Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2002-01-31
2003-07-29
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C502S104000, C502S105000, C502S208000, C502S235000, C502S236000, C502S238000, C502S239000, C502S242000, C502S251000, C502S256000, C502S414000, C502S439000, C502S514000, C526S096000, C526S098000, C526S104000, C526S105000, C526S106000
Reexamination Certificate
active
06600011
ABSTRACT:
BACKGROUND OF THE INVENTION
Polymer hydrogels, or superabsorbent polymers, have become an extremely important class of materials over the last two decades (Buchholz, F. L. and N. A. Peppas (eds), Superabsorbent Polymers: Science and Technology, American Chemical Society, Washington, DC (1994)). Polymer hydrogels are characterized in part by their ability to absorb water and retain it under pressure. These materials are widely used in the manufacture of personal hygiene products. Polymer hydrogels also have important new pharmaceutical applications. With these new applications, though, extremely stringent purity requirements must be met. The hydrophilic nature of these materials complicates their purification and drying and consequently increases manufacturing expenses.
Typically, polymer hydrogels are isolated from manufacture as wet gels containing impurities from manufacture such as monomers, initiator residues, salts, solvents, and soluble oligomers. Depending upon their intended application, the polymers are purified and dried to the extent required. Drying is usually necessary because it helps to minimize transportation and packaging costs and it conditions the polymers to absorb large quantities of liquid. Drying may also stabilize the product against microbial or chemical degradation.
Pharmaceutical applications, particularly, demand the control of soluble oligomer content. With many pharmaceuticals, the polymer is preferably insoluble. Soluble components can be considered “contaminants” or undesired components. ICH Guidelines have been established to control the levels of such contaminants in bulk active pharmaceuticals (ICH, November 1999, CPMP/ICH/2737/99; Federal Register, 65, No. 130, July 2000, 45085. ICH, July 1977, CPMP/ICH/283/95; Federal Register, 62, No. 247, December 1997, 67377). Variation of the polymerization conditions is generally used to control levels of soluble polymer (Buchholz, F. L. and N. A. Peppas (eds), Superabsorbent Polymers: Science and Technology, American Chemical Society, Washington, DC (1994), p. 27). Soluble polymer can also be generated during post-reaction processing. Polymer hydrogels are shear sensitive and are subject to thermal degradation. Purification and drying processes can break high molecular weight polymer chains, increasing oligomer concentrations in the product.
Many polymeric hydrogels experience a cohesive phase at certain levels of moisture content. During this phase, polymer particles adhere to each other and equipment surfaces. This can make drying the hydrogel particularly challenging. In dryers that use mechanical agitation, hydrogels in a cohesive phase can cause strain upon and damage to impellers, turbines, and end seal assemblies. The motors and gearboxes of such driers need to be suitably robust which is reflected in the capital and operating costs.
Alternatively, attempts have been made to avoid a cohesive phase. Dry product can be back mixed to lower the moisture content of the dryer feed. However the size of equipment required is correspondingly increased. Further, it is unsuitable for materials which are cohesive at very low moisture content or for materials that are very wet at the beginning of the drying step. Other methods use additives to assist in drying, such as azeotrope-forming solvents or agents that affect the surface wetting of the product. However, the use of additives and organic solvents, such as methanol or isopropanol, can be detrimental to drug purity and generally increases production costs.
Drying of polymer hydrogels can be further complicated because some polymer hydrogels are sensitive to the atmosphere they are prepared in, especially when they are wet. For example, some wet polymer hydrogels may be subject to undesired oxidation upon thermal treatment. Controlling the drying atmosphere can add to the cost of manufacturing. Thus, processes which avoid the need to control drying atmosphere can be desired.
A further aspect of polymer hydrogel production often includes controlling the swell index of the product. The swell index measures the amount of a standard solution that is absorbed by the polymer under controlled conditions and is a common measure of the degree of cross-linking in a polymer (Buchholz, F. L.,
Chemistry and Industry
, 56 (1999)). Other factors also can be important in determining the swell index (e.g., concentration of monomer, Mathur, A. M. et al.,
Journal of Controlled Release
54:177 (1998); or presence of gas or vapor during gelation, Chen, J. et al.,
J Biomed. Mater. Res
. 44:53 (1999)). The swell index also can be influenced by the morphology of the product. Morphology can be affected by thermal treatment (For example, Sperling, L. H.,
Introduction to Physical Polymer Science
(John Wiley & Sons, Inc., New York, (1992))) such as that involved in many types of drying.
A need exists to simplify existing manufacturing techniques to reduce production costs. Manufacturers need a process that does not use organic solvents or unnecessary additives, has high product throughput, maintains high purity standards, and maintains desired physical and chemical polymer characteristics.
SUMMARY OF THE INVENTION
This invention relates to a method for purifying and drying a polymer hydrogel. This invention is based in part upon the discovery that rapid drying of polymer hydrogels can eliminate the problem of unacceptable levels of soluble oligomers caused by prolonged thermal treatment. Rapid drying techniques allow drying hydrogels containing more water than was previously considered possible without a loss in product quality. Furthermore, it was discovered that slurries comprising polymer hydrogels and large quantities of water can be spray dried and that spray drying can be conducted with only minimal oligomer formation.
Spray drying polymer hydrogels has many advantages over previously known drying techniques. Spray drying provides adequate separation of hydrogel particles as they pass through the cohesive state, thus solving the problems of agglomeration that are associated with that drying regime. By reducing agglomeration, spray drying reduces the need for size reduction processing of the dried polymer hydrogel.
Furthermore, spray drying allows the use of previously unavailable purification options without resorting to organic solvents that are expensive and that present processing and waste disposal challenges. Because slurries containing large quantities of water can be spray dried using the present invention, repeated water washing of the hydrogel can be used to remove undesired contaminants. Spray drying solves the problems arising from prolonged thermal treatment. Prolonged drying times are not needed to remove excess water, and it is not necessary reduce drying time by using volatile organic solvents.
Spray drying avoids damaging shear-fragile polymer hydrogels passing through the cohesive phase. Conventional thermal dryers often damage fragile hydrogels during the cohesive phase, resulting in soluble oligomer formation. Spray drying also permits improved particle size control.
Further, the method of the present invention permits continuous processing units, achieving high throughput and having low operating and capital costs.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to a method for purifying and drying a polymer hydrogel. The method comprises (a) washing the polymer hydrogel with a water wash medium until the measured conductivity of the resulting slurry comprising the hydrogel and wash water medium is about less than about 5 mS/cm and/or the resulting slurry is in the substantial absence of monomer, oligomer, and other contaminants and (b) spray drying the resulting slurry. The method of the present invention allows repeated water washing and/or water washing with significant concentrations of water because the use of spray drying allows the moisture content of the resultant slurry to be higher than previously thought possible without undesired oligomer formation. Preferably, the water wash medium is free of other solvents. Using water such
Bodmer, Jr. Richard V.
Larrousse Mark F.
McDonnell Peter D.
Rea Gary S.
Thomas Peter W.
Boykin Terressa M.
Genzyme Corporation
Hamilton Brook Smith & Reynolds P.C.
LandOfFree
Process for purification and drying of polymer hydrogels does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for purification and drying of polymer hydrogels, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for purification and drying of polymer hydrogels will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3012973