The stability of poly( m-carborane-siloxane) elastomers exposed to heat and gamma radiation

• Published in: Polymer degradation and stability Vol. 91; no. 3; pp. 548 - 554
• Main Authors: Patel, Mogon, Swain, Anthony C., Cunningham, Jenny L., Maxwell, Robert S., Chinn, Sarah C.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 01-03-2006; Elsevier Science
• Subjects: Ageing; Applied sciences; Chain dynamics; Degradation; Exact sciences and technology; NMR; Physical properties; Poly( m-carboranyl-siloxane); Polymer industry, paints, wood; Properties and testing; Technology of polymers; Degradation; NMR; Chain dynamics; Poly( m-carboranyl-siloxane); Carborane copolymer; Thermal ageing; Poly(m-carboranyl-siloxane); Thermooxidative degradation; Temperature effect; NMR spectrometry; Experimental study; Segmental movement; Thermal stability; Thermal properties; Gamma radiation; Investigation method; Reaction mechanism; Artificial ageing; Radiochemical degradation; Kinetics; Dimethylsiloxane copolymer; Silicone elastomer; Radiochemical stability
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2005.03.026

Poly(
m-carboranyl-siloxane) elastomers containing a mixture of di-methyl- and methylphenyl-silyl units were synthesised using the ferric chloride catalysed condensation reaction between di-chloro-diorganosilane and bis(di-methylmethoxysilyl)-
m-carborane. These elastomeric materials were originally developed to have greater stability to extreme thermal environments and retain tailorable physical and chemical properties relative to comparable non-carborane containing elastomers. Prepared samples were aged either by heating in air at elevated temperatures or by gamma irradiation from a
60Co source. Multinuclear (
1H,
13C and
11B) solid and solution state nuclear magnetic resonance (NMR) was used to assess degradation. This included measurements of segmental chain dynamics using a solid-echo pulse sequence reflecting changes in crosslink density and assessing changes to the carborane fragment by
11B and
1H Magic Angle Spinning (MAS) methods. Thermogravimetric measurements were also performed to assess thermal stability. Gamma radiation (to a dose of 1
MGy) was found to induce only a small degree of elastomer hardening as evidenced by a reduction in segmental chain dynamics. The carborane cage however, remained intact at these dose levels. Thermal degradation was observed to lead to oxidative crosslinking, the degree of which is dependent on temperature. At temperatures below 350
°C, only small changes in segmental dynamics were observed commensurate with only minor weight loss at this temperature. At temperatures above 350
°C, the degradation of the elastomer increased dramatically with decreased segmental dynamics and presumed partial oxidation of the carborane cage. The integrity of the
m-carborane cage and the segmental dynamics were found to be significantly reduced at temperatures above 580
°C, in line with the known cage rearrangement temperature for icosahedral carboranes.