Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1996-02-09
1997-02-11
Schofer, Joseph L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526328, 5263285, 526346, 526347, 5262196, C08F 426, C08F 2010, C08F 1208, C08F 404
Patent
active
056022204
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/ GB94/01693, filed Aug. 2, 1994.
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 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 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 effectively achieved with a further class of cobalt chelate complexes which have not been disclosed in the prior art for such use.
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, wherein said polymerisation is performed in the presence of a compound for effecting molecular weight control, said molecular weight control compound being selected from cobalt II chelates of the following formulae I, II and III: ##STR2## wherein: x and y are independently 2 to 50; each R.sup.1, R.sup.2, R.sup.3 and R.sup.4 is independently selected from H, C1-C12 alkyl, optionally substituted aryl (preferably optionally substituted phenyl), OR.sup.5 where R.sup.5 is C1 to C12 alkyl or optionally substituted aryl (preferably optionally substituted phenyl), CO.sub.2 R.sup.5, SO.sub.3 H, C(.dbd.O)R.sup.5, CO.sub.2 H, NO.sub.2, OH, NR.sup.5.sub.2, NH.sub.2, NHR.sup.5, SR.sup.5, SH, CN, SO.sub.3 R.sup.5, halogen (preferably C1, Br, I or F), 2-furyl and 3-furyl; (CR.sup.6.sub.2 O).sub.n, optionally substituted o-phenylene, and optionally substituted 1,8-naphthylene, where each R.sup.6 is independently selected from H and C1 to C12 alkyl, and n is 1 to 10; charge of 2 and are associated with an anion or anions for balancing the positive charge, while that of formula III is neutral; III in which the Co atom is additionally covalently bonded, in a direction at right angles to the macrocyclic chelate ring system, to H, a halide ion (e.g. Cl.sup.-) or other anion, or a homolytically dissociatable organic group.
It is to be understood that, as defined above, the defined cobalt chelates of formulae I and II are positively charged (of charge 2) and are
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Haddleton David M.
Muir Andrew V. G.
Cheng Wu C.
Schofer Joseph L.
Zeneca Limited
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