Using　isobutyl　alcohol　polyoxyethylene　ether(HPEG)　as　macromonomer　and　acrylic　acid　(AA),　ammonium　persulfate　(APS,　1%)　as　initiator,　the　copolymer　with　low　conversion　rate　was　synthesized　by　free　radical　polymerization　reaction　under　the　condition　of　50water　solution.　By　gel　permeation　chromatography(GPC)　and　high　performance　liquid　chromatography　(HPLC),　the　monomer　amount　of　residual　andmacromonomer　conversion　rate　of　copolymer　were　measured.　And　then　according　to　the　monomer　feed　ratio,　the　reactivity　ratio　was　calculated　through　the　K-T　method.　The　results　show　that　under　the　conditions　of　low　conversion　rate,　the　reactivity　ratio　of　isobutyl　alcohol　polyoxyethylene　ether　(HPEG)　with　acrylic　acid(AA)　is　r1=0.017(HPEG),　r2=1.70(AA).　Micro-structure　and　chains　distribution　of　P(HPEG-co-AA)　were　analyzed　when　the　feed　ratio　of　HPEG　and　acrylic　acid　was　1:4.　In　the　main　chain　of　P(HPEG-co-AA),　the　length　of　HPEG　is　one　monomer　unit.　Acrylic　acid　forms　segments　mainly　at　less　than　10　monomer　unit　segments.　The　average　length　of　the　acrylic　acid　is　7.8,　dominated　with　3~15　monomer　units.　©　2018,　Editorial　Board　of　Polymer　Materials　Science　&　Engineering.　All　right　reserved.