DE3305727A1 - Process for the free-radical polymerisation of acrylic monomers - Google Patents

Abstract

A process for the polymerisation of acrylic monomers is demonstrated. In the process, a reactor is used which in general is designed as a screw extruder with temperature control devices. Acrylic monomers having a viscosity of 10 poise or less at room temperature are continuously fed to the reactor. The acrylic monomers are continuously conveyed through the reactor and moved in the reactor by the screw, so that the acrylic monomers come into contact with continuously renewed surfaces within the reactor. The temperature in the reactor is adjusted in two or more zones within the reactor, in order to increase the viscosity of the acrylic monomers in the reactor by rapid polymerisation within an inlet surface, whereupon the polymerisation is then allowed to proceed in one or further surfaces of the reactor at a prescribed conversion rate. The polymerised products are then continuously removed from the reactor.

Description

Process for the radical polymerization of AcrZlmono-

mers The invention relates to a process for radical polymerization of acrylic monomers.

In the radical polymerization of ethylenically unsaturated monomers the polymerization in emulsion or suspension, in solution or as bulk polymerization carried out. The emulsion or suspension polymerization has the disadvantage that practical because of contamination by emulsifiers or dispersants cannot obtain pure polymers. When recovering the polymers from the emulsion or suspension are also considerable costs due to the expenditure of time and energy required to evaporate the water. Solution polymerization has the disadvantage that there are pollution problems and that the cost are significant because of the use of large amounts of solvents. In the Recovery of the polymers obtained by solution polymerization occur in addition, the same problems as in emulsion and suspension polymerization.

The bulk polymerization does not know the aforementioned problems and is therefore particularly advantageous from a technical point of view. Bulk polymerization processes are For example, described in U.S. Patents 2,530,409, 2,745,824 and 2,931,793. at the bulk polymerizatibn there is the problem that the polymerization except Control, because the reaction temperature due to the increase in viscosity, which occurs when the polymerization proceeds rapidly, is difficult to control can. Therefore, bulk polymerization of such monomers is dangerous. Besides that it is also difficult to control the molecular weight distribution and the Prevent the formation of by-products such as gels and breakdown products. That's why it gets In practice there are no homogeneous products and the polymers are further processed difficulties arise in the further processing stages due to the by-products on.

It is known that bulk polymerization can be used until to a relatively high transition point, compared to other ethylenic unsaturated monomers. Therefore, bulk polymerization of styrene has been used technically for a long time. Most technical processes monomeric styrene is converted to a degree of conversion of 30 to 70% in a prepolymerization reactor, which is in kettle form, polymerizes and the remaining monomers are then removed and give end products or the prepolymerization products are in one Extruder introduced and there under mild conditions a further polymerization reaction subjected to a degree of conversion of 95 to 96%.

The bulk polymerization of acrylic monomers can, however, according to do not carry out the aforementioned polymerization process for styrene satisfactorily, because the temperature of the polymerization reaction in acrylic monomers because of the large heat of reaction cannot monitor without difficulty. That's why the Bulk polymerization of acrylic monomers has not yet been carried out in practice been.

The object of the invention is to provide a process for industrial radical polymerization of acrylic monomers in substance. Associated with this task is to show a process with which one can continuously free radical acrylic monomers in bulk can polymerize and where you can see the rapid increase in viscosity due to the during the polymerization can use developed heat.

The invention relates to a method for radical bulk polymerization of acrylic monomers, which is a raw material for bulk polymerization from acrylic monomers with a viscosity of 10 poise or less at normal temperature (i.e. at about 20 to 30 ° C) is continuously introduced into a reactor and then continuously on a support course that is equipped with temperature monitoring devices, is promoted, bringing the mixture into contact with renewed surfaces of the reactor comes and the temperature is controlled in such a way that the viscosity of the material through rapid polymerization of the acrylic monomer in the first half of the course can be increased, and the polymerization then with a prescribed degree of conversion in the second half of the course, after which one then continuously the bulk polymers wins from the reactor.

The figure is a sectional view. represents and describes a single screw extruder, which is used to carry out the method according to the invention.

The radical polymerization process according to the invention is as follows explained with reference to the figure.

In the figure, 1 denotes a cylinder with a feed funnel at the end 2 is provided for receiving a mixture of the raw materials. On the other end of The cylinder is an opening 3 for the recovery of the polymerization products intended. A number of screws 5 are on a shaft 4, which is in the cylinder 1 rotated, trained. The augers 5 mix the mixture of raw materials, which are introduced in the feed hopper 2 and promote this forward.

Between the screws 5 and the cylinder 1 can be used for good mixing a gap can be provided for the mixture. Generally a gap is from 0.5 to 2 mm suitable. Along the lengthwise direction of the cylinder 1 are thermal control devices 6, 7, 8 and 9 are provided, which the respective parts of the extruder on a suitable Keep temperature. The cylinder 1 can be uniform over its entire longitudinal direction be heated as described in the examples below.

A raw material for bulk polymerization is put into the extruder from acrylic monomers having a viscosity of 10 poise or less at room temperature (about 20 to 300C) continuously at a desired rate through the feed hopper 2, preferably after purging with nitrogen beforehand. The raw material is mixed by the rotation of the screws 5 and conveyed forward, whereby the raw material comes into contact with new surfaces of the extruder or reactor comes. To get the viscosity of the raw material within the first half on the demand course, which is denoted as a in the figure, to increase by rapid polymerization, the temperature in cylinder 1 is determined by the heat control devices 6 and 7 set, that the raw material gradually in the zones a1 and a2 and more strongly in the zone a3 is heated so that the polymerization reaction of the raw material immediately in the zone a3 can begin and expires very quickly in the same zone. By changes depending on the decomposition temperature of the radical polymerization initiator used, the temperatures in zones a1 and a2 are preferably from 40 to 1200C and in the zone a3 is preferably set to 60 to 1500C, and the temperature in zones a1 and a2 is equal to or lower than the temperature in zone a3.

The polymerized material with an increased viscosity is then promoted to the second half of the promotion course (i.e. zone b in cylinder 1), where the material is further conveyed with renewal of the surface and temperature monitoring (preferably to 100 to 1800C) by the heat control devices 8 and 9, so that the polymerization reaction takes place up to a desired degree of conversion (from about 93 to 99% by weight). The polymerized products are then made taken from opening 3.

Although in the present figure the shaft 4 is uniform everywhere Diameter, it is also possible to vary the diameter from part to part, by changing the amount of raw material conveyed or the amount polymerized Materials to control the reaction.

In the present case, a single screw extruder was used as the reactor. According to the invention, however, a twin-screw extruder can likewise be used for the polymerization be used. When using a twin screw extruder, the screws Rotate either in the same or in opposite directions.

In this case too, the gap between the cylinder and the Snails preferably about 0.5 to 2 mm. The gap between the two snails is preferably about 0.5 to 2 mm. In general, the speed gradient is in the case of the extruders used according to the invention / namely: (ratio of the circumference to the diameter (7?))) x (number of turns) x (outer diameter of the screw / gap between cylinder and screw) 7 preferably not less than 1,000 / min and in particular 3,000 to 50,000 rpm. To carry out the process according to the invention, one can use any reactor except for an extruder of the type mentioned above, provided that it is able to continuously renew its contents while renewing the surfaces to promote and that it has temperature control devices over its entire length vers-marriage is. The term "renewal of the surface" means that new reactor surfaces come into contact with its content. The surface renewal enables suppress unwanted side reactions due to the effective heat exchange between the reactor surfaces and its contents.

In the aforementioned method according to the invention, the viscosity is increased (at least 100 poise) des polymerized material in the first Half of the passage inside the cylinder is a key factor to stable To ensure conveying of the material and at the same time to keep its temperature to control. In the reactor used for the invention (e.g. a screw extruder of the aforementioned kind) its content can be easily conveyed in a stable manner, if there is no change in viscosity in the longitudinal direction of the cylinder. But when there is a large viscosity gradient in the longitudinal direction of the cylinder and the viscosity of the contents is relatively low over a long distance in the Cylinder is, then the content cannot be conveyed in a stable manner because the screws run empty and therefore a zero current or a reverse current of the Content can enter. As a result, the content must have a low viscosity gradient have as long as possible on the remedial course.

As mentioned earlier, the polymerization reaction consists of acrylic monomers the tendency for this to run off very quickly and thereby an increase in viscosity caused. This increase in viscosity can be an obstacle to bulk polymerization of acrylic monomers. In the method according to the invention, however, this tendency is exploited the acrylic monomers.

This means that in the process according to the invention the viscosity of the raw material within a few minutes thanks to rapid polymerisation in the first half of the production cycle to such a degree as to achieve stable funding is required is, can be increased, even if the raw material is made of acrylic monomers having a viscosity of 10 poise or less. In addition, the temperature of the material can be divided into narrowly divided Areas in the course of the passage of the material are monitored because the promotion takes place under "Surface renewal". You can start the polymerization reaction in this way monitor well and there is no risk of it getting out of control.

In general, the polymerization is as required for stable Promotion of the material needed is 100 to several thousand poise, although they on the type and size of the reactor, the type of acrylic monomer, the desired ones Properties of polymeric products and compare depends on. Of course the rapid polymerization can also take place in a zone a2 instead of zone a3 of the cylinder shown in the figure.

In the previous solution polymerization of acrylic monomers, which by the dilution controlled with organic solvents were long times from 1 to 10 hours are required to achieve a degree of conversion that corresponds to corresponds to the aforementioned viscosity grade.

The training used in the process according to the invention.

Raw materials can be liquid and have a viscosity of 10 poise or less at normal temperature (20 to 30 "C). These include acrylic monomers, how for example alkyl esters of acrylic and methacrylic acid and their derivatives. The raw materials can include radical polymerization initiators, molecular weight regulators, etc., as well as other ethylenically unsaturated monomers that are copolymerizable with acrylic monomers included. Examples of such ethylenically unsaturated monomers are acrylic acid, Methacrylic acid, maleic acid, styrene, vinyl acetate, acrylonitrile and the like. the Ethylenically unsaturated monomers can be present in amounts up to about 50% by weight.

Examples of radical polymerization initiators suitable according to the invention are organic peroxides such as benzoyl peroxide, cumene hydroperoxide, di-t-butyl peroxide and lauroyl peroxide; Azo compounds such as azobisisobutyronitrile and the like. The amount of the initiator used is preferably 0.01 to 1 part by weight per 100 parts by weight of the monomers. One can also use redox initiators that operate at low levels Temperatures use, generate radicals. If you use redox initiators, then a reducing agent such as dimethylaniline or triethylamine is used together with these, used.

Examples of molecular weight regulators in the present invention are chain transfer agents such as thioglycol, thioglycolic acid, lauryl mercaptan and decyl mercaptan.

To the bulk polymerization products obtained according to the invention To impart desired properties, the raw materials can still be made low Amounts of solvents, plasticizers, polymers and like that to add. The total amount of such additives is preferably less than 25 Parts by weight per 100 parts by weight of monomers.

The radical polymerization initiators and the molecular weight regulators can be added to the starting materials before they are converted. Likewise is it possible to add such additives to the mixture after entering them into a reactor was to admit. For example, using a reactor of the type shown in the figure Type, you can enter or

Outlet 10, which is provided in zone a3, to add these additives. In the figure, 11 denotes an outlet for during the polymerization reaction released gases or an inlet for further desired additives.

In the continuous polymerization of the type described above can one the temperature of the respective parts of the reactor, depending on the nature of the monomers uncl the polymerization initiators used, the amount of the Parts of passing content and the like. The temperature -der Starting materials (or the contents of the reactor) are controlled in such a way that they are in the is generally from 40 to 1800C and preferably from 60 to 1500C. In particular, must the heating temperature in the zone in which the starting material polymerizes rapidly and its viscosity increases depending on the type and amount of polymerization initiators, the type of reactor used and the delivery conditions adjust. Those obtained by bulk polymerization in the process according to the invention Products generally have a degree of conversion of 93 to 99%, i.e. they are 93 to 99% polymerized.

As already mentioned, the method according to the invention makes it possible acrylic monomers can also be obtained by bulk polymerization. It also receives homogeneous bulk polymerization products with a relatively small one Molecular weight distribution and a reduced content of by-products, such as Gels and degradation products, and the polymers can be obtained continuously.

The invention is described in the following examples. All Parts and percentages are based on weight.

Example 1 A continuous bulk polymerization was under Use of a mixture of 50 parts of methyl methacrylate, 50 parts of ethyl acrylate and 0.15 part of azobisisobutyronitrile, which has a viscosity of 0.6 centipoise 25 ° C. The polymerization reaction was carried out in a single screw extruder, as shown in the figure, with an outer screw diameter of 50 mm, a cylinder length of 1,000 mm, a gap between the cylinder and the Screw edge of 1 mm and a speed gradient of 7,850 / min. The mixture was fed to the extruder at a rate of 50 cc / min with nitrogen displacement and the temperature in the cylinder was over its entire length to 1000C held.

Bulk polymerization products with one degree of conversion were obtained of 98.9%. The product had a weight average molecular weight (Mw) of 400,000 and a number average molecular weight (Mn) of 55,000 such that the ratio of Mw / Mn was 7.3. This shows that the product has a relatively small molecular weight distribution and is therefore homogeneous.

Example 2 In the same way as in Example 1, a continuous Bulk polymerization durcllgciüllrt, using a mixture of 90 parts of n-butyl acrylate, 10 parts of styrene, 0.7 part of 2-hydroxyethyl ethylate and 0.1 part of benzoyl peroxide with a viscosity of 0.9 centipoise at 25 "C. Used in this polymerization reaction became a twin-screw extruder (self-cleaning type) with an outer diameter of the screws of 40 mm, a barrel length of 1,000 mm, a gap between the barrel and the screw edges of 0.5 mm and a speed gradient of 5,000 rpm is used. The mixture was in the Extruder in fed at a rate of 50 cm3 / min with nitrogen displacement and the temperature the cylinder was held at 90 ° C. over its entire length.

A bulk polymerization product with one degree of conversion was obtained from 96.3 t. The product had an Mw of 530,000, an Mn of 65,000 and the ratio Mw / Mn was thus 8.2. This shows that the product is a relatively small one Has molecular weight distribution and is therefore homogeneous.

The invention has been detailed in terms of specific embodiments however, it will be apparent to those skilled in the art that numerous changes and modifications are possible without departing from the spirit and scope of the invention.

Claims (13)

Process for the radical polymerisation of acrylic monomers P A T E N T A N S P R U c N E Process for the radical polymerization of acrylic monomers, thereby it is not noted that the following steps are to be carried out: (a) Providing a reactor with temperature control devices; (b) continuous introduction of acrylic monomers having a viscosity of 10 poise or less at room temperature into the reactor; (c) continuously conveying the acrylic monomers fed through the conveyor course of the reactor, the acrylic monomer being fed continuously comes into contact with renewed surfaces of the reactor; (d) Controlling the Temperature of the monomers introduced into the reactor such that the viscosity of the monomers introduced into the reactor by rapid polymerization of the acrylic monomers in an initial area of the reactor can be increased and the polymerization then in a second area of the reactor at a prescribed conversion rate can expire; and (e) continuously recovering the polymerization product from the reactor. 2. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that the reactor is a single screw extruder. 3. The method according to claim 1, characterized in that g e k e n nz e i c h n e t that the reactor is a twin screw extruder. 4. The method according to claim 2, characterized in that g e k e n n -z e i c h n e t that the single-screw extruder reactor is provided in a cylinder (1) Has screw (5), wpbei durch'die rotation of the screw through the acrylic monomer open the reactor the remedial course is moved. 5. The method according to claim 2, characterized in that g e k e n n -z e i c h n e t that the distance between the outer part of the screw (5) and the inner diameter of the cylinder (1) is 0.5 to 2 mm. 6. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that in the reactor an initiator in an amount of 0.1 to 1 part by weight per 100 parts by weight of the acrylic monomer is added. 7. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that in the reactor further additives in an amount of 25 parts by weight or less per 100 parts by weight of the acrylic monomer are added. 8. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that the temperature of the acrylic monomers in the reactor is in the range of 40 to 1800C is maintained. 9. The method according to claim 8, characterized in that g e k e n n -z e i c h n e t that the temperature of the acrylic monomers in the reactor is in the range of 60 to 1500C is held. 10. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that the prescribed conversion rate is in the range of 93 to 99 s. 11. The method according to claim 3, characterized in that there is no e n n -z e i c h n e t that the distance between the outer part of the screw and the inner diameter-des Cylinder is 0.5 to 2 mm. 12. The method according to claim 6, characterized in that g e k e n n -z e i c h n e t that the initiator is a redox initiator. 13. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that the temperature at the inlet space of the reactor 40 to 1200C and the temperature in the second space of the reactor is 60 to 1500C.