Ethylene polymerization monomer conversion

The molecular weight distribution of a polymer produced with a chain shuttling catalyst/CSA system is highly dependent on reaction conditions. The extent of reversibility with the catalyst/CSA pairs was therefore further explored through a series of polymerizations over a range of monomer conversions (i.e., yield). A representative example from this secondary screening process is described below for precatalyst 17. Several members from this well-studied bis(phenoxyimine)-based catalyst family [39] were identified as poor incorporators in the primary screen. A series of ethylene/octene copolymerizations using 17 was performed across a... 

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The polymerization of ethylene oxide (epoxyethane, EO) with 17 also proceeded by irradiation with visible light. For example, the polymerization with the mole ratio [EO]o/[17]o of 190 in benzene at room temperature, where the monomer conversion after 205 min was very low (<2%, determined by H NMR) in the dark, proceeded to 97% conversion in only 80 min under irradiation. The Mn of the polymer, as estimated from the GPC chromatogram, was 8700, which is in excellent agreement with the expected value of 8100 provided that the numbers of the molecules of the produced polymer and 17 (X=SPr) are equal [81]. The Mw/Mn of the polymer (1.05) was close to unity, indicating the livingness of the visible Hght induced polymerization of EO initiated with (NMTPP)ZnSPr (17). 

Table III shows the increase of molecular weight of BCMO polymerization with conversion, although the polymer tends to precipitate. The monomer reactivity ratios of DOL-BCMO copolymerization were previously determined as rx (DOL) = 0.65 0.05, r2 (BCMO) = 1.5 0.1 at 0°C. by BF3 Et20 (8). Table IV shows a preparation of block copolymer of DOL, St, and BCMO. In the first step we polymerized DOL and St in the second step we added BCMO to this living system. The copolymer obtained showed an increase of molecular weight, and considerable BCMO was incorporated in the copolymer still remaining soluble in ethylene dichloride. The solubility behavior together with the increase of molecular weight with addition of BCMO shows that this polymer consists of block sequences of DOL-St and (St)-DOL-BCMO. This we call block and random copolymer of DOL-St—BCMO. We can deny the presence of BCMO, St, or DOL homopolymers in this system, but some chain-breaking reactions are unavoidable, leading to copolymer mixtures. Thus, the principle of formation of block copolymers by cationic system is partly substantiated.

This high tendency of poly(ethylene oxide) to solvate cations and from the polymeric shell around the counterion leads to autoacceleration in polymerization (polymerization faster on solvated ion-pairs), and increase of conductivity with monomer conversion. Moreover, polymerization is not sensitive to the "external" solvating agents, e.g. crown ethers. 

For the ring-opening metathesis polymerization (ROMP) in heterophase [81], a water-soluble ruthenium alkylidene was employed for the emulsion polymerization of norbornene, and an oil-soluble catalyst for the miniemulsion polymerization of norbornene and 1,5-cyclooctadiene. Similar to the polymerization of ethylene in heterophase, an organic solution of the catalyst was first miniemulsified in water, after which the monomer was added to the miniemulsion. This resulted in a high monomer conversion for norbornene ( up to 97%), and a particle size of 250nm. 

Ziegler-Natta polymerizations generally occur with olefins or dienes, or, in certain cases, also with vinyl or acrylic compounds. However, not every initiator system is equally effective with a given monomer. All Ziegler catalysts which polymerize a-olefins will also polymerize ethylene, but the converse does not equally apply. Compounds of metals from groups IV to VI of the periodic table initiate the polymerization of a-olefins as well as that of dienes. Transition metals from group VIII, on the other hand, are effective with dienes but not with a-olefins. 

Eor all these reasons heat removal and reliable temperature control are key factors in all technical ethylene polymerization processes to ensure an economical and safe process. The different processes may chose different ways to limit or remove the reaction heat (e.g., by limited conversion per reactor pass, cooling of unreacted monomer, large surface area for heat exchange) in all concepts heat management is a key aspect of the reactor design. 

Polymerization of phenylalanine catalyzed by a-chymotry in-poly(ethylene glycol) complex was examined [48]. The solvent used is chloroform saturated by Tris buffer (pH 7). The monomer conversion was 72% giving the dimer and then the hexamer. 

Capek and Chudej [87] studied the emulsion polymerization of styrene stabilized by polyethylene oxide sorbitan monolaurate with an average of 20 monomeric units of ethylene oxide per molecule (Tween 20) and initiated by the redox system of ammonium persulfate and sodium thiosulfite. It is interesting to note that the constant reaction rate period is not present in this polymerization system. The maximal rate of polymerization is proportional to the initiator and surfactant concentrations to the -0.45 and 1.5 powers, respectively. The final number of latex particles per unit volume of water is proportional to the initiator and surfactant concentrations to the 0.32 and 1.3 powers, respectively. In addition, the resultant polymer molecular weight is proportional to the initiator and surfactant concentrations to the 0.62 and -0.97 powers, respectively. Some possible reaction mechanisms may explain the deviation of the polymerization system from the classical Smith-Ewart theory. Lin et al. [88] investigated the emulsion polymerization of styrene stabilized by nonylphenol polyethoxylate with an average of 40 monomeric units of ethylene oxide per molecule (NP-40) and initiated by sodium persulfate. The rate of polymerization versus monomer conversion curves exhibit two nonsta-tionary reaction rate intervals and a vague constant rate period in between. 

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