Melt memory in propene–pentene isotactic copolymers: the case of defects hosted in the crystals

Abstract

Incorporation of pentene in isotactic polypropylene produces a memory of the crystalline state in the melt that persists up to temperatures higher than the melting temperature giving self-nucleation and favoring crystallization of the γ form.

The Influence of Thermal Parameters on the Self-Nucleation Behavior of Polyphenylene Sulfide (PPS) during Secondary Thermoforming

“…Furthermore, within the processing melt temperature range of 292-323 • C, the SN behavior of PPS remains unchanged with temperature variations [26]. A similar melt memory effect is observed in many copolymers [27][28][29][30][31][32] and some homopolymers [33][34][35][36][37][38]. They all demonstrate SN behaviors a few to several tens of degrees above their melting point.…”

Melt memory in random ethylene-1-alkene copolymers

“…Similar observations were reported by De Rosa et al in the a-phase of propylene-pentene isotactic copolymers, which were ascribed to the inclusion of pentene co-units in acrystal. 21,[52][53][54] However, a common feature in ethylene-1-alkene copolymers is that co-units larger than methyl are excluded from the crystal lattice. Therefore, the expansion in the unit cell dimensions of the orthorhombic phase can be interpreted by a strain effect caused by congregation of co-units at the interphase of crystallites.…”

“…18,33 They both attributed this effect to a shifting-up of the local melting point, which was proposed to be the complex topology of the amorphous phase generated during the crystallization of constitutionally inhomogeneous polymer chains with relatively long ethylene sequences. In addition, De Rosa et al reported a remarkable melt memory in propene–pentene isotactic copolymers 21 and stereodefective iPP. 35 Their results indicated that the melt memory effect of iPP, which persists in the melt up to high temperatures, is evident not only in copolymers with non-crystallizable comonomers, but also in those with small defects largely included in the crystals.…”

“…16,17 Subsequently, more polymers have been reported to understand the possible factors on the effect. [18][19][20][21][22][23][24] The exact origin of melt memory is still under debate and has led to several hypotheses about their origin and nature. 13 The melt memory effect was attributed to the survival of annealed crystal fragments by Fillon et al in their work on isotactic polypropylene (iPP).…”

“…Furthermore, Domain II was divided into two subdomains by Mu ¨ller et al based on the different origin of the melt memory effect: 13 (a) Domain IIa or melt memory sub-Domain, at a temperature high enough to melt the polymer crystals but without erasing their thermal history; (b) Domain IIb or self-seeding sub-Domain, at a temperature high enough to melt the majority of the polymer crystals but low enough to leave some crystal fragments. Extensive studies have been reported on the melt memory in polymers, including the effect of holding temperature and time in the melt, 23 polymorphism, 22,25,26 chain topology, 21,27,28 confinement, 19,29,30 and so on. 18,[31][32][33] Different views to interpret the melt memory effect have been proposed in various polymers.…”