All-Acrylic Multigraft Copolymers: Effect of Side Chain MolecularWeight and Volume Fraction on Mechanical Behavior.

We present the synthesis of poly(n-butyl acrylate)-g-poly(methyl methacrylate)(PnBA-g-PMMA) multigraft copolymersvia a grafting-through (macromonomer) approach. The synthesis wasperformed using two controlled polymerization techniques. The PMMAmacromonomer was obtained by high-vacuum anionic polymerization followedby the copolymerization of n-butyl acrylate and PMMAmacromonomer using reversible addition–fragmentation chaintransfer (RAFT) polymerization to yield the desired all-acrylic multigraftstructures. The PnBA-g-PMMA multigraftstructures exhibit randomly spaced branch points with various PMMAcontents, ranging from 15 to 40 vol %, allowing an investigation intohow physical properties vary with differences in the number of branchpoints and molecular weight of grafted side chains. The determinationof molecular weight and polydispersity indices of both the PMMA macromonomerand the graft copolymers was carried out using size exclusion chromatographywith triple detection, and the structural characteristics of boththe macromonomer and PnBA-g-PMMAgraft materials were characterized by 1H and 13C NMR. Matrix-assisted laser desorption/ionization time-of-flightmass spectrometry was employed for monitoring the macromonomer synthesis.Thermal characteristics of the materials were analyzed using differentialscanning calorimetry and thermogravimetric analysis. The mechanicalperformance of the graft materials was characterized by rheology anddynamic mechanical analysis, revealing that samples with PMMA contentof 25–40 vol % exhibit superior elastomeric properties as comparedto materials containing short PMMA side chains or <25 vol % PMMA.Lastly, atomic force microscopy showed a varying degree of microphaseseparation between the glassy and rubbery components that is stronglydependent on PMMA side chain molecular weight. [ABSTRACT FROM AUTHOR]