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We carried out molecular dynamics (MD) simulations on polyethylene (PE) with linear, ring, and four‐arm symmetrical star structures at various molecular weights (420 − 5700 g ⋅ mol−1) and temperatures (410−450 K). We then analyzed the MD data using the technique of proper orthogonal decomposition (POD) to obtain the time correlation functions of different eigenmodes, thereby calculating the viscosity of the aforementioned macromolecules. The time correlation functions show that the ring and star PEs relax much faster than their linear counterpart. Free volume size distributions and the mean fractional free volume of the equilibrated PE melts were determined by Voronoi tessellation (VT). The mean fractional free volume and the corresponding effective pressure were then used to calculate viscosity using a polymer free volume theory recently developed in our lab. The POD and VT approaches yielded similar viscosity values. Furthermore, they both successfully predicted the crossover in the molecular weight dependence of viscosity. It is interesting to note that the difference in the free volume parameters (ϕ+ − F) of various structures always fall within the range of 0.02−0.06. Here, F and ϕ+ signify the probability of a bead having enough free volume for the activation of diffusive motion or momentum transfer and the minimum required fraction of such beads, respectively. The temperature dependence of viscosity as obtained from the POD and VT approaches gave comparable apparent activation energy (Eaapp) values of 5.8−6.4 and 5.4−6.4 kcal ⋅ mol−1, respectively, for the three structures. [ABSTRACT FROM AUTHOR]

The relative concentrations of the chains (TCs) in six single-site linear low-density polyethylene blown films (LLDPE) were measured using a polarized Fourier transform infrared (FTIR) technique along with a newly developed sample preparation strategy. Before the FTIR measurements, the films were first subjected to a tensile strain of 20% using a homemade appliance and then annealed at a temperature of 60 °C over a time period of 24 h to relax all nonTCs in the amorphous phase. The relative TC concentrations were inferred from the FTIR measurement of the orientation order of the amorphous chains in the stretched films. It is believed that a greater concentration of TCs leads to a higher orientation order for the amorphous chains. The results showed that the quantity of TCs is essentially determined by the chains with the appropriate branch frequency (~12 branches per 1000 backbone carbons based upon the films used in this work), especially those of the high molar mass chains as formation of TCs requires suitable ethylene sequence lengths between branches. The dart impact strength of the films appeared to be positively related to the relative concentration of TCs; films with greater concentrations showed higher dart impact strength. No clear correlations were observed between the relative concentration of TCs and the tear resistance of the films. However, the TC concentration seems to be related to the magnitude of the difference between the transverse direction and machine direction tear resistance. Key words: tie chains, polarized Fourier transform infrared (FTIR), linear low-density polyethylene (LLDPE) blown films, dart impact. Faisant appel a la technique d'infrarouge a transformee de Fourier polarisee (IR-TF) et a une nouvelle strategie de preparations des echantillons, on a etudie les concentrations relatives de chames liees (CL) de six films souffles de polyethylene de faible densite, lineaire et a site unique, Avant d'effectuer les mesures IR-TF, les films ont ete soumis a une force tensile de 20 % a l'aide d'un appareil maison et ils ont ensuite ete recuits a une temperature de 60 °C pour une periode de 20 heures afin de detendre toutes les chames non liees dans la phase amorphe. Les concentrations relatives de chaines liees ont ete deduiles de la mesure IR-TF de l'ordre d'orientation des chaines amorphes dans les films etires. On croit qu'une concentration plus elevee de chaines liees conduit a un ordre d'orientalion plus eleve pour les chaines amorphes. Les resultals montrent que la quantile de chaines liees est essenliellement determinee par les chaines comportant la frequence appropriee de ramification (environ 12 branches par 1000 atonies de carbone dans le squelette si on se base sur les films utilises dans cette etude), particulierement pour les chaines de masse moleculaire elevee puisque la formation de chaines liees necessite des longueurs appropriees de sequence d'ethylene entre les branches. Le force d'impact au dard des films semble etre liee d'une facon positive a la concentration des chaines liees; les films en comportant de plus grandes concentrations presentent une force d'impact au dard plus elevee. On n'a observe aucune correlation entre la concentration relative des chaines liees et la resistance aux dechirures des films. Toutefois, la concentration des chaines liees semble etre liee a l'amplitude de la difference entre la direction transverse et la direction mecanique de la resistance aux dechirures. Mots-des : chaines liees, infrarouge a transformee de Fourier, films souffles de polyethylene de faible densite et lineaire, impact au dard. [Traduil par la Redaction], Introduction Among the structural features in polyethylene blown films, tie chains (TCs) are believed to play a significant role in determining their physical properties as TCs bridge adjacent lamellae. (1) [...]

The cover image is based on the Research Article Effect of hexyl‐branched backbone size on the size distribution and coalescence of free volume around an amphiphilic molecule by Sajjad Kavyani et al., https://doi.org/10.1002/pen.26705. [ABSTRACT FROM AUTHOR]