Densely-Grafted and Double-Grafted PEO Brushes via ATRP. A Route to Soft Elastomers

Two macromonomers containing ethylene oxide (EO) segments with different degrees of polymerization (DP_PEO = 5 and 23), capped by a methoxy and a methacrylate group (PEOMA), were polymerized by atom transfer radical polymerization (ATRP) in organic solvents. In addition to the direct preparation of densely grafted brush copolymers by "grafting through" the macromonomers, the lower molecular weight PEOMA (MW_av = 300 g/mol, DP_PEO = 5) was also employed in a "grafting from" reaction using a well-defined multifunctional macroinitiator poly(2-(2-bromopropionyloxy)ethyl methacrylate) (PBPEM, M_n,app = 82 x 103 g/mol, M_w/M_n = 1.16, degree of polymerization of backbone DP_b = 428). This procedure allowed the preparation of densely double-grafted brush copolymers with various degrees of polymerization of the side chains (DP_sc = 12-43). Attempts to prepare double-grafted brushes with DP_sc > 50 or to use a macromonomer with a longer PEO chain (MW_av = 1100 g/mol, DP_PEO = 23) in the "grafting from" reaction resulted in formation of a cross-linked gel. Both the cross-linked mono- and double-grafted brush copolymers are examples of a new class of elastomeric materials with soft rubbery properties (G ~ 10⁴ Pa).