Polymerization proton acid-initiated

Carbonyl monomers can be polymerized by acidic initiators, although their reactivity is lower than in anionic polymerization. Protonic acids such as hydrochloric and acetic acids and Lewis acids of the metal halide type are effective in initiating the cationic polymerization of carbonyl monomers. The initiation and propagation steps in polymerizations initiated with protonic acids can be pictured as... 

Cationic Polymerization. Protonic acids such as HBF, HPFg, HSbFg, etc., derived from the photolysis of onium salts I-III are well known initiators of cationic polymerization (9). In equations 13-15 is shown the proposed mechanism of cationic polymerization using a triarylsulfonium salt and a typical monomer, M. 

These oligomers are prepared by polymerization of THF with protonic acid initiators, and according to the patent literature and other available information, fluosulfonic acid has been used on a technical scale. A recent paper describes the successful application of H2S04/S03 mixtures 11). The diol of Mn = 1000 is a white opalescent solid at 24 C it melts at 32 °C giving a syrupy liquid with a hydroxyl number of 112-116, an acid number less than 0.05, a carbonyl number less than 4.0 and a Ca content le>s than 5 ppm Na and K are less than 10 ppm 8). 

Lewis acids, carbon cations, salts of oxonium ions, and strong protonic acids initiate polymerizations of tetrahydrofuran. The reactions can be conducted in solution or without a solvent. It was originally polymerized with a trialkyloxonium salt, R30-BF4 . 

Sawada [406] described the thermodynamics of cationic polymerization as follows The process of protonic acid initiation of cationic polymerization starts with heterolytic bond dissociation of the acid. The energy of this process can be designated by the quantity C2, the affinity of the proton for the olefin. The potential energy between ion pairs separated at a distance r is... 

Proton Acid-initiated Polymerization Using Microflow Systems... 

It has been shown that in certain systems, for example, in the protonic acid-initiated polymerization of DXL or 1,3,6,9-tetraoxacycloundecane, end-to-end cyclization may dominate over random backbiting at the early stages of polymerization, that is, when the growing chains are still relatively short (Scheme 25). 

A combination of a sulfide and a strong protonic add induces living polymerization. In this system, a sulfonium salt is produced from a sulfide and the growing carbocation shortly after a protonic acid initiates polymerization. The sulfonium salts are dormant species, which change reversibly into free ionic species (Scheme 6). This initiating system is available only for VE polymerization. 

Cationic polymerization occurs in a similar manner, except for the fact that the initiator system produces cations instead of flee radicals. Any catalyst system in cationic polymerization normally requires a cocatalyst. For example, protonic acid initiators (or catalysts) such as sulfuric acid, perchloric acid, and Irifluoro-acetic acid require a cocatalyst (e.g., acetyl perchlorate or water). Together, the two generate cations in the reaction mass. The reaction of boron Irrfluoride with water as the cocatalyst and styrene as the monomer is an example ... 

Complexation of the initiator and/or modification with cocatalysts or activators affords greater polymerization activity (11). Many of the patented processes for commercially available polymers such as poly(MVE) employ BE etherate (12), although vinyl ethers can be polymerized with a variety of acidic compounds, even those unable to initiate other cationic polymerizations of less reactive monomers such as isobutene. Examples are protonic acids (13), Ziegler-Natta catalysts (14), and actinic radiation (15,16). 

Dimerization and polymerization can be initiated by electrophilic attack on an oxirane by a protonated or Lewis acid coordinated oxirane (Section 5.04.3.2.2). 

Strong protonic acids can affect the polymerization of olefins (Chapter 3). Lewis acids, such as AICI3 or BF3, can also initiate polymerization. In this case, a trace amount of a proton donor (cocatalyst), such as water or methanol, is normally required. For example, water combined with BF3 forms a complex that provides the protons for the polymerization reaction. 

Polymerization of 33 occurred very readily with a variety of cationic initiators. Protonic acids gave high conversion to soluble polymer which was of moderate molecular weight (T jnh = 0.35), liquid (rubber), and consisted of a 60 40 mixture of iso-... 

Protonic acids are less suitable because the conjugate base is too active a nucleophile. HC1, for example, will not initiate polymerization because chloride ion adds immediately to the carbenium ion before the latter can propagate. Other initiators which have been studied include electroinitiation, photoinitiation and ionizing radiation. 

Ionic polymerization may also occur with cationic initiations such as protonic acids like HF and H2SO4 or Lewis acids like BF3, AICI3, and SnC. The polymerization of isobutylene is a common example, shown in Fig. 14.5. Note that the two inductively donating methyl groups stabilize the carbocation intermediate. Chain termination, if it does occur, usually proceeds by loss of a proton to form a terminal double bond. This regenerates the catalyst. 

Protonic (Brpnsted) acids initiate cationic polymerization by protonation of the olefin. The method depends on the use of an acid that is strong enough to produce a resonable concentration of the protonated species... 

Strong protonic acids such as trifluoroacetic, fluorosulfonic, and trifluoromethanesulfonic (triflic) acids initiate polymerization via the initial formation of a secondary oxonium ion... 

A variety of protonic and Lewis acids initiate the cationic polymerization of lactams [Bertalan et al., 1988a,b Kubisa, 1996 Kubisa and Penczek, 1999 Puffr and Sebenda, 1986 Sebenda, 1988]. The reaction follows the mechanism of acid-catalyzed nucleophilic substitution reactions of amides. More specibcally, polymerization follows an activated monomer mechanism. Initiation occurs by nucleophilic attack of monomer on protonated (activated) monomer (XXIV) to form an ammonium salt (XXV) that subsequently undergoes proton exchange with monomer to yield XXVI and protonated monomer. The conversion of XXIV to XXV involves several steps—attachment of nitrogen to C+, proton transfer from... 

Cationic polymerization has been initiated by a variety of protonic and Lewis acids [Kubisa, 1996 Toskas et al., 2001]. The cationic process is more complicated and less understood than the anionic process. Polymerization under most reaction conditions involves the presence of a step polymerization simultaneously with ROP. This appears to be the only way to reconcile the observed (complicated) kinetics for the overall process [Chojnowski and Wilczek, 1979 Chojnowski et al., 2002 Cypryk et al., 1993 Rubinsztain et al., 1993 Sigwalt, 1987 Wilczek et al., 1986],... 

Some common initiators for cationic polymerization reactions are protonic acids, Friedel-Crafts catalysts (Lewis acids), compounds capable of generating cations, or ionizing radiation. 

Inorganic Lewis acids, specifically, Friedel-Crafts catalysts, such as SnCU, TiCl4, AICI3, AlBr3, and BF3, usually require a cocatalyst (e.g., H20 always considered to be present), and in this case, initiation is also induced by the proton formed [Eq. (13.18)]. Pioneering work on the role of proton acids as catalysts and cocatalysts in acid-catalyzed polymerization was carried out by Polanyi and... 

When exposed to UV radiation, these salts dissociate and react with a proton (impurities, ROH), to liberate a protonic acid that is able to initiate a cationic chain polymerization of epoxy groups. 

Note Moderately polar solvent, ethereal odor soluble in water and most organic solvents flammable moderately toxic incompatible with strong oxidizers can form potentially explosive peroxides upon long standing in air see the relevant tables in the chapter on laboratory safety commercially, it is often stabilized against peroxidation with 0.5 to 1.0% (mass/mass) p-cresol, 05 to 1.0% (mass/mass) hydroquinone, or 0.01% (mass/mass) 4,4 -thiobis(6-ferf-butyl-m-cresol) can polymerize in the presence of cationic initiators such as Lewis acids or strong proton acids. Synonyms THF, tet-ramethylene oxide, diethylene oxide, 1,4-epoxybutane, oxolane, oxacyclopentane. 

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