Polymers and polymerization processes

Details Polymers and polymerization processes Polymers and polymerization processes

2001-11-15

2004-08-24

Cheung, William (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S801000, C524S832000

Reexamination Certificate

active

06780930

ABSTRACT:

The present invention relates to polymers formed from radical polymerization of ethylenically unsaturated monomers including an ammonium phosphate ester zwitterionic monomer, and processes for producing them. In particular, the invention relates to emulsion polymerization processes for forming high solids emulsions without the incorporation of non-polymerisable emulsifier, and to the use of these emulsions to biocompatibilise substrates.
Yamaguchi et al in Makromol. Chem. (1989), 190, 1195-1205, describe an oil-in-water emulsion polymerization of styrene in the presence of polymerisable and non-polymerisable phosphoryl choline compounds as emulsifier. The latex product is stable, the non-polymerisable emulsifiers giving more regular shaped and sized spherical particles than the polymerisable emulsifiers. The polymerizations were conducted to form latexes having around 10 wt % solids. The mole percent of polymerisable emulsifier based on total monomer is around 10%. The base monomer on which the polymerizations were based was styrene.
Sugiyama et al in Polym. J. (1993) 25(5), 521-527, describe an emulsifier free radical polymerization of ethylenically unsaturated monomers comprising methylmethacrylate, in the presence of an ethylenically unsaturated ammonium phosphate ester zwitterionic monomer, using a water-soluble initiator. The latex product had a concentration of around 10% by weight polymer. Increasing the amount of zwitterionic monomer resulted in reduced stability of the latex. Whilst low levels of zwitterionic monomer reduced the particle size of microspheres in the latex product as compared to a process containing no such monomer, increasing the level from a mole % of 0.01, based on total monomer, to 0.5 resulted in an increase in the diameter of the microsphere of the product. The microspheres themselves were found to have low levels of adsorption of albumin as compared to polymethylmethacrylate polymerised in the absence of the ammonium phosphate ester zwitterionic monomer.
Sugiyama et al, in J. Polym. Sci., Part A (1997) 35, 3349-3357, describe oil-in-water emulsion polymerization of methylmethacrylate, optionally with a comonomer of hydroxypropyl methacrylamide, in the presence of 2-methacryloyloxyethyl-2′-trimethylammoniumethyl phosphate inner salt (MPC). The MPC is present at a level of about 1% based on total ethylenically unsaturated monomer. The latex product had a polymer solids concentration of around 10% by weight. Again the presence of MPC resulted in a decrease in the stability of the latex product with more aggregates being formed. The process was dependent on the choice of initiator, between potassium peroxodisulphate, and 2,2′-azobis[2-(imidazolin-2-yl)propane]dihydrochloride (ABIP). The ABIP initiated products were more influenced by the presence of the MPC monomer in terms of particle size and level of aggregates. In both Sugiyama papers, the reaction mixture was agitated at high speed, with all monomers being included in the reaction vessel at the commencement of the polymerization. It is not clear how the methylmethacrylate dispersed phase is maintained in suspension during the process for example with no MPC monomer.
Zimehl et al, in Colloid Polym. Sci. (1990) 268, 924-933 describe emulsion polymerization of polystyrene using potassium peroxodisulphate in the presence of N-(3-sulphopropyl)-N-methacrylomidyl propyl (N,N-dimethylammonium betaine) (SPP) at SPP concentrations in the range 5 to 70% by weight based on total monomer. The particle size of the latex product was dependent upon the initiator and the level of betaine comonomer. Again, all of the monomers were dispersed into the aqueous continuous phase before polymerization was initiated. The solids concentration of product latex was around 10% by weight.
In U.S. Pat. No. 3,497,482 Hwa et al describe a copolymerization of N,N-dimethyl-N-(2-methacryloyloxyethyl)-N-(3-sulphopropyl ammonium inner salt) (SPE), with ethyl methacrylate and acrylamide, in an aqueous continuous phase. Hwa produces a metastable oil-in-water product. He does not describe the particle size of the latex.
In WO-A-93/01221 we describe a range of copolymers of zwitterionic monomer with comonomers such as hydrophobic comonomers, ionic comonomers or reactive comonomers. The copolymers are formed by co-dissolving all the monomers into a solvent in which monomers and polymer are soluble and recovered by precipitation techniques. It is suggested that the product might be a micro emulsion but no examples of emulsion polymerization are given. The polymers are used to coat substrates in order to improve their biocompatibility. Whilst improvements in biocompatibility may be achieved by using molar percentages of 1% or lower of zwitterionic monomer, based on total ethylenically unsaturated monomer, it is often found that at least 20 mol % zwitterionic monomer is needed for satisfactory levels of improved biocompatibility. The higher the level of zwitterionic monomers, the greater the expense.
Zwitterionic polymers made by the techniques such as are described in WO-A-93/01221, may be blended with physically or mechanically desirable copolymers to provide blends which have good biocompatibilising properties. The level of zwitterionic monomer in the total blend is reduced, thereby rendering the product more cost effective than single component zwitterionic polymer products. Such blends are described in, for instance, WO-A1-94/14897 and PCT/GB00103985 (unpublished at the priority date of this application). PCT/GB00/03985 describes blends of MPG copolymers with higher alkyl methacrylate comonomers, blended with alkyl(meth)acrylate polymers. Such blends, co-dissolved in a suitable organic solvent may be coated onto a surface to form a coating having micro-domains of relatively hydrophilic and relatively hydrophobic character. The blends may express higher levels of phosphorylcholine groups at the surface than in the bulk of the coating. This should allow the properties of a substrate coated with the polymer to be tailored for particular biocompatibility.
It would be desirable to produce a latex having high solids, in which a zwitterionic monomer is one of the ethylenically unsaturated monomers. It would furthermore be desirable to produce a copolymer of an ammonium phosphate ester zwitterionic monomer including low levels of that monomer. It would be desirable to carry out an emulsion polymerization to produce a stable latex product having a small particle size, and low particle size distribution and which forms coatings having desirable biocompatibilising properties without using high levels of ammonium phosphate ester zwitterionic monomer.
In a new emulsion polymerization process according to the invention, a mixture of ethylenically unsaturated monomers including water-insoluble monomers is polymerised in the dispersed phase of an oil-in-water emulsion in the presence of a water-soluble radical initiator, ethylenically unsaturated monomers including an ammonium phosphate ester zwitterionic monomer the process being characterised by being carried out at component concentrations to give a latex product having a polymer solids concentration of at least 20% by weight.
In the new process, the solids concentration of the product is usually no more than 60%, preferably in the range 25 to 50% by weight.
The process of the invention may be carried out in the presence of non-polymerisable emulsifiers and/or stabilisers. It is found that it is possible for the emulsion and latex product to be adequately stabilised by the presence of the ammonium phosphate ester zwitterionic monomer, optionally in combination with other surface active monomers. The process is preferably carried out therefore in the substantial absence of non-polymerisable surfactant/emulsifier and stabiliser.
The ammonium phosphate ester zwitterionic monomer is preferably included in an amount in the range 0.01 to 5% by weight, based on the total weight of monomers. More preferably the level of the zwitterionic monomer is in the range 0.05 to 2% by weight, f

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