A method for making a plasticized polymer comprises polymerizing a polymerizable monomer, such as an ethylenically unsaturated monomer, in a plasticizer, such as mineral oil, and in the presence of a catalyst system. The plasticized polymer may be mixed with a tackifying resin in a method for making an adhesive. A composition, which may be useful as an adhesive, comprises a polymer system comprising a first polymer; a plasticized system comprising a first plasticizer that was in the presence of the first polymer during the polymerization step to make the first polymer; and a tackifier. The method can be used to make compositions having polymers with a low density or a low molecular weight or both. The final compositions made by methods of the invention include adhesives, sealants, coating, or lubricants.