Novel peroxyketals derived from alkoxyacetones

Novel peroxyketals having the general formula ##STR1## are provided, wherein R' represents a tert.alkyl group having 4-12 carbon atoms and R.sup.2 represents a branched or a non-branched alkyl group having 1-12 carbon atoms or a substituted or unsubstituted cycloalkyl group having 5-12 carbon atoms. The peroxyketals can be used to advantage for initiating the copolymerization reaction of ethylenically unsaturated compounds such as unsaturated polyester resins containing both an unsaturated polyester and an ethylenically unsaturated monomer such as styrene.

The invention relates to novel peroxyketals derived from alkoxyacetones and 
are of the general formula: 
##STR2## 
wherein R' represents a tert.alkyl group having 4-12 carbon atoms and 
R.sup.2 a branched or a non-branched alkyl group having 1-12 carbon atoms 
or a substituted or unsubstituted cycloalkyl group having 5-12 carbon 
atoms, and to processes for the preparation of these peroxyketals as well 
as to the application thereof in chemical reactions taking place under the 
influence of free radicals, more particularly the compression moulding of 
unsaturated polyester resin moulding compounds. It is known that 
unsaturated polyester resins can be cured under the influence of free 
radicals. By unsaturated polyester resins are to be understood solutions 
of unsaturated polyesters in reactive monomers containing one or more 
CH.sub.2 .dbd.CH&lt;groups, such as styrene, vinyl toluene, methyl 
methacrylate, diallylphthalate, and divinyl benzene. The ratio of reactive 
monomer to unsaturated polyester is generally 30-50% by weight of monomer 
to 70-50% by weight of polyester. 
The unsaturated polyester is obtained by condensation of approximately 
equivalent amounts of a divalent alcohol, such as ethylene glycol, 
propylene glycol, diethylene glycol, neopentyl glycol, dipropylene glycol 
and an unsaturated dibasic carboxylic acid or the anhydride thereof, such 
as maleic acid, maleic anhydride, fumaric acid, itaconic acid in the 
presence, if desired, of an aromatic dicarboxylic acid such as phthalic 
acid or its anhydride, isophthalic acid, tetrachlorophthalic acid or its 
anhydride, saturated dicarboxylic acids such as malonic acid, adipic acid, 
sebacic acid, succinic acid and the like. 
If such polyester resins are employed as moulding compounds, then it is 
desirable that they should contain thickeners, more particularly chemical 
thickeners, such as magnesium oxide and hydroxide or oxides and hydroxides 
of other metals of the second group of the periodic system. These 
thickeners are generally added in amounts of 0.5 to 25 parts, and 
preferably 1 to 5 parts per 100 parts of unsaturated polyester resin. Into 
the unsaturated polyester resin moulding compounds there may, besides 
thickeners, be incorporated mould release agents, such as zinc stearate, 
calcium stearate and polyethylene; fillers, such as calcium carbonate; 
clay; pigments, such as titanium dioxide, ferric oxide, zinc oxide; 
shrinkage reducing agents, such as polyvinyl acetate and other 
thermoplastics; and reinforcing agents, such as glass fibres. 
The curing of unsaturated polyester resin moulding compounds can be 
effected under pressure and at elevated temperature in the presence of 
radical generating organic peroxides. The known 2,2-ditert.butyl 
peroxypropane, a peroxyketal derived from acetone or 2-propanone, is not 
suitable to be used for this purpose because it is too volatile and too 
hazardous. The peroxyketals derived from alkyl-substituted acetones, such 
as 2,2-ditert.butylperoxybutane, derived from methylethyl ketone and 
2,2-ditert.butylperoxy-4-methylpentane, derived from methylisobutyl ketone 
are not suitable either, because the moulded articles prepared from 
polyester resin moulding compounds cured under pressure and at elevated 
temperature in the presence of the peroxyketals do not display a 
satisfactory gloss and have a relatively high residual styrene content. 
The U.S. Pat. No. 3,686,102 describes .beta.-substituted peroxyketals and 
the use thereof as initiators in the polymerization of ethylenically 
unsaturated monomers, as curing catalysts in the curing of unsaturated 
polyester resins and as curing, cross-linking or vulcanizing catalysts for 
.alpha.-olefinic polymerisates or copolymerisates. Said patent mentions, 
inter alia, the use of 2,2-di(t-butylperoxy)-4-methoxy-4-methylpentane. 
This peroxyketal, however, has the disadvantage that the preparation 
thereof from tert.butylhydroperoxide and 4-methoxy-4-methyl-2-pentanone in 
an acid medium is readily attended with the formation of carbonium ions, 
which give rise to undesirable side reactions, as a result of which the 
yield of the peroxyketal desired is considerably reduced. Moreover, the 
starting ketone causes skin and eye irritation. 
It has now been found that peroxyketals derived from alkoxyacetone which 
have not been described before and are of the general formula 
##STR3## 
wherein R' represents a tert.alkyl group having 4-12 carbon atoms and 
R.sup.2 a branched or a non-branched alkyl group having 1-12 carbon atoms 
or a substituted or unsubstituted cycloalkyl group having 5-12 carbon 
atoms are excellently suitable to be used in reactions carried out under 
the influence of free radicals, such as the polymerization of unsaturated 
monomers and the vulcanization of elastomers, more particularly however, 
in the compression moulding of unsaturated polyester moulding compounds. 
For it has been found that the moulded products thus obtained have a very 
good gloss and a very low content of residual monomer. For this purpose 
the peroxyketals according to the invention may be used in amounts of 
0.05-5.0% by weight, and preferably in an amount of 0.2-2.0% by weight, 
calculated on the amount of unsaturated polyester resin. 
The novel peroxyketals according to the invention can be obtained in a 
simple manner by reacting a hydroperoxide of the formula R'OOH with an 
alkoxy acetone of the general formula 
##STR4## 
wherein R' and R.sup.2 have the above-indicated meaning, in a molar ratio 
of 2:1, at a temperature in the range of -10.degree. to +50.degree. C., 
preferably however at a temperature in the range of -5.degree. to 
15.degree. C., in the presence of a strongly acid catalyst, such as 
sulphuric acid, hydrochloric acid, perchloric acid and para-toluene 
sulphonic acid. If desired, the water evolved during the reaction may be 
removed by distillation. The peroxyketal formed can be extracted from the 
reaction mixture in a known manner with the aid of hexane or some other 
suitable solvent and subsequently isolated by distilling the solvent off 
under reduced pressure. 
As examples of starting hydroperoxides may be mentioned: t.butyl-, t.amyl-, 
t.octyl-, such as 2,4,4-trimethylphenyl-, and t.dodecylhydroperoxide. 
As examples of alkoxyketones may be mentioned: methoxyacetone, 
ethoxyacetone, n-butoxyacetone, n-hexyloxyacetone, n-octyloxyacetone, 
n-dodecyloxyacetone, isopropoxyacetone, isobutoxyacetone, 
2-ethylhexyloxyacetone, cyclopentyloxyacetone, cyclohexyloxyacetone, 
4-tert.butylcyclohexyloxyacetone, cyclooctyloxyacetone, and 
cyclododecyloxyacetone. The invention will be further described in the 
following examples, which illustrate the subject invention and are not in 
limitation thereof. By the term standard resin used in the examples is to 
be understood a commercial product prepared from 1.2 moles of maleic 
anhydride, 1 mole of phthalic anhydride, 1.0 mole of diethylene glycol and 
1.3 moles of 1,2-propanediol, diluted with about 30% by weight of styrene. 
To stabilize this produce 0.01% by weight of hydroquinone and 0.01% by 
weight of paratert.butylcatechol were added to it. The product has an acid 
number of 30 and a viscosity at 20.degree. C. of 2,400 mPa.s. To determine 
the flow of a moulding compound 5 grams of this material were placed 
between two flat plates and over a period of 60 seconds subjected to a 
compression moulding load of 1 MPa. at a temperature of 140.degree. C. The 
resulting diameter of the compression moulded compound is a measure of the 
flow. The gloss was determined in accordance with DIN 67 530 at an angle 
of reflection of 45.degree.. The residual styrene content was determined 
in accordance with DIN 16 945.

EXAMPLE I 
Into a 3-neck 250-ml flask provided with a drain cock, a stirrer and a 
thermometer there were charged 18.9 grams of a 70%-methoxyacetone and 30.9 
grams of 93%-tert.butylhydroperoxide. Subsequently, the contents of the 
flask were cooled down to 0.degree. C., after which over a period of 30 
minutes and at a temperature in the range of 0.degree.-5.degree. C., 30.8 
grams of 70%-H.sub.2 SO.sub.4 were added, with stirring. The stirring was 
continued for 45 minutes at 0.degree. C. To isolate the peroxyketal formed 
110 ml of hexane were added to the reaction mixture. After the aqueous 
lower layer had been drained off, the organic upper layer was washed 5 
times with 5 ml of 4 N KOH solution and subsequently with water until 
neutral. 
Finally, the hexane was distilled off under reduced pressure and at a 
temperature of 20.degree. C. The liquid product obtained weighed 31.6 
grams and contained 96.2% of 1-methoxy-2,2-ditert.butylperoxypropane, 
which was found by determination of the active oxygen content. The 
structure was confirmed by IR and NMR analyses. Likewise, the following 
peroxyketals were synthesized and their contents determined. 
1-ethoxy-2,2-ditert.butylperoxypropane (content 100% 
1-n.octyloxy-2,2-ditert.butylperoxypropane (content 72.1%) 
1-n.dodecyloxy-2,2-ditert.butylperoxypropane (content 81.5%) 
1-isopropoxy-2,2-ditert.butylperoxypropane (content 92.3%) 
1-(2-ethylhexyloxy)-2,2-ditert.butylperoxypropane (content 75.4%) 
1-(cyclohexyloxy)-2,2-ditert.butylperoxypropane (content 64.7%) 
1-(4.tert.butylcyclohexyloxy)-2,2-ditert.butyl-peroxypropane (content 
68.9%) 
1-cyclododecyloxy-2,2-ditert.butylperoxypropane (content 70.5%). 
EXAMPLE II 
Into a 3-neck 250 ml flask provided with a drain cock, a stirrer and a 
thermometer there were charged 14.4 grams of a 70%-methoxyacetone and 32.2 
grams of 95.1%-2,4,4-trimethylpentyl-2-hydroxyperoxide. Subsequently, the 
contents of the flask were cooled to 10.degree. C., after which over a 
period of 15 minutes and at a temperature of 10.degree. C. 24.9 grams of 
70%-H.sub.2 SO.sub.4 were added, with stirring. The stirring was continued 
for 4 hours at the same temperature. Next, 24.8 grams of water were added. 
After the aqueous, sulphuric acid-containing layer had been drained off, 
the organic layer was washed 5 times with 30 ml of 2 N KOH solution and 
subsequently with water until neutral. Then the organic layer was 
dissolved in petroleum ether having a boiling point of 
48.degree.-60.degree. C., and stirring for 1 hour at 20.degree.-25.degree. 
C. while adding a solution of 3.1 grams of Na.sub.2 SO.sub.3 and 0.9 
grams of Na.sub.2 S.sub.2 O.sub.5 in 50 ml of water. Next, the aqueous 
phase was drained off and the petroleum ether evaporated off under reduced 
pressure. The liquid product obtained weighed 23.2 grams and contained 
90.7% of 2,2-bis(2,4,4-trimethylpentyl-2-peroxy)-1-methoxypropane, which 
was found via determining the active oxygen content. The structure was 
confirmed by IR and NMR analyses. 
EXAMPLE III 
Into a 3-neck, 500-ml flask provided with a stirrer, a thermometer and a 
distillation set up suitable for the azeotropic removal of water, there 
were charged 58.5 grams of 92%-tert.butylhydroperoxide, 75 grams of 
toluene, 33.6 grams of 78.4%-methoxyacetone, 3 grams of 4-N sulphuric acid 
and 2 drops of a defoamer. Subsequently, the mixture was heated to a 
temperature of 30.degree. C. and the reaction water removed by azeotropic 
distillation under reduced pressure. After 2 hours, during which 13.2 
grams of water had been distilled off, the reaction was completed. Next, 
the reaction mixture was washed twice with 40 ml of 4-N NaOH and 40 ml of 
water. There were obtained 156.2 grams of reaction product containing 37% 
of 1-methoxy-2,2-ditert.butylperoxypropane. 
EXAMPLE IV 
To a moulding compound of the following composition: 
standard resin--30.5 parts by weight 
styrene--2.5 parts by weight 
zinc stearate--0.5 parts by weight 
calcium carbonate--46.0 parts by weight 
magnesium oxide--0.5 parts by weight 
glass fibres, 6 mm long--20.0 parts by weight 
contained in a Z-blade mixer there were added, at a temperature of 
20.degree. C., 0.30 parts by weight of 
1-methoxy-2,2-ditert.butylperoxypropane. The compound was thickened by 
leaving it at room temperature for 3 days. Next the flow of the compound 
was determined, In a steel mould the compound was compressed into a 4 mm 
thick moulding over a period of 60 seconds at a temperature of 140.degree. 
C. and a load of 10 MPa.Of the moulding thus obtained the gloss and the 
residual styrene content were determined. 
Corresponding measurements were carried out on moulding compounds 
containing the same amounts by weight of other peroxyketals according to 
the invention and on moulding compounds containing the same amounts by 
weight of the known compounds 2,2-ditert.butylperoxybutane and 
2,2-ditert.butylperoxy-4-methyl pentane. 
The peroxyketals and the compression times used and the results obtained 
are listed in the following Table A. 
TABLE A 
______________________________________ 
Moulding 
time (in Flow Residual 
Peroxyketal sec.) (in cm) Gloss Styrene (%) 
______________________________________ 
1-methoxy-2,2- 
30 42 0.02 
ditert . butylperoxy 
60 11.6 51 0.02 
propane 120 51 0.01 
1-ethoxy-2,2- 
30 40 0.04 
ditert . butylperoxy- 
60 12.9 48 0.03 
propane 120 48 0.01 
1-n . octyloxy-2,2- 
30 35 0.07 
ditert . butylperoxy- 
60 12.2 38 0.05 
propane 120 38 0.03 
1-n . dodecyloxy-2,2- 
30 37 0.09 
ditert . butylperoxy 
60 13.1 41 0.07 
propane 120 42 0.05 
1-isopropoxy-2,2- 
30 36 0.10 
ditert . peroxypropane 
60 11.5 40 0.08 
120 45 0.05 
1-(2-ethylhexyloxy)- 
30 38 0.08 
2,2-ditert . butyl- 
60 13.4 38 0.04 
peroxypropane 
120 45 0.03 
1-cyclohexyloxy- 
30 33 0.11 
2,2-ditert . butyl- 
60 12.9 50 0.08 
peroxypropane 
120 45 0.03 
1-(4-tert . butyl- 
30 40 0.07 
cyclohexyloxy) 
60 12.5 40 0.04 
2,2-ditert . butyl- 
120 41 0.02 
peroxypropane 
1-cyclododecyloxy- 
30 32 0.11 
2,2-ditert . butyl- 
60 13.5 38 0.07 
peroxypropane 
120 42 0.05 
2,2-ditert . butyl- 
60 13.5 22 0.28 
peroxybutane 120 26 0.16 
2,2-ditert . butyl- 
60 13.3 30 0.25 
peroxy-4 methyl 
120 31 0.13 
pentane 
______________________________________ 
EXAMPLE V 
To a moulding compound of the composition described in Example IV contained 
in a Z-blade mixer there were added at a temperature of 20.degree. C., 0.2 
parts by weight of 2,2 bis 
2,4,4-trimethylpentyl-2-peroxy)-1-methoxy-propane, calculated on the 
unsaturated polyester resin. To thicken the compound it was stored for 3 
days at room temperature. Subsequently, the flow of the compound was 
determined. In a steel mould the compound was compressed into a moulding 
over a period of 60 seconds, at a temperature of 140.degree. C., and a 
load of 10 MPa. Of this moulding the gloss and the residual styrene 
content was determined. 
Corresponding measurements were carried out on moulding compounds 
containing different amount by weight of 2,2 
bis(2,4,4-trimethylpentyl-2-peroxy)-1-methoxypropane. The amount by 
weight, the compression times and the results obtained are listed in the 
following Table B. 
TABLE B 
______________________________________ 
Residual 
Compres- Styrene 
Weight sion time 
Flow content 
Peroxyketal 
(%) (in sec.) 
(in cm) 
Gloss (%) 
______________________________________ 
2,2-bis(2,4,4- 60 44 0.39 
trimethyl-2- 
0.2 90 14.0 48 0.22 
peroxy)-1- 250 48 0.07 
methoxypropane 
2,2-bis(2,4,4- 60 60 0.01 
trimethyl-2- 
0.6 90 12.9 57 0.01 
peroxy)-1- 250 58 0.002 
methoxypropane 
2,2-bis(2,4,4- 30 63 0.02 
trimethyl-2- 
1.0 60 11.4 66 0.004 
peroxy)-1- 120 65 0.000 
methoxypropane 
______________________________________