Polymerization of cyclic ethers

Details Polymerization of cyclic ethers Polymerization of cyclic ethers

1992-01-27

1994-05-17

Cintins, Marianne M.

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

568614, 568615, 568620, 568622, 568623, 568624, 558483, 558484, 558485, 552 11, 528408, 528409, 528417, 528420, 528421, C07C 3118, C07C20100, C07C 4103

Patent

active

053130006

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a process of polymerising cyclic ether monomers, especially oxiranes, capable of undergoing cationic oxonium ion ring-opening polymerisation. The invention further relates to certain hydroxy-terminated poly(alkylene ether) polymers produced by this process.
Cationic polymerisation of cyclic ethers by quasi-living chain extension is a well-known mechanism by which polymers can be prepared. In such polymerisation reactions, a cationic oxonium ion forms with acidic catalyst at the end of the chain which reacts with incoming monomer molecules. The incoming molecules then acquire this cationic reactivity as they bond to the chain end to promote further chain growth (ie propagation). These quasi-living chain polymerisation reactions are frequently "seeded" by an initiator compound, present in small quantities in the reaction mixture which may form an initial part of the propagating polymer chain. Chain growth can be controlled by quenching the reaction at the appropriate time with an appropriate terminating agent eg water to give hydroxyl terminal groups.
In theory, cationic quasi-living chain polymerisation of cyclic ethers produces high purity polymers of narrow polydispersity, and since all the chains within the reaction mixture would be expected to grow at approximately the same rate. In practice, however close control over chain growth is difficult to achieve because the highly reactive chain ends to the growing polymer chains will usually undergo rapid reaction with any available unreacted monomer. Furthermore, the basicity of the monomer strongly affects the mode of the reactions involved during chain growth, since various nucleophiles other than the monomer, such as the linear ether group in the polymer chain and the counter anion at the growing end, are also present in the reaction system. Thus, chain growth competes with various side reactions, and as a result, polydispersivity is broadened and the production of unwanted impurities increased.
These problems apply in particular to the cationic polymerisation of substituted oxiranes to produce hydroxy-terminated polyether prepolymers suitable for use in elastomer-forming cross-linking reaction with appropriate curing agents. Such polymerisations, conducted within chloroalkane solvents, have been described by Hammond et al (J Polymer Science 9 pp 265-279, 1971) who used small amounts (typically less than 2 mol %) of diols as initiators and protonic acids (specifically BF.sub.3 etherate) as catalysts.
More recent attempts at producing poly(chloroalkylene) ethers by living chain polymerisation are disclosed in UK Patent Application GB 2021606A, which describes the reaction of chloroalkylene oxide monomers with an organic hydroxy-containing compound (typically a diol) in the presence of a catalyst system consisting of a fluorinated acid and a polyvalent organo-tin compound. Highly reactive oxonium ions which form at the chain ends during propagation readily react back into the polymer chain by attacking the oxo linking species to produce cyclic oligomers and short chain byproducts. These unwanted impurities can represent up to 50% contamination in the resultant prepolymer and can considerably broaden its polydispersivity, and as such seriously affect the cure of such prepolymers, the density of cross-links within the cured material, and hence its elastomeric properties.
Cyclic oligomer contamination can be reduced or even avoided in such polymerisation reactions, but only by deliberately choosing to produce polymers of low molecule weight. This is because it is usually found that the most common cyclic oligomer contaminants produced during the polymerisation of oxiranes are cyclic tetramers which occur in substantial amounts by the aforementioned back-reaction mechanism once the growing chain contains at least 5-6 alkylene oxide repeat units. By terminating chain growth before it reaches this size, the formation of these oligomers is avoided. However, this also effectively limits the maximum molecular weight of substantially oligome

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