Polyethylene long chain branched

Figure 16 Formation of long-chain branched polyethylene by a constrained-geometry catalyst through macromonomer insertion.

Figure 3.10 Predictions of the temporary network model [Eq. (3-24)] (lines) compared to experimental data (symbols) for start-up of uniaxial extension of Melt 1, a long-chain branched polyethylene, using a relaxation spectrum fit to linear viscoelastic data for this melt. (From Bird et al. Dynamics of Polymeric Liquids. Vol. 1 Fluid Mechanics, Copyright 1987. Reprinted by permission of John Wiley Sons, Inc.)...

The synthesis of homo- (Ti-Ti) and heterobinuclear (Ti-Zr) complexes linked by 1,2-G2H4 linker groups as shown in Scheme 316 has been reported. The molecular structures of the dimethylamido derivatives have been determined by X-ray diffraction methods. In the presence of binuclear borate activators, the methyl complexes produce long-chain branched polyethylene and polystyrene in homopolymerization reactions and ethylene-styrene co-polymers. The polymerization behavior differs from that obtained with the mononuclear compound (3-ethylindenylSiMe2-NBiOTiMea (Scheme 3 1 7).762"764... 

Wang, W.-J. Kharchenkob, S. Miglerb, K. Zhu, S. Triple-detector GPC characterization and processing behavior of long-chain-branched polyethylene prepared by solution polymerization with constrained geometry catalyst. Polymer 2004, 45 (19), 6495-6505. 

Lohse, D.J. Milner, S.T. Fetters, L.J. Xenidou, M. Hadjichristidis, N. Mendelson, R.A. Garcia-Franco, C.A. Lyon, M.K. Well-defined, model long chain branched polyethylene. 2. Melt rheological behavior. Macromolecules 2002, 35 (8), 3066-3075. 

LCB-PE (long chain branched polyethylene) is not accessible through simple ethyl-ene/a-olefin copolymerization. Therefore, a bifunctional bimetallic catalyst was developed, in which one active center oligomerizes ethene to long-chain a-olefins, while the other copolymerizes them with ethene. 

Blends of HOPE with long-chain branched polyethylenes (HBPE) prepared from metallocene catalysts have been studied by DSC and their crystal stmcmres interpreted in terms of phase behavior. The HBPE contained long-chain branches and short branches formed form octane comonomer. HBPE with 7.5-12.0% octane exhibited phase separation, whereas HBPE with 2% octane were found to be miscible with HOPE over the whole composition range. Eong branches were few and did not contribute to the immiscibility (16). 

N. Mieda, M. Yamaguchi, Flow instability for binary blends of linear polyethylene and long-chain branched polyethylene. J. Nonnewton. Fluid Mech. 166, 231-240 (2011)... 

Figure 2 Time-dependent elongational viscosity (Ji(f,eo) measured at constant elongation rate for long-chain branched polyethylene (LDPE lUPAC A, LDPE 111), linear polyethylene (HOPE I) and polystyrene (PS I). The number of long-chain branches is indicated by the number of CHj groups per 1000 CHj groups (CHj/lOOOCHj). (From Laun [2], by permission of Plenum Publishing.)...

Jaewhan Kim, Dong Hak Kim, and Younggon Son, (2009). Rheological properties of long chain branched polyethylene melts at high shear rate. Polymer 49985001. 

In analyzing polyethylene-diluent mixtures it was noted that for certain diluents and concentrations the melting temperature remained invariant with composition. This is not an isolated observation. Besides linear polyethylene, this phenomenon has also been observed in long chain branched polyethylene,(21) poly(chlorotrifluoroethylene),(22) poly(N,N -sebacoyl piperazene),(23) isotactic poly(propylene),(24) and poly (acrylonitrile) (25) when the polymers are admixed... 

Long chain branched polyethylene, commonly termed low density polyethylene typifies this class of polymers. Thermodynamic measurements, such as heat capacity (148,149) and specific volume,(150,151) indicate that long chain branched... 

Fig. 5.21 Plot of relative volume against temperature. Curve A for linear polyethylene (polymethylene) curve B for long chain branched polyethylene.(151)...

Stearates, such as calcium and zinc stearates, are present in several commercial resins of both linear and long-chain branched polyethylenes. Stearates are not used as processing aids for linear low-density polyethylenes. They have strong evidence of promoting slip and aid in the reduction of instabilities with long chain branching material [24]. 

Long-chain branched polyethylenes can be also obtained by copolymerization of ethene with ethene oligomers by tandem polymerization in one step [100] or with ethene/propene oligomers in two steps [101]. In the latter case, polymers are obtained with crystalline polyethylene backbone chains and amorphic ethene/ propene copolymer side chains [102]. 

The incorporation of the macromer was investigated and calculated by NMR measurements. The maximum incorporation rate was 0.52 mol%. This means that about 59.7 wt% of the polymer is composed of macromer units and, on average, every 400th carbon atom of the backbone chain is branched. The melting point of the long-chain branched polyethylene decreases from 136 to 12 PC, and the zero shear-rate viscosity increases from 142 to 280 Pa s. Such long-chain branched copolymer can be produced much more easily by metallocene/MAO catalysts than by Ziegler-Natta catalysts. 

Long-Chain Branched Polyethylenes Formed In Situ. 194... 

Fig. 3 Molecular weight dependence of the rjo or r) (a) = 0.01 rad s ) of linear (IUPAC5A) and long-chain branched polyethylenes. Filled symbols denote rio determined with creep experiments open symbols give rf from dynamic analysis at < = 0.01 rad s. A deviation from the solid line indicates the presence of LCB. Reprinted from [94], with kind permission from Elsevier...

Fig. 9 Illustration of possible structures of long-chain branched polyethylene. Multiple branched comb-like branching left), one 3-arm branch (Y-structure center) and two 3-arm branches (H-structure right)...

Kokko E (2002) Metallocene-catalyzed ethylene polymerization long-chain branched polyethylene. Acta Polytechnica Scandinavica, Chemical Technology Series, No. 290... 

Another important type of chain irregularity is branching, since the branch points are stmcturally different from the other repeating units in the chain. Long-chain branches are not usually of uniform length but are most often sufficiently long that they also can participate in the crystallization. Long-chain branched polyethylene. 

The synthesis of low-density (long-chain branched) polyethylene (LDPE), which proceeds along a free radical mechanism, is performed in bulk ethylene at temperatures and pressures far above those of the liquid-vapor critical point of the monomer ethylene. The production of LDPE takes place in autoclaves at pressures between 1400 and 3500 bar and temperatures up to 600 K. About 10 35% of the ethylene is converted into LDPE. The separation of LDPE from the... 

This polymer has been used as an additive in long chain branched polyethylene used in food packaging. 

Figure 3.3 Ternary diagram based on Monte Carlo simulations showing all possible combinations of linear molecules, free arms and inner backbones in long-chain branched polyethylenes made using a single, constrained-geometry catalyst in a single reactor. From Coseux etal. [94].

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