Macromolecules, Vol.53, No.24, 11051-11064, 2020
Strategy of "Block Blends" to Generate Polymeric Thermogels versus That of One-Component Block Copolymer
Polymer alloys are usually classified into polymer blends and block copolymers. Herein, we combine the two alloying strategies to endow materials with a thermoinduced sol-gel transition. Our system is composed of two amphiphilic block copolymers in water, and we suggest terming it a "block blend." A series of "computer experiments" by dynamic Monte Carlo simulations were carried out to verify our idea of "block blends" and revealed the mechanism of the underlying physical gelation. A thermogel was achieved after blending two amphiphilic block copolymers with different lengths of hydrophobic and hydrophilic blocks and thus different extents of the hydrophilicity-hydrophobicity balances, in which one copolymer could otherwise always flow and the other could be insoluble in water prior to the blending. It is thus interesting that "block blends" can make non-thermogellable copolymers useful in thermogellable systems. We also examined "averaged" copolymers which shared the same composition with the block blends, and our comparative studies illustrated that the block blends impregnated richer physics. A thermogel has a percolated micelle network. Although the amphiphilicity of the copolymer determines the micelle formation, the spatial heterogeneity of two copolymers is crucial in further formation of the network, where semibald micelles are connected by hydrophobic channels rich in the relatively more hydrophobic copolymer. The block-blend strategy paves a way to generate an intelligent material, in particular, a biomaterial by hierarchical self-assembly.