Macromol. React. Eng. 5–6/2011

Molecular Weight Distribution of Ethylene/1‐Olefin Copolymers: Generalized Bimodality Criterion

“…At each peak location, the term in the square root of Equation (9) is equal to zero and there is only one solution, r = r − = r + . Therefore, the upper and lower bound for m calculated with Equations (13) and (14) are also the same, m − (r n1 , r n2 ) = m + (r n1 , r n2 ). Table 1 summarizes three hypothetical case studies for ethylene/1-olefin copolymers used to validate the proposed bimodality criterion; these polymers have the same values of r n1 and m but different values of r n2 .…”

“…The algorithm used to create the comprehensive 3D MWD bimodality map is described in Figure 1. This algorithm calculates the values of m − and m + at each r n1 and r n2 with Equations (13) and (14). These set of data (m − and m + for each r n1 and r n2 ) delineates a 3D map determining whether a combination of two single-site-type metallocene catalysts produces copolymers with bimodal or unimodal MWDs.…”

“…Our group has previously developed different bimodality criteria for MWD, CCD, and SLD. [14,15] A simple MWD bimodality criterion for ethylene/1-olefin copolymers made with two single-site-type catalysts was first proposed by Soares and Kim and validated with simulation data and experimental results. [16][17][18] Later, Nele and Pinto have further developed the MWD bimodality criterion for linear polymers made at steady-state conditions for n single-site-type catalytic systems.…”

Development of Bimodality Criterion for the Sequence Length Distribution of Ethylene/1‐Olefin Copolymers

“…An MWD bimodality criterion to determine appropriate combinations of two metallocene catalysts that would produce ethylene/1‐olefin copolymers with a bimodal MWD was proposed and validated with both simulation data and experimental gel permeation chromatography (GPC) of ethylene/1‐hexene copolymers produced with mixed metallocene system . More recently, a similar CCD bimodality criterion was also developed and tested with simulation data and experimental crystallization analysis fractionation (CRYSTAF) and crystallization elution fractionation (CEF) of ethylene/1‐octene copolymer blends . However, a SLD bimodality criterion is not available even though SLD is regarded as one of important microstructural distributions.…”

Simultaneous Deconvolution of Molecular Weight and Chemical Composition Distribution of Ethylene/1‐Olefin Copolymers: Strategy Validation and Comparison

“…Multiple‐site‐type catalysts such as heterogeneous Ziegler‐Natta and Phillips catalysts, mixed metallocene catalysts, or hybrid catalysts, typically produce ethylene/1‐olefin copolymers with broad molecular weight distribution (MWD) and chemical composition distribution (CCD) because each site type has a different set of polymerization kinetic parameters, producing chains with distinct average microstructural properties 1–8. Ethylene/1‐olefin copolymers made with these catalysts can be considered to be a blend of chains that follow various single‐site MWDs and CCDs.…”