Differences between Ziegler–Natta and Single‐Site Linear Low‐Density Polyethylenes as Characterized by Inverse Gas Chromatography

Abstract

Summary: Zero‐pressure weight‐fraction‐based Henry's constants $(H_{{\rm 12}}^0 )$ of two alkanes, two alkenes, and benzene in Ziegler–Natta (ZN) and single‐site (ss) linear low‐density polyethylenes (LLDPE) with different average branch contents, molecular‐weight averages ($\overline M _{\rm n}$ and $\overline M _{\rm w}$), and polydispersity indices (PDI) were measured in the temperature range of 170 to 230 °C using the technique of inverse gas chromatography. For both types of LLDPEs, the measured $H_{{\rm 12}}^0$ was insensitive to molecular weight and PDI. However, the branch content dependence differed significantly. In particular, ZN‐LLDPE exhibited a strong branch content dependence on $H_{{\rm 12}}^0$ while ss‐LLDPE did not. In fact, depending on the temperature and solvent used, $H_{{\rm 12}}^0$ of ZN‐LLDPE could drop as much as 21% with an increase in an average branch content from 13 to 35 branches per 1 000 backbone carbons, while the differences of $H_{{\rm 12}}^0$ between ss‐LLDPEs with comparable differences in branch content were well within experimental uncertainties (5%). This observation is also supported by the fact that comparable ZN‐ and ss‐LLDPEs exhibited larger differences in $H_{{\rm 12}}^0$ at higher average branch contents. The above findings strongly suggested that the liquid morphologies of ZN‐ and ss‐LLDPEs differ considerably. In particular, the local chain conformation and free volume characteristics (i.e., the size distribution and/or spatial distribution of the free volume holes) of them are rather different. Such differences become more pronounced at higher temperatures.

Effect of Humidity on the Permeability of Alcohols in Hydroxypropyl Xylan Films

“…To predict possibility of water clustering, Henry’s law was used to estimate the amount of water absorbed in the polymer films at different levels of RH. Using the specific retention volumes, V g 0 , as defined in eq , of water at infinite dilution in HPX films, the weight-fraction-based Henry’s constants were calculated as follows: where M 1 is the molecular weight of water and R is the universal gas constant. Using the above equation, water contents at different levels of RH for the three films were calculated and are summarized in Table .…”

Molecular Origin of the Anomalous Thermodynamic Behavior of Single-site Ethylene-1-octene Copolymer Liquids with Different Branch Contents

“…Most recently, using the technique of inverse gas chromatography (IGC), we have demonstrated that the two types of copolymers with comparable molecular characteristics (e.g., molecular weight averages, average branch content (i.e., number of branches per 1000 backbone carbons), etc.) in their liquid state exhibit very different abilities to absorb hydrocarbon solvents at elevated temperatures . This was somewhat surprising, considering the fact that both polymers possess similar chemical structures and that they are in their amorphous state at high temperatures.…”

“…in their liquid state exhibit very different abilities to absorb hydrocarbon solvents at elevated temperatures. 2 This was somewhat surprising, considering the fact that both polymers possess similar chemical structures and that they are in their amorphous state at high temperatures. In particular, at a fixed temperature and for a given hydrocarbon solvent, our previous work showed that zero-pressure-weight-fraction Henry's constants (H 12 0 ) of ss-EO exhibit a slightly increasing trend with increasing branch content over the range from 10 to 35 while that of ZN-EO decreases significantly.…”