Poly(etherurethane)s(PEU),includingPEUI15andPEUH15,werepreparedthroughchain-extensionreactionofpoly(ethyleneglycol)(PEG-1500)usingdiisocyanateasachainextender,includingisophoronediisocyanate(IPDI)andhexamethylenediisocyanate(HDI).ThesePEUswereusedtotoughenpolylactide(PLA)byphysicalandreactiveblending.Thermal,morphological,mechanicalandagingpropertiesoftheblendswereinvestigatedindetail.ThesePEUswerepartiallycompatiblewithPLA.Theelongationatbreakofthereactiveblendsinthepresenceoftriphenylphosphate(TPP)forPLAwithPEUH15orPEUI15wasmuchhigherthanthatofthephysicalblends.Theagingtestwascarriedoutat-20°Cfor50hinordertoacceleratethecrystallizationofPEUs.ThePEUsinthePLA/PEUblendsproducedcrystallizationandformednewphaseseparationwithPLA,resultinginthedeclinedtoughnessofblends.Fortunately,undertheagingcondition,althoughPEUH15inblendscouldalsoformcrystallization,thereactiveblendofPLA/PEUH15/TPP(80/20/2)hadhighertoughnessthantheotherblends.TheelongationatbreakofPLA/PEUH15/TPP(80/20/2)droppedto287%fortheagingblendfrom350%fortheoriginalblend.ThetensilestrengthandmodulusofPLA/PEUH15/TPPblenddidnotchangeobviouslybecauseofthecrystallizationofPEUH15.