One-Component Nanocomposites Made from Diblock Copolymer\nGrafted Cellulose Nanocrystals

Abstract

Cellulose\nnanocrystals (CNCs) are bio-based, rod-like, high-aspect-ratio\nnanoparticles with high stiffness and strength and are widely used\nas a reinforcing nanofiller in polymer nanocomposites. However, due\nto hydrogen-bond formation between the large number of hydroxyl groups\non their surface, CNCs are prone to aggregate, especially in nonpolar\npolymer matrices. One possibility to overcome this problem is to graft\npolymers from the CNCs’ surfaces and to process the resulting\n“hairy nanoparticles” (HNPs) into one-component nanocomposites\n(OCNs) in which the polymer matrix and CNC filler are covalently connected.\nHere, we report OCNs based on HNPs that were synthesized by grafting\ngradient diblock copolymers onto CNCs via surface-initiated atom transfer\nradical polymerization. The inner block (toward the CNCs) is composed\nof poly(methyl acrylate) (PMA), and the outer block comprises a gradient\ncopolymer rich in poly(methyl methacrylate) (PMMA). The OCNs based\non such HNPs microphase separate into a rubbery poly(methyl acrylate)\nphase that dissipates mechanical energy and imparts toughness, a glassy\nPMMA phase that provides strength and stiffness, and well-dispersed\nCNCs that further reinforce the materials. This design afforded OCNs\nthat display a considerably higher stiffness and strength than reference\ndiblock copolymers without the CNCs. At the same time, the extensibility\nremains high and the toughness is increased up to 5-fold relative\nto the reference materials.