Kooji Mizunuma

Chain transfer reaction by trialkylaluminum (AIR3) in the stereospecific polymerization of propylene with metallocene - AIR3/Ph3CB(C6F5)4

Abstract Stereospecific polymerization of propylene was carried out with rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind)2ZrCl2) (1), rac-dimethylsilylenebis(indenyl)zirconium dichloride (rac-Me2Si(Ind)2ZrCl2) (2) and isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (i-Pr(Cp)(Flu)ZrCl2) (3) combined with trialkyl-aluminum (AIR3: R = C2H5, i-C4H9)/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)4) (4). In isospecific polymerization with 1 and 2, the molecular weight of polypropylenes decreased with increase in the molar ratio of AlEt3 (Et = C2H5)/Zr, whereas, an effect of AliBu3 (iBu = i-C4H9) concentration on molecular weight was not observed. The microstructures of resulting polypropylenes were studied by 13C n.m.r. and an increase in the molar ratio of ethyl end groups (derived from chain transfer to AlEt3) to n-propyl end groups (derived from β-hydrogen transfer) was observed with increase in the molar ratio of AlEt 3 Zr (1 and 2). The chain transfer reactions by both AlEt3 and AliBu3 were also detected in syndiospecific polymerization with 3. The molar ratio of alkyl (R) end groups (derived from chain transfer to AIR3) to n-propyl end groups was higher in the polypropylene obtained with AlEt3 than that obtained with AliBu3. The relative constants k trA k p (ktrA = rate constant of chain transfer to AIR3, kp = rate constant of propagation) were determined by kinetic study.

36. Polymerization of Styrene and Copolymerization of Styrene with Olefin in the Presence of Soluble Ziegler-Natta Catalysts

Titanium complex catalysts including 2,2′-thiobis(4-methyl-6-tbutylphenoxy) (TBP) group as ligand are highly active toward styrene when combined with methylalumoxane (MAO) as cocatalyst, yielding completely syndiotactic polystyrene with up to 37 kg polymer per g titanium and hour. Copolymerizations of styrene and ethylene have been carried out with these catalysts. The 13 C NMR analysis of the copolymer obtained indicates that the copolymer is an alternating copolymer having isotactic styrene units. The isotactic alternating copolymer is a crystalline polymer with a melting point of 166°C.

Stereochemical control in propylene polymerization with non-bridged metallocene dichloride/methylaluminoxane

Abstract Propylene polymerization was carried out with non-bridged bis (substituted-cyclopentadienyl)zirconium dichloride ((RCp) 2 ZrCl 2 /methylaluminoxane (MAO) and bis (substituted indenyl)zirconium dichloride ((RInd) 2 ZrCl 2 )/MAO catalyst at various polymerization temperature. In the case of (RCp) 2 ZrCl 2 , the pentad meso sequence ([mmmm]) increased with lowering polymerization temperature. The isotactic sequence of polypropylene increased with an increase of formula weight of substituents in the case of mono-alkyl substituted bis (cyclopentadienyl)zirconium dichloride. The number of methyl (Me) substituents in [(CH 3 ) n −(C 5 H 5−n )] 2 ZrCl 2 effected the stereo control of polymerization of propylene, and one or two Me substitution resulted in higher isotacticity than the usage of non- or full substituted ligands. Lowering polymerization temperature gave higher isotacticity as observed in Cp 2 TiCl 2 . The (RInd) 2 ZrCl 2 (R = non or 2-Me) showed minimum meso sequence ([mmmm]) at 0°C. Chain-end control was predominant for producing the isotactic portion. The stereoregulation energies were evaluated from the stereochemical dyad composition of the obtained polypropylenes by the Arrhenius plot of ln ([m]/[r]) versus 1/ T ( T = polymerization temperature (K)).

Isothermal crystallization of syndiotactic poly(propylene-co-olefin)s

Abstract Isothermal crystallization of syndiotactic poly(propylene-co-olefin)s (olefin=ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene) was studied. The melting behavior of isothermally crystallized polymers was investigated by differential scanning calorimetry, and the equilibrium melting temperature (Tm0) was determined by Hoffman–Weeks plot. Crystallization rate and Avrami exponent of isothermally crystallized copolymers from the melt were measured by depolarized light intensity technique. The half time of crystallization (t1/2) was found to be dependent on the degree of supercooling (ΔT), but independent of the comonomer. The Avrami exponents (n) of copolymers were detected by the Avrami plot and the average n ranged from 2.0 to 2.8 for the primary crystallization process in any copolymer. The effect of isothermal crystallization temperature (Tc) on the crystalline structure of copolymers was studied by wide-angle X-ray diffraction (WAXD). The WAXD patterns of all the copolymers were similar to the pattern of Cell II in the syndiotactic polypropylene. The WAXD pattern of 1-butene copolymer with small amount of 1-butene indicated the existence of Cell III.

Molecular weight and molecular weight distribution of polyethene obtained with rac-Me2Si(Ind)2ZrCl2/methylaluminoxane

Ethene and propene polymerizations were carried out with the rac-Me 2 Si(Ind) 2 ZrCl 2 (Me = CH 3 , Ind = indenyl)/methylaluminoxane (MAO) catalyst in toluene. The molecular mass distribution index (MMD = M w /M n ) of polypropenes was almost 2,0, while a bimodal MMD was observed for polyethene. The MMD of polyethene was independent of the [Al]/[Zr] ratio and the [Zr] concentration. However, the high molecular weight fraction disappeared when the polymerization was performed either at a low temperature or by using dry MAO. Addition of AlMe 3 to the MAO caused an increase of the low molecular weight fraction at the initial stage of polymerization. The low molecular weight fraction was also increased when the polymerization was conducted in a mixture of toluene and CH 2 Cl 2 as the solvent. From these results, the active species formed in the catalyst system are discussed.

13. Microtacticity Distribution of Polypropylenes Prepared with MgCl2 Supported Ti Catalyst Systems

The effect of phenyltrimethoxysilane as an external donor on the microtacticity distribution of the isotactic parts of polypropylenes prepared with MgCl 2 -supported Ti catalyst-AlEt 3 system was studied by programmed temperature column fractionation (PTCF) technique. Both catalysts produce two kinds of isotactic polymers, i.e., low isotactic and highly isotactic. The proportion of highly isotactic polymer increases and the microtacticities of low and highly isotactic polymers increase by the addition of the electron donor. Models for active sites on the Mg-Ti catalyst system and the action of PTMS to each active site are discussed based on these results.