The effects of γ-radiation on the thermal, mechanical, and segmental dynamics of a silica filled, room temperature vulcanized polysiloxane rubber

Maxwell, Robert S.; Cohenour, Rebecca; Sung, William; Solyom, David A.; Patel, Mogon

doi:10.1016/s0141-3910(03)00028-4

Cited by 108 publications

(83 citation statements)

References 19 publications

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“…H vs. Y crosslinking via varying free radical mechanisms), bonding to the filler matrix, etc. [1][2][3][4][6][7][8][9][10][11][12][13][14][15] For both thermally and radiation induced degradation multiple, competing reaction pathways can exist and occur simultaneously to varying extent dependent on variables such as total input energy, monomer types (i.e. stabilizing phenyl groups), additives (fillers, stabilizers, etc.…”

Section: Spectrometry (Gc/ms) the Mechanical Data Andmentioning

confidence: 99%

MQ NMR and SPME Analysis of Nonlinearity in the Degradation of a Filled Silicone Elastomer

et al. 2010

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Radiation-induced degradation of polymeric materials occurs through numerous, simultaneous, competing chemical reactions. Although degradation is typically found to be linear in adsorbed dose, some silicone materials exhibit nonlinear dose dependence due to dose-dependent dominant degradation pathways. We have characterized the effects of radiative and thermal degradation on a model filled-PDMS system, Sylgard 184 (commonly used in electronic encapsulation and in biomedical applications), using traditional mechanical testing, NMR spectroscopy, and sample headspace analysis using solid-phase microextraction (SPME) followed by gas chromatography/mass spectrometry (GC/MS). The mechanical data and 1H spin−echo NMR spectra indicated that radiation exposure leads to predominantly cross-linking over the cumulative dose range studied (0−250 kGy) with a rate roughly linear with dose. 1H multiple-quantum NMR spectroscopy detected a bimodal distribution in the network structure, as expected from the proposed structure of Sylgard 184. The MQ NMR spectra further indicated that the radiation-induced structural changes were not linear in adsorbed dose and that competing chain scission mechanisms made a greater contribution to the overall degradation process in the range of 50−100 kGy (although cross-linking still dominated). The SPME−GC/MS data were analyzed using principal component analysis (PCA), which identified subtle changes in the distributions of degradation products (the cyclic siloxanes and other components of the material) as a function of age that provide insight into the dominant degradation pathways at low and high adsorbed dose.

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Section: Spectrometry (Gc/ms) the Mechanical Data Andmentioning

confidence: 99%

MQ NMR and SPME Analysis of Nonlinearity in the Degradation of a Filled Silicone Elastomer

et al. 2010

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“…The data is interpreted in combination with solvent swelling and DSC studies. Though there has been significant application of NMR to silicone based polymeric materials [see, for example, references [4][5][6][7][8][9][17][18][19][22][23], no systematic study of the effects of radiation on DC745 nor the application of these multiple quantum methods to radiation induced damage at the filler-polymer interface in silicones have been reported previously.…”

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“…The bimodal decay is a common observance in 1 H NMR relaxation studies of silicone polymers. [4][5][6][7][8][9] Following these studies, the rapidly decaying component is assigned to the proton spins in the crosslinked network while the slower decaying component is assigned to the nonnetwork, sol-species. The non-exponential decay rate has also been observed previously in silicone elastomers and is a consequence of the anisotropic motions causing incomplete averaging of the dipolar couplings leading to mixed Gaussain (solid like) and exponential (liquid like) decay.…”

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Radiation-Induced Cross-Linking in a Silica-Filled Silicone Elastomer As Investigated by Multiple Quantum ¹H NMR

et al. 2005

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RECEIVED DATERunning title: "MQ-NMR of Radiation damage in filled siloxanes" CORRESPONDING AUTHOR FOOTNOTE: Mail code: L-231, (925) 423-4991, (925) 422-3750, maxwell7@llnl.gov 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 Maxwell, et al. MQ-NMR of radiation damage in filled silicones p.2 environments. However, little data exists on the radiation resistance of this commonly used silicone elastomer. We report static 1 H NMR studies of residual dipolar couplings in DC745 solid elastomers subject to exposure to ionizing gamma radiation. 1 H spin-echo NMR data shows that with increasing dose, the segmental dynamics decrease is consistent with radiatively induced crosslinking. 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, <Ω d >, that were dose dependent. The domain with the lower <Ω d > has been assigned to the polymer network while the domain with the higher <Ω 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 ºC showed the presence of a second melt feature at T m ~ -70 ºC consistent with a network domain with significantly reduced segmental motion.

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“…Unfortunately, many siloxane-based compounds undergo degradation such as outgassing and stiffening with time in a dry environment [4], or modification of polymer chain lengths by exposure to radiation or elevated temperatures [5][6][7][8][9][10][11][12][13]. The changes to the network structure are understood to occur by competing chain-scissioning and cross-linking reactions [6,13].…”

Section: Introductionmentioning

confidence: 99%

Molecular weight distributions of irradiated siloxane-based elastomers: A complementary study by statistical modeling and multiple quantum nuclear magnetic resonance

Dinh

Mayer

Maiti

et al. 2011

Journal of Applied Physics

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ABSTRACT:The statistical methodology of population balance (PB) has been applied to predict the effects of cross-linking and chain-scissioning induced by ionizing radiation on the distribution of molecular weight between cross-links (MWBC) of a siloxane-based elastomer. Effective molecular weight distributions were extracted from the quantification of residual dipolar couplings by multiple quantum nuclear magnetic resonance (MQ-NMR) measurements and are taken to reflect actual MWBC distributions. The PB methodology is then applied to the unirradiated MWBC distribution and considers both chain-scissioning and the possibility of formation of three types of cross-links: random recombination of scissioned-chain ends (endlinking), random covalent bonds of free radicals on scissioned-chain ends (Y-cross-linking), and formation of random cross-links from free radicals on side groups (H-cross-linking). The qualitative agreement between the statistical modeling approach and NMR data confirms that it is possible to predict trends for the evolution of the distribution of MWBC of polymers under irradiation. The approach described herein can also discern heterogeneities in radiation effects in different structural motifs in the polymer network.--

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The effects of γ-radiation on the thermal, mechanical, and segmental dynamics of a silica filled, room temperature vulcanized polysiloxane rubber

Cited by 108 publications

References 19 publications

MQ NMR and SPME Analysis of Nonlinearity in the Degradation of a Filled Silicone Elastomer

MQ NMR and SPME Analysis of Nonlinearity in the Degradation of a Filled Silicone Elastomer

Radiation-Induced Cross-Linking in a Silica-Filled Silicone Elastomer As Investigated by Multiple Quantum ¹H NMR

Molecular weight distributions of irradiated siloxane-based elastomers: A complementary study by statistical modeling and multiple quantum nuclear magnetic resonance

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The effects of γ-radiation on the thermal, mechanical, and segmental dynamics of a silica filled, room temperature vulcanized polysiloxane rubber

Cited by 108 publications

References 19 publications

MQ NMR and SPME Analysis of Nonlinearity in the Degradation of a Filled Silicone Elastomer

MQ NMR and SPME Analysis of Nonlinearity in the Degradation of a Filled Silicone Elastomer

Radiation-Induced Cross-Linking in a Silica-Filled Silicone Elastomer As Investigated by Multiple Quantum 1H NMR

Molecular weight distributions of irradiated siloxane-based elastomers: A complementary study by statistical modeling and multiple quantum nuclear magnetic resonance

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Radiation-Induced Cross-Linking in a Silica-Filled Silicone Elastomer As Investigated by Multiple Quantum ¹H NMR