Betulin and Betulinic Acid-Derived Thermoplastics: Where Is the Upper Limit of the Glass Transition Temperature for Alicyclic Biobased Polymers?

Biobased polymers have long been recognized as alternatives to fossil-based counterparts. Although tremendous progress in this field has been witnessed in the last decades, performance-advantaged biobased polymers are still rarely reported. Herein, betulin and betulinic acid-derived high glass transition temperature ( T g ) thermoplastics are prepared and preliminarily developed as functional materials. At first, norbornene derivatives (monomers M1 and M2 ) having betulinic units were obtained by means of esterification. Subsequently, homopolymers P1 and P2 in conjunction with statistical copolymers P3 - P6 were synthesized via ring-opening metathesis polymerization (ROMP). In spite of their amorphism, these samples all possess T g s exceeding 202.5 °C owing to the bulkiness and rigidity of their alicyclic pendent groups. Notably, an increase in T g is observed as the molar fraction of the M1 unit becomes pronounced within the polymer composition. In particular, homopolymer P1 exhibits an exceptionally high T g at 241.6 °C among alicyclic biobased polymers. Meanwhile, these specimens show good thermal stability, reprocessability, anticorrosiveness, hydrolysis resistance, and high tolerance to boiling water/nonsolvent given the hydrophobicity and structural rigidity of their frameworks. On the other hand, homogeneous mixing inorganic fillers (e.g., toner, magnetite, and terbium-containing particles) with these polymer matrices readily produce colored, magnetic, and phosphorescent hybrid materials. Furthermore, a postmodification strategy was employed to create fluorescent polymer P7 by anchoring pyrene units on the side chains of pristine polymer P1 . This modified polymer can be potentially used in information encryption (optical anticounterfeiting).