Pressurization of ethylenically unsaturated monomers

Details Pressurization of ethylenically unsaturated monomers Pressurization of ethylenically unsaturated monomers

1999-12-02

2002-02-26

Teskin, Fred (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S204000, C526S318600, C546S014000

Reexamination Certificate

active

06350827

ABSTRACT:

The present invention relates to a process for pressurizing ethylenically unsaturated monomers to 200-5000 bar in the absence of a polymerization initiator, which comprises effecting said pressurizing in the presence of nitroxyl compounds of the formula I
where
R
1
and R
2
are singly C
1
-C
4
-alkyl or combine with the joining carbon atom to form a 5- or 6-membered saturated hydrocarbon ring,
R
3
is C
1
-C
4
-alkyl, and
R
4
is hydrogen or C
1
-C
12
-alkyl.
The present invention further relates to a process for preparing copolymers by such pressurization and subsequent polymerization and to copolymers obtainable thereby.
Derivatives of sterically hindered amines have long been known for use as stabilizers of plastics and of free-radically polymerizable monomers.
EP-A-178 168 discloses a method of inhibiting &agr;,&bgr;-ethylenically unsaturated monocarboxylic acids, for example acrylic acid, in the course of their distillative workup.
U.S. Pat. No. 5 449 724 describes a process for preparing thermoplastic ethylene homopplymers and copolymers at 40-5000° C. and 500-5000 bar in the presence of a free-radical initiator and a stable free radical compound. The presence here of the stable free radical compound, especially of derivatives of 2,2,6,6-tetramethylpiperidine-N-oxyl, leads to a particularly narrow molecular weight distribution and, associated therewith, to special physical properties on the part of the polymers.
EP 0 811 590 describes a process for pressurizing ethylenically unsaturated monomers to 500-5000 bar in the presence of polymerization inhibitors. Those mentioned include nitroxyl compounds.
Examples 1 to 3 of EP 0 811 590 demonstrate the advantageous effect of various amounts of N,N′-bis(2,2,6,6-tetramethyl-piperidin-1-oxyl-4-yl)-N,N′-bisformylhexamethylenediamine with regard to the inhibition of the premature polymerization of an ethylene/acrylic acid mixture.
For instance, the presence of the inhibitor mentioned enables the second compressor to run for not less than 124 h compared with only 27 h in the absence of the inhibitor. The longer running times are possible because of the distinctly reduced formation of polymer, since the latter leads to deposits and hence to leaks in the second compressor and makes it necessary to switch off and clean the second compressor.
The pressurization of ethylenically unsaturated monomers to 500-5000 bar, especially the pressurization of monomer mixtures comprising ethylene and acrylic acid or acrylic acid derivatives, is generally observed to be accompanied—frequently even prior to the desired polymerization—by instances of unwanted, premature polymerization in the compressors and precompressors, leading to the formation of deposits and making it necessary to clean the compressors on a regular basis at short intervals.
Customary inhibitors, such as methylhydroquinone and hydroquinone, provide only minimal inhibition and have to be added in high concentrations. Nitroxyl compounds as known from EP 0 811 590 provide a distinctly better effect, but there is still a permanent need for even more effective inhibitors.
It is an object of the present invention to provide a process for pressurizing ethylenically unsaturated monomers which is even more effective than existing processes at reducing deposit formation due to premature polymerization during pressurization.
We have found that this object is achieved by a process for pressurizing ethylenically unsaturated monomers to 200-5000 bar in the absence of a polymerization initiator, which comprises effecting said pressurizing in the presence of nitroxyl compounds of the formula I shown at the beginning.
All customary ethylenically unsaturated monomers are pressurizable by the process of the invention. Examples of suitable monomers are ethylene, propylene, butene and butadiene and also vinyl esters of C
2
-C
18
-alkanecarboxylic acids such as vinyl acetate and vinyl propionate, C
2
-C
18
-alkyl esters of acrylic and methacrylic acid such as methyl, ethyl, propyl, butyl and 2-ethylhexyl acrylate and methacrylate, esters of monoethylenically unsaturated dicarboxylic acids such as mono-and diesters of maleic and fumaric acid, monoethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and fumaric acid, amides of monoethylenically unsaturated carboxylic acids such as acrylamide, methacrylamide, N-mono(C
1
-C
18
)alkylacrylamide, N-mono(C
1
-C
18
)alkylmethacrylamide, N-di(C
1
-C
18
)alkylacrylamide and N-di(C
1
-C
18
)alkylmethacrylamide, monoethylenically unsaturated alcohols, C
1
-C
4
-alkyl vinyl ethers and N-vinyl heterocyclic compounds such as N-vinylpyrrolidone, N-vinylcaprolactam and N-vinylimidazoles and also N-vinylformamide.
Suitable monomer mixtures include in particular those comprising ethylene, propylene, butene and/or butadiene and optionally one or more of the comonomers mentioned above. The process of the invention is particularly useful for pressurizing monomer mixtures used for copolymerization.
More particularly, suitable monomers/comonomers also include acrylic acid and/or methacrylic acid and/or derivatives thereof.
Examples of suitable derivatives of these acids are the C
1
-C
18
-alkyl esters, C
1
-C
18
-mono- and dialkylamides and also the unsubstituted amides. Examples of useful C
1
-C
18
-alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, tert-pentyl, neopentyl and also the various isomeric hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl and octadecyl radicals.
The process of the invention is particularly useful for pressurizing mixtures of ethylene and acrylic acid or methacrylic acid.
Examples of possible C
1
-C
4
-alkyl for R
1
, R
2
and R
3
in formula I include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl or tert-butyl.
R
1
and R
2
each preferably represent the same C
1
-C
4
-alkyl. Particularly preferably, R
1
and R
2
are both methyl.
R
1
and R
2
may also combine with the joining carbon atom to form a 5- or 6-membered saturated hydrocarbon ring. For instance, R
1
and R
2
together may be a tetra- or pentamethylene group.
The R
3
radicals can be different, but they are preferably each the same C
1
-C
4
-alkyl. Preferably, every R
3
is tert-butyl or every R
3
is i-propyl, particularly preferably methyl.
C
1
-C
12
-alkyl R
4
includes for example the abovementioned C
1
-C
4
-alkyl groups and also pentyl, sec-pentyl, tert-pentyl, neopentyl, hexyl, 2-methylpentyl, heptyl, 2-methylhexyl, octyl, isooctyl, 2-ethylhexyl, nonyl, 2-methylnonyl, isononyl, 2-methyloctyl, decyl, isodecyl, 2-methylnonyl, undecyl, isoundecyl, dodecyl and isododecyl (the designations isooctyl, isononyl and isodecyl are trivial names derived from the carbonyl compounds obtained by the oxo process; cf. Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. Al. pages 290-293, and also Vol. A10, pages 284 and 285).
In addition to the nitroxyl compounds of the formula I, the process of the invention may also utilize costabilizers. Examples of suitable costabilizers are aromatic nitro or nitroso compounds and also hydroxylamines.
Examples of useful aromatic nitro compounds are 1,3-dinitrobenzene, 1,4-dinitrobenzene, 2,6-dinitro-4-methylphenol, 2-nitro-4-methylphenol, 2,4,6-trinitrophenol, 2,4-dinitro-1-naphthol, 2,4-dinitro-6-methylphenol, 2,4-dinitrochlorobenzene, 2,4-dinitrophenol, 2,4-dinitro-6-sec-butylphenol, 4-cyano-2-nitrophenol, 3-iodo-4-cyano-5-nitrophenol, particularly preferably 2,6-dinitro-4-methylphenol, 2-nitro-4-methylphenol, 2,4-dinitro-6-sec-butylphenol or 2,4-dinitro-6-methylphenol.
Examples of useful aromatic nitroso compounds include p-nitrosophenol, p-nitroso-o-cresol and p-nitroso-N,N′-diethylaniline.
Useful costabilizers further include compounds selected from the group consisting of the quinones, the phenothiazines and the phenols, alone or combined with the aforementioned aromatic nitro or nitroso compounds and also hydroxylamines.

Affiliated with

Also associated with

Rating

Pressurization of ethylenically unsaturated monomers does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Pressurization of ethylenically unsaturated monomers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pressurization of ethylenically unsaturated monomers will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2984304