The macroligand effect of the catalytic system WCl6-Et2AlCl for ring opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) was investigated. The experimental results show that macroligand effect varies with the structure of the ligands. The macroligands bearing benzene group and steric hindered phenolic unit not only can obviously increase the yield of synthesized polydicyclopentadiene (PDCPD) but also improve the synthesized polymer's mechanical properties. The mechanism of macroligand effect is discussed. The synthesized PDCPD was characterized by methods of scanning electron microscopy (SEM) and X-ray diffraction.

Ring-opening polymerization (ROP) of L-lactide (LLA) was carried out in bulk and toluene solution, respectively, using sodium bis (2-methoxyethoxy) aluminum hydride (Red-Al) as the catalyst (initiator). Experimental results show that Red-Al possesses typical characteristics of a living polymerization initiator. Bulk polymerization (110℃, 48 h) of LLA gives a snowwhite polymer of high isotacticity (≥95.2%), moderate molecular weight (MW) (Mn=2.3×104), and quite narrow MW distribution (MWD, PDI=1.12). Investigation of the kinetics of the polymerization in toluene shows that plots of In ([M]0/[M]t) versus time and Mn (numberaverage MW) of synthesized PLLA versus monomer conversion are linear, which is a typical feature of living polymerization. The mechanism of the ROP was postulated on the basis of 1H NMR monitoring of the polymerization. The synthesized PLLA shows high isotacticity. The degree of transesterification and stereoselectivity of the ROP by Red-Al were estimated according to 13C NMR characterization of poly rac-LA.

Neither dimethylhafnocene nor [1, 2-bis (tetrahydroindenyl) ethane] dimethylzirconium, 1, reacts at anappreciable rate with phenylsilane. In the case of the hafnium compound, this results in complete masking of catalytic activity toward dehydrocoupling of phenylsilane, while in the case of 1 activity is greatly suppressed. This behavior is governed by the low reactivity of the M-C bonds toward σ-bond metathesis with silanes. Catalysts generated by reaction of MeLi and PhSiH3 with hafnocene dichloride or [1,2-bis (tetrahydroindeny1)-ethune] dichlorozirconium, 2, show high activities toward PhSiH3coupling. The molecular weights of the resulting polymers are significantly higher than those of polymers derived from CpzTiMez and CpzZrMez catalysts, and the hafnocene catalyst gives unusually low proportions of low molecular weight cyclic products. It is proposed that the catalyst species, probably a hydrido silyl complex, in these new systems are generated by reaction of a reactive lithium hydride, resulting from rapid reaction of MeLi with PhSiH3, with the chloro complexes.

Hexabutyl guanidinium acetate (HBG•OAc) was synthesized and successfully used as a catalyst for the ring-opening polymerization (ROP) of lactides. The experimental results indicated that the guanidinium salt HBG•OAc showed satisfactory catalytic behavior. Polymerization in bulk (120℃, 18h) produced polylactides with moderate molecular weights (number-average molecular weight=2.0×104) and very narrow molecular weight distributions (polydispersity index=1.07-1.12). A kinetic study of polymerization in bulk with HBG•OAc as an initiator revealed that the polymerization possessed typical characteristics of living polymerization. A ROP mechanism by HBG•OAc was proposed on the basis of the additive effect of the polymerization and the 1H NMR characterization of the microstructure of the product polymers.

Ring-opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) was conducted by using catalyst systems WCl6-Et2AlCl, (WCl6-PhCOMe)-Et2AlCl and their polystyrene supported counterparts. Experimental results indicate that the acetophenone modified catalyst system shows better catalytic properties than the unmodified system does and that supporting the catalysts on a polystyrene can improve further the catalyst systems'catalytic properties. As a result, the polymer yield of the ROMP increased, the mechanical properties of NIS (notched impact strength), TS (tensile strength) of synthesized polydicyclopentadiene (PDCPD) enhanced. The mechanism in which supporting improves the properties of the catalyst systems is discussed.