Alternating Copolymerization of Epoxides and Isothiocyanates to Diverse Functional Polythioimidocarbonates and Related Block Polymers^†

Abstract

Comprehensive SummarySynthesis of diverse polythioimidocarbonates via ring‐opening copolymerization of epoxides and isothiocyanates catalyzed by organoboron catalyst was reported herein. Both aromatic and aliphatic isothiocyanates underwent successful copolymerization with terminal and internal epoxides, allowing for the precise tuning of the performance of the resultant copolymers over a broad range. The wide scope of available isothiocyanates and epoxides enables the direct construction of sulfur‐containing functional polymers featuring both high glass transition temperature and refractive index. Additionally, it was observed that aromatic isothiocyanates polymerize much faster than aliphatic ones, and the reactivity difference facilitated the one‐step synthesis of block polymers from mixed aromatic isothiocyanates, aliphatic isothiocyanates and epoxides due to the preferential incorporation of aromatic isothiocyanates than the aliphatic analogues during their alternating copolymerization with epoxides. The produced polythioimidocarbonates can be used as positive resists for electron beam lithography (sensitivity of 130 μC/cm2 and contrast of 1.53 for poly(CHO‐alt‐EITC)). Coupling with their high refractive index (1.58‐1.68), polythioimidocarbonates might find functional applications in optics. These results render ring‐opening copolymerization of epoxides and isothiocyanates a facile route to enrich functional polymer library.This article is protected by copyright. All rights reserved.

Organoboron-mediated polymerizations

“…Isothiocyanates bear similar cumulated double bonds to isocyanates, and their copolymerization with epoxides in the presence of organoboron was also investigated by Zhao 280,281 and Wu's groups. 282 It was discovered that isothiocyanates displayed inferior reactivity to isocyanates, which might originate from the lower electron withdrawing ability of the sulfur atom compared to the oxygen atom. Interestingly, common side reactions in the ROCOP of epoxides/isocyanates such as trimerization and cyclization were almost eliminated.…”

Terpolymerizations of cyclohexene oxide, CO2, and isocyanates or isothiocyanates for the synthesis of poly(carbonate–urethane)s or poly(carbonate–thioimidocarbonate)s

“…11 On the other hand, the epoxide/isothiocyanate ROCOP for the synthesis of poly(thioimidocarbonate)s (PTICs) was reported by three groups independently in 2021, and strong bases were used to activate isothiocyanates with poor reactivity as compared with isocyanates. 12 These pioneering works suggest that the terpolymerizations of epoxides, CO 2 , and isocyanates or isothiocyanates might be difficult to achieve especially with a single catalyst because the ideal reaction conditions for the epoxide/CO 2 ROCOPs are quite different from those for the epoxide/iso(thio)cyanate ROCOPs.…”

Easy Synthetic Access to High‐Melting Sulfurated Copolymers and their Self‐Assembling Diblock Copolymers from Phenylisothiocyanate and Oxetane

“…[15] Much work has focused on the copolymerization of substituted epoxides to produce polythiocarbonates. [16][17][18][19][20][21][22][23][24][25][26][27] However, these polymers are amorphous if the tacticity of the resulting stereocenter is not controlled. In contrast, unsubstituted epoxides, namely ethylene oxide, can lead to semi-crystalline materials in the ROCOP with sulfurated comonomers, as in this case, no tacticity control is required.…”