Free radical polymerisation process

Details Free radical polymerisation process Free radical polymerisation process

1996-10-11

1997-11-04

Schofer, Joseph L.

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

526 94, C08F 412

Patent

active

056841019

DESCRIPTION:

BRIEF SUMMARY
This application is the national phase of international application PCT/GB95/00577, filed Mar. 17, 1995.
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.
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 bean 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 EP-A-0199436, 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.
We have now discovered that molecular weight control in the free-radical polymerisation of olefinically unsaturated monomers may be very 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 methacrylic monomer(s)) using a free-radical initiator, the polymerisation being performed in the presence of a compound for effecting molecule weight control, the molecular weight control compound being a CoII chelate of the following formula I: ##STR2## wherein each group X is a divalent group which forms with the two carbon atoms to which it is bonded a pericondensed polycyclic group, this being a group having 3 or more carbocylic rings where the oxime-containing carbocyclic ring has carbon atoms in common with 2 or more of the other rings, said polycyclic group preferably having at least one aromatic ring, and said polycyclic group being unsubstituted (apart from the oxime groups) or having at least one hydrocarbyl substituent; and wherein each group Q is independently selected from F, Cl, Br, OH, C.sub.1-12 alkoxy, aryloxy (preferably C.sub.6-10, more preferably phenoxy), C.sub.1-12 alkyl and aryl (preferably C.sub.6-10, more preferably phenyl); or two Q groups taken together provide on one or both boron atoms a group --O--(G)--O-- where G is a divalent aryl or alicyclic linking group or an alkylene linking group; or two Q groups taken together on one or both boron atoms provide a 1,5-cyclooctanediyl linking group; or being a CoIII analogue of said cobalt II chelate of formula I in which the Co atom is additionally covalently bonded, usually in a direction at right angles to the macrocyclic chelate ring system, to H, halide or other anion, or a homolytically dissociable organic group.
As reci

REFERENCES:
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patent: 4680352 (1987-07-01), Janowicz et al.
patent: 4680354 (1987-07-01), Lin et al.
patent: 5602220 (1997-02-01), Haddleton et al.
N.S. Enikolopyan et al, J. Polym. Sc. Polymer Chem Ed., vol. 19, 879 (1981) .

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