Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1996-08-28
1998-06-23
Page, Thurman K.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526133, 526328, 526172, 556 7, 556138, C08F 412, C08F 480, C08F 2018, C07F 502
Patent
active
057706654
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.
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 control appropriately 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 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 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: ##STR1## wherein each group R is an organic group which, independently, is a monovalent group which comprises a cyclic structure, or taken together as two adjacent groups provides a divalent group completing a cyclic structure comprising a first cyclic ring containing the said adjacent carbon atoms and optionally including a second cyclic ring, and wherein further one or more of the groups R includes at least one heteroatom selected from O, N, S, P, halogen and Si, which heteroatom provides a substituent group or part of a substituent group on the cyclic structure, or a heteroatom of a heterocyclic ring of the cyclic structure; and wherein each group Q is independently selected from F, Cl, Br, OH, C.sub.1-2 alkoxy and C.sub.1-2 alkyl; or being a CoIII analogue of the cobalt II chelate of formula I in which the Co atom is additionally covalently bonded, usually in a direction at rights angles to the macrocyclic chelate ring system, to H, a halide or other anion, or a homolytically dissociable organic group; see WO-A-87/03605 for compounds of such a CoIII chelate type.
The groups R may, independently, be monovalent groups of aromatic or aliphatic character, or may have a combination of aromatic and aliphatic character. Adjacent groups R and R taken together may also provide a divalent group, preferably having or including a cyclic structure (i.e. a structure
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Haddleton David M.
Leeming Stephen W.
Muir Andrew V. G.
Cheng Wu C.
Page Thurman K.
Zeneca Limited
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