External and Reversible CO₂ Regulation of Ring-Opening Polymerizations Based on a Primary Alcohol Propagating Species

We report the use of an organic catalyst system capable of switching between active and dormant propagating states during the ROP of cyclic monomers. While the ROP of both ε-caprolactone and trimethylene carbonate proceeds under nitrogen, the simple addition of CO₂ results in a dormant “off” state. Cycling between atmospheres provides the ability to regulate the molecular weights of the resulting polymers without appreciable loss of catalytic activity for several “on/off” cycles

Poly(ω-pentadecalactone)‑<i>b</i>‑poly(l‑lactide) Block Copolymers via Organic-Catalyzed Ring Opening Polymerization and Potential Applications

Poly­(pentadecalactone)-<i>b</i>-poly­(l-lactide) (PPDL-<i>b</i>-PLLA) diblock copolymers were prepared via the organic catalyzed ring-opening polymerization (ROP) of l-lactide (l-LA) from PPDL macroinitiators using either 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU) or 1,5,7-triazabicyclo[4.4.0]­dec-5-ene (TBD). Synthesis of PLLA blocks targeting degrees of polymerization (DP) up to 500 were found to yield diblock copolymers with crystalline PPDL and PLLA segments when TBD was used as the catalyst. The synthesis was further improved in a one-pot, two-step process using the same TBD catalyst for the synthesis of both segments. The application of these diblock copolymers as a compatibilizing agents resulted in homogenization of a biobased PLLA/poly­(ω-hydroxytetradecanoate) (90:10) blend upon a melt-process, yielding enhanced material properties

Design of Multistimuli-Responsive Shape-Memory Polymer Materials by Reactive Extrusion

Shape-memory polymers (SMPs) are a class of stimuli-responsive materials that have attracted tremendous attention in various applications, especially in the medical field. While most SMPs are thermally actuated, relating to a change of thermal transition (e.g., melting temperature), SMPs that can be actuated upon exposure to light are emerging. Recently, there has been new interest into multiple stimuli-responsive SMPs in order to cover the range of applications for these smart materials. In this work, poly­(ester-urethane)­s (PURs) made of heating-responsive poly­(ε-caprolactone) (PCL) segments of various degrees of crystallinity and photoresponsive <i>N</i>,<i>N</i>-bis­(2-hydroxyethyl) cinnamide (BHECA) monomer were successfully prepared using reactive extrusion technology to design dual-stimuli-responsive SMPs (DSRSMP). In order to tune the SMP properties (temperature or light), the crystallinity of the PCL segment was finely adjusted by the copolymerization of ε-caprolactone with para-dioxanone in bulk at 160 °C using tin­(II) octoate. The resulting polyester segments were then coupled with BHECA using <i>n</i>-octyl diisocyanate at 130 °C. The SMP properties of resulting PURs were correlated with DSC and DMTA measurements. Further addition of di- and tetracinnamate PCL segments into these SMPs was also studied in order to enhance the photoactuated SMP properties