Ideal Polyethylene Nanocrystals

Abstract

The water-soluble catalyst precursor [[(2,4,6-(3,5-(CF3)2C6H3)3-C6H2)-N═C(H)-(3-(9-anthryl)-2-O-C6H3)-κ(2)-N,O]Ni(CH3)(TPPTS)] (TPPTS = tri(sodiumphenylsulfonate)phosphine) polymerizes ethylene to aqueous dispersions of highly ordered nanoscale crystals (crystallinity χ(DSC) ≥ 90%) of strictly linear polyethylene (<0.7 methyl-branches/1000 carbon atoms, Mn = 4.2 × 10(5) g mol(-1)). SAXS in combination with cryo-TEM confirms this unusually high degree of order (χ(SAXS) = 82%) and shows the nanoparticles to possess a very thin amorphous layer on the crystalline lamella, just sufficient to accommodate a loop, but likely no entanglements. This ideal chain-folded structure is corroborated by annealing studies on the aqueous-dispersed nanoparticles, which show that the chain can move through the crystal as evidenced by lamella thickening without disturbing the crystalline order as concluded from an unaltered low thickness of the amorphous layers. These ideal chain-folded polyethylene nanocrystals arise from the crystallization in the confined environment of a nanoparticle and a deposition of the growing polymer chain on the crystal growth front as the chain is formed by the catalyst.

Remote Perfluoroalkyl Substituents are Key to Living Aqueous Ethylene Polymerization

“…To understand their role in catalysis, we investigated the influence of long perfluoroalkyl substituents (linear C 6 F 13 groups) in different established salicylaldiminato Ni II motifs under a set of polymerization reaction conditions. We targeted the N ‐(quar)terphenyl‐based 1‐R F /L and 2‐R F /L (Figure ), known to be active in aqueous and nonaqueous ethylene polymerization to linear high‐molecular‐weight polyethylene . We also modified the N‐naphthyl‐type catalyst 3‐R F /L (Figure ), capable of a controlled/living ethylene polymerization in a variety of solvents, and introduced C 6 F 13 ‐substituents to selected positions .…”

“…During polymerization in aqueous surfactant solution with Ni II salicylaldiminato catalysts, the polyethylene is formed in the very unusual form of nanoscale single crystals . They are characterized by a high degree of order, which arises from the unique particle growth mechanism, where the active center's growing chain is directly deposited on the crystal growth front, leaving no opportunity for any disorder . This process allows effective generation of anisotropic polymer nanoparticles, which are otherwise difficult to access…”

Crystalline and Spherulitic Morphology of Polymers Crystallized in Confined Systems

“…Confinement of polymer systems can be generally classified into three categories according to their confined environments, and they are one, two and three dimensions, respectively. Confined crystallization of polymers has been found in a variety of systems, such as polymer ultrathin films [1][2][3][4][5], polymer blends [6][7][8][9][10], block copolymers [11][12][13][14], polymer droplets [15][16][17], self-assembled polymer nanostructures [18][19][20][21][22], polymers segregated inside nanoporous templates [23][24][25][26][27][28][29] and polymer nanocomposites [30][31][32][33]. In the past few years, the crystallization of polymers or polymer segments confined in ultrathin films (thickness <100 nm), miscible polymer blends and block copolymers has been widely studied for various systems.…”

Makroskopische kristalline 2D‐Polymere

“…Entsprechend umfassen mçgliche Anwendungsfelder Elektronik, [1][2][3][4][5][6] Optoelektronik, [7][8][9][10][11] Katalyse, [12][13][14] Energiespeicherung und Energieumwandlung [15][16][17][18][19][20] sowie Membranen. [71][72][73][74][75][76][77][78] Entsprechend dieser großen Diversität finden sich unter den 2D-Materialien sowohl Strukturen mit hoher struktureller Regularität(Kristallinität) als auch Stoffe mit geringerer interner Ordnung.Die Stärke der Bindungen, welche die Netzwerke zusammenhalten, variiert in dieser Auflistung ebenfalls stark. Beispiele sind Graphen und Graphenoxid, [1,10,23,25] Übergangsmetalldichalkogenide, [7,12,[26][27][28][29][30][31] Metalloxide und -hydroxide, [32] Metallcarbide und -nitride, [33] hexagonales Bornitrid, [34] zweidimensionale kovalente organische Gerüstverbindungen (2D-COFs) [35][36]…”