CA2011079A1 - Urazole derivatives as initiators of free radical polymerization - Google Patents

Abstract

O.Z. 0050/40678 Abstract of the Disclosure: Initiators for free radical chain polymerization are urazoles of the general formula Ia or Ib

Description

2 0 1 1 0 7 9 o. z . 0050/~0678 Urazole derivatives as initiator~ of free radical Polymerization The present invention relates to the use of 1,4-disubstituted urazoles as initiators for free radical chain polymerization.
It i8 known that oxygen acts as an inhibitor in free radical polymerization, and it is for this reason that certain reaction mixtures are thoroughly flushed with an inert gas (eg. N2) for polymerization (B.
Vollmert, Grundriss der Makromolekularen Chemie, Volume I, page 74; E. Vollmert Verlag, Karlsruhe, 1985).
It i~ an object of the present invention to pro-vide an initiator system which is at least insensitive to oxygen or as far a~ possible requires oxygen in order to produce primary free radicals.
~ e have found that this object is achieved by 1,4-disubstituted urazoles.
~ he pre~ent invention therefore relate~ to a process for the preparation of polymers from monomers which are capable of undergoing free radical chain poly-merization, by the addition of a substance capable of forming prLmary free radicals and initiation of the poly-merization by formation of primary free radicals, wherein a urazole of the general formula Ia or Ib Rl Rl Rl N--NH ~NH N--NH
O~C~ /C=O ( I a ) O=C C=O O=C\ C=O ( I b ) where Rl and R2 are each (cyclo)alkyl, (cyclo)alkenyl, (cyclo)alkynyl, aryl, aralkyl or alkylaryl, each of not more than 30 carbon atoms, or a S-membered to 8-membered heterocyclic structure containing nitrogen, oxygen or sulfur, or -NR3R4, or toge~her form an alkylene bridge of 2 to 4 carbon atoms, R3 and R4 have the same meanings as 201~079 _ ~ _ o.Z. 0050/40678 R1 except for -NR3R4 and Z is a chemically inert bridge member, is used as the substance capable of forming primary free radicals.
The desired primary free radicals are formed, for example, by means of oxygen.
W.H. Pirkle and P.Z. Gravel, J. Org. Chem. 43 (1978), 808-815, disclose that 1,4-disubstituted urazoles can be reacted with oxidizing agents to give more or less stable urazole radicals. What was not known to date was that the radicals produced are capable of initiating free radical polymerization. This is all the more surprising since similar N-N radicals act as inhibitors in free radial polymerization, for example diphenylpicryl-hydrazole (DYPH) (B. Vollmert, Grundriss der Makro-molekularen Chemie, Volume I, page 74).
The formation of reactive urazole radicals byoxidation with oxygen presumably takes place in accord-ance with the following equation R~ R~

O--C C=O ~ 1/2 2 ~ C=O + H20 ( 1 ) N N

These radicals can also readily be produced using other oxidizing agents having sufficiently high oxidation potential. The free radicals can be produced either in ~itu in the monomer mixture or, since they have a suf-ficiently long life, can be metered into the monomer mix-ture in an inert solvent after production, a step which may be carried out continuously or batchwise.
For the in situ production~ the amounts of oxygen usually dissolved in the monomers are sufficient to initiate free radical polymerization.
In the case of the 1,4-disubstituted urazoles Ia and Ib, R1 and R2 may be identical or different and may 20~1079 - 3 O.~. 0050/~0678 each be unsubstituted or substituted alkyl, cycloalkyl, aryl, aralkyl or alkylaryl of not more than 30 carbon atoms, a 5-membered to 8-membered heterocyclic structure containing nitrogen, oxygen or sulfur as the heteroatom or -NR3R4, where R3 and R4 are each Cl-C4-alkyl or, in particular, hydrogen.
R1 and R2 may furthermore be (cyclo)alkenyl or (cyclo)alkynyl radicals of 2 to 30 carbon atoms.
Examples of alkyl radicals are methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, neopentyl, 3,5,5-trimethylhexyl, 3-methylhexyl, 2-ethylhexyl and 2,5,5-trimethylhexyl.
An example of a cycloalkyl radical is cyclohexyl.
Examples of aralkyl radicals are benzyl and phenethyl.
Unsubstituted aryl radicals are, for example, phenyl and naphthyl.
Substituted aryl radicals are alkylaryl, cyclo-alkylaryl, aryl-substituted alkylaryl and aryl-substituted aryl.
Examples of alkylaryl radicals are 2-, 3- and 4-tolyl, 2,6- and 2,4-dimethylphenyl, trimethylphenyl, 2-, 3- and 4-isopropylphenyl, nonylphenyll tert-butylphenyl, 2,4-diisopropylphenyl and triisopropylphenyl. An example of a cycloalkylaryl radical is 2-cyclohexylphenyl. Ex-amples of a aryl-substituted alkylaryl radicals are p-benzylphenyl and p-phenylethylphenyl.
An example of aryl-substituted aryl i~ biphenyl.
As free radical initiators, bisurazoles Ib, ie.
urazoles having more than one urazole group, lead to branched polymers or to polymers having a narrower molecular weight distribution. Preferred bisurazoles are those of the structure Ib Rl~1 ~H ~H
=o ~ C=o (Ib) _ Z - N

- 4 - O.Z. 0050~40678 where ~ i8 one of the bridge members below.
Suitable bridge members Z are divalent radicals, for example of the following structures:
-(CH2)n- where n is 1 to 12 ~3 ' ~ (CH2)m ~ where m is 1 to 12 and ~>

Z may also be the following, where p and q are each, for example, fro~ 1 to 20:

~(CH2)q ~3 t (CH2)q~
-C~2)p~
--~CH2) 20(CH2) 2----(C1~2) 20(CH2) 2----CH----ICH`- jCH 3 CH 2--CH~

--`ICH--rH3--C6H5 --C~

--C~
CH2 ~ and --C~
CH(CH3) ~

~011079 - 5 - O.Z. 0050/40678 Compounds I and II can be prepared as described by N.H. Pirkle and P.L. Gravel in J. Org. Chem. 43 (1978), 808.
Suitable monomer~ which can be polymerized with the compounds (I) and/or (II) are the conventional unsaturated vinyl compounds capable of undergoing free radical `~omopolymerization and/or copolymerization.
Examples include styrene, t-methylstyrene, p~methyl-styrene, methacrylates, acrylates, (meth)acrylamide derivatives, acrylonitrile, vinyl esters, vinyl chloride, vinyl alcohol and maleimides.
The polymers prepared using the compound~ Ia and~or Ib described do not differ from the polymers prepared using peroxides.
Suitable monomers which can be reacted with the novel compounds are the conventional unsaturated vinyl compounds capable of undergoing polymerization. Examples are styrene, ~-methylstyrene, p-methylstyrene, meth-acrylates, acrylates, (meth)acrylamide derivatives, acrylonitrile, vinyl esters, vinyl chloride, vinyl alcohol, maleic anhydride and maleimides.
EXAMPLES 1-3, CO~PARATIVE EXPERIMENT
The experiments for Examples 1-3 and the Compara-tive Experiment were carried out batchwise by the mass-suspension method in a 5 1 reactor equipped with ananchor stirrer.
In each case, 1,500 g of styrene and 500 g of acrylonitrile were mixed with one another in the reactor and 1.58 x 10-2 mole of a 1,4-disubstituted urazole Ia and R2 are ~tated in each ca~e) was dissolved therein.
The reactor content was then heated to 80C while stirring (100 xpm) and kept at 80C by cooling. The progress of the polymerization was monitored by determining the solids content of the reaction mixture at 30 minute interval~:

20t1 079 6 - O.Z. 0050/40678 ExamF~e 1 2 3ComPariSon R2 Phenyl Phenyl Phenyl Rl Phenyl Cyclo- n-~utyl hexyl ~nount of urazole [g] 4.0 4.1 3.7 Solids content in ~ by weight after 60 [min] 5.7 4.7 4.2 0 90 [min] 10.8 8.9 8.7 0 120 [min] 15.7 13.7 12.6 0 150 [min] 19.3 18.9 16.3 180 [min] 23.7 21.3 20.6 0.5 210 [min] 27.9 26.8 24.7 1.0 240 [min] 33.2 31.5 29.3 2.0 270 [min] 36.8 36.2 32.7 3.0 300 [min] 41.2 39.9 38.1 4.0 After a solids content of 40% by weight had been reached, 1.5 g of dicumyl peroxide were added to the polymer mixture and the resulting mixture was dispersed in an aqueous solution of 1.8 g of Na phosphate, 18 g of Luviskol K 90~ and 50 g of Ertivinol (Luviskol K9 and Ertivinol are commercial suspending agents and emul-sifiers, respectively) in 1,800 g of water by vigorous stirring (300 rpm).
A conversion of 99% was achieved by polymeriza-tion for 3 h at 110C (Example 1) 3 h at 130C ~Example 2) 4 h at 140C (Example 3).
Tha bead polymer obtained in each case was washed thoroughly with distilled water and dried overnight at 80C under reduced pressure.
The properties of the polymers are summarized in the Table below.

201.tO79 - 7 - o.z. 0050/40678 Parameter Method of Dimen- Example measurement sion 1 2 viscosity number DIN 53,726 [ml/g] 96.2 ~7.4 95.1 [0.5~ strength in DMF ]
Melt flow index DIN 53,735 [g/10 12.2 12.1 ~.1 [200~C/21.6 kp] min]
Vicat B (VST/B/50) DIN 53,460 [C] 99.3 98.7 100.3 EXAMPLES 4 - 6, COMPARATIVE EXPERI~IENT
The procedure described in Examples 1-3 was followed, except that in each case 1.58 x 10-2 mole of 1,4-disubstituted urazole was mixed only with 2,000 g of styrene. The polymerization took place under the same conditions as in Examples 1-3.
Example 4 5 6 Comparison R2 Phenyl Phenyl Phenyl R1 Phenyl Cyclo- n-Butyl hexyl Amount of urazole [g] 4.0 4.1 3.7 Solids content in % by weight after 60 [min] 4.2 3.4 1.7 0 90 [min] 5.2 5.1 3.4 0 120 [min] 7.4 6.9 6.0 0 150 [min] 8.5 8.2 7.7 o 180 [min] 9.6 10.8 9.5 0.2 210 [min] 12.1 13.4 12.8 0-7 240 ~min] 13.6 16.1 15.3 1.2 270 [min] 15.9 18.9 17.3 1.8 300 [min] 16.3 19.6 18.5 2.0 After a solids con~ent of about 20% by weight had been reached, 1.5 g of dicumyl peroxide were added to the polymer mixture and the resulting mixture was dispersed in an aqueous solution of 1.8 g of Na phosphate, 18 g of Luviskol K 90 and 50 g of Ertivinol in l,800 g of water.

- 8 - O.Z. 0050/40678 A conversion of more than 98~ was achieved by polymerization for, in each case, 3 h at 110C~ 120C and 130C.
The resulting bead polym~r was washed with di~-til~ed water and dried overnight at 80C under reducedpressure. The properties are summarized in the Table below.

Example 4 5 6 Viscosity number DIN 53,726[ml/g] 65.0 63.7 6.8 [0.5% strength in toluene3 Melt flow index DIN 53,735[g/10 5.3 5.6 4.9 [200C/5 kp] min]
Vicat B (VST/B/50) DIN 53,460[C]90 0 91.0 ~3.0 1,500 g of styrene and 500 g of acrylonitrile were mixed in a 5 1 reactor, and 4.0 g of 1,4-diphenyl-urazole were dissolved therein. Thereafter, the mixture was flushed 3 times with nitrogen and heated to 80C.
After 150 minutes, it was observed that the polymeriza-tion had come to a stop; polymerization could be started again by flushing the reactor content once with air after 240 minute~.
EXAMPLE
25 Solids content in ~ by weight after 60 min 5.8 90 min 10.7 120 min14.9 150 min17.4 30 180 min17.6 210 min17.8 240 min18.0 ~flushing with air) 270 min20.0 300 min24.4 35 333 min29.5 The reactor content was completely polymerized as 2nll07s - 9 - O.Z. 0050/40678 described above. The properties of the polymer likewise correspond to those of the products obtained in Examples 1-3:
Viscosity number DIN 53,726 [ml/g~ 105 S [0.5% strength in DMF]
Melt flow index DIN 53,735 [g~10 min.]9.6 Vicat B (VST/B/S0) DIN 53,460[C] 101.3 l,900 g of methyl methacrylate, lO0 g of methyl acrylate and 6 g of tert-dodecyl mercaptan were mixed in a S l reactor. Thereafter, the mixture was flushed 3 times with nitrogen and then hea~ed to 100C.
In order to bypass the initiation phase which iq typical of MMA polymerizations and only after which the reaction attains its full reaction rate, the reaction was initially started with a conventional initiator. For this purpose, tert-butyl perpivalate (as a 1% strength ~olution in MMA) was first metered in continuously at a rate of 0.02% by weight per hour, based on the total conversion.
After a conversion of 15% had been reached, the reaction mixture was left for one hour at 100C in order to allow initiator residues to react. It was then cooled to 65C, after which 1.82 g of 4-methylurazole (0.091~, based on monomers), dissolved in 75 ml of DMF, were added. The mixture was then heated to 80C and the solids content was measured as a function of time.
After the reaction had died down, the mixture was cooled to 65~C and a further 1.23 g (0.09%, based on monomers) of 4-methylurazole were then added and the - progress of the reaction was further monitored at 80C.
The results are shown in ~he Table below.

20110~9 - 10 - O.Z. 0050/40678 Example 8 9 (Comparative Reaction time Solids content Experiment) ~h] [~ by wt.]
0.5 12 12 1.0 14 1.5 15 (lst addition of 15 4-methylurazole) 1.9 17 2.2 19 2.4 20.5 15.5 2.9 22.5 3.2 23.5 3.5 23.5 3.7 23.5 (2nd addition of 15.5 4-methylurazole) 4.0 24.0 4.3 25.5 4.6 26.5 5.7 28.0 16.~
The polymethyl methacrylate prepared in the Example was precipitated in methanol and dried. The viscosity number of a 0.5% strength solution in cyclo-hexane was determined according to DIN 53,726 as 119 ml/g.

Claims (2)

1. A process for the preparation of polymers from monomers which are capable of undergoing frea radical chain polymerization, by the addition of a substance capable of forming primary free radicals and initiation of the polymerization by formation of primary free radicals, wherein a urazole of the formula Ia or Ib (Ia¦ (Ib) where R1 and R2 are each (cyclo)alkyl, (cyclo)alkenyl, (cyclo)alkynyl, aryl, aralkyl or alkylaryl, each of not more than 30 carbon atoms, or a 5-membered to 8-membered heterocyclic structure containing nitrogen, oxygen or sulfur, or -NR3R4, or together form an alkylene bridge of

2 to 4 carbon atoms, R3 and R4 have the same meanings as R1 except for -NR3R4 and Z is a chemically inert bridge member, is used as the substance capable of forming primary free radicals, and the polymerization is in-itiated by oxidation.
2. A polymer which is obtained by free radical chain polymerization and some or all of whose chain molecules have a chain end derived from a urazole of the formula Ia or Ib of claim 1.