A block copolymer was designed to functionalise the surface of polystyrene-based polymersomes via coaggregation. An alpha,omega-diacetylene-functionalised poly(ethylene glycol) (PEG) was coupled to an azide-terminated polystyrene via a Cu(I)-catalysed cycloaddition to produce a PS-b-PEG polymer with an acetylene at its hydrophilic extremity. Incorporation of this 'anchor' compound in the bilayer of a polymersome places its bio-orthogonal group at the surface of this aggregate. Its accessibility was demonstrated using an azido-functionalised Candida antarctica Lipase B (CalB), which retained its activity while immobilised on the polymersome.