EPR and Mössbauer characterization of RTV polysiloxane foams and their constituents

Blair, Michael W.; Muenchausen, R. E.; Taylor, R. D.; Labouriau, Andrea; Cooke, D. W.; Stephens, Thomas

doi:10.1016/j.polymdegradstab.2008.04.014

Cited by 19 publications

(10 citation statements)

References 11 publications

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“…The addition of fillers to polymer melts, or uncured or precured polymers such as silicones, 16 leads to enormous increases in viscosity, 17 to a degree such that processing frequently becomes problematic. 17 The presence of stabilized allyl-PEG droplets in uncured silicone elastomers, particularly at 20% loading, will similarly increase the viscosity by acting as a filler.…”

Section: Discussionmentioning

confidence: 99%

Silicone foams stabilized by surfactants generated in situ from allyl-functionalized PEG

Fawcett

Brook

2010

Soft Matter

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Silicone foams normally require the use of agents or chemical reactions that blow gases, and a surfactant for bubble stabilization. We have discovered that the presence of monoallyl-functionalized poly(ethylene glycol) (PEG) leads to large increases in the viscosity of silicone pre-elastomers such that stable foams form with bubbles mostly being generated by coalescence of dissolved gases during the normal degassing process. Although silicone elastomer cure may take up to 24 h for completion, the foams remain stable during this time when appropriate concentrations of allyl-PEG and curing catalyst are used. No traditional surfactant is required, but PEG-modified silicone surfactants are formed in situ by covalent grafting of the PEG to the silicone matrix, leading to the increase in viscosity. The presence of allyl-PEG decreases elastomer cure efficiency, but this is readily overcome, if necessary, to generate more rigid foams by the use of additional platinum catalyst, in which case foaming occurs both due to loss of dissolved gases and to hydrogen evolution. Foam stabilization with appropriate allyl-PEG compounds is a consequence of an initial viscosity increase.

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Section: Discussionmentioning

confidence: 99%

Silicone foams stabilized by surfactants generated in situ from allyl-functionalized PEG

Fawcett

Brook

2010

Soft Matter

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“…As previously mentioned, tin octoate slowly oxidizes producing tin(IV) species and undergoes hydrolysis producing octanoic acid [15,24,25]. The presence of the acid in the RTV foam may lead to the polymer degradation by protonation of the siloxane chain, which eases the barrier for hydrolysis [26].…”

Section: Catalytic Activity Of Tin Residuesmentioning

confidence: 99%

Aging mechanisms in RTV polysiloxane foams

Labouriau

Robison

Meincke

et al. 2015

Polymer Degradation and Stability

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a b s t r a c tThe long-term use of polysiloxane foams requires a good understanding of the diverse factors that may influence their performance. The aim of the present work was to understand the interplay between inservice environments and reactive species that reside in the foams. Two foams (SX358 and S5370) were thermally aged under compressive strain to gauge the onset of compression set, an indicator of degradation. Experiments were performed by either aging the foams in open air containers or in high humidity environments. Our results indicated that foams aged in open air environments exhibited less compression set than when aged in presence of moisture. These results were analyzed in terms of postcuring reactions, hydrolysis and rearrangement of the network, which are promoted by active residues that are left in the foam from the curing process. In particular, the residues from tin octoate, the catalyst used in the cure of the foams, were identified and their role in promoting aging was determined. Reactions were either catalyzed by tin(II) species or by a combination of trace amounts of water and octanoic acid, a product of the hydrolysis of tin octoate. More precisely, this work demonstrated that reactive residues promote chemical changes in the polymer, which resulted in compression set. On the other hand, the oxidized residues of the tin octoate show no catalytic activity towards promoting condensation reactions between silanol groups. Our work established that, depending on service conditions, certain residues are more harmful to the foam's lifetime than others.

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“…The results for the aged samples are summarized in Figure 14. These spectra have been normalized so that the resonance shapes can be more easily compared, as previous research 16 has shown that the EPR linewidth (not intensity) is indicative of iron hydroxide changes. This initial view indicates that the EPR lineshape does change for samples aged at 120 and 160°C, but Figure 15 shows that the unaged baseline curves (in black) have the same shapes as their respective thermally aged samples (red curves).…”

Section: Electron Paramagnetic Resonance (Epr)mentioning

confidence: 99%