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
2000-08-16
2002-04-09
Seidleck, James J. (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...
C525S328200, C525S328400, C525S330500, C525S054100, C526S264000, C526S261000, C514S091000, C514S093000
Reexamination Certificate
active
06369165
ABSTRACT:
The present invention relates to a process for preparing polymers of N-vinyl compounds. Furthermore, the present invention relates to the use of free radicals for preparing polymers of N-vinyl compounds. The present invention also relates to the polymers obtainable by the process of the present invention and also to their use.
A customary process for polymerizing N-vinyl compounds such as 1-vinyl-2-pyrrolidone (N-vinylpyrrolidone, hereinafter referred to as NVP) or N-vinylformamide (hereinafter referred to as NVF) is free-radical polymerization. It also allows the copolymerization of the N-vinyl compounds with other monomers. However, due to unavoidable secondary reactions such as chain transfer, disproportionation, recombination or elimination, the molecular weight distribution can be controled only with great difficulty. Normally, polymers having a polydispersity PD of 2.0 or more are obtained. PD is defined as PD =M
w
/M
n
, where M
w
is the weight average molecular weight and M
n
is the number average molecular weight. The architecture and structure of the polymers can also be influenced only with difficulty.
For these reasons, controled free-radical polymerization, sometimes also known as living radical polymerization, has been developed for preparing polymers having a narrow molecular weight distribution. This method is described, for example, in M. K. Georges et al., Trends in Polymer Science, Vol. 2, No. 2 (1994), pages 66 to 72. The basic strategy of this method is to block the reactive free-radical chain ends of the growing polymer chain periodically and then to reactivate them in a controled way (reinitiation). The dynamic equilibrium between active and dormant form leads to a small, static concentration of free polymer radicals.
EP-A 135 280 describes the use of stable N-oxyl radicals which combine reversibly with the reactive chain ends. However, this process does not give high molecular weight polymers, but only oligomers.
A particular group of initiators for controled free-radical polymerization are compounds which can be dissociated into free-radical initiators and N-oxyl radicals (Trends in Polymer Science, 4(6), 1996, 183-188). These compounds make it possible, for example, to produce branched polymers. However, only selected monomers can be polymerized and the reaction temperatures are unsatisfactorily high.
In general, the reaction rates in the polymerization of monomers in the presence of N-oxyl radicals are too low for many industrial purposes. For this reason, concomitant use has been made of, for example, strong organic acids (U.S. Pat. No. 5,322,912). However, these can cause difficulties in the work-up of the products.
DE-A 195 16 967 describes processes in which vinylic monomers are polymerized in the presence of customary free-radical initiators and electron donors which stabilise the free-radical chain end.
WO 94/18241 describes the polymerization of NVP using a plurality of initiators which have different decomposition temperatures. Such regulation is cumbersome and the polymers obtained are not terminated by functional groups which can be utilized for reinitiation.
In Polym. Mater. Sci. Eng., Vol. 76, pp. 147-148 (1997), Matyjaszewski describes the controled free-radical polymerization of NVP by atom transfer radical polymerization (ATRP). However, this ATRP method requires heavy metals. The reaction product poly-NVP is a good complexing agent for these heavy metals, which is why the poly-NVP prepared by ATRP contains heavy metals and is therefore unsuitable for use in medicine.
Polymers which have been free-radically polymerized using a regulator can be converted into block copolymers by reinitiation in the presence of a further monomer. In Eur. Polym. J., Vol. 26(5), pp. 515-520 (1990), Abadie discloses that block copolymers comprising NVP can, in principle, also be obtained by a change in the reaction mechanism. This process has the disadvantage that an additional process step is required compared to a purely free-radical method.
In Polym. Reprints (Am. Chem. Soc., Div. Polym. Chem.) (1988), Vol. 29(2), p. 6-7, Turner discloses the synthesis of a block copolymer comprising NVP and styrene, but the molar mass of the product is lower than that of the starting polymers.
In J. Chem. Coc. Faraday Trans. 1, Vol. 74(7), pp. 1738-1749 (1978), Munam Lee describes a controled free-radical polymerization of NVP. However, the polymerization proceeds very slowly: after a reaction time of 40 hours, only “traces” of polymer are found.
As regulators for free-radical polymerization, it is also possible to use triazolyl radicals, as taught by the earlier application DE-P 19636996.7, which is not a prior publication. The application nominates vinylaromatics, alkyl esters of acrylic acid and methacrylic acid, and acrylonitrile as preferred monomers. Homopolymers and random copolymers of N-vinyl compounds are not mentioned.
It is an object of the present invention to provide a novel process for preparing polymers comprising N-vinyl compounds such as NVP and NVF, which process does not have the abovementioned disadvantages. Furthermore, the new process should allow very good control over both the molecular weight distribution and the architecture and structure of the polymers. In addition, the process should have a sufficiently high reaction rate, even at relatively low temperatures. The polymers obtained should be free of heavy metals so that they can be used in medicine. The process should also make it possible to prepare block copolymers from blocks of N-vinyl compounds and blocks of other monomers in a simple manner without changing the reaction mechanism.
We have found that this object is achieved by a process for preparing polymers of N-vinyl compounds, in which process the N-vinyl compounds are polymerized in the presence of free radicals of the formula I
where Q is NR
2
or S and T is CR
3
R
4
or S and R
1
, R
2
, R
3
and R
4
can be identical or different and are, independently of one another, hydrogen, C
1
-C
20
-alkyl or C
6
-C
18
-aryl. For the purposes of the present invention, the free radicals represented by the formula I also include their tautomers and positional isomers. The alkyl groups can be either linear, branched or cyclic. They can be either unsubstituted or substituted, for example by one or more halogen atoms such as chlorine, nitrile groups, NO
2
, sulfonic acid groups, hydroxy groups, alkyl ester or aryl ester groups. Furthermore, the alkyl groups can contain sulfoxide or carbonyl groups. The alkyl groups include C
1
-C
12
-alkyl, preferably C
1
-C
10
-alkyl, for example methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, cyclopentyl, n-hexyl or cyclohexyl. Among these, particular preference is given to methyl. The preferred aryl groups include phenyl, naphthyl and biphenyl. The aryl groups can either be substituted by one or more substituents or be unsubstituted. Possible substituents are alkyl groups, for example C
1
-C
10
-alkyl, preferably C
1
-C
6
-alkyl such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl or t-butyl, or hydroxy groups or halogen atoms such as chlorine. Furthermore, the aryl groups can also be substituted by one or more halogen atoms such as chlorine, nitrile groups, NO
2
, sulfonic acid groups, alkyl ester or aryl ester groups. Among the aryl groups, particular preference is given to phenyl.
Examples of suitable free radicals I are thiatianolyls of the formula
or dithiadianolyls of the formula
Preference is given to 2,5-dihydro-1H-1,2,4-triazol-2-yl free radicals (triazoyl radicals) of the formula
Particular preference is given to triazolyl radicals in which R
3
and R
4
are identical. In the very particularly preferred triazolyl radicals, R
1
is phenyl, R
2
is phenyl or methyl and R
3
and R
4
are each phenyl, biphenyl-2,2′-diyl, 6,6′-dimethylbiphenyl-2,2′-diyl or 5,5′-dimethylbiphenyl-2,2′-diyl.
2,5-Dihydro-1H-1,2,4-triazol-2-yl free radicals are known per se or are obtainable by methods known per se. Thus, the triazolyl free radicals ar
Braun Frank
Klapper Markus
Müllen Klaus
Paulus Wolfgang
Raether Roman Benedikt
Asinovsky Olga
BASF Akiengesellschaft & Max-Planck-Gesellschaft
Keil & Weinkauf
Seidleck James J.
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