Commercial aminoalcohols, namely, 2-(methyl amino)­ethanol (1) and diethanolamine (2), are investigated as direct initiators, i.e., with no need of protection of the hydroxyl groups, for the N-heterocyclic carbene-organocatalyzed ring-opening polymerization (NHC-OROP) of 2-methyl-N-p-toluenesulfonyl aziridine. NHC-OROP’s are performed at 50 °C in tetrahydrofuran, in the presence of 1,3-bis­(isopropyl)-4,5­(dimethyl)­imidazol-2-ylidene (Me5-IPr) as organocatalyst. Thus, nonprotected and nonactivated aminoalcohol initiators 1 and 2 provide a direct access to metal-free α-hydroxy-ω-amino- and α,α′-bis-hydroxy-ω-amino telechelics on the basis of polyaziridine (PAz), respectively. Excellent control over molar masses, narrow dispersities ( Đ ≤ 1.20), and high chain-end fidelity are evidenced by combined analyses, including NMR spectroscopy, size exclusion chromatography, and MALDI ToF mass spectrometry. The amino-initiated NHC-OROP is therefore tolerant to the presence of nonprotected hydroxyl group(s). The as-obtained hydroxyl-ended PAz can be further derivatized in reaction with phenyl isocyanate, highlighting the accessibility of the hydroxyl groups in α-position. Moreover, block copolymer synthesis can be readily achieved by sequential NHC-OROP of 2-methyl-N-p-toluenesulfonyl aziridine and l-lactide, from 1 used in this case as a double-headed initiator. Remarkably, each of the two NHC-OROP steps proves highly chemoselective, with PAz and poly­(l-lactide) (PLLA) segments being grown from the secondary amino- and the primary hydroxy- function, respectively. In this way, a well-defined PAz-b-PLLA diblock copolymer is synthesized in the presence of the same Me5-IPr organocatalyst, i.e., following a completely metal-free strategy.

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This work focuses on the temperature-dependent structural and rheological characterization of polystyrene- b-poly( n-butyl acrylate)- b-polystyrene triblock copolymers (PS- b-P nBA- b-PS) in the melt and, in particular, on their ability to show a lower disorder-to-order temperature (LDOT). To this aim, copolymers of varying block lengths, but keeping the P nBA block as a major component, were synthesized. Small-angle x-ray scattering revealed that the copolymers with short PS blocks (∼10 kg/mol) approach an LDOT but do not cross it. At room temperature, these copolymers exhibit higher moduli compared to a P nBA homopolymer due to the reinforcing effect of the PS but are flowing at temperatures above the glass transition of the PS. Increasing the PS and P nBA block length, to keep the same PS fraction, induces more profound changes in the structural and viscoelastic behaviors. Such a copolymer crosses the LDOT, leading to a microphase-separated and ordered state at high temperature. Contrary to the copolymers with short PS blocks, the flow regime was not reached, even at temperatures well above the glass transition of the PS. Instead, a low-frequency plateau was observed in rheology, showing the increased lifetime of the microphase-separated PS domains. ABA triblock copolymers exhibiting an LDOT behavior could, thus, be of interest for the design of thermoplastic elastomers or pressure-sensitive adhesives that can resist the flow at high temperatures.