Complementary multiple hydrogen bonding interactions mediate the self-assembly of supramolecular structures from thymine-containing block copolymers and hexadecyladenine

Abstract

In this study we used nitroxide-mediated radical polymerization to synthesize poly(styrene-b-4-vinylbenzyl azide) (PS-b-PVBN₃) and then used click chemistry to react it with propargyl-thymine (PT) to obtain a series of thymine (T)-containing block copolymers, poly(styrene-b-4-vinylbenzyl triazolylmethyl methylthymine) (PS-b-PVBT). We then added an amphiphilic surfactant, hexadecyladenine (A-C16), to complex with the PVBT units in the PS-b-PVBT copolymers through complementary multiple hydrogen bonding interactions. The resulting supramolecular comb–coil diblock copolymers formed lamellae-within-lamellae self-assembled structures, with PS lamellar domains (diameter: ca. 20–25 nm) in a matrix consisting of lamellar mesophases (lamellar inter-distance: ca. 2.3 nm) organized by the PVBT/A-C16 complex. Fourier transform infrared spectroscopy provided evidence for multiple hydrogen bonding between the A-C16 and T groups of the PS-b-PVBT copolymers. The small-angle X-ray scattering patterns of these self-assembled supramolecular systems were very temperature-sensitive. A striking feature was the appearance of the ordered scattering of the lamellar structure at temperatures higher than the melting point of A-C16 (>120 °C), with A-C16 becoming fully miscible with both the PS and PVBT phases at higher temperature; A-C16 was miscible only with the PVBT domains at room temperature, thereby influencing the volume fraction of the PS segment.