Polymer Chains Fold Prior to Crystallization

Abstract

There are long-standing debates in crystallization mechanism of polymer chains at the molecular levels: Which comes first, chain folding or lamellae formation during crystallization? In this study, we report the local chain trajectory of 13 C-labeled semicrystalline polymer in an extreme case of rapidly quenched glassy state as well as thermodynamically stable crystals formed via different pathways from glass and melt. Magnetically dipole interactions do not require a long-range order of molecular objects and thus enable us to trace the local chain trajectory of polymer chains even in a glassy state. To accurately characterize the local chain trajectory of polymer glass, the natural abundance effect on 13 C− 13 C double-quantum (DQ) nuclear magnetic resonance (NMR) signal is re-examined using extended chain conformation. As results, it is found that glassy chains adopt the same adjacent re-entry structure (adjacent re-entry number, n = 1) with the melt-and cold-grown crystals. From these results, it is concluded that (i) folding occurs prior to crystallization and (ii) melt and cold crystallization do not induce additional folding but proceed with rearrangements of polymer chains in the existing templates.

The effect of melt drawing ratio on the crystal structural change and performance of polyketone extrusion cast film

“…As Blundell et al pointed out, the thickness of the lamellae in POK has an almost linear relationship with the crystallization temperature 12 . Increasing the supercooling rate will weaken rearrangement ability of the folded POK chain, resulting in a decrease in the average size of the ordered part, which results in a smaller period length measured by SAXS 42,43 . By calculating the ratio of Lc and L, we find that the linear crystallinity of all samples hardly changes, which is consistent with the results obtained by DSC.…”

“…12 Increasing the supercooling rate will weaken rearrangement ability of the folded POK chain, resulting in a decrease in the average size of the ordered part, which results in a smaller period length measured by SAXS. 42,43 By calculating the ratio of Lc and L, we find that the linear crystallinity of all samples hardly changes, which is consistent with the results obtained by DSC. The higher chain regularity makes the crystal perfection almost unaffected by melt stretching.…”

Competitive Mechanism of Stereocomplexes and Homocrystals in High-Performance Symmetric and Asymmetric Poly(lactic acid) Enantiomers: Qualitative Methods

“…The overhanging segments of PDLA 60 on the substrate surfaces of SCs could be further associated with an additional PLLA 30 . Due to chain folding, the formation of HCs would also become possible. ,, To further emphasize the mole ratio effect ( n L > n D ), L 30 /D 60 with different compositions (2:1, 3:1, 4:1, and 5:1) were parallelly prepared, following the same protocol ( x D ≥ 2 x L ). According to the above-mentioned argument, the optimal mole ratio for the L 30 /D 60 blends to form SCs is 2:1 and 3:1, while there will be excess PLLA 30 in the case of 3:1.…”

Crystallization with Nodular Aggregation near the Glass Transition Temperature for Syndiotactic Polypropylene

“…Recently, the multifaceted aggregates with a diameter of several tens of nanometers in sPP quenched at 0 °C have been found by atomic force microscopy. , The HNG process near T g has been detected for several polymers by fast DSC . The direct evidence of the cooperative coarsening of the nodules has been reported by nuclear magnetic resonance techniques. − PTT crystallizes with the nodular aggregation near T g . , The results in this Letter show that in sPP both the crystalline and the mesomorphic nodules randomly aggregate by the same mechanism in spite of their different helical structures. They may indicate that the growth mechanism of the nodular aggregation is related to the formation of precursors, which can transform into both the crystal and the mesophase, on the growth front, and that the probability of the transition from the precursor into either phase is determined by T c .…”