High Speed SSA Thermal Fractionation and Limitations to the Determination of Lamellar Sizes and Their Distributions

Abstract

Summary: The technique of successive self‐nucleation and annealing (SSA) has been applied using differential scanning calorimetry (DSC) to a model hydrogenated polybutadiene prepared by anionic polymerization and to a commercial Ziegler‐Natta ethylene/1‐butene copolymer. Here, it is shown that the use of high scanning rates (50 °C · min−1) in the SSA protocol can reduce the thermal fractionation time to only 78 min in length (if 6 fractions are produced with a fractionation window of 5 °C), taking into consideration the need to compensate the increment in heating rates by reducing the sample mass. This time is much shorter than those previously achieved by thermal fractionation in the literature, where fractionation times of 12 or 24 h are common. Potentially, much higher rates could be employed by further reducing the fractionation times by SSA. For the first time, a distribution of lamellar thicknesses has been obtained by transmission electron microscopy after SSA fractionation and compared to distributions calculated by the Thomson‐Gibbs equation. It is shown that the results are highly dependent on the equilibrium melting temperatures employed in the calculations, and it is recommended that the values of lamellar thicknesses obtained are checked by comparing with methylene sequence lengths derived from calibration measurements available in the literature. The Thomson‐Gibbs equation is useful for comparing lamellar thickness distributions obtained by SSA with different polymers only on a semi‐quantitative basis.

Metallocene-catalyzed ethylene−α-olefin isomeric copolymerization: A perspective from hydrodynamic boundary layer mass transfer and design of MAO anion

“…Note that in SSA fractionation, the polymer undergoes multiple alternate melting and crystallization processes (without physical separation of the chains) as the temperature decreases. Therefore, it is sensitive to linear and uninterrupted chain sequences; hence to both intra-and inter-chain defects [26][27][28][29][30][31]. The 13 C NMR results, reported earlier, complement this remark.…”

“…The synthesized copolymers were thermally fractionated using the above DSC instrument, and following the successive selfnucleation and annealing (SSA) experimental procedure reported in the literature [26][27][28][29][30][31][32]. Seven annealing steps (160, 125, 119, 114, 111, 107, and 103°C) were applied.…”

Molecular chain heterogeneity of a branched polyethylene resin using cross-fractionation techniques

“…(c) The sample was heated at 10°C/min from 0°C to a selected self-seeding temperature (termed as T s ). Special care should be taken to choose the first T s temperature as described in the literatures [37][38][39][40]. The sample was kept at T s for 5 min.…”

Probing the early stages of thermal fractionation by successive self-nucleation and annealing performed with fast scanning chip-calorimetry

“…Müller et al designed and implemented the SSA thermal fractionation protocol based on the idea of accumulating self‐nucleation (SN) and annealing steps in a successive manner. SSA is therefore based on the SN concept presented by Fillon et al…”

“…Given the usefulness of information gained by SSA, some efforts for further speeding up the process have been done . Scanning rates of 50 and 200 °C/min have been employed with DSC and High Performance‐DSC, respectively.…”