Department of Chemistry and Industrial Chemistry, University of Genova, Via Dodecaneso 31, Genova, 16146, Italy.
POLYMAT and Department of Polymers and Advanced Materials: Physics, Chemistry and Technology, Faculty of Chemistry, University of the Basque Country UPV/EHU, Paseo Manuel de Lardizábal 3, Donostia-San Sebastián, 20018, Spain.
Macromol Rapid Commun. 2024 Jun;45(12):e2400011. doi: 10.1002/marc.202400011. Epub 2024 Apr 3.
The melt memory effect on crystallization is an intriguing phenomenon displayed by semicrystalline 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, it is demonstrated 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 1 kg 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.
熔体记忆效应对结晶是半晶态聚合物表现出的一种有趣现象，与低摩尔质量分子不同。它涉及熔体温度对再结晶时成核的影响。通常，聚合物晶体必须被显著过热，以消除先前形态对后续结晶的影响，避免过程加速。尽管这种现象已经存在了几十年，但它的起源仍未完全理解。通过研究广泛摩尔质量范围的模型聚（氧化乙烯），证明熔体记忆源于链之间的拓扑约束，即缠结，对于存在醚基团的 PEO 来说，由于弱分子间相互作用的存在，这种缠结是存在的。事实上，在形成缠结的临界摩尔质量（约 1kg/mol）以下的样品中，不会观察到记忆现象。摩尔质量的增加增加了缠结的数量，并诱导折叠链晶体的形成，这两个因素都导致了拓扑复杂的非晶相的形成，从而增强了熔体记忆效应。因此，具有弱分子间相互作用的聚合物中熔体记忆效应的分子起源归因于晶体中原先包含的链段在熔体中的各向同性化速度较慢，这是由于链之间存在缠结。本研究从熔体记忆的角度定义了小分子和聚合物之间的区别。
