Chemical Origins of Permanent Set in a Peroxide Cured Filled Silicone Elastomer - Tensile and 1H NMR Analysis

Journal Article · Fri Oct 29 00:00:00 EDT 2004 · Polymer Degradation and Stability

OSTI ID:875962

Chinn, S; Deteresa, S; Shields, A; Sawvel, A; Balazs, B; Maxwell, R S

The aging of a commercial filled siloxane polymeric composite in states of high stress and Co-60 {gamma}-radiation exposure has been studied. DC-745 is a commercially available silicone elastomer consisting of dimethyl, methyl-phenyl, and vinyl-methyl siloxane monomers crosslinked with a peroxide vinyl specific curing agent. It is filled with {approx}30 wt.% mixture of high and low surface area silicas. This filled material is shown to be subject to permanent set if exposed to radiation while under tensile stress. Tensile modulus measurements show that the material gets marginally softer with combined radiation exposure and tensile strain as compared to material exposed to radiation without tensile strain. In addition, the segmental dynamics as measured by both uniaxial NMR relaxometry and Multiple Quantum NMR methods indicate that the material is undergoes radiatively-induced crosslinking in the absence of tensile strain and a combination of crosslinking and strain dependent increase in dynamic order parameter for the network chains. The MQ-NMR also suggests a small change in the number of polymer chains associated with the silica filler surface. Comparison of the prediction of the relative change in crosslink density from the NMR data as well as solvent swelling data and from that predicted from the Tobolsky model suggest that degradation leads to a deviation from Gaussian chain statistics and the formation of increased numbers of elastically ineffective network chains.

• Research Organization: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 875962
• Report Number(s): UCRL-JRNL-207686; PDSTDW; TRN: US200604%%274
• Journal Information: Polymer Degradation and Stability, Vol. 91; ISSN 0141-3910
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AGING
CURING
ELASTOMERS
FILLERS
MIXTURES
MONOMERS
ORDER PARAMETERS
PEROXIDES
POLYMERS
RADIATIONS
SILICA
SILICONES
SILOXANES
SOLVENTS
STATISTICS
STRAINS
SURFACE AREA
SWELLING