A liquid phase reactor comprising a screw within a barrel, the screw and barrel being relatively rotatable and defining a mixing zone therebetween, the barrel having at least two inlets for introduction of components for mixing into the barrel and an outlet for discharge of a product of mixing from the barrel, the screw comprising a spiral groove whereby relative rotation of the screw and barrel is adapted to axially transport the components between the screw and barrel while mixing the components and to extrude the product through the outlet, wherein the reactor is adapted to achieve a substantially constant flow ratio of components into the barrel during operation of the reactor.