Polymerization of tetrahydrofuran

Cyclic ether and acetal polymerizations are also important commercially. Polymerization of tetrahydrofuran is used to produce polyether diol, and polyoxymethylene, an excellent engineering plastic, is obtained by the ring-opening polymerization of trioxane with a small amount of cycHc ether or acetal comonomer to prevent depolymerization (see Acetal resins Polyethers, tetrahydrofuran). 

The polymerizations of tetrahydrofuran [1693-74-9] (THF) and of oxetane [503-30-0] (OX) are classic examples of cationic ring-opening polymerizations. Under ideal conditions, the polymerization of the five-membered tetrahydrofuran ring is a reversible equiUbtium polymerization, whereas the polymerization of the strained four-membered oxetane ring is irreversible (1,2). 

The polymerization of tetrahydrofuran was first studied ia the late 1930s (3,4). In 1960, this work was summarized (4), and the Hterature on tetrahydrofuran polymers and polymerization has been growing ever siace. Polytetrahydrofuran with hydroxy end groups has become a large-scale commercial product, used mainly as the flexible polyether segment ia elastomeric polyurethanes and polyesters. It is commercially available under the trade names Terathane (Du Pont), Polymeg (QO Chemicals), and PolyTHF (BASF). Comprehensive review articles and monographs have been pubUshed (2,5-8). 

Cationic polymerization of tetrahydrofuran with the or bis(3,5-di-bromomethyl) benzoyl peroxide and AgPp6 pairs of 4,4 -bromomethyl benzoyl peroxide and AgPp6 yield active poly-THP having peroxide group in the main... 

It has been shown for many metal halides and monomers that binary mixtures of these can be prepared (usually in a solvent) without any polymerization taking place. Such a quiescent mixture can be made to react by the addition of a suitable third compound, which is called the co-catalyst. This term is preferable to the word promoter , because in certain contexts a substance is called promoter which enhances the rate or yield of a reaction that will also go in the absence of the promoter herein lies the true distinction between promoter and co-catalyst [28]. (For example, small quantities of epoxides or epichlorohydrin act as promoters in the cationic polymerization of tetrahydrofuran.) I will take it that in the above quotation the word promoter was inadvertently used in place of co-catalyst , for only thus does it become really meaningful. 

Another reaction, related to this, is the initiation of the polymerization of tetrahydrofuran by the triphenymethyl cation. This involves H-abstraction from the monomer, but is certainly more complicated [70a] than was believed at one time [70b]. 

Reactions in which a reagent is cloven (i) The termination reactions of the type (IX) in which an anionic fragment is abstracted from the anion, so that the chain-carrier is neutralised. This type of termination has been claimed to occur in many systems for example, in the polymerization of tetrahydrofuran by PF5 a terminal F from PF 6 was indeed found [119]. 

This is not the first time that the kinetics of bulk polymerizations has been analysed critically. Szwarc (1978) has made the same objection to the identification of the rate constant for the chemically initiated bulk polymerization of tetrahydrofuran as a second-order rate constant, k, and he related the correct, unimolecular, rate constant to the reported by an equation identical to (3.2). Strangely, this fundamental revaluation of kinetic data was dismissed in three lines in a major review (Penczek et al. 1980). Evidently, it is likely to be relevant to all rate constants for cationic bulk polymerizations, e.g., those of trioxan, lactams, epoxides, etc. Because of its general importance I will refer to this insight as Szwarc s correction and to (3.2) as Szwarc s equation . 

Fig. 7-1 Determination of the equilibrium monomer concentration [M]c for the (CiHs O1 (Blvi) initiated polymerization of tetrahydrofuran in dichloroethane at 0°C. After Vofsi and Tobolsky [1965] (by...

Fig. 7-2 Disappearance of monomer in the polymerization of tetrahydrofuran by 2CH+(SbCl6) at 25°C a plot of Eq. 7-45. After Afshar-Taromi et al. [1978] (by permission of Huthig and Wepf Verlag, Basel and Wiley-VCH, Weinheim).

Fig. 4. Rate of cationic polymerization of tetrahydrofuran to polyether at 0° C as function of monomer concentration. Reproduced, with permission, from Vofsi and Tobolsky J. Polymer ScL 3 A, 3261 (1965).

Imai, H., T. Saegusa, S. Matsumoto, T. Tadasa, and J. Furukawa Polymerization of tetrahydrofuran by triethyl-aluminum-water system. Makromol. Chem. (in press). 

Saegusa, T., S. Matsumoto, T. Ueshima, and H. Imai Preprint of paper Polymerization of tetrahydrofuran by AlEt3—H20-promotor system, behavior of promotor given at International Symposium on Macromolecular Chemistry, Japan, 1966. 

Pseudoliquid-phase catalysis (bulk type I catalysis) was reported in 1979, and bulk type II behavior in 1983. In the 1980s, several new large-scale industrial processes started in Japan based on applications of heteropoly catalysts that had been described before (5, 6, 72) namely, oxidation of methacro-lein (1982), hydration of isobutylene (1984), hydration of n-butene (1985), and polymerization of tetrahydrofuran (1987). In addition, there are a few small- to medium-scale processes (9, 10). Thus the level of research activity in heteropoly catalysis is very high and growing rapidly. 

The current work on Friedel-Crafts polymerization of cyclic ethers may be considered to date from about 1940 when Meerwein and his associates prepared a series of tertiary oxonium salts and applied them to the polymerization of tetrahydrofuran. These salts, of the general form R30+... M X4i, are easily prepared from the corresponding metal halide in a reaction with an epoxide (preferably epichlorohydrin) in ether solution. According to Meerwein et al. (3) this reaction takes place in the following steps ... 

The polymerization of tetrahydrofuran is a small and perhaps relatively simple part of the general field of polymerization of cyclic ethers by Friedel Crafts catalysis. The existence of such catalysis has of course been known for a long time (10) but it is only in recent years that the complexity of the reactions has been recognized and an effort made to study them. It is now apparent that the reactions are not only highly complex but vary considerably with the particular catalyst or monomer employed so a good deal of careful research will be required to clarify them. 

Coupling to produce dimeric product was a side reaction in these systems also, e.g. 75 % dimer formation was reported for poly(styryl)lithium and 23 % dimer formation with the poly(styryl)-Grignard reagent 326). However, it should be noted that the only reported characterizations of these reactions were size exclusion chromatography traces and silver catalyzed polymerization of tetrahydrofuran using the polymeric halogen compounds as co-initiator. 

In the patent literature, there are several reports of the cationic polymerization of tetrahydrofuran (THF) with Nafion-H. In most cases, small amounts of acetic anhydride were added so the initial polymer had a terminal acetate group that could be hydrolyzed to the free hydroxyl. THF has also been homopolymerized936 938 and copolymerized with ethylene oxide and propylene oxide in the presence of Nafion-... 

Until now we have been concerned mostly with crystalline polyethylene. In this section we consider the solid-state structure of poly(tetramethylene oxide) [22]. Since the melting temperature of this polymer is 42 °C, we examined the structure at temperatures below room temperature. The sample was prepared by ringopening polymerization of tetrahydrofuran by using triethyloxonium hexa-... 

Cationic initiation is used in the polymerization of tetrahydrofurane and cyclic siloxanes. 

The formation of cyclic oligomers in the polymerization of tetrahydrofuran has not been observed (23). In the case of 1,3-dioxolane small amounts of oligomers going from dimer to nonamer have been isolated (24). Under the influence of borontrifluo-ride etherate in methylene chloride at 35 °C small amounts of 1,3,5-trioxepane are formed (25). Miki, Higashimura and Okamura (25) ascribed the formation of this substance to a backbiting reaction in the polymerization of dioxolane ... 

In the polyurethane industry, the polymeric glycols are prepared by anionic polymerization of epoxides such as ethylene oxide and propylene oxide. Poly(tetra-methylene glycol), which was prepared by polymerization of tetrahydrofuran, was subjected to chain extension by reaction with diisocyanate (polyurethane formation) and with dimethyl terephthalate (polyester by alcoholysis). 

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