Effect of stannous 2-ethylhexanoate on the network formation and chain extension reactions of α,ω-dihydroxy terminated poly(dimethylsiloxane)

Clarson, Stephen J.; Zaiming, Wang; Mark, J. E.

doi:10.1016/0014-3057(90)90217-r

Cited by 27 publications

(12 citation statements)

References 7 publications

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“…This viscosity increase correlates with the molecular weight build of the growing siloxane chains. Similar results have been seen in PDMS silanol chain extension reactions that we have reported elsewhere [23,24].…”

Section: The Effect Of the Tin Catalyst Concentrationsupporting

confidence: 90%

On the Role of Tin Catalysts in Step-Growth Polymerization Reactions

Kuo

Clarson

2012

J Inorg Organomet Polym

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Organotin compounds have been used to catalyze the condensation of various a,x-dihydroxyl terminated organosiloxane diols. This tin catalyzed reaction extends the length of siloxane chains and it also produces narrow molar mass distribution polyorganodisilanols (M w /M n = 1.4). The reaction occurs between a variety of siloxanes that are terminated with hydroxyl groups and it does not depend on the organic side groups connected to silicon for the systems studied here. These systems include silicon atoms bearing dimethyl, methylphenyl or methyl 1,1,1 trifluoropropyl substituents. The organotin catalyst in the reaction facilitates the organosilanol condensation releasing water as a byproduct. However it does not appear to facilitate the opening of siloxane bonds nor the redistribution of siloxane bonds under the conditions employed here. Copolymerization of linear oligomeric dimethylsiloxane diol and linear oligomeric methylphenylsiloxanediol was found to give a relatively equal reactivity of homo polymerization and hetro polymerization in the condensation and randomly alternating segmented block copolymers that were formed. The reaction kinetics of the polymerization was used to experimentally verify the fact that there is a chain length dependence of the reacting silanol endgroups. The molar mass values during the polymerizations were determined using gel permeation chromatography.The chromatography, viscosity and FTIR results demonstrate that the reactivity of the hydroxyl end-groups in the polycondensation reaction decreases upon increasing the chain length of the siloxane. It therefore appears that these tin catalyzed siloxane systems deviate from the widely demonstrated hypothesis of Paul Flory on the ''equal reactivity of functional groups'' for step-growth polymerizations.

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Section: The Effect Of the Tin Catalyst Concentrationsupporting

confidence: 90%

On the Role of Tin Catalysts in Step-Growth Polymerization Reactions

Kuo

Clarson

2012

J Inorg Organomet Polym

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“…For example, low molecular weight alkoxysilane cross-linkers tend to evaporate from the elastomer mixture and are prone to premature hydrolysis-condensation reactions ( Figure 1 a,b) [ 10 , 11 , 12 , 13 , 14 ]. In addition, HO-PDMS-OH condenses in the presence of a tin catalyst, which further contributes to network formulation difficulties due to the loss of reactive groups participating in the crosslinking reaction ( Figure 1 c) [ 10 , 15 ]. The cross-linker volatility and condensation of HO-PDMS-OH affect the true stoichiometric ratio between the functional group of cross-linker and polymer: r = f[cross-linker]/2[HO-PDMS-OH, where […] denotes the original concentration of the species.…”

Section: Introductionmentioning

confidence: 99%

Reliable Condensation Curing Silicone Elastomers with Tailorable Properties

Jurásková

Olsen²,

Dam‐Johansen

et al. 2020

Molecules

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The long-term stability of condensation curing silicone elastomers can be affected by many factors such as curing environment, cross-linker type and concentration, and catalyst concentration. Mechanically unstable silicone elastomers may lead to undesirable application failure or reduced lifetime. This study investigates the stability of different condensation curing silicone elastomer compositions. Elastomers are prepared via the reaction of telechelic silanol-terminated polydimethylsiloxane (HO-PDMS-OH) with trimethoxysilane-terminated polysiloxane ((MeO)3Si-PDMS-Si(OMe)3) and ethoxy-terminated octakis(dimethylsiloxy)-T8-silsesquioxane ((QMOEt)8), respectively. Two post-curing reactions are found to significantly affect both the stability of mechanical properties over time and final properties of the resulting elastomers: Namely, the condensation of dangling and/or unreacted polymer chains, and the reaction between cross-linker molecules. Findings from the stability study are then used to prepare reliable silicone elastomer coatings. Coating properties are tailored by varying the cross-linker molecular weight, type, and concentration. Finally, it is shown that, by proper choice of all three parameters, a coating with excellent scratch resistance and electrical breakdown strength can be produced even without an addition of fillers.

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“…In this case, an excess of hydroxyl groups from the HO-PDMS-OH would be present in the system. Clarson et al 18 have reported that a condensation reaction between the HO-PDMS-OH takes place in the presence of tin 2-ethylhexanoate in concentrations above 0.1wt%. Because the concentration of dibutyltin-diacetate catalyst used in this study is 1wt%, the condensation reaction between the HO-PDMS-OH cannot be ruled out.…”

Section: Reaction Between the Hydroxyl Groups Of The Ho-pdms-ohmentioning

confidence: 99%

“…In general, the type, concentration, and purity of the cross-linker, catalyst concentration, curing environment, and sample dimensions (thickness) can significantly affect the properties of the silicone network in both the short-and long-term. While some of these factors have been previously pointed out by other research groups, 18,19 a comprehensive overview of all the necessary considerations when working with condensation curing silicone elastomers is missing from the literature. To provide such an overview, we present our own various mistakes in the preparation of the silicone networks and bring a small summary on what must be considered while working with condensation curing silicone elastomers.…”

Section: Design Of Stable Networkmentioning

confidence: 99%

Factors influencing mechanical long-term stability of condensation curing silicone elastomers

Jurásková

Dam‐Johansen

Olsen³

et al. 2020

J Polym Res

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Effect of stannous 2-ethylhexanoate on the network formation and chain extension reactions of α,ω-dihydroxy terminated poly(dimethylsiloxane)

Cited by 27 publications

References 7 publications

On the Role of Tin Catalysts in Step-Growth Polymerization Reactions

On the Role of Tin Catalysts in Step-Growth Polymerization Reactions

Reliable Condensation Curing Silicone Elastomers with Tailorable Properties

Factors influencing mechanical long-term stability of condensation curing silicone elastomers

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