Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1999-01-14
2000-11-28
Warzel, Mark L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525308, 525309, 525314, C08F29300, C08F 238, C07C32916
Patent
active
061537055
DESCRIPTION:
BRIEF SUMMARY
This application is an application under 35 U.S.C. Section 371 of International Application Number PCT/FR98/01316, filed on Jun. 23, 1998.
The present invention relates to a novel radical polymerization process for obtaining block copolymers.
Block polymers are usually prepared by ionic polymerization. This type of polymerization has the drawback of only allowing the polymerization of certain types of non-polar monomers, especially styrene and butadiene, and of requiring a particularly pure reaction mixture and temperatures which are often below room temperature so as to minimize parasitic reactions, and hence of severe operational constraints.
Radical polymerization has the advantage of being easily carried out without having to comply with excessive purity conditions, and at temperatures greater than or equal to room temperature. However, until recently a radical polymerization process allowing block polymers to be obtained did not exist.
Since then, a new radical polymerization process has been developed, namely "controlled" or "living" radical polymerization. Controlled radical polymerization takes place by the growth, by propagation, of macroradicals. These macroradicals, which have a very short lifetime, recombine irreversibly by coupling or dismutation. When the polymerization takes place in the presence of several comonomers, the compositional variation of the mixture is infinitely slow compared with the lifetime of the macroradical so that the chains have a sequence of random monomer units and not a block-type sequence.
Recently, controlled radical polymerization techniques have been developed in which the ends of polymer chains may be reactivated in the form of a radical by homolytic bond (for example, C--O or C-halogen) scission.
Controlled radical polymerization therefore has the following distinct characteristics: molar ratio, and
The controlled character is even more pronounced when the rate of reactivation of the chains into radicals is very much greater than the rate of growth of the chains (propagation). There are cases where this is not always true (i.e. the rate of reactivation of the chains into radicals is greater than or equal to the propagation rate) and conditions 1 and 2 are not observed, nevertheless it is always possible to prepare block copolymers.
Several approaches have been described for controlling radical polymerization. The most commonly cited consists in introducing, into the mixture, counter radicals which combine reversibly with the growing macroradicals, such as, for example, nitroxyl radicals (Georges et al., Macromolecules, 26, 2987, (1993)). This technique is characterized by high temperatures for labilizing the C--O bond.
Another method, called Atom Transfer Radical Polymerization, makes use of transition metal salts combined with organic ligands and an initiator generally consisting of an organic halide; control of the polymerization is made possible by the reversibility of the C-halogen bond (K. Matyjaszewski, PCT WO 96/30421). One drawback with this polymerization is that a stoichiometric quantity of metal per chain remains.
Otsu (Otsu et al., Makromol. Chem. Rapid Comm., 3, 127-132, (1982), Otsu et al. ibid, 3, 123-140, (1982), Otsu et al., Polymer Bull., 7, 45, (1984), ibid, 11, 135, (1984), Otsu et al, J. Macromol. Sci. Chem., A21, 961, (1984) and Otsu et al., Macromolecules, 19, 2087, (1989)) has shown that certain organic sulphides, particularly dithiocarbamates, allowed chains to be grown in a controlled manner under UV irradiation, according to the principle: ##STR3##
The principle relies on the photolysis of the C--S bond, which regenerates the carbon macroradical, on the one hand, and the dithiocarbamyl radical, on the other hand. The controlled character of the reaction is due to the reversibility of the C--S bond under UV irradiation. It is thus possible to obtain block copolymers. On the other hand, the equilibrium constant of reaction 1 above is not very large compared with the rate of propagation, this having the consequence of generating relativel
REFERENCES:
patent: 2396997 (1946-03-01), Fryling
Biadatti Thibaud
Charmot Dominique
Corpart Pascale
Michelet Daniel
Zard Samir Z.
Rhodia Chimie
Seugnet Jean-Louis
Warzel Mark L.
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