This invention relates to copolymers of maleic anhydride and a ^~ _- ^~ alkyl vinyl ether, and, more particularly, to a process for making such copolymers of high specific viscosity.

What is described herein is a process for making a copolymer of high specific viscosity by polymerization of maleic anhydride and a C^^ alkyl vinyl ether monomer. The invention involves polymerizing said monomers to form a slurry of said copolymer in excess alkyl vinyl ether as solvent and toluene or an aliphatic organic compound as cosolvent, and is characterized by the steps of: (a) precharging a reactor with alkyl vinyl ether as solvent at a reaction temperature, (b) feeding a mixture of maleic anhydride and a C_-C^ alkyl vinyl ether in substantially stoichiometric amounts, preferably with a slight excess of the alkyl vinyl ether, and at a selected rate, into said precharged reactor, and (c) simultaneously feeding a predetermined mixture of toluene or an aliphatic organic compound as cosolvent, and a polymerization initiator continuously over substantially the entire period of polymerization.

In this method, a suitable reactor is provided with appropriate inlet tubes, agitation means, and heater and temperature control means. The reactor is first purged with nitrogen to remove air from the system. Generally three separate purges are employed, at about 3 bars pressure and about 40°C. Then the reactor is precharged with a substantial excess of C _^ -C^ alkyl vinyl ether, preferably methyl vinyl ether, which functions as a solvent to facilitate agitation of the contents of the reactor before and during the polymerization. The alkyl vinyl ether solvent then is heated to a reaction temperature, generally about 50-90°C. , and preferably about 60°C.

Then separate feed tubes carrying molten anhydride and alkyl vinyl ether are combined in a static mixer and fed into the precharged reactor while agitating the solvent. The maleic anhydride and alkyl vinyl ether reactants usually are combined in substantially stoichiometric ratios of about 1:1, although a slight excess of alkyl vinyl ether monomer is preferred in order to assure that all the maleic anhydride reactant will be complexed by the vinyl ether. Suitably a mole ratio of about 1:1.05 to about 1:1.7 is used, although a 1:1.5 mole ratio is preferred.

The combined maleic anhydride-alkyl vinyl ether feed stream is added to the reactor at a substantially constant feed rate over a suitable period of polymerization. Generally, a period of about 3 hours for addition the mixture of both monomers is typical of the process.

The mole ratio of MVE:MA in total present in the reactor during the polymerization suitably is about 3:1 to about 10:1, although lower and higher ratios also may be used. Preferably, a mole ratio of about 8:1 is used.

As a feature of the invention, during substantially the entire period of the polymerization, predetermined amounts of toluene or an aliphatic organic compound as cosolvent and polymerization initiator are introduced continuously into the reactor to control the course of the polymerization. Any suitable initiator known in the art may be used including but not limited to peroxides such as lauryl peroxide. Tertiary-butyl or tertiary-amylperoxy pivalates are preferred. The concentration of initiator may vary widely, but is suitably about 0.05 to 2% by weight of maleic anhydride present, although about 0.1% by weight usually will suffice for carrying out an effective polymerization.

After the polymerization, the reactor is cooled, excess alkyl vinyl ether (which contains e.g. about 10% toluene) is vented off, and additional toluene is added as a solvent to replace the vented vinyl ether. Then the resultant copolymer slurry in toluene is discharged from the reactor. The copolymer powders can be recovered by filtration and drying. The product is a fine white powder of high specific viscosity with very low residual toluene, generally less than 1%. The copolymer also is quite stable as evidenced by the fact that its viscosity remains substantially constant even after a period of weeks or months.

The vented alkyl vinyl ether-10% toluene mixture can be recycled to function as the precharge in the reactor.

The presence of toluene in the process acts to stabilize the copolymer produced. A suitable amount of toluene for use in the process will produce a reaction slurry mixture at about a 25% solids level after venting alkyl vinyl ether.

The specific viscosities obtained in this process generally range from about 2 to 4, and usually about 3, as determined as a 1% solution in 2-butanone.

Suitable aliphatic organic compounds for use as cosolvents herein include methyl t-butylether, ethyl acetate, butyl acetate, propyl acetate, hexane, heptane and cyclohexane.

The compositions containing copolymers of vinyl alkyl ethers with maleic anhydride, and particularly vinyl methyl ether-maleic anhydride interpolymers generally are stable against changes in viscosity in non-aqueous systems, and particularly when such copolymers are present either in the solid state, in non-aqueous solvent solutions, or in non-aqueous liquid suspensions. Preferably, howeve.. , when an aliphatic organic compound is used as cosolvent, stability is enhanced by the addition to or admixture with

the vinyl alkyl ether-maleic anhydride copolymers of small amounts of free radical inhibiting compounds. Such compounds are characterized as free radical inhibitors and include quinones, hydroquinones, phenols, mercaptans, aromatic amines and aromatic nitro compounds. Butylated hydroxy toluene is a preferred stabilizer compound. The addition of traces of such compounds in amounts of the order of from 0.00001% to 1% based on the weight of the copolymer effects a substantially complete stabilization of the copolymers with which this invention is concerned, whether the latter are present either in the solid state, as a suspension or slurry in a non-aqueous liquid or in a solution in a suitable solvent. The amount of stabilizer which is preferred ranges from about 0.0001% to about 0.1% based on the weight of the copolymer.

The invention will now be described by reference to the following working examples of the invention.

EXAMPLE 1

A reactor equipped with suitable inlet tubes, agitation means, and heater and temperature control means, was purged three times with nitrogen at 3 bars pressure and at 40°C. The purged reactor then was precharged with a recycled mixture of 192.4 g. of methyl vinyl ether containing 19.24 g. of toluene, and heated to 60°C. Then separate streams of 52.5 g. of molten maleic anhydride and 48.0 g. of methyl vinyl ether were combined in a static mixer and introduced into the reactor over a period of 3 hours while agitating the reaction mixture. After 5 minutes, and thereafter simultaneous with addition of monomers, a solution of 128 g. of toluene and 0.066 g. of lauryl peroxide were introduced into the reactor over the 3-hour period of polymerization. The contents of the reactor then were held at 60°C. for 1 hour, cooled to room temperature, and excess methyl vinyl ether was vented.

Then 100 g. of toluene was added. The resultant slurry was discharged from the reactor, filtered, and the solid obtained was dried. 75 g. (90.2% yield) of the desired copolymer was collected as a fine white powder. The specific viscosity of the copolymer powder was 2.54, determined as a 1% solution in 2-butanone. A triphenylphosphite test was negative showing the substantial absence of residual monomers. The toluene level in the copolymer was only 0.75%. The viscosity of the copolymer was observed to remain substantially constant during a test period of 3 months.

Table 1 below summarizes the experimental conditions of this Example.

TABLE I

SUMMARY OF EXPERIMENTAL CONDITIONS OF EXAMPLE 1

Monomer

Precharged Reactor Feed Composition

Excess Toluene Temp. MA MVE Mole Ratio

MVE (g) (% of MVE) (°C. ) (g) (mole) (g) (mole) MA:MVE

(g) (moles)

192.4 3.3 19.24 10 60 52.5 0.54 47.99 0.83 1:1.5

Toluene and Initiator Feed Composition Total Addition of Polymerization Period

Monomer Toluene/

Toluene Initiator Mole Ratio Initiator

(g) (g) (% wt.) MVE:MA ^y (g) (hrs)

128 0.066 0.125 8:1 147.24/0.066

EXAMPLE 2

A reactor equipped with suitable inlet tubes, agitation means, and heater and temperature control means, is purged three times with nitrogen at 3 bars pressure and at 40°C. The purged reactor then is precharged with a 192.4 g. of methyl vinyl ether and heated to 60°C. Then separate streams of 52.5 g. of molten maleic anhydride and 48.0 g. of methyl vinyl ether are combined in a static mixer and introduced into the reactor over a period of 3 hours while agitating the reaction mixture. After 5 minutes, and thereafter simultaneous with addition of monomers, a solution of 128 g. of methyl t-butylether and 0.066 g. of lauryl peroxide are introduced into the reactor over the 3-hour period of polymerization. The contents of the reactor then are held at 60°C. for 1 hour, cooled to room temperature, and excess methyl vinyl ether vented. Then 100 g. of methyl t-butylether is added. The resultant slurry is discharged from the reactor, filtered, and the solid obtained is dried. 75 g. (90.2% yield) of the desired copolymer was collected as a fine white powder. The specific viscosity of the copolymer powder is about 3, determined as a 1% solution of the copolymer in 2-butanone. A triphenylphosphite test is negative showing the substantial absence of residual monomers.

EXAMPLE 3

The procedure of Example 2 is followed using ethyl acetate, butyl acetate, propyl acetate, hexane, heptane and cyclohexane in place of methyl t-butylether with similar results.