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Higahinada-h , Kobe658-0032, J- JntroductionIn recent yeam there have been increasing activities in block copolymer synthesis and characterization. Many studies have shown that block copolymm form micelles of close association upon dissolution into a selective solvent, which acts th-dy as a good solvent for one block and a poor solvent for the other block. 'Ihe impo-ce of these synthetic activities has been emphasized by block copolymer micelles, which have been demonstrated as potential drug c a~i e r s ,~*~ and other investigations have revealed their excellent utility in cancer chemo-thexapy .Block copolymers that are comprised solely of water-soluble block units are best rep-ted by ply( ethylenwide)poly(propylen&de)-ply( ethyleneoxide) tri-block polymers (PEO-PPO-PEO). lhese commercially available materials w i t h important properties are v q useful b a technological point of view, such as steric stabilizexa for latex particles and as dye or pigment vehicles in pMting technologiess as well as drug delivery ' Ihia =port describes the pqamtion of block copolymer nonionic surfactants comprised of polyethyleneimine and * Email: nb1005@nl.roevir.co.jp polyethylene oxide blocks (PEO-PEI-PEO) and the utility of these copolymem in terms of surface tension and clay dispersancy as a function of copolymer chain and block length. The preparation of these materials is based on our investigations on the ring opening polymerization of 2-methyl-2-0xazoline (MeOZO) by terminauy di-functionlized aUcyl sulphonate initiators to produce poly( N-acylethylenimine) segments. W i t h this "living" *-opening a csaeiil control of the number of amide p u p , and subsequently the number of amine units in the f d tri-block copolymer after hydrolysis and purification may be obtained. 'Ihis careful control gives a better understanding of the effect of PEI block size on the surface tension and clay dispexsancy properties of the final ABA tri-block copolymers. ExperimentalMaterials 2-Methyl-Zoxazoline ( MeOZO) was supplied from Aldrich Chemical Co. and purified by repeated distillations over KOH pellets in an inert atmosphere. Mehesulfonyl chloride was a commercial reagent ( Kanto Chemical GI. ) and was used as received. Acetonitrile ( Kanto Chemical Co. ) was dried over CaHz and distilled. Triethylamine ( Kanto Chemical Co. ) and dehydrated benzene ( Kanto Chemical Co. ) were dried over KOH and distilled in an inert a msphere prior to use. Commercial PEO samples ( nominal molecular weights of 600, 1 O O O ,~, 4 O O O and uW300 daltons) were pwhased from Wako Pure C h b c a l Industries Ltd. and used as received. Preparetion of m e -& acid diests of PEO (Ms- PEO)As a typical example, a solution of methanesulfonyl chloride (17.2 g, 0.15 a d ) diluted in 60 mL of anhydrous benzene was dripped over a period of 1 h to a stirred solution