Preparation of keto-functional polyethylene waxes

A process for preparing keto-functional polyethylene waxes having a molecular weight of from 150 to 1000 g/mol by telomerization of ethylene with aldehydes at from 500 to 5000 bar and from 100 to 280.degree. C., wherein ethylene and aldehyde are employed in a molar ration of from 5:1 to 50:1.

The present invention relates to a process for preparing keto-functional 
polyethylene waxes by telomerization of ethylene with aldehydes at from 
1000 to 5000 bar and from 100 to 280.degree. C. 
The present invention also relates to the keto-functional polyethylene 
waxes obtainable in accordance with the novel process, to secondary amines 
and alcohols obtainable from the keto-functional polyethylene waxes and to 
the use of the keto-functional polyethylene waxes for preparing secondary 
amines and alcohols. 
Oxidized polyethylene waxes have been known for a long time. The 
preparation of such waxes can be effected, for example, by 
copolymerization of ethylene with oxygen-containing monomers such as 
alkenecarboxylic acids and/or their esters (see eg. DE-A-1 770 777) or 
vinyl esters (DE-A-2 102 469) or by oxidation of paraffins with oxidants 
such as chromic acid and peroxides (Houben-weyl, vol. 7, part 2b, pp. 1287 
et seq., Georg Thieme Verlag, Stuttgart 1976). These synthetic routes, 
however, always produce random mixtures in which the oxidized carbon atoms 
may be located at various positions in the polyethylene matrix. The 
subsequent oxidation of previously prepared polyethylene moreover also 
gives rise to various oxidation states such as keto, aldehyde, acid or 
ester groups. 
To control the molecular weight of olefin polymerizations the 
polymerization mixture is often admixed with regulators. Examples of 
regulators used are hydrogen, but also aldehydes such as propionaldehyde. 
Thus DE-A-1 770 777 describes the copolymerization of ethylene with 
C.sub.3 -C.sub.12 -carboxylic acids and C.sub.4 -C.sub.8 -alkenes and 
possibly additionally esters of alkenecarboxylic acids at from 100 to 4000 
bar and at from 110 to 350.degree. C., the polymerization mixture being 
admixed with regulators, for example propionaldehyde in a molar proportion 
of from 0.5 to 6, based on 100 parts by moles of ethylene. These 
copolymers, which in any case comprise randomly distributed oxidized 
groups, do not appear to include any detectable proportion of keto groups 
from the propionaldehyde, according to the polymer analyses described; the 
sole function of propionaldehyde with these copolymerizations appears to 
be that of a molecular weight regulator. 
It is then an object of the present invention to find a process for 
preparing keto-functional polyolefin waxes, which leads to polyethylene 
waxes in which the oxo function can be found at a defined position of the 
molecule and which, in terms of their chain length and degree of 
substitution, exhibit but low variability. 
We have found that this object is achieved by a process for preparing 
keto-functional polyethylene waxes by telomerization of ethylene with 
aldehydes at from 500 and 5000 bar and from 100 to 280.degree. C., wherein 
ethylene and aldehyde are employed in a molar ratio of from 5:1 to 50:1. 
Furthermore, novel keto-functional polyethylene waxes obtainable according 
to the novel process were found, as were secondary amines and alcohols 
which can be prepared as secondary products from these polyolefin waxes. 
The novel preparation process can be carried out under the generally known 
conditions of high-pressure polymerization of ethylene. The pressure at 
which the telomerization takes place is from 500 to 5000 bar, preferably 
from 1000 to 4000 bar, particularly preferably from 1500 to 3000 bar. The 
reaction temperature may be from 100 to 280.degree. C., preferably from 
150 to 250.degree. C., temperatures above 250.degree. C. generally 
producing waxes having a lower degree of functionalization. 
The reactor used for carrying out the telomerization reaction can be any 
conventional pressure reactor, the reaction preferably being carried out 
in continuous tubular reactors or continuous stirred autoclaves. 
Both the mean molecular weight of the polyolefin wax and the degree of 
functionalization can be influenced via the molar ratio of ethylene and 
aldehyde. Suitable keto-functional polyolefin waxes are obtained at molar 
ratios of ethylene to aldehyde of from 5:1 to 50:1. Preferably this molar 
ratio is from 5:1 to 20:1, particularly preferably from 5:1 to 15:1. 
The properties of the polyethylene waxes according to the invention can 
also be modified by the choice of aldehyde. Particularly suitable 
aldehydes for use in the novel telomerization process are compounds of the 
formula I 
##STR1## 
where R.sup.1 is C.sub.1 -C.sub.20 -alkyl or C.sub.2 -C.sub.20 -alkenyl, 
in which nonadjacent and nonterminal CH.sub.2 groups may also be replaced 
by --O--CO--, --CO--O--or --CO--and which may be substituted by phenyl or 
--CHO, or is C.sub.6 -C.sub.20 -aryl. 
Examples to be mentioned of C.sub.1 -C.sub.20 -alkyl are methyl, ethyl, 
n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl and the 
various branched or unbranched isomers of pentyl, hexyl, heptyl, octyl, 
nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, 
hexadecyl, heptadecyl, octadecyl, nonadecyl and eicosyl. Possible C.sub.2 
-C.sub.20 -alkenyls include the corresponding singly or multiply 
unsaturated radicals, the ethenyl group being less suitable in many cases 
because of the tendency of acroleine to be randomly integrated into the 
polyethylene chain. Preferred alkenyls are those having a terminal double 
bond, since the polyethylene waxes resulting from such aldehydes can be 
readily derivatized further at the end of the molecule, for example by 
epoxidation followed by nucleophilic attack or by addition reactions to 
the double bond. 
The alkyls or alkenyls R.sup.1 may also be substituted by further aldehyde 
functions. Thus it is also possible, for example, for dialdehydes such as 
succinaldehyde or glutaraldehyde to be used as aldehydes of formula I in 
the preparation process according to the invention. 
To be mentioned in particular among the C.sub.6 -C.sub.20 -aryls R.sup.1 
are phenyl and naphthyl, which aromatic radicals may be substituted by 
ester or alkyl groups. 
Preferred radicals R.sup.1 are C.sub.1 -C.sub.5 -alkyls, the aldehyde used 
therefore being acetaldehyde, propionaldehyde, butyraldehyde, pentanal or 
hexanal. 
The keto-functional polyethylene waxes obtainable in accordance with the 
novel preparation process have some remarkable properties. They exhibit a 
high degree of functionalization, so that generally more than 60%, 
preferably more than 70% of the molecules carry a keto group. On the other 
hand, they are distinguished by a very narrow molecular weight 
distribution, expressed as the quotient Q=M.sub.w /M.sub.n. This quotient 
generally ranges from 1.4 to 2.0, with molecular weights of from about 150 
to 1000 g/mol. 
This low variability, both in terms of chain length and of the low 
proportion of nonfunctionalized molecules means that the novel 
keto-functional polyethylene waxes are of interest not only for the known 
applications of oxidized polyethylene waxes such as floor polishes or 
coating compounds, but also as an intermediate for further reactions to 
produce interesting classes of products which are in some cases not 
otherwise readily accessible. 
Thus it is possible to subject the keto-functional waxes to reductive 
amination, thereby producing secondary amines which are used, for example, 
as fuel additives. Said reductive amination can be carried out by any of 
the methods known to those skilled in the art. 
The keto-functional waxes may also be subjected to reduction, thereby 
producing secondary alcohols which in turn can be converted into various 
esters. The reduction likewise can be carried out by any method known to 
those skilled in the art.

The invention is illustrated by the following examples: 
EXAMPLES 1 TO 4 
Gaseous ethylene (10 kg/h) was compressed to 220 bar in three stages by a 
diaphragm compressor. With the aid of a piston pump the respective 
aldehyde was pumped into the supercritical ethylene, and the mixture was 
then compressed further to 1500 bar and pumped continuously into a stirred 
flow autoclave which had been set to 220.degree. C. The autoclave had a 
volume of 1 l and a length/diameter ratio of 5:1. The oligomerization was 
started by a solution of 0.2 wt % of tert-butyl peroxypivalate and 0.5 wt 
% of tert-butyl peroxy-3,5,5-trimethylhexanoate in isodecane (wt % each 
based on the total weight of the solution) being pumped in continuously 
(metering rate 105 ml/min). The mean residence time of the reaction 
mixture in the autoclave was about 90 seconds. 
The results are shown in the following table: 
______________________________________ 
Molar ratio Degree of 
Ex- ethylene/ M.sub.n 
Q function- 
ample Aldehyde aldehyde (g/mol) 
M.sub.w /M.sub.n 
alization* 
______________________________________ 
1 Propionaldehyde 
10:1 460 2.0 71% 
2 Propionaldehyde 
8:1 250 1.9 75% 
3 Propionaldehyde 
5:1 220 1.9 78% 
4 Undec-.omega.-enal 
20:1 430 1.9 62% 
______________________________________ 
*Degree of functionalization determined by IR analysis of the CO bands