Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-03-18
2002-09-24
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S135000, C526S146000, C526S147000, C526S220000, C526S319000, C526S328000
Reexamination Certificate
active
06455645
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a novel process for the production of oligomeric and polymeric telechelic substances, to the telechelic substances produced in this manner and to the use thereof in the plastics, fibers or lacquer sectors.
BACKGROUND OF THE INVENTION
Telechelic substances are generally defined as linear oligomers or low molecular weight linear polymers having functional groups on both chain ends. A comprehensive review of the production of telechelic substances may be found, for example, in
Adv. Polym. Sci.
81, 168 (1987). They are significant, inter alia, as additives and as structural units (prepolymers) for copolymers having a defined structure (e.g., block copolymers, comb polymers, star polymers). When used as structural units in copolymers, telechelic substances must be as precisely bifunctional as possible.
The best known reactions for the production of telechelic substances which have a functionality of exactly two are (1) polyaddition reactions (for example, to yield polyurethanes or polyureas), (2) polycondensation reactions (for example, to yield polyesters, polycarbonates, or polyamides) as well as (3) ring-opening anionic or cationic polymerization reactions of heterocyclic monomers (for example, cyclic esters, carbonates, acetals or ethers), optionally with terminating reagents containing the desired functional groups.
Telechelic polyacrylates, i.e. low molecular weight acrylate polymers having two defined functional end groups which can participate in crosslinking, chain extension and/or coupling reactions conventionally used in lacquer chemistry are of great interest for use in the lacquer industry Telechelic polyacrylates, however, cannot be produced using any of the above-stated processes.
Various methods are known in polymer chemistry for incorporating functional end groups into polyvinyl or polyacrylate compounds, for example, oxidative chain scission (e.g., with oxygen, ozone, osmium or ruthenium tetroxide). However, these methods are non-specific and/or require the presence of double bonds in the polymer chains as a point of attack for scission. It is virtually impossible to achieve exact bifunctionality with these methods.
If monomers having the desired functional group are used in a free-radical polymerization in a quantity calculated to yield a functionality of two, a product mixture is obtained having an average functionality of two. The product, however, contains not only bifunctional molecules, but also tri- and more highly functional molecules, monofunctional molecules as well as non-functional polymer molecules.
If initiators and/or terminating reagents having the desired functional groups (such as functionalized diazo compounds, functionalized peroxides or redox initiators) are used instead of the monomers having functional groups, a functionality of two is generally not achieved because various termination reactions co-occur, e.g. disproportionation, recombination, termination by initiator radicals or termination by the terminating reagent.
In “dead and” polymerization, a large excess of an initiator having the desired end group is used. In this technique, each polymer chain can be terminated with an initiator molecule and is accordingly bifunctional. However, only very low molecular weight polymers are formed and large quantities of initiator are required.
Telomerization (i.e., polymerization of vinyl or arcrylate monomers in the presence of chain-transfer reagents having elevated chain-transfer constants) also yields only low molecular weights and this method is restricted to a few instances (e.g., Polymerization in the presence of tetrachloromethane, dibromomethane or disulfides having functional groups). since it is not entirely possible to suppress disproportionation as a termination reaction between two active chain ends, telechelic substances are obtained having functionalities of less than two. At least in the case of the halogen compounds, it is also necessary to perform a subsequent polymer-analogous reaction of the halogen substituents to yield the desired functional groups.
Telechelic polymethacrylates may be produced by group transfer polymerization with ketene silyl acetals, wherein the functional groups are formed by transformation of the silyl groups. Disadvantages of this method are (1) the requirement of high purity monomers and solvents and (2) the price and availability of the initiators which are needed, requirements which make such a process useful only for special applications.
EP-A 613,910 and EP-A 622,378 disclose the production of &agr;-&ohgr;-polymethacrylate diols by selective transesterification of the terminal ester group of an &agr;-hydroxy-functional polyalkyl methacrylate. This process has various disadvantages. First, the &agr;-hydroxy-functional polyalkyl methacrylate is produced by free-radical polymerization in the presence of large quantities of mercaptoethanol, a compound which has a considerable odor nuisance. Second, the method is a multi-stage, energy-intensive and time-consuming process; the process involves the removal of the excess mercaptoethanol and the solvent used by distillation, transesterification with an excess of a diol in the presence of a catalyst, removal of the methanol by distillation, repeated washing of the product to remove the catalyst and excess diol as well as still further purification stages. Third, this reaction is restricted solely to the use of alkyl methacrylates, since the transesterification reaction otherwise no longer proceeds sufficiently selectively on the terminal ester group of the chain.
Another special technique which has a limited range of applications and no economic potential is ring-opening polymerization of unsaturated heterocyclics (for example, cyclic ketene acetals, unsaturated spiroorthocarbonates); such monomers are not industrialy avilable.
None of the methods so far mentioned is thus suitable for the production of the desired telechelic polyacrylates, because the desired functionality is not achieved, the method is restricted to only a few specific cases and/or polymer-analogous subsequent reactions are required. There is a need for a polymerization process which combines ease of performance with good control of the polymerization and in particular of the end groups of the polymer chains. Living free-radical polymerization is one such process.
Living free-radical polymerization is a relatively recent method for the performance of controlled free-radical polymerization. It combines the advantages of conventional free-radical polymerization (simple production process, low costs and a wide range of monomers) with those of living polymerization (polymers of a defined structure, molecular weight, molecular weight distribution and end group functionality). In this process, the objective of precise control of the free-radical polymerization is achieved by reversible chain termination/blocking (“end-capping”) after each growth stage. The equilibrium concentration of the actively polymerizing chain ends at this point is so low in comparison with the equilibrium concentration of the blocked (“dormant”) chain ends that termination and transfer reactions are largely suppressed in comparison with the growth reaction. since the end-capping is reversible, all the chain ends remain “living” providing that no terminating reagent is present. This allows control of the molecular weight, a narrow molecular weight distribution and purposeful functionalization of the chain end by terminatig reagents.
Initial attempts at controlled free-radical polymerization (using the iniferter method) were described, for example, in
Makromol. Chem., Rapid Commun.
3 (1982), 127 and 132. The iniferter method here describes a class of free-radical initiators which can enter into initiation, transfer and reversible termination reactions, e.g., tetraalkylthiuram disulfides which are photolytically cleaved and activated. In this manner, it is possible to produce polymers having dithiocarbamate end groups and which may be reactivated by irradiation.
U.S. Pat. 4,
Höcker Hartwig
Keul Helmut
Margotte Dieter
Melchiors Martin
Neumann Andreas
Bayer Aktiengesellschaft
Gil Joseph C.
Roy Thomas W.
Wu David W.
Zalukaeva Tanya
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