Incorporation of POSS to improve thermal stability of bio‐based polymethacrylates by nitroxide‐mediated polymerization: Polymerization kinetics and characterization

Nitroxide‐mediated polymerization (NMP) was used to polymerize methacrylate‐functionalized polyhedral oligomeric silsesquioxane, POSSMA, in a controlled manner with bio‐based C13 methacrylate (C13MA) to improve the thermal stability of the latter by copolymerization (using 10 mol% acrylonitrile controlling comonomer). Kinetic experiments (80–110 °C) revealed the relatively low ceiling temperature of POSSMA (135 °C). Synthesis of poly(POSSMA‐ co ‐AN) with f AN , 0 = 0.10 at 90 °C resulted in low dispersity (1.16) and relatively high conversion (~50%) after 3 hr in 50 wt% toluene. Assuming binary statistical copolymerizations, POSSMA was slightly less reactive than C13MA toward the propagating species ( r POSSMA = 0.91 ± 0.07 and r C13MA = 1.94 ± 0.13). Incorporating POSSMA up to 68 mol% improved decomposition temperature of C13MA‐based copolymers from 190 to 262 °C. Chain end fidelity of POSSMA‐rich compositions was confirmed by subsequent chain extensions to make block and gradient copolymers. Differential scanning calorimetry revealed multiple transition temperatures in block copolymers, suggesting microphase separation. Powder X‐ray diffraction confirmed crystalline domains ~30 nm in POSSMA‐rich statistical copolymers while transmission electron microscopy revealed weakly ordered lamellar morphology for poly(C13MA‐ co ‐AN)‐ b ‐(POSSMA‐ co ‐AN) block copolymer at a smaller length scale. Oscillatory shear measurements of block copolymers indicated primarily viscous character below 200 s −1 but crossover above this frequency, indicating POSS–POSS interactions were increasing the elasticity of the block copolymers.