Blends, molecular weight distribution

Transamidation is an important process in the melt phase for polyamides because it is usually the process by which an equiUbrium molecular weight distribution is reestabUshed and, in the case of the melt blending of two or more polyamides to form a copolymer, it is the process by which randomi2ation of the individual monomers along the chain is effected. In the soHd phase, chain mobiUty is restricted and equiUbrium in either case often is not achieved. 

Geresin wax [8001 -75-0] originally was a refined and bleached o2okerite wax, but now is a paraffin wax of very narrow molecular weight distribution or blend of petroleum waxes. 

Figure 8.7. The blend W of high and low molecular weigh polymers (curves 1 and 2) becomes non-Newtonian at a lower shear rate than a polymer of narrow molecular weight distribution...

Addition of low molecular weight resins with narrow molecular weight distribution produces compatible resin-elastomer blends, while incompatible blends are obtained with resins having a wide molecular weight distribution. In a recent study... 

Narrow molecular weight distribution, which is characteristic of metallocene-based polyethylene (Fig. 7), causes processing difficulty in certain applications due to increased melt pressure, reduced melt strength, and melt fracture [14,15]. This problem can be overcome by blending the metallocene polymer with other prod-... 

Note (1) Polymer D was made up of blending A and C (50 50) in the latex stage. The result was a bimodal molecular weight distribution having an average value close to B (2) All compounds used the same formulation. 

The poly(styrene-b-isoprene) (P(S-b-IP)) and poly(-styrene-b-2-vinyl pyridine) (P(S-b-2VP)) block copolymers with narrow molecular weight distributions for blending with the microspheres were also synthesized using the additional anionic polymerization technique. The number-average molecular weights (Mns) and PS contents are also shown in Table 1. 

In summary, the attributes of the elastomer that contribute to the enhanced impact strength of a plastic in plastic mbber blend include the type of mbber, plastic to mbber ratio, particle size, particle size distribution, cross-Unk density, and degree of grafting, if any. Molecular weight and molecular weight distribution of the plastic also exert some influence. For example, for high-impact PS, the optimal molecular weight of PS is between 170,000 and 220,000. The dispersity index is... 

In practice, product developers often blend two or more resins together in order to obtain a product that has the required melt flow and solid-state characteristics. Thus, we frequently combine metallocene catalyzed linear low density polyethylene, having a most probable molecular weight distribution, with low density polyethylene, having a broad molecular weight distribution. The linear low density polyethylene provides good impact resistance, while the low density polyethylene improves melt flow characteristics. 

The GPC traces in Fig. 24 reveal a broad molecular weight distribution, MJMn = 4.42, for the dual reactor blend sample. On the other hand, the diblock OBC displays an overall MJMn of 1.67. The narrowing of the distribution indicates that the polymerization has CCTP characteristics. The theoretical molecular weight distribution from an ideal living polymerization in a series of two CSTR reactors is given by the following equation, where/j and/2 are the mass fractions of polymer comprising the two blocks [11] ... 

The use of two or more different catalysts in the same reactor, sometimes known as in situ reactor blending or tandem catalysis, has been widely employed industrially as means of controlling the properties of a polyolefin (e.g. molecular weight and the molecular weight distribution). Recent years have seen a variety of reports emerge on the use of bis(imino)pyridine iron/cobalt systems as one component of the process [169, 170, 171, 172, 173, 174, 175, 176, 177,178, 179],... 

Figure 20. Comparison of molecular weight distributions of Butarez CTL blend H by solvent precipitation and gel chromatography fractionation (molecular weight by intrinsic viscosity)...

The synthesis of polyoctenamer has been commercialized by Huels.150 In contrast with the transformation of cyclooctene to 1,9-decadiene [Eq. (12.31)], homogeneous catalyst compositions, such as WClg + EtAlCl2, are used to promote ring-opening metathesis polymerization of cyclooctene. A polymer of narrow molecular-weight distribution with high trans content (55-85%) called Vestenamer is produced and used as blend component in different rubbers and thermoplastics. 

Fig. 23. Effectiveness behavior of PAAm blends, (c = 30 ppm in distilled water, Mw = 3.9 106 g/mol, d = 2.08 mm). The part of the high molecular tail of the molecular weight distribution decreases from the left to the right side Bind-Blend > Ter-Blend 1 > Ter-Blend 3 > PAAm M3...

Finishing Thermal degradation of molecular weight Molecular-weight distribution by blending Finishing... 

The viscoelastic behaviour of dilute blends of polymers of different length and narrow molecular weight distributions was investigated experimentally for polybutadiene by Yanovski et al. (1982) and by Jackson and Winter (1995) and for polystyrene by Watanabe and Kotaka (1984) and Watanabe et al. (1985) (the results can be found in the work by Jackson and Winter (1995)). The results for polybutadiene were approximated by Pokrovskii and Kokorin (1984) by the dependencies... 

Watanabe H, Kotaka T (1984) Viscoelastic properties and relaxation mechanism of binary blends of narrow molecular weight distribution polystyrene. Macromolecules... 

Watanabe H, Sakamoto T, Kotaka T (1985) Viscoelastic properties of binary blends of narrow molecular weight distribution polystyrene. 2. Macromolecules 18(5) 1008-1015 Watanabe H, Yao M-L, Osaki K (1996) Comparison of dialectric and viscoelastic relaxation behaviour of polyisoprene solutions Coherence in subchain motion. Macromolecules 29(1) 97—103... 

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