Pyranine Based Ion-Paired Complex as a Mechanophore in Polyurethanes.

A new mechanophore for polyurethane thermoplastic elastomers based on ion-paired complexes is developed. 8-(2-hydroxyethoxy)pyrene-1,3,6-trisulfonate (HEPTS) is incorporated into polyurethanes as an end-capper and aggregates in apolar media. Aggregation of the ionic HEPTS end groups in solution depends on concentration solvent polarity. The addition of dimethylformamide to a tetrahydrofuran solution of the polymer results in the dissociation of the aggregates and a significant shift in fluorescence emission from yellow to blue. The same shift in fluorescence emission is induced by stretching the solid polymer at strains larger than 1 and stresses above 7.5 MPa, with a clear increase above 12.5 MPa. Strain induced dissociation of HEPTS aggregates not attached to the polymer chain leads to fluorescence changes that are much less reproducible.

Light-Induced RAFT Single Unit Monomer Insertion in Aqueous Solution-Toward Sequence-Controlled Polymers.

First report on the sequential, visible light-initiated, single unit monomer insertion (SUMI) of N,N-dimethylacrylamide (DMAm) into the reversible addition fragmentation chain transfer (RAFT) agent, 4-((((2-carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid (CTA1 ), in aqueous solution is provided. The specificity for SUMI over formation of higher oligomers and/or RAFT agent-derived by-products is higher for longer irradiation wavelengths. Red light provides the cleanest product (selective SUMI), showing a linear pseudo-first order kinetic profile to high (>80%) conversion, but also the slowest reaction rate. Blue light provides a relatively rapid reaction, but also gives some by-products (<2%) and the kinetic profile displays a conversion plateau at >65% conversion. Higher specificity with red light is attributed to CTA1 absorbing at longer wavelengths than the SUMI product, which allows selective excitation of CTA1 . The use of a higher reaction temperature (65 °C vs ambient) results in a higher reaction rate and a reduction in oligomer formation.