DE2523587B2 - Process for continuous photopolymerization - Google Patents

Description

Light initiated polymerizations of ethylenically unsaturated monomers in the presence of or Absence of photoinitiators are generally carried out on a laboratory scale so that the monomer solution, -emulsion or suspension in a flask with a diving lamp, the light of suitable wavelength releases, irradiated with stirring. Such a method is only unfavorable on a larger scale transferable. In addition, it is technically more advantageous to carry out processes continuously. For the continuous However, there are only a few possible solutions to carry out the photopolymerization.

DE-OS 20 09 748 describes a continuous process for photopolymerization in a more concentrated manner aqueous solutions of ethylenically unsaturated water-soluble monomers, which is characterized by that the reaction solution poured in a 2 to 12 mm thick layer on a moving belt and on this is irradiated with light. A method closely related to this method is described in DE-AS 20 50 988 described. This type of implementation is advantageous if the reaction solution during the Polymerization becomes highly viscous or solidifies glassy, as in the application examples of DE-OS 20 09 748 and DE-AS 20 50 988 is the case. However, the process is unfavorable when the reaction solution has a low viscosity remain. It also has other decisive disadvantages: There is one over the irradiated layer Nitrogen atmosphere has to be maintained, special measures for inward and outward transfer are required the reaction mixture required. Therefore, the process is not to be regarded as technically simple. Further the polymerization does not proceed homogeneously because the reaction mixture is not circulated. The reaction takes place under heating and, despite the use of coolant, not isothermally. This can be done with thermal sensitive monomers easily crosslink and thereby impair the quality of the polymers to lead. When scraping the product, it cannot be avoided that deposits are formed on the belt form. Finally, the known process can be transferred very unfavorably to emulsion polymerization where the light penetration depth is very small.

From the Austrian patent specification 2 81 417 is a Process for the continuous photopolymerization of acrylonitrile is known, after the polyacrylonitrile with narrow molecular weight distribution can be produced

■ 5 can. Aqueous solutions of acrylonitrile are used for the polymerization, zinc chloride and optionally still contain alkali or alkaline earth chlorides

ίο the acrylonitrile solution flows through from bottom to top will. The reaction mixture and radiation source are spatially separated from one another by an intermediate one Cooling or heating jacket, which must be permeable to UV radiation.

It has now been found that water-in-oil emulsions of water-soluble monomers, isothermal and homogeneous, can also be polymerized to complete conversion in a technically very simple manner, by placing the monomers on the inner wall of a vertically arranged, optionally thermostated Tube, in which a UV light source is mounted concentrically, flows down continuously and freely it is polymerized by irradiation.

It is surprising that certain monomers already do

2) when going through an exposure path once can be polymerized to complete conversion from less than 150 cm. The actual exposure time of the water-in-oil emulsion running through is only a few minutes and is around one

jo power of ten smaller than when irradiating the same Water-in-oil emulsions in standard laboratory stirred vessels with immersion lamps until complete conversion is required. Finally, even with continuous polymerization, there are no disruptive

r, bearings on.

The flow rate through the exposure section can be infinitely varied according to the effective polymerization rate be adjusted so that the highest possible space-time yield is achieved. The procedure can also easily transferred to water-in-oil emulsions of less reactive water-soluble monomers v. earth.

The present invention relates to a process for continuous photopolymerization

v, of ethylenically unsaturated, water-soluble monomers in the presence of conventional photoinitiators, using UV light and using conventional polymerization aids, which is characterized in that a water-in-oil emulsion of

w Monomers on the inner wall of a vertically arranged, possibly thermostated tube, in which a UV light source is attached concentrically, flowing down continuously and thereby is polymerized by irradiation.

Vy The process for continuous photopolymerization can optionally be carried out in such a way that the reaction liquid is polymerized by irradiation in the manner described above, it being cycled several times over the same exposure

bo stretch runs while part of the reaction mixture is continuously withdrawn and replaced with fresh monomers.

For the process according to the invention, water-in-oil emulsions can be water-soluble, ethylenically ungear, Saturated monomers, which are described in particular in DE-PS 10 89 173, can be used.

In an advantageous embodiment of the method is the reaction mixture with a suitable

Device, ζ. B. an overflow channel, a distributor cone or a suitable nozzle system, evenly on the inside of a vertical pipe distributed so that a closed layer on the inner wall of the pipe flows evenly down Im The center of the tube is the radiation source, the light of a suitable wavelength, preferably UV light, sends out; a fluorescent tube for superactinic light is particularly preferred. The length of the tube is Freely selectable in the PrLizip and only limited by the external conditions The pipe length is expedient selected according to the intended irradiation time or irradiation distance

The diameter of the tube is determined by the light output of the radiation source, its heat radiation as well as the space required for the electrical supply lines and the brackets; with a fluorescent tube of approx. 100 W, a diameter of 70 to 200 mm is preferred. The tube is also provided with devices to carefully maintain an inert gas atmosphere.

If the pipe is double-walled, it can easily be thermostated; It is surprisingly possible, in this embodiment, even the normally difficult to control the polymerization of acrylamide, the case of overheating easily lead to crosslinking by simple cooling with water at temperatures below 40 ⁰ C to allow run.

The method has the following advantages: it is technically simple to carry out; the throughput rate can be continuously adapted to the reactivity of the monomers; those with very responsive The high heat of reaction occurring in systems can be safely dissipated; despite the use Inexpensive and easy-to-use fluorescent tubes result in good space-time yields; the Cleaning of the apparatus, which essentially consists of a smooth tube, is easy and quick accomplish.

The implementation of the process according to the invention for continuous photopolymerization can be based on can be done in two different ways. In the first variant, the reaction mixture runs through a single one Sometimes a sufficiently long exposure distance and is removed at the end as a finished polymer product. Even if it is possible in principle, all monomer systems can be used by lengthening the exposure stretcher accordingly to polymerize according to this process, it is preferred for those who are very reactive Systems of water-in-oil emulsions of water-soluble monomers applied.

The second variant, on the other hand, is particularly suitable for less reactive water-soluble monomer systems. In this case, a certain amount of the reaction mixture is first polymerized: this can be done on a laboratory scale done both by exposure to light and using thermal initiators; it is also possible to set the "starting amount of polymerized To generate reaction mixture that the monomers sufficiently long in the circuit over the Exposure path is guided.

While the prepolymerized mixture is circulated over the exposure section, it is removed one continuously takes a small part of the total amount at the end of the route and replaces it at the beginning of the Route through fresh monomers. This way you can start with a small amount polymerized mixture, produce any amount of polymer and recover after completion of the polymerization the starting amount again. A steady state is created and polymerized under conditions similar to the technically-often used seed emulsion polymerization, which mostly results in products particularly great uniformity

Suitable water-soluble ethylenically unsaturated monomers with which the process according to the invention can be carried out are, for example, unsaturated carboxylic acids, their amides, nitriles, esters and vinyl-substituted inorganic acids and their derivatives and mixtures of the monomers mentioned.

The following are individually polymerizable monomers according to the invention:

Acrylic acid, methacrylic acid, acrylic acid esters and methacrylic acid esters of optionally N-substituted ones Amino alcohols, acrylamide and methacrylamide and their alkylamino derivatives, acrylonitrile and methacrylonitrile, Vinylphosphonic acid and its esters.

In the polymerization by the process according to the invention, customary stabilizers are optionally used and emulsifiers used, e.g. B. those of the cationic type, such as quaternary alkyl and aryl ammonium compounds, of the anionic type, such as fatty acids, fatty alcohol sulfates, alkyl sulfates and sulfonates, alkylbenzenesulfonates and resin soaps (abielinates) or of the nonionic type, such as ethoxylation products of Fatty alcohols, fatty acids or alkylphenols as well as ethylene oxide-propylene oxide copolymers, as well Fatty acid sugar alcohol esters such as stearic acid, palmitic acid or oleic acid sorbitol esters.

The polymerization formulations can also contain customary auxiliaries, such as flame retardants, regulators, such as marcaptans or halogen compounds, as well as crosslinkers, e.g. B. contain divinylbenzene. For the creation of usual Polymerization recipes is z. B. on Houben-Weyl, Methods of Organic Chemistry, Volume 14-1.

In the process according to the invention, the polymerization is brought about by exposure to UV light with conventional photoinitiators in amounts from 0.001 to 10, in particular 0.01 to 1% by weight of the amount of monomers carried out.

Suitable photoinitiators are, for example, benzoin and benzoin derivatives of the general formula I

R ₁ R ₂

wherein

Ri -O-Y or -S-Y and

Y hydrogen, trimethylsilyl, Ci-da-alkyl, C6-Ci5-aryl, C ₇ -C, 5-aralkyl,

R _{2 is} hydrogen, C-Cia-alkyl, C ₆ -C ₁₅ -AlyI, Cz-CrMralkyl, carboxyl or CH.-OR 'and R' is hydrogen or the acid residue of a carboxylic acid or a sulfonic acid,

and R ₄ hydrogen, Ci -C ₄ -alkyl, halogen such as F. Cl. Br and J or -OR "and R" are d — Ci "-alkyl;

Benzophenone and benzophenone derivatives of the general formula II

-R,

R, CH ₂ -XiCH-X ₂ ICX ₃ ;

R ₂ H; CH ₃ ; CH ₂ -X; CH-X ₂ ; CX3 and

X chlorine, bromine, iodine

mean.

The other photoinitiators known from the literature, such as aromatic ones, can also be used Sulfochlorides, phenacyl bromide, aromatic disulfides or anthraquinone derivatives.

Further examples of such suitable initiators are given in DE-OS 17 69 168, 17 69 853, 17 69 854, 18 07 297, 18 07 301, 19 19 678, 19 49010 and in DE-AS 16 94 149 (cf. also J. Kosar,, Light-Sensitive Systems', Wiley-Verlag, New York 1965).

The following examples illustrate the invention. The percentages are always percentages by weight.

example 1

Water-in-oil emulsion polymerization
Water phase: 2000 g water

2000 g of acrylamide

oil phase: 2000 g Cu-Cie paraffin mixture

500 g oleic acid sorbitesler
1 g of benzoin isopropyl ether

With the help of an intensive mixer, a stable water-in-oil emulsion is produced from the phases. These is carefully gassed with nitrogen and with a throughput of 5.4 l / h once through an exposure apparatus pumped according to figure 1:

In a vertical glass tube (1) according to the figure with a cooling jacket (2) 160 cm long and 9 cm Diameter is, arranged concentrically, a 150 cm long, superactinic fluorescent tube (3) (120W, radiation maximum, 360 nm). The distance between the inner wall of the pipe and the light source is approx. 24 mm. At the At the top of the glass tube there is a distributor cone (4) for evenly distributing the reaction mixture on the inner wall of the pipe. At the lower end of the tube, the reaction mixture reaches a drain cock (5): When the tap is closed, it continues to run into a flask (6) with a stirrer and dropping funnel (mixing flask). at With the tap open, the reaction mixture runs into the product container. This can be done from the mixing flask Mixture are conveyed with a pump (7) to the distributor cone at the upper end of the light reactor.

The entire apparatus is carefully kept under a nitrogen atmosphere.

The fully polymerized water-in-oil emulsion is removed from the open drain cock. That The tube is cooled with water, which is heated to approx. 39 ° C by the heat of reaction.

Example 2

Water phase: 2000 g ammonia water 2000 g acrylic acid

oil ph

iase:

2000 g decahydronaphthalene 500 g stearic acid sorbitol ester 1 g benzoin isopropyl ether

Carry out the experiment as in the example throughput: 4.7 l / h; temperature 40 ° C

B e i s ρ i e 1 3

Water phase: 1700 g water

300 g conc. Hydrochloric acid 1400 g acrylamide 600 g N.N-dimethylaminoethyl methacrylate

oil phase: 2000 g of C ^ -Cs paraffin mixture

500 g oleic acid sorbitol ester 2 g benzoin isopropyl ether

Carry out the experiment as in the example, throughput 5.2 l / h; temperature 25 ° C

Example 4

Water phase: 1900 g acrylamide

2000 g of water, oil phase: 100 g of divinylbenzene

2000 g petroleum ether b.p. 80-100 ° C 500 g oleic acid sorbitol ester 4 g of benzoin isopropyl ether

Carry out the experiment as in the example. Throughput: 5.7 l / h! Temperature: 40 ° C

Example 5

Water phase: 1800 g of acrylamide

200 g vinylphosphonic acid dimethyl

ester

2000 g of water

Oil phase: 2000 g Q ₂ -C | _B -paraffin mixture

500 g oleic acid sorbitol ester 2 g benzoin isopropyl ether

Carrying out the experiment as in the example throughput: 4.51 / h; temperature: 28 ° C

1 sheet of drawings

Claims (2)

Patent claims: 1. Process for continuous photopolymerization of ethylenically unsaturated, water-soluble monomers in the presence of conventional photoinitiators, using UV light and using conventional polymerization aids, characterized in that a water-in-oil emulsion of the monomers on the inner wall of a vertically arranged, optionally thermostated tube, in which one concentrically UV light source is attached, continuously flowing down freely and polymerized by irradiation will. 2. The method according to claim 1, characterized in that the monomers acrylic acid, methacrylic acid, their esters of optionally N-substituted amino alcohols, acrylamide and methacrylamide and their alkylamino derivatives are used for the polymerization.