Bimodal blend

Materials. The following Epon prepolymers (Shell Chemical Company) were used Epons 825, 828, 834 (all liquid to semisolid) and 1001, 1002, and 1004 (all solids). Approximate compositions (degree of polymerization) were determined by gel permeation chromatography. Bimodal blends were made by mixing Epon 825 with Epon 1004, as shown in Table 1. Sample preparation and the method of curing have been described in the preceding paper (29). 

Figure 1. Glass transition temperature as a function of Me for Series E and Series F networks (O) commercial resins fn) bimodal blends...

Furthermore, the bimodal blend samples F-1 to F-4 have slopes close to that of sample E-1, prepared from the commercial resin whereas sample F-5 (bimodal blend) has a slope close to that of sample E-7 (commercial resin) The lower values of slope observed in the blend samples F-1 to F-4 are a result of a broader distribution of relaxation times which is not present in the respective counterparts of Series E. Similarly, sample F-5 showed a higher slope than its counterpart E-5 (even though the slope measured for E-5 is lower than it should be), because the former had a narrower distribution of molecular weights which resulted in a narrower distribution of relaxation times (see Table I). 

Las La Scala, J. J., Orlicki, J. A., Winston, C., Robinette, E. J., Sands, J. M., Palmese, G. R. The use of bimodal blends of vinyl ester monomers to improve resin processing and toughen polymer properties. Polymer 46 (2005) 2908-2921. 

Theoretical arguments suggested that the low molecular weight component in a bimodal blend tend to locate preferentially to the surface in order to minimize loss of conformational entropy at the material boundary [52]. Indeed, the surface tension... 

Reactor blends are prepared during polymerization. The strategy has been often explored in syntheses of multimodal PE compositions for the blown film with MD/TD tear balance and good processability. In bimodal blend, the optimum was usually found between 35 and 75 wt% of the higher-MW component ... 

PE blends were prepared during polymerization. This strategy has been widely implemented in syntheses of multimodal PE compositions. The blown film showed MD/TD tear balance. The bimodal blend eontained 0.35-0.75 weight fraction of a higher-MW component Ali A.H. et al. to Mobil Oil Co. Dammert et al. to Borealis. Catalyst TiCLj ntanol deposited on MgO/acetic acid and that treated with tri-n-hexyl-alummum solution... 

In Crystaf, a dilute solution of a semicrystalline polymer is slowly cooled from a high temperature to room or subambient temperatures, while the polymer concentration is monitored as a fimction of crystallization temperature by an on-line mass detector to obtain its cumulative distribution. The differential distribution is calculated by taking the first derivative of the cumulative distribution with respect to the crystallization temperature. Both cumulative and differential Crystaf curves for a bimodal blend of two ethylene/a-olefin copolymers are shown in Figure 11. A calibration curve must be used to translate the crystallization temperature distribution into a pol5mier microstructural distribution, as will be explained later in this section. 

A HDPE resin in the 0.9555 density and fractional melt flow range with bimodal MWD was prepared with a 50/50 blend of high and low molecular weight resins from the slurry process using the INSITE technology. When compared with a bimodal blend of the same density and melt flow rate made with a conventional ZN catalyst, ESCR of the new resin was found to be several times higher and Charpy impact strength at —20°C improved by 60%. 

The constraint-release models discussed above have been tested by comparing their predictions to experimental data, as shown in Figures 7.9 and 7.10. For linear polymers for which the molecular weight distribution is unimodal, and not too broad, dynamic dilution is not very important, and theories that account for constraint release without assuming any tube dilation are adequate. Such is the case with the version of the Milner-McLeish theory for linear polymers used to make the predictions shown in Fig. 6.13. The double reptation theory also neglects tube dilation. The dual constraint theory mentioned in Chapter 6 does include dynamic dilution, although its effect is not very important for narrowly dispersed linear polymers. As described above, dynamic dilution becomes important for some bimodal blends, and is certainly extremely important for branched polymers, as discussed in Chapter 9. 

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