Comparison of the cationic polymerization of octamethylcyclotetrasiloxane and hexamethylcyclotrisiloxane

Wilczek, Lech; Rubinsztajn, Sławomir; Chojnowski, Julian

doi:10.1002/macp.1986.021870104

Cited by 67 publications

(41 citation statements)

References 11 publications

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“…This shows clearly the inhibitory effect of water on the polymerization of D4 . For D 6 polymerization with the monohydrate, similar results 18 were obtained at higher acid concentration (e.g., 5.5 x 10-3 M of hydrate) for the initial rate that decreased by a factor of about 7. However, there was only an induction period for the formation of the high polymer which was not inhibited.…”

Section: Role Of Added Watersupporting

confidence: 71%

“…There is first a rapid monomer consumption giving various cyclic oligomers (sometimes with kinetic enhancement) 18 and contrarily to the D 3 case, the first order plots obtained later on extrapolate higher than the origin. A more complex dependence of RP 0 on [D 4 ] 0 was found in ref 5, the rate increasing with [D] 0 at the lower concentrations and decreasing at higher concentrations. But this was found for CF 3 SO 3 H concentrations lower than those used by Lebrun et al 3 • 4 Simpler and more precise results were obtained from the slope of the first order plots giving kP [ 9 The differences observed in the RP 0 for these two monomers reflect probably the large variation in rates .…”

Section: Kinetics Of D 3 and D4 Pol Ymeriza Tio Ns Initiated With Trisupporting

confidence: 54%

“…During 0 6 polymerization by triflic acid, 8 it was found that the concentrations of 0 4 and 0 5 increased slowly up to their equilibrium values, and that the polymer was formed rapidly after a short induction period.…”

Section: Formation Of Small Cycles In Polymerization Of Cyclosiloxanesmentioning

confidence: 99%

“…5 It should be pointed out that initial rates in the case of D4 (and also for D 5 and D 6 ) are not representative of the main reaction. There is first a rapid monomer consumption giving various cyclic oligomers (sometimes with kinetic enhancement) 18 and contrarily to the D 3 case, the first order plots obtained later on extrapolate higher than the origin.…”

Section: Kinetics Of D 3 and D4 Pol Ymeriza Tio Ns Initiated With Trimentioning

confidence: 99%

“…The main argument against ring expansion was that the concentration of the -0 3 x rings was found to correlate well with the conformational probability p of the ring closure: p -n-1. 5 But since end-to-end ring closure cannot explain the results discussed above for D6 and D 9 , the most likely possibility for the formation of large quantities of D 3 x cycles, together with a high polymer in constant molar concentration, seems to be a ring expansion occurring on oxonium sites of the o; type: For D 3 polymerization, it had formerly been concluded by Chojnowski et al that triflic esters are not able by themselves to open the siloxane bond. This was based on the near zero extrapolation of the reaction rate of D 3 at decreasing water concentration in the system.…”

Section: Formation Of Small Cycles In Polymerization Of Cyclosiloxanesmentioning

confidence: 99%

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New Developments in Cationic Polymerization of Cyclosiloxanes

Sigwalt

1987

Polym J

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ABSTRACT:Some recent publicationss-s have shown the analogies or the differences in the behavior of cyclosiloxanes of various sizes (particularly D3 and D4) when they are initiated by triflic acid. They are discussed in the present article, the analogies being found mainly in the general kinetics, and the differences in the rates, in the nature of the cyclic oligomers formed, and in the effect of water on the reaction. New data are given, for D3 polymerization, on the absence of reaction with triflate esters in the absence of acid or water, on the effect of water on polymerization and on the variation of the polymer mo! wt with conversion. Even if it is too early to come to definite conclusions about the nature of the different types of active species, the various possibilities are discussed. KEY WORDSThe main theoretical problem in cationic polymerization of cyclosiloxanes is that of the knowledge of the nature of the active species and of their concentration, and it is linked to the important practical question of the control of cyclic oligomers formation versus linear polymer formation. Protonic acids such as sulfuric acid or trifluoromethanesulfonic (triflic) acid have been generally used as cationic initiators, and the possibility of using nonprotonic initiators to give high polymers is still being discussed. The most extensive studies published until now have been made either with hexamethylcyclotrisiloxane (D 3 ) 1 • 2 or octamethylcyclotetrasiloxane (D 4 ). 3 • 4 The polymerization of D 3 is much more rapid which has been assumd to result (as in anionic polymerization) from a higher ring strain. In a recent publication,5 it was concluded that these two monomers were polymerized by similar mechanisms and that the differences could be explained by differences in hydrogen bonding, easier with the more "basic" D 3 • The available publications and also some more recent data shall be discussed in the present article and lead us to somewhat different conclusions. We shall also examine the problem of the reactivity of triflic esters in these systems and also that of higher cyclosiloxanes (D 5 , D 6 ).The main analogies and differences in the benavior of D 3 and D 4 may be observed in the kinetic equations, in formation of the high polymer and of the various cyclic species, and in the effect of added water on the reaction. 6 • 7 They will be discussed successively for reactions ip.itiated by triflic acid in methylene chloride solution at room temperature.

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Section: Role Of Added Watersupporting

confidence: 71%

Section: Kinetics Of D 3 and D4 Pol Ymeriza Tio Ns Initiated With Trisupporting

confidence: 54%

Section: Formation Of Small Cycles In Polymerization Of Cyclosiloxanesmentioning

confidence: 99%

Section: Kinetics Of D 3 and D4 Pol Ymeriza Tio Ns Initiated With Trimentioning

confidence: 99%

Section: Formation Of Small Cycles In Polymerization Of Cyclosiloxanesmentioning

confidence: 99%

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New Developments in Cationic Polymerization of Cyclosiloxanes

Sigwalt

1987

Polym J

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Mechanism of Octamethylcyclotetrasiloxane Polymerization in the Presence of Siloxanediols

Bischoff

Sigwalt

1996

Polym. Int.

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Mechanism of hexamethylcyclotrisiloxane polymerization in the presence of siloxanediols

Bischoff

Sigwalt

1999

Polym. Int.

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Polymerization of hexamethylcyclotrisiloxane (D3 ) in CH2Cl2 at 30°C, initiated by triflic acid (TfOH) was studied in the presence of siloxanediols (HD2OH or HDxOH) which polycondense giving water, or in the presence of water alone for comparison. D represents a siloxane unit OSiMe2. In the second case, the relative amounts of cyclic oligomers (D6, D9) and of linear high polymer (HP) vary strongly with the molar ratio r =[H2O]/[TfOH]. When r increases from 1 to 100 (in homogeneous phase), D9 /D6 increases from 0.2 to 2 and D6 /HP decreases from 1 to 0.3. The large decrease of D6 amount and the increase in D9/D6 are attributed to the suppression of their formation through oxonium ions and to their exclusive formation, for r>100, by cyclization of silanol‐esters, which is more rapid for HD9OTf than for HD6OTf. For polymerization of D3 in the presence of HD2 OH, there is a fast and limited ring‐opening of D3 (about 10% conversion over 6 min) at the beginning, without formation of cyclics (D6, D9 , etc). Then reaction with D3 stops. Polymerization of HD2OH takes place simultaneously, at the same rate as in the absence of D3, with slow formation of high polymer. At the end of the polycondensation (after, eg, 4 h) D3 polymerization starts again, giving D6 , D9, etc, and HP. The inhibition period for D 3 is attributed to the complexation of triflic acid hydrates by silanol groups. These activated silanol groups do not react with D3. A comparison of D3 polymerization with the addition of water, HD2OH or HD15OH leads to the conclusion that when r is not too large, propagation involves silylester end‐groups, but that for large r ratios (100 or higher), it probably occurs mainly on silanol groups reacting with an activated monomer. © 1999 Society of Chemical Industry

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Comparison of the cationic polymerization of octamethylcyclotetrasiloxane and hexamethylcyclotrisiloxane

Cited by 67 publications

References 11 publications

New Developments in Cationic Polymerization of Cyclosiloxanes

New Developments in Cationic Polymerization of Cyclosiloxanes

Mechanism of Octamethylcyclotetrasiloxane Polymerization in the Presence of Siloxanediols

Mechanism of hexamethylcyclotrisiloxane polymerization in the presence of siloxanediols

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