Linear polyglycerols are highly valued for their excellent hydrophilicity and biocompatibility as well as their multihydroxy nature. We report here a convenient route for the controlled synthesis of polyglycerols through ring-opening polymerization (ROP) of commercialized glycidyl butyrates (GBs). Starting from enantiopure GBs, well-defined poly(glycidyl ester)s with controlled molar mass and stereoregularity are achieved thanks to the chemoselectivity of the bicomponent metal-free catalyst that prevents both transesterification and epimerization. The pendant butyrate groups are readily cleaved by organobase-catalyzed methanolysis, yielding linear polyglycerols that inherit isotacticity and regioregularity from the parent polymers. Copolymerization of SGB and propylene oxide occurs in a random manner resulting in a series of narrowly distributed copolyethers with a precisely regulated number of pendant hydroxyl groups to afford tunable aqueous thermosensitivity. The method is further extended to construct polyglycerol-based amphiphilic and double-hydrophilic copolyethers by block copolymerization of RGB with tert-butyl glycidyl ether and ethylene oxide, respectively.