INITIATOR FOR CATIONIC POLYMERIZATION, A PROCESS FOR ITS PREPARATION, USES AND A POLYMER THAT CAN BE OBTAINED USING THE INITIATOR

Abstract: The invention relates to Xn(alkoxy)(6-n)alkyl melamine, in which X = halide, n = 1-6, and the alkoxy group and the alkyl group contain 1 to 6 carbon atoms, a process for the preparation of these compounds and the use of these compounds as initiator in a cationic polymerization of monomers to form a polymer. The invention also relates to the polymer obtained with this initiator and to the use of the resulting polymer as impact modifier in melamine, phenol or urea containing resins.

Description: INITIATOR FOR CATIONIC POLYMERIZATION. A PROCESS FOR ITS PREPARATION, USES AND A POLYMER THAT CAN BE OBTAINED USING THE INITIATOR The invention relates to an initiator for a cationic polymerization. A cationic polymerization is an electrophilic addition of carbocations to an alkene. A carbocation is an ion that carries a positive charge on a carbon atom. A carbocation is formed in the presence of a Brδnstedt or Lewis acid from an alkene or from an initiator. An initiator is used if it is desirable for the reaction to start with a molecule other than the alkene. The mechanism of cationic polymerization is extensively described by J.P. Kennedy in 'Cationic polymerization of olefines : a critical inventory', Ed. J. Wiley & Sons, New York, 1975. A feature that known initiators have in common is that, for stabilization of the carbocation, they possess an oxygen atom, an unsaturation and/or a substituted carbon atom at the carbon atom where polymerization takes place. Kennedy does not hint at other atoms or atom groups that could be capable of stabilizing the carbocation. As a consequence, the group of initiators for the cationic polymerization is relatively restricted, and there is a need for other initiators. X n (alkoxy) (6-n) alky1 melamine have now been found in which X = halide, n = 1-6 and the alkoxy group and the alkyl group contain 1 to 6 carbon atoms . These compounds prove to be excellent initiators for cationic polymerization. A further advantage of the compounds according to the invention is that their functionality can easily be selected by means of the number (n) of halide-substituted alkoxy groups. Unexpectedly, it was found that the carbon atom at which cationic polymerization takes place may also possess a nitrogen atom for stabilization of the carbocation. Thus, a new class of compounds was found, which can be used as initiator in cationic polymerization. The invention also relates to the use of X n (alkoxy) (6 _ n) alkyl melamine, in which X = halide, n = 1- 6 and the alkoxy group and the alkyl group contain 1 to 6 carbon atoms, in a cationic polymerization of monomers to form a thermoplastic polymer, in the presence of a Lewis acid. Many thermoplastic polymers are used in coatings, oil additives, or processed into plastic objects via a solution or via the melt phase. The high viscosity of the polymer is often a limiting factor in the processing of thermoplastic polymers . This high viscosity is a result of the high molar mass of the polymer, which is generally desirable for achieving good mechanical properties. Since branched polymers generally have a lower viscosity than linear polymers of the same molar mass, branched polymers have an advantage in processing. The number of branches of the thermoplastic polymer formed increases with the number of alkoxy groups substituted by a halide when using X n (alkoxy) (s . n) alkyl melamine in a cationic polymerization, and as a result the ratio between viscosity and molar mass is increasingly improved. An initiator in which all six alkoxy groups have been substituted by halide atoms forms a six-armed polymer during cationic polymerization. An advantage of a six-armed polymer over a less-branched polymer having the same molar mass is that the viscosity of the melt is significantly lower, so that processing of the product is facilitated. A special form of branched polymers are star- shaped polymers. A star-shaped polymer is here and hereinafter understood to be a polymer that consists of a core, usually formed by an initiator, and at least three polymer arms. Star-shaped polymers can be prepared using different methods. To prepare well- defined star-shaped polymers use is made of, inter alia, a living polymerization on a polyfunctional initiator. In the past decade, much progress has been made in the field of the living cationic polymerization. Star-shaped polymers, too, are now well capable of being prepared by means of cationic polymerization. Such star-shaped polymers, prepared by cationic polymerization, are described, for instance, by H. Shohi et al . in Macromolecules 1991, 24, 4926- 4931. Shohi et al . describe star-shaped polyvinyl ethers, with an initiator prepared from a triether on the basis of the sodium salt of 1,1,1-tris- (hydroxyphenyl) ethane and 2-chloroethyl vinyl ether. The star-shaped polymers thus prepared have three arms. A disadvantage of the initiator used by Shohi et al . is that it is prepared from a custom-synthesized, and therefore relatively expensive, precursor. Another method for the preparation of star- shaped polymers is described by S. Kanaoka et al . in Macromol. (1991), 24, 2309-2313. Kanaoka describes how linear, cationically polymerized chains are crosslinked by means of divinyl ethers to form star-shaped polymers, the core of which consists of a gel. A disadvantage of this method is that the number of arms of the star-shaped polymer is poorly defined. This disadvantage is overcome by use of X n (alkoxy) , 6-n) alkyl melamine, in which X = halide, n = 3-6 and the alkoxy group and the alkyl group contain 1 to 6 carbon atoms, in a cationic polymerization of monomers to yield a star-shaped polymer. Thus, depending on the value of n, a three- to six-armed polymer is formed. The polymer arms can be formed by the methods known for this for the cationic polymerization of monomers. Such a method is described, for instance, by B. Ivan and J.P. Kennedy in Journal of Polymer Science; A: Polymer Chemistry Vol. 28, 89-104, 1990. When using X n (alkoxy) (6-n) alkyl melamine, in which X = halide, n = 3- 6 and the alkoxy group and the alkyl group contain 1 to 6 carbon atoms, these compounds can replace the initiator from the known method, or if no initiator was used, the alkene with which the polymerization reaction starts . The polymerization, which may proceed spontaneously by adding X n (alkoxy) (6-n) alkyl melamine to the monomer, is preferably carried out in the presence of a Lewis acid. This ensures a more living character of the polymerization. A living polymerization is here and hereinafter understood to mean a cationic polymerization in which the active site, that is to say the site on which the propagation takes place, remains connected to the initiator. The advantage of a living polymerization is that no chain transfer takes place. As a result, no new polymer chains are formed besides those connected to the initiator, and a polymer with a narrower molar mass distribution is obtained. A polymer with a narrower molar mass distribution generally has a lower viscosity than one having the same molar mass but a broader molar mass distribution, which is advantageous for processing of the polymer. Suitable Lewis acids include ZnCl 2 , ZnBr 2 , Znl 2 , I 2 , AlRj-Clj.,., where x = 1, 2 or 3 , and R 4 NC10 4 , where R is an alkane with 1-6 carbon atoms. Preferably, the Lewis acid is ZnCl 2 . The advantage of ZnCl 2 as Lewis acid is that is a relatively cheap and colourless salt, which readily dissolves in most solvents. Monomers that are suitable for cationic polymerization can be chosen from the group formed by vinyl ethers, isobutenes, styrenes, dienes and heterocyclic monomers. Suitable heterocyclic monomers are epoxides, oxetanes, oxazolines and THF. The monomer preferably contains a vinyl ether. It has been found that with vinyl ethers a living polymerization can readily be carried out . Suitable vinyl ethers for the cationic polymerization are methyl vinyl ether, ethyl vinyl ether and isobutyl vinyl ether. The process is also suitable for the preparation of star-shaped (block) copolymers, which are obtained by, respectively, adding several monomers successively or by adding a mixture of different monomers . The polymerization reaction can be carried out in a solvent at temperature that is between -100 and 100 °C. Preferably, the polymerization is effected at a temperature between -60 and 0°C. It has been found that little chain transfer takes place at a temperature between -60 and 0°C, so that the reaction is mainly of the character of a living polymerization reaction. Suitable solvents for carrying out the polymerization include toluene, cyclohexane, dichloromethane and sulpholane . The invention also relates to the use of hexa-alkylalkoxy melamine as precursor for an initiator for the preparation of a thermoplastic polymer by means of cationic polymerization. The precursor can be converted into a halogen salt, which acts as initiator. The invention also relates to a polymer that can be obtained through the use of X n (alkoxy) (6-n) alkyl melamine, in which X = halide, n = 1-5 and the alkoxy group and the alkyl group contain 1 to 6 carbon atoms, in a cationic polymerization of monomers. The resulting polymer still has at least one alkoxy group . The advantage of such polymers is that they can be incorporated, by means of the alkoxy group (s) still present, into a matrix of melamine, phenol or urea containing resins during the polymerization of such a matrix. The invention also relates to the use of the polymer thus obtained as impact modifier in melamine, phenol or urea containing resins . Use of such impact modifiers in a matrix of the above-mentioned thermosetting resins ensures that the impact modifiers are homogeneously distributed over, and are chemically embedded in, the matrix in which they are used. As a result, a relatively small amount of impact modifier will suffice for a good improvement of the impact resistance. An impact modifier generally has a lower modulus than the matrix in which it is applied. The advantage of the above-mentioned impact modifier, which can be used in a relatively small amount, is that the reduction of the modulus is small, while yet a good improvement of the impact resistance is obtained. The invention also relates to a process for the preparation of X n (alkoxy) (6 _ n) alkyl melamine, in which X = halide, n = 1-6 and the alkoxy group and the alkyl group contain l to 6 carbon atoms. The process is characterized in that hexa-alkoxyalkyl melamine is contacted in a solvent with at most n mol of a halide containing compound per 6 gramme equivalents of the alkoxy groups contained in the hexa-alkoxyalkyl melamine. When use is made of 6 mol of a halogen containing compound all alkoxy groups are replaced by a halogen. Halogen containing compounds may be HX, BX 3 and TiX 4 , where X = CI, Br or I . It has been found that BC1 3 exchanges one chlorine atom with the alkoxy group of hexa-alkoxyalkyl melamine. Of compounds which can exchange several halogen atoms with the alkoxy group, the amount added should be proportionally lower. Preferably, the alkoxy group is a methoxy group and the alkyl group is a methyl group in the compounds, the uses, the polymer and the process according to the invention. If the alkoxy group of X n (alkoxy) (6-n) alkyl melamine is a methoxy group and the alkyl group a methyl, hexamethylmethoxy melamine (HMMM) can be used as precursor for the initiator. HMMM is used in large amounts as crosslinking agent in the paint industry, which makes it better accessible than products produced in much smaller amounts for use as precursor for star-shaped polymers. HMMM therefore satisfies a need for a cheap precursor. HMMM may also occur in small amounts in the dimer and trimer forms. From dimers or trimers of hexa- methoxymethyl melamine, star-shaped polymers with more than six polymer arms can be formed. The invention will be elucidated with reference to a number of examples. Example I At 0°C 2.89 1 of hydrochloric acid was passed through a solution of 5.94 g of HMMM (Cymel 303 of American Cyanamid) in 20 ml of toluene. The mixture was then evaporated. A portion of the resulting powder was dissolved in DMSO. A peak at 14.4 ppm in the H-NMR spectrum of this solution showed that the HMMM.HC1 salt had formed. Addition of 1 g of this salt to 15 ml of isobutyl vinyl ether (IBVE) gives a fast polymerization, yielding polymers with a relatively broad molar mass distribution (Mn = 730, Mw = 2130, D = 2.9) . Example II At room temperature 3 ml of 1 M BC1 3 in ether (= 30 mol%) was added to a solution of 0.66 g of HMMM in 50 ml of dichloroethane. After the reaction had proceeded for 15 minutes at 23 °C the temperature was lowered to -55 °C and 10 ml of IBVE was added. From an evaluation of the amount of monomer present in the GC spectrum it appeared that no polymerization had taken place. After 50 minutes 1 ml of 1M ZnCl 2 was added. The decrease in the monomer concentration in the GC spectrum showed that a polymerization reaction had started, After the GC spectrum had shown that about 100% conversion had been attained (35 minutes at - 55°C) , a sample was taken and subsequently a second portion of 20 ml of IBVE was added. Again polymerization took place. The reaction mixture was eventually neutralized using methanol/ammonium hydroxide. The GPC chromatogram (Mn = 4500, Mw = 6500, D = 1.4) of the sample after the first IBVE addition shows that no or hardly any HMMM is still present. The high UV signal at 254 nm of this polymer, isolated through GPC, also indicates that the poly-IBVE (PIBVE) formed is bound to the HMMM, for pure PIBVE hardly exhibits UV absorption at 254 nm, while HMMM absorbs at 254 nm. The GPC chromatogram of the second sample (Mn = 16,800, Mw = 9200, D = 1.8) shows that the chains connected to the initiator have grown further. This is indicative of a living polymerization. Example III Analogous to experiment II, only now 10 ml of BC1 3 was added (= 100 mol%) . After reaction for 15 minutes at 23 °C the temperature was lowered to -55°C and 15 ml of IBVE was added. No polymerization took place. After 35 minutes 1 ml of IM ZnCl 2 was added and a polymerization started. After neutralization a polymer was obtained with Mn = 4900, Mw = 9700 and D = 2. The narrow molar mass distribution (D) is indicative of a living polymerization.

Claims: C L A I M S 1. X n (alkoxy) (6-n) alkyl melamine, in which X = halide, n = 1-6 and the alkoxy group and the alkyl group contain 1 to 6 carbon atoms. 2. Use of X n (alkoxy) (6-n) alkyl melamine, in which X = halide, n = 1-6 and the alkoxy group and the alkyl group contain 1 to 6 carbon atoms, in a cationic polymerization of monomers to form a polymer in the presence of a Lewis acid. 3. Use of X n (alkoxy) (s . n) alkyl melamine, in which X = halide, n = 3-6 and the alkoxy group and the alkyl group contain 1 to 6 carbon atoms, in a cationic polymerization of monomers to form a star-shaped polymer. 4. Use according to claim 2 or claim 3, in which the monomers are a vinyl ether. 5. Use according to any one of claims 2-4, in which the cationic polymerization is carried out at a temperature between -60 and 0°C. 6. Polymer obtainable according to any one of claims 2, 4 or 5, in which n = 1-5. 7. Use of the polymer according to claim 6 as impact modifier in melamine, phenol or urea containing resins. 8. Use of hexa-alkylalkoxy melamine as precursor for an initiator for the preparation of a thermoplastic polymer by cationic polymerization. 9. Process for the preparation of X n (alkoxy) , 6-n) alkyl melamine, in which X = halide, n = 1-6 and the alkoxy group and the alkyl group contain 1 to 6 carbon atoms, by contacting hexa-alkoxyalkyl melamine in a solvent with at most n mol of a halide containing compound per 6 gramme equivalents of the alkoxy groups present in the hexa-alkoxyalkyl melamine. 10. Compound, use, polymer and process according to any one of the preceding claims, in which the alkoxy group of X n (alkoxy) (6 . n) alkyl melamine, in which X = halide and n = 1-6, is a methoxy group and the alkyl group is a methyl group.

Inventors: DERKS FRANCISCUS JOHANNES MARI, LOONTJENS JACOBUS ANTONIUS, DERKS, FRANCISCUS, JOHANNES, MARIE, LOONTJENS, JACOBUS, ANTONIUS
Applicants: DERKS FRANCISCUS JOHANNES MARI, DSM NV, LOONTJENS JACOBUS ANTONIUS, DERKS, FRANCISCUS, JOHANNES, MARIE, DSM N.V., LOONTJENS, JACOBUS, ANTONIUS
Application year: 1997
Main classification: C07D251
IPC codes: C07D251, C08F16, C08G65