No abstract

The value and merit of triethylborane (TEB)-based ate complexes for the synthesis of various oxygenated polymers have been recently illustrated through successful examples of homopolymerization of epoxides and of their copolymerization with CO2, CS2, COS, anhydrides, isocyanates, etc. To further expand the scope of TEB-based initiating systems to a broader family of oxygenated polymers, they were used in this study to anionically polymerize cyclic esters and to copolymerize the latter monomers with propylene oxide (PO). To promote a fast and controlled ring-opening polymerization (ROP) of cyclic esters, hydrogen-bonding donors such as amines and (thio)­ureas were added to TEB-based ate complexes used as initiators. Only under these conditions could the ROP of ε-caprolactone (CL), δ-valerolactone (VL), and l-lactide (LLA) proceed under controlled conditions with hardly detectable intra- or intermolecular transesterifications. The role of amines and (thio)­ureas when used alone or together in association with these boron-based initiators is discussed in detail. The controlled character of the polymerization of CL, VL, and LLA is attested by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF MS) and other characterization techniques. As examples of the far-reaching potential of these borane-based ate complexes, random P­(PO-co-VL) copolymers were derived by statistical copolymerization of VL with PO and various well-defined block copolymersPPO-b-PVL, PVL-b-PPO, PPO-b-PCL, PPO-b-PLLA, and PPO-b-PVL-b-PPOwere grown by sequential polymerization of the corresponding monomers.

In this report, a series of ABA triblock copolymers composed of a poly(propylene carbonate-co-propylene oxide)s (PPPC) middle block flanked by two poly(N-tosyl propylene urethane) (PTPU) outer blocks were synthesized in one-pot, using a difunctional initiator in the presence of triethyl borane (TEB). In the first step, the central PPPC block was obtained through the copolymerization of propylene oxide (PO) with CO2. Varying the polymerization pressure of CO2, the carbonate content in the PPPC central block could be adjusted, giving access to PPPC blocks with different glass transition temperatures. In the second step, p-tosyl isocyanate (TSI) was subsequently added and copolymerized with the remaining PO, affording the growth of two outer PTPU blocks without any incorporation of polyether or polycarbonate and the formation of well-defined ABA triblock copolymers as confirmed by 1H NMR and size exclusion chromatography (SEC). Their thermal and mechanical properties were measured using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and universal testing machine (UTM). PTPU-b-PPPC-b-PTPU (U-PC-U) triblock copolymers with PTPU (hard blocks) weight fraction of 28% and 80–85 wt % of carbonate content in the middle PPPC block show higher toughness than commercial polyolefins.