Radiation grafted and sulfonated poly(vinylidene fluoride), PVDF, membranes have been studied by thermal analysis and X-ray diÂraction to determine the changes in membrane crystallinity and structure during preparation. Commercial PVDF films were irradiated with an electron beam, grafted with styrene and finally sulfonated. Both the crystallinity and the size of the crystallites of PVDF decrease in the grafting reaction. A further decrease in crystallinity is observed in the sulfonation reaction. The residual crystallinity of PVDF was considerable (10-20%) even in membranes which had been subjected to severe reaction conditions. These results can be explained by assuming that the grafting takes place mainly in the amorphous region of the PVDF, and close to the surfaces of the crystals, but that grafts do not penetrate into the crystals. The proton conductivity of the grafted and sulfonated PVDF membranes reached values comparable to those of Nafion membranes.
The influence of siloxy substitution of ethylene-bridged bis(indenyl)- and bis(tetrahydroindenyl)zirconium dichlorides on ethylene/α-olefin copolymerization and ethylene homopolymerization
performance was investigated. Ethylene was copolymerized with 1-hexene and 1-hexadecene over rac-[ethylenebis(1-(tert-butyldimethylsiloxy)-3-indenyl)]zirconium dichloride (1), rac-[ethylenebis(1-(tert-butyldimethylsiloxy)-4,5,6,7-tetrahydro-3-indenyl)]zirconium dichloride (H1), rac-[ethylenebis(2-(tert-butyldimethylsiloxy)-1-indenyl)]zirconium dichloride (2), and rac-ethylenebis(1-indenyl)zirconium dichloride
(EBI) using methylaluminoxane (MAO) as cocatalyst. 1-Siloxy substitution was found to remarkably
improve the copolymerization ability and 2-siloxy substitution to enhance the polymerization activity of
ethylenebis(indenyl)zirconium dichlorides. Optimum homo- and copolymerization performance was
observed at a very low Al(MAO) concentration, which for 2 could be reduced to a level of 0.2 mmol/dm3
by using a small amount of triisobutylaluminum. The 1-siloxy-substituted metallocene catalysts 1 and
H1 (hydrogenated 1) revealed decreasing comonomer incorporation and increasing induction times with
increasing Al(MAO) concentration, which indicates the presence of unfavorable interactions between these
metallocenes and MAO. Chain termination occurred mainly by chain transfer to the monomer and
β-hydrogen transfer to the metal for catalysts with indenyl and tetrahydroindenyl ligands, respectively.
Porous poly(vinylidene fluoride) membranes were
graft modified with acrylic acid by radiation-induced grafting utilizing electron beam. When the grafted
membranes were characterized by
the measurements of convective permeability, diffusion, and ion
exchange properties, the
membranes showed properties of variable permeability membranes with
respect to the
permeability of solvent and the ionic semipermeability. The
permeability for the studied
membranes (extent of grafting varied from 0 to 93 wt %) can be
controlled by the ionic strength
and pH of the permeate. The more grafted the membranes are the
greater are the changes in
the permeability; e.g., for the extent of grafting of 85 wt
% the permeability increases ca. 4
orders of magnitude when the electrolyte concentration is increased
from 10 mM to 1 M. The
membranes with the extent of grafting of ca. 10 wt
% or more appeared to have equal charge
density on the pore walls resulting in the same cation transference
number.
The preparation and crystal structure of the first
group 4 ansa-metallocene with an oxygen
atom directly bonded to the 2-position of an η5-indenyl
moiety,
rac-[ethylenebis(2-(tert-butyldimethylsiloxy)indenyl)]zirconium dichloride
(3), is reported. In combination with
methylaluminoxane (MAO), complex 3 polymerizes propylene to
highly isotactic crystalline
polypropylene (T
m = 148 °C;
M
w = 19 000;
M
w/M
n = 2.4).
Under similar conditions, the
propylene polymerization activity of 3/MAO exceeds that of
the conventional ansa-metallocene
catalyst system
(dimethylsilyl)bis(4,5,6,7-tetrahydroindenyl)zirconium
dichloride (4)/MAO
by a factor of 2 (5300 vs 2300 kg of PP/mol of Zr/h; Tp =
20 °C; P(C3H6) = 2.0 bar;
[Al]:[Zr]
= 3 000:1). Complex 3 crystallizes in the unusual
indenyl-backward conformation. The
molecular structure is consistent with the expected
C
2 symmetry.
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