Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1992-02-06
1993-08-17
Welsh, Maurice J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
528 68, 528 76, 528 77, 524590, 524591, 524839, C08G 1814
Patent
active
052369668
DESCRIPTION:
BRIEF SUMMARY
This invention relates to linear chain extended polymers, to processes for the production and to their utility inter alia in controlled release compositions.
Chemically cross-linked polymeric hydrogel compositions comprising polyalkylene glycols and their use in controlled release compositions have been described e.g. in British Patents 2047093 and 2047094. Whilst these compositions exhibit highly desirable release properties the cross-linked nature of these polymers means that their fabrication into useful devices is complicated by the fact that the hydrogel can only be formed by casting the reactant mixture. Although simple shapes can be produced relatively easily the fabrication of more complex shapes will normally require a machining step.
The cross-linking of these compositions has been found to be essential for the production of essentially water insoluble hydrogals since the omission of the cross-linking agent leads to the production of urethane chain-extended polyalkylene glycols which are not water insoluble and which have insufficient mechanical strength to be useful.
British patent 1551620 describes linear block polymers which are useful as components of controlled release compositions wherein the polymers are amphipathic materials comprising alternating blocks of hydrophilic and hydrophobic regions. The polymers preferably comprise at least 30% by weight of hydrophilic regions. Yui et al. in Journal of Controlled Release 6 1987 p329-342 describe multi-block copolymers consisting of sequences of soft and hard segments which form a microphase separated structure composed of hard segment clusters and surrounding soft segment matrices. the actual materials reported being segmented polyether-poly(urethane-urea)s.
We have now discovered a novel class of chain extended linear poly(alkylene oxide) hydrogels which are swellable rather than soluble in water and soluble in an organic solvent medium. The incorporation of a proportion of chain extending groups which comprise a hydrophobic hydrogen bonding group has surprisingly been found to insolubilise the polyalkylene glycols which would otherwise be soluble in water.
As a result the novel polymeric hydrogels of this invention can be manufactured in or dissolved in a solvent to form novel solutions which can be utilised for coating, dipping, rolling or spraying to form surface coatings or complex shapes and as thermoplastics in conventional manufacturing procedures, for example compression, injection or extrusion molding processes which enables the novel hydrogels to be produced in a variety of forms both quickly and cheaply. The novel hydrogels can also be prepared as emulsions in water or in mixtures of suitable solvents and water.
From one aspect this invention provides a solvent soluble linear chain extended polymer which comprises hydrophilic poly(alkylene oxide) segments which is characterised in that the hydrophilic segments are connected by a hydrophobic hydrogen bonding chain extending group.
In this specification the term "solvent soluble polymer" is used to mean a polymer which is soluble rather than swellable in at least one organic solvent medium. The solvent (or mixture of solvents) is preferably a polar organic solvent such as a chlorinated hydrocarbon solvent e.g. chloroform or an alcohol such as methanol.
In accordance with this invention the hydrophilic segments comprise poly(alkylene oxide) and most preferably poly(ethylene oxide) residues. These residues may comprise a minor amount of an additional component either as a random or block copolymer with the poly(alkylene oxide). However the nature and amount of such a component should not render the segment hydrophobic or having hydrophobic/hydrophilic nature. Generally the proportion of such a component will comprise no more than 20% and preferably no more than 10% by weight of the hydrophilic segment. Examples of monomers which may be used as such a component include epihalohydrins. cyclic mono or poly ethers such as oxetane. tetrahydrofuran, dihydrofuran, dihydropyran, dioxolane and t
REFERENCES:
patent: 4130517 (1978-12-01), Lundberg et al.
Graham Neil B.
Moran Christopher R.
British Technology Group Limited
Welsh Maurice J.
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