Process for the production of polyethers derived from oxetanes

Details Process for the production of polyethers derived from oxetanes Process for the production of polyethers derived from oxetanes

1992-01-28

1993-05-11

Kight, III, John

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From heterocyclic reactant containing as ring atoms oxygen,...

528403, 528409, 528417, 528421, 528361, 528362, C08G 6510, C08G 6518, C08G 6520, C07C 4311

Patent

active

052101797

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to the production of polyethers derived from oxetanes using cationic polymerization initiators. The polyethers are an important class of polymers finding application as detergents, disinfectants, absorbents and elastomer prepolymers amongst other uses. For many of these uses it is highly desirable to produce a pure product of controlled molecular weight and controlled polydispersity.
The cationic polymerization of oxetanes involves the opening of the heterocyclic oxetane ring under catalytic conditions. This mechanism of polymerization is described in U.S. Pat. No. 4393100 (Manser). The catalyst described by Manser combines with a preinitiator precursor to form an adduct capable of forming a cationic initiator with the oxetane monomer. Polymer chains are built up as oxetane molecules add on to the reactive end groups of the initiator molecules, the number of such chains being proportional to the number of preinitiator precursor molecules present.
In the process described in U.S. Pat. No. 4393199, the preinitiator precursor followed by the catalyst are added to bulk solutions of the oxetane. In some examples, the precursor is first added to the catalyst to form the adduct which is then added to the bulk solution of monomer. Principal examples given of the precursor and catalyst are, respectively, 1,4-butane diol (a difunctional alcohol) and boron trifluoride etherate, the diol replacing the ether to give the active adduct. A catalyst-to-diol molar ratio of at least 1.5:1 was found necessary to polymerise the monomer, whereas at a ratio of 3:1 and higher, loss of polymer molecular weight control occurred and the polydispersivity of the product become much higher. However, within the preferred catalyst-to-diol molar ratio of from 1.5:1 to less than 3:1, the yield of polymer was only 63-68% when using 1,4-butane diol as the precursor, indicating the presence of significant amounts of impurities in the product.
A further example of this process of polymerization as applied to 3-nitratomethyl, 3-methyloxetane (NIMMO) is provided in a technical report by Morton Thiokol (Defence Technical Information Centre publication No. 85837, Defence Logistics Agency, Cameron Station, Alexandria, Va., page E4 to E5.) This document relates to a bulk reaction polymerization of NIMMO using the methods of U.S. Pat. No. 4393199 and provides a product containing about 25% impurity.
The present invention seeks to provide an improved process for the production of polyethers by quasi-living cationic polymerization of oxetanes which provides products of increased reproducibility, reduced impurity levels and more complete control of molecular weight.
Accordingly, the present invention provides a process for the polymerization of oxetanes monomers comprising the steps of (a) mixing together a catalyst capable of catalysing the cationic polymerization of the monomer with a preinitiator precursor to yield an active adduct of the catalyst and precursor, (b) bringing the adduct into contact with the monomer so as to cause the adduct to form an initiating species with the monomer and thereafter undergo chain extension polymerization with further of said monomer, and (c) allowing the polymerization to proceed substantially to completion, wherein step (b) is performed by slowly adding the monomer at a controlled rate to a quantity of the adduct in solution over a period of several hours.
The rate of addition is preferably such that the catalyst is always in stoichiometric excess over the monomer. Advantageously the rate of the polymerization of the monomer in the presence of the catalyst is first determined and the rate of addition is set such that it is slower than this so that the catalyst remains in stoichiometric excess.
Whereas the prior art process of Manser uses the initial stoichiometry and the reaction temperature to provide molecular weight control the present process adds monomer at a rate such that the ratio of the monomer to the catalyst does not exceed levels known to produce cyclic oligomerisation. On

REFERENCES:
patent: 4707540 (1987-11-01), Manser et al.
patent: 4764586 (1988-08-01), Manser et al.
patent: 5099042 (1992-03-01), Wardle et al.

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