Ecofriendly Autoxidation of Castor Oil/Ricinoleic Acid. Multifunctional Macroperoxide Initiators for Multi Block/Graft Copolymers

Ecofriendly autoxidation is a reaction of air oxygen with unsaturated organic molecules at room temperature. Castor oil and ricinoleic acid were ecofriendly autoxidized for 5 months to obtain castor oil macroperoxide with a Mn of 1935 g mol⁻¹ (Pcast5m) and the ricinoleic acid macroperoxide initiator (Prici5m) with a Mn of 1169 g mol⁻¹. Peroxide groups thermally initiated the free radical polymerization of methyl methacrylate (MMA), n-butyl methacrylate (nBMA), and styrene (S). Peroxide formation in the oxidized castor oil and ricinoleic acid was confirmed using iodometric analysis, elemental analysis, and differential scanning calorimetry technique. Peroxide decomposition in both macroperoxide initiators was observed at 166 °C for Prici5m and 170 °C for Pcast5m. Hydroxyl groups of Pcast5m were reacted with methacryloyl chloride to obtain methacrylated castor oil macroperoxide (PcastMA). The polymerization rates of the obtained macroinitiators were compared. The polymerization rate order is Pcast5m > Prici5m > PcastMA. Polymerization of styrene by PcastMA resulted in an increase in molar masses and an increase in the polymerization time while those of the styrene polymerization by Pcast5m and Prici5m remained constant. Carboxylic acid groups were reacted with amine-terminated polyethylene glycol (PEG), polydimethyl siloxane (PDMS), and polytetrahydrofuran (PTHF) while the hydroxyl functionality initiated the ring-opening polymerization of ε-caprolactone (CL). Prici-PEG-PMMA, Prici-PS-PDMS, Prici-PS-PTHF, Pcast-PS-PCL, Pcast-PCL-PMMA, and Pcast-PS-PnBMA multiblock copolymers were prepared and characterized using spectrometric, thermal, and stress–strain measurement techniques.