The present invention relates to a method and apparatus for substitution of functional groups on polymers, which may be suitable for functionalisation of medical devices. More particularly it relates to treatment of polymers which do not contain functional groups normally considered to be readily reactive. The invention also relates to further treatment of substituted polymers wherein, for example, monomers, polymers, biomolecular species and dyes may be grafted onto the substituted polymer.
Mechanical properties of synthetic polymers are such that they can be tailored for use in a wide range of applications in the field of biomaterals. However biocompatibility is often a problem Thus for example such materials frequently exhibit poor haemocompatiblity, excessive complement activation, sensitivity to bacterial attack, and poor tissue compatibility and so on. Such surface properties can be modified by functionalisation of the polymer surfaces. Processes for functionalisation of polymer surfaces are known, as for example described in European patent publication No EP 0643730. The method described consists of functionalisating of a polymer wherein the polymer is reacted in an aqueous medium with an oxidising agent to produce oxygen centred radicals which are responsible for introducing hydroxyl groups into the polymer. The reaction is carried out in the absence of (a) added oxygen, (b) a cationic surfactant and (c) any additive which is preferentially oxidised or is reactive toward the radical as produced by the oxidising agent. The oxidising agent used is a peroxy salt of a metal, preferably a peroxy-disulphate or monosulphate. This method produces hydroxyl radicals from decomposition of the peroxy oxidising agent The method overcomes certain disadvantages of pre-existing methods (for example action of high energy radiation, photo initiation, surface flaming etc) such as for example reducing the severity of degradation of the polymer and allowing processing to be undertaken in aqueous media. However, a problem with existing methods for functionalisation of a polymer, is that the amount of degradation is more than ideal. Furthermore, processing time tends to be long and the amount of oxidising agent required is generally considerable. Additionally known systems tend to involve many side reactions delaying formation of required functional groups and side products tend to interfere with the polymeric material, thus enhancing degradation.
From the above it is clear that there is a requirement for a method and apparatus for substitution of functional groups on a polymer, wherein polymeric degradation is reduced and reaction times are speeded up.
According to a first aspect of the present invention, there is provided a method of producing a functionalised polymer, comprising steps of reacting a polymer in aqueous medium with a water soluble azo compound to produce oxygen-centred radicals, wherein said radicals are responsible for introducing functional groups into the polymer.
In a preferred embodiment, the polymer is selected from the group consisting olefin, aliphatic polymers, polymers that contain an aromatic ring, carbonate polymers, vinyl polymers, polyurethanes, nylons, polyglycols or polyaldehydes.
Preferably, the method is carried out in the absence of any additive which is preferentially oxidised or is reactive towards the radicals produced by the azo compounds. Preferably, no cationic surfactants are added but an additional oxidising agent may be added, possibly in the form of oxygen gas.
According to a second aspect of the present invention, there is provided apparatus for producing a functionalised polymer, configured to react a polymer in aqueous medium with a water soluble azo compound to produce oxygen-centred radicals, wherein said radicals are responsible for introducing functional groups into the polymer.
Preferably, the apparatus is configured to produce a functionalised polymer in which said azo compound is 4,4xe2x80x2-azobis (cyanovaleric acid) or 2,2xe2x80x2-azobis (2-methylpropionamidine) dihydrochloride.
Preferably, the apparatus is configured to attach a bio-molecular species (such as heparin) to the functionalised polymer. The functionalised polymer may be fabricated as a medical device, such as a blood pump etc or as a prosthetic device such as a contact lens.