Alexander Penlidis

Case studies and literature review on the estimation of copolymerization reactivity ratios

The enhanced features of a computer program ( RREVM ) for the estimation of copolymerization reactivity ratios using statistically sound techniques are illustrated with experimental and simulated case studies. In parallel, a literature review is given on the estimation of reactivity ratios. Both aspects are extensions based on the articles by Dube et al. 1 and Rossignoli and Duever.

Mathematical modeling and computer simulator/database for emulsion polymerizations

Though emulsion polymerization has been commercialized for more than half a century, some important aspects like particle nucleation, coagulation, etc. are still not well understood. To simulate this complicated process, a general approach has been adopted. Information from classical modeling sources in the literature (e.g. [J Macromol Sci, Rev Macromol Chem C11 (1974) 177; J Polym Sci Chem 19 (1981) 25; ACS Symp Ser 313 (1986) 219; J Macromol Sci, Rev Macromol Chem 38 (1998) 207]; just to mention a few) has been carefully reviewed and general mass (molar), energy, population (dead polymer molecules and radicals) and particle balances have been written and evaluated with experimental data, with the final aim to develop a model that is flexible, reliable and practical at the same time.

ON-LINE SENSORS FOR POLYMERIZATION REACTORS

Abstract The main goals in operating a polymer reactor are high yield (productivity), high product quality, and safe operation (of course, within some overall economic framework). These goals are very difficult, if not impossible, to achieve without efficient and reliable online measurement [characterization, monitoring, sensing) techniques. Although considerable advances have been made in the last twenty years in many aspects of polymer reaction engineering and production technology, sensor technology has remained rather static. It is only recently, mainly in the last five years or so, that we have started seeing more reliable on-line sensors, especially with the parallel advancements in computer and process control technology. The complex nature of polymerization systems is undoubtedly the first good reason for major difficulties in on-line sensor technology. Another good reason is the fact that sensor development is a multidisciplinary task, including statistics mathematical modeling, process knowledge...

A Comprehensive Simulator/Database Package for Reviewing Free-Radical Homopolymerizations

Abstract Several models have been proposed in the literature over the last two decades in order to simulate free-radical homopolymerizations. However, most of these models deal with one specific monomer system, usually under restricted polymerization conditions.

A systematic approach to the study of multicomponent polymerization kinetics—the butyl acrylate/methyl methacrylate/vinyl acetate example: 1. Bulk copolymerization

Abstract A systematic study of the terpolymerization of butyl acrylate/methyl methacrylate/vinyl acetate (BA/MMA/VAc) is being conducted. In the first stage of this study, bulk copolymerizations of BA/MMA, BA/VAc and MMA/VAc were performed. The polymers produced were characterized for conversion, composition and molecular weight. For the vinyl acetate-containing copolymerizations, during the first period of the reaction the acrylic monomer virtually ‘homopolymerized’ and thus the reaction exhibited the characteristics of a ‘solution’ polymerization with the vinyl acetate acting as the ‘solvent’. Typical solution polymerization behaviour, i.e. a dampened autoacceleration or gel effect, was in evidence for the first period of the reaction. After the virtual depletion of the acrylic monomer, the remaining vinyl acetate polymerized and exhibited its own characteristic gel effect. We refer to this phenomenon as the ‘double gel effect’. Estimates of the copolymerization reactivity ratios were calculated and were found to predict copolymer composition accurately through the full conversion range for each copolymer system. Extremely high-molecular-weight polymer was produced attesting to the high degree of branching in these copolymer systems.

Controlling molecular weight distributions of polyethylene by combining soluble metallocene/MAO catalysts

A critical look at the possibility of controlling the molecular weight distribution (MWD) of polyolefins by combining metallocene/methylalumoxane (MAO) catalysts is offered. Catalysts investigated were bis(cyclopentadienyl)zirconium dichloride (Cp2ZrCl2), its titanium and hafnium analogues (Cp2TiCl2 and Cp2HfCl2), as well as rac-ethylenebis(indenyl)zirconium dichloride (Et(Ind)2ZrCl2). As observed by other researchers, the MWD of polyethylene can be manipulated by combining soluble catalysts, which on their own produce polymer with narrow MWD but with different average molecular weights. Combined in slurry polymerization reactors, the catalysts in consideration produce ethylene homopolymer just as they would independently. Unimodal or bimodal MWDs can be obtained. This effect can be mimicked by blending polymers produced by the individual catalysts. We demonstrate how a variability in catalyst activity translates into a variability in MWD when mixing soluble catalysts in polymerization. Such a variability in MWD must be considered when setting goals for MWD control. We introduce a more quantitative approach to controlling the MWD using this method.

An approach to interval estimation in partial least squares regression

Abstract Although partial least squares regression (PLS) is widely used in chemometrics for quantitative spectral analysis, little is known about the distribution of the prediction error from calibration models based on PLS. As a result, we must rely on computationally intensive procedures like bootstrapping to produce confidence intervals for predictions, or, in many cases, we must do with no interval estimates at all, only point estimates. In this paper we present an approach, based on the linearization of the PLS estimator, that allows us to construct approximate confidence intervals for predictions from PLS.

Polymerization mechanism for in situ supported metallocene catalysts

The polymerization of ethylene was carried out with a novel in situ supported metallocene catalyst that eliminated the need for a supporting step before polymerization. In the absence of trimethyl aluminum (TMA), in situ supported Et[Ind]2ZrCl2 was not active, but the addition of TMA during polymerization activated the catalyst. Et[Ind]2Zr(CH3)2 was active even in the absence of TMA, whereas the addition of TMA during polymerization enhanced the catalytic activity. The polymerization-rate profiles of the in situ supported metallocene catalysts did not show rate decay as a function of time. A polymerization mechanism for the in situ supported metallocene catalysts is proposed for this behavior. During polymerization, the in situ supported metallocene catalysts may deactivate, but homogeneous metallocene species present in the reactor may form new active sites and compensate for deactivated sites.

Effect of operating conditions on the molecular weight distribution of polyethylene synthesized by soluble metallocene/methylaluminoxane catalysts

Investigations of the effects of polymerization conditions on the molecular weight distribution (MWD) of polyethylene synthesized with soluble metallocene/methylaluminoxane (MAO) catalysts have been performed. The following variables were investigated in this study: catalyst type, polymerization temperature, catalyst concentration, MAO concentration, chain transfer agent, ethylene partial pressure, as well as the substitution of MAO with trimethylaluminium (TMA), and of different catalyst activities of polyethylene. Similarities and differences with other published results are highlighted. In all cases, an effort was made to illustrate the significance of the effects by presenting replicate measurements. Catalysts investigated were bis(cyclopentadienyl)zirconium dichloride (Cp 2 ZrCl 2 (1)), its titanium and hafnium analogues (Cp 2 TiCl 2 (2) and Cp 2 HfCl 2 (3)), as well as rac-ethylenebis(indenyl)zirconium dichloride (Et(Ind) 2 ZrCl 2 (4)) and rac-ethylenebis(4,5,6,7-tetrahydroindenyl)zirconium dichloride (Et(H 4 Ind) 2 ZrCL (5)). According to a 2 2 factorial experiment, independent increases in the concentrations of catalyst or MAO cause a decrease in average molecular weight, with no interaction between these two factors. Replacing MAO with TMA at constant overall aluminium concentration causes a drastic decrease in average molecular weight. Extremely high polymerization rates were observed to impart only a slight increase in the breadth of the MWD. The effects of ethylene partial pressure suggest that for the zirconium catalysts, transfer to monomer is the main chain transfer mechanism, while for hafnium catalysts, this is not the case.

Mechanical properties of ethylene/1-hexene copolymers with tailored short chain branching distributions

Abstract Recently, we have investigated a metallocene catalyst system that can produce polyethylene and ethylene/α-olefin copolymers with tailored molecular weight and short chain branching distributions (SCBD). Ethylene/α-olefin copolymers produced with this system have narrow molecular weight distributions as expected from metallocene catalysts. However, these copolymers are quite unique in that their SCBDs are broad and sometimes bimodal, similar to Ziegler–Natta LLDPE. To examine the effect of these broad SCBDs on the polymer properties, a series of poly(ethylene- co -1-hexene) resins with very distinct, and in some cases bimodal crystalline distributions, were synthesized. The attractive feature of the resins in this study is that their molecular weight distributions are similar but each possesses a different SCBD, thus effectively minimizing the effect of molecular weight on the properties investigated. It was found that the tensile properties of a copolymer could be controlled by the ratio of the crystalline species present in the sample. In this study, a balance of stiffness and toughness was exhibited by a copolymer containing a large proportion of crystalline material and a small fraction of material of lower crystallinity.