Episulfide Anionic Ring-Opening Polymerization Initiated by Alcohols and Primary Amines in the Presence of γ-Thiolactones

Abstract

Among the sulfur-containing polymers, polythioethers remains very attractive structures due to their high sulfur atom content, making them interesting candidates for various industrial applications, for example in the fields of energy storage or biomedical applications.Although anionic ring-opening polymerization of episulfides is known since decades, only a limited number of efficient initiating systems enable the synthesis of well-defined polymer chains. In this work, a one-pot, two step method was developed in order to efficiently initiate the anionic ring-opening polymerization of propylene sulfide with alcohol or amine moieties using the latent thiol functionality of γ-thiolactones. First, the ring-opening of γ-thiolactones by alcohols or amines was investigated in the presence of various bases (BEMP, DBU, DMAP, tBuP 1 and tBuP 4 ). Then, the polymerization conditions were optimized allowing the synthesis of well-defined α,ω-heterotelechelic poly(propylene sulfide)s with controlled molar mass up to 10 kg.mol -1 as evidenced by SEC, 1 H, 13 C, and 2D NMR and MALDI-TOF mass spectrometry. Depending on the initiating function (alcohol or amine), the initiator and the polythioether chains are connected either by an ester or by an amide bond. The stability of these bonds was studied under basic conditions.

Recent advances in the ring-opening polymerization of sulfur-containing monomers

“…Polymerization experiments focused on the anionic ROP of thiirane derivatives revealed that simple and diverse nucleophiles can be utilized as initiators. 73 In particular, thiolate species derived from thiols have been demonstrated as promising initiators for the ROP of propylene sulfide (M34) (Scheme 15a), resulting in pure regiochemical regulation (i.e., head-to-tail microstructure) within the polymer backbone. [74][75][76] Interestingly, anionic ROP initiated by thiolates has been demonstrated to follow first order kinetics, hence possessing 'living' character.…”

Thiolactone chemistry, a versatile platform for macromolecular engineering

“…Very recently, BTL was used to introduce an ester linker between an hydroxy initiating compound and a polythioether chain. 66…”

“…Very recently, BTL was used to introduce an ester linker between an hydroxy initiating compound and a polythioether chain. 66 The group of Albertson studied the thiolation of hemicellulose using γ-thiobutyrolactone. 70 In the absence of a catalyst, hemicellulose hydroxyl groups are not sufficiently strong to undergo the 1,2-nucleophilic addition leading to the ringopening of the thiolactone ring.…”

“…3 AROP of propylene sulfide initiated using benzyl amine/BTL as initiating system in the presence of BEMP superbase. 66 Fig. 4 CALB-catalyzed caprolactone polymerization and subsequent thiolation with BTL.…”

“…Figure3. AROP of propylene sulfide initiated using benzyl amine / BTL as initiating system in the presence of BEMP superbase 66. …”