Melt memory of a spherulite nucleus formed through a seeding process in the crystal growth of isotactic polystyrene

Abstract

The melt memory effect on the crystal growth of isotactic polystyrene is investigated using optical microscopy. After a spherulite is melted at a slightly higher temperature than the melting point and completely disappears, a polymer crystal nucleates and grows at the same position as the original spherulite when the temperature is decreased below the melting point. After the melting-recrystallization processes are repeated by raising and lowering the temperature, the melt memory effect becomes weak. This effect completely disappears at~40°C above the equilibrium melting point when the melt temperature is gradually increased during the melting-recrystallization processes. The formation of spherulite nuclei is promoted by the seeding process, which consists of the following consecutive procedures: quenching a sample to a temperature below the glass transition temperature and annealing the sample slightly above the glass transition temperature. At the initial stage, the number density of spherulites rapidly decreases with the cumulative melting time. After the initial stage, the number density of spherulites exponentially decays with the cumulative melting time and approaches a finite value. This asymptotic value decreases with the melt temperature.

Effect of annealing time and molecular weight on melt memory of random ethylene 1‐butene copolymers

“…However, Hashimoto et al . have recently reported an increase of characteristic times for iPS, related to the decrease of nuclei density upon melt annealing, with increasing melt temperature …”

“…Even at 250 °C, ca 300 min of annealing is required for erasing persistent memory of the flow‐induced precursors. Hashimoto et al . also demonstrated by time‐dependent experiments with isotactic polystyrene (iPS) that spherulite nuclei formed by quenching and subsequent annealing are more stable and persist longer in the melt compared to those formed just by quenching or only by annealing.…”

Melt Memory Effect beyond the Equilibrium Melting Point in Commercial Isotactic Polybutene-1

“…The temperature to desorb chains may be rather high and eventually leads to the melt memory effect even though the sample is heated above the equilibrium melting temperature of the crystals. , This melt memory effect is confirmed to have rather good repeatability in this commercial i PB sample so that additives in the production formulation play an important role in this case. We noticed that in other cases of the melt memory effect beyond the equilibrium melting point, such as isotactic polybutene, isotactic polystyrene, and trans -1,4-polyisoprene, the used samples were all commercial samples. Therefore, one should be cautious when investigating the memory effect of the commercial samples.…”