Castor Oil-Based Bioplastics via Polyesterification: Synthesis, Characterization, and Functionalization

Synthesis and application of biobased polymers are at the forefront of polymer science. Herein, we report the synthesis, characterization, and functionalization of castor oil-based bioplastics. At first, polymer P1 was synthesized via polyesterification by using monomer 11-bromoundecanoic acid (1) to demonstrate the feasibility of this step-growth polymerization method. The success of this polycondensation technique relies on the high substitution efficiency between terminal groups, carboxylic acid, and carbon-bromide moieties under alkaline conditions. Subsequently, copolymers P2–P5 with varied compositions were obtained by random copolymerization of monomers 1 and 6-bromohexanoic acid (2) in different feed ratios. Linear positive correlation is disclosed between the crystallization (Tc) and melting (Tm) temperatures of P1–P5 and the molar fraction of 1 within these specimens. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) results illustrate good crystallinity of these bioplastics. Furthermore, the degradation of polymers P1–P5 is propelled by an external basic environment while hindered by their intrinsic hydrophobicity, indicating that alkalinity and composition are two essential factors to manipulate the degradation behaviors of biobased polyesters in the bulk state. Ultimately, polymerization of 1 in the presence of 1-pyrenebutyric acid (3), an end-capping agent, was carried out to yield α-pyrene functionalized polymer P7. This material is capable of serving as a practical fluorescent probe and multiwalled carbon nanotube (MWNT) dispersion stabilizer. Polyesterification reported herein represents a facile and cost-effective synthetic strategy and shows great prospects in sustainable polymer materials.