Segmental mobility in the noncrystalline regions of nascent polyethylene synthesized using two different catalytic systems with implications on solid-state deformation

Yao, Yefeng; Rastogi, Sanjay; Xue, Huai‐Jun; Chen, Q.; Graf, Robert; Verhoef, R.

doi:10.1016/j.polymer.2012.11.002

Cited by 13 publications

(32 citation statements)

References 44 publications

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“…The topology can be tailored by controlling the crystallization kinetics either by dissolution and crystallization or controlled polymerization [2,3,4,5]. The influence of molar mass on the topology of non-crystalline phase has been a subject of interest where the nature of the mobile phase is probed by solid state NMR [6,7]. Yao et al investigated the influence of polymerization conditions on the non-crystalline region of the semi-crystalline region [7].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, in UHMWPE, it has been shown that the melting temperature of the as-synthesized polymer (nascent) approaches the equilibrium melting temperature because of the restricted mobility of the methylene segments in the non-crystalline region [10]. Differentiation between the non-crystalline regions of the polymer synthesized using Ziegler-Natta (Z-N) and single site catalytic systems can be made by following kinetics in the melting of the crystals [7,10]. To recall, when the nascent sample is left to anneal at the onset of the melting temperature of the endothermic peak, having peak melting temperature close to 141.5 °C, crystals tend to melt via consecutive detachment of chains from the crystal surface followed by reeling-in of the chain stems into melt [10].…”

Section: Introductionmentioning

confidence: 99%

“…The influence of molar mass on the topology of non-crystalline phase has been a subject of interest where the nature of the mobile phase is probed by solid state NMR [6,7]. Yao et al investigated the influence of polymerization conditions on the non-crystalline region of the semi-crystalline region [7]. To recall, the authors demonstrated that the non-crystalline region in the polymer synthesized using Ziegler-Natta differed from the polymer synthesized using a single-site catalytic system [7].…”

mentioning

confidence: 99%

“…Yao et al investigated the influence of polymerization conditions on the non-crystalline region of the semi-crystalline region [7]. To recall, the authors demonstrated that the non-crystalline region in the polymer synthesized using Ziegler-Natta differed from the polymer synthesized using a single-site catalytic system [7].The absence of structural order in the non-crystalline region of semi-crystalline polymers imposes challenges to an extent that the issue of adjacent or non-adjacent re-entry remains unsolved even today, despite the discovery of chain folded crystals in 1957 [2,8,9]. Recently, in UHMWPE, it has been shown that the melting temperature of the as-synthesized polymer (nascent) approaches the equilibrium melting temperature because of the restricted mobility of the methylene segments in the non-crystalline region [10].…”

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confidence: 99%

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Heterogeneous Distribution of Entanglements in a Nonequilibrium Polymer Melt of UHMWPE: Influence on Crystallization without and with Graphene Oxide

et al. 2016

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Recently, the influence of reduced graphene oxide nanoplatelets (rGON) on the rheological response of polymers has been a subject of interest. In the case of disentangled UHMWPE, it has been shown that the chain-filler interaction in the UHMWPE/rGON composite results into an everlasting non-equilibrium melt state having heterogeneous distribution in entanglement density. In this study, a thermal analysis protocol is used to follow the influence of the non-equilibrium polymer melt on the crystallization kinetics of disentangled UHMWPE with, and without, rGON. The analysis is carried out by means of differential scanning calorimetry (DSC) and the results are supported by rheology. When the disentangled UHMWPE sample, without the filler rGON, is left to crystallize under isothermal condition after melting, two endothermic peaks are observed: the high temperature peak (close to the equilibrium melting point, 141.5 °C) is related to the melting of crystals obtained on crystallization from the disentangled domains of the heterogeneous (nonequilibrium) polymer melt, whereas the low melting temperature peak is related to the melting of crystals formed from entangled domains of the melt. On increasing the annealing time in melt (160 °C), the enthalpy of the lower melting temperature peak increases at the expense of the high melting temperature peak, confirming a transformation of the nonequilibrium polymer melt to a fully entangled equilibrium melt state. However, independent of the equilibrium or non-equilibrium melt state, the recurrence of the high melting temperature peak is observed when the samples synthesized using the single-site catalytic system are left to isothermal crystallization at a specific temperature. The recurrence of the high melting temperature, close to the equilibrium melting point of the polymer, questions the differences in entanglements formed before and after polymerization in these high molar masses. The differences in the topological constraints are likely to influence the difference in melting temperatures of the isothermally crystallized samples. In the presence of rGON, the melting response of disentangled UHMWPE crystallized from its heterogeneous melt state changes; at a specific filler concentration, it is observed that the high endothermic peak remains independent of the annealing time in melt. This observation strengthens the concept that in the presence of the filler, chain dynamics is arrested to an extent that the nonequilibrium melt state having lower entanglement density is retained, facilitating the formation of crystals having high melting temperature. IntroductionThe topology of methylene segments in the non-crystalline region of the semi-crystalline polymer Ultrahigh Molecular Weight Polyethylene (UHMWPE), has a profound influence on the mechanical deformation either uniaxially or biaxially [1]. The topology can be tailored by controlling the crystallization kinetics either by dissolution and crystallization or controlled polymerization [2,3,4,5]. The influence of mo...

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Heterogeneous Distribution of Entanglements in a Nonequilibrium Polymer Melt of UHMWPE: Influence on Crystallization without and with Graphene Oxide

et al. 2016

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“…The peaks at 32.4 and 33.8 ppm refl ect crystalline PE chains adopting all-trans conformations in orthorhombic and monoclinic phases respectively, [ 56,57 ] whereas the signal at 30.6 ppm corresponds to the mobile PE chains in amorphous (noncrystalline) domains adopting interchanging trans and gauche conformations. [ 10,58,59 ] In Figure S3 (Supporting Information), the collected spectra from PEX and PEX/5 wt% NDs are presented. Detail inspection revealed a slight broadening of the main signal at 32.4 ppm induced by incorporating ND particles into the polymer matrix.…”

Section: Resultsmentioning

confidence: 99%

Modified Crystalline Structure of Silane-Crosslinked Polyethylene in the Proximity of Nanodiamonds

Roumeli

Brus

Policianova

et al. 2016

Macromol. Mater. Eng.

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The introduction of nanodiamond particles (NDs) in silane‐crosslinked polyethylene is found to lead to a notable and systematic deformation of the polymer unit cell. X‐ray diffraction evidence of the existence of a modified crystalline structure in the bulk of the polymer due to the presence of NDs is reported here for the first time. The covalent bonding between NDs and the surrounding macromolecular chains may support that the excessive local stress field ultimately distorts the polymer conformation, yielding a new distorted but still crystalline interface. Supporting data from solid‐state NMR experiments confirm the existence of a modified crystalline interface of about 1–2 nm in all the nanocomposite materials.

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Thickening of Isolated and Multilayered Crystals and Its Implications on Melting Kinetics; The Role of Inter‐ and intra‐crystalline Regions

Rastogi¹,

Romano²

2022

Macromolecular Engineering

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Melting of crystalline region in a semicrystalline polymer is a complex phenomenon, which is strongly influenced by the topological constraints present in the noncrystalline region. In an isolated crystal, detachment of chain stems from its crystalline surface can occur in succession or in cluster. The difference in detachment of the chain stems strongly depends on the topological constraints of the chain segments on the fold surface. Successive detachment of the chain stems, observed on melting of crystals while annealing at the onset of the peak melting temperature, appears to occur when chain folding is facilitated by adjacent reentry. In the annealing process, no crystal thickening in isolated crystals, having molar mass sufficiently high to suppress the effect of chain ends, is observed, as the crystal thickening will require cooperative chain mobility of the chain stems within the crystal linked by the chain segments in the fold. Retrospectively, because of the possibility of successive chain detachment, melting temperature decreases with decreasing heating rate, contradicting the assumption of increase in melting temperature on annealing. In the isolated crystals, having complex reentrant chains on the fold surface, successive detachment of chains from a crystal surface is frustrated, and cluster melting is promoted. Such crystals, though isolated, do not show melting on annealing. However, in contrast to the isolated crystals, in multilayered crystals instead of melting on annealing at the onset melting temperature, crystal thickening will occur that would cause increase in the melting temperature. This thickening process is facilitated, as it requires the localized motion only rather than the cooperative motion of the chain stems within the crystals. Thickening in the isolated crystals, if observed during polymerization or due to the appearance of a transient mobile phase, is referred as the primary thickening, whereas the crystal thickening in the multilayered crystals is called the secondary thickening.

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Segmental mobility in the noncrystalline regions of nascent polyethylene synthesized using two different catalytic systems with implications on solid-state deformation

Cited by 13 publications

References 44 publications

Heterogeneous Distribution of Entanglements in a Nonequilibrium Polymer Melt of UHMWPE: Influence on Crystallization without and with Graphene Oxide

Heterogeneous Distribution of Entanglements in a Nonequilibrium Polymer Melt of UHMWPE: Influence on Crystallization without and with Graphene Oxide

Modified Crystalline Structure of Silane-Crosslinked Polyethylene in the Proximity of Nanodiamonds

Thickening of Isolated and Multilayered Crystals and Its Implications on Melting Kinetics; The Role of Inter‐ and intra‐crystalline Regions

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