Fluorescent Visualization of Bond Breaking in Polymer Glasses

Mechanofluorescent polymer probes were used to visualize stresses and bond scission in polystyrene and polycarbonate. Sonication of polystyrene probes with a molar mass of 1.1 × 105 g·mol-1 in solution resulted in 30% activation after 1 h, while shorter probes showed lower activation percentages. Single-asperity sliding friction tests were performed on mechanophore-containing polystyrene and polycarbonate films. Polystyrene showed clearly visible crack formation with a correlated pattern in the friction force, penetration depth, and fluorescent activation of the mechanophore. Significant mechanophore activation in polystyrene was observed for an applied normal load of 100 mN, whereas in polycarbonate, activation only occurred at a normal load higher than 400 mN. The different degrees of activation correlate well with the toughness of polycarbonate compared to polystyrene.</p

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

High Molar Mass Polycarbonate via Dynamic Solution Transcarbonation Using Bis(methyl salicyl) Carbonate, an Activated Carbonate

High molar mass polycarbonate is synthesized via a solution transcarbonation of bis(methyl salicyl) carbonate and bisphenol-A at temperatures between 60 and 160 °C without the removal of the condensate, allowing the incorporation of thermosensitive monomers into polycarbonate. Kinetic and equilibrium studies show that the polymerization is 20–30 times faster at 120 °C compared to 60 °C, whereas the equilibrium Mw increases from 11 × 103 g mol−1 at 120 °C to 16 × 103 g mol−1 at 60 °C. This polycondensation is characterized by very high equilibrium constants ranging from 0.8 × 103 at 160 °C to 4.1 × 103 at 60 °C, corresponding to standard enthalpies and entropies of polymerization: −19 kJ mol−1 < ΔH0 < −11 kJ mol−1 and 13 J mol−1 K−1 < ΔS0 < 28 J mol−1 K−1. Without removal of the condensate, the system is shown to be dynamic and completely reversible when changing the temperature. Good predictability of this polycondensation is reported, where only at very low starting monomer concentrations, the formation of cyclics leads to deviations from the predicted behavior