PolyTHF

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). 

An amine-terminated poly ether (ATPE) is prepared as follows. Charge poly(tetramethylene oxide) diol (PolyTHF 1000, BASF, 75.96 g, 0.0759 m) to a 500-mL three-neck round-bottom flask fitted with a thermocouple, a mechanical stirrer, and a vacuum port. Add tert-butylacetoacetate (24.04 g, 0.1582 m) and apply vacuum. Heat at 175° C for 4 h, Fourier transform infrared (FTIR) analysis should indicate complete loss of the polyol OH absorption at 3300 cm. The room temperature viscosity of the product should be about 520 mPa-s. React this acetoacetylated product (85.5 g, 0.0649 m) with cyclohexylamine (14.5 g, 0.1465 m) at 110° C under vacuum for several hours. Cool the resultant cyclohexylaminocrotonate poly ether product to room temperature (1790 mPa-s at room temperature). 

This polymeric oxocarbenium salt readily initiates the cationic ring opening polymerization of oxolane to produce a polystyrene-polyTHF block copolymer. Molecular weight control is provided, polydispersity is narrow and compositional heterogeneity is small59). 

The values of /labs were determined from the experimentally measured absorption anisotropy with Eq. 6. In viscous polyTHF, the rotational movement of dye molecules on a lOOps time scale is assumed to be negligible, and thus, does not reduce the limiting value of anisotropy. For the concentrated fluorene solutions (5 x 10 M, 1 mm cuvette), the anisotropy Tabs was not affected by FOrster depolarization mechanisms [13] due to the short time delay, tD, between probe and pump pulses when td/ti 1 [35]. 

Fig. 14 Excited state absorption (AD (1), ADx (2)) and absorption anisotropy (3) spectra of compoiuids 16 (a) and 22 (b) in polyTHF...

Fig. 18 Two-photon excitation anisotropy spectra (1, 1, top scales) for compound 6 (a, 1), 11 (a, 1 ), 9 (b, 1) in polyTHF and 17 (b, 1 ) in silicon oil. Solid lines (2, 2 ) are the corresponding linear absorption spectra...

The values of two-photon anisotropy as a function of calculated by Eq. 9 at several angles = P + k/2, are shown in Fig. 19. The parameters /3em were chosen in accordance with the experimentally observed range of the corresponding angles for lluorene derivatives in polyTHF [15,21,22,25]. As fol-... 

The photochemical stabihty of the molecules is characterized by the quantum yield of photodecomposition, (P = N/Q [69], where N and Q are the numbers of decomposed molecifles and absorbed photons, respectively. The photochemical properties of the fluorene derivatives were investigated in different organic solvents (hexane, CH2CI2, ACN, and polyTHF) at room temperature by the absorption and fluorescence methods and comprehensively described [70-72]. These methods are based on measurements of the temporal changes in the steady-state absorption and fluorescence spectra during irradiation. For the absorption method, the quantum yield of the photodecomposition under one-photon excitation, c >ipa, can be obtained by the equation [73] ... 

It has now become well established that living cationic polyTHF can be prepared under carefully controlled conditions which ensure that no appreciable transfer reactions occur. 

The reaction of pyridine with living polyTHF at -10eC has been examined in detail by gpc and H nmr, and the formation of polymer pyridinium salts (equation 6) has been shown to be rapid and quantitative.8. The salt is stable and does not exchange with any excess oxonium ions present in solution. Interestingly,... 

A number of other heterocycllcs have been similarly studied and shown by H nmr, to produce quaternary ammonium salts with living polyTHF.2- Moreover, their rates of reaction are a direct function of their basicities, the following order of reactivities being observed ethyl pyridine > pyridine > isoquinoline > quinoline > acridine. Aliphatic tertiary amines also react in the same way the order of reactivities was found to be triethylame > tributylamlne > dlethylanillne. In all cases studied, the quaternary ammonium salt once formed did not exchange with any excess oxonium lone. 

Lastly, living polyTHF has been shown to react rapidly and efficiently with the pendant pyridine units of an AB poly(styrene-b-4-vlnylpyrldlne) which had been prepared anlonlcally. The resulting graft copolymer possessed distinctly different solubility characteristics from Its parent block copolymer and Its composition and hence Its properties could be closely controlled by suitable selection of the relative reagent concentrations. 

Reactions analogous to that outlined with tertiary amines may be carried out with other amines. The reaction of secondary amines with polyTHF should result in tertiary amines terminated polymers (equation 7), and experimentation Involving gpc and H nmr analysis has broadly confirmed this expectation. The reaction with dlethylamlne, dicyclohexylamlne and piperidine... 

Of course the tertiary amine terminated polymer thus produced Is capable of being quaternlzed by alkyl halides and this has been confirmed experimentally. Moreover, It can be reacted with further living polyTHF to yield a polymer possessing a quaternary ammonium salt moiety at a point along the chain controlled by the relative molecular weights of the two living THF polymers reacted In the system, and again experiments have shown this to occur. 

Fig. 2.1. GPC-traces of polyTHF initiated by the HSbF6/Ac20 system (fE-content of ester groups in...

Until recently it was claimed that in the cationic polymerization of THF the final THF-polyTHF mixture contains no cyclic oligomers u. Further examination reveals that cyclic oligomers are formed, albeit slowly, when the living system is kept at the living polymer-monomer equilibrium for longer reaction times 2- 3). This is illustrated in Fig. 3.7, showing the increase of concentration of cyclic tetramer (in arbitrary units) with time 3). Under these conditions the monomer-polymer equilibrium is reached in about 1 hr. 

Using similar conditions the synthesis of block copolymers was attempted 33,34). Thus, ECH was polymerized in the presence of a macromolecular diol based on polyTHF and the products were analysed by liquid chromatography. 

Another important synthetic application of this concept is in preparation of block copolymers of THF and EO (cf. Sect. 15) e.g., addition of EO to hydroxyl terminated polyTHF in the presence of strong acid. 

Another approach for the preparation of BCMO graft copolymers was based on the use of macromolecular initiators 38). Polystyrene or polyTHF containing dioxole-nium groups in the chain were prepared and used as initiators of BCMO polymerization as shown for polystyrene ... 

The synthesis of high-molecular-weight poly THF became possible after the discovery of the living nature of THF polymerization. This discovery started with the work of Meerwein u and the observations were then formulated in, terms of a living process simultaneously and independently by Rosenberg et al. 1,) Dreyfuss and Drey-fuss 3) and Vofsi and Tobolsky 4) (cf. Adv. Pol. Sci. 37). Further development at DuPont, BASF and other companies led eventually to commercialization of polyTHF... 

The desired end-groups can be introduced after the living polymer-monomer equilibrium is reached. The preparation of polyTHFs, terminated at both ends with primary amino, bromine, isocyanate, and thiol end-groups, has been described by Smith and Hubin5). 

Properties of the high-molecular-weight polyTHF, which to our knowledge has not been commercialized, are given in the reviews on polyTHF by Dreyfuss and Dreyfuss 3,8). 

PolyTHF is a crystalline (up to 80%) material 9), melting at 42 °C, although higher values (up to 60 °C) have also been reported and it behaves as an elastomer above this temperature. 

Telechelic polyTHF oligodiols (DuPont, BASF, Quacker Chem.) have found important applications, mostly as soft segments in multiblock elastoplastic materials such as polyurethanes (e.g. Spandex ) and polyesters (Hytrel ). 

---