Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2003-04-07
2004-10-05
Zalukeva, Tatyana (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S204000, C526S220000, C526S236000, C526S328500, C526S340000, C526S342000, C526S346000, C525S267000
Reexamination Certificate
active
06800708
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a new process for the preparation of telechelics based on vinyl polymers, the telechelics prepared in this way and their use in the plastics, fibers or coatings sector.
Linear oligomers or low molecular weight linear polymers with functional groups on both chain ends are in general called telechelics. A comprehensive overview of the preparation of telechelics is to be found in Adv. Polym. Sci., 1987, 81, 168. They have acquired importance inter alia as additives and as building units (prepolymers) for higher molecular weight copolymers of defined structure (block copolymers, comb polymers, star polymers). An exact bifunctionality is necessary in particular for use of telechelics as building units for copolymers. The most widely known reactions for the preparation of telechelics having an exact functionality of 2 are polyaddition reactions (to give polyurethanes or polyureas), polycondensations (to give polyesters, polycarbonates or polyamides) and ring-opening anionic or cationic polymerizations of heterocyclic monomers (cyclic esters, carbonates, acetals or ethers). Optionally these reactions are performed with termination reagents which contain the desired functional groups.
Telechelic polyacrylates, i.e. linear oligomers of acrylates or low molecular weight acrylate polymers or copolymers with two defined functional end groups which can participate in the crosslinking, chain lengthening and/or coupling reactions conventionally used in coating chemistry, are of great interest for use in the coating industry.
However, these telechelic polyacrylates cannot be prepared by any of the processes described above for the preparation of telechelics.
Various methods are known in polymer chemistry for providing polyvinyl or poly-acrylate compounds with functional end groups. Oxidative chain cleavages (with oxygen, ozone and osmium tetroxide or ruthenium tetroxide) proceed non-specifically and/or require double bonds in the polymer chains as the point of the cleavage. An exact bifunctionality can scarcely be achieved in this way.
The same problem occurs in a free radical polymerization. If a content of monomers which carry the desired functional group calculated for a functionality of two is used, a product mixture is obtained which has only an average functionality of two. Bi-functional molecules are present alongside trifunctional and more than trifunctional, monofunctional and also non-functional polymer molecules. This is based on the statistical character of free radical polymerization and on an influence of the various termination reactions which is difficult to control.
If initiators and/or termination reagents which carry the desired functional groups (functionalized diazo compounds, functionalized peroxides or redox initiators) are employed instead of the monomers carrying functional groups, a functionality of 2 is in general not achieved because the ratio of the competing termination reactions. Disproportionation, recombination and termination cannot be controlled in a targeted manner by initiator radicals or the termination reagent. In so-called “dead end polymerization”, a large excess of an initiator having the desired end group is used so that practically every polymer chain is terminated by an initiator molecule and is thus bifunctional. Only very low molecular weights are achieved in this way and the products formed become uneconomically expensive because of the large amounts of initiator.
In the case of telomerization, i.e. the polymerization of vinyl or acrylate monomers in the presence of chain transfer reagents with high chain transfer constants, likewise only low molecular weights are achieved, and the use of this remains limited to a few cases (polymerization in the presence of carbon tetrachloride, dibromomethane or disulfides carrying functional groups). Since disproportionation as a termination reaction between two active chain ends cannot be suppressed entirely, functionalities of the telechelics of less than 2 are found. In the case of halogen compounds at least, subsequent polymer-analogous reaction of the halogen substituents to give the desired functional groups is also necessary.
Telechelic polymethacrylates can be prepared by group transfer polymerization with ketene silyl acetals, the functional end group being formed by conversion of the silyl groups. However, disadvantages here are the high purity requirements on the monomer and solvent and the price and availability of the initiators required, which means that such a process would be applicable only for special applications.
It is known from EP-A 613910 and EP-A 622378 to prepare &agr;,&ohgr;-polymethacrylate diols by selective transesterification of the terminal ester group of an &agr;-hydroxy-functional polyalkyl methacrylate. This process has several disadvantages. On the one hand, the &agr;-hydroxy-functional polyalkyl methacrylate is prepared by free radical polymerization in the presence of large amounts of mercaptoethanol, which is associated with a considerable odor nuisance. On the other hand it is a multi-stage, energy- and time-consuming process which comprises distilling off the excess mercaptoethanol and the solvent used, transesterification with an excess of a diol in the presence of a catalyst, removal of the methanol by distillation, washing of the product several times to remove the catalyst and the excess diol and other purification steps. Furthermore, this reaction remains limited to the exclusive use of alkyl methacrylates, since otherwise the transesterification reaction no longer proceeds sufficiently selectively on the terminal ester group of the chain.
Ring-opening polymerization of unsaturated heterocyclic compounds is also a special case without a wide application and economic potential (cyclic ketene acetals or unsaturated spiroorthocarbonates); such monomers are not available industrially.
None of the methods described so far is therefore suitable for the preparation of the desired telechelic polyacrylates, since either the required functionality is not achieved, the method remains limited to only a few special cases and/or polymer-analogous after-reactions are necessary. A polymerization process which allows a good control of the polymerization and in particular of the end groups of the polymer chains, while being easy to carry out, is needed. Such a process is living free radical polymerization.
Living free radical polymerization is a relatively young method of controlled free radical polymerization. It combines the advantages of a conventional free radical polymerization (simple synthesis process, inexpensive, broad monomer base) with those of a living polymerization (polymers of defined structure/molecular weight and distribution and end group functionality). The aim of precise control of free radical polymerization is achieved here by a reversible chain termination or blocking (“end-capping”) after each growth step. The equilibrium concentration of the polymerization-active chain ends is so low here in comparison with the equilibrium concentration of the blocked (“dormant”) chain ends that termination and transfer reactions are severely suppressed compared with the growth reaction. Since end-capping proceeds reversibly, all the chain ends remain “living” if no termination reagent is present. This allows control of the molecular weight, a low polymolecularity index and controlled functionalization of the chain ends by termination reagents.
Controlled free radical polymerization using tetraalkylthiuram disulfides is described by Otsu et al. (Makromol. Chem., Rapid Commun. 1982, 3, 127-132). The preparation of telechelics having functional groups capable of a further reaction or crosslinking with functional groups used in coating chemistry is not disclosed.
Atom Transfer Radical Polymerization (ATRP) is a method, in which a transition metal complex compound ML
x
abstracts a transferable atom or atomic group X (Cl or Br) from an organic compound RX to form an oxidized complex compound ML
x
X and an organic radical R
Achten Dirk
Höcker Hartwig
Keul Helmut
Melchiors Martin
Bayer Aktiengesellschaft
Gil Joseph C.
Matz Gary F.
Zalukeva Tatyana
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