Organocatalytic Ring-Opening Polymerization Strategies for Synthesis of Poly(phosphothioesters) with a Pendent Phenyl Group

Abstract

A novel type of phosphothioester substrate, 2-phenyl-1,3,2-dioxaphospholane 2-sulfide (PTP), has been synthesized and subjected to ring-opening polymerization. DBU/thiourea served as an efficient cooperative organocatalyst for the synthesis of poly(PTP), delivering the polymer with a well-defined structure, a relatively narrow molecular-weight distribution (1.14–1.20), and high molecular weight (up to 45.2 kg/mol). The ring-opening polymerization process showed a controlled/living nature. In addition, diblock copolymers of PTP with rac-lactide with well-defined structures were also synthesized.

Key words

organocatalysis - ring-opening polymerization - polyphosphothioesters - living polymerization - phenyldioxaphospholane sulfide - block copolymerization

• References and Notes

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• 22 Poly(2-phenyl-1,3,2-dioxaphospholane 2-sulfide) (Table [1], Entry 9) In a typical polymerization reaction, a 5 mL Schlenk tube equipped with a stirring bar was dried and charged with argon three times, and then placed in a glovebox. In the glovebox, TU (7.4 mg, 0.02 mmol), a 1 M solution of DBU in toluene (20 μL, 0.02 mmol), a 1 M solution of PPA in toluene (20 μL, 0.02 mmol), CH₂Cl₂ (0.5 mL), and PTP (100 mg, 0.5 mmol) were added sequentially to the Schlenk tube. The tube was then removed from the glovebox and kept in an ice bath for 20 min. The reaction was quenched by addition of a 1 M solution of AcOH in CH₂Cl₂ (50 μL). The polymer was precipitated several times from cold Et₂O, and dried under vacuum to a constant weight. The molecular-weight distribution and number-average molecular weight of the polymer were determined by GPC: M _n = 4400 g/mol; Ð = 1.19.