Polymerization of tetrahydrofuran, THF

The polymerization of this 1,4 epoxide has been widely studied [115] and the polymer produced, polytetramethylene oxide or polytetrahydro-furan, has found commercial application. The most characteristic feature of the polymerization is the occurrence of a ceiling temperature within the range of normal laboratory experiments, 85°C. In any polymerization the propagation reaction is normally shown as a reaction going 100% to completion although in fact this reaction, and the other elementary steps, are really chemical equilibria. Some reactant, usually monomer in the case of propagation, is present at the end of the reaction although the value of the 

A number of determinations [118] of these parameters have been made 

In many instances the polymerization of tetrahydrofuran seems to proceed without termination, and living polymers, in which transfer reactions are also absent, have been prepared [40, 41]. A simple kinetic scheme suffices therefore to describe the situation, i.e. 

Here fej, kp and fej are the rate coefficients for initiation, propagation and depropagation respectively, and, for convenience only, the counter-ion is shown as accompanying the reactive cation. For such a scheme Vofsi and Tobolsky [119] have expressed the rate of polymerization, —d[M] /dt, as 

Preformed triethyl ox onium tetrafluoroborate, Etj O BF, has been used by Vofsi and Tobolsky [119] as an initiator at 0°C in ethylene dichloride solvent. Using C labelled catalyst, it was possible to show that the initial initiator concentration corresponded to the concentration of active centres formed. When only 15% of the monomer had been consumed, the initiator conversion was better than 90%. The rate at which the initiator disappeared followed the experimental law 

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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-... 

In the polymerization of tetrahydrofuran (THF) initiated with HO-SO2CF3 in CD3NO2 solvent at 35° C (molar ratio [THF]/[CD3N02]/ [CF3SO3H] = 20.8/24.6/1), the equilibrium monomer concentration (i.e., the ultimate conversion of monomer to polymer) is reached in 2 hr. At this stage of polymerization, concentration of cyclic oligomers is still very low [90]. 

Synthetic applications of the cationic polymerization of tetrahydrofuran (THF) are related to two groups of products, namely high-molecular-weight polymer and lower-molecular-weight products with controlled DPn and well defined end-groups which are being used as telechelics. 

Here, the cationic ring-opening polymerization of tetrahydrofuran (THF) using silver triflate (AgOTf) in the presence of 2-bromopropionylbromide produces a Br-terminated PTHF. Block copolymers can then be prepared using S, MMA, and MA, employing a CuBr/(dNbpy)2 catalyst. 

The cationic polymerization of tetrahydrofuran is used commercially to produce a,CD-dihydroxypoly(tetramethylene oxide) (PTMO glycol). Although this polymer is not used by itself as an elastomer, it is used as one of the elastomeric block components for preparation of segmented thermoplastic polyurethane [133] and thermoplastic polyester [134] elastomers. The cationic polymerization of tetrahydrofuran (THF) is a living polymerization under proper experimental conditions [135-139], i.e., it does not exhibit any termination step, very much like the analogous anionic polymerizations which are discussed in Section VIII. However, these polymerizations are complicated by the fact that the ceiling temperature, where the free energy of polymerization is equal to zero, is estimated to be approximately 83 2°C in bulk monomer solution [140] therefore, the polymerization is reversible and incomplete conversion is often observed, especially in the presence of added solvent. For... 

Significant differences in reactivity were observed between p-methylbenzyl bromide and benzyl bromide in the formation of carbenium ions by reaction with silver hexafluorophosphate. The former compound in conjunction with AgPFj was found to be a highly efficient initiator for the cationic polymerization of tetrahydrofuran (THF) at —10 °C. In situ formation of the benzyl ion was much slower, rendering syntheses of monodisperse poly(THF) impossible. 

Heterocyclic Monomers.—Reviews of the polymerization of tetrahydrofuran (THF) were published. Rate constants of propagation of THF on macroesters and macroions were measured. In the polar solvent nitromethane, where macroesters are not important, it was shown that k and k t are identical within experimental error, and are not influenced by the nature of the counterion. It was postulated that the active centres are so highly solvated by monomer that free ions and ion-pairs are indistinguishable in terms of reactivity. 

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). 

A 100-ml autoclave was charged with ethyl acetate (24 parts), 1,4-dioxene (20 parts), and t-bu ty 1 pcrox pi val ate (0.3 parts) and then treated with chlorotrifluoroethylene (31 parts) and polymerized at 55°C for 13 hours. The precipitated polymer was isolated and dissolved in 150 ml of tetrahydrofuran (THF) and then precipitated in methanol, the process being repeated twice. Thirty-five grams of product were isolated having a Tg of 154°C and an Mn of28,000 Da with a refractive index of 1.459. The material was soluble in most organic solvents and formed transparent films. 

In a more recent study Sigwalt et al. [41] investigated the use of carbazyl sodium to initiate PS polymerization in tetrahydrofuran (THF). This initiator produced only one living end per chain. Excellent agreement with the results obtained on amphianionic polymer was obtained. At levels of living ends below 10 molel the rate coefficient found for ion pairs was 3 x 10" 1 mole sec and for free ions 4 1 mole sec . The dissociation constant (determined kinetically) was 6.4 x 10 mole 1 . ... 

Researches previously attempted to treat the mechanism of the polymerization of cyclic acetals as being similar to the mechanism of tetrahydrofuran (THF) polymerization. The above data show an essential difference between the cationic polymerization mechanisms of cyclic ethers and cyclic acetals. 

Matyjaszewski, K., Kubisa, R, Penczek, S., 1975. Kinetics and mechanism of cationic polymerization of tetrahydrofuran in solution 1. THF-Ccl4 system. J. Polym. Sci. Part A Polym. Chem. 13 (4), 763-784. 

Ray S, Singha NR, Ray SK. 2009. Removal of tetrahydrofuran (THF) from water by pervaporation using homo and blend polymeric membranes. Chem. Eng. J. 149 153-161. 

Cationic polymerization has also been used for the synthesis of macromonomers, especially after the development of living cationic polymerization techniques (73). Macromonomers were prepared by the cationic ringopening poljnnerization of tetrahydrofuran (THF) using methyltriflnoromethane sulfonate, followed by termination with 3-sodio-propyloxydimethylvinylsilane to give a macromonomer with vinyl silane end groups (74) (eq. 18). 

By applying cationic polymerization of tetrahydrofuran starting from the carbonyl chloride group-functionalized multiwalled carbon nano tubes (MWNT) with silver perchlorate as a catalyst poly-THF was chemically anchored to MWNT surfaces affecting their properties. 

Monosubstituted derivatives of tetrahydrofuran (THF) have been known to be difficult to polymerize due to thermodynamic reasons. Bednarek and Kubisa extended cationic multibranching polymerizations to the class of five-membered cyclic ethers containing hydroxyl groups as substituents. They polymerized 2-(hydroxymethyl)tetrahydroftiran, using a trifluoromethanesulfonic acid initiator. MALDI-TOF mass... 

Figure 3 Effect of tetrahydrofuran (THF) on isoprene polymerization in hexane at 30 °C fipfreq. poiymerization rate in the presence of added THF fip(hexane), polymetization rate in hexane. From Morton, M. Fetters, L. J. Bostick, E. E. J. Polym. Sci. Part C-/1963,311-323 reprinted by permission of John Wiley and Sons.

Gel Permeation Chromatography. The instrument used for GPC analysis was a Waters Associates Model ALC - 201 gel permeation chromatograph equipped with a R401 differential refractometer. For population density determination, polystyrene powder was dissolved in tetrahydrofuran (THF), 75 mg of polystyrene to SO ml THF. Three y -styragel columns of 10, 10, 10 A were used. Effluent flow rate was set at 2.2 ml/min. Total cumulative molar concentration and population density distribution of polymeric species were obtained from the observed chromatogram using the computer program developed by Timm and Rachow (16). 

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