A VINYL LACTAM AND A POLYMERIZABLE CARBOXYLIC ACID

IN AN ALIPHATIC HYDROCARBON SOLVENT

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to precipitation polymerization of copolymers of a vinyl lacta and a polymerizable carboxylic acid, and, more particularly, to such copolymers having a wide compositional range, prepared in high yield, as a white powder, which can be filtered and dried easily, and which have advantageous physical properties.

2. Description of the Prior Art

Copolymers of vinyl lactams, e.g. vinyl pyrrolidone (VP) or vinyl caprolactam (VCL) , and polymerizable carboxylic acids, e.g. acrylic acid (AA) or methacrylic acid (MAA) , have found application in the photographic industry, as coatings, as biological membranes, in drug release systems, as preservatives, in oil recovery processes, in immunochemicals, and in cosmeti materials.

Solution polymerization and precipitation polymerization are two available methods for making these copolymers; see in U.S. Patent Nos. 3,044,873; 3,862,915; and 4,283,384; and articles by Takeski, in J. Makro ol. Chem. 148, 205 (1971); and by Uelzmann, in J. Polymer Sci. 33, 377 (1958).

The solution polymerization process is used when both reactant monomers and the copolymer product are soluble in a reaction solvent. However, this method suffers from the following disadvantages:

(1) Desirable compositions of the copolymer may not be soluble in a selected solvent; (2) the yields of such copolymer may be low; (3) the copolymer may be colored; (4) the solvent may be a high boiling liquid which is difficult to separate from the copolymer; and (5) the solvent may be a protic liquid, e.g. water or mixtures thereof, which causes considerable hydrolysis of the vinyl lactam under acidic reaction conditions.

The precipitation polymerization method is useful when the monomers are soluble in the reaction solvent and the copolymers are insoluble in the solvent. Benzene, tetrahydrofuran, acetone and methyl ethyl ketone are known precipitation polymerization solvents. Unfortunately, these solvents have one or more of the following disadvantages:

(1) Useful copolymer compositions may not be insoluble in a selected reaction solvent, which restricts the process to a narrow copolymer compositional range; (2) the copolymer may precipitate only as a gelatinous mass which is difficult to filter; (3) low yields of polymer may be obtained; and (4) the solvent may be toxic.

For these and other reasons, present solution polymerization and precipitation polymerization processes for making copolymers of a vinyl lactam and an acrylic acid have not been very successful on a commercial scale.

Accordingly, it is an object of this invention to provide an improved method of making copolymers of a vinyl lactam and a polymerizable carboxylic acid.

Another object of the present invention is to provide an effective reaction solvent in a precipitation polymerization process which will provide copolymers having advantageous physical properties, including low hygroscopicity, high glass transition temperatures, a high average molecular weights, polyelectrolyte behavior.

Yet another object herein is to provide a precipitation polymerization process in which the copolymers will precipitate in high yield as a fine white powder which is insoluble in the reaction solvent over the entire compositional range of the copolymer.

A feature of the invention is the provision of a precipitation polymerization process for making copolymers of a vinyl lactam and a polymerizable carboxylic acid in which an aliphatic hydrocarbon is used as the reaction solvent.

Another feature of the invention is the provision of copolymers of a vinyl lactam and a polymerizable carboxylic acid made by a precipitation polymerization process in which the reaction solvent is selected from heptane and cyclohexane.

Still another feature of the invention is the provision of copolymers of a vinyl lactam and a polymerizable carboxylic acid over the complete compositional range of monomers, which copolymers are characterized by having a high average molecular weight, low hygroscopicity, a high glass transition temperature, being a white powder, exhibiting polyelectrolyte behavior, and which are soluble in an aqueous basic solution of pH 8 and insoluble in an aqueous acid solution of pH 3.

SUMMARY OF THE INVENTION

What is described herein is a precipitation polymerization process and copolymer products produced thereby. The polymerization is carried out in reaction mixture of a vinyl lactam, e.g. vinyl pyrrolidone or vinyl caprolactam, and a polymerizable carboxylic acid, e.g. acrylic acid or methacrylic acid, in the presence of a polymerization initiator, e.g. a free radical initiator, in an aliphatic hydrocarbon solvent, preferably, a C ₃ -C ₁₀ saturated, branched or unbranched, cyclic or acyclic, and preferably heptane or cyclohexane.

The process herein provides copolymers having a weight ratio of vinyl lactam to polymerizable carboxylic acid of 1:99 to 99:1, and as a white powder, which powder precipitates readily from the aliphatic hydrocarbon solvent and is easily filtered and dried.

The copolymers herein have a unique set of physical and chemical properties which are advantageous for commercial use.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the invention, copolymers of a vinyl lactam and a polymerizable carboxylic acid are made by a precipitation polymerization process in an aliphatic hydrocarbon solvent in the presence of a polymerization initiator.

Suitable vinyl laσtams for use herein include vinyl pyrrolidone, vinyl caprolactam and alkylated vinyl derivatives thereof. Suitable polymerizable carboxylic acids include e.g. acrylic acid, methacrylic acid, itaconic acid, maleic acid, and crotonic acid. Acrylic acid itself, or methacrylic acid, is a preferred coreactant monomer in

the polymerization. These monomers may be employed in weight ratios over the entire compositional range of the copolymers, i.e. from 1-99 weight percent vinyl lactam and 99:1 weight percent of acrylic acid. Accordingly, weight ratios of VP:AA in the copolymer of 99:1, 75:25, 50:50, 25:75 and 1:99, for example, may be conveniently prepared in this invention in substantially quantitative yields.

The reaction solvent of the invention suitably is a C ₃ -C ₁₀ saturated hydrocarbon which is branched or unbranched, cyclic or acyclic. Preferably the solvent is a C ₅ -Cg aliphatic hydrocarbon or mixtures thereof.

A preferred aliphatic hydrocarbon solvent over other known precipitation polymerization solvents is selected from heptane and cyclohexane. Heptane, the most preferred solvent provides high yields of a precipitate of the desired copolymer composition as a fine white powder which is easy to filter and dry. This advantageous result is surprising since vinyl pyrrolidone itself readily homopolymerizes in heptane to produce gummy products.

The amount of solvent used in the process of the invention should be sufficient to dissolve an appreciable amount of the reactants and to maintain the copolymer precipitate in a stirrable state at the end of the polymerization. Generally, up to about 40% solids, preferably 15-20% solids, is maintained in the reaction mixture.

The precipitation polymerization process of the invention is carried out in the presence of a polymerization initiator, preferably a free radical initiator, and most suitably, a peroxy ester, e.g. t-butylperoxy pivalate, although other free radical initiators such as acylperoxides, alkyl peroxides and azo-nitriles, known in the art or described in the aforementioned references, may be used as well.

The amount of such initiator may vary widely; generally about 0.2-5.0% is used, based on the weight of total monomers charged.

The reaction temperature may vary widely; generally the reactants are maintained at about 50°-150°C, preferably 60°-70°C. , during the polymerization. Pressure usually is kept at atmospheric pressure, although higher and lower pressures may be used as well.

The reaction mixture should be stirred vigorously under an inert atmosphere, e.g. nitrogen, during the polymerization. A stirring rate of about 400-600 rpm in a 1-liter lab reactor is quite adequate to effect the desired polymerization and to keep the precipitate in a stirrable state during the polymerization.

The monomers and initiator used herein are commercially available materials, as described below.

Monomers Source Form

Vinyl pyrrolidone GAF Liquid or

Vinyl caprolactam Aldrich Solid

Acrylic acid Rohm and Liquid or

Methacrylic acid Aldrich Liquid

Initiator t-Butylperoxy Pennwalt Corp. Liquid; 75% solution pivalate (Lupersol 11) in mineral spirits

The precipitation polymerization process of the invention may be carried out by first precharging a suitable reactor with a predetermined amount of a vinyl lactam in the aliphatic hydrocarbon solvent, and heating the solution to a desired reaction temperature while

stirring vigorously under an inert gas atmosphere. The initiator is then charged into the reactor. Then a selected amount of the polymerizable carboxylic acid, e.g. acrylic acid, is admitted into the reactor over a period of time, generally about an hour or more. Then the reaction mixture is held for an additional period of time for polymerization to occur. Finally, the mixture is cooled to room temperature. Filtering, washing with solvent, and drying provides the copolymer in yields approaching quantitative, and, substantially, in a composition predetermined by the weight ratio of monomers introduced into the reactor.

Alternatively, the aliphatic hydrocarbon solvent can be precharged into the reactor, purged with nitrogen, heated to reaction temperature, the initiator added, and then separate streams of the vinyl lactam monomer and the acrylic acid monomer are introduced over a period of time into the precharged reactor. Other process variations will be apparent to those skilled in the art.

The copolymers of the invention are generally characterized by their having high average molecular weights, low hygroscopicity, high glass transition temperatures, and exhibiting polyelectrolyte behavior in water, as described below.

a. Molecular Weight

The weight average molecular weight for a 75:25 wt. ratio VP:AA copolymer, for example, having a Fikentscher K-value of about 70, was about 180,000, as determined by light scattering.

b. Hygroscopicity

The hygroscopicity of the copolymers is lower than the weighted average of the homopolymers. This effect is maximized for copolymers, for example, having a VP:AA mole ratio of about 1:1, where the hydroscopicity may be actually lower than the value of either homopolymer. Hygroscopicity is measured by the equilibrium moisture pickup of the copolymer powders at 50% relative humidity.

c. Glass Transition Temperature, Tg

This property shows the effect of strong hydrogen bonding in the copolymer which causes a strong positive deviation from typical behavior, which is most prominent at a vinyl lactam:acrylic or methacrylic acid mole ratio of about 1:1.

d. Solubility

The copolymer exhibits very unusual solubility characteristics: it is insoluble in aqueous acid solution of pH 3 but soluble in basic solution of pH 8. Table I below illustrates the solubility characteristics of copolymers of different compositions in several aqueous and organic solvents.

TABLE I

P(VP/AA) SOLUBILITY

VP/AA W/W 95/5 85/15 75/25 50/50 25/75 10/90

VP/AA M/M 92/8 79/21 66/34 39/61 18/82 7/93

WATER S I I I I I

0.1N NaOH S S S S S S

ETHANOL PS I I I I I

DMF S s s s s S

NMP S S S S S s

ACETONE I I I I I I

CHLOROFORM PS I I I I I

TOLUENE I I I I I I

HEPTANE I I I I I I

SYMBOLS

P = Polymer

VP = Vinyl Pyrrolidone

AA = Acrylic Acid

DMF = Dimethylformamide

NMP = N-methylpyrrolidone

W/W = Weight to weight

M/M = Mole to mole

S = Soluble

I = Insoluble

PS = Partly soluble

e. Viscosity

The viscosity in water is pH dependent in the pH range of about 4-12. The maximum viscosity occurs at a pH of about 8-9. Dilute aqueous solutions exhibit polyelectrolyte behavior.

The invention will be illustrated hereinafter by the following working examples.

EXAMPLE 1

1. PREPARATION OF COPOLYMERS OF VINYL PYRROLIDONE AND ACRYLIC ACID

A 1-liter, 4-necked reaction kettle was equipped with a mechanical stirrer, thermometer, dropping funnel and a nitrogen purge tube. The reactor was precharged with 75 g. of vinyl pyrrolidone in 500 g. of heptane. The solution then was heated to 65°C. during 20 minutes and held there for 30 min. , while stirring under nitrogen gas. Then 260 microliter (0.3 g.) of t-butylperoxy pivalate initiator was added. Then 25 g. of acrylic acid was admitted during a period of 1 hour and the mixture was held for an hour. Then an additional 140 microliter (0.2 g.) of initiator was admitted into the reaction mixture and the solution was maintained at 65°C. with stirring for another 2 hours. Then another 100 microliter of initiator was added and the mixture held for 2 hours.

The reaction product then was cooled to room temperature during a period of about an hour. A fine white powder precipitate of copolymer product was obtained which was filtered, washed twice with heptane and dried overnight at 100°C. and then overnight again in a vacuum oven at 100°C.

A 75:25 VP:AA copolymer (wt. ratio) was obtained in 97% yield.

PROPERTIES OF COPOLYMER PRODUCT

K-VALUE AND AVERAGE MOLECULAR WEIGHT

The product had a K-value of about 70 (1% copolymer in 0.1 N NaOH and 0.2N LiN0 ₃ aqueous solution).

The weight average molecular weight of the copolymer was about 180,000, as measured by light scattering in dimethylformamide solvent.

EXAMPLES 2-6

The procedure of Example 1 was followed using 99, 95, 50, 25 and 1 g. of vinyl pyrrolidone and 1, 5, 50, 75 and 99 g. of acrylic acid, to produce the corresponding 99:1, 95:5, 50:50, 25:75 and 1:99 wt. ratio VP:AA copolymers.

EXAMPLES 7-8

The procedure of Examples 1-6 was followed using cyclohexane and hexane in place of heptane, with similar results.

EXAMPLE 9

The procedure of Examples 1-8 was repeated using vinyl caprolactam in place of vinyl pyrrolidone to produce the corresponding vinyl caprolactam/acrylic acid copolymer in 95-100% yield.

EXAMPLE 10

The procedure of Examples 1-8 was repeated using methacrylic acid in place of acrylic acid to produce the corresponding vinyl pyrrolidone/methacrylic acid copolymer in 95-100% yield.

COMPARATIVE EXAMPLES 11-14

The procedure of Example 1 was followed to compare the efect of using different reaction solvents at various copolymer compositions. The results are shown in Table 2 below.

TABLE 2

COMPARATIVE EXAMPLES 11-14

Precipitation Polymerization of P(VP/AA) in Different Solvents

Copolymer P(VP/AA) (by Wt.)

Ex. No. Solvent 99/1 95/5 75/25 50/50 25/75

11 Tetrahydrofuran — — S S F (1)

12 Acetone F (2) F (3)

13 Benzene F (4) F (5) S

14 Heptane S S S S S

S : Successful, (easy to filter, high yield (> 90%), white powder). F : Failure (for reasons 1-5 below) .

(1) Gummy product formed during polymerization.

(2) 10% of a yellow chunk product, 90% of product remained in solution.

(3) 36% of a yellow chunk product, 64% of product remained in solution.

(4) Viscous solution, difficult to filter.

(5) 67% of a slight yellow chunk product, 33% product remained in benzene solution.

The results in comparative Examples 11-14 above show that heptane is the solvent of choice in the precipitation polymerization of copolymers of vinyl pyrrolidone and acrylic acid. Successful products were obtained in heptane over the entire compositional range of monomers, whereas failure in one or more respects was evident with either tetrahydrofuran, acetone or benzene as the solvent.

The copolymer products of the invention find particular utility in such applications as thickeners, adhesives, in paper manufacture and coatings thereon, in ion-exchange resins and membranes, in controlled release polymers, in textile sizings, as dispersants, in oil recovery chemicals, in surface cleaning, as anti-scaling agents in boilers, and in personal care products.

While the invention has been described with particular reference to certain embodiments thereof, it will be understood that changes and modifications may be made which are within the skill of the art. Accordingly, it is intended to be bound only by the following claims, in which: