Saturated polyesters containing imide groups and terminal carboxyl groups

Saturated polyesters containing terminal carboxyl groups and, per molecule, at least one side chain, containing imide groups, of the formula I ##STR1## in which R.sup.1 and R.sup.2, for example, together with the carbon atoms to which they are attached, are a cyclohexane ring and R.sup.3 is ethylene, the side chains of the formula I being attached via ester linkages to tribasic or tetrabasic aromatic carboxylic acids present in the polyester main chain, the average molecular weight M.sub.w of the polyester being between 3,000 and 20,000 and the polyester having an acid number of 10 to 200. The polyesters are suitable, for example as a composition containing epoxide resins, for use as casting resins or in surface protection, particularly for the preparation of heat-resistant and weather-resistant powder paints.

The invention relates to saturated polyesters containing terminal carboxyl 
groups and, per molecule, at least one side chain containing imide groups, 
to the curable compositions containing epoxide resins obtained therefrom 
and to the use of these compositions, particularly for the preparation of 
heat-resistant and weather-resistant powder paints. 
Polyesters containing imide groups are known. 
Thus USSR Patent Specification No. 318,227 and German Auslegeschrift No. 
1,570,273 describe unsaturated polyesters prepared by subjecting 
dicarboxylic acids and polyhydric alcohols to polycondensation in the 
presence of a dicarboxylic or polycarboxylic acid imide as a modifying 
agent. These modified unsaturated polymers are cured, for example in the 
presence of styrene, by means of butyl perisooctoate and cobalt 
naphthenate. 
German Offenlegungsschrift No. 2,856,050 describes a process for the 
preparation of unsaturated polyesters containing imide groups, in which 
unsaturated oils are employed as the starting material. The polyesters 
thus obtained are used for the preparation of copolymers with olefinically 
unsaturated monomers, for example vinyl compounds. 
U.S. Pat. No. 4,446,301 describes polyesters containing imide or amide 
groups, obtained as the reaction products from an imide or amide, a 
polyester-forming polyol and a polyester-forming polybasic carboxylic acid 
or derivatives thereof and, if appropriate, an oil or an unsaturated fatty 
acid derived from an oil. The imides or amides used are, in turn, prepared 
from specific branched primary alkanolamines and polycarboxylic acids or 
derivatives thereof. The imide or amide groups can be constituents of the 
polyester main chain or can be present as side chains. The polyesters are 
particularly suitable for the preparation of air-drying paints of high 
solids content and also certain inks. 
The present invention relates to saturated polyesters containing terminal 
carboxyl groups and, per molecule, at least one side chain, containing 
imide groups, of the formula 
##STR2## 
in which R.sup.1 and R.sup.2 independently of one another are each 
hydrogen or a C.sub.1 -C.sub.4 -alkyl group or, together with the carbon 
atoms to which they are attached, are a cyclopentane, cyclohexane or 
benzene ring, and R.sup.3 is a linear C.sub.2 -C.sub.12 -alkylene radical, 
a C.sub.6 -C.sub.12 -arylene radical or a group of the formula II 
##STR3## 
in which T is methylene, propylidene, NH, CO, SO.sub.2, O or S, the side 
chains of the formula 1 being attached via ester linkages to tribasic or 
tetrabasic aromatic carboxylic acids present in the polyester main chain, 
the average molecular weight M.sub.w of the polyester being between 3000 
and 20,000 and the polyester having an acid number from 10 to 200. 
The polyesters according to the invention are suitable, for example, for 
the preparation of curable compositions which contain epoxide resins and 
which are suitable, in particular, for the production of heat-resistant 
and weather-resistant powder paints. 
If R.sup.1 and R.sup.2 in the side chain of the formula I are a C.sub.1 
-C.sub.4 -alkyl group, this can be methyl, ethyl, propyl, isopropyl and 
n-, sec.- and tert.-butyl. 
The polyesters according to the invention preferably contain side chains of 
the formula I in which R.sup.1 and R.sup.2 independently of one another 
are hydrogen or methyl or, together with the carbon atom to which they are 
attached, are a benzene ring, and contain, in particular, side chains in 
which R.sup.1 and R.sup.2, together with the carbon atoms to which they 
are attached, are a cyclohexane ring. 
If R.sup.3 in the side chain of the formula I is a linear C.sub.2 -C.sub.12 
-alkylene radical, this can be, for example, ethylene, 1,3-propylene, 
1,4-butylene, 1,5-pentylene or 1,6-hexylene. 
A C.sub.6 -C.sub.12 -arylene radical R.sup.3 is, for example, phenylene, 
bisphenylene or naphthylene. 
R.sup.3 in the side chain of the formula I is preferably a linear C.sub.2 
-C.sub.4 -alkylene radical, such as ethylene, 1,3-propylene or 
1,4-butylene, or is phenylene, such as 1,2-phenylene, 1,3-phenylene and 
particularly 1,4-phenylene. R.sup.3 is particularly preferably ethylene. 
The polyester main chain of the polyesters according to the invention is 
built up by reacting one or more polyester-forming polyols with one or 
more polyester-forming, polybasic carboxylic acids or derivatives thereof. 
Examples of suitable derivatives of polyester-forming, polybasic 
carboxylic acids are anhydrides, acid halides, for example bromides or 
especially chlorides, or esters with C.sub.1 -C.sub.4 -alcohols, in 
particular methyl esters. 
Preferred polyesters according to the invention are those in which 50 to 80 
mol % of the polyester-forming, polybasic carboxylic acid component in the 
polyester main chain are derived from a dicarboxylic acid, and the 
remaining 50 to 20 mol % are derived from a tricarboxylic or 
tetracarboxylic acid. Suitable dicarboxylic acids are compounds of the 
formula III 
EQU A HOOC--R.sup.4 --COOH (III) 
in which R.sup.4 is C.sub.6 -C.sub.12 -arylene, linear or branched C.sub.2 
-C.sub.12 -alkylene, C.sub.6 -C.sub.12 -cycloalkylene or a group of the 
formula II. 
Preferred radicals R.sup.4 are C.sub.2 -C.sub.6 -alkylene, preferably 
tetramethylene, or are o-, m- or p-phenylene. The tricarboxylic or 
tetracarboxylic acids present in the polyester main chain are preferably 
compounds of the formula IV 
EQU R.sup.5 (COOH).sub.m (IV) 
in which m is 3 or 4 and R.sup.5 is a trivalent or tetravalent C.sub.6 
-C.sub.12 -aromatic radical or a trivalent or tetravalent radical of the 
formula II. 
The following may be mentioned as suitable polybasic, polyester-forming 
carboxylic acids: adipic acid, azelaic acid, 1,2-, 1,3- and 
1,4-cyclohexanedicarboxylic acid, 1,2-cyclopentanedicarboxylic acid, 
1,3-cyclopentanedicarboxylic acid, glutaric acid, phthalic acid, 
isophthalic acid, terephthalic acid, biphenyl-di-, -tri- or 
-tetra-carboxylic acid, benzophenone-di-, -tri- or -tetra-carboxylic acid, 
naphthalenetetracarboxylic acid, 4,4'-oxy-, 4,4'-thio- or 
4,4'-methylene-diphthalic acid, trimellitic acid and pyromellitic acid. 
Preferred polybasic carboxylic acids of the formula IV are trimellitic acid 
and pyromellitic acid. 
The polyesters according to the invention preferably contain, in the 
polyester main chain, at least 80 mol % of the polyester-forming polyol 
component of a diol, the remaining 0 to 20 mol % being the component of a 
triol or tetraol. 
The polyol preferably has the formula V 
EQU R.sup.6 (OH).sub.n (V) 
in which n is 2, 3 or 4 and R.sup.6 is a divalent to tetravalent C.sub.6 
-C.sub.12 cycloaliphatic radical or C.sub.6 -C.sub.12 aromatic radical, a 
divalent to tetravalent radical of the formula II or, in particular, a 
divalent to tetravalent, linear or branched, C.sub.2 -C.sub.12 aliphatic 
radical. 
Preferred polyols of the formula V are dihydric to tetrahydric aliphatic 
polyols, in particular ethylene glycol, propylene glycol, butylene glycol, 
1,5-pentanediol, 1,6-hexanediol, neopentylglycol, glycerol, 
1,1,1-tris-(hydroxymethyl)propane and 
2,2-bis-(hydroxymethyl)-1,3-propanediol. 
The most preferred polyols of the formula V are neopentylglycol and 
1,6-hexanediol. 
As already mentioned, the side chains of the formula I in the polyesters 
according to the invention are attached via ester linkages to tribasic or 
tetrabasic aromatic carboxylic acids present in the polyester main chain. 
The polyester therefore has the following repeating units 
##STR4## 
in which o is the number 1 or 2 and the radicals R.sup.1, R.sup.2, 
R.sup.3, R.sup.4 and R.sup.5 are as defined above. For the sake of 
simplicity, only bifunctional polyol or polycarboxylic acid radicals 
R.sup.6 and R.sup.4 have been used in illustrating the repeating units of 
the polyester main chain. 
The polyesters according to the invention can be prepared by known methods 
of polyester synthesis. The reaction is suitably carried out at elevated 
temperatures, for example between 120.degree. and 250.degree. C., 
preferably between 160.degree. and 230.degree. C., and in an inert 
atmosphere, such as nitrogen or argon. The reaction can be carried out 
with or without a catalyst. If a catalyst is used, it is possible to 
employ catalysts which are customary for the preparation of polyesters, 
for example catalytic amounts of acids or transition metal compounds, for 
example inorganic or organic compounds of antimony, titanium or tin. 
Examples of preferred catalysts are phosphoric acid, p-toluenesulphonic 
acid, tin oxide and organic titanium or tin compounds, for example alkyl 
tin carboxylates, such as dibutyltin dilaurate, and titanium carboxylic 
acid salts. In general, the catalyst is employed in an amount of 0.01 to 
1% by weight, relative to the total amount of the educts. 
It is suitable to carry out the reaction in such a way that the 
alkanolamine H.sub.2 N--R.sup.3 --OH is first reacted with an 
imide-forming dicarboxylic acid or a derivative thereof to give a 
hydroxyimide of the formula VI 
##STR5## 
and then to esterify the compound of the formula VI with a tribasic or 
tetrabasic carboxylic acid of the formula IV 
EQU R.sup.5 (COOH).sub.m (IV) 
or a derivative thereof to give a compound of the formula VII 
##STR6## 
in which the radicals R.sup.1, R.sup.2, R.sup.3 and R.sup.5 and also the 
indices m and o are as defined above. The compounds of the formula VI and 
VII can each be isolated, but it is preferable to carry out the whole 
reaction in a one-pot process, by adding the appropriate educts to the 
reaction mixture one after the other and heating them together. The amount 
of the alkanolamine H.sub.2 NR.sup.3 OH is preferably 2 to 15, in 
particular 3 to 10%, by weight, relative to the total weight of all the 
educts employed in the synthesis of the polyesters according to the 
invention. The reaction of the dicarboxylic acid of the formula VII with 
further polybasic, polyester-forming carboxylic acids or derivatives 
thereof and with polyols, in which the polyester main chain is formed, is 
carried out by the previously mentioned, known methods of polyester 
synthesis. 
The progress of the reaction can be followed by determining the amount of 
distillate, for example water, formed in the course of the reaction, or by 
withdrawing samples of the reaction mixture at specific intervals of time 
and determining the properties of the polymer, for example the acid 
number, the molecular weight or the viscosity. 
The reaction can be carried out without a solvent in the melt or in 
solution in a suitable inert solvent, for example toluene or xylene. 
The polyester according to the invention has an average molecular weight 
M.sub.w of between 3000 and 20,000, preferably between 3500 and 10,000, 
and an acid number of 10 to 200, preferably 30 to 100. The molecular 
weight can be determined, for example, by means of gel permeation 
chromatography in a suitable solvent, for example tetrahydrofuran. 
The amount of the individual components in the synthesis of the polyester 
is preferably so chosen that at least two, particularly five to ten, side 
chains, containing imide groups, of the formula I are present per molecule 
of polyester. 
The polyesters according to the invention are preferably solid at room 
temperature and have a softening point of about 80 to 150.degree. C. In 
order to obtain polyesters having terminal carboxyl groups, it is possible 
for example, to react polymers having terminal hydroxyl groups with a 
tricarboxylic or tetracarboxylic acid or an anhydride thereof. 
The polyesters according to the invention are suitable, for example, as 
curing agents for epoxide resins. 
The invention therefore also relates to curable compositions containing 
(a) a polyester according to the invention and 
(b) an epoxide resin, 
the amounts of the components (a) and (b) being so chosen that 0.5 to 2, 
preferably 0.8 to 1.5, epoxide groups of the epoxide resin are present per 
carboxyl group of the polyester. 
The curable compositions according to the invention are suitable, for 
example, for use as casting resins or in surface protection and, 
particularly, for the preparation of heat-resistant and weather-resistant 
powder paints. 
The invention also relates to the use of the curable compositions according 
to the invention for the preparation of powder paints. 
Single-substance compounds or mixtures of different compounds can in each 
case be used as the components (a) and (b) of the compositions according 
to the invention. 
The customary epoxide resins which are suitable for powder coatings can be 
used as the component (b). Compounds of this type are described, for 
example, in German Offenlegungsschrift No. 2,838,841. 
The resins used preferably have an epoxide content of 0.5 to 12 equivalents 
per kg. The preferred epoxide resins are solid at room temperature and 
can, if necessary, be advanced by reaction with, for example, a dihydric 
phenol. 
Epoxide resins which are particularly preferred are those which contain, on 
average, more than one epoxide group per molecule and are polyglycidyl 
derivatives of aromatic or heteroaromatic compounds. 
Particularly preferred resins are optionally advanced polyglycidyl ethers 
of 2,2-bis-(4'-hydroxyphenyl)propane (bisphenol A), 
2,2-bis-(3',5'-dibromo-4'-hydroxyphenyl)-propane (tetrabromobisphenol A), 
bis-(4-hydroxyphenyl)-methane (bisphenol F) and novolaks, and polyglycidyl 
derivatives of 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone 
and, in particular, 2,4,6-trihydroxy-1,3,5-triazine (cyanuric acid), for 
example triglycidyl isocyanurate. Preferred resins are also polyglycidyl 
esters, for example diglycidyl terephthalate or triglycidyl trimesate 
(=benzene-1,3,5-tricarboxylate). 
The epoxide resin (b) and the polyester (a) are preferably so chosen that 
the sum of the epoxide equivalents and of the carboxyl equivalents is 
between 0.8 and 2.5 per kg of the binder (a)+(b). 
If desired, further additives customary in the paint industry, for example 
extenders, light stabilizers, delustering agents, dyestuffs, grinding 
aids, accelerators, plasticizers and especially degassing agents, flow 
control agents and/or pigments can be added to the powder paints. 
Examples of flow control agents are polyvinyl acetals, such as polyvinyl 
butyral ("Movital" B 30 H.RTM. made by HOECHST), polyethylene glycol, 
polyvinylpyrrolidone, glycerol and acrylic copolymers, such as 
"Modaflow".RTM. or "Acrylon" MFP.RTM. made by MONSANTO and PROTEX, 
respectively. 
Benzoin is preferably employed as the degassing agent. 
The powder paints containing the compositions according to the invention 
can be prepared merely by mixing the ingredients, for example in a ball 
mill. Another possible means of preparation consists in combining the 
ingredients by melting, preferably in an extruder, for example in a Buss 
Kokneter, and then comminuting the cooled mass. The mixtures preferably 
have a particle size within the range from 0.015 to 500 .mu.m, 
particularly 10-75 .mu.m. 
The powder paint is applied to the article to be coated, for example by 
means of an electrostatic powder spray gun and is advantageously heated to 
at least 120.degree. C., preferably to 150.degree. to 250.degree. C., in 
order to cure the resin completely. 
The cured coatings obtained in accordance with the application are 
distinguished by excellent resistance to heat and weathering. In 
particular, the cured powder-paint coatings prepared using the polyesters 
according to the invention do not undergo any thermal chalking when 
subjected to heat ageing.

The preparation of some polyesters according to the invention and of the 
powder paints obtainable therefrom and the use of the latter as 
heat-resistant and weather-resistant coatings is described in the 
following examples. 
1. Preparation of the Polyesters 
Example 1.1 
168 parts by weight of hexahydrophthalic anhydride and 67 parts by weight 
of monoethanolamine are reacted under nitrogen at a temperature of 
200.degree. C. to give the imide, 211 parts by weight of trimellitic 
anhydride are then added and the mixture is kept at 200.degree. C. for 30 
minutes. 468 parts by weight of neopentylglycol and 524 parts by weight of 
isophthalic acid are added to this melt, and esterification is carried out 
up to a maximum temperature of 230.degree. C., to give an acid number &lt;50, 
95.75 parts by weight of trimellitic anhydride are then added and 
esterification is again carried out to give an acid number of 52. The 
softening point of the product as specified in DIN 51,920 is 114.3.degree. 
C. and the average molecular weight M.sub.n is 1166 and M.sub.w 4186 (gel 
permeation chromatography in THF on Styragel; calibration by means of 
polystyrene). 
Example 1.2 
168 parts by weight of hexahydrophthalic anhydride are reacted with 67 
parts by weight of monoethanolamine analogously to Example 1, and the 
mixture is then reacted with 211 parts by weight of trimellitic anhydride. 
468 parts by weight of neopentylglycol, 349 parts by weight of isophthalic 
acid and 153 parts by weight of adipic acid are added to this melt, and 
esterification is carried out up to a maximum temperature of 230.degree. 
C. to give an acid number &lt;50, 96 parts by weight of trimellitic anhydride 
are then added and esterification is carried out to give a product having 
an acid number of 57. The softening point of the product as specified in 
DIN 51,920 is 95.6.degree. C. and the average molecular weight M.sub.n is 
1145 and M.sub.w 4161 (gel permeation chromatography in THF on Styragel; 
calibration with polystyrene). 
Example 1.3 
168 parts by weight of hexahydrophthalic anhydride are reacted with 67 
parts by weight of monoethanolamine analogously to Example 1, and the 
mixture is then reacted with 211 parts by weight of trimellitic anhydride. 
313 parts by weight of neopentylglycol, 177 parts by weight of 
1,6-hexanediol and 524 parts by weight of isophthalic acid are added to 
this melt, followed by 77 parts by weight of trimellitic anhydride. The 
product has an acid number of 52, a softening point as specified in DIN 
51,920 of 107.9.degree. C. and an average molecular weight M.sub.n of 1329 
and M.sub.w of 6430 (gel permeation chromatography in THF on Styragel; 
calibration with polystyrene). 
Example 1.4 
305 parts by weight of hexahydrophthalic anhydride and 122 parts by weight 
of monoethanolamine are reacted under nitrogen to give the imide, 218 
parts by weight of pyromellitic dianhydride are then added and the mixture 
is kept at 200.degree. C. for 2 hours. 502 parts by weight of 
1,6-hexanediol and 583 parts by weight of dimethyl terephthalate are added 
to this melt and esterification is carried out up to a maximum temperature 
of 233.degree. C. to give an acid number &lt;50, 48 parts by weight of 
trimellitic anhydride are then added and esterification is carried out to 
give a product having an acid number of 42. 
2. Epoxide Resin 
The epoxide compound employed in all the use examples is triglycidyl 
isocyanurate having an epoxide equivalent weight of .ltoreq.108, an 
epoxide number of .gtoreq.9.3 equivalents/kg and a melting range from 
86.degree. to 97.degree. C. 
3. Powder Paints 
The powder paints are prepared by intimately mixing the ground products, 
polyester, epoxide resin and flow control agent with a white pigments 
(TiO.sub.2) in a gyro-wheel (Rhonrad), and then homogenizing the mixture 
in an extruder at 40.degree. to 90.degree. C. After cooling, the extruded 
material is broken up and ground to a particle size of &lt;100 .mu.m in a 
pinned disc mill. The powder prepared in this way is applied by means of 
an electrostatic powder spray gun at 60 kV to degreased steel sheets, and 
is stoved in a circulating air drying cabinet. 
Example 3.1 
A powder paint of the following formulation is prepared and applied by the 
procedure described. 
900 parts by weight of polyester according to Example 1.1 
100 parts by weight of epoxide resin according to Example 2 
10 parts by weight of Modaflow-Powder II.RTM. .sup.1 
500 parts by weight of white pigment (TiO.sub.2) 
2 parts by weight of benzoin 
FNT .sup.1 Flow control agent made by Monsanto, based on poly-(2-hydroxyethyl) 
acrylate adsorbed onto silica gel. 
Stoving conditions: 30 minutes at 200.degree. C. 
Gel time (B-time) at 180.degree. C.: 60 seconds 
Film thickness (.mu.m): 60 
Erichsen indentation 
(DIN 53,156) mm: 3.6 
Acetone test* (rating): 2 
FNT * Acetone test: A wad of cottonwool dipped into acetone is placed for 1 
minute on the sample sheet to be tested. Assessment: Rating 0=surface 
unaffected; 1=softening hardly noticeable, cannot be scratched with 
fingernail; 2=can be scratched by fingernail, but not to the bottom; 3=can 
be scratched to the bottom; 4=film can be removed or rubbed off with the 
wad; 5=virtually completely dissolved out. 
______________________________________ 
Helmen chalking value (DIN 53,223) 
120.degree. C./ 
120.degree. C./ 
120.degree. C./ 
120.degree. C./ 
24 hrs 200 hrs 1 month 5 months 
______________________________________ 
Relative % 
of chalking 
0 0 0 0 
______________________________________ 
RESISTANCE TO WEATHERING 
Testing by accelerated weathering on aluminium sheet using the Atlas 
Weather-O-Meter, model DCM (carbon arc lamp). The daily cycle in the test 
was as follows: 20 hours exposure in accordance with cycle disc No. 10 (17 
minutes exposure, 3 minutes exposure and sprinkling), 1 hour's storage in 
tap water, 1 hour's cooling to -20.degree. C. (frost) and 2 hours' storage 
at room temperature. 
______________________________________ 
Initial 
value 1000 hrs. 
2000 hrs. 
______________________________________ 
60.degree. angle gloss (%)(DIN 67,550) 
85 90 86 
Yellowness value (DIN 6167) 
-2 -2 1.8 
______________________________________ 
Example 3.2 
892 parts by weight of polyester according to Example 1.2 
108 parts by weight of epoxide resin according to Example 2 
10 parts by weight of Modaflow-Powder II.RTM. 
500 parts by weight of white pigment (TiO.sub.2) 
2 parts by weight of benzoin 
Stoving conditions: 15 minutes at 200.degree. C. 
(B-time) at 180.degree. C.: 45 seconds 
Film thickness (.mu.m): 60 
Erichsen indentation 
(DIN 53,156) (mm): 9.3 
Acetone test* (rating): 3 
______________________________________ 
Helmen chalking value (DIN 53,223) 
120.degree. C./ 
120.degree. C./ 
120.degree. C./ 
120.degree. C./ 
24 hrs. 200 hrs. 1 month 3 months 
______________________________________ 
Relative % of 
chalking 0 0 0 0 
______________________________________