Acid catalysed polymerization

The Acid-Catalysed Polymerization of Pyrroles and Indoles G. F. Smith... 

Conflicting interpretations of the mechanism responsible for the acid-catalysed polymerization have been proposed, particularly by the prolific group of Kamens-kii136 and by Isacescu, Gavat and Ursu137. Essentially, the problem consisted in establishing the predominance of one or more of the following reactions in the initial phase of the process ... 

This type of acid-catalysed polymerization does not produce high polymers. 

Resist Chemistry. The basic chemistry of epoxy novolac based chemically amplified resists has been proposed in the past by Stewart et al. (9J. According to this the Bronsted acid generated either photochemically or through electron beam exposure from the onium salt induces acid catalysed polymerization of the epoxy functionality. This mechanism implies that the proton generated by the exposure is actually bound to the polymer. Since the lithography consequences of this mechanism are obvious we decided to seek possible experimental evidence for the proton binding in the resist film under conditions of lithographic interest. 

Indole (benzopyrrole) 9 is sulfonated by treatment widi the pyridine-sulfur trioxide adduct to avoid acid-catalysed polymerization. If the reaction is conducted at low temperature, iV-sulfonation occurs to give the 1-sulfonic acid 10, whereas at 120 C, the reaction gave indole-3-sulfonic acid 11 (Scheme 1). ... 

In the case of acid-catalysed polymerization, an equilibrium condition between temporarily positively charged and nentral species of monomeric silicic acid is proposed [13]. This equilibrium is shifted greatly to the right. The cationic monomeric silicic acid is formed due to the addition of an H" " ion [5]. 

The stirred tank reactor is used for both types of catalysis and bimodal distributions are determined. In the case of acid-catalysed polymerization, the peak at d ss 10 xm splits up into one peak at 8 xm and a second at tf 50 xm. With increasing time t, the first peak diminishes and develops towards the second. The fragment size distribution of the base-catalysed polymerization behaves vice versa. Two peaks at d 10 xm and c/ 130 xm develop from the initial peak of d 90 xm, but the first one grows and is shifted to smaller fragments with time t. 

While both 2- and 3-vinylindole have been synthesized and characterized[l,2], they arc quite reactive and susceptible to polymerization. This is also true for simple l-alkyl derivatives which readily undergo acid-catalysed dimerization and polymerization[3]. For this reason, except for certain cases where in situ generation of the vinylindoles is practical, most synthetic applications of vinylindoles involve derivatives stabilized by EW-nitrogen substituents[4]. 

This section deals with investigations specifically aimed at producing homopolymers and copolymers of furan carbonyl compounds by the selective opening of the carbonyl bond. The many reports on polymerization of 2-furaldehyde which in fact deal with complicated acid-catalysed resinification reactions which involve both the formyl group and the furan ring are reviewed in Chapter VI. 

The concept of extractive reaction, which was conceived over 40 years ago, has connections with acid hydrolysis of pentosans in an aqueous medium to give furfural, which readily polymerizes in the presence of an acid. The use of a water-immiscible solvent, such as tetralin allows the labile furfural to be extracted and thus prevents polymerization, increases the yield, and improves the recovery procedures. In the recent past an interesting and useful method has been suggested by Rivalier et al. (1995) for acid-catalysed dehydration of hexoses to 5-hydroxy methyl furfural. Here, a new solid-liquid-liquid extractor reactor has been suggested with zeolites in protonic form like H-Y-faujasite, H-mordenite, H-beta, and H-ZSM-5, in suspension in the aqueous phase and with simultaneous extraction of the intermediate product with a solvent, like methyl Aobutyl ketone, circulating countercurrently. 

The use of a rotating reactor to provide efficient mixing has been proposed and tested for viscous polymerizations and acid-catalysed rearrangement reactions [6], The principle of these spinning disc reactors is that the centrifugal force... 

Nonpolymerizable cyclic imides like N-methylsuccinimide undergo condensation in the presence of basic catalysts (56). Similar condensations, remembering Claisen condensations of esters can occur also with imides which were added or which were formed by disproportionation during the base catalysed polymerization of caprolactam. The water which could be set free as a result of such a condensation consumes one equivalent of sodium caprolactam which is converted into the inactive sodium 6-amino-capronate. On the other hand the condensation products can take off directly another equivalent of the base because of their acidic nature. 

As any of the degradation reactions depends on the presence of a strong base, it is evident that neutralizing the base supports to the stabilization of the polymer. Thus, after having extracted the polymer either by water or by diluted acids, and after having dried the polymer, the decrease of the viscosity is much slower than in the case of non extracted polymer (103) (fig. 4). This makes it possible to apply the base catalysed polymerization for the production of polyamides for extruding and molding purposes. 

Percarboxylic acids have been used widely in Baeyer-Villiger oxidation. Peracetic acid is one of the most commonly used peracids distilled peracetic acid is employed commercially by Solvay Interox for the production of e-caprolactone.246 The use of distilled peracetic acid is essential, as it contains no strong protic acids which can catalyse polymerization of the resulting lactone and cause other side reactions. Figure 3.53 illustrates the use of pre-formed peracetic acid for the Baeyer-Villiger oxidation of ketones.247,248... 

When adequate precautions (largely addition of low concentrations of EDTA) are taken to exclude extraneous reactions, the rate decreases above pH 12 in general agreement with the extent of formation of HOO . With these precautions, polymerization of acrylonitrile is not observed (despite an earlier contrary report). There is thus no reason to invoke radical paths. Two investigations agree that the acid-catalysed reaction includes the process... 

The polymerization of naturally occurring sterculic acid (2) in the presence of proton sources has been known for over 40 years and proceeds via acid-catalysed opening of the cyclopropene ring. The rearrangement of carboxylic acid 264a to lactone 265 is... 

They acted on 2-nitratoethanol with chlorides of acrylic (a), methacrylic (b) and croionic (c) acids in the presence of cuprous chloride as a polymerization inhibitor. The radical polymerization was initiated by benzoyl peroxide in nitrogen atmosphere. It lasted 20 min at 100 C. In the absence of a catalyst polymerization occurred at 20 C in the course of a few days. This observation is in agreement with the finding reported in V ol. II, p. 19 that nitrate esters can catalyse polymerization reaction, contrary to C-nitro compounds (Chapter IV). 

Protonic Acids. The polymerization of vinyl monomers by protonic acids has stimulated considerable research effort over a period of many years and the complexity of these apparently simple systems has proved enormous. Styrene polymerizations catalysed by perchloric acid have served as an arena for discussion for some time now, and in particular the question of whether a covalent perchlorate ester species occurs in the reaction, and whether or not such an entity can propagate and contribute to polymer formation, has been argued at... 

Polymers that have been synthesized by a stepwise condensation route (Section 1.2.1) that involves the evolution of water are susceptible to degradation by hydrolysis since this involves the reversal of the polymerization reaction. The conditions of high temperature and the presence of tmces of an acidic or basic catalyst are easily met in an extruder. The reaction is often auto-catalytic since the product of hydrolysis will be an acid end group. This shown in Scheme 1.73 for the acid-catalysed hydrolysis of poly(ethylene terephthalate) (PET). 

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