Wide- and Small-Angle X-ray Analysis of Poly(ethylene-co-octene)

Abstract

Wide-angle X-ray data point to a three-phase structure in isotropic and drawn specimens of a homogeneous poly(ethylene-co-octene) (7.3 mol % 1-octene). In addition to the amorphous halo, the unoriented polymer exhibits Bragg reflections characteristic of the orthorhombic crystalline phase and an additional reflection that is assigned to the hexagonal mesophase. On stretching 800%, the degree of crystallinity increases from ∼25% to ∼50%, due mainly to the formation of smaller hexagonal crystallites, while the proportions of the orthorhombic and amorphous phases decline. Small-angle X-ray data reveal a distinct long period, pointing to the existence of lamellae that become oriented perpendicular to the draw direction. On releasing the specimen, there is a considerable permanent set (∼350% extension), and the crystallinity declines to ∼30% as the hexagonal crystallites appear to revert to the amorphous structure. The results suggest that the hexagonal mesophase is formed by chain segments that have octene side chains, once these segments become oriented by deformation.

Structure development in melt spinning of poly(ethylene‐co‐octene) filaments with various comonomer contents

“…The second and third reflections are identified as (110) and (200) of the orthorhombic phase. The first reflection is identified as (100) of the hexagonal unit cell, suggested by Androsch et al 16,17 for this type of copolymers. No other crystal plane of the hexagonal crystal was observed.…”

“…The hexagonal form has also been found in copolymers of polyethylene with propylene 51 and octene. 16,17,19 These authors all observed only the (100) reflection of the hexagonal form. As we know, for a perfect crystal, there should be different reflection crystal planes and those should be observed from the WAXS pattern.…”

“…However, this anisotropy was relatively small. By use of the method proposed by Androsch et al 16 the amorphous background was subtracted from the area detector data. The scattering contained in the three equatorial reflections (i.e., that attributed to the crystalline components) was thus estimated.…”

“…In recent years, there has been an increasing number of articles 10 -21 describing the characteristics of polyethylene copolymers with high comonomer contents, especially octene-1, but still containing substantial levels of crystallinity. Both the orthorhombic phase 9 and a hexagonal phase 16,17 have been found. In the present article, we considered structure development in melt spinning of polyethylene copolymers.…”

Reversible melting of polyethylene extended‐chain crystals detected by temperature‐modulated calorimetry

“…32 After transformation to the orthorhombic phase, ECC is close to perfect and has coherently scattering grain sizes of more than 200 nm normal to the direction of the molecular chain, as revealed by X-ray analysis. 33,34 Reversing and reversible melting of crystals with repeating units of CH 2 have been investigated for paraffins, 6 fractions of PE, 7 high-density PE, 7,[35][36][37][38][39][40][41][42] homogeneous linear low-density PE [poly(ethylene-co-octene-1)], 35,37,[43][44][45][46][47][48][49] and ultrahigh molar mass PE (UHMMPE). 50 -54 In this article, information gained from these research reports is combined to gain a clearer understanding of the melting of PE.…”