Effects of Branch Content and Branch Length on Polyethylene Crystallization: Molecular Dynamics Simulation

Abstract

Influences of branch content (BC) and branch length (BL) on isothermal crystallization of precisely branched polyethylene are studied by molecular dynamics simulation. Branch acts as a defect both in nucleation and crystal growth process. BC affects not only crystallization kinetics but also final morphologies. Crystallization rate and crystallinity decrease as BC increases. Morphology Regimes change from lamellae crystal to bundle crystal at critical BC (20/1000 C) because of different folding pattern. 50 CH2 is the critical methyl sequence length to form lamellae crystal. Lamellae thicknesses of final morphologies decrease in gradient corresponding to Morphologies Regimes. BL has no influence on the crystallization kinetics, and only affects the final morphologies when more branches inclusion happens with BL increasing. Trans‐rich phenomenon in pre‐crystalline state is observed. Crystallization process begins at the end of induction stage when trans state population reaches a critical value, and this value is independent of BC and BL.

Long‐Range Self‐Assembly of an Electron‐Deficient Hexaazatrinaphthylene with Out‐of‐Plane Substituents

“…Many will conclude incorrectly that HATN endowed with three cyclic ketal side chains cannot form self‐assembly structures. We reasoned that the cyclic ketal with long branch length in 2 C10 and 2 C12 must have increased the induction time for self‐assembly of growth, similar to the phenomena of the reported molecular dynamic simulation on branched polyethylene having different branching chain content and chain length . To our great surprise, we observed under POM a unique phenomenon whereby compounds 2 C10 and 2 C12 on leaving the sample from isotropic cooling after 24 hours at room temperature led to the formation of highly‐ordered spherulites texture, nucleated randomly whose columns are parallel to the surface over the whole sample (Figure a, 1b).…”

Predicting experimental results for polyethylene by computer simulation

“…On close inspection of the semicrystalline state through the local bond-orientational parameter, we can define the crystalline stem length and overall crystallinity of the models: both magnitudes decrease with SCB content, as in experiments [244,259]. Recently, the effects of both different types and contents of precisely placed SCB and chain length (up to C 10000 and polydisperse systems) have been explored [290,291]. Results confirm that the branch acts as a defect both for nucleation and growth processes, decreasing the crystallization rate, crystallinity, and lamellar thickness.…”

Designing polymer crystallinity: An industrial perspective

“…In general, a wide range of properties can be accessed by properly tuning the density and the melt flow rate, MFR, used in industrial environment as a proxy to molecular weight distribution (MWD). Density is related to the microstructure of the polymer, that is, to short chain branching and comonomer content, therefore being a PE characteristics that can be substantially influenced via polymer design. Increasing density provides stiffness at the expense of toughness, which on the other hand can be imparted by higher MFR .…”