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

Abstract

We present the synthesis of poly(n-butyl acrylate)-g-poly(methyl methacrylate) (PnBA-g-PMMA) multigraft copolymers via a grafting-through (macromonomer) approach. The synthesis was performed using two controlled polymerization techniques. The PMMA macromonomer was obtained by high-vacuum anionic polymerization followed by the copolymerization of n-butyl acrylate and PMMA macromonomer using reversible addition−fragmentation chain transfer (RAFT) polymerization to yield the desired all-acrylic multigraft structures. The PnBA-g-PMMA multigraft structures exhibit randomly spaced branch points with various PMMA contents, ranging from 15 to 40 vol %, allowing an investigation into how physical properties vary with differences in the number of branch points and molecular weight of grafted side chains. The determination of molecular weight and polydispersity indices of both the PMMA macromonomer and the graft copolymers was carried out using size exclusion chromatography with triple detection, and the structural characteristics of both the macromonomer and PnBA-g-PMMA graft materials were characterized by 1 H and 13 C NMR. Matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry was employed for monitoring the macromonomer synthesis. Thermal characteristics of the materials were analyzed using differential scanning calorimetry and thermogravimetric analysis. The mechanical performance of the graft materials was characterized by rheology and dynamic mechanical analysis, revealing that samples with PMMA content of 25−40 vol % exhibit superior elastomeric properties as compared to materials containing short PMMA side chains or <25 vol % PMMA. Lastly, atomic force microscopy showed a varying degree of microphase separation between the glassy and rubbery components that is strongly dependent on PMMA side chain molecular weight. ■ INTRODUCTIONGraft and other branched architectures often exhibit superior physical and mechanical properties as compared to their linear counterparts, while often exhibiting lower melt viscosity and improved processability, making them attractive for numerous applications. 1−7 Thus, control of macromolecular architecture provides an avenue for tailoring materials to achieve improved performance. Architectural parameters that can be tuned with multigraft copolymers include the side chain chemical composition, molecular weight, volume fraction, and branch point symmetry, all of which influence the bulk properties, i.e., dynamics, self-assembly, and long-range nanoscale order. 8−11 More recently, the incorporation of both plastic and rubbery segments into multigraft copolymer architectures has yielded a new class of thermoplastic elastomers, termed "superelastomers", that demonstrate superior properties including improved elongation at break, lower residual strain after stretching, and a highly tunable modulus. Superelastomers are composed of a low glass transition temperature (T g ) backbone (for example, polyisoprene (PI)) with multiple high-T g side chains (for example, polystyre...

Design and Synthesis of Multigraft Copolymer Thermoplastic Elastomers: Superelastomers

“…Different factors that influence the mechanical properties of all‐acrylic multigraft thermoplastic elastomer were first discussed by Goodwin et al Their copolymers were prepared by randomly copolymerizing n ‐butyl acrylate with PMMA macromonomers of different molecular weights. As compared to linear PMMA‐ b ‐PBA‐ b ‐PMMA triblock copolymers, the PBA‐ g ‐PMMA graft copolymers exhibited an improved microphase separation.…”

Thermoplastic Elastomers Based on Block, Graft, and Star Copolymers

“…Inspired by this work, the same group prepared graft all-acrylic TPEs based on PMMA side chain and PnBA backbone [81]. The PMMA macromonomers were synthesized by living anionic polymerization and copolymerized with nBA by RAFT polymerization.…”

Design, synthesis, and characterization of lightly sulfonated multigraft acrylate-based copolymer superelastomers

“…Recently developed procedures allowed for the synthesis of PS-g-PI and all-acrylic multigra copolymers showing very good thermal and mechanical properties. [17][18][19][20] The macromonomer approach is a very useful method to synthesize multigra copolymers since it readily controls the molecular weight and polydispersity of the side chains as well as the desired average number of branch points. 21 The combination of this method with free radical polymerization provides a scalable and facile polymerization procedure with relatively good control of the molecular characteristics of the nal multigra copolymers.…”