The invention provides alternatives to traditional polycondensation processes for preparing copolymers. For example, in certain embodiments, the invention provides a process that includes an extrusion step and a solid state polymerization step to prepare high molecular weight block copolymer with a "hard block" contributed by a macrocyclic polyester oligomer (MPO) and a "soft block" contributed by a dihydroxyl-functionalized polymer, an oligoether, and/or a dimerized fatty acid (i.e. a polyol). The invention also provides new copolymer compositions made possible by the new processes--for example, copolymers of higher molecular weight, copolymers with higher weight ratio of soft block units to hard block units, copolymers made with higher molecular weight polyol, and copolymers with hard block units that are themselves random copolyesters of units contributed by a MPO and a cyclic ester.