Protonic acids polymerization

P2O5 to give cyclic acylamldlnes. In this way N-(aza-cyclohepten-(1)-yl-(2))-caprolactam as well as the corresponding butyrolactam derivative were obtained in 7o-80% yield on a preparative scale ( l). They are obviously formed by elimination of water from the tetrahedral intermediate which results from the reaction of the Lewis acid adduct and free lacteun during the Initiation step. In the presence of cocatalysts, however, which are capable of transforming the Lewis acid into a proton acid, polymerization proceeds following the usual mechanism, e.g. with boron trifluoride and water. 

The catalysts for cationic polymerization are either protonic acids or Lewis acids, such as H2SO4 and HCIO4 or BF3, AICI3, and TiCl4 ... 

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). 

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. 

The esters differ from each other in stability. To decompose the isopropyl ester, higher temperatures and higher acid strengths are needed than for decomposition of the s-butyl ester. It is claimed that the resulting carbenium ions are stabilized by solvation through the acid (25-27). Branched alkenes do not form esters. It is believed that they are easily protonated and polymerized (28). 

Tables 4.S-4.7 and Fig. 4.6 list organic acids commonly used as metal extractants. When the acids are not protonated, dissociated, polymerized, hydrated, nor form adducts, the distribution ratio of the acid HA is constant in a given solvent extraction system ...

An interesting bifunctional system with a combination of In(OTf)3 and benzoyl-quinine 65 was developed in p-lactam formation reaction from ketenes and an imino ester by Lectka [Eq. (13.40)]. High diastrereo- and enantioselectivity as well as high chemical yield were produced with the bifunctional catalysis. In the absence of the Lewis acid, polymerization of the acid chloride and imino ester occurred, and product yield was moderate. It was proposed that quinine activates ketenes (generated from acyl chloride in the presence of proton sponge) as a nucleophile to generate an enolate, while indium activates the imino ester, which favors the desired addition reaction (66) ... 

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. 

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... 

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

In another research laboratory, surprised by the lack of success of other research groups and the previous statements about the impossibility of applying biocatalytic chemistry to polithiophenes and polypyrroles, special attention was paid to the enzymatic polymerization of the EDOT monomer [43]. In this case, the first trials succeeded and a blue-colored polymer solution was obtained after 16h of reaction (Scheme 4). As is well-known, an acidic reaction medium is suitable to increase the rate of polymerization. Protonic acids and a variety of Lewis acids catalyze the equilibrium reaction of EDOT to the corresponding dimeric and trimeric compounds without further oxidation or reaction [44]. In this work, three different pHs were evaluated (pH = 2, 4, and 6) in order to establish the optimum for adequate synthesis of EDOT. The UV-visible (UV-Vis) spectra for these three reactions are... 

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

Cationic mechanisms are much more characteristic of the polymerization of oxygen heterocycles, both ethers and acetals. A wide variety of catalysts has been used, including protonic acids, such Lewis acids as boron trifluoride, phosphorus pentafluoride, stannic chloride, antimony pentachloride, titanium tetrachloride, zinc chloride, and ferric chloride, and salts of carbocations or tri-alkyloxonium ions having anions derived from Lewis acids. Some complex, coordination catalysts that appear to operate by a mechanism... 

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... 

Basicity and Acidity Measurements The formation of salts, or adducts, in the reactions between pyrroles and proton acids or Lewis acids has been described by numerous investigators.z4,178-197 In many instances it has been shown these products are the salts of the pyrrole dimer and in the case of the unsubstituted pyrrole it is known that a trimer is readily formed in dilute aqueous acid.178,179,198 Higher polymeric products have also been reported.199 Relatively few monomeric pyrrole salts have been isolated,186,188 but proof of their existence in solution has been reported.189-198 200-202... 

Infrared spectra of pyridine adsorbed on kaolinite indicated that the dry clay (110°C) contained both Brtfnsted and Lewis acid sites (235). At 1% water content only protonic acid sites were observed. It was not possible to assign the polymerization activity to either type of acid site, since both were present on samples which were catalytically active. 

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. 

Chemical Composition. In polyamide 6 (PA 6, polymerization product of e-caprolactam) and polyamide 66 (PA 66, adipic acid polymerized with hexamethylene-diamine) one chain end consists of an amino group, which can be present in the free state or in the acylated form. Amino groups are of special importance for dyeing because they form ammonium groups in an acidic dyebath by addition of protons. The lower dye uptake in comparison to wool is caused by the comparatively low number of amino groups. The depth of color achieved on PA 6 is somewhat less than that on PA 66. 

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. 

The generation of a protonic acid (HX) is responsible for the initiation of cationic polymerization. Various monomers are polymerized by sulfonium photoinitiators. Especially this system has been shown to be potentially useful for UV curable coatings of metal and plastics with epoxy resins. 

Lewis acids readily isomerize both 1,3-dioxolanes and 1,3-oxathiolanes in ether solution. The reaction proceeds by coordination with the oxygen atom in the latter case since 1,3-dithiolanes do not isomerize under the same conditions. With trityl carbonium ion, an oxidative cleavage reaction takes place as shown in Scheme 6. Hydride extraction from the 4-position of 2,2-disubstituted 1,3-dioxolanes leads to an a-ketol in a preparatively useful reaction. 1,3-Oxathiolanes are reported to undergo similar cleavage but no mention of products other than regeneration of the ketone has been made (71CC861). Cationic polymerization of 1,3-dioxolane has been initiated by a wide variety of proton acids, Lewis acids and complex catalytic systems. The exact mechanism of the polymerization is still the subject of controversy, as is the structure of the polymer itself. It is unclear if polymerization... 

In addition, by-products of the initiation process may consume some of the protonic acid. The most probable by-products are furans, which could interact with the strong acid to form dark-colored resins. Polymerizations initiated with trityl or diazonium salts develop very dark colors which are not characteristic of the growing THF ion. 

By dissociation, strong mineral acids liberate a proton-initiating polymerization... 

---