Chemical Cross-linking of Polypropylenes Towards New Shape Memory Polymers

In this work, syndiotactic polypropylene (sPP) as well as isotactic polypropylene (iPP) are cross‐linked to gain a shape memory effect. Both prepared PP networks exhibit maximum strains of 700%, stored strains of up to 680%, and recoveries of nearly 100%. While x‐iPP is stable for many cycles, x‐sPP ruptures after the first shape‐memory cycle. It is shown by wide‐angle X‐ray scattering (WAXS) experiments that cross‐linked iPP exhibits homoepitaxy in the temporary, stretched shape but in contrast to previous reports it contains a higher amount of daughter than mother crystals. Shape memory polypropylene is prepared by cross‐linking of syndiotactic as well as isotactic polypropylene (iPP). Cross‐linked iPP is a shape‐memory polymer with excellent stored strain, fixity‐, and recovery‐ratios. Wide angle X‐ray scattering (WAXS) experiments reveal that the crystals in programmed x‐iPP show a microstructure with mother and daughter crystals. In contrast to previous reports, the amount of daughter crystals exceeds that of the mothers.