Coordination polymerization elastomers

Table 5.1 shows the main families of polymers obtained by coordination polymerization (most of them commercial polymers), which were grouped according to their thermomechanical behavior, such as polymer and copolymers, thermoplastics, elastomers, and plastomers. Most of the polymers synthesized by coordination mechanisms correspond to different grades of polyolefins and polydienes, made with Ziegler-Natta or Phillips catalyst [31]. 

Elastomers based on biological monomers can be obtained by the stereoselective coordination polymerization of /S-myrcene (14). By the combination of a neodymium pre-catalyst with triisobutyl aluminmn in the presence of a boron activator results in a polymer in good yield, but there is evidence for crosslinking since the material displays a low solubility. 

These linear elastomers are produced by coordination polymerization using a Phillips or Z-N catalyst at low P and T. Here belongs Mxsten XLDPE from Eastman Chem. and Attane ULDPE from Dow. The first metallocene-catalyzed VLDPE was a hexene copolymer with p = 0.912 g mL made in the UNIPOL gas-phase process with Z-N catalyst and introduced by ExxonMobil as Exceed metallocene VLDPE. The resin has outstanding sealing properties (hot tack and seal strength) compared with ZN-VLDPE. The solution polymerization in a hydrocarbon usually is carried out in a continuously stirred tank reactor (CSTR), at r = 160-300 °C and P = 2.5-10 MPa with the residence time of 1-5 min [Dow in 1992 and UCC in... 

Coordination polymerization also produces high sterospecificity in the polymerization of alkenes. Isotactic and syndiotactic polymers can be obtained by appropriate choice of the catalyst components although such polymers are not useful as elastomers. However, Ziegler-Natta catalysts are used to produce EPR and EPDM rubbers. (Coordination polymerization is important for the synthesis of linear polyethylene and isotactic polypropylene which find extensive utility as plastics.) The Symposium paper by Su and Shih describes the synthesis of propylene-l-hexene block copolymers using several catalysts based on titanium and aluminum components. 

The first polymerization of an oxetane, trimethylene oxide, by coordination polymerization has been described. Copolymers of TMO with epoxides were readily made. Such copolymers provide an interesting family of new elastomers. One such elastomer, the im-AGE copolymer, was investigated in some detail and found to have a desirable combination of properties. Such TM) elastomers. 

Coordination polymerization in solution by means of Ziegler-Natta systems allows the preparation of elastomers with excellent properties since the corresponding polymer chains can contain more than 95% of 1,4-cm units this isomerism is most often required due to the corresponding mechanical characteristics of the material. 

Epichlorohydrin Elastomers without AGE. Polymerization on a commercial scale is done as either a solution or slurry process at 40—130°C in an aromatic, ahphatic, or ether solvent. Typical solvents are toluene, benzene, heptane, and diethyl ether. Trialkylaluniinum-water and triaLkylaluminum—water—acetylacetone catalysts are employed. A cationic, coordination mechanism is proposed for chain propagation. The product is isolated by steam coagulation. Polymerization is done as a continuous process in which the solvent, catalyst, and monomer are fed to a back-mixed reactor. Pinal product composition of ECH—EO is determined by careful control of the unreacted, or background, monomer in the reactor. In the manufacture of copolymers, the relative reactivity ratios must be considered. The reactivity ratio of EO to ECH has been estimated to be approximately 7 (35—37). 

Ethylene reacts by addition to many inexpensive reagents such as water, chlorine, hydrogen chloride, and oxygen to produce valuable chemicals. It can be initiated by free radicals or by coordination catalysts to produce polyethylene, the largest-volume thermoplastic polymer. It can also be copolymerized with other olefins producing polymers with improved properties. Eor example, when ethylene is polymerized with propylene, a thermoplastic elastomer is obtained. Eigure 7-1 illustrates the most important chemicals based on ethylene. 

Some of the most useful polyphosphazenes are fluoroalkoxy derivatives and amorphous copolymers (11.27) that are practicable as flame-retardant, hydrocarbon solvent- and oil-resistant elastomers, which have found aerospace and automotive applications. Polymers such as the amorphous comb polymer poly[bis(methoxyethoxyethoxy)phosphazene] (11.28) weakly coordinate Li " ions and are of substantial interest as components of polymeric electrolytes in battery technology. Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming and bioerodable materials and hydrogels have been prepared. 

The products are elastomers (recall that the starting material for natural rubber is isoprene). Butadiene can give almost complete 1,2- or 1,4-polyme depending primarily upon the coordination catalyst and the polymerization conditions ... 

Propylene oxide-based elastomers became commercially available in 1972 under the trademark Parel 12). Parel elastomers are sulfur curable copolymers of PO and alkyl glycidyl ether prepared with an aluminumalkyl-water-acetylacetone catalyst. Thus, the polymerization mechanism should be classified as coordinative anionic. 

With respect to titanium catalysts for polymerization of ethylene or propylene, Ziegler synthesized the first high-density polyethylene and Natta prepared isotactic polypropylene by means of coordination catalysts about 50 years ago. The preparation methods of catalysts have been studied extensively. These TiCL3 catalysts have very high activity for homopolymerization of ethylene and propylene, whereas, they exhibit low activity for random copolymerization of ethylene with propylene when compared to vanadium catalysts. Refer to Ziegler-Nata Catalyst, Vanadium Catalysts, and EP Terpolymer, (Source Elastomer Technology Handbook, N. P. Cheremisinoff - editor, CRC Press, Boca Raton, Florida, 1993). 

The polymerization o oxetanes with cationic catalysts has been studied by many investigators. (1.H2) RoseC. ), in particular, first reported the homopolymerization of the parent compound, tri-methylene oxide (TMO), with a Lewis acid catalyst, boron trifluoride. The use of coordination catalysts to polymerize oxetanes has been reported in the patent literature by Vandenberg.W In this work, Vandenberg polymerized oxetanes with the aluminum trialkyl -water-acetylacetone coordination catalyst (referred to as chelate catalyst) that he discovered for epoxide polymerization . This paper describes the homo- and co-polymerization of TMO with these coordination catalysts. Specific TMO copolymers, particularly with unsaturated epoxides such as allyl glycidyl ether (AGE), are shown to provide the basis for a new family o polyether elastomers. These new elastomers are compared with the related propylene oxide-allyl glycidyl ether (PO-AGE) copolymer elastomers. The historical development and general characteristics of polyether elastomers and, in particular, the propylene oxide elastomers, are reviewed below. 

Hydroxylic compounds of various types have been polymerized with uncoordinated and coordinated metalloidal monomers. Diols have also been used instead of water in polymerizations by this method (55). Hydroxyl-terminated dimethylsiloxanes polymerize with coordinated titanium compounds to yield high molecular weight elastomers (5, //, 59). Bulk polymerization at 180 C in vacuo was effective for reaction (XI-18). The products are elastomeric and possess very high molecular weights. Tetrahydroxy compounds such as pentaerythritol, 2,5-dihydroxyhydroquinone, and 3,3 -... 

The preparation of ethylene copolymers (or terpolymers) such as linear low-density polyethylenes (LLDPE), ethylene/propylene elastomers (EP), ethylene/ propylene/diene terpolymers (EPDM) is also based on these catalytic systems. Stereoregular polyisoprene and polybutadiene elastomers are also obtained by this method of polymerization the formation of 1,4-m-polydienes requires the prior double coordination of the monomer onto the growing active center ... 

Addition polymers are made by use of three processes free radical, ionic, and complex coordination catalyst. Ionic polymerization can be either anionic or cationic. Except for some elastomers that are made by ionic polymerization, commercial polymers are made by free radical polymerization or by using complex coordination catalysts. So-called living polymers are widely used in polymer research, because they can be made with very narrow molecular weight distributions. These were traditionally made using anionic polymerization, but it has been shown that living polymers can also be made using a free-radical or cationic process. 

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