Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-10-26
2003-02-04
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S035000, C524S042000, C524S043000, C524S044000, C524S046000, C524S457000
Reexamination Certificate
active
06515049
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The present invention is described in the German priority application No. 19849441.6 filed Oct. 27, 1998 which is hereby incorporated by reference as is fully disclosed herein.
BACKGROUND OF THE INVENTION
The present invention relates to water-soluble, sulfoalkyl-containing, hydrophobically modified cellulose ethers, to processes for preparing them and to their use as protective colloids in polymerizations.
The preparation of vinyl polymers by free-radical polymerization in an aqueous, solvent-free medium makes it necessary to emulsify the hydrophobic monomers and, after polymerization is complete, to stabilize the polymer. For this reason, the polymerization of monomer systems comprising water-insoluble vinyl monomers in aqueous systems requires not only surfactants but also protective colloids which, on the one hand, have hydrophilic character and, on the other hand, should also have a dispersing action.
The quality of a polymer dispersion is decisively influenced by the choice of the protective colloid. Important quality criteria which can be influenced by the protective colloids are, for example, the stability, viscosity, rheology, the particle size of the polymer particles of the dispersion, and also the amount of coagulum which remains on filtering the dispersion through a sieve. The molecular weight is also influenced by the protective colloid. A further quality criterion is the water absorption of a film which has been produced by spreading and drying a dispersion. This property too is influenced by the protective colloid. In suspension polymerization, the protective colloid controls the particle size of the polymer formed.
It has been known for a long time that polymeric carbohydrates such as starch, dextrans and water-soluble cellulose derivatives are suitable protective colloids for water-based polymerization systems. The protective colloid used most frequently in the commercial production of polyvinyl acetate dispersions is hydroxyethylcellulose (Cellulose and its Derivatives, chapter 26, Ellis Horwood Limited 1985), which is produced on an industrial scale from cellulose and ethylene oxide.
The decisive process in the use of protective colloids in emulsion polymerization is regarded as being free-radical formation on the protective colloid and subsequent grafting of the monomer onto the colloid. The degree of grafting depends on the choice of free-radical initiator. Free-radical initiators customarily used are diazo compounds, redox initiators, organic and inorganic peroxo compounds. On the other hand, the degree of grafting also depends on the nature of the protective colloid. If the degree of grafting is low, the chosen concentration of the protective colloid must be appropriately high in order to achieve a sufficient effect. However, a high protective colloid concentration is undesirable, on the one hand, for cost reasons and, on the other hand, it also leads to increased hydrophilicity of the filmed polymer, in conjunction with increased water absorption.
DESCRIPTION OF THE RELATED ART
In U.S. Pat. No. 4,845,175 it is shown that the use of hydroxyethylcellulose which has been hydrophobically modified with arylalkyl groups enables the amount of protective colloid to be produced. Hydrophobically modified cellulose ethers, however, possess a reduced solubility in water.
U.S. Pat. No. 4,868,238 describes carboxymethyl-bearing, hydrophobically modified cellulose ethers as protective colloids in suspension polymerization. Carboxymethyl groups, however, are sensitive to polyvalent cations as are used as electrolytes.
P. Talaba, I. Srokova, P. Hodul and G. Cik in Chem. Papers 50 (2), 101 (1996) describe hydrophobically modified sulfoethylcelluloses. High degrees of substitution are necessary in these compounds, however, because of the absence of other substituents. They are water-soluble only at low degrees of polymerization, and possess a strong tendency to form foam, which is undesirable for use in emulsion paints. EP-A-0 781 780 describes sulfoalkylated cellulose ethers modified hydrophobically using C
10
-C
40
alkyl chains, these ethers likewise possessing a high surfactant action and being used as thickeners in cosmetic formulations. For these compounds a degree of sulfoalkylation of from 0.1 to 1 is claimed.
SUMMARY OF THE INVENTION
The object of the present invention was therefore to develop new kinds of protective colloids for polymerizations in aqueous systems, which ensure the same or better quality of the polymer dispersions or polymer suspensions prepared, with a reduction in the amount used and with good processing properties.
It has been found, surprisingly, that hydrophobically substituted sulfoalkyl-HECs are outstandingly suitable as a protective colloid in emulsion polymerization if the degree of substitution in terms of hydrophobic alkyl groups is greater than or equal to 0.001 but does not exceed 1.0, preferably 0.2, alkyl groups per monomer unit. When protective colloids of this kind are used, the amount required is substantially lower than in the case of conventional HEC protective colloids.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention accordingly provides water-soluble ionic cellulose ethers from the group of hydroxyalkylcelluloses which are substituted by on average from 0.001 to 1.0, preferably from 0.001 to 0.2, alkyl group per anhydroglucose unit and carry from 0.01 to 0.1 sulfoalkyl group per anhydroglucose unit.
Preferred cellulose ethers are those of the formula
[C
6
H
7
O
2
(OR
1
)(OR
2
)(OR
3
)]
m
where C
6
H
7
O
2
is an anhydroglucose unit,
m is 50-3000, especially 100-1000,
and R
1
, R
2
, R
3
independently of one another are each a polyalkylene oxide chain of the formula
where X=H, C
n
H
2n+1
, C
n
H
2n+1
O, CH
2
—CH
2
—SO
3
Y or CH
2
—CHOH—CH
2
SO
3
Y,
n=4-20
and Y=H, Na or K,
and in which
p, q, and r independently of one another in R
1
, R
2
and R
3
can each independently assume values from 0 to 4, the sum of all (p+q+r) added over R
1
, R
2
and R
3
per anhydroglucose unit is on average greater than 1.3 and less than 4.5, preferably from 1.5 to 3.0, the sequence of the oxyalkylene units in the polyalkylene oxide chain is arbitrary, and the average number of hydrophobically modified groups per 10 anhydroglucose unit (DS HM) is from 0.001 to 0.2, preferably from 0.01 to 0.04, and the average number of sulfoalkyl groups per anhydroglucose unit is from 0.01 to 0.1, preferably from 0.01 to 0.09. The sulfoalkyl groups are preferably sulfoethyl groups.
The present invention also provides processes for preparing the cellulose ethers of the invention by etherifying cellulose with an etherifying agent from the group of the alkylene oxides and etherifying with an alkyl halide or an alkyl glycidyl ether and a sulfonate, with base catalysis, or by etherifying ethers from the group of hydroxyalkylcelluloses with an alkyl halide or an alkyl glycidyl ether and a sulfonate, with base catalysis, preferably
A) by etherifying cellulose with ethylene oxide, propylene oxide and/or glycidyl alcohol and an alkyl halide or an alkylene oxide or an alkyl glycidyl ether and an alkenylsulfonate or chloroalkylsulfonate, with base catalysis, preferably in a suspension medium;
B) by etherifying hydroxyethylcellulose, hydroxypropylcellulose, dihydroxypropylcellulose or a cellulose ether having two or more of said hydroxyalkyl substituents with an alkyl halide or an alkylene oxide or an alkyl glycidyl ether and an alkenylsulfonate or chloroalkylsulfonate, with base catalysis, preferably in a suspension medium.
Suspension media preferably used are lower alcohols or ketones, an example being isopropanol, tert-butanol or acetone, in a weight ratio to the cellulose of from 3:1 to 30:1, preferably from 8:1 to 15:1. As the base it is usual to use aqueous solutions of alkali metal hydroxides, especially sodium hydroxide. The molar ratio of base to anhydroglucose unit is determined by the carbohydrate (derivative) used. When using cellulose (method A) the molar ratio
Doenges Reinhard
Wurm Horst
Biscula Anthony A.
Clariant GmbH
Egwim K C
Wu David W.
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