Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Patent
1997-12-11
1999-11-30
Gorr, Rachel
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
424486, 526 75, 523353, C08G 1848
Patent
active
059944927
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for the production of a microgel. The process enables the production of microgels in a simple and economic manner. The invention also relates to microgels themselves, particularly when compressed or melted into a solid body.
BACKGROUND
Prior patent specification GB2090264 discloses a solution polymerisation process for the preparation of polymeric materials comprising cross-linked particles which are capable of forming sols, that is to say, a class of hydrogels which are referred to as microgels. The process involves polymerising one or more monomers in a solvent having particular characteristics and terminating the polymerisation before macrogelation occurs.
Microgels may be defined as intramolecularly cross-linked macromolecules. In common with other cross-linked polymers, microgels have a cross-linked structure and fixed surfaces. On the other hand, microgels may generally speaking be dissolved in certain solvents in the same way as non-cross-linked linear or branched polymers of similar molecular weight. In conventional cross-linked polymers, macrogelation occurs such that an extensive three-dimensional network is set up, which generally speaking resists dissolution in solvents. In microgels, the cross-linking structure exists predominantly within individual globular molecules.
The special molecular structure of microgels and their ability to exist as globular particles makes the microgel a promising material for pharmaceutical applications, such as carriers for controlled drug delivery. Patent specifications GB2090264, GB2143733 and GB2230952 disclose sustained release devices comprising an active ingredient and a hydrogel.
It is therefore foreseen that microgels may have a variety of potential industrial uses, and it would be desirable to provide an improved production process capable of producing microgels in a simple efficient and economical manner. Originally, microgels had to be produced at high dilutions which favour intramolecular rather than intermolecular cross-linking. Patent specification GB2090264 exemplifies an improved process for the production of microgels at higher concentrations in solvents having particular defined characteristics and under certain conditions which favour microgel formation. Generally speaking, the microgels formed have good solubility in the solvents used in the production process, so that solid microgel granules are generally obtained by precipitation of the microgel from solution by the addition of an organic liquid such as hexane, cyclohexane, petrol ether or methanol. However, the addition of a further organic liquid to the solvent used in the microgel production reaction means that the solvent cannot be directly reused without costly procedures for recovering the solvent from the mixture formed with the organic liquid. Furthermore, the microgel granule size or shape may not be suitable for direct use as a tabletting excipient, so that further processing such as grinding and sieving may be needed. These expedients are undesirable and detract from the industrial applicability of such microgel production processes.
It is an object of the present invention to mitigate these disadvantages.
SUMMARY OF THE INVENTION
One aspect of the present invention provides a process for the production of a microgel, which comprises at least one monomer in a reaction mixture substantially free of solvent therefor; and solvent and completing the polymerisation to produce a microgel.
Polymerisation may generally be taken to completion without macrogelation occurring, and there is therefore usually no need to terminate polymerisation prior to completion (though this is not excluded).
Another aspect of the present invention relates to the microgel polymer, particularly in granular form. The process of the present invention has been found to provide microgels having higher molecular weights than those obtained by conducting the polymerisation in a solvent in the absence of the solvent-free first polymerisation ste
REFERENCES:
patent: 3850880 (1974-11-01), Hakanson et al.
patent: 4293679 (1981-10-01), Cogliano
Graham Neil Bonnette
Mao Jianwen
Gorr Rachel
University of Strathclyde
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