Abstract:The synthesis and characterization of three complexes of the type (N-(3-tert-butylsalicylidene)-R) 2 TiCl 2 [R = 2,6-difluorophenyl 1, R = 2,6-dimethylphenyl 2, R = phenyl 3] is reported and compared with the highly active R = 2,3,4,5,6,-pentafluorophenyl 4. The complexes were tested for ethylene polymerization when activated with different co-catalysts, giving high catalytic activity when activated with methylaluminoxane for complexes 3 and 4. Complex 3 is the only catalyst to be inactive when activated with … Show more
“…However, the reported procedure makes use of TiBA, which is found to deactivate the Cat. 1 used to produce dis -UHMWPE; moreover, there are no indications on the processability of the synthesized polymer and its entangled state. The magnesium chloride based activator used in this work was synthesized by slightly modifying the reported protocol; 1 equiv of MgCl 2 was refluxed in n -decane with 3 equiv of 2-ethyl-1-hexanol for 4 h, resulting in a clear solution of the MgCl 2 / 2-ethyl-1-hexanol adduct.…”
Section: Resultsmentioning
confidence: 99%
“…The catalytic system composed of a bis[ N -(3- tert -butylsalicylidene)pentafluoroanilinato] titanium(IV) dichloride complex ( Cat. 1 ) has been proven to be an excellent candidate in producing UHMWPE with a reduced number of entanglements in high yields and with high molar masses and has established a well-defined route to unprecedented mechanical properties. − ,,− Therefore, it was appealing to use Cat. 1 for the synthesis of dis -UHMWPE in heterogeneous conditions.…”
Several homogeneous postmetallocene complexes are known
to produce
weakly entangled ultrahigh-molecular-weight polyethylene (disentangled UHMWPE) under controlled polymerization conditions
leading to ultimate mechanical properties. Major challenges in using
a homogeneous catalyst system exist such as reactor fouling and uncontrolled
polymer morphology, which could be addressed by heterogenization of
the single-site complex. In such a scenario, a heterogeneous catalytic
system that can synthesize ultrahigh-molecular-weight polyethylene
with a reduced number of entanglements, to an extent that the mechanical
properties are equivalent to those obtained using a postmetallocene
catalyst in a homogeneous condition, remains a challenge. Herein,
a magnesium chloride based in situ formed activator/support,
MgCl
x
/Et
n
Al
y
(2-ethyl-1-hexoxide)
z
, is employed with a highly active bis[N-(3-tert-butylsalicylidene)pentafluoroanilinato] titanium(IV)
dichloride (Cat. 1) for the synthesis of ultrahigh-molecular-weight
polyethylene with a reduced number of entanglements. A novel route
is adopted to make a nano-support that allows tailoring of the entangled
state and control over the resultant morphology without reactor fouling
and wall sheeting, thus providing the feasibility of pursuing the
polymerization via a continuous process. The synthesized nascent polymer
shows the formation of single crystals of linear UHMWPE, identifying
the fold surface and crystal thickness and suggesting a low entangled
state. The topological differences with the commercial entangled sample
are identified by chain diffusion from the noncrystalline to crystalline
region via solid-state NMR, following melting kinetics via DSC, and
transformation of the nonequilibrium melt into the equilibrium state
via rheology. Thus, the obtained disentangled crystals can be compressed
in the solid state, without melting, to an extent that the macroscopic
forces can be transferred to the molecular level. This allows the
desired chain orientation for securing the ultimate tensile modulus
(>200 N/tex) and tensile strength (>4.0 N/tex) in the synthesized
low entangled linear polyethylene having a weight average molar mass
exceeding a million grams per mole. These mechanical properties are
equivalent to those perceived using a homogeneous catalytic system
and are the first of their kind reported in a polymer synthesized
using a heterogeneous catalytic system.
“…However, the reported procedure makes use of TiBA, which is found to deactivate the Cat. 1 used to produce dis -UHMWPE; moreover, there are no indications on the processability of the synthesized polymer and its entangled state. The magnesium chloride based activator used in this work was synthesized by slightly modifying the reported protocol; 1 equiv of MgCl 2 was refluxed in n -decane with 3 equiv of 2-ethyl-1-hexanol for 4 h, resulting in a clear solution of the MgCl 2 / 2-ethyl-1-hexanol adduct.…”
Section: Resultsmentioning
confidence: 99%
“…The catalytic system composed of a bis[ N -(3- tert -butylsalicylidene)pentafluoroanilinato] titanium(IV) dichloride complex ( Cat. 1 ) has been proven to be an excellent candidate in producing UHMWPE with a reduced number of entanglements in high yields and with high molar masses and has established a well-defined route to unprecedented mechanical properties. − ,,− Therefore, it was appealing to use Cat. 1 for the synthesis of dis -UHMWPE in heterogeneous conditions.…”
Several homogeneous postmetallocene complexes are known
to produce
weakly entangled ultrahigh-molecular-weight polyethylene (disentangled UHMWPE) under controlled polymerization conditions
leading to ultimate mechanical properties. Major challenges in using
a homogeneous catalyst system exist such as reactor fouling and uncontrolled
polymer morphology, which could be addressed by heterogenization of
the single-site complex. In such a scenario, a heterogeneous catalytic
system that can synthesize ultrahigh-molecular-weight polyethylene
with a reduced number of entanglements, to an extent that the mechanical
properties are equivalent to those obtained using a postmetallocene
catalyst in a homogeneous condition, remains a challenge. Herein,
a magnesium chloride based in situ formed activator/support,
MgCl
x
/Et
n
Al
y
(2-ethyl-1-hexoxide)
z
, is employed with a highly active bis[N-(3-tert-butylsalicylidene)pentafluoroanilinato] titanium(IV)
dichloride (Cat. 1) for the synthesis of ultrahigh-molecular-weight
polyethylene with a reduced number of entanglements. A novel route
is adopted to make a nano-support that allows tailoring of the entangled
state and control over the resultant morphology without reactor fouling
and wall sheeting, thus providing the feasibility of pursuing the
polymerization via a continuous process. The synthesized nascent polymer
shows the formation of single crystals of linear UHMWPE, identifying
the fold surface and crystal thickness and suggesting a low entangled
state. The topological differences with the commercial entangled sample
are identified by chain diffusion from the noncrystalline to crystalline
region via solid-state NMR, following melting kinetics via DSC, and
transformation of the nonequilibrium melt into the equilibrium state
via rheology. Thus, the obtained disentangled crystals can be compressed
in the solid state, without melting, to an extent that the macroscopic
forces can be transferred to the molecular level. This allows the
desired chain orientation for securing the ultimate tensile modulus
(>200 N/tex) and tensile strength (>4.0 N/tex) in the synthesized
low entangled linear polyethylene having a weight average molar mass
exceeding a million grams per mole. These mechanical properties are
equivalent to those perceived using a homogeneous catalytic system
and are the first of their kind reported in a polymer synthesized
using a heterogeneous catalytic system.
“…In the overwhelming majority of cases, disentangled UHMWPE suitable for solid‐phase processing is synthesized on phenoxy‐imine Group 4 metal complexes (FI catalysts [ 9 ] ), activated with alkylaluminoxanes. [ 10–14 ] However, these activators have significant drawbacks that lie in the high Al/M ratios needed to achieve optimal catalytic performance and in its still ill‐defined structures (mixture of oligomers (AlO(Alk)) n evolving with time). In addition, these activators increase considerably the catalyst costs.…”
New alkoxo‐titanium(IV) complexes with diolate ligand containing additional donor oxygen atom have been synthesized from readily available and scalable precursors. The structure of complex 4 was established by X‐ray diffraction. Titanium atom adopts a distorted tetrahedral geometry formed by six oxygen atoms of ligands. The resulting complexes 3–4 are moderately or highly active in ethylene polymerization in the presence of {EtnAlCl3–n + Bu2Mg} binary cocatalysts. The influence of the nature of the solvent, the organoaluminum cocatalyst and the polymerization temperature on the activity of catalytic systems, and the properties of the resulting polymers were studied. The obtained polymers are linear polyethylene of ultrahigh molecular weight (up to 5.8·106 g mol−1) with a broad molecular weight distribution. The polymers are suitable for the modern methods of polymer processing—the solventless solid‐state formation of super high‐strength (breaking strength up to 2.8 GPa) and high‐modulus (elastic modulus up to 140 GPa) oriented films and film tapes. The possibility of scaling up the synthesis of ultrahigh molecular weight polyethylene (UHMWPE) without a significant drop in the productivity of the catalytic system and polymer properties is shown. UHMWPE samples have been investigated by small‐angle X‐ray scattering (SAXS) methods to study the structural changes induced by solid‐state drawing of nascent reactor powders.
“…Therefore, in recent years, significant efforts of researchers have been directed to the development of new types of activators. In particular, attempts have been made (generally not very successful) to use traditional trialkylaluminum and alkylaluminum chlorides for FI catalysts activation [ 12 , 13 , 14 , 15 ]. Many efforts have been made to replace MAO with non-coordinating anions (e.g., [B(C 6 F 5 ) 4 ] − ); however, their cost is also very high.…”
A series of bis(phenoxy-imine) (FI) titanium(IV) and zirconium(IV) complexes have been synthesized. The effect of the nature of the activator (MAO, combinations EtnAlCl3-n + Bu2Mg and iBu3Al + [Ph3C]+[B(C6F5)4]−) on the catalytic activity and properties of the resulting polymers was studied. It was found that Ti-Fi complexes, despite the nature of the outgoing ligands (Cl or iPrO) in the presence of Al/Mg activators, effectively catalyze the polymerization of ethylene (with the formation of UHMWPE); copolymerization of ethylene with 1-octene (with the formation of ultra-high molecular weight copolymers); and the ternary copolymerization of ethylene, propylene and 5-vinyl-2-norbornene (with the formation of polyolefin elastomers). It has been shown that Zr-FI complexes are not activated by these Al/Mg compositions. The resulting UHMWPE can be processed by a solventless method into high-strength and high-modulus oriented films; however, their mechanical characteristics do not exceed those obtained using MAO.
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