Engineering Methacrylic Block Copolymers by Organic Catalysis Group Transfer Polymerization-Induced Self-Assembly in Nonpolar Media at Room Temperature

In this work, we exemplify the sequential approach we recently discovered, where group transfer polymerization (GTP) of methacrylic monomers is carried out in n-heptane as a nonpolar medium, with the former monomer leading to an n-heptane-soluble dispersing block and the other forming an n-heptane-insoluble structuring block. This approach, called group transfer polymerization-induced self-assembly (GTPISA), is applied here to directly elaborate nanoparticles stable in n-heptane. GTPISA is achieved at RT in the presence of 1-methoxy-1-(trimethylsiloxy)-2-methylprop-1-ene as a GTP initiator and tetrabutylammonium bis-benzoate as the organic catalyst. Stable, metal-free, odorless, and colorless nanoparticles of various sizes and morphologies are thus accessed from two distinct families of diblock copolymers, namely, poly(stearyl methacrylate)-b-poly(benzyl methacrylate) (PSMA-b-PBzMA) and poly(lauryl methacrylate)-b-poly(methyl methacrylate) (PLMA-b-PMMA). In order to mitigate the presence of a residual amount of the parent stabilizing homopolymer, two optimization strategies of GTPISA have been developed. One method consists in slowly adding the monomer creating the core-structuring blocks by a semicontinuous process, while the other advantageous option is to form a short copolymer based on MMA and LMA monomer units by mixing the two monomers before the growth of the PMMA structuring block. Different morphologies, from spheres to worms to vesicles, can be achieved by increasing the PBzMA block length for the PSMA-b-PBzMA diblock copolymers, while the morphology of PLMA-b-PMMA diblock copolymers is restricted to spheres showing sizes varying with the PMMA chain length. The structural characteristics of GTPISA nano-objects are further assessed by dynamic light scattering, transmission electron microscopy, and small-angle X-ray scattering, which are presented for the first time for GTPISA formulations.