The self-assembly of cellulose-based amphiphilic dense grafting copolymer ethyl cellulose graft poly(acrylic acid) (EC-g-PAA) in a selective solvent was measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Our aim is to realize the intra- or inter-molecular association by collapsing the backbone of dense grafting copolymers. The effects of grafting density, grafting length and solvent on the formation of the unimolecular or multimolecular micelles of EC-g-PAA were discussed. It was shown that the self-association of the grafting copolymers could occur in the mixed solvents of THF and water. The shorter graft chain could induce the multimolecular micelles, while the longer graft chain could lead to the unimolecular micelles. The possible micellization mechanism was proposed from the aspect of chain conformation.Graphical abstractHighlights► Self-assembly behavior of cellulose-based dense graft copolymers. ► Backbone-collapsed intra- and inter-molecular self-assembly. ► Unimolecular micellar structure.

The chain conformation and individual chain structures of the graft copolymers ethyl cellulose grafting poly (acrylic acid) (EC-g-PAA) were investigated by laser light scattering (LLS) and atom force microscopy (AFM). The EC-g-PAA graft copolymers with two different side chain lengths and side chain grafting densities were synthesized via atom transfer radical polymerization (ATRP) from ethyl cellulose as the backbone. The graft copolymer molecules are adsorbed on the mica surface, and the observed single molecule structures by AFM reflect the molecular conformation in solution. An increase of the graft density of the graft copolymer induces the conformational transition due to the repulsion between side chains from coil to rod conformation. The observed disclike and rodlike single chain structures response to the coil and rod conformations, respectively. The results provide a direct visual experimental evidence of chain conformational and single chain structural transitions for graft copolymers in common solvents induced by graft density.