Effect of Short-Chain Branching on the Rheology of Polyolefins

Rheology and Tack Properties of Biodegradable Isodimorphic Poly(Butylene Succinate)-Ran-Poly(e-Caprolactone) Random Copolyesters and Their Potential Use as Adhesives

The sole effect of the microstructure of biodegradable isodimorphic poly(butylene succinate)-ran-poly(ε-caprolactone) random copolyesters on their rheological properties is investigated. To avoid the effect of molecular weight and temperature, two rheological procedures are considered: the activation energy of flow, E_a, and the phase angle versus complex modulus plots. An unexpected variation of both parameters with copolyester composition is observed, with respective maximum and minimum values for the 50/50 composition. This might be due to the peculiar chain configurations of the copolymers that vary as a function of comonomer distribution within the chains. The same chain configuration variations are responsible for the isodimorphic character of the copolymers in the crystalline state. Tack tests, performed to study the viability of the copolyesters as environmentally friendly hot melt adhesives (HMA), reveal a correlation with rheological results. Tackiness parameters, particularly the energy of adhesion obtained from stress-strain curves during debonding experiments, are enhanced as melt elasticity increases. Based on the carried-out analysis, the link microstructure-rheology-tackiness is established, allowing selecting the best performing HMA sample considering the polymer chemistry of the system.

Dynamics and healing behavior of metallosupramolecular polymers

Self-healing or healable polymers can recuperate their function after physical damage. This process involves diffusion of macromolecules across severed interfaces until the structure of the interphase matches that of the pristine material. However, monitoring this nanoscale process and relating it to the mechanical recovery remain elusive. We report that studying diffusion across healed interfaces and a correlation of contact time, diffusion depth, and mechanical properties is possible when two metallosupramolecular polymers assembled with different lanthanoid salts are mended. The materials used display similar properties, while the metal ions can be tracked with high spatial resolution by energy-dispersive x-ray spectrum imaging. We find that healing actual defects requires an interphase thickness in excess of 100 nm, 10 times more than previously established for self-adhesion of smooth films of glassy polymers.

Mechanoresponsive, Luminescent Polymer Blends Based on an Excimer-Forming Telechelic Macromolecule

A well-known approach toward mechanochromic polymers relies on the incorporation of excimer-forming fluorophores into a matrix polymer and the disruption of aggregated chromophores when such materials undergo macroscopic mechanical deformation. However, the required aggregates and stress-transfer processes have so far only been realized with select dye/polymer combinations. As demonstrated here, the utility of this approach can be extended by tethering an excimer-forming cyano-substituted oligo(p-phenylene vinylene) fluorophore to the two ends of a telechelic poly(ethylene-co-butylene) and blending small amounts (0.1-2 wt%) of the resulting aggregachromic macromolecule into polymer matrices such as poly(ε-caprolactone), poly(isoprene), or poly(styrene-b-butadiene-b-styrene). All blends display mechanofluorochromic responses, and the ratio between the monomer and excimer emission intensities can be used to correlate the luminescence signal to the extent of deformation and to follow subsequent relaxation processes. The developed approach significantly expands the scope of blend-based mechanoresponsive luminescent materials.