Coordination polymerization copolymers

Copolymers of VDC can also be prepared by methods other than conventional free-radical polymerization. Copolymers have been formed by irradiation and with various organometaHic and coordination complex catalysts (28,44,50—53). Graft copolymers have also been described (54—58). 

Coordination polymerization is the most versatile method of preparing PCL and its copolymers, affording high molecular weights and conversions, and either block or random copolymers depending on the conditions. As with the preceding classes of initiators, the product... 

The first example of Iiving polyolefin with a uniform chain length was found in the low-temperature polymerization of propylene with the soluble catalyst composed of V(acac)3 and Al(C1Hi)2Cl. The mechanism of the living coordination polymerization is discussed on the basis of the kinetic and stereochemical data. Subsequently, some applications of living polypropylene are introduced to prepare tailor-made polymers such as terminally functionalized polymers and block copolymers which exhibit new characteristic properties. Finally, new types of soluble Ziegler-Natta catalysts are briefly surveyed in connection with the synthesis of living polyolefins. 

The first example of a living polyolefin with a uniform chain length was disclosed in 1979 by Doi, Ueki and Keii 47,48) who used the soluble Ziegler-Natta catalyst composed of V(acac)3 (acac = acetylacetonate anion) and A1(C2H5)2C1 for the polymerization of propylene. In this review, we deal with the kinetics and mechanism of living coordination polymerization of a-olefins with soluble Ziegler-Natta catalysts and the synthesis of well-defined block copolymers by the use of living polyolefins. 

Various types of well-defined block copolymers containing polypropylene segments have been synthesized by Doi et al. on the basis of three methods (i) sequential coordination polymerization of propylene and ethylene 83-m>, (ii) transformation of living polypropylene ends to radical or cationic ones which initiate the polymerization of polar monomers 104, u2i, and (iii) coupling reaction between iodine-terminated monodisperse polypropylene and living polystyrene anion 84). In particular, the well-defined block copolymers consisting of polypropylene blocks and polar monomer unit blocks are expected to exhibit new characteristic properties owing to the effect of microphase separation. 

Well-defined diblock (P—R) and triblock (P R — P) copolymers consisting of the polypropylene block (P) and the ethylene-propylene random copolymer block (R) were prepared by adding ethylene monomer during the living coordination polymerization of propylene with the soluble V(acac)3/Al(C2H5)2Cl/anisole catalyst U1). 

Poly(e-caprolactone) (PCL) is synthesized by anionic, cationic or coordination polymerization of e-caprolactone. Degradable block copolymers with polyethylene glycol, diglycolide, substituted caprolactones and /-valerolactone can also be synthesized. Like the lactide polymers, PCL and its copolymers degrade both in vitro and in vivo by bulk hydrolysis, with the degradation rate affected by the size and shape of the device and additives. 

Coordination polymerizations are often accompanied by isomerization. By means of the ternary catalytic system VC14, (acac)3Fe, and Et3Al, propene can yield crystalline polyethylene and the amorphous ethylene—propene copolymer. Many more such cases have, of course, been observed. Probably of greatest importance are those where a non-polymerizing 2-alkene is is-omerized to 1-alkene prior to propagation [355]. 

By far the most important industrial coordination polymerization processes are Ziegler-Natta polymerizations of 1-olefins [107-110], most notably the production of high-density polyethene [111] and stereo-specific olefin polymers and copolymers [108], However, these processes employ solid catalysts, and the complex kinetics on their surfaces have no place in a book on homogeneous reactions. 

Coordination polymerization of dienes has progressed significantly within the last decade. Selective polymerization of 1,3-dienes is reinforced by conventional transition metal catalysts and by new organolanthanide catalysts. Nonconjugated dienes also polymerize selectively to produce polymers with cyclic units or vinyl pendant groups. Living polymerization of dienes has become common, which enabled preparation of block copolymers of dienes with alkenes and other monomers. Another new topic in this field is the polymerization of allenes and methylenecycloalkanes catalyzed by late transition metal complexes. These reactive dienes and derivatives provide polymers with novel structure as well as functionalized polymers. The precision polymerization of 1,2-, 1,3-, and l,n-dienes, achieved in recent years, will be developed to construct new polymer materials with olefin functionality. 

Constitutional isomers, 22, 45, 172, 291 of alkanes, number of, 60 table Coordination polymerization, 246, 383, 567-570, 573 Copolymer, 383 Copper (1) salts... 

The three major classes of polyethylene are described by the acronyms HOPE. LDPE. and LLDPE. High-density polyethylene (HOPE) is a linear, semicrystalline ethylene homopolymer Tm 135 °C) prepared by Ziegler—Natta and chromium-based coordination polymerization technology. Linear low-density polyethylene (LLDPE) is a random copolymer of ethylene and a-olefins (e.g.. 1-butene. 1-hexene, or... 

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]. 

The development of novel titanium carbene complexes by Grubbs has opened up a route to living polymer systems, using coordinating polymerizations as opposed to those derived from ionic initiators, which can be used to form block copolymers or produce chains with a functionalized end group. The initiating species are formed by the reaction of norbomene with a titanocyclobutane derived from 3,3-dimethyl cycloprene... 

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