Consequences of block sequence on the orthogonal folding of triblock copolymers

ABA- and BAB-type triblock copolymers possessing pendant, self-assembling motifs in the A and B blocks were synthesized, with 2-ureidopyrimidinone (UPy) and benzene-1,3,5-tricarboxamide (BTA) for the A and B block, respectively. They were investigated to assess if and how the polymer's microstructure influences the self-assembly behavior of the supramolecular motifs and, as a result, the single-chain folding process. BAB-type triblock copolymers were synthesized via atom transfer radical polymerization (ATRP) with molecular weights ranging from 30 to 120 kg mol⁻¹; the BTA and UPy motifs were attached using a post-functionalization approach. The ABA-type triblock copolymers were available from previous work. In highly dilute solutions, both types of triblock copolymers fold into single-chain polymeric nanoparticles (SCPNs) via thermally induced BTA self-assembly and photo-triggered UPy dimerization. Chain collapse induced by intramolecular UPy dimerization was evaluated using size-exclusion chromatography (SEC). The BTA self-assembly was monitored by circular dichroism (CD) spectroscopy. The microstructures of SCPNs were visualized by atomic force microscopy (AFM). SEC analysis indicated a more loose packing for the BAB-type folded nanoparticles than for the ABA-type ones, which implies that topological differences in the polymer architecture do affect the folding behavior, although only slightly. The facile synthetic protocol developed here provides topologically different triblock architectures and opens up the area for single-chain folding technology that is applicable in artificial enzymatic systems with compartmentalized domains.