Nitroxide-mediated Polymerization of Styrene and Limonene in the Framework of Synthesis of Potentially Functional Polymers Using Naturally Occurring Terpenes

In the framework of synthesis of potentially functional macromolecules based on commodity polymers with naturally occurring compounds, the nitroxide-mediated polymerization of styrene with limonene was investigated here. Various ratios of styrene and limonene were used, and the incorporation of limonene in the final polymer was monitored. Results from benzoyl peroxide/TEMPO-initiated polymerization showed small incorporation of limonene in the polystyrene chains, while it was also involved in forming oligomers (such as dimers or trimers). The presence of limonene resulted in a reduction in polymer average molecular weight through chain transfer reactions. From the kinetic analysis, limonene was found to inhibit styrene thermal auto-polymerization at high temperatures, acting as a radical scavenger. Using TEMPO-functionalized polystyrene macroinitiators to initiate the polymerization, no limonene oligomers in the final product were observed. Finally, when polystyrene macroinitiators and limonene were reacted in the absence of styrene monomer, limonene moieties were identified in the final polymer, resulting thus in polystyrene functionalization. This functionalization can be extended to the synthesis of novel materials based on naturally occurring terpenes, considering the variety of structures that can be obtained by applying NMP.