DFT Investigation of Polyethylene-co-vinyl Acetate: Kinetics of Initiation and Propagation, Copolymer Composition, and Unit Sequence Distribution

Abstract

We conducted a kinetic investigation of initiation and propagation of copolymerization between ethylene and vinyl acetate (VAc) based on the density functional theory. Two initiators azodiisobutyronitrile and dibenzoyl peroxide were compared, and the former tends to initiate ethylene, while the latter tends to initiate β C of VAc. A calibration was performed to validate the calculation. For monomers, the reactivity follows the order α C of VAc < β C of VAc ≈ C of ethylene, while for radicals, the order is tail radical < alkyl radical < head radical. Reactivity ratios were discussed, indicating that the copolymerization is close to ideal copolymerization, especially around 430 K, and temperature is unfavorable for VAc content in the product. The relationship between monomer composition, copolymer composition, conversion, and temperature is discussed based on the kinetics calculated. Additionally, the unit sequence distribution was predicted, and the number of repetitive ethylene units can be 8–10, while VAc units often appear as 1–2. Our work gives highly reliable and comprehensive evaluation of propagation kinetics for secondary radicals in EVA copolymerization and explores the inherences of kinetic results by energy decomposition analysis. Compared with the literature, our calculation employed conformation search to average conformational deviations and considered pressure dependence, and all self- and cross-propagation modes for secondary radicals have been considered for the first time. Besides, reactivity inherences were illustrated from orbital, dispersion, repulsion, electrostatic, and entropic interactions.

Theoretical Insights into Midchain Radicals and Branching Characteristics in Solution Copolymerization of Ethylene and Vinyl Acetate

“…After employing the penultimate model (ECR with penultimate fragment), to describe ECRs, 6 ECRs are combined out: H – E *, E – E *, H – H *, E – H *, H – T *, and E – T *. The structures of ethylene, VAc, and ECRs are shown in Figure , all ECRs are truncated to 5 fragment lengths after an energy barrier test done by us before . Lengths of all copolymer chains are balanced between precision and computation.…”

“…1, all ECRs are truncated to 5 fragment lengths after an energy barrier test done by us before. 23 Lengths of all copolymer chains are balanced between precision and computation. We may abbreviate the monomers as e and v, respectively, and use t and h to represent the tail and head C of VAc in later sections.…”

A Novel Bipolar Surfactant, BETX, for Selective Flotation of Chalcopyrite: Folding-Synergistic Mechanism Based on Intramolecular Weak Interactions

“…Prior research efforts have predominantly focused on intermolecular interactions, with limited attention directed toward the intrinsic synergies emerging within single molecules through interactions among their constituent functional groups. ,, This skewed focus is primarily attributed to the inherent challenges associated with fully elucidating molecular conformations via conventional research methodologies. , Notably, functional groups within the same molecule exhibit a greater propensity for interaction due to their closer proximity compared to those between molecules. , Such proximity can stabilize conformations through sp 3 bond rotation and intergroup interactions, leading to dominant conformations. − These conformations can subsequently interact with active centers to produce properties distinct from the independent functional groups, as shown by cryptands or metal proteins. − Our previous work has successfully examined the conformation of thionocarbamate compounds through a combination of molecular dynamics (MD) simulations and density functional theory (DFT) calculations, shedding light on the molecular structure of thionocarbamate compounds . This research paradigm promises to advance our understanding of the molecular structure and mechanisms of multipolar surfactants.…”

“…17,21,22 This skewed focus is primarily attributed to the inherent challenges associated with fully elucidating molecular conformations via conventional research methodologies. 23,24 Notably, functional groups within the same molecule exhibit a greater propensity for interaction due to their closer proximity compared to those between molecules. 25,26 Such proximity can stabilize conformations through sp 3 bond rotation and intergroup interactions, leading to dominant conformations.…”