DOI: 10.3724/SP.J.1105.2008.00161

Acta Polymerica Sinica (高分子学报) 2008/08:2 PP.161-167


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 ofN-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 (—NHCH2in 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 atδ = 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= 1.10~133) 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

Key words:Block copolymer, PEOz, PLGlu, PCL, Temperature-sensitivity, Ph-sensitivity

ReleaseDate:2014-07-21 14:13:04

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