Solvent-free, fine white powders of high molecular weight copolymers of maleic anhydride and a C1-C4 alky vinyl ether without odor or taste

Solvent-free, fine white powders of high molecular weight copolymers of maleic anhydride and C.sub.1 -C.sub.4 alkyl vinyl ethers, which are particularly useful as starting materials for denture adhesives. A solvent-free process for making such copolymers also is described.

CROSS-REFERENCE TO RELATED APPLICATIONS
 This application is related to application Ser. No. 08/942,830, filed Oct.
 2, 1997 now U.S. Pat. No. 5,959,506.
 BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to copolymers of maleic anhydride (MAN) and a
 C.sub.1 -C.sub.4 alkyl vinyl ether (AVE), and, more particularly, to
 solvent-free, fine white powders of such copolymers having advantageously
 high molecular weights and without taste or odor, for use in oral care
 products, particularly denture adhesives, and to a solvent-free process
 for making such copolymers.
 2. Detailed Description of the Prior Art
 British Pat. 906,230 described the preparation of copolymers of maleic
 anhydride and methyl vinyl ether in benzene as solvent. Example 1 also
 disclosed a copolymerization process in absence of solvent in which
 powdered maleic anhydride, methyl vinyl ether and initiator were
 precharged into an autoclave and reacted at 55.degree. C. The specific
 viscosity (SV) of the product, however, was only 3.45 (1% in methyl ethyl
 ketone, MEK).
 U.S. Pat. No. 5,047,490 described a polymerization process substantially
 the same as Example 1 of British 906,230. However, the reference does not
 disclose any procedure for separation of remaining traces of MVE from the
 product, other than distilling off the MVE from the reactor. Accordingly,
 such polymers inevitably carry a bad taste and odor which is unacceptable
 for oral care products such as denture adhesives. Furthermore, the SV of
 the polymers obtained therein was only 2 to 5.
 Accordingly, it is an object of this invention to provide a solvent-free
 process for making high molecular weight copolymers of MAN and an AVE,
 particularly having an SV of &gt;6, and which are without taste or odor, so
 that they can be used advantageously in commercial oral care products such
 as denture adhesives.
 These and other objects and features of the invention will be made apparent
 from the following more particular description of the invention.
 SUMMARY OF THE INVENTION
 What is described herein is a solvent-free process for making fine powders
 of high molecular weight alternating copolymers of maleic anhydride (MAN)
 and a C.sub.1 -C.sub.4 alkyl vinyl ether (AVE), having a molecular
 structure of (A-B).sub.n, where A=MAN and B=AVE, and n is an integer which
 is indicative of its molecular weight.
 The copolymers obtained herein have a specific viscosity (SV) which is
 .gtoreq.6 (1% in MEK, 25.degree. C.), corresponding to an absolute weight
 average molecular weight in excess of 3,500,000 (GPC/MALLS, water pH 9).
 The solvent-free process of the invention is carried out by precharging an
 alkyl vinyl ether in an amount substantially greater than the 1:1 mole
 ratio required to provide a 1:1 mole ratio of AVE to MAN in the copolymer,
 adding a free radical initiator, heating the mixture to a reaction
 temperature of about 50.degree. to 100.degree. C., thereafter feeding
 molten MAN into the reactor over a predetermined period of time and
 holding the reactants at a defined temperature for a predetermined time.
 Unreacted AVE is then stripped off and a stabilizer antioxidant is added
 to the copolymer and the copolymer is dried.
 The high molecular weight copolymers obtained thereby are odorless and
 tasteless and free of trace amounts of solvents characteristic of other
 known processes for making such copolymers.
 DETAILED DESCRIPTION OF THE INVENTION
 In accordance with the invention, there is provided herein a solvent-free
 process for making solvent-free, fine white powders of high molecular
 weight copolymers of maleic anhydride and a C.sub.1 -C.sub.4 alkyl vinyl
 ether, preferably methyl vinyl ether (MVE). In this invention, the
 specific viscosity (SV) of the solvent-free copolymers is &gt;6 (1% wt/vol in
 MEK, 25.degree. C.), corresponding to an absolute weight average molecular
 weight of at least 3,500,000 (GPC, water, pH 9).
 The solvent-free polymerization process of the invention is carried out
 using an excess of alkyl vinyl ether as the reaction medium, preferably by
 precharging the alkyl vinyl ether into the reactor, adding a radical
 initiator, heating to a reaction temperature of about 50.degree. to
 100.degree. C., and, thereafter, feeding molten maleic anhydride into the
 reactor over a predetermined period of time, followed by holding at a
 defined temperature for a predetermined period of time.
 An effective amount of a food grade antioxidant stabilizer, such as t-butyl
 hydroquinone (TBHQ), butylated hydroxy-anisole (BHA), butylated
 hydroxy-toluene (BHT), propyl gallate (PG) and the like, preferably is
 added to the copolymer product before drying.
 After adding stabilizer, the remaining AVE is stripped off, and the polymer
 is dried at about 40-100.degree. C. under vacuum, to remove any remaining
 traces of AVE. The desired copolymer is obtained as a solvent-free, fine
 powder, of desired high SV, and it is odorless and tasteless.
 In the preferred embodiments of the process of the invention, the MAN
 reactant is introduced into the precharged MVE over a period of at least 1
 hour and the % solids of the copolymer in the polymerization mixture is
 about 10-40%. The MVE:MAN mole ratio is maintained at about 25:1 to 5:1,
 most preferably 12:1 to 7:1. The initiator concentration is 0.01 to 0.2%,
 most preferably 0.05 to 0.1% by wt., based on the copolymer obtained.

The invention will now be described with reference to the following
 examples.
 EXAMPLE 1
 A 1-liter Buchi pressure reactor was sparged with nitrogen and charged with
 400 ml (300 g, 5.16 mol) of methyl vinyl ether (MVE) and 0.055 g of
 Trigonox.RTM. 21 (t-butylperoxy-2-ethylhexanoate, Akzo Nobel Chemicals,
 Inc.), as initiator, a concentration of 0.08% based on copolymer obtained,
 which was rinsed into the reactor with MVE. The precharged reactor then
 was heated to 75.degree. C. with agitation over a period of 15 min.
 Thereafter 41 g (0.418 mol) of molten maleic anhydride MAN (MVE/MAN=12.3
 by mol) was fed in over a period of 1 hour. The solids content of the
 resultant reaction mixture was 16%. The temperature of the mixture was
 maintained at 75.degree. C. for 1.5 hour. Then 0.03 g t-butyl hydroquinone
 (TBHQ) antioxidant, rinsed into reactor with 25 ml MVE, was blended into
 the reaction slurry and the contents were agitated for 15 min. Excess MVE
 was stripped off whereupon the pressure in the reactor dropped to
 atmospheric. Upon opening the reactor, a fine, free-flowing copolymer
 powder product was observed. The product obtained was dried in a vacuum
 oven at 65.degree. C. for 4 hr. A total of 64.8 g of fine, free-flowing,
 solvent-free copolymer powder without taste or odor was recovered (99.37%
 of theoretical yield) which was a 1:1 MVE/MAN copolymer (based on .sup.13
 C NMR) having a specific viscosity SV of 10.3 (1% wt/vol, MEK, 25.degree.
 C.). This specific viscosity corresponds to an absolute M.sub.w of
 6,300,000 (GPC/MALLS, water, pH 9).
 EXAMPLES 2-5
 The procedure of Example 1 was repeated under different reaction
 conditions. Results similar to Example 1 were obtained.
 The Table below is a summary of the experimental conditions and results of
 Examples 1-5.
 TABLE
 Ex. No. 1 2 3 4 5
 MVE:MAN 12.3 12.3 15.0 12.3 7.3
 (mole ratio)
 Initiator (In) Trigo- Luper- Trigo- Deca- Alper-
 nox .RTM. 21 sol .RTM. 11 nox .RTM. 21 nox .RTM. F ox .RTM. F
 Conc. of In 0.08 0.08 0.08 0.06 0.04
 (% on
 copolymer)
 Reaction 75 75 75 70 65
 Temp. (.degree. C.)
 MAN addition 1 1.5 1.5 2.0 2.0
 Time (hrs)
 Total Reaction 2.5 2.5 3.0 3.0 3.0
 Time (hrs.)
 Specific 10.3 9.9 9.5 6.5 10.1
 Viscosity Of
 Copolymer
 (SV, 1%
 w/v MEK)
 Appearance of copolymer: The copolymers were solvent-free, fine white
 powders, without odor or taste
 INITIATORS
 Trigonox.RTM. 21=t-butylperoxy-2-ethylhexanoate (Akzo Nobel Chemicals,
 Inc.)
 Lupersol.RTM. 11=t-butylperoxypivalate, 75% in odor free mineral oil (Elf
 Atochem)
 Decanox.RTM. F=didecanoyl peroxide (Elf Atochem)
 Alperox.RTM. F=dilauroyl peroxide (Elf Atochem)
 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: