WO2011061076A1

WO2011061076A1 - Method for producing graft copolymers based on polyethers

Info

Publication number: WO2011061076A1
Application number: PCT/EP2010/066920
Authority: WO
Inventors: Jürgen DECKER; Achim Pommer; Ulrich Filges
Original assignee: Basf Se
Priority date: 2009-11-17
Filing date: 2010-11-05
Publication date: 2011-05-26

Abstract

The invention relates to a method for producing graft copolymers based on polyethers and vinyl esters by converting polyethers, vinyl esters, and further hydrophobic monomers in the presence of an organic solvent and a polymerization initiator forming radicals under return flow conditions, at a monomer composition of a) 5 to 50 wt % of polyether, b) 40 to 95 wt % of vinyl ester, and c) 0 to 50 wt % of a further hydrophobic monomer, the total amount of components a) to c) being 100 wt %, characterized in that the reaction is controlled as a function of the amount of heat dissipated by means of the return flow cooler.

Description

Process for the preparation of graft copolymers based on polyethers Description

The present invention relates to an improved process for preparing polyether graft copolymers by reacting hydrophobic monomers and a polyether in the presence of a radical initiator system. Such graft polymers are known per se. However, it has been found that in the known procedures on an industrial scale, the safety of the process is not guaranteed, because no adequate control of the reaction is possible.

EP-A 1 125 954 describes the reaction of vinyl carboxylic esters with polyethers in the presence of a free-radical initiator system and using a polyalkylene glycol which is liquid at room temperature as a solvent for the initiator system. The reaction takes place at constant bath temperature.

In DE-AS 1077430 the preparation of corresponding graft polymers is described, wherein a part of a solution of polypropylene glycol, vinyl ester and initiator is initially charged and heated and then treated with further solution of the components.

In WO 00/18375 the preparation of graft polymers of polyethylene glycol and vinyl acetate is described, wherein initially a template with polyethylene glycol is heated to 80 ° C and treated in a water bath at a constant temperature with vinyl acetate and an initiator solution.

DE 10 055 473 A1 describes the preparation of graft polymers of polyethylene glycol and vinyl acetate, the reaction being controlled by the temperature difference between the inner and outer walls of the reactor. However, it has been found that the control of the reaction in this way does not always result in the desired manner to homogeneous molecular weight products. There is the problem that under certain circumstances, no uniform product is obtained because can be formed by insufficient control of the heat of reaction temperature peaks in the often quite highly viscous reaction mass. Furthermore, an accumulation of the reactive monomers for safety (avoidance of an uncontrollable Durchgehreaktion) and for quality reasons (uniform course of the grafting reaction) must be avoided. The object of the present invention was therefore to find an improved process for the preparation of such graft polymers.

The object has been achieved by a process for the preparation of polyether-polyvinyl ester graft polymers by reacting polyethers and hydrophobic monomers in the presence of an organic solvent and a radical-forming polymerization initiator under reflux conditions, with a monomer composition of

a) 5 to 50% by weight of polyether,

b) 40 to 95% by weight of vinyl ester, and

c) 0 to 50% by weight of a further hydrophobic monomer,

wherein the total amount of the components a) to c) is 100 wt .-%, which is characterized in that the control of the reaction in dependence on the amount of heat removed via the reflux condenser.

Suitable vinyl esters are vinyl acetate or vinyl propionate, with vinyl acetate being preferred.

In addition to the hydrophobic vinyl ester are suitable as further hydrophobic comonomers monoolefinically unsaturated monomers which have boiling temperatures of 65 to 80 ° C in particular at atmospheric pressure. Suitable comonomers are, for example, acrylonitrile, methyl acrylate and methyl methacrylate. Such relatively low-boiling hydrophobic comonomers reach the reflux under the conditions of the polymerization. Preference is given to using methyl acrylate as further hydrophobic monomer.

Polyether components which can be used according to the invention are polyethylene glycol, polypropylene oxide, polyethylene oxide-polypropylene oxide block copolymers or polytetramethylene oxide. Preference is given to using polyethylene glycol. The weight average molecular weight of the polyether component may be from 1,000 to 35,000, preferably from 1,500 to 15,000, more preferably from 6,000 to 9,000.

The composition of the starting monomer mixture is preferably chosen such that from 5 to 35% by weight of the polyether is reacted with from 65 to 95% by weight of comonomers, the percentages being based on the total amount of polyether and comonomer, which is equal to 100% by weight. % is refer. Preferably, 10 to 30 wt .-% polyether are reacted with 70 to 90 wt .-% comonomers. Particularly preferred are graft polymers containing only vinyl acetate as a comonomer. In the case where a further hydrophobic monomer is used, the amount of component c) is preferably 15 to 45% by weight.

As radical-forming initiators, the following polymerization initiators can be used: tert-butyl peroxy-2-ethyl-hexanoate, acetylcyclohexanesulfonyl peroxide, di- n-butyl peroxydicarbonate, tert-butyl peroxypivalate, di-octanoyl peroxide, di-tert-butyl peroxycyclohexanedicarboxylate, tert-butyl peroxy-3,5,5-trimethylhexanoate,

The polymerization initiators are fed to the polymerization mixture in the form of an organic solution. Suitable organic solvents are preferably methanol and furthermore linear C 2 -C 4 -alcohols such as ethanol, propanol or n-butanol, and also esters such as ethyl acetate or ethers such as tetrahydrofuran or dioxane. Also suitable at room temperature are liquid polyalkylene glycols which preferably have molecular weights of from 100 to 600, in particular polyethylene glycols. The polymerization is carried out under reflux of the volatile under the reaction conditions components, ie the hydrophobic monomers b) and c) and the solvent for the initiator. A suitable device is a reactor equipped with a reflux condenser. The reactor is usually equipped with a jacket heating and cooling system. At the reflux condenser customary measuring devices for measuring the heat of reaction are attached. The reactor is equipped with conventional pressure control devices, so that a vacuum can be applied as desired or an increased pressure can be set.

Furthermore, devices for supplying inert gas are provided. Preferably, the polymerization takes place under a nitrogen atmosphere.

The polymerization is carried out as a feed process. In this case, initially the polyether component can be initially charged and the template heated. The temperature at which the original is heated depends, among other things, on the initiator selected. Furthermore, the melting point of the polyether has an influence on the template temperature to be selected. The temperature must be high enough that an easily stirrable melt is present so that a uniform mixing of the reactor contents is ensured when the vinyl acetate and the initiator are added.

Usually, the original can be heated to 75 to 120 ° C, preferably 80 to 100 ° C.

Subsequently, the addition of the vinyl acetate, the initiator system and, if desired, component c) can be carried out in the feed process. The liquid vinyl acetate and the liquid components c) are preferably added via feeds separated from the feed of the initiator solution. With the addition of the vinyl acetate and the initiator, the internal temperature of the reactor, after the polymerization reaction has started, adjusts to the boiling point of the monomer / solvent mixture, depending on the starting materials and the reaction pressure set. According to a further embodiment of the process according to the invention further vinyl acetate can be added via an inlet after completion of the feed of radical initiator. The control of the reaction can be carried out as described below.

The temperature of the system is advantageously chosen so that the temperature of the reactor jacket after the heating phase to start the reaction substantially (+/- 3 ° C) corresponds to the temperature inside the reactor (the reaction mixture). This can be achieved in a particularly simple manner by switching off the heating or cooling of the jacket after the reaction has started, and merely circulating the cooling medium. The heat of reaction is removed by means of a reflux condenser. The amount of heat dissipated at the cooler (flow and temperature difference of the cooling medium) serves to monitor the reaction and allows a good follow-up of the conversion of the polymerization. The reaction temperature of the polymerization is given by the boiling point of the volatile components (unreacted monomer, solvent). The boiling point can be adjusted precisely by the pressure.

The molecular weight (K value) of the polymer can be controlled by means of the reaction temperature (higher temperature => K value lower and vice versa). The reaction temperature can be adjusted by the pressure as described above.

The measurement of the heat of reaction removed at the reflux condenser can be carried out in a simple manner with the aid of customary measuring technology. In each case, the temperature of the inflowing cooling medium and of the outflowing cooling medium is measured. The

Temperature difference ΔΤ = TAUS - ΤΕΙ _Π multiplied by the flow rate of the cooling medium results in the amount of heat removed at the radiator:

Q = ΔΤ ^* V

On the basis of this amount of heat, the conversion of the polymerization by comparison with the supplied amount of monomer (taking into account the specific heat of polymerization) can be easily determined. The conversion should not fall below a defined range, since otherwise the danger of a runaway reaction of accumulated monomers arises. The desired reaction temperature is set above the boiling point of the monomer / solvent mixture. The boiling point can be controlled very effectively via the reaction pressure. For this purpose, the reactor is equipped with a device for pressure control, which includes a pressure-maintaining valve in the exhaust gas of the radiator and the required IM2 and vacuum ports.

Typically, the polymerization is carried out at internal temperatures between 50 and 120 ° C, preferably between 60 and 80 ° C. Depending on the monomer / solvent mixture used, pressures between 500 mbar (absolute, corresponds to 0.05 MPa) and 5000 mbar (absolute, corresponds to 0.5 MPa) are required for this, preferably between 500 mbar (absolute, corresponds to 0.05 MPa) and 2500 mbar (absolute, corresponds to 0.25 MPa). Particularly preferably, the reaction pressure is between 750 mbar (absolute, corresponds to 0.075 MPa) and 1500 mbar (absolute, corresponds to 0.15 MPa). After completion of the feeds a Nachpolymerisation can take place. In this case, the polymerization mixture can be heated by heating the reactor jacket to 70-120 ° C., particularly preferably to 70-100 ° C.

If desired, the ester or nitrile groups of the polymers can subsequently be saponified partially or completely. This can be done in a conventional manner, for example by adding bases. Suitable bases are, for example, alkali metal hydroxides such as sodium hydroxide or potassium hydroxide or alkali metal alkoxides such as sodium methoxide. The bases are preferably added in the form of their aqueous or alcoholic solutions. As alcoholic solvents are methanol, ethanol, preferably methanol is used. It may also be advisable to remove unreacted components b) and c) before adding the base. Preferred degrees of saponification range from .5 to 100 mol%, more preferably between 70 and 100 mol%.

The K values of the polymers can be from 20 to 50 (measured .1% by weight in water).

Compared with the methods known from the prior art, the method according to the invention offers the following advantages:

In the reactor there is a homogeneous temperature profile, in particular there is no temperature gradient to the wall.

The control on the basis of the amount of heat removed at the cooler allows a particularly secure monitoring of the reaction and a very good control of sales. The molecular weight can be controlled very well over the polymerization temperature, which is adjusted via the reaction pressure.

With the aid of the process according to the invention, it is thus possible to obtain polymers with a more homogeneous property profile. This is particularly important when using the polymer for pharmaceutical applications. Examples

General rule

polymerization:

In a reactor with a volume of 8 l polyethylene oxide was placed under nitrogen. The reactor had a reflux condenser (with pressure-maintaining valve in the exhaust gas), a heating or cooling bath and several regulated inlets.

After the polyethylene oxide was melted at a jacket temperature of 90 ° C, tempered to a temperature of 84 ° C, the melt. With the help of Pressure control, the desired reaction pressure was set. When the desired internal temperature had been reached, feed 2 (starter solution) and, shortly after, feed 1 (monomer mixture) were started. Initially, a small drop in the temperature of the reaction mixture was observed by the feed of the cold starting materials (temperature drop in the range of 3 to 7 ° C.). After a period in the range of 5-10 minutes after the start of feed 1, the internal temperature of the reactor rose sharply (temperature increase in the region of 10 ° C), whereby the onset of the reaction was clearly visible. At this time, the heating or cooling of the reactor jacket was turned off and the cooling medium was pumped around.

The feed rates of the starter solution (feed 1) and of the monomer mixture (feed 2) were varied independently of one another (see Table 1). The internal temperature of the reactor was adjusted by the incipient reflux cooling of the solvent / monomer mixture and kept approximately constant throughout the feed. The temperature of the reactor jacket adjusted to temperatures in the range of 5 ° C below the internal temperature.

After the end of the feeds, the reactor jacket was heated to 90 ° C and held at this temperature for 3 h (postpolymerization). Details are given in Table 1 below.

To the above reaction mixture was first 2.5 l of methanol and then at a temperature of about 55 - 60 ° C, a solution of 10 g of a base (NaOH, KOH or NaOMe) added in 100 ml of methanol. After a gel phase had formed (noticeable increase in viscosity), the reaction mixture was maintained at 55-60 ° C for a further 30 min. Then 5 l of water were added in several portions and the solvent was removed by means of a steam distillation from the reaction mixture. A solution of the polymer in water was obtained.

The K values (measured .1 wt .-% in water) were between 25.0 and 45.0

Table 1

(1) Polyethylene oxide of specified molecular weight and weighed amount

(2) Mixture of vinyl acetate (A) and methyl acrylate (B) in the stated proportions, total amount 2 kg

(3) Starter quantity in% resp. on the monomer used, dosing as a 10% solution in the indicated solvent a) t-butyl-peroxy-2-ethyl-hexanoate

b) t-butyl peroxy-pivalate

% Data [wt%]

Claims

claims

1 . Process for the preparation of graft polymers based on polyethers and vinyl esters by reacting polyethers, vinyl esters and other hydrophobic monomers in the presence of an organic solvent and a free-radical-forming polymerization initiator under reflux conditions, with a monomer composition of a) from 5 to 50% by weight of polyethers, b) From 40 to 95% by weight of vinyl ester, and c) from 0 to 50% by weight of a further hydrophobic monomer, the total amount of components a) to c) being 100% by weight, characterized in that the control of the reaction as a function of the amount of heat removed via the reflux condenser.

2. The method according to claim 1, characterized in that the dissipated heat of reaction is determined by measuring the temperature difference between inflowing coolant and outflowing coolant and the amount of coolant at the reflux condenser.

3. The method according to claim 1 or 2, characterized in that the polymerization temperature is adjusted via the reaction pressure.

4. The method according to any one of claims 1 to 3, characterized in that the polymerization is carried out at temperatures of 50 to 120 ° C.

5. The method according to any one of claims 1 to 4, characterized in that the polymerization is carried out at temperatures of 60 to 80 ° C.

6. The method according to any one of claims 1 to 5, characterized in that the molecular weight of the polymer is adjusted via the reaction pressure.

7. The method according to any one of claims 1 to 6, characterized in that the reaction pressure is 0.05 to 0.5 MPa.

8. The method according to any one of claims 1 to 7, characterized in that the reaction pressure is 0.05 to 0.2 MPa.

9. The method according to any one of claims 1 to 8, characterized in that a Ci-C4-alkanol is used as the organic solvent.

10. The method according to any one of claims 1 to 9, characterized in that the hydrophobic monomer passes into the reflux.

1 1. Method according to one of claims 1 to 10, characterized in that vinyl acetate is used as the vinyl ester.

12. The method according to any one of claims 1 to 1 1, characterized in that 10 to 30 wt .-% of component a) and 70 to 90 wt .-% of component b) are used.

13. The method according to any one of claims 1 to 12, characterized in that a polyethylene glycol having average molecular weights of 1 .500 to 35,000 Dalton is used as the polyether.

14. The method according to any one of claims 1 to 13, characterized in that as component c) a monomer having a boiling point at normal pressure of 65 to 70 ° C is used.

15. The method according to any one of claims 1 to 14, characterized in that as component c) methyl acrylate or methyl methacrylate is used.

16. The method according to any one of claims 1 to 15, characterized in that the amount of component c) is 20 to 45 wt .-%.