Triblock copolymers;poly(2-ethyl-2-oxazoline)-b-poly(ε-caprolactone)-b-poly(L-glutamic acid) (PEOz-b-PCL-b-PLGlu)s with thermo-sensitive PEOz and pH-sensitive PLGlu have been successfully synthesized.Synthetic procedure includes the following steps.(1) PEOz capped with hydroxyl groups was prepared by ring-opening polymerization of 2-ethyl-2-oxazoline using methyl-p-toluenesulfonate as initiator

and following transformation of terminal cationic ions into hydroxyl groups in the presence of KOH.The molecular weights of the resultant polymers increased with increasing the molar ratio of monomer to initiator.(2) The block copolymers

PEOz-b-PCL were synthesized by ring-opening polymerization of ε-caprolactone using PEOz-OH as macroinitiator and Sn(Oct)2 as catalyst.Their structure was confirmed by their 1H-NMR and FT-IR spectra.In comparison with FT-IR spectrum of its precursor PEOz

a new absorption band at υ = 1734 cm-1 was observed

and the characteristic signals of PEOz and PCL could be found in the 1H-NMR spectra

δ= 3.47

2.21~2.56 and 1.14 for PEOz

δ = 4.12、2.35、1.68 and 1.43 for PCL.The relative amount of the two monomer units in the resultant copolymers is determined by their molar ratio in the feed.Their Mn (NMR) agrees well with the theoretical number-average molecular weight

and their molecular weight distribution is relatively narrow.(3) For application of PEOz-b-PCL-OH as macroinitiator in the ring-opening polymerization of N-carboxyl anhydride of γ-benzyl-L-glutamate (BLG-NCA)

it is necessary to convert the terminal hydroxyl group into primary amine.This transformation was achieved by condensation reaction of PEOz-b-PCL-OH with Phe-NBOC in the presence of DCC

and successively the protective group BOC was removed to produce amine-terminated copolymer after treated with TFA.Based on the integration ratio of ester methylene protons in PCL to the new signal at δ = 7.38 corresponding to phenyl protons in the terminal phenylalanine group

we can estimated that this reaction efficiency was very high.(4) The triblcok copolymer

PEOz-b-PCL-b-PBLG was obtained by ring-opening polymerization of BLG-NCA derived from benzyl glutamate using PEOz-b-PCL-NH2 as macroinitiator

and the polymerization was carried out in CH3Cl at 30℃ for 72 h.Its FTIR spectrum showed the absorption bands of NH and benzene ring at υ = 3292

697 and 749 cm-1

indicating the occurrence of the block copolymerization.The structure of the resultant triblock copolymer was further verified by its 1H-NMR spectrum

the characteristic signals of PEOz

PCL and PBLG appeared at δ = 3.47 (—NHCH2 in PEOz)

4.12 Ｄ(COOCH2Ｆ in PCL) and 5.07 Ｄ(PhCH2Ｆ in PBLG) respectively.Based on their integration ratio

their relative amount in the copolymer can be calculated.(5) The protective benzyl groups in PEOz-b-PCL-b-PBLG was removed and the target triblock copolymer

PEOz-b-PCL-b-PLGlu was obtained after treated with HBr.Complete disappearance of benzyl signals at δ = 5.07 and 7.28 in their 1H-NMR spectra indicates the complete removal of benzyl groups.The molecular weights and molecular weight distributions of the polymers obtained at every synthetic step were measured by GPC

we can see that the GPC curves of PEOz

PEOz-b-PCL and PEOz-b-PCL-b-PLGlu were shifted to high molecular weight position completely

no corresponding precursors were detected and all of them were single and symmetrical

indicating high initiation efficiency of the (macro) initiator.All the molecular weight distributions (Mw/Mn = 1.10~1.33) are relatively narrow.Generally

the molecular weights can be controlled by their feed molar ratios of monomer to (macro) initiators.The thermo and pH sensitivities of the triblock copolymers are under investigation

the results will published in another paper.