Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-09-11
2004-11-02
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S267000, C525S286000, C525S291000, C525S293000, C525S299000, C525S308000, C525S309000
Reexamination Certificate
active
06812291
ABSTRACT:
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 several drawbacks:
it only allows the polymerization of certain types of non-polar monomers, especially styrene and butadiene,
it requires a particularly pure reaction mixture and temperatures which are often below room temperature so as to minimize parasitic reactions.
The operational constraints are therefore severe.
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. During this polymerization, 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 low compared with the lifetime of the macroradical so that the chains have a random sequence of monomer units and not a block-type sequence.
Consequently, 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. This controlled radical polymerization takes place by the growth, by propagation, of macroradicals.
At the present time, several controlled radical polymerization techniques are known, 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:
1. the number of chains is fixed throughout the duration of the reaction,
2. the chains all grow at the same rate, resulting in:
a linear increase in the molecular masses with conversion,
a narrow distribution of masses,
3. the average molecular mass is controlled by the monomer/chain-precursor molar ratio, and
4. the possibility of preparing block copolymers.
The controlled character is even more pronounced when the rate of consumption of the chain precursor is very much greater than the rate of growth of the chains (propagation). There are cases where this is not always true 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 reversible activation of the C-halogen bond (K. Matyjaszewski, PCT WO 96/30421). One drawback with this polymerization is that it requires a stoichiometric quantity of metal per chain precursor.
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:
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 rate of exchange in propagating species and “dormant” species of reaction 1 above is not very large compared with the rate of propagation, this having the consequence of generating relatively broad molecular mass distributions. Thus, the polydispersity index (PI=M
w
/M
n
) is between 2 and 5 (Otsu et al., 25, 7/8, 643-650, (1989)).
Xanthate disulphides and dithiocarbamate disulphides are themselves well known as transfer agents in conventional radical polymerization in thermal mode and in the presence of an initiator, but no one has hitherto been able to control the polymerization, or even less to produce block copolymers.
Up till now it was known that disulphides (tetraalkylthiuram disulphide, diisopropylxanthate disulphide and mercaptobenzothiazol disulphide) were activatable thermally or under UV irradiation, whereas monosulphides (substituted xanthates, dithiocarbamates) were activatable only under UV irradiation (Roha et al.,
Macromol. Symp
., 91, 81-92, (1995), and Okawara et al., Bull. of the Tokyo Inst. of Techn., No. 78, 1966).
However, controlled radical polymerization making use of a UV irradiation source is very difficult to carry out, especially from an industrial standpoint, since the penetration of the UV photons into the polymerization medium is limited, both by absorption phenomena (most of the ethylenic monomers absorb in the 210-280 nm range) and by diffusion phenomena in disperse media (suspension, emulsion).
Moreover, it has been shown (Turner et al.,
Macromolecules
, 23, 1856-1859, (1990)) that photopolymerization in the presence of dithiocarbamate generates carbon disulphide and may be accompanied by a loss of polymerization control.
For these reasons, it has thus been sought to develop a technique which can be used to obtain block copolymers by a process without UV irradiation, preferably by thermal initiation. Until the present time, no controlled radical polymerization system has been able to be demonstrated using dithiocarbamate compounds in the absence of a UV source.
Document WO 98/01478 describes a process for preparing block polymers by controlled radical polymerization. According to that document, such a process cannot be implemented with the aid of compounds, called chain-transfer agents, chosen from dithiocarbamates, of general formula:
Controlled radical polymerization has an advantage over conventional radical polymerization when it is a question of preparing low-molecular-weight functionalized chains (reactive telomers). Such polymers are desirable for specific applications such as, for example, coatings and adhesives.
Thus, when it is attempted to synthesize chains grafted with, on average, 2 functional comonomers, the fraction of chains with at most one functional site becomes large when the average degree of polymerization is less than a threshold value (e.g. 20 or 30). Controlled radical polymerization makes it possible to reduce, or even to inhibit, the formation of these oligomers having zero or one functional site which degrade the performance in terms of application.
One object of the present invention is to provide a novel controlled radical polymerization process for the synthesis of block polymers from dithiocarbamates.
Another object of the present invention is to provide a novel controlled radical polymerization process for the synthesis of block polymers from dithiocarbamates in the absence of a UV source.
Another object is to provide a controlled radical polymerization process for the synthesis of block polymers from all types of monomers.
Another object is to provide a controlled radical polymerization process for the synthesis of block polymers containing no metal impurities deleterious to their use.
Another object is to provide a controlled radical polymerization process for the synthesis of block copolymers, the said polymers being chain-end functionalized.
Another object is to provide a controlled radical polymerization process for the synthesis of block polymers and block copolymers having a low poly
Bouhadir Ghenwa
Charmot Dominique
Corpart Pascale
Franck Xavier
Zard Samir
Mullis Jeffrey
Rhodia Chimie
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