Origin of Melt Memory Effects in Poly(ethylene oxide): The Crucial Role of Entanglements

Abstract

The melt memory effect on crystallization is an intriguing phenomenon displayed by semi‐crystalline polymers, as opposed to low molar mass molecules. It concerns the effect of melt temperature on nucleation upon recrystallization. Typically, polymer crystals must be considerably superheated to erase the effect of previous morphology on the subsequent crystallization, avoiding an acceleration of the process. Despite being known for decades, its origin is still not fully understood. Investigating model poly(ethylene oxide) covering a wide range of molar mass, we demonstrate that melt memory originates from topological constraints among the chains, i.e., entanglements, for PEO in which weak intermolecular interactions are present due to the ether groups. In fact, no memory is observed for samples below the critical molar mass for the formation of entanglements (about 1kg/mol). The increase in molar mass raises the number of entanglements and induces the formation of folded chains crystals, both factors leading to a topologically complex amorphous phase, enhancing the melt memory effect. The molecular origin of the melt memory effect in polymers with weak intermolecular interactions is thus ascribed to a slower isotropization in the melt of the chain segments originally contained in the crystals, due to the presence of entanglements among the chains. This study defines the distinction between small molecules and polymers from the point of view of melt memory.This article is protected by copyright. All rights reserved

Self-Nucleation Ability and Intermolecular Interactions Mechanism in Fluoropolyolefins

“…However, a remarkably wide Domain IIa of 14 °C emerges, which indicates the strong melt memory effect of PVDF. This melt memory effect can be also contributed from the intermolecular interactions. ,, Since the Domain IIb locates at the low-temperature side of Domain IIa, the melt memory effect could be stronger and contributes to the self-nuclei in Domain IIb, besides the self-seeding effect of the existing crystal fragments. Consequently, considering the influence of the intermolecular interactions, it is reasonable to correlate the whole Domain II with ε.…”

“…Since its discovery, the SN behavior has been widely observed in a variety of polymers, such as polyesters, − polyamides, − polyethers, , and polyolefins. ,− But, the intrinsic nature is still under debate. According to the literature, numerous factors impact the SN behavior of polymers, including temperature, , treatment time, , chemical structure, , molecular weight, ,− chain topology, ,− and confinement conditions. , As a result, several hypothetical models have been proposed, including “unmolten crystal fragments”, ,, “phase topology or nonisotropic melts”, , “topological constraints (i.e., entanglements)”, , “precursor phase”, and “short-range ordered conformations”. ,, Yet, the lack of direct detection techniques has made it difficult to precisely describe the exact structure of self-nuclei, as the detailed difference between the isotropic melt and the self-nucleated melt is not easily captured.…”