Metal-free synthesis and self-assembly of poly(ethylene glycol) methyl ether-block-poly(ε-decalactone)-block-poly(methyl methacrylate) triblock terpolymers

Abstract

Derived from sustainable sources, ε-decalactone (ε-DL) emerges as a renewable alternative to synthetic cyclic esters. However, its copolymerization with different monomers often requires using metal complexes potentially toxic to humans and the environment. Here, we report the synthesis and self-assembly of poly(ethylene glycol) methyl ether-block-poly(ε-decalactone)-block-poly(methyl methacrylate) (mPEG-block-PDL-block-PMMA) triblock terpolymers via two synthetic pathways using a simple phosphazene- or phosphate-based metal-free catalytic system. Our size exclusion chromatography (SEC) results showed that the two-step synthetic mechanism combining bis(4-nitrophenyl) phosphate (BNPP) and 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)-phosphoranylidenamino]-2λ5,4λ5-catenadi(phosphazene) (t-BuP4) provided a better polymerization control than sequential copolymerization. In addition, our SAXS and AFM analysis also demonstrated that the blocks are incompatible in the terpolymers, further promoting their self-assembly into multicompartment micelles in water, as confirmed by cryo-TEM. Therefore, mPEG-block-PDL-block-PMMA triblock terpolymers may be used as both environmentally friendly alternatives to metal-catalyzed polymers and drug delivery systems.