Thermal and Structural Properties of Biologically Derived Monodisperse Hairy-Rod Polymers

Abstract

Monodisperse derivatives of poly(γ-4-(hexadecyloxy)benzyl α,l-glutamate) (PHBG-X, X = 3 or 4) with backbone sequence GluAsp(Glu_(17)Asp)_xGluGlu were prepared by reaction of 4-(hexadecyloxy)phenyldiazomethane with the corresponding monodisperse poly(α,l-glutamate) (PLGA) derivatives (PLGA-X, X = 3 or 4). PHBG-3 and -4 exhibited strong endotherms near 45 °C and weak endotherms near 86 °C when analyzed by differential scanning calorimetry. X-ray diffraction suggested that these polymers aggregate to form layerlike solid structures at room temperature, with extended alkyl side chains forming paraffinlike crystallites. Most of the side chain order disappears at the first melting transition; however, the layerlike structure remains. Both polymers are isotropic above the second melting transition; no ordered melts were observed at higher temperatures, possibly due to the small aspect ratios of PHBG-3 and -4. In contrast, polydisperse poly(γ-4-(hexadecyloxy)benzyl α,l-glutamate) (PDI = 1.2, DP = 98) (PHBG-P1), prepared from commercial PLGA, formed liquid crystalline (LC) phases between 97 and 105 °C.

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