Computer simulation of polyolefin interfaces

Interfaces, thin films and amorphous cells of several hydrocarbon polymers are studied with atomistic computer simulation. Solubility parameters, surface tensions and interfacial tensions are evaluated from the computed structures. These structures are constructed using Molecular Dynamics and Molecular Mechanics techniques. The various components of the energetic interactions (torsional, vdW, etc.) are examined in detail in order to gain an insight into the nature of the regular and anomalous interactions between these films. The polymers studied in this article are all are atactic Linear hydrocarbons and have approximately 200 carbons in the backbone chain. These include polypropylene (PP), head to head polypropylene (hhPP), a polymer which is termed P78 (a random copolymer composed of 22% of a linear (-CH2CH2CH2CH2-) monomer and 78% of a branched (-CH2CH(C2H5)-) monomer), polyethylenepropylene (PEP), and PE2P2 (an alternating copolymer consisting of two ethylene (E) and two propylene (P) monomers in the repeating pattern (-(EEPP)(n)-)). The primary difference between the different polymers studied is the type of side group (ethyl or methyl) and the location, frequency and spacing of that group. Interfaces formed with the same polymer type (PP-PP, PEP-PEP, P78-P78) yield a surface tension close to zero as expected. Attractive interactions between some of the pairs of films is found in the simulation. The distribution among the energetic terms seems to indicate that this attractive interaction is brought about by favorable local intramolecular energetic terms rather than simply by van der Waals interactions alone. (C) 1999 Elsevier Science Ltd. All rights reserved.