High Molecular‐Weight Cyclic Polyesters from Solvent‐Free Ring‐Opening Polymerization of Lactones with a Pyridyl‐Urea/MTBD

Abstract

(Thio)urea/base systems have been widely used in the ring‐opening polymerization (ROP) of lactones based on their superior performance in activity and selectivity. Herein, a pyridyl‐urea (6C‐PU)/7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene catalytic system is used to prepare the polyesters with cyclic topology via the ROP of lactones in the absence of initiator under solvent‐free conditions. The catalytic system shows high activity in the ROP of δ‐valerolactone (δ‐VL) and cyclic polyvalerolactones (PVLs) with high molecular weights and narrow molecular weight distribution are obtained despite the existence of some linear products generated during the precipitation process. The structure of the resulting polymers is determined by proton and carbon nuclear magnetic resonance spectra, matrix assisted laser desorption/ionization time of flight mass spectrometry, and intrinsic viscosity studies. A possible mechanism is proposed on the basis of NMR analysis and characteristics of polymerization. Thermal and mechanical properties of cyclic PVLs are investigated through differential scanning calorimetry, thermogravimetric analysis, and tensile test.

Bifunctional and Recyclable Polyesters by Chemoselective Ring-Opening Polymerization of a δ-Lactone Derived from CO2 and Butadiene

“…Consequently, chemoselective ring-opening homopolymerization of EVP should provide opportunities for post-functionalization of polyesters, via hydrolysis, click reaction, and cross-linking, thus opening new avenues for the synthesis of CO2-based polymers with tailor-made structures and properties. [37][38] Using a synergistic organobase/urea binary catalytic system, [39][40][41][42] the chemoselective ROP of α-methylene-γ-butyrolactone (MBL) and α-methylene-δ-valerolactone (MVL) producing unsaturated polyesters has been achieved. [43][44] The anion generated by deprotonation of urea with the organobase effectively promotes the lactone ROP rather than the vinyl-addition polymerization of the exocyclic C=C double bond.…”

Cyclodextrin-Oligocaprolactone Derivatives—Synthesis and Advanced Structural Characterization by MALDI Mass Spectrometry

“…PCLs have been prepared previously with very good results using alcohol initiators and various organocatalysts, such as acids [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ] and binary systems comprised of thioureas with different bases [ 36 , 37 , 38 , 39 ] or with trifluoroacetic acid [ 40 ], as well as mixtures of DMAP and its protonated form with trifluoromethanesulfonic acid [ 41 ]. In general, acid organocatalysts are more active for the ring-opening of ε-CL, but when dealing with CDs as initiators, the organocatalysts have to be carefully chosen, as CDs may undergo hydrolysis in acidic media—which increases with temperature and concentration [ 2 ]; however, in basic media, CD molecules are stable.…”