Initiation ethylene/carbon monoxide

Catalysts for ethylene/carbon monoxide copolymerisation were initially obtained from Ni(II) derivatives, such as K2Ni(CN)4 and (w-Bu4N)2 Ni(CN)4, and Pd(II) derivatives, such as [(w-Bu3P)PdCl2]2, Pd(CN)2 and HPd(CN)3, often combined with alcohol or protonic acid as a cocatalyst [241]. It must be emphasised that, in contrast to titanium-, zirconium- or vanadium-based catalysts, nickel- and palladium-based catalysts tolerate polar functional groups (including hydroxyl, carboxylic and sulfonic groups)... 

Initiation reactions in ethylene/carbon monoxide copolymerisation systems with palladium-based catalysts are presented by the schemes [107]... 

The most recent addition to the engineering polymer field is the ethylene/carbon monoxide (COPO) alternating copolymers initially introduced by Shell. The commercial polymer is highly crystalline and believed to contain small amounts of propylene to reduce the crystalline melting point to allow a broad window of process-ability. COPO should offer serious competition to polyacetal, PA, and PBT. With the favorable raw materials cost, COPO should be a successful and competitive entry. As is now expected with new polymers, intense blend patent activity accompanies the introduction. This has also occurred with COPO as is noted in various U.S. patents involving COPO blends (See Table 17.4). COPO polymers are available from Shell (Carilon ) and BP (Ketonex ). 

Mitsubishi [101] claimed a unique biodegradable polycarboxylate (Scheme 8) containing ethylene, carbon monoxide, and maleic anhydride monomers. The initial degradation step is photoactivation to yield low-molecular-weight fragments as indicated in Table 12.2. Unfortunately, no biodegradation data were reported on these fragments. 

Other recent patents include copolymers of tdnyl ketones with acrylates, methacrylates, and styrene (O Brien, 1993) an ethylene/carbon monoxide (1-7 wt%) blend as a photo initiator in polycaprolactone/polyethylene blends (Hirsoe, 1992) ethylene/ carbon monoxide for degradable golf tees (Akimoto) a vinyl ketone analog of Exxon s carbon monoxide/dioxapane/ethylene (Priddy, 1992) a photodegradable food wrapper based on blends of a polyolefin/starch and photo activators for the... 

In recent years, chemically modified polymers have gained an increasing importance in the manufacture of rubbers and plastic materials. Unsaturated polymers are particularly suitable for such transfomiations. It seemed to us in 1990 that a complementary approach to radical-initiated copolymerization of ethylene-carbon monoxide would be the reaction of polybutadiene with carbon monoxide under free radical conditions (eq 3). Due to the entropy factors, which are favorable in unimolecular reactions, it was expected that mild experimental conditions would be suitable, i.e. relatively low reaction temperature and pressure. Furthermore, it was hoped to find some special properties in this material containing polycyclopentanonic units. From the chemical point of view, the expectation turned out to be partidly correct. 

We consider first some experimental observations. In general, the initial heats of adsorption on metals tend to follow a common pattern, similar for such common adsorbates as hydrogen, nitrogen, ammonia, carbon monoxide, and ethylene. The usual order of decreasing Q values is Ta > W > Cr > Fe > Ni > Rh > Cu > Au a traditional illustration may be found in Refs. 81, 84, and 165. It appears, first, that transition metals are the most active ones in chemisorption and, second, that the activity correlates with the percent of d character in the metallic bond. What appears to be involved is the ability of a metal to use d orbitals in forming an adsorption bond. An old but still illustrative example is shown in Fig. XVIII-17, for the case of ethylene hydrogenation. 

Fig. 3. Pressure required for ignition of mixtures of acetylene and a diluent gas (air, oxygen, butane, propane, methane, carbon monoxide, ethylene, oil gas, nitrogen, helium, or hydrogen) at room temperature. Initiation fused resistance wire. Container A, 50 mm dia x 305 mm length (73) B,...

Carbon monoxide also reacts with olefins such as ethylene to produce high molecular weight polymers. The reaction of CO with ethylene can be initiated by an x-ray irradiator (62) or transition-metal cataly2ed reactions (63). The copolymeri2ation of ethylene with carbon monoxide is cataly2ed by cationic Pd (II) complexes such as Pd[P(CgH )2] (CH CN) (BF 2 where n = 1-3. With this catalyst, copolymeri2ation can be carried out at 25°C and pressures as low as 2.1 MPa. 

In the ethylene atmosphere, carbon monoxide and ethylenimine copolymerized with a radical initiator to form a terpolymer239. The following radical mechanism may be proposed ... 

This industrial process remains essentially unchanged from the 1950s [25], Here, a free-radical initiator is added to the ethylene monomer at supercritical conditions (276 MPa and 200-300 °C). The polyethylene remains in the supercritical solution until the pressure is lowered to around 5 MPa, whereupon it precipitates. A range of other monomers can be copolymerized, including carbon monoxide to give polyketones, as shown in Scheme 10.19 [26],... 

The typical Phillips catalyst comprises chemically anchored chromium species on a silica support. The formation of a surface silyl chromate, and eventually silyl dichromate [scheme (29)], is significant during the catalyst preparation, because at the calcination temperature chromium trioxide would decompose to lower-valent oxides. Chromium trioxide probably binds to the silica as the chromate initially, at least for the ordinary 1% loading. However, some rearrangement to the dichromate at high temperature may occur. It is incorrect to regard only one particular valence state of chromium as the only one capable of catalysing ethylene polymerisation. On the commercial CrOs/silica catalyst the predominant active species after reduction by ethylene or carbon monoxide [scheme (59)] is probably Cr(II), but other species, particularly Cr(III), may also polymerise ethylene under certain conditions ... 

It should be added, for the sake of correctness, that ethylene and carbon monoxide insertions in initiation and propagation steps, shown in schemes (80) to (83), are preceded by the coordination of ethylene (Figure 2.1) and carbon monoxide (Figure 2.2) respectively ... 

The compatibility of blends of poly (vinyl chloride) (PVC) and a terpolymer (TP) of ethylene, vinyl acetate, and carbon monoxide was investigated by dynamic mechanical, dielectric, and calorimetric studies. Each technique showed a single glass transition and that transition temperature, as defined by the initial rise in E" at 110 Hz, c" at 100 Hz, and Cp at 20°C/min, agreed to within 5°C. PVC acted as a polymeric diluent which lowered the crystallization temperature, Tc, of the terpolymer such that Tc decreased with increasing PVC content while Tg increased. In this manner, terpolymer crystallization is inhibited in blends whose value of (Tc — Tg) was negative. Thus, all blends which contained 60% or more PVC showed little or no crystallinity unless solvent was added. 

Such a mechanism of carbon monoxide interaction with active centers is compatible with the data on the slow copolymerization of CO with ethylene found for the ethylene polymerization by some one-component catalysts This copolymerization may proceed also in the case of two-component catalysts resulting in an increase of the number of radioactive tags in the polymer with time (see Fig. 1). Arguments have been given that the rapid increase of polymer radioactivity in the initial period (5-10 min) is due to the insertion of the first CO molecule into the active metal-carbon bond. 

After activation, the catalyst is intrcxiuced into the polymerization reactor as slurry in a saturated hydrocarbon such as isobutane. The precise mechanism of initiation is not known, but is believed to involve oxidation-reduction reactions between ethylene and chromium, resulting in formation of chromium (II) which is the precursor for the active center. Polymerization is initially slow, possibly because oxidation products coordinate with (and block) active centers. Consequently, standard Phillips catalysts typically exhibit an induction period. The typical kinetic profile for a Phillips catalyst is shown in curve C of Figure 3.1. If the catalyst is pre-reduced by carbon monoxide, the induction period is not observed. Unlike Ziegler-Natta and most single site catalysts, no cocatalyst is required for standard Phillips catalysts. Molecular weight distribution of the polymer is broad because of the variety of active centers. 

At atmospheric pressure, when the mixture was admitted through the aluminum tip, no ignition took place with hydrogen, cyanogen, and methane (ozone rate 6 cc. per second). Carbon monoxide and ethylene, however, ignited spontaneously and burned normally afterwards without initiating an explosion or detonation in the ozone line. 

Ludwig Mond (1839-1909) a German chemist who had emigrated from Kassel, discovered the first binary metal carbonyl, the volatile, colorless liquid Ni(CO)4, in his soda factory at Widnes, UK [75], This discovery not only initiated systematic research in this particular area but also hadgreat relevance to the activation of carbon monoxide by transition metals. Mond s discovery initiated Paul Sabatier s study of the nickel chemistry of ethylene, in which context he found the catalytic hydrogenation of C-C double bonds. 

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