The present invention relates to processes for synthesis of polymer compositions with reduced catalyst content, wherein ethylenically unsaturated monomers containing less than 0.5 wt % of ethylenically unsaturated monomers with at least one carboxylic group, sulfonic acid group and/or at least one phosphonic acid group relative to the total weight of the ethylenically unsaturated monomers are polymerized by means of initiators containing a transferable group of atoms and of one or more catalysts comprising at least one transition metal in the presence of ligands which can form a coordination compound with the metal catalyst or catalysts and, after the polymerization, the catalyst present in the polymer is at least partly separated. The present invention also relates to polymer compositions obtainable by the inventive method as well as to the use of same.
Radical polymerization is an important commercial process for synthesis of diverse polymers, such as PMMA and polystyrene. It suffers from the disadvantage that it is relatively difficult to control the composition of the polymers, the molecular weight and the molecular weight distribution.
One solution to this problem is offered by the so-called ATRP process (=Atom Transfer Radical Polymerization). It is assumed that this process comprises xe2x80x9clivingxe2x80x9d radical polymerization, although the description of the mechanism is not to be construed as limitative. In this process a transition metal compound is reacted with a compound containing a transferable group of atoms. Under these conditions the transferable group of atoms is transferred to the transition metal compound, whereby the metal is oxidized. A radical that adds onto ethylenic groups is formed in this reaction. The transfer of the group of atoms to the transition metal compound is reversible, however, and so the group of atoms is transferred back to the growing polymer chain, whereby a controlled polymerization system is formed. Accordingly it is possible to control the composition of the polymer, the molecular weight and the molecular weight distribution.
This reaction procedure is described, for example, by J -S. Wang et al., J. Am. Chem. Soc., Vol. 117, pp. 5614-5615 (1995), and by Matyjaszewski, Macromolecules, Vol. 28, pp. 7901-7910 (1995). Furthermore, International Patent Applications WO 96/30421, WO 97/47661, WO 97/18247, WO 98/20050, WO 98/40415 and WO 99/10387 disclose modifications of the aforesaid ATRP.
The mechanism described hereinabove is not undisputed. WO 97/47661, for example, states that polymerization takes place by insertion, and not by a radical mechanism. Such a differentiation is not pertinent to the present invention, however, since in the reaction procedure disclosed in WO 97/47661 there are used compounds which are also employed for ATRP.
The monomers, transition metal catalysts, ligands and initiators are chosen on the basis of the polymer solution desired. It is assumed that a high rate constant of the reaction between the transition metal/ligand complex and the transferable group of atoms, plus a low equilibrium concentration of free radicals, is essential for a narrow molecular weight distribution. If the free radical concentration is too high, typical termination reactions, which are responsible for a broad molecular weight distribution, will occur. The exchange rate depends, for example, on the transferable group of atoms, on the transition metal, on the ligands and on the anion of the transition metal compound. The person skilled in the art will find valuable advice on selection of these compounds in, for example, International Patent WO 98/40415. The advantages of known ATRP processes, however, are largely limited to monomers which are themselves polar or which are readily soluble in polar media. Certainly the occasional use of nonpolar aprotic hydrocarbons such as benzene, toluene, xylene, cyclohexane and hexane is also known from the literature, but the polymers synthesized with these solvents exhibit much greater polydispersity. This effect is described in, for example, WO 98/40415.
The same document also discloses the possibility of polymerizing polar monomers such as methyl methacrylate or styrene by means of metallic copper, but the molecular weight distribution is much more unfavorable than in the use of a mixture of Cu0/CuBr or Cu0/CuBr2.
In Pol. Preprint (ACS, Div. Pol. Chem)., 1999, 40(2), 432, M. J. Ziegler et al. state among other facts that the polymerization of t-butyl methacrylate is difficult to control if the said process takes place in bulk. Both the molecular weight and the polydispersity can be improved by using approximately 20 to 25 wt % of polar solvents. Of course, because of the limited solubility in polar solvents of ethylenically unsaturated ester compounds containing alkyl or heteroalkyl groups with at least 8 carbon atoms, it is difficult by means of the known ATRP processes to polymerize ethylenically unsaturated monomer mixtures that contain at least 50 wt % of ethylenically unsaturated ester compounds containing alkyl or heteroalkyl chains with at least 8 carbon atoms. Furthermore, depending on use, these large volumes of polar solvents must be separated from the composition after synthesis of the polymers.
A further disadvantage of the known ATRP processes can be seen in the fact that the resulting polymers and polymer solutions contain residues of the metal catalysts used. These catalyst residues can be detrimental for many applications, since they adversely influence the product properties of the polymer and also can lower its environmental compatibility.
Because of the high viscosity of the polymer solution and the small particle size of the catalyst, separation of the catalyst residues by means of filtration is possiblexe2x80x94if at allxe2x80x94only with difficulty and by means of time-consuming and costly procedures. It requires the use of relatively large quantities of filter aids, which are known in themselves, such as cellulose, silica gel, Kieselgur (such as Celite(copyright)), perlite, wood charcoal and sawdust, whereby the filtration rate is reduced so severely that practical application of such processes for separation of catalyst residues is not possible on the large industrial scale.