Copoly(γ,DL-glutamate)s containing octadecyl and dodecyl side chains: Synthesis and characterization

Abstract

Copoly(-alkyl γ,DL-glutamate)s containing octadecyl and dodecyl side chains in a wide range of compositions (coPAAG-18,12) were synthesized from microbial racemic poly(γ,DL-glutamic acid) (PGGA). Feed ratios of 1-octadecanol to 1-dodecanol were 100:0, 75:25, 50:50, 25:75, and 0:100. The procedure of synthesis consisted of two-steps: Poly(-ethyl γ,DL-glutamate) (PAAG-2) was prepared by esterification of PGGA and then transesterified with 1-octadecanol or/and 1-dodecanol to obtain the corresponding copolymers coPAAG-18,12 (x:y). The polyglutamates and copolyclutamates synthesized in this work were characterized by Nuclear Magnetic Resonance (1H-NMR), Fourier Transform Infrared (FTIR), Gel Permeation Chromatography (GPC) and Intrinsic Viscosity (IV). Their thermal properties were evaluated by Thermogravimetry (TGA) and Differential Scanning Calorimetry (DSC). These copolymers display the following features: a) First melting temperature (Tm 1) ( 50 oC) according to antecedents; b) Second melting temperature (Tm 2) (~100 oC) striking and without explanation; c) No melting temperature (Tm) in the case of PAAG-12; d) A Tm value in copolyesters going down with the content in dodecanol units.