Effect of the Sequence Length Distribution on the Lamellar Crystal Thickness and Thickness Distribution of Polyethylene: Perfectly Equisequential ADMET Polyethylene vs Ethylene/α-Olefin Copolymer.

Abstract

The morphology of ADMET-synthesized polyethylene with n-butyl branches precisely spaced on every 39th carbon (EH39) was studied in comparison with an ethylene/1-hexene addition copolymer possessing the same branching probability, the goal being to elucidate the effect of the intramolecular sequence length heterogeneity on the lamella crystal thickness and its distribution. EH39 was found to have an orthorhombic crystalline polymorphism, which is normal for commercialized polyethylenes and different from that of the other ADMET polyethylenes with shorter CH 2 spacing (C15, C21). EH39 exhibits a narrow lamella thickness distribution; the average thickness (l c,av. ) corresponds exactly to the space length between two consecutive branches, suggesting the complete exclusion of n-butyl branches from the crystal stem. The average thickness, l c,av. mentioned above is also coincident with that obtained from WAXS and SAXS. On the other hand, the 1-hexene copolymer forms much thicker lamellae and a broader thickness distribution than ADMET polyethylene. Here, the average thickness l c,av. determined by TEM observation of the copolymer is 1.5 times larger than that calculated from the most probable ethylene sequence length obtained from 13 C NMR, or for a theoretical ethylene sequence length distribution, indicating that the lamellae are composed predominantly of the sparsely branched longer ethylene sequences that are statistically included. The intramolecular sequence distribution is considered significant to determine the lamella thickness and thickness distribution for short chain-branched polyethylenes with a narrow intermolecular chemical composition distribution.

(nBuCp)2ZrCl2‐catalyzed ethylene‐4M1P copolymerization: Copolymer backbone structure, melt behavior, and crystallization

“…28 and 29 and the citations therein. We shall pursue the modeling work using Flory equation, 30,31 Gibbs-Thompson (GT) lamellar thickness equation, [31][32][33][34][35] and a new nonisothermal Avrami-Arofeev crystallization model that we published in 2013. 36 We trust that this study will hopefully add new insight to metallocene-catalyzed ethylene homopolymerization and copolymerization and broaden our comprehension.…”

Metallocene-catalyzed ethylene−α-olefin isomeric copolymerization: A perspective from hydrodynamic boundary layer mass transfer and design of MAO anion

“…This means that the structural/enchainment defects due to 4M1P or 1-hexene were excluded from the pure polyethylene-phase crystal lattice. The [ECC] and [CCC] values (where C = H or 4M1P) of Table 2 as well as the relevant literature support this conclusion [41,[78][79][80][81][82]. The 4M1P or 1-hexene homosequence was not long enough to arrange in a crystal lattice.…”

“…The thermodynamically predicted theoretical distribution of ethylene sequence length (between the pendant side chains), that is, the equilibrium crystal length was calculated using the Flory equation [40,41]. According to this, the normalized weight fraction W n of the sequence of n ethylene units is related to the ethylene perpetuation probability p through the following expression:…”

“…For a statistical copolymer with very long chains, p is related to experimental reactivity ratio product r E r C and ethylene mole fraction X E as follows [41]:…”

“…We calculated them applying Gibbs-Thompson (GT) equation, the related literature expressions [24,41,[74][75][76][77], and the DSC data. We valued the most probable lamellar thickness L MPDSC GT from the peak of each (equilibrium melting temperature of the copolymer) was found as reported in the literature [41,[74][75][76][77]. L MPDSC GT was next converted into the most probable ethylene sequence n E MPDSC GT by dividing it with the length of an ethylene repeat unit (0.254 nm).…”