On the Mechanism of the Ring‐Expansion Polymerization of Thiiranes

Abstract

Ring polymers are synthesized using a cyclic bifunctional thioester as initiator for REP of thiiranes. PMT yields satisfactory results, whereas polymerization with MT appears to develop dead polymeric material as by‐product and TBMT gives only negligible conversion rates. The process produces high yields and high conversion rates. The corresponding molecular weight distributions show increasing broadening and multimodal character with increasing reaction time due to thermodynamically controlled ring‐merging reactions between macrocycles. The polymerization rate of PMT obeys a pseudo first‐order kinetics with an activation energy of 38.8 kJ mol−1. 1H NMR, ESI‐MS, and glass transition temperatures independent of the molecular weight demonstrate the presence of cyclic polymer. magnified image

Titin-mimicking polycyclic polymers with shape regeneration and healing properties

“…The general ring expansion process used for this synthesis is described in our former work in detail. 29,30 To incorporate the necessary H-bonding functionality, a novel monomer 3 (see Fig. 1), which is structurally similar to 2-( phenoxymethyl)thiirane (PMT, 2), which we studied extensively in earlier work, was synthesized in a convenient five-step process (see ESI †).…”

“…In contrast to the functional polymer of the Guan group, which was mainly formed in a multistep organic synthesis approach, we here propose a more modular polymer chemistry approach towards the mimicking of titin's structure, which is easier to implement and provides higher flexibility in terms of polymer properties. Based on the living-like ring-expansion polymerization of thiiranes developed by Nishikubo et al, 27,28 which was investigated intensively by our group, 29,30 we synthesized a cyclic triblock-copolymer as precursor, which contains self-complementary hydrogen-bonding moieties that may reversibly unfold (see Scheme 1). Dialing the exact composition of this ring polymer containing three different monomers provided the possibility of tuning the stiffness of the targeted material.…”

“…Dialing the exact composition of this ring polymer containing three different monomers provided the possibility of tuning the stiffness of the targeted material. The overall ring size of the precursor was, on the one hand, adjusted via the block lengths of the individual blocks; on the other hand, it was taken advantage of the ring-merging mechanism (cross-over ring fusion) occurring in these ring-expansion polymerizations, 29,30 by which the amount of doubled macrorings could be controlled. We could thus easily incorporate at least two hydrogen-bonding blocks per ring polymer, which is necessary for the intramolecular interaction within the ring (see Scheme 1).…”

Controlled ring‐expansion polymerization of thiiranes based on cyclic aromatic thiourethane initiator

“…Cyclic polysulfides have been reported to show higher glasstransition temperature (T g ) than linear polysulfides, 39,48 which is one of the characteristic properties of cyclic polymers without chain terminus. 49,50 On the other hand, the trend of the T g s of a series of cyclic polysulfides with different ring sizes are yet to be reported.…”

A Catalyst‐Free and Chemoselective Synthesis of Episulfides from Epoxides in 2,3‐Butanediol without Formation of Poly(episulfide)s

“…Accordingly, various methods for the synthesis of episulfides have been developed. One of the most common process is transformation of epoxy ring into thiirane ring with thiourea, ammonium thiocyanate (NH 4 SCN) or potassium thiocyanate (KSCN), including metal complexes, silica‐supported catalysts, polymer catalysts, ionic liquids, water, methanol (MeOH) and so on . However, many of these reactions involve the use of acidic, oxidizing or high‐temperature conditions, and also entail undesirable polymerization of highly reactive episulfides.…”