GB1590173A - Bulk polymerisation of olefinically unsaturated compounds - Google Patents

Description

(54) BULK POLYMERISATION OF OLEFINICALLY UNSATURATED COMPOUNDS (71) We, LUPEROX GMBH, a body corporate organised according to the laws of the Federal Republic of Germany, of Denzingerstrasse 7 8871 Wasserburg bei Gunzburg, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to homo- and copolymerisation of one or more olefinically unsaturated monomers by a bulk polymerisation process.

Bulk polymerisation, that is the polymerisation of monomers in the absence of water or other solvents has a number of advantages over other methods of polymerisation, for example, polymers are produced directly and do not have to be obtained from a suspension or emulsion. A further advantage of bulk polymerisation is that the proportion of polymerisation auxiliaries which remain in the finished polymer and may impair the properties thereof, is low and in some cases almost non-existant. One major disadvantage of bulk polymerisation processes however, is that there is a certain proportion of residual non-reacted monomers in the finished polymer which may reduce its thermal stability and increase its tendency to yellow. For this reason, the presence of unreacted monomers may make a polymer unsuitable for certain uses, such as, for example, for packaging materials.

The use of combinations of polymerisation initiators have been proposed for bulk polymerisation of monomers, especially of styrene. The term "polymerisation initiator" is intended to mean compounds frequently also called polymerisation catalysts and radical-formers, which decompose into radicals at certain temperatures and as a result effect the polymerisation of the unsaturated polymerisable compound.

The term "bulk polymerisation" used to mean any process carried out without relatively large quantities of water or other solvents which form a second phase.

The content of monomers in polymers produced by bulk polymerisation can be due to the difficulty of effecting polymerisation of the residual quantities of monomers in the polymer during polymerisation. The polymerisation of the residual monomers requires a long time at medium temperatures, as was possible when using hitherto customary initiators. Long polymerisation times, however, reduce the productive capacity, and the obvious alternative of increasing the polymerisation temperature necessitates the use of special initiators which take effect at high temperatures in order to achieve low residual monomer contents and short polymerisation times.

British Patent Specifications Nos. 1,329,859 and 1,330,896 describe processes in which combinations of polymerisation initiators are used, the combination containing a catalyst taking effect at a relatively low temperature combined with a catalyst taking effect only at a relatively high temperature. In these cases peroxides which decompose into radicals at different temperatures are used as polymerisation initiators. By the co-use of peroxides that take effect at relatively high temperatures, as shown in the two Patent Specifications, the residual monomer content in the polymer, especially in the case of polystyrene, can be considerably reduced. It is thus possible in the bulk polymerisation of styrene to reduce the proportion of volatile substances, consisting essentially of styrene monomer, to 0.1 to 0.30to. Azo compounds and peroxides have been proposed as radical-forming polymerisation initiators. Apart from the special peroxides of British Patent Specifications 1,329,859 and 1,330,896, which take effect at relatively high temperatures, azo compounds which decompose to form radicals at relatively high temperatures have also been proposed, for example in US Patent Specification 3,282,912. In this Specification, a,a'-azoalkanes are described and their suitability is mentioned as polymerisation catalysts instead of peroxides or other azo catalysts in the homopolymerisation or copolymerisation of monomers.

The present invention provides a process for homo- or copolymerising one or more olefinically unsaturated monomers by a two-stage bulk polymerisation in which the second stage involves polymerisation of substantially all of the monomer(s) remaining after the first stage and in which the second stage is carried out with, as polymerisation initiator(s), at least one compound of the general formula I

wherein R represents an alkyl group having from I to 6 carbon atoms, a cycloalkyl, aryl or aralkyl group, or a group of the formula R3CO- wherein R3 represents a hydrogen atom, an alkyl group having from 1 to 5 carbon atoms or a cycloalkyl, aryl or aralkyl group; R' and R2, any two or more of which may be the same or different, each represents an alkyl group having from 1 to 8 carbon atoms or a cycloalkyl or aralkyl group, or R1 and R2 together attached to the same carbon atom represent an alkylene group having 4 or 5 carbon atoms in the carbon chain; or R2 is as defined above and R and R' together represent an alkylenecarbonyl group having 3 or 4 carbon atoms in the carbon chain; the groups R, R1, R2 and R3 being unsubstituted or substituted by one or more alkyl groups, at a temperature of at least 1500C but not more than 230"C at which said compound of the formula I becomes effective as an initiator; and in which the first stage involves polymerisation of at least some of the monomer(s) and is carried out at below said temperature with one or more other initiators and/or by thermal polymerisation.

By means of the process according to the present invention it is generally possible to reduce the proportion of residual monomers in the finished polymers prepared by bulk polymerisation by a greater extent than has hitherto generally been possible. A further advantage of the present invention is that it is possible to reduce the residual monomer content using as few radical-forming initiators as possible, or by using the initiators in smaller quantities. The process of the invention is particularly applicable to the bulk homo- or copolymerisation of styrene.

In the compounds of the general formula I, the groups R, R', R2 and R3 on one side of the azo group are generally identical to the corresponding groups on the other side of the azo group i.e. the compounds are symmetrical about the azo group; however, it is possible for any one or more of the groups R, R1, R2 and R3 on one side of the azo group to differ from the corresponding group(s) on the other side of the azo group, in which case the compounds are unsymmetrical.

As or azo compounds of the general formula I, there may be mentioned azo ethers and azo-esters such as; 2,2' - azo - bis - (2 - methoxypropane), 2,2' - azo bis - (acetoxypropane), 2,2' - azo - bis - (2 - propionoxypropane), 1,1' - azo bis(l - methoxycyclohexane), 1,1' - azo - bis - (1 - phenoxycyclohexane), I, I azo - bis - (I - acetoxycyclohexane), 2,2' - azo - bis - (2 - acetoxybutane), 2,2' azo - bis - (2 - ethoxy - 4 - methylpentane), 2,2' - azo - bis - (2 - acetoxy - 4 methylpentane), 1,1' - azo - bis - ( I - acetoxy - 1 - phenylethane), 1,1' - azo bis - (I - acetoxymethylcyclohexane), 1,1' - azo - bis - (1 - methoxy - 3,3,5 trimethylcyclohexane), 1,1' - azo - bis - (1 - acetoxy - 3,3,5 trimethylcyclohexane), ,y' - azo - bis - (y - valerolactone, 2,2' - azo - bis - (2 formyloxypropane), 1,1' - azo - bis - (I - formyloxycyclohexane), 1,1' - azo bis - (I - propionoxycyclohexane), 1,1' - azo - bis - (I - benzoyloxycyclohexane), 2,2' - azo - bis - (2 - formyloxy - 4 - methylpentane) or 2,2' - azo - bis - (2 formyloxybutane), and, in particular: y,' - azo - bis - (y - valerolactone), 1,1' azo - bis - (I - acetoxycyclohexane), 2,2' - azo - bis - (2 - acetoxypropane) and 2,2' - azo - bis - (2 - acetoxy - 4 - methylpentane).

The process of the invention may be used especially for the polymerisation of styrene; acrylic acid esters such as methyl acrylate, ethyl acrylate and methyl methacrylate; esters of unsaturated alcohols, such as vinyl acetate; acrylonitrile; methacrylonitrile; and ethylene. Such monomers may be polymerised alone (i.e.

homopolymerised) or with one another (i.e. copolymerised), for example, styrene together with acrylonitrile or ethylene with vinyl acetate, or with other monomers.

However, the process according to the invention is most especially useful for the bulk polymerisation of styrene.

Bulk polymerisation may be effected according to methods known per se, and may be carried out in conventional apparatus, for example in vessels with a stirrer or in stirring autoclaves, and the polymerisation may be carried out in a discontinuous or continuous manner.

The polymerisation according to the present invention is carried out in two stages, the first stage being initiated thermally and/or by means of an initiator other than a compound of the general formula I and involving polymerisation of at least some, especially at least 50 /,, of the monomer(s), and the final (second) stage being initiated by means of one or more compounds of the general formula I at a temperature of from 150 to 230"C, preferably from 180 to 2200C, and involving polymerisation of substantially the whole of the remainder of the monomer(s). The second stage of the reaction preferably involves polymerisation of at most 20%, more preferably at most 10% and most preferably at most the final 1% of the monomer(s).

The precise proportion of monomer(s) polymerised in the second stage will, however, depend upon a number of factors, for example the decomposition temperature of the particular initiator of the general formula I employed and the rate at which the temperature of the polymerisation mixture increases during the first stage. The latter feature itself also depends upon a number of factors, for example the degree to which the polymerisation is exothermic.

The bulk polymerisation is generally started at about 70"C in the presence of one or more initiators which take effect at that temperature. As the polymerisation progresses, the temperature of the mixture generally increases and, as the monomer content decreases, the viscosity increases. The increase in temperature, however, ensures that the mixture is sufficiently mobile to be stirred or able to flow.

When the temperature has increased to the temperature in the range of from 150 to 230"C at which the particular initiator(s) of the general formula I (which may be added at that time, or may have been present initially) becomes effective, that initiator initiates polymerisation of substantially all of the remaining monomer(s).

For the homo- or copolymerisation of styrene, however, the presence of one or more other initiators during the first stage is not necessary, since the polymerisation of styrene can be initiated thermally; hence, the presence of a single initiator of the general formula I is sufficient in this case.

The total amount of all initiators used in the bulk polymerisation of the present invention is suitably from 0.005 to 1%, preferably from 0.01 to 0.25%, by weight, based on the total monomer(s). The total amount of initiator(s) of the general formula I is suitably from 0.03 to 0.4%, preferably from 0.1 to 0.25%, by weight, based on the total monomer(s).

In order totes the ability of the azo compounds to be used in the invention to reduce the residual monomer content in the finished polymer, they are compared with a series of peroxides which take effect at relatively high temperatures. Two peroxides that were particularly recommended for reducing the residual monomer content in the mentioned British Patents 1,329,859 and 1,330,896 were used as comparison substances.

These are the peroxides II (1,1,4,4,7,7 - hexamethylcyclo - 2,5 diperoxynonane) and 111(3,5 - dimethyl - 3,5 - bis - (t - butylperoxy) - 1,2 dioxolane). The result of this comparison demonstrated the superiority of the azo compounds according to the invention.

The methods for the production of the azo compounds according to the invention are known. The majority of the azo compounds used in the Examples are likewise known. The azo compounds 1,1' - azo - bis - (I - methoxycyclohexane), 1,1' - azo - bis - (1 - phenoxycyclohexane), 1,1' - azo - bis - (1 acetoxymethylcyclohexane) and 1,1' - azo - bis - (1 - acetoxy - 3,3,5 trimethylcyclohexane) are believed to be new.

The point of taking effect (=temperature of taking effect) of a peroxide as a measure of its activity can be established by determining the half-like period; the 10-hour half-life temperature (10 hHt) corresponds approximately to the temperature of taking effect. An even simpler and quicker method of establishing the approximate activity of an initiator and thus also an approximate point of taking effect consists in the comparison of several initiators in the heat-curing of unsaturated polyester resins (a solution of unsaturated polyesters in styrene) where the activity of at least one of these initiators must be known.

The polymerisation processes were carried out with inhibitor-free monomers in hermetically-closed ampoules (test tubes) in a drying chamber. The residual styrene content was determined by gas chromatography. For this purpose the polymer was cooled to room temperature after polymerisation was complete and a small portion thereof was dissolved in a solvent such as benzene or chloroform containing 0.001 /" of 4-t-butylcatechol as the inhibitor. Approximately 0.5 to 1 y1 of these solutions was injected into the gas chromatographs.

Since an exact reproducibility of the individual polymerisation test series was not possible the initiators to be compared were used in the same test series at the same time under the same conditions. It is possible only under certain conditions to compare one test series with another.

When comparing the effectiveness of different initiators, these must be in equivalent quantities. 1 mol of benzoyl peroxide and 1 mol of perbenzoate are equivalent to 1 mol of an azo compound containing an azo group or 1 mol of a peroxide with only one peroxide group, but they are equivalent to 1/2 mol of a bifunctional peroxide such as, 2,5 - bis - (t - butylperoxy) - 2,5 - dimethylhexane or even to only 1/3 mol of a trifunctional peroxide such as 3,5 - bis - (t butylperoxy) - 3,5 - dimethyl - 1,2 - dioxalane (III) which must be borne in mind in the following Examples.

Benzoyl peroxide gnd t-butyl perbenzoate (hereinafter referred to as 'perbenzoate') are the peroxides most frequently used in the industrial production of polystyrene. In many cases di-t-butyl peroxide also is used for this purpose.

In the following Examples, polymerisations are carried out in accordance with the process of the invention, that is to say polymerisation is started at a temperature below that at which the particular compound(s) of the formula I employed becomes effective as an initiator so that polymerisation of at least some of the monomer(s) occurs below that temperature.

The 10-hour half-life temperatures of the initiators I used in the following Examples are: y,y'-azo-bis-(y-valerolactone) 2l20C l,l'-azo-bis-(l -formyloxycyclohexane) approx. 2060 C 1,1 '-azo-bis-( 1 -acetoxycyclohexane) 197"C 2,2'-azo-bis-(2-acetoxybutane) approx. 1910C 2,2'-azo-bis-(2-acetoxypropane) 189"C 2,2'-azo-bis-(2-acetoxy-4-methylpentane) approx. 1790 C l,l'-azo-bis-(l -methoxycyclohexane) approx. 178"C 1,1 '-azo-bis-( 1 -phenoxycyclohexane) approx. 175"C 1,1 '-azo-bis-( 1 -acetoxy-methylcyclohexane) approx. 1960 C 1,1 '-azo-bis-( l-acetoxy-3,3,5-trimethyl cyclohexane) approx. 1940C The invention is illustrated by the following Examples: Example 1 Bulk polymerisation of styrene. In the quantity data for the initiators, benzoyl peroxide with a molecular weight of 242.22 was used as the reference peroxide. The quantity of initiator used was indicated in " /n benzoyl peroxide equivalents" ( /n bp equ.). Since 0.08% of perbenzoate with a molecular weight of 194.22 is equivalent to 0.10/, of benzoyl peroxide a quantity indication in our Example runs, for example, 0.1 /O bp equ. perbenzoate (and not 0.08% perbenzoate) or 0.1% bp equ.

of the bifunctional 2,5 - di - (t - butylperoxy) - 2,5 - dimethylhexyne - (3) (and not 0.059% 2,5 - di - (t - butylperoxy) - 2,5 - dimethylhexyne - (3)). The total polymerisation time was 8 hours+l0 minutes; it was started at 1200C and the temperature was increased at the following rhythm: to 2200 C: 3 hours at 120 C, 50 minutes at 130 C, 40 minutes at 1400C, 40 minutes at 1506C, 35 minutes at 160"C, 35 minutes at 1700C, 25 minutes at 180 C, 25 minutes at 190 C, 20 minutes at 200"C, 20 minutes at 210 C, 20 minutes at 220"C, Residual styrene content detected Initiator in the polystyrene a) 0.2 benzoyl peroxide 0.074 / b) 0.1 benzoyl peroxide 0.060% + 0.1% bp equ. perbenzoate c) 0.08% benzoyl peroxide 0.067% + 0.08% bp equ. perbenzoate + 0.04% bp equ. 2,5-bis-(t-butylperoxy) dimethylhexyne-(3) d) 0.08% benzoyl peroxide 0.016% + 0.08% bp equ. perbenzoate + 0.04% bp equ. y,y'-azo-bis-(y-valerolactone) The initiator combination d), in which the azo-bis-valerolactone constitutes 1/5 of the total quantity, thus gave the best result.

Example 2 Bulk polymerisation of styrene under the same conditions as in Example 1 with the following initiator systems in which the quantity data correspond to those mentioned in Example 1: Residual styrene content detected Initiator in the polystyrene a) 0.2% bp equ. perbenzoate E062U/ b) 0.05 /n bp equ. perbenzoate + 0.05% bp equ. 2,5-bis-(t-butylperoxy) 2,5-dimethylhexyne-(3) 0.25% c) 0.05 / > bp equ. perbenzoate 0.37% + 0.05 % bp equ. di-t-butyl peroxide d) 0.05 /n bp equ. perbenzoate + 0.05% bp equ. 2,5-bis-(t-butylperoxy) 2,5-dimethylhexane 0.60% e) 0.05% bp equ. perbenzoate + 0.05% bp equ. y,y'-azo-bis-(y-valerolactone) 0.14% In test a) double the equivalent quantity of perbenzoate was used intentionally.

In this case, too, the combination e) containing the azo compound proved the most effective.

Example 3 Bulk polymerisation of styrene under the same conditions as in Examples 1 and 2 with the following initiator combinations in which the quantity data correspond to those mentioned in Example 1: Residual styrene content detected Initiator in the polystyrene a) 0.2% bp equ. perbenzoate 0.67 /n b) 0.1% bp equ. perbenzoate + 0.1% bp equ. 2,5-bis-(t-butylperoxy)- 0.56% 2,5-dimethylhexyne-(3) c) 0.1% bp equ. perbenzoate + 0.1% bp equ. di-t-butyl peroxide 0.31 /n d) 01 /n bp equ. perbenzoate + 0.1% bp equ. 2,5-bis-(5-butylperoxy)- 0.34 2,5-dimethylhexane e) 0.1% bp equ. perbenzoate + 0.1% bp equ. y,y'-azo-bis-(y-valerolactone) 0.12 /n f) 0.1% bp equ. perbenzoate + 0.1% bp equ. 2,2'-azo-bis-(2-acetoxy-4- 0.044% methylpentane) In this Example, too, the combinations containing azo compounds (e and f) proved to be the best.

Example 4 Bulk polymerisation of styrene at 155 to 2200C for a period of 9 hours with the following temperature adjustments: 3 hours at1550C, Ihour at 170 C Ihour at1800C, Ihour at 1900C, 1 hour at 200 C, 1 hour at2100C, 1 hour at 2200 C, The same type and quantity of initiators were used as in Example 3: Residual styrene content detected Initiator in the polystyrene a) 0.2% bp equ. perbenzoate 0.174% b) 0.1% bp equ. perbenzoate + 0.1 /" bp equ. 2,5-bis-(5-butylperoxy)- 0.203% 2,5-dimethylhexyne-(3) c) 0.1% bp equ. perbenzoate 0.152% + 0.1 /n bp equ. di-t-butylperoxide 0.152 , d) 0.1% bp equ. perbenzoate + 0.1% bp equ. 2,5-bis(t-butylperoxy) 2,5-dimethylhexane 0.258% e) 0.1% bp equ. perbenzoate + 0.1 / bp equ. y,y'-azo-bis-(y-valerolactone) 0.086% f) 0.1% bp equ. perbenzoate + 0.1% bp equ. 2,2'-azo-bis-(2-acetoxy-4- 0.075 /n methylpentane) In this case, too, the two combinations containing azo compounds brought about the lowest residual styrene content.

Example 5 Bulk polymerisation of styrene at 155 to 220 C for a period of 9 hours; the temperature adjustments were the same as in Example 4. In contrast to the preceding Examples the initiators are tested individually and not in combination: Residual styrene content detected Initiator in the polystyrene a) 0.2% bp equ. perbenzoate 0.242% b) 0.2% bp equ. 2,5-bis(t-butylperoxy) 2,5-dimethylhexyne-(3) 0.136% c) 0.2% bp equ. di-t-butyl peroxide 0.167% Residual styrene content detected Initiator in the polystyrene d) 0.2% bp equ. 2,5-bis-(t-butylperoxy) 2,5-dimethylhexane 0.156% e) 0.2% bp equ. y,y'-azo-bis-(y-valerolactone) 0.063% f) 0.2% bp equ. 2,2'-azo-bis-(2-acetoxy-4- methylpentane) 0.048% In this case, too, the two azo initiators yield the lowest residual styrene content.

Example 6 Bulk polymerisation of styrene at 155 to 2200C for a period of 9 hours; the temperature adjustments were the same as in Example 4. In this case 4 azo compounds are compared with peroxides which take effect at high temperatures, all being good cross-linking agents for polymers. Each initiator is used individually: Residual molar equiv- styrene content ratio valent detected initiator: ratio in the Initiator bp polystyrene a) 0.2% bp equ. 2,2'-azo-bis-(2- 1 1 0.113% acetoxypropane) b) 0.2%bpequ. l,l'-azo-bis-(l- 1 1 0.123% methoxycyclohexane) c) 0.2% bp equ. l,l'-azo-bis-(l- 1 1 0.031% acetoxycyclohexane) d) 0.2% bp.equ. l,l'-azo-bis-(l- 1 1 0.057% phenoxycyclohexane) e) 0.6% bp equ. 3,5-bis-(t-butyl- 1 3 0.042% peroxy)-3,5-dimethyl-l ,2- dioxolane (III) f) 0.4bpequ. 1,1,4,4,7,7-hexa- 1 2 0.230% methylcyclo-2,5-di peroxynonane (II) g) 0.4% bp equ. 2,5-bis-(t-butyl- 1 2 0.330% peroxy)-2,5-dimethyl hexyne-(3) h) 0.2% bp equ. 2,5-bis-(t-butyl- 1/2 1 0.400% peroxy)-2,5-dimethyl hexyne-(3) i) 0.4% bp equ. 2,5-bis-(t-butyl- 1 2 0.140% peroxy)-2,5-dimethylhexane j) 0.2 /n bp equ. 2,5-bis-(t-butyl- 1/2 1 0.150% peroxy)-2, 5-dimethylhexane k) 0.2% bp equ. di-t-butyl peroxide 1 1 0.230% As in all the preceding tests the best (lowest) residual styrene contents are obtained in this case, too, with the azo compounds. The very good value of 0.042% residual styrene content, obtained with the trifunctional peroxide III, may not be used for comparison since 3 equivalents of this peroxide were used.

Example 7 Bulk polymerisation of styrene at 160 to 2200C for a period of 8 hours with the following temperature adjustments: 3 hours at 1600C, lhour at 1800C, 1 hour at 1900C, 1 hour at 2000 C, Ihour at 2100C, lhour at2200C, In this case 2 azo compounds are compared with 3 hydroperoxides, with dicumyl peroxide, di-t-butyl peroxide and 2,5 - bis - (t - butylperoxy) - 2,5 dimethylhexane, each initiator being used individually: Residual styrene content detected Initiator in the polystyrene a) 0.2% bp equ. 1,1'-azo-bis-(1-acetoxy- 0.058 /" cyclohexane b) 0.2% bp equ. y,y'-azo-bis-(y- 0.0310;, valerolactone) c) 0.2% bp equ. cumene hydroperoxide 0.150'M d) 0.2% bp equ. diisopropylbenzene 0.120 , monohydroperoxide e) 0.2% bp equ. t-butyl hydroperoxide 0.250 / f) 0.2% bp equ. dicumyl peroxide 0.140 / g) 0.2% bp equ. di-t-butyl peroxide 0.3200j h) 0.4% bp equ. 2,5-bis-(t-butylperoxy)- 0.120% 2,5-dimethylhexane i) 0.2% bp equ. 2,5-bis-(5-butylperoxy)- 0.210% 2,5-dimethylhexane In this test, too, the azo compounds proved the best initiators.

Example 8 Bulk polymerisation of styrene at 155 to 1900C for a period of 7 hours with the following temperature adjustments: 3 hours at 1550C, 1.5 hours at 1700C, 0.5 hours at 1800C, and 2 hours at 190 C.

In this test the same initiators are tested as in Example 6 as well as, in addition, 3 - (t - butylperoxy) - 3 - phenyl phthalide (III), dicumyl peroxide, cumene hydroperoxide and diisopropylbenzoyl monohydroperoxide, each initiator being used individually: Residual molar styrene content ratio equiva- detected initiator: lent in the Initiator bp ratio polystyrene a) 0.2% bp equ. y,y'-azo-bis-(y- 1 1 0.47% valerolactone) b) 0.2% bp equ. 2,2'-azo-bis-(2- 1 1 0.76 /O acetoxypropane) c) 0.2%bp equ.1,1'-azo-bis-(1- 1 1.15% methoxycyclohexane) d) 0.2%bpequ. l,l'-azo-bis-(l- 1 1 0.490/0' acetoxycyclohexane) e) 0.2%bpequ. l,l'-azo-bis-(l- I 1 0.79% phenoxycyclohexane) f) 0.6% bp equ. 3,5-bis-(t-butyl- 1 3 0.67% peroxy)-3,5-dimethyl 1,2-dioxolane (III) g) 0.4% bp equ. 3,5-bis-(t-butyl- 2/3 2 1.20% peroxy)-3,5-dimethyl 1,2-dioxolane (III) h) 0.2% bp equ. 3,5-bis-(t-butyl- 1/3 1 1.41% peroxy)-3,5-dimethyl 1,2-dioxolane (III) i) 0.4%bpequ. 1,1,4,4,7,7- 1 2 0.19% hexamethylcyclo-2,5-di peroxynonane (II) j) 0.2% bp equ. 1,1,4,4,7,7- 1/2 1 1.22% hexamethylcyclo-2,5-di peroxynonane (II) k) 0.4% bp equ. 2,5-bis-(t-butyl- 1 2 1.16% peroxy)-2,5-dimethyl hexyne-(3) 1) 0.2% bp equ. 2,5-bis-(t-butyl- 1/2 1 1.91% peroxy)-2,5-dimethyl hexyne-(3) Residual molar styrene content ratio equiva- detected initiator: lent in the Initiator bp ratio polystyrene m) 0.4% bp equ. 2,5-bis-(5- 1 2 0.78% butylperoxy)-2,5-dimethyl hexane n) 0.2% bp equ. 2,5-bis-(t-butyl- 1/2 1 1.16% peroxy)-2,5-dimethyl hexane o) 0.2% bp equ. di-t-butyl peroxide 1 1 1.58 p) 0.2% bp equ. dicumyl peroxide 1 1 2.17% q) 0.2% bp equ. 3-(t-butylperoxy)- 1 1 0.90% 3-phenylphthalide (IV) r) 0.2% bp equ. cumene hydroperoxide I 1 1.05% s) 0.2% bp equ. diisopropyl- 1 1 1.08% benzene monohydroperoxide As in the preceding Examples the best residual styrene contents were obtained from the azo compounds in this case too although this time the residual styrene content (1.15%) of the worst azo compound (1,1' - azo - bis - (1 methoxycyclohexane) is of the same order as the residual styrene content of the best peroxides (phthalide IV, 0.90%; cumene hydroperoxide, 1.05 /n; diisopropylbenzene monohydroperoxide, 1.08%, and 2,5 - bis - (t - butylperoxy) 2,5 - dimethylhexane, 1.16%). The residual styrene contents obtained when using 2 or 3 equivalents of the polyfunctional peroxides must, of course, not be used for comparison or must be used only to show that even 2 or 3 equivalents of these peroxides are no better than most of the azo compounds. Below is the structural formula of 3 - (t - butylperoxy) - 3 - phenyl phthalide (IV).

Example 9 Bulk polymerisation of styre Residual styrene content detected Initiator in the polystyrene c) 0.1% di-t-butyl peroxide 0.3710;, + 0.2% di equ. 2,5-bis-(t-butylperoxy) 2,5-dimethylhexane d) 0.1% di-t-butyl peroxide 0.742 + 0.1 /O di equ. 2,5-bis-(t-butylperoxy) 2,5-dimethylhexane e) 0.2% di equ. y,y'-azo-bis-(y- 0.137? valerolactone) f) 0.2% di equ. 1,1'-azo-bis-(1- 0.157",', acetoxycyclohexane) g) 0.2% di-t-butyl peroxide 0.725%, h) 0.4% di equ. 2,5-bis-(t-butylperoxy)- 0.683% 2,5-dimethylhexane i) 0.2% di equ. 2,5-bis-(t-butylperoxy)- 1.003% 2,5-dimethylhexane Therefore, in this test also, the azo compounds, individually or in combination, yield the lowest residual styrene contents.

Example 10 Bulk polymerisation of styrene at 150 to 2200C for a period of 9 hours with the following temperature adjustments: 1 1/2 hours at 1500C, 1 1/2 hours at 1600C, 1 hour at 1700C, I hour at 1800C, 1 hour at 1900C, 1 hour at 2000C, 1 hour at 2100C, 1 hour at 2200 C. In this test azo compounds which have not been tested hitherto are tested individually, also combinations of two and three azo compounds as well as a combination of 2 azo compounds and I peroxide in comparison to a series of peroxides: Residual equiv- styrene content alent detected in Initiator ratio the polystyrene a) 0.2% bp equ. y,y'-azo-bis-(y- 1 0.12% valerolactone) b) 0.2% bp equ. I,l'-azo-bis-(l- 1 0.073% acetoxycyclohexane) c) 0.2 bp equ. 2,2'-azo-bis-(2- 1 0.24 /O acetoxy-4-methylpentane) d) 0.2% bp equ. I,l'-azo-bis-(l- 1 0.21% methoxycyclohexane) e) 0.2% bp equ. 2,2'-azo-bis-(2- 1 0.12% acetoxypropane) f) 0.2%bpequ. I,l'-azo-bis-(l- 1 0.20% acetoxy-3,3,5-trimethylcyclohexane) g) 0.2% bp equ. 1,1'-azo-bis-(1- 1 0.16% acetoxymethylcyclohexane)

h) 0.1% bp equ. 1,1'-azo-bis-(1- # methoxycyclohexane) + 0.1% bp equ. l,l'-azo-bis-(l- r 0.038% acetoxycyclohexane) i) 0.1% bp equ. I,l'-azo-bis-(l methoxycyclohexane) + 0.1% bp equ. γ,γ'-azo-bis-(γ- # 1 0.10/n valerolactone) j) 0.067% bp equ. 1,1'-azo-bis-(1- methoxycyclohexane) + 0.067% bp equ. 1,1 '-azo-bis-( 1 0.15% acetoxycyclohexane 2 + 0.067% bp equ. 2,2'-azo-bis-( acetoxy-4-methylpentane)

Residual equiva- styrene content lent detected in Intiator ratio the polystyrene k) 0.067%bpequ. l,l'-azo-bis-(l- methoxycyclohexane) + 0.067% bp equ. 2,2'-azo-bis- # (2- l r O acetoxypropane) 1 0.11% + 0.067% bp equ. di-t-butyl 1) 0.2% benzoyl peroxide . 1 0.45% m) 0.2% bp equ. perbenzoate 1 0.33% n) 0.2% bp equ. di-t-butyl peroxide 1 0.45% o) 0.2% bp equ. dicumyl peroxide 1 0.30% p) 0.2% bp equ. cumene hydroperoxide 1 0.39% q) 0.4% bp equ. 3,3-bis-(t-butylperoxy)- 2 0.27% butyric acid ethyl ester r) 0.2% bp equ. 3,3-bis-(t-butylperoxy)- 1 0.34% butyric acid ethyl ester s) 0.4% bp equ. a,a'-bis-(t-butylperoxy)- 1 0.25% p-diisopropylbenzene t) 0.2% bp equ. a,a'-bis-(t-butylperoxy)- 1 0.26% p-diisopropylbenzene u) 0.6% bp equ. 1 ,3,5-tris-(2-(t-butyl- 3 0.24% peroxy)-propyl-(2))-benzene v) 0.4% bp equ. 1,3,5-tris-(2-(t-butyl- 2 0.28% peroxy)-propyl-(2))-benzene w) 0.2 bp equ. 1,3,5-tris-(2-(t-butyl- 1 0.31 peroxy)-propyl-(2))-benzene All azo compounds, their combinations and the combinations of one peroxide and two azo compounds thus give a polystyrene with a lower residual styrene content than the peroxides even when 2 or even 3 of their equivalents are used.

Noteworthy are the residual styrene contents that are obtained when using the three acetoxy azo compounds b) (-cyclohexane), g) (-methylcyclohexane, 61% of the methyl groups are in the 3-position) and f) (-3,3,5-trimethylcyclohexane), viz.

0.073 %, 0.16% and 0.20% respectively. This is explained by the reduction of the temperature of taking effect with increasing substitution in the A-position (=3and/or 5-position of the cyclohexane ring), which is linked with an increase in the residual styrene content.

Example 11 Bulk polymerisation of styrene under the same conditions as in Example 10.

2,2' - azo - bis - (2 - acetoxybutane), which has not yet been tested, is tested individually and in combination with 1,1 - azo - bis - (I - acetoxycyclohexane) in comparison to peroxides and azo compounds.

Residual equiv- styrene content alent detected in Initiator ratio the polystyrene a) 0.2%bpequ. l,l'-azo-bis-(l- 1 0.073% acetoxy-cyclohexane) b) 0.2%bpequ.l,l'-azo-bis-(l- 1 0.21% methoxycyclohexane) c) 0.2% bp equ. 2,2'-azo-bis-(2- 1 0.12 /n acetoxypropane) d) 0.2% bp equ. 2,2'-azo-bis-(2- 1 0.28% acetoxybutane) e) 0.1% bp equ. l,l'-azo-bis-(l- 1 0.11% acetoxycyclohexane) + 0.1% bp equ. 2,2'-azo-bis-(2 acetoxybutane) f) 0.2% bp equ. perbenzoate 1 0.33% g) 0.2% bp equ. dicumyl peroxide 1 0.31% h) 0.2% bp equ. di-t-butyl peroxide 1 0.45% i) 0.2% bp equ. cumene hydroperoxide 1 0.40% In this case, too, the azo compounds yield a polystyrene with a lower residual styrene content than the peroxides.

The production of some of the azo compounds to be used according to the invention are described below; Production of I, I '-azo-bis-( l -methoxycyclohexane):

2.62 g of sodium (0.114 mol) were added to 100 ml of methanol. A solution of 10 g of 1,1' - azo - bis - (1 - chlorocyclohexane) (0.038 mol) in 75 ml of n-hexane are added dropwise at 200 C, while stirring, to the sodium methylate solution thus obtained. Afterwards, stirring was continued for 90 minutes at 25 to 300C and the whole was then poured into 400 ml of water while stirring. The organic phase was washed with 50 ml of water and dried with K2CO3. The hexane was completely drawn off in vacuo at 400C. Yellow oil that solidifies when stored at OOC and contains 89% of 1,1' - azo - bis - (I - methoxycyclohexane). Yield: 6.2 g (57 /n of the theoretical yield).

Production of 1, l'-azo-bis-(l-phenoxycyclohexane):

35 g of sodium phenolatex3H2O (0.21 mol) were suspended in 400 ml of n-hexane.

26.3 g of 1,1' - azo - bis - (1 - chlorocyclohexane) (0.10 mol)-dissolved in 100 ml of n-hexane-are then added at 200C while stirring. The whole was stirred vigorously for 3 hours at 20"C and for 3 hours at 300 C. Afterwards the whole was poured, while stirring, into 400 ml of water, stirred for 15 minutes and the aqueous phase was separated in a separating funnel. The organic phase was washed twice with IN sodium hydroxide solution and then washed with water and dried with K2CO3. The hexane was completely drawn off in vacuo at 400C and the yellow residue remaining in the flask was recrystallised from acetone. White powder with melting point of 115 to 1200C and a content of 53% of 1,1' - azo - bis - (I phenoxycyclohexane). Yield: 7.5 g.

Production of 1,1 '-azo-bis-( 1 -acetoxymethylcyclohexane): a) Methylcyclohexanone azine:

At approximately 20 to 400 C, 50 g of hydrazine hydrate, 50 /n strength (0.50 mol), are added while stirring and cooling to Ill g of methylcyclohexanone isomer mixture (consisting of 61% of 3-methylcyclohexanone, 31% of 4methylcyclohexanone and 8% of cyclohexanone (1.00 mol) in a 4-necked flask provided with a reflux cooler, stirrer, dropping funnel and a thermometer. The whole is then stirred for 6 hours at 200C. The whole reaction mixture is poured into a separating funnel which is left to stand for 40 hours at room temperature after being closed. The lower aqueous phase is separated, the upper phase is washed three times with 70 ml of water and dried with approximately 5 g of MgSO4x3H2O.

The 103 g of crude azine thus obtained are distilled in vacuo and pass over at 1900C/30 torr. 74 g (68% of the theoretical yield) of the methylcyclohexanone azine mixture are thus obtained as a yellow oil.

b) 1,1 '-azo-bis-( l-chloromethylcyclohexane):

21 g of the above methylcyclohexanone azine (0.0965 mol) are dissolved in 150 ml of CCl4 in a 4-necked flask provided with a reflux cooler, stirrer, thermometer and a tube for introducing chlorine. While stirring and cooling and under the exclusion of atmospheric moisture approximately 2.6 1 of chlorine gas (approximately 0.105 mol) are introduced at 100C to 150C and stirring is continued at 10 to 15"C for 10 minutes and afterwards a slow nitrogen stream is blown through the entire apparatus in order to bring all the chlorine into reaction with the azine. The CCl4 is then drawn off in a water jet vacuum at 60 to 700 C. 60 g of the 1,1' - azo - bis - (I - chloromethylcyclohexane) are thus obtained as a reddishbrown oil with a degree of purity of 51%.

c) 1,1 '-azo-bis-( l -acetoxymethylcyclohexane):

28.4 g of the above 1,1' - azo - bis(l - chloromethylcyclohexane) were added portionwise, while stirring and cooling, to a suspension of 41 g of anhydrous sodium acetate in 300 ml of glacial acetic acid at 200C. The mixture was stirred for 3 hours at room temperature, then poured into 1.5 1 of water and stirred for 30 minutes. For a better phase separation the azo compound was dissolved in 100 ml of ethyl acetate and the whole mixture was allowed to settle in a separating funnel.

After separating the lower aqueous phase the organic phase was washed with excess NaHCO3-solution until there was an alkaline reaction and dried with MgSO4x3H2O. The ethyl acetate was drawn off in vacuo at 600C. 51 g of 1,1' azo - bis - (I - acetoxymethylcyclohexanone) remained in the flask as a darkreddish-brown liquid with a slight smell and a degree of purity of 55%.

Production of I,l'azo-bis-(l -acetoxy-3,3,5-trimethylcyclohexane): a) 3,3,5-trimethylcyclohexanone azine:

701 g of 3,3,5-trimethylcyclohexanone (5.0 mol) and 200 ml of isopropanol are placed in a 4-necked flask provided with a reflux cooler, stirrer, dropping funnel and thermometer. 125 g of hydrazine hydrate, 80% strength (2.0 mol) are added while stirring and cooling at temperatures below 40"C. Stirring is then continued for 3 1/2 hours at 850 C, the whole is poured while stirring into 11 of water and allowed to settle in a separating funnel. After separating the lower aqueous phase the organic phase is shaken with 500 ml of water; in so doing the azine separates as a solid white product that is suction-filtered, washed with water and dried in the air.

64 g (11.5% of the theoretical yield) of the 3,3,5-trimethylcyclohexanone azine is thus obtained as a white powder with a melting point of 135 to 1370C.

b) 1,1 '-azo-bis-( 1 -chloro-3,3,5-trimethylcyclohexane):

55.3 g of the above 3,3,5-trimethylcyclohexanone azine (0.20 mol) are dissolved in 400 g of CCl4 in a 4-necked flask provided with a reflux cooler, stirrer, thermometer and a tube for introducing chlorine. Approximately 15 g of chlorine gas (approximately 5.3 1; approximately 0.21 mol) are introduced slowly at 10 to 150C while stirring and cooling and under the exclusion of atmospheric moisture. The whole is afterwards stirred for 10 minutes and then a slow nitrogen stream is blown through the entire apparatus in order to bring all the chlorine into reaction with the azine. The CCl4 is distilled off in vacuo at 600C and 50 g (72% of the theoretical yield) of the crude dichloro-azo compound is thus obtained as an orange powder.

After recrystallising from n-pentane, 27 g (38% of the theoretical yield) of the pure 1,1' - azo - bis - (I - chloro - 3,3,5 - trimethylcyclohexane) are obtained as an almost white, slightly yellow, odourless powder with a melting point of 149 to 151 C and a degree of purity of 98.1%.

c) I, I '-azo-bis-( 1,1 -acetoxy-3,3,5-trimethylcyclohexane):

26.5 g of the above 1,1' - azo - bis - (1 - chloro - 3,3,5 trimethylcyclohexane) (0.075 mol) were added portionwise, while stirring and cooling, to a suspension of 32 g of anhydrous sodium acetate (0.39 mol) in 280 ml of glacial acetic acid at approximately 200C. The mixture was stirred for 3 hours at room temperature, then poured, while stirring, into 1.5 1 of water, the acetoxy azo compound precipitating as a pale, finely crystalline substance, and stirred for a further 30 minutes. After suction-filtering, washing with water and drying in the air, 1,1' - azo - bis - (1 - acetoxy - 3,3,5 - trimethylcyclohexane) is obtained as a good greyish-white powder in a yield of 29.7 g (98% of the theoretical yield) and with a melting point of 109 to 1130C. After recrystallising from acetone 16 g of the white crystalline azo compound are obtained with a melting point of 111 to 11 50C and an iodometrically specific content of 104%.

Production of the 1,1' - azo - bis - (1 - acetoxycyclohexane) in one stage from the cyclohexanone azine:

22 g of cyclohexanone azine (0.114 mol) are dissolved in 300 ml of glacial acetic acid in a 4-necked flask provided with a CaCl2 tube, a stirrer, thermometer and a tube for introducing chlorine. 38 g of anhydrous sodium acetate (0.464 mol) are added, stirred for 10 minutes and 8.5 g of chlorine (approx. 3 1, 0.12 mol) are slowly introduced at 200C under the exclusion of atmospheric moisture.

Afterwards, a slow nitrogen stream is blown through the entire apparatus and then stirring is effected for 30 minutes at 200 C. The whole is poured, while stirring, into 2 1 of water, the azo compound precipitating as a finely crystalline product, and stirred for a further 30 minutes, suction-filtered, washed well with water and dried in the air. 25 g (71 /n of the theoretical yield) of 1,1' - azo - bis - (1 acetoxycyclohexane) are thus obtained as an almost colourless, slightly yellow, crystalline powder having a melting point of 91 to 940C and a degree of purity of 99%.

Production of 2,2' - azo - bis - (2 - acetoxy - 4 - methylpentane) in one stage from methyl isobutyl ketone azine:

30 g of methyl isobutyl ketone azine (0.153 mol) are dissolved in 400 ml of glacial acetic acid in a 4-necked flask provided with a CaCI2 tube, a stirrer, thermometer, and a tube for introducing chlorine. 50 g of anhydrous sodium acetate (0.61 mol) are added, the whole is stirred for 10 minutes and 11.6 g (approx. 4.1 1) of chlorine (0.164 mol) are introduced slowly at 200C under the exclusion of atmospheric moisture. Afterwards a slow nitrogen stream is blown through the apparatus and then stirring is effected for 1 hour at 200 C. The whole is poured, while stirring, into 1500 ml of water, the azo compound separating as an oil, stirred for a further 30 minutes, allowed to settle in a separating funnel and the lower aqueous phase is separated. The upper azo phase is washed with excess NaHCO3 solution until there is an alkaline reaction. After the settling and separation of the aqueous phase the azo compound is dried with MgSO4x3H2O. 31.5 g (64% of the theoretical yield) of 2,2' - azo - bis - (2 - acetoxy - 4 - methylpentane) are thus obtained as a yellowish oil with a fairly strong smell dnd a degree of purity of 97%.

Example 12 Bulk polymerisation of styrene at 110 to 2250C for a period of 10 hours with the following temperature adjustments: 1/2 hour at 1 100C, 1/2 hour at 1200C, 1/2 hour at 1300C, 1/2 hour at 1400C, 1/2 hour at 1500C, 1/2 hour at 1600C, 1/2 hour at 170"C, 1/2 hour at 1800C, 1/2 hour at 1900C, 1/2 hour at 2000C, 1 hour at 2050C, 1 hour at 2100C, 1 hour at 2150C, 1 hour at 2200C, 1 hour at 2250C.

In this test 1,1' - azo - bis - (I - formyloxycyclohexane) is tested individually and in combination with other initiators (azo compounds and peroxides): Residual styrene content detected Initiator in the polystyrene a) 0.2% bp equ. l,l'-azo-bis-(l-formyloxy- 0.023% cyclohexane) b) 0.2% bp equ. l,l'-azo-bis-(l-acetoxy 0.052% cyclohexane) c) 0e2 /n bp equ. 2,2'-azo-bis-(2-acetoxy- 0.021 / > propane) d) 0.2% bp equ. 2,2'-azo-bis-(2-acetoxy-4- 0.044% methylpentane) e) 0.2% bp equ. y,y'-azo-bis-(y-valerolactone) 0.035% f) 0.2% bp equ. I,l'-azo-bis-(l-methoxy- 0.054% cyclohexane) g) 0.2 /n benzoyl peroxide 0.16% h) 0.2% bp equ. perbenzoate 0.10% Residual styrene content detected Initiator in the polystyrene i) 0.2% bp equ. d-t-butyl peroxide 0.20% j) 0.2% bp equ. dicumyl peroxide 0.220/" k) 0.2% bp equ. 2,5-bis-(t-butylperoxy)-2,5- 0.086 dimethylhexane 1) 0.4% bp equ. 2,5-bis-(5-butylperoxy)-2,5- 0.087% dimethylhexane m) 0.2% bp equ. 2,5-bis-(t-butylperoxy)-2,5- 0.21 / dimethylhexyne-(3) n) 0.4% bp equ. 2,5-bis-(t-butylperoxy)-2,5- 0.12% dimethylhexyne-(3) o) 0.2% bp equ. 3,3-bis-(t-butylperoxy)-butyric 0 l09/" acid ethyl ester p) 0.4% bp equ. 3,3-bis-(t-butylperoxy)-butyric 0.095 /n acid ethyl ester q) 0.2% bp equ. l,l-bis-(t-butylperoxy)-3,3,5- 0.20 /n trimethylcyclohexane r) 0.4% bp equ. 1,1-bis-(t-butylperoxy)-3,3,5- 0.16% trimethylcyclohexane s) 0.1% bp equ. l,l'-azo-bis-(l-formyloxy-cyclo- 0.057 / hexane) + 0.1% bp equ. 1,1'-azo-bis-(1-methoxycyclohexane) t) 0.1% bp equ. 1,1'-azo-bis-(1-formyloxy- 0.038% cyclohexane) + 0.1% bp equ. l,l'-azo-bis-(l-acetoxy- cyclohexane) u) 0.067% bp equ. l,l'-azo-bis-(l-formyloxy- 0.054 / cyclohexane) + 0.067% bp equ. l,l'-azo-bis-(l-methoxy cyclohexane) + 0.067% bp equ. y,y'-azo-bis-(y-valerolactone) v) 0.067% bp equ. l,l'-azo-bis-(l-formyloxy- 0.043% cyclohexane) + 0.067% bp equ. 2,2'-azo-bis-(2-acetoxypropane) + 0.067% bp equ. 2,2'-azo-bis-(2-acetoxy 4-methylpentane) w) 0.1% benzoyl peroxide 0.082 /n + 0.1% bp equ. l,l'-azo-bis-(l -formyloxy- cyclohexane) x) 0.067% bp equ. perbenzoate 0.054% + 0.067% benzoyl peroxide + 0.067% bp equ. l,l'-azo-bis-( l-formyloxy- cyclohexane) y) 0.067% bp equ. perbenzoate 0.030 / + 0.067% bp equ. I, I '-azo-bis-( l -acetoxy- cyclohexane) + 0.067% bp equ. l,l'-azo-bis-(l-formyloxy- cyclohexane) As in all the preceding Examples, the azo compounds according to the invention (azo esters and azo ethers) yield, in this case, too, a polystyrene with a better (=lower) residual styrene content than the peroxides, the 1,1' - azo - bis (1 - formyloxycyclohexane) yielding the outstanding value of 0.023% of residual styrene. The combinations of 1,1' - azo - bis - (I - formyloxycyclohexane) with peroxides or azo compounds or both together yield a polystyrene with a slightly worse (=higher) residual styrene content than with 1,1' - azo - bis - (1 formyloxycyclohexane) alone; the residual styrene contents thus obtained are, however, still lower than those obtained with peroxides.

Production of 1,1' - azo - bis - (I - formyloxycyclohexane) in one stage from cyclohexanone azine:

64 g of anhydrous sodium formate (0.94 mol) are added, while stirring, to 300 ml of anhydrous formic acid in a 4-necked flask provided with a CaC12 tube, a stirrer, thermometer and a tube for the introduction of chlorine. 44 g of cyclohexanone azine (0.228 mol) are added at 200C while stirring, the whole is stirred for 10 minutes, cooled to OOC and 17.6 g (approx. 6.2 litres; 0.248 mol) of chlorine gas are introduced slowly while stirring and under the exclusion of atmospheric moisture at OOC (ice/sodium chloride cooling). Afterwards a slow nitrogen stream is blown through the entire apparatus and the whole is stirred for 1 1/2 hours, the temperature being increased in the following manner from 0 C to +25"C: 15 minutes at OOC, 15 minutes at +50C, 15 minutes at +100C, 15 minutes at +15"C, 15 minutes at +200C and 15 minutes at +250C. While stirring, the reaction mixture is poured into 2 1 of water, the azo compound precipitating as a white, finely crystalline product, stirred for a further 20 minutes, suction-filtered and washed with water. The azo compound is taken from the suction filter, added to 800 ml of 8% sodium bicarbonate solution, stirred for 20 minutes, suction filtered, washed well with water and dried in the air. 49.5 g (77 /n of the theoretical yield) of 1,1' - azo - bis - (I - formyloxycyclohexane) are thus obtained as a snow-white odourless powder having a melting point of 97--99.5"C and a degree of purity of 99.5%. The azo compound is not sensitive to impact does not undergo any detectable decomposition up to 2000C and has no explosive properties (a value of < 1 mm was determined in the pressure vessel test).

WHAT WE CLAIM IS: 1. A process for homo- or copolymerising one or more olefinically unsaturated monomers by a two-stage bulk polymerisation in which the second stage involves polymerisation of substantially all of the monomer(s) remaining after the first stage and in which the second stage is carried out with, as polymerisation initiator(s), at least one compound of the general formula I

wherein R represents an alkyl group having from 1 to 6 carbon atoms, a cycloalkyl, aryl or aralkyl group, or a group of the formula R3CO-- wherein R3 represents a hydrogen atom, an alkyl group having from 1 to 5 carbon atoms or a cycloalkyl, aryl or aralkyl group; and R1 and R2, any two or more of which may be the same or different, each represents an alkyl group having from 1 to 8 carbon atoms or a cycloalkyl or aralkyl group, or R' and R2 attached to the same carbon atom together represent an alkylene group having 4 or 5 carbon atoms in the carbon chain; or R2 is as defined above and R and R' together represent an alkylenecarbonyl group having 3 or 4 carbon atoms in the carbon chain; the groups R, R1, R2 and R3 being unsubstituted or substituted by one or more alkyl groups, at a temperature of at least 150"C but not more than 230"C at which said compound of the formula I becomes effective as in initiator; and in which the first stage involves poymerisation of at least some of the monomer(s) and is carried out at below said temperature with one or more other initiators and/or by thermal polymerisation.

2. A process as claimed in claim 1, wherein any compound of the general formula I specifically mentioned herein is used as an initiator in the second stage of polymerisation.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (23)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   Production of 1,1' - azo - bis - (I - formyloxycyclohexane) in one stage from cyclohexanone azine:

   64 g of anhydrous sodium formate (0.94 mol) are added, while stirring, to 300 ml of anhydrous formic acid in a 4-necked flask provided with a CaC12 tube, a stirrer, thermometer and a tube for the introduction of chlorine. 44 g of cyclohexanone azine (0.228 mol) are added at 200C while stirring, the whole is stirred for 10 minutes, cooled to OOC and 17.6 g (approx. 6.2 litres; 0.248 mol) of chlorine gas are introduced slowly while stirring and under the exclusion of atmospheric moisture at OOC (ice/sodium chloride cooling). Afterwards a slow nitrogen stream is blown through the entire apparatus and the whole is stirred for 1 1/2 hours, the temperature being increased in the following manner from 0 C to +25"C: 15 minutes at OOC, 15 minutes at +50C, 15 minutes at +100C, 15 minutes at +15"C, 15 minutes at +200C and 15 minutes at +250C. While stirring, the reaction mixture is poured into 2 1 of water, the azo compound precipitating as a white, finely crystalline product, stirred for a further 20 minutes, suction-filtered and washed with water. The azo compound is taken from the suction filter, added to 800 ml of 8% sodium bicarbonate solution, stirred for 20 minutes, suction filtered, washed well with water and dried in the air. 49.5 g (77 /n of the theoretical yield) of 1,1' - azo - bis - (I - formyloxycyclohexane) are thus obtained as a snow-white odourless powder having a melting point of 97--99.5"C and a degree of purity of 99.5%. The azo compound is not sensitive to impact does not undergo any detectable decomposition up to 2000C and has no explosive properties (a value of < 1 mm was determined in the pressure vessel test).

   WHAT WE CLAIM IS: 1. A process for homo- or copolymerising one or more olefinically unsaturated monomers by a two-stage bulk polymerisation in which the second stage involves polymerisation of substantially all of the monomer(s) remaining after the first stage and in which the second stage is carried out with, as polymerisation initiator(s), at least one compound of the general formula I

   wherein R represents an alkyl group having from 1 to 6 carbon atoms, a cycloalkyl, aryl or aralkyl group, or a group of the formula R3CO-- wherein R3 represents a hydrogen atom, an alkyl group having from 1 to 5 carbon atoms or a cycloalkyl, aryl or aralkyl group; and R1 and R2, any two or more of which may be the same or different, each represents an alkyl group having from 1 to 8 carbon atoms or a cycloalkyl or aralkyl group, or R' and R2 attached to the same carbon atom together represent an alkylene group having 4 or 5 carbon atoms in the carbon chain; or R2 is as defined above and R and R' together represent an alkylenecarbonyl group having 3 or 4 carbon atoms in the carbon chain; the groups R, R1, R2 and R3 being unsubstituted or substituted by one or more alkyl groups, at a temperature of at least 150"C but not more than 230"C at which said compound of the formula I becomes effective as in initiator; and in which the first stage involves poymerisation of at least some of the monomer(s) and is carried out at below said temperature with one or more other initiators and/or by thermal polymerisation.
2. 2. A process as claimed in claim 1, wherein any compound of the general formula I specifically mentioned herein is used as an initiator in the second stage of polymerisation.
3. 3. A process as claimed in claim I, wherein the initiator for the second stage of

   the polymerisation is y,y' - azo - bis - (y - valerolactone) or 1,1' - azo - bis - (I acetoxycyclohexane) or 2,2' - azo - bis - (2 - acetoxypropane) or 2,2' - azo - bis (2 - acetoxy - 4 - methylpentane) or a mixture thereof.
4. 4. A process as claimed in any one of claims 1 to 3, wherein the temperature in the range of from 150 to 2300C prevails during polymerisation of at most the final 50 percent of the monomer(s).
5. 5. A process as claimed in claim 4, wherein said temperature prevails during polymerisation of at most the final 20% of the monomer(s).
6. 6. A process as claimed in claim 5, wherein said temperature prevails during polymerisation of at most the final 10 percent of the monomer(s).
7. 7. A process as claimed in claim 6, wherein said temperature prevails during polymerisation of at most the final percent of the monomer(s).
8. 8. A process as claimed in any one of claims 4 to 7, wherein the temperature during the second stage of polymerisation is in the range of from 180 to 2200C.
9. 9. A process as claimed in any one of claims I to 8, wherein the total quantity of initiator present is in the range of from 0.005 to 1 percent by weight, based on the weight of the monomer(s).
10. 10. A process as claimed in any one of claims 1 to 9, wherein the total quantity of the or each compound of the general formula I as defined in claim 1 present is in the range of from 0.03 to 0.4 per cent by weight, based on the weight of the monomer(s).
11. 11. A process as claimed in any one of claims I to 9, wherein the total quantity of initiator present is in the range of from 0.01 to 0.25 percent by weight, based on the weight of the monomer(s).
12. 12. A process as claimed in any one of claims 1 to 11, wherein the total quantity of the or each compound of the general formula I as defined in claim 1 present is in the range of from 0.1 to 0.25 percent by weight, based on the weight of the monomer(s).
13. 13. A process as claimed in any one of claims 1 to 12, wherein any one or more of the monomers is styrene, an a,punsaturated acid, ester or nitrile, an ester of an a,p-unsaturated alcohol, or ethylene.
14. 14. A process as claimed in any one of claims 1 to 13, wherein any one or more of the monomers is any one of those specifically mentioned herein.
15. 15. A process as claimed in any one of claims 1 to 14, wherein the or at least one of the monomers is styrene.
16. 16. A process as claimed in claim 15, wherein styrene is homopolymerised.
17. 17. A process as claimed in claim 15 or claim 16, wherein no initiator other than a compound of the general formula I as defined in claim I is present, and wherein the first stage of the polymerisation is initiated thermally.
18. 18. A process as claimed in any one of claims 1 to 16, wherein at least one initiator other than a compound of the general formula I as defined in claim 1 is present.
19. 19. A process as claimed in claim 1, carried out substantially as hereinbefore described in any one of the non-comparative tests of any one of Examples 1 to 11.
20. 20. A process as claimed in claim 1, carried out substantially as hereinbefore described in any one of tests (a) to (f) and (s) to (y) of Example 12.
21. 21. A process as claimed in any one of claims 1 to 20, wherein the resulting homo- or copolymer has a residual monomer content which is less than that of a polymer prepared by an analogous bulk polymerisation carried out in the absence of a compound of the general formula I as defined in claim 1.
22. 22. A homo- or copolymer whenever produced by a process as claimed in any one of claims 1 to 21.
23. 23. Polystyrene, whenever prepared by a process as claimed in any one of claims 1 to 21.