Polytetrahydrofuran

Tetrahydrofuran, just as other cyclic ethers, can be submitted to a cationic polymerization. It leads to polytetrahydrofuran (PTHF). Schematically, this can be expressed as follows  

The mechanism of the reaction is determined by the characteristic of the initiator. Of the numerous known initiator systems, so far only four are being used for the industrial production of PTHF  

The process (3), developed by the BASF, yields an almost colorless polyether, and the initiator (siliceous earth), after being separated in a centrifuge, can be reused. 

The process (4), developed by DU PONT, is associated with extensive experience in fluorine chemistry and requires a very special know-how for the production of the initiator resin. 

The sytem (3) is viewed as the most elegant process, and for this reason it is dis- 

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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). 

Table 1. Typical Properties of High Molecular Weight Polytetrahydrofuran...

Both polyethers and polyesters may be used as polyols. For example, Du Pont use polytetrahydrofuran for Lycra whilst US Rubber originally used a polyester of molecular mass of about 2000 obtained by condensing adipic acid with a mixture of ethylene and propylene glycols. A polyether-based mixture was used for Vyrene 2 introduced in 1967. All the polyols have terminal hydroxyl groups. 

Examples shown in this chapter are for PMMA. Other polymers can be separated as well. The polymers separated so far (1,2) include polystyrene, poly(a-methylstyrene), polycaprolactone, polycarbonate, poly(hexyl isocyanate), polytetrahydrofuran, poly (vinyl methyl ether), and polyvinylpyrrolidone. 

In this manner, growing polytetrahydrofuran cations can be terminated by using sodium salt of cumene-hydroperoxide [10]. 

Of recent interest is the living cation of tetrahydrofuran. The oxonium ion with suitable counter ions is stable and exists in equilibrium with the monomer47. Bifunctional initiators were found to produce the polytetrahydrofuran dication. 

Polystyrene-polytetrahydrofuran block copolymers121122 are an interesting case of coupling between functional polymers The mutual deactivation of living anionic polystyrene and living cationic polyoxolane occurs quantitatively to yield polystyrene-polyoxolane block copolymers. Since either of the initial polymer species can be mono- or difunctional, diblock, triblock or multiblock copolymers can be obtained. 

Polytetramethyleneglycol (polytetrahydrofuran) is formed by ring opening polyetherification of tetrahydrofuran. Branched polyalkyleneoxides are formed using polyfunctional alcohols such as trimethylolpropane and pentaerythrite. The products are liquids or waxes depending on the molar mass. Polyalkyleneoxides are often precursors for demulsifiers. 

Particular attention was placed on the crossover from segmental diffusion to the center of mass diffusion at Q 1/Rg and to the monomer diffusion at Q /i, respectively, by Higgins and coworkers [119,120]. While the transition at small Q is very sharp (see Fig. 43, right side), a broader transition range is observed in the regime of larger Q, where the details of the monomer structure become important (see Fig. 44). The experimental data clearly show that only in the case of PDMS does the range 2(Q) Q3 exceed Q = 0.1 A-1, whereas in the case of PS and polytetrahydrofurane (PTHF) it ends at about Q = 0.06-0.07 A-1. Thus, the experimental Q-window to study the internal dynamics of these polymers by NSE is rather limited. 

A third example combines cationic ROP and ATRP for the synthesis of (polytetrahydrofurane)(poly-l,3-dioxepane)(PS) miktoarm stars (Scheme 99). The initiating sites for the above polymerization were created step-by-step from amino-succinic acid (Scheme 99). 

Nitroxide attached to macromolecules also induces the living radical polymerization of St. Yoshida and Sugita [252] prepared a polymeric stable radical by the reaction of the living end of the polytetrahydrofuran prepared by cationic polymerization with 4-hydroxy-TEMPO and studied the living radical polymerization of St with the nitroxide-bearing polytetrahydrofuran chain. The nitroxides attached to the dendrimer have been synthesized (Eq. 69) to yield block copolymers consisting of a dendrimer and a linear polymer [250,253]. 

A hydroxy-containing polymer can be coupled with living polytetrahydrofuran carbocation [Cameron and Duncan, 1983] ... 

To the first category belong the homo- and copolymerization of macromonomers. For this purpose, macromolecules with only one polymerizable end group are needed. Such macromonomers are made, for example, by anionic polymerization where the reactive chain end is modified with a reactive vinyl monomer. Also methacrylic acid esters of long-chain aliphatic alcohols or monofunctional polyethylene oxides or polytetrahydrofurane belong to the class of macromonomers. 

Another way of synthesizing block copolyers it to have two polymers which possess mutually reacting chain ends. A picturesque example is the mutual deactivation of living" cationic polytetrahydrofuran and of "living" anionic polystyrene.12... 

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