Two new remendable highly cross-linked polymers, 2ME4F and 2MEP4F, were prepared
without solvent. Solid-state NMR (nuclear magnetic resonance) was used to study the thermal reversibility
of Diels−Alder (DA) cross-linking, and it was found that DA connections and disconnections of both
polymers are thermally reversible. Differential scanning calorimeter and dynamical mechanical analysis
were applied to study thermal and mechanical properties of these materials, and it is found that the
glass transition temperature (T
g) of 2ME4F is about 30−40 °C and that of 2MEP4F is about 80 °C. A
qualitative study of the healing efficiency of 2MEP4F showed that cracks can be healed effectively with
a simple thermal healing procedure. This process can be repeated to heal cracks multiple times.
In this work, an impact copolymer polypropylene (ICPP) was separated into 4 fractions, A, B, C, and D. The phase structure, thermal behavior, and crystalline morphology of the ICPP and its 4 fractions were studied thoroughly using scanning electron microscopy (SEM). Dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and polarized light microscopy (PLM). Results of SEM and DMA show that ethylene-propylene rubber (EPR) and part of the ethylene-propylene segmented copolymer disperse as toughening particles in the ICPP. The size and size distribution of these particles are determined by chain structure of the fractions of ICPP. From fraction A to fraction D, the morphology changes from noncrystalline to semicrystalline gradually, as shown by DSC. DSC results also indicate that thermal behavior of the ICPP agrees greatly with its chain structure. PLM demonstrates that it is difficult for the ICPP to grow perfect spherulites, that is, partially, because the matrix of ICPP, fraction D, has defects in its macromolecular chain. Another cause is that there is a good compatible structure in the ICPP and so the noncrystalline component (including all fractions) hinders the growth of the spherulite.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.