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 degrees C) revealed the relatively low ceiling temperature of POSSMA (135 degrees C). Synthesis of poly(POSSMA-co-AN) with f(AN,0) = 0.10 at 90 degrees C resulted in low dispersity (1.16) and relatively high conversion (similar to 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 degrees 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 similar to 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.