Live-coordinate

The anionic polymerization of isocyanates using NaCN as an initiator was first reported in I960.998 The living coordinative polymerization of n-hexylisocyanate has been described using the titanium(IV) complexes (345) (348).999-1001 A trifunctional initiator has also been used to prepare star polyisocyanates.1002... 

The purpose of this review is to report on the recent developments in the macromolecular engineering of aliphatic polyesters. First, the possibilities offered by the living (co)polymerization of (di)lactones will be reviewed. The second part is devoted to the synthesis of block and graft copolymers, combining the living coordination ROP of (di)lactones with other living/controlled polymerization mechanisms of other cyclic and unsaturated comonomers. Finally, several examples of novel types of materials prepared by this macromolecular engineering will be presented. 

The formation of the live-coordinate axial complexes ZnTPP(L) has been studied electro-chemically, and thin-layer spectroelectrochemical techniques have been used to demonstrate the electrochemical and spectrochemical reversibility of the process 1184,1185... 

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. 

The active centers for the living coordination polymerization of propylene are formed by the reaction of V(acac)3 with dialkylaluminum monohalide. The oxidation state of the active vanadium ion has been studied on the basis of the UV, visible and ESR spectra of the soluble V(acac)3/A1(C2H5)2C1 catalyst82). 

Molecular hydrogen has been known for a long time as an effective chain-transfer agent in the coordination polymerization of ethylene and a-oiefms with Ziegler-Natta catalysts 99-101,50). The mechanism for the reaction of a growing polymer chain with H2 has not been established, The living coordination polymerization system is well suited for an elucidation of the mechanism, since the reaction with H2 can be studied independently of any interference from other chain-terminating processes. 

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). 

Mixture B K[SiPh(3-fcat)2 and K[SiPh(dbcat)2] (3-fcat 2,3-dihydroxybenzaldehyde, dbcat 3,5-di-f-butylcatechol) contained two complexes with asymmetric catechols. Each complex showed the presence of two resonances due to the isomerism described above. The equilibrated mixtures showed the presence of two further species (Figure 9). These are attributed to isomers of the [SiPh(3-fcat) (dbcat)]- anion. Equilibrium was not established even after 8 weeks, whereupon decomposition prevented a more quantitative kinetic analysis. Flowever, it is apparent from the two experiments described that the kinetics of redistribution of ligands between complexes varies dramatically according to the cate-cholate involved. It is reasonable to conclude that the rate of redistribution decreases as the strength of the catecholate derivative increases. The nonstatistical distribution of complexes in a mixture indicates a thermodynamic stability of the complexes in Me2SO. The likely explanation lies in the electronic rather than the steric effects in the complex, since the live-coordination imposes little steric constraint. 

H and 13C NMR studies of the diamagnetic [La(DOTP)]5 and [Lu(DOTP)]5-complexes revealed a high degree of stereochemical rigidity in these compounds [91]. In addition, [Ln(DOTP)]5- complexes possess a remarkable thermodynamic stability with long-lived coordinate bonds rendering them extremely... 

Fig. 2.21. Generic radial distribution functions for (a) a well-coordinated liquid with a long-lived coordination shell and (b) a weakly coordinated liquid. (Reprinted fromJ. E. Enderby, Chem. Soc. Rev. 24 159, 1995.)...

Oionge in LFSE"i >on chonging o six-coordmote complex to a live-coordinate (square pyromidol) or a seven-coordinate (pentagonal bipyramidai) species ... 

Doi, Y. Suzuki, S. Soga, K. A perfect initiator for living coordination polymerization of pro-pene tris(2-methyl-l,3-butanedionato)vanadium/ diethylaluminum chloride system. Makromol. Chem., Rapid Commun. 1985, 6, 639-642. 

Thermodynamic studies of the enthalpy of addition of aldehydes and acyl chlorides to [Rh(P Pr3)2Cl]2 and the hypothetical monomer Rh(P Pr3)2Cl gave unsaturated live-coordinate Rh(III) compounds according to equations (16) and (17) and afforded the values shown in Table 17. 

---