The present invention relates to a method of preparing a pressure-sensitive adhesive comprising the steps of: (i) providing an essentially solvent-free mixture comprising one or more free radically polymerizable monomers having one ethylenically unsaturated group and at least one free-radical polymerization initiator, (ii) partially polymerizing said mixture to provide a partially polymerized mixture exhibiting a Brookfield viscosity of between 1,000 and 125,000 mPa·s at 20° C. and a degree of conversion of monomers to polymer of between 30-60 wt. % with respect to the initial mass of the monomers prior to polymerization, (iii) adding one or more free-radical radiation polymerization initiators to the partially polymerized mixture to provide a radiation-curable precursor, (iv) applying the radiation-curable precursor to a substrate, and (v) further polymerizing the radiation-curable precursor by subjecting it to actinic irradiation to provide said pressure-sensitive adhesive.