Tominaga Keii

Stopped flow polymerization of propene with typical MgCl2-supported high-yield catalysts

Abstract A new method, viz. stopped flow polymerization, has been employed to observe the quasi-living polymerization state of propene. It was found that the molecular weight distribution was maintained constant from the very start of the polymerization process (i.e. after 0.1 s) and that the concentration of Al(C2H5)3 used as well as method of catalyst preparation influenced some of the kinetic parameters.

Titanium distribution on the surface of Ziegler-Natta catalysts observed by scanning Auger electron microscopy

Abstract Scanning Auger electron microscopy (SAM) with a field emission electron gun was used to analyze the surface of two different types of Ziegler-Natta catalysts. The SAM revealed the chemical composition, morphology, and distribution of the specific elements on the surface of the catalysts. The analysis also showed the difference between the surface distribution of titanium on MgCl 2 -supported catalyst and that on TiCl 3 . The results obtained in this study demonstrate that the SAM has great potential as an effective tool for the characterization of Ziegler-Natta catalyst.

Mechanistic Studies On Ziegler-Natta catalysis-A Methodological Reconsideration-

Although our present fundamental understanding of Ziegler-Natta catalysis is one of the most advanced among the commercial catalysts, it is still far from perfect. Here, the kinetic approaches are critically summarized on the basis of a three-stage methodological classification system: characterization, phenomenological formalism and mechanistic approach. Under characterization the present conception of stereoregularity is criticized. In the second stage the proposed rate equations are discussed in light of experimental precision and kinetic models. The contradictions of our models with the experimental data found in studies on the effect of hydrogen on polymerization are pointed out, and the theories proposed for molecular weight distributions are discussed. Under mechanistic approach, the confusion in defining polymerization centers are pointed out. The definition suffers from both the definition in radical polymerizations and experimental operations. Reconsideration reveals some problems which remain unsolved and these are listed herein. Finally, an attempt is made to explain the effect of hydrogen on both polymerization rate and molecular weight.

Kinetic Behavior During Initial Stage (less than 1 s) of Propene Polymerization with Supported Catalyst

The most reasonable method for determining values of the rate constants of propagation, transfer and the concentration of polymerization centers, kp, ktr and C*, is that based upon the observation of both transitional changes of number average degree of polymerization \({{\bar{P}}_{n}}\) and polymer yield Y in the initial stages of polymerization. This method has been used for long time, however, the results reported before the development of GPC are not so precise because of the use of viscosity average molecular weight in place of number average molecular weight. In addition, the use of viscosity average molecular weight in place of number average molecular weight may be possible only in the case of constant polydispersity independent of polymerization time, as pointed out by the present author (Keii 1986). Furthermore some limitations in the application of the method should be noted. For example, the method can not be applied for polymerizations of rapid transfer reaction. The applicability of the method is determined by value of the mean lifetime of growing chain, τ, i.e. the reciprocal of transfer rate constant, 1/ktr, as below.

An Absolute Test of Rival Theories for MWDs in Heterogeneous Polymerization-MWDs during Quasi-Living Polymerization

Many rival theories proposed for the origin of the broad MWDs of polymers produced with heterogeneous catalysts still persist. As an absolute test for them, the importance of the transitional behavior of MWDs during the quasi-living stage of polymerization is emphasized. Based upon the different mechanisms, all the rival theories have been constructed so as to explain the broad MWDs at the stationary state. Therefore, all competing rate processes are balanced in the stationary state, and any specification of the kinetic mechanism can not be tested by the stationary MWDs. However, for the transitional MWD from the living stage to the stationaiy state, all the rival theories predict respective behavior in response to their different mechanisms. The observed transitional MWDs show that MWDs in the living stages are always broad and then mostly narrow or remain unchanged for which all the rival theories are invalid. To understand this situation, a new theory of non-uniform sites not only with propagation but also slightly with transfer rate is proposed. The non-uniformity that conforms to a popular kinetic model gives a unified explanation about the abnormal decay kinetics recognized in many systems as well as that of the supported Ziegler catalyst.

An Intrinsic Defect of Slow Monomer Diffusion Theory for Explaining Broad MWDs

The theory of slow monomer diffusion to catalyst site through polymer matrix explains broad molecular weight distribution(MWD) of polymer produced with heterogenous Ziegler catalysts as well as rate-decay during polymerization with hydrogen dominant transfer can not be applied for polymerization with monometer dominant transfer, which is an intrinsic defect of the theory. The theory should predict that the narrowest MWD(Mw/Mn =2) for the latter case and reduction of the monomer contribution by changing concentration of monomer or by hydrogen-addition broaden MWD, which gives the basis of useful method to evaluate the theory itself. The accumulated experimental results of propene polymerizations with traditional and supported catalysts refute the above prediction.

1. Articulation of Kinetics of Quasi-Living Stages to those of Slurry Polymerization and an Unified Explanation-Propene Polymerization with MgCl2/EB/TiCl4-Al(C2H5)3-

Publisher Summary The kinetic behavior of the polymerization in a slurry system is so complex that the usual kinetic analysis cannot be applied. The kinetic behavior is supposed to be suffering from the rapid rate decay of the polymerization, the chapter attempts to develop some new method that is applicable for observing kinetic behavior of the polymerization free from any rate decay or those, at least, with a negligibly small rate decay. A stopped flow reactor was useful to carry out the polymerization for a short time, such as 0.03–1s at room temperature, where the polymerizations were those of quasi-polymerization with constant rates. From the results of the quasi-living stages of the polymerizations, one can determine precise values of rate constants of propagation and transfer reaction as well as concentrations of polymerization centers. In addition, the observation provides some important key points to understand the kinetic data of the slurry polymerization together with those reported by Giannini and Hsu et al., based on a unified kinetic model, the description of which is the purpose of this chapter.