Acidolytic ring opening of cyclic siloxane and acetal monomers. Role of hydrogen bonding in cationic polymerization initiated with protonic acids

Wilczek, Lech; Chojnowski, Julian

doi:10.1021/ma50002a002

Cited by 53 publications

(32 citation statements)

References 13 publications

(15 reference statements)

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“…Such an activation has been suggested by Chojnowski et al 19 to result from the increase of both acidity and nucleophilicity of the hydrate:…”

Section: Role Of Added Watermentioning

confidence: 84%

“…5 How is it possible to understand why the initial ring opening reaction is more limited for 0 3 , which is intrinsically a more reactive monomer than D 4 in the same conditions (as has been observed in copolymerization experiments initiated by CF 3 COOH 19 or by CF 3 S0 3 H 9 )? A possibility could be that as soon as a quantity of water corresponding to about one or two moles per mole of acid is present (around 70% conversion of the acid into ester) it would form a mixed ternary complex 0 3 , H 2 0, HA with the acid and 0 3 in which the acid would be much less reactive than "free" acid for the opening of D 3 .…”

Section: And Its Behavior Intermediate Between Those Of 04 _s1smentioning

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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“…Such an activation has been suggested by Chojnowski et al 19 to result from the increase of both acidity and nucleophilicity of the hydrate:…”

Section: Role Of Added Watermentioning

confidence: 84%

Section: And Its Behavior Intermediate Between Those Of 04 _s1smentioning

confidence: 99%

New Developments in Cationic Polymerization of Cyclosiloxanes

Sigwalt

1987

Polym J

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“…We may assume that a stationary state in -SiD; concentration is resulting from the following reactions: If reaction (14) is much more rapid than reaction (13) D6 is resulting from the reformation of the ester by exocyclic reaction of TfO-with a Si6+:…”

Section: Mechanism Of Polymer Growthmentioning

confidence: 99%

Cationic polymerization of hexamethylcyclotrisiloxane by trifluoromethanesulfonic acid and its derivatives, 2. Reaction involving activated trifluoromethylsulfonates

Toskas

Besztercey

Moreau

et al. 1995

Macro Chemistry & Physics

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SUMMARY:Silyl trifluoromethanesulfonates are inactive for the polymerization of cyclosiloxanes in the complete absence of trifluoromethanesulfonic (triflic) acid, but polymerization occurs in its presence. Using a triflic ester as tagged silyl triflate (benzyldimethylsilyl triflate) the degree of polymerization (FP,) of the linear polymer formed with hexamethylcyclotrisiloxane (D,) in CH2Cl, at 20 "C is inversely proportional to the ester concentration and near to the theoretical value. The polymer contains one PhCH,(CH,),Si group per macromolecule, in agreement with a propagation occurring on the monoester PhCH,(CH,),SiD,OTf.By comparison with experiments using the acid alone, polymerizations made in the presence of this ester lead to the suppression of the formation of macrocycles and to a strong decrease of that of D, and Dlz. But the amount of D, is only slightly reduced, which agrees with the hypothesis of its main direct formation on the active sites and not by ring closure of a silanol ester. The rate of D, polymerization is internally 1'' order in [D,] and externally proportional to both acid and ester initial concentrations, in agreement with a propagation involving silyl triflates activated by the acid, interconverting with transitory siloxonium ions leading to D, formation by a ring expansion involving the polymer chain.

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“…For the CROP of cyclic siloxanes two propagation reactions have been proposed [82,83] (see Figure 32). In contrast to the chain growth polymerization of olefins, where the termination leads to an active species being destroyed, the termination of cyclic monomers containing a heteroatom (such as the siloxane shown in Figure 32) leads in the first instance to the chain growth being stopped but the resulting monomer unit can start a new chain as long as monomer is available.…”

Section: Chain Growthmentioning

confidence: 99%

Ring-Opening Polymerization—An Introductory Review

Nuyken

Pask²

2013

Polymers

354

265

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We would like to dedicate this article to P. H. Plesch, a pioneer of cationic polymerization and a mentor and friend for many of those who are now at the forefront of this field of science. He passed away 5 March 2013 at the age of 95. We will miss him. Abstract: This short, introductory review covers the still rapidly growing and industrially important field of ring opening polymerization (ROP). The review is organized according to mechanism (radical ROP (RROP), cationic ROP (CROP), anionic ROP (AROP) and ring-opening metathesis polymerization (ROMP)) rather than monomer classes. Nevertheless, the different groups of cyclic monomers are considered (olefins, ethers, thioethers, amines, lactones, thiolactones, lactams, disulfides, anhydrides, carbonates, silicones, phosphazenes and phosphonites) and the mechanisms by which they can be polymerized involving a ring-opening polymerization. Literature up to 2012 has been considered but the citations selected refer to detailed reviews and key papers, describing not only the latest developments but also the evolution of the current state of the art.

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Acidolytic ring opening of cyclic siloxane and acetal monomers. Role of hydrogen bonding in cationic polymerization initiated with protonic acids

Cited by 53 publications

References 13 publications

New Developments in Cationic Polymerization of Cyclosiloxanes

New Developments in Cationic Polymerization of Cyclosiloxanes

Cationic polymerization of hexamethylcyclotrisiloxane by trifluoromethanesulfonic acid and its derivatives, 2. Reaction involving activated trifluoromethylsulfonates

Ring-Opening Polymerization—An Introductory Review

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