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Title: Radiation induced crosslinking in a silica-filled silicone elastomer as investigated by multiple quantum H NMR

Abstract

DC745 is a commercially available silicone elastomer consisting of dimethyl, methylphenyl, and vinyl-methyl siloxane monomers crosslinked with a peroxide vinyl specific curing agent. It is generally considered to age gracefully and to be resistant to chemical and thermally harsh environments. However, little data exists on the radiation resistance of this commonly used silicone elastomer. We report static {sup 1}H NMR studies of residual dipolar couplings in DC745 solid elastomers subject to exposure to ionizing gamma radiation. {sup 1}H spin-echo NMR data shows that with increasing dose, the segmental dynamics decrease is consistent with radiatively induced crosslinking. {sup 1}H multiple quantum NMR was used to assess changes in the network structure and observed the presence of a bimodal distribution of residual dipolar couplings, <{Omega}{sub d}>, that were dose dependent. The domain with the lower <{Omega}{sub d}> has been assigned to the polymer network while the domain with the higher <{Omega}{sub d}> has been assigned to polymer chains interacting with the inorganic filler surfaces. In samples exposed to radiation, the residual dipolar couplings in both reservoirs were observed to increase and the populations were observed to be dose dependent. The NMR results are compared to Differential Scanning Calorimetry (DSC) and a two-stepmore » solvent swelling technique. The solvent swelling data lend support to the interpretation of the NMR results and the DSC data show both a decrease in the melt temperature and the heat of fusion with cumulative dose, consistent with radiative crosslinking. In addition, DSC thermograms obtained following a 3 hr isothermal soak at -40 C showed the presence of a second melt feature at T{sub m} {approx} -70 C consistent with a network domain with significantly reduced segmental motion.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
875929
Report Number(s):
UCRL-JRNL-212538
TRN: US0600942
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Journal Article
Journal Name:
Macromolecules
Additional Journal Information:
Journal Volume: 38
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CALORIMETRY; CURING; ELASTOMERS; FILLERS; FUSION HEAT; GAMMA RADIATION; MONOMERS; PEROXIDES; POLYMERS; RADIATIONS; SILICONES; SILOXANES; SOLVENTS; SPIN ECHO; SWELLING

Citation Formats

Maxwell, R S, Chinn, S C, Solyom, D, and Cohenour, R. Radiation induced crosslinking in a silica-filled silicone elastomer as investigated by multiple quantum H NMR. United States: N. p., 2005. Web.
Maxwell, R S, Chinn, S C, Solyom, D, & Cohenour, R. Radiation induced crosslinking in a silica-filled silicone elastomer as investigated by multiple quantum H NMR. United States.
Maxwell, R S, Chinn, S C, Solyom, D, and Cohenour, R. 2005. "Radiation induced crosslinking in a silica-filled silicone elastomer as investigated by multiple quantum H NMR". United States. https://www.osti.gov/servlets/purl/875929.
@article{osti_875929,
title = {Radiation induced crosslinking in a silica-filled silicone elastomer as investigated by multiple quantum H NMR},
author = {Maxwell, R S and Chinn, S C and Solyom, D and Cohenour, R},
abstractNote = {DC745 is a commercially available silicone elastomer consisting of dimethyl, methylphenyl, and vinyl-methyl siloxane monomers crosslinked with a peroxide vinyl specific curing agent. It is generally considered to age gracefully and to be resistant to chemical and thermally harsh environments. However, little data exists on the radiation resistance of this commonly used silicone elastomer. We report static {sup 1}H NMR studies of residual dipolar couplings in DC745 solid elastomers subject to exposure to ionizing gamma radiation. {sup 1}H spin-echo NMR data shows that with increasing dose, the segmental dynamics decrease is consistent with radiatively induced crosslinking. {sup 1}H multiple quantum NMR was used to assess changes in the network structure and observed the presence of a bimodal distribution of residual dipolar couplings, <{Omega}{sub d}>, that were dose dependent. The domain with the lower <{Omega}{sub d}> has been assigned to the polymer network while the domain with the higher <{Omega}{sub d}> has been assigned to polymer chains interacting with the inorganic filler surfaces. In samples exposed to radiation, the residual dipolar couplings in both reservoirs were observed to increase and the populations were observed to be dose dependent. The NMR results are compared to Differential Scanning Calorimetry (DSC) and a two-step solvent swelling technique. The solvent swelling data lend support to the interpretation of the NMR results and the DSC data show both a decrease in the melt temperature and the heat of fusion with cumulative dose, consistent with radiative crosslinking. In addition, DSC thermograms obtained following a 3 hr isothermal soak at -40 C showed the presence of a second melt feature at T{sub m} {approx} -70 C consistent with a network domain with significantly reduced segmental motion.},
doi = {},
url = {https://www.osti.gov/biblio/875929}, journal = {Macromolecules},
number = ,
volume = 38,
place = {United States},
year = {Tue May 24 00:00:00 EDT 2005},
month = {Tue May 24 00:00:00 EDT 2005}
}