Dynamic DSC, SAXS and WAXS on homogeneous ethylene-propylene and ethylene-octene copolymers with high comonomer contents

Abstract

Ethylene-propylene (EP) and ethylene-octene (EO) copolymers polymerized with the aid of homogeneous vanadium and metallocene catalysts were compared by DSC and time-resolved simultaneous SAXS-WAXS-DSC at scanning rates of 10 and 20~ rain -1 using synchrotron radiation. An EP eopolymer with a density of 896 kg m -3 (about 89 mol% ethylene) after compression moulding gave orthorhombic WAXS reflections. The crystallinity as a function of temperature [wC(7)] calculated from these reflections using the two-phase model was in good agreement with we(T) calculated from Cp measurements using DSC. The Cp measurements also enabled calculation of the baseline Cp and the excess Cp. The SAXS measurements revealed a strong change in the long period in cooling and in heating. The SAXS invariant as a function of temperature showed a maximum in both cooling and heating, which could be explained from the opposing influences of the crystallinity and the electron density difference between the two phases. Two EO eopolymers with densities of about 871 kg m -3 (about 87 mol% ethylene) no longer showed any clear WAXS reflections, although DSC and SAXS measurements showed that these eopolymers did crystallize. The similarity between the results led to the conclusion that the copolymers, though based on different catalyst systems -vanadium and metallocene -did not have strongly different sets of propagation probabilities of chain growth during polymerization. On the basis of a Monte Carlo simulation model of crystallization and morphology, based on detailed knowledge of the mierochain structure, the difference between WAXS on the one hand and DSC and SAXS on the other could be explained as being due to loosely packed cryz,tallized ethylene sequences in clusters. These do cause the density and the electron density of the cluster to increase (which is measurable by SAXS) and the enthalpy to decrease (which is measurable by DSC) but the clusters are too small and/or too imperfect to give constructive interference in the case of WAXS. Of an EP copolymer with an even lower ethylene content (about 69 mol%), the crystallization and melting processes could still be readily measured by DSC and SAXS, which proves that these techniques are eminently suitable for investigating the crystallization and melting behaviour of the copolymers studied.

Partitioning of Main and Side-Chain Units between Different Phases: A Solid-State 13C NMR Inversion-Recovery Cross-Polarization Study on a Homogeneous, Metallocene-Based, Ethylene-1-Octene Copolymer

“…A homogeneous, metallocene-based ethylene-1-octene copolymer (Engage 8200) was produced by Dow's constrained geometry catalyst [1,7,8,11]. In the text below, the sample is denoted by EOM.…”

“…The DSC continuous heat capacity measurements [1,11] were performed with a Perkin-Elmer differential scanning calorimeter DSC-7 at a scanning rate of 208C= min: Heat capacity measurements were performed in the temperature range from À2688C to 1278C with an adiabatic calorimeter using stepwise heating at averaged rates in the range of 18C=h to 348C=h; after the sample was cooled down to À2688C at rates varying from 88C=h to 48C=min [18].…”

“…Ethylene copolymers show a very interesting and intriguing crystallization behaviour [1,11] and morphology [14,16,17] upon increasing the comonomer content from zero to very high values. As has been remarked, most important for crystallization are the sequences of the crystallizable units present in the copolymer chains}ethylene in the present case.…”

“…This is in line with the experience in the past where, contrary to expectations, linear low density polyethylene (LLDPE) did not oust low density polyethylene (LDPE) but found its own markets. Among the metallocene-based ethylene copolymers [2][3][4][5][6][7][8][9][10][11], ethylene-1-octene copolymers with densities of between 870 and 910 kg=m 3 attract the most attention at the moment. Over the past few years, these copolymers have been commercialized by companies such as DEXPLASTOMERS (a 50/50 DSM/Exxon Mobil Chemical joint venture) and DOW Chemical Company.…”

Influence of the Type of Fiber on the Structure and Viscoelastic Relaxations in Composites Based on a Metallocenic Ethylene-1-octene Copolymer

“…The origin of this extra reflection is not clear, since it can be ascribed to either monoclinic or hexagonal crystals. [21][22][23][24][25] It seems evident, however, that it arises from very imperfect crystals, 26,27 probably with a bundle-like structure instead of a lamellar one. Therefore, we will designate it as "disordered" crystals or "disordered" modification.…”