Polyethylene modified catalysts

The discovery of the Ni effect led to the invention of polyethylene production catalysed by TiCI4 combined with Et3Al, the so-called the Ziegler catalyst, in 1953. Soon after, the process for isotactic polypropylene was invented by Natta using a slightly modified catalyst prepared from TiCl3 and Et3Al, which is called the Natta catalyst (eq. 1.7) [7],... 

Copolymerization with a-olefins over a Phillips catalyst is a key method for controlling the density and microstmctures of the polyethylene products in industrial processes. Table 5 also listed the energy barriers for the primary 1,2-insertion of 1-butene and 1-hexene, and the subsequent chain transfer by p-H elimination for all the three kinds of Ti-modified models. The calculated energy barriers showed that Ti-modification could also promote the activity for ethylene copolymerization with a-olefins. The energy differences between comonomer insertion and chain transfer can lead to a conclusion on the effect of Ti-modification on the distribution of the inserted comonomers in polyethylene chains. As listed in Table 5, the difference between energy barriers for chain propagation and for chain transfer decreased for model sites 4g, 12g, and 15g. Therefore, it was reasonable to conclude that Ti-modified catalyst was likely to make low MW polyethylene with much less comonomer insertion because the inserted comonomer mainly led to a chain transfer reaction and left the inserted comonomer at the chain end. As a result, the increased chain termination by comonomer resulted in less SCBs in the low MW fraction and higher density of the polyethylene product for the Ti-modified Phillips catalyst. 

Paixao and coworkers showed that a sulfur-modified catalyst C5 was able to efficiently catalyse the Michael addition of malonates to enals in EtOH/ brine mixture (Scheme 8.7). The sulfur-containing catalyst was efficient for the Michael addition of aldehydes to nitroalkenes in polyethylene glycol (PEG). The most important feature of this system was its reusability. After extraction of the reaction products, the PEG solution containing the organocatalyst was reused at least four times with no adverse effects on yield or enantioselectivity. ... 

H. Czarczynska and W. Trochimczuk, Changes the Structure of Chloromethylated Polyethylene Modified with Styrene and Divinylbenzene Foils due to Friedel-Crafts Catalysts, J. Polym. Sci. 47C, 111 (1974). Semi-II IPNs and IPNs. Chloromethylated structures as points of crosslinking. Effects of AICI3, ZnCl2, and SnCU as catalysts. Optical microscopy of phase separation. 

The modified catalyst formulation was then tested in an ethylene polymerization experiment carried out at 225-235 F in isobutane at a total pressure of 500 psig. A control catalyst prepared under. similar conditions without the titanium compoimd was also examined in a similar polymerization experiment. The results showed that the Melt Index of the polyethylene prepared with the titanium-containing catalyst was 3.5, while the control catalyst produced polyethylene with a Melt Index of only 0.48. Hence, the Melt Index data showed that the molecular weight of the... 

Thermal aging of the chromocene-based catalyst in an inert atmosphere at 100-600°C resulted in the complete loss of the cyclopentadienyl ligands that provides a modified catalyst with only 10-30% of the original activity and introduces a high level of terminal unsaturation into the polyethylene [29]. 

Chemically Modified Waxes. Hydrocarbon waxes of the microcrystaHine, polyethylene, and polymethylene classes are chemically modified to meet specific market needs. In the vast majority of cases, the first step is air oxidation of the wax with or without catalysts (11). The product has an acid number usuaHy no higher than 30 and a saponification number usuaHy no lower than 25. An alternative step is the reaction of the wax with a polycarboxyHc acid, eg, maleic, at high temperature (12). Through its carboxyl groups, the oxidised wax can be further modified in such reactions as saponification or esterification. Oxidised wax is easily emulsified in water through the use of surfactants or simple soaps, and is widely used in many coating and poHsh appHcations. 

Rubber blends with cure rate mismatch is a burning issue for elastomer sandwich products. For example, in a conveyor belt composite structure there is always a combination of two to three special purpose rubbers and, depending on the rubber composition, the curatives are different. Hence, those composite rubber formulations need special processing and formulation to avoid a gross dissimilarity in their cure rate. Recent research in this area indicated that the modification of one or more rubbers with the same cure sites would be a possible solution. Thus, chlorosulfonated polyethylene (CSP) rubber was modified in laboratory scale with 10 wt% of 93% active meta-phenylene bismaleimide (BMI) and 0.5 wt% of dimethyl-di-(/ r/-butyl-peroxy) hexane (catalyst). Mixing was carried out in an oil heated Banbury-type mixer at 150-160°C. The addition of a catalyst was very critical. After 2 min high-shear dispersive melt mix-... 

The effect of incorporating p-hydroxybenzoic acid (I) into the structures of various unsaturated polyesters synthesised from polyethylene terephthalate (PET) waste depolymerised by glycolysis at three different diethylene glycol (DEG) ratios with Mn acetate as transesterification catalyst, was studied. Copolyesters of PET modified using various I mole ratios showed excellent mechanical and chemical properties because of their liquid crystalline behaviour. The oligoesters obtained from the twelve modified unsaturated polyesters (MUP) were reacted with I and maleic anhydride, with variation of the I ratio with a view to determining the effect on mechanical... 

A number of highly active ethylene polymerisation catalysts have resulted from the combination of functionalised NHC ligands with Ti, the first of these was the bis(phenolate)carbene ligated complex 3 [8], Upon activation with modified MAO (MMAO), this species gave an activity of 290 kg-mol bar h in the one test reported, making it one of the most active carbene-based olefin polymerisation catalysts known. In later work the same complex was evaluated with straight MAO activation, and activities of up to ca. 100 kg mol -bar" -h" were reported for linear polyethylene production [9],... 

The modified supported powder electrodes used in the experiments hitherto described on the anodic activity of CoTAA are out of the question for practical application in fuel cells, as they do not have sufficient mechanical stability and their ohmic resistance is very high (about 1—2 ohm). For these reasons, compact electrodes with CoTAA were prepared by pressing or rolling a mixture of CoTAA, activated carbon, polyethylene, and PTFE powders in a metal gauze. The electrodes prepared in this way show different activities depending on the composition and the sintering conditions. Electrodes prepared under optimal conditions can be loaded up to about 40 mA/cm2 at a potential of 350 mV at 70 °C in 3 M HCOOH, with relatively good catalyst utilization (about 5 A/g) and adequate stability. 

Finally the ESR spectrum of Nb(7r-allyl)4/alumina was unaffected by the addition of ethylene gas to the ESR sample tube. It is assumed that polyethylene is produced in this process since polymer can be isolated from larger scale reactions under similar conditions. The accepted mechanism for the ethylene growth reaction postulates a steady-state concentration of a a-bonded transition metal-hydrocarbon species which would be expected to modify the ESR spectrum of the supported complex. A possible explanation for the failure to detect a change in the ESR spectrum may be that only a small number of the niobium sites are active for polymerization. Although further experiments are needed to verify this proposition, it is consistent with IR data and radiochemical studies of similar catalyst systems (41, 42, 43). 

---