Free radical polymerisation process

Details Free radical polymerisation process Free radical polymerisation process

1997-07-15

1999-10-05

Wilson, Donald R.

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

526133, 526172, 526328, 556 7, 556138, C08F 238, C07F 502

Patent

active

059626097

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for the free-radical initiated polymerisation of olefinically unsaturated monomer(s) in which molecular weight control is achieved by the presence of certain cobalt chelate complexes. The invention also relates to the cobalt chelate complexes themselves and to a process for their production.
Polymers of low molecular weight, known as oligomers, are often desired for various applications (such as coating compositions) either in their own right or as precursors for other polymers. In order to form oligomers it is necessary to appropriately control the polymerisation process being used to yield the desired type of product. In free-radical polymerisations, which are widely used for polymerising olefinically unsaturated monomers, various conventional means are employed for controlling and limiting the molecular weight of the growing polymer chains. Of these, the addition of thiol compounds to the polymerisation has probably been used the most extensively; the thiol acts as an effective chain transfer agent but unfortunately contaminates the system to which it has been added by virtue of its distinctive and persistent odour.
More recently, attention has turned to the use of various transition metal complexes, particularly cobalt chelate complexes, as chain transfer agents for use in controlling molecular weight when radically polymerising olefinically unsaturated monomers.
For example, various literature references, such as N. S.Enikolopyan et al, J.Polym.Sci., Polym. Chem. Ed., Vol 19, 879 (1981), disclose the use of cobalt II porphyrin complexes as chain transfer agents in free radical polymerisation, while U.S. Pat. No. 4,526,945 discloses the use of dioxime complexes of cobalt II for such a purpose. Various other publications, e.g. U.S. Pat. No. 4,680,354, EP-A-0196783 and U.S. Pat. No. 4,694,054, describe the use of certain other types of cobalt II chelates as chain transfer agents for the production of oligomers of olefinically unsaturated monomers by free-radical polymerisation. WO-A-87/03605 on the other hand claims the use of certain cobalt III chelate complexes for such a purpose. Whether or not a particular cobalt chelate complex (or class of cobalt chelate complexes) is effective as a chain transfer agent in a radical polymerisation process is unpredictable; some are effective and some are not.
We have now discovered that molecular weight control in the free-radical polymerisation of olefinically unsaturated monomers may be effectively achieved with a further class of cobalt chelate complexes which have not been disclosed in the prior art.
According to the present invention there is provided a process for the free-radical polymerisation of olefinically unsaturated monomer(s) (especially methacrylate monomer(s)) using a free-radical initiator, the polymerisation being performed in the presence of a compound for effecting molecular weight control, the molecular weight control compound being a CoII chelate of the following formula I: ##STR2## wherein each group X, independently in each ring and in different rings, is a substituent selected from alkyl of 1 to 14 carbon atoms and cycloalkyl of 6 to 14 carbon atoms; n, independently in each ring, is 0 to 5 provided that in at least one ring, n is 1 to 5; Z, independently on each boron atom, is selected from F, Cl, Br, OH, alkoxy of 1 to 12 carbon atoms, aryloxy of 6 to 12 carbon atoms, alkyl of 1 to 12 carbon atoms, and aryl of 6 to 12 carbon atoms; --O--(Q)--O-- where Q is a divalent aryl or alicyclic linking group or an alkylene linking group, or two Z groups taken together on one or both boron atoms provide a 1,5-cyclooctanediyl linking group; atom is additionally covalently bonded, in a direction at right angles to the macrocyclic chelate ring system, to H, halide or other anion, or a homolytically dissociable organic group; and wherein optionally at least one further ligand is coordinated to the Co II or Co III atom, being a ligand(s) which does not alter the Co valency state.
Preferably X is alkyl of 1 to 14

REFERENCES:
patent: 4526945 (1985-07-01), Carlson et al.
patent: 4680354 (1987-07-01), Lin et al.
patent: 4694054 (1987-09-01), Janowicz
patent: 5770665 (1998-06-01), Haddleton et al.
Enikolopayan et al, J. Polym. Sc. Polymer Chem. Ed., vol. 19, 879 (1981).

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