Polyethers, Tetrahydrofuran and Oxetane Polymers

Abstract

This article reviews tetrahydrofuran and oxetane polymers and polymerization. The physical and chemical properties of polytetrahydrofurans and polyoxetanes are discussed, as well as the polymerization mechanism, including initiation, propagation, termination, chain transfer, kinetics, and copolymerization to give block, graft, and star copolymers. The most important commercial product is poly(tetramethylene ether) glycol (PTMEG), sold under the trade names Terathane (Du Pont), PolyTHF (BASF), and Polymeg (QO Chemicals). The manufacture of PTMEG is described in some detail, including the most recent industrial processes. Storage and handling of PTMEG, as well as specifications and standards of commercial products, are given. Test methods used in the 1990s are referenced, such as hydroxyl number, polymer molecular weight, and molecular weight distribution. Health and safety factors are discussed, as well as the economic aspects of PTMEG production. Most important uses of PTMEG are in elastomeric polyurethanes and polyesters. The same type of information is given for oxetane polymers, although no oxetane polymer has found any practical application and is thus not available commercially as of 1995.

Aliphatic Polyethers: Classical Polymers for the 21st Century

“…The polymer shows a relatively high heat distortion temperature (99 °C) and a low water absorption which renders it interesting for items that require sterilization, e.g., in biomedical applications. Furthermore, the polymer is stable against common solvents and only attacked by strong‐acids . Applications were mainly in the chemical processing and precision injection‐molded industrial parts like valves, precision gears, corrosion‐free coatings, films and adhesives.…”

“…To prevent these undesired high molecular weight species, transfer agents can be added: first, they allow the control of molecular weight and, second, functional groups can directly be introduced at the chain end. For example, the addition of acetic anhydride as transfer agent directly leads to acetate end groups which can be hydrolyzed after the polymerization thereby giving a bishydroxy functional compound with adjusted molecular weight …”

“…Strong nucleophiles, like chloride are not able to form that necessary ion pair. [ 169 ] In contrast to Dreyfuss and Dreyfuss who performed the polymerization in bulk, Penczek and coworkers investigated the polymerization of THF in solution using different catalysts and solvents. [170][171][172] More recently, the use of a novel bifunctional organohalide initiator systems enables the synthesis of block copolymers through a combination of CROP and radicalic polymerizations.…”

Studies on mechanism of tetrahydrofuran polymerization initiated by a heteropolyacid

“…Polymerization of tetrahydrofuran (THF) is one of the most widely studied and generally best understood cationic ring-opening polymerization 1) . The products of THF polymerization are commercially used as mediate materials for polyurethane and polyester elastomers 2) . Since the original report of oxonium salt initiated polymerization of THF by Meerwein in the late 1930's 3,4) , various types of compounds have been reported as suitable initiators including strong protonic acids [5][6][7] , Lewis acids 8,9) , carbenium ions 10) , oxocarbenium ions 11) , metal salts 12) , rare earth complexes 13,14) , esters of strong acids [15][16][17] and photoinitiators such as iodonium and sulfonium salts 18) .…”

Ionic Polymerization

“…Newer processes use solid catalysts like zirconium oxide together with acetic anhydride to form poly-THF with two acetate end groups, which later are hydrolyzed to give the dihydroxy polymer. Other acidic catalysts such as zeolites or acid montmorillonite clay are also described [245][246][247].…”