Molding of a polymer

Details Molding of a polymer Molding of a polymer

2002-01-15

2004-05-04

Sanders, Kriellion A. (Department: 1714)

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

Synthetic resins

Processes of preparing a desired or intentional composition...

C523S511000

Reexamination Certificate

active

06730721

ABSTRACT:

This application is a continuation of prior international application No. PCT/NL00/00554, filed Aug. 4, 2000; which claims priority from European Patent Application No. EP 99202599.9, filed Aug. 6, 1999.
The invention relates to a process for molding a polymer. More in particular, the invention relates to a process for molding a copolymer of a polyalkylene glycol terephthalate and an aromatic ester.
Copolymers of a polyalkylene glycol terephthalate and an aromatic esters have been found to possess highly favorable properties, such as biodegradability and biocompatibility. For these reasons, they are finding application in tissue engineering applications, such as in the function of scaffolds for seeding cells of different types. Particularly, copolymers of polyethylene glycol terephthalate (PEGT) and polybutylene terephthalate, which are known under the name of Polyactive®, have been found to give promising results in this regard.
In order for the copolymers to be suitable for use in these applications, it is necessary that their shape can be efficiently controlled. Solid bodies of different shapes can be formed of these copolymers, and in fact of polymers in general, in several ways. Well-known examples include injection molding and extrusion.
Most methods for giving a desired shape to a polymer material comprise the step of preparing a melt of the polymer so that it can be formed into the desired shape. Once formed into the desired shape, it is hardened or cured. In order to prepare the melt it is usually necessary to work at the very high temperatures required for obtaining a melt.
Under certain circumstances, it is desired to be able to produce a solid body of a polymer without subjecting it to the high temperatures required for obtaining a melt. Often the thermal strain imposed on a polymeric material during extrusion is undesired. Particular (partial) oxidation of the polymeric material is to be avoided. It is accordingly an object of the present invention to provide a method of molding a copolymer of a polyalkylene glycol terephthalate and an aromatic ester which leads in an efficient manner to a solid body of a desired shape under mild conditions.
Further, in particular in view of the above referred to applications of the copolymers it is often desired to be able to incorporate (bioactive) additives in the solid bodies to be formed. For instance, the presence of growth factors may be very much desired in order to enhance cell growth or differentiation. As many of these bioactive additives are very sensitive compounds the need for working under mild conditions becomes even more important. It is thus a further object of the invention to provide a method for molding a copolymer of a polyalkylene glycol terephthalate and an aromatic ester under mild conditions, which method can conveniently be adapted in order to incorporate additives into the solid body to be formed.
Surprisingly, it has now been found that the properties of copolymers of a polyalkylene glycol terephthalate and an aromatic ester make it possible to produce solid bodies of them in a gel molding process. Accordingly, the invention relates to a process for molding a copolymer of a polyalkylene glycol terephthalate and an aromatic ester, comprising the steps of:
a) preparing a solution of the copolymer in as suitable first solvent; and
b) forming a gel of the solution.
The present process does not involve the preparation of a melt of the copolymer. It has been found that, in accordance with the invention, the copolymer may be molded into any desired shape under very mild conditions. The solvents used can advantageously be recovered and recycled.
The copolymer which is formed into a solid body according to the invention, is a copolymer of a polyalkylene glycol terephthalate and an aromatic polyester. Preferably, the copolymer comprises 20-90 wt. %, more preferably 40-70 wt. % of the polyalkylene glycol terephthalate, and 80-10 wt. %, more preferably 60-30 wt. % of the aromatic polyester. A preferred type of copolymers according to the invention is formed by the group of block copolymers.
The polyalkylene glycol terephthalate may have a weight average molecular weight of about 150 to about 4000. Preferably, the polyalkylene glycol terephthalate has a weight average molecular weight of 200 to 1500. The aromatic polyester Preferably has a weight average molecular weight of from 200 to 5000, more preferably from 250 to 4000. The weight average molecular weight of the copolymer preferably lies between 10,000 and 300,000, more preferably between 40,000 and 120,000.
The weight average molecular weight may suitably be determined by gel permeation chromatography (GPC). This technique, which is known per se, may for instance be performed using chloroform as a solvent and polystyrene as external standard. Alternatively, a measure for the weight average molecular weight may be obtained by using viscometry (see NEN-EN-ISO 1628-1). This technique may for instance be performed at 25° C. using chloroform as a solvent. Preferably, the intrinsic viscosity of the copolymer lies between 0.2289 and 1.3282 dL/g, which corresponds to a weight average molecular weight between 10,000 and 200,000. Likewise, the more preferred ranges for the, weight average molecular weight measured by GPC mentioned above can also be expressed in terms of the intrinsic viscosity.
In a preferred embodiment, the polyalkylene glycol terephthalate component has units of the formula —OLO—CO—Q—CO—, wherein O represents oxygen, C represents carbon, L is a divalent organic radical remaining after removal of terminal hydroxyl groups from a poly(oxyalkylene)glycol, and Q is a divalent organic radical.
Preferred polyalkylene glycol terephthalates are chosen from the group of polyethylene glycol terephzalate, polypropylene glycol terephthalate, and polybutylene glycol terephthalate and copolymers thereof, such as poloxamers. A highly preferred polyalkylene glycol terephthalate is polyethylene glycol terephthalate.
The terms alkylene and polyalkylene generally refer to any isomeric structure, i.e. propylene comprises both 1,2-propylene and 1,3-propylene, butylene comprises 1,2-butylene, 1,3-butylene, 2,3-butylene, 1,2-isobutylene, 1,3-isobutylene and 1,4-isobutylene (tetramethylene) and similarly for higher alkylene homologues. The polyalkylene glycol terephthalate component is preferably terminated with a dicarboxylic acid residue —CO—Q—CO—, if necessary to provide a coupling to the polyester component. Group Q may be an aromatic group having the same definition as R, or may be an aliphatic group such as ethylene, propylene, butylene and the like.
The polyester component preferably has units —O—E—O—CO—R—CO—, wherein O represents oxygen, C represents carbon, E is a substituted or unsubstituted alkylene or oxydialkylene radical having from 2 to 8 carbon atoms, and R is a substituted or unsubstituted divalent aromatic radical.
In a preferred embodiment, the polyester is chosen from the group of polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate. A highly preferred polyester is polybutylene terephthalate.
The preparation of the copolymer will now be explained by way of example for a polyethylene glycol terephthalate/polybutylene terephthalate copolymer. Based on this description, the skilled person will be able to prepare any desired copolymer within the above described class. An alternative manner for preparing polyalkylene glycol terephthalate/polyester copolymers is disclosed in U.S. Pat. No. 3,908,201.
A polyethylene glycol terephthalate/polybutylene terephthalate copolymer may be synthesized from a mixture of dimethyl terephthalate, butanediol (in excess), polyethylene glycol, an antioxidant and a catalyst. The mixture is placed in a reaction vessel and heated to about 180° C., and methanol is distilled as transesterification proceeds. During the transesterification, the ester bond with methyl is replaced with an ester bond with butylene and/or the polyethyene glycol.
In accordance with the invention, the copolymer is first dis

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