomers of bromotrifluoro ethylene

The photo-initiated oligomerization of bromotrifluoroethylene in chlorotrifluoromethane medium was found to yield a complex mixture of products. 19F-nmr, infrared and GC-MS spectra revealed the presence of -CF2Br and —CF = CF2 and the absence of —CF Br2 and —CF3 end groups in the products. Oligomers up to pentamers were identified and their structures elucidated by GC-MS. A plausible mechanism for their formation is suggested.