Sequence-Controlled Copolymerization of Salicylic O-Carboxyanhydrides by Organocatalysts

Abstract

The composition sequence of a copolymer is intricately linked to its physical and mechanical properties. However, achieving chemical selectivity for copolymerization monomers and controlling the sequence structure of copolymers remain a challenge. This study delves into a strategy that involves tuning the organocatalyst transition from hydrogen bonding interaction to ionic pair to realize copolymerization sequence control in one-pot reactions. Ring-opening copolymerization (ROCOP) of salicylic acid O-carboxyanhydride (SAOCA) and its analogous monomers, including 5-methylsalicylic acid Ocarboxyanhydride (5-MeSAOCA) and 4-fluor-salicylic acid Ocarboxyanhydride (4-FSAOCA), is successfully conducted in tetrahydrofuran (THF) at ambient conditions, resulting in narrow chain distributions (Đ < 1.25). This accomplishment is made possible by utilizing a catalytic combination of 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU) and thioureas (TUs) with varying pK a values. The acidity of TU influences its interaction with DBU to generate the transition states of hydrogenbonding or ionic pair, while the quantity of TU affects the steric hindrance around the anion; both are crucial factors in regulating the sequence distribution of PSA-series copolymers ranging from random to block architecture.