Plumber’s Nightmare Phase from Self-Assembly of Polylactide-Containing Asymmetric Triblock Terpolymers

Herein, a peculiar network phase, a plumber's nightmare phase, can be found from the self-assembly of triblock terpolymers, polyisoprene-block-polystyrene-block-poly(L-lactide) (PI-b-PS-b-PLLA) and polyisoprene-block-polystyrene-block-poly(D-lactide) (PI-b-PS-b-PDLA). Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) results suggest the formation of a cubic lattice structure with network morphology from the self-assembly of the triblock terpolymers. Reconstruction images (i.e., electron tomography results) from OsO₄ stained samples confirm the formation of PI network and scanning electron microscopy (SEM) results from templated synthesis with the replacement of polylactide by Ni assure the formation of polylactide network, suggesting the formation of an alternating primitive phase (P^A) composed of two interpenetrating six-strut networks. Notably, the primitive phase from the self-assembly of diblock copolymers is commonly thermodynamically metastable due to high packing frustration. Theoretically, in the present triblock system with compositional asymmetry, the packing frustration can be partially relieved by the relatively high persistence lengths of both PI and polylactide blocks as compared to PS block (i.e., conformational asymmetry), giving stretched polymer chains toward network nodes. In contrast to chiral triblock terpolymers, achiral polyisoprene-block-polystyrene-block-poly(D,L-lactide) (PI-b-PS-b-PLA), also exhibits the formation of the P^A, reflecting that chirality should not play an important role. As a result, the formation of the thermodynamically stable P^A phase is mainly governed by the combined effects of compositional asymmetry and conformational asymmetry in the triblock terpolymers.