Polycarbodiimides are a young, versatile class of helical, semi-flexible macromolecules with a nitrogen rich backbone and several attractive properties such as liquid crystallinity, chiroptical switching, and chiral sensing. These polymers are synthesized via controlled, �living� transition metal mediated polymerizations with either titanium(IV), copper(I)/(II), or nickel(II) initiators. Herein, we report the synthesis of two functional Ni(II) initiators to specifically end functionalize polycarbodiimides with alkyne and alkene moieties. These end groups were easily observed in the 1H NMR spectra of the resulting polymers and further confirmed using MALDI-TOF mass spectrometry. Furthermore, these end capped, helical polycarbodiimides were coupled with conventional random coil polymers through post-polymerization modification of the end groups to form a new class of helical-b-random coil and helical-b-random coil-b-helical di- and tri- block copolymers. Copper-mediated alkyne-azide [3+2] cycloaddition was applied to couple azido and bis(azido) terminated poly(ethylene glycol) (PEG) with alkyne end functionalized polycarbodiimides to form amphiphilic block copolymers. Additionally, the alkene terminated polycarbodiimides were coupled with bis(silane) terminated polydimethylsiloxane (PDMS) via hydrosilation. The nano-phase separation and aggregation behavior of these polymers were studied by tapping-mode atomic force microscopy (TMAFM), polarized optical microscope (POM), and dynamic light scattering (DLS). The thermal and chiroptical properties of these polymers were also studied using differential scanning calorimetry (DSC), polarimetry, and circular dichroism (CD).

End-functionalization of chiral, helical polycarbodiimides: A facile route to novel rod-coil block copolymers

247th National Meeting (2014)

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