Helix-coil transformation of poly(γ-benzyl-L-glutamate) with polystyrene attached to the N or C terminus in trifluoroacetic acid-chloroform mixtures

Abstract

The helix-coil transformations of block copolymers composed of poly(γ-benzyl-L-glutamate) (PBLG) and polystyrene (PS), in which PS was attached to either the N terminus (PBLG n-N-PS m) or the C terminus (PS n-C-PBLG m) of PBLG, were investigated in trifluoroacetic acid (TFA)-chloroform mixtures with TFA concentrations in the range of 0.7-10 vol%. The helical content (f H) estimated from 1H nuclear magnetic resonance measurements indicated that the PBLG segment in PBLG 55-N-PS 160 underwent a gradual helix-coil transformation from f H=1 to f H=0.75 over the range of 3.6-5.7 vol% TFA and then a drastic transformation to f H=0 at 9.5 vol% TFA, in a manner similar to that of the PBLG 55 homopolymer. In PS 120-C-PBLG 55, the helical deformation of the PBLG segment was observed by adding a very small amount of TFA (0.7-3.6 vol%), followed by gradual and drastic transformations at higher TFA concentrations. The results indicate that the conformational stability of the C terminus in a PBLG chain differs from that of the N terminus. Transformations of PBLG/PS block copolymers with various molecular weights and compositions were also studied. © 2012 The Society of Polymer Science, Japan (SPSJ) All rights reserved.