Polymer-diluent mixtures polyethylene

The phase diagram of polyolefins and hydrocarbon diluents is exemplified for high-density polyethylene in Figure 1. When the polymer-diluent mixture is heated, dissolution of the semicrystalline polymer takes place along the borderline 1 (turbidity curve) [43, 44], This line depends on the polymer (e. g., polyethylene, isotactic polypropylene), average chain length, and copolymer composition. 

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... 

An analysis of the overall crystallization rate with composition requires that the comparison be made either at constant undercooling or at one of the nucleation temperature quantities, T / T AT or T /T(AT). This requirement is essential because of the importance of nucleation to the crystallization process. The overall crystallization kinetics of a variety of polymer-diluent systems have been reported. Many different relations between the overall crystallization rate and composition have been observed. For example, as is shown in Fig. 13.17 there is a continuous decrease in the crystallization rate with dilution for linear polyethylene-a-chloronaphthalene mixtures.(42) The results for poly(trans-1,4-isoprene) in methyl oleate follow a similar pattem.(80) In contrast, the rates for poly(dimethyl siloxane) crystallizing from toluene, at compositions V2 = 0.32 to 0.79, are the same at all undercoolings, but are faster than that of the pure polymer.(78) Another example is found with poly(ethylene oxide)-diphenyl ether mixtures.(77) In this case the crystallization rates for the pure polymer and composition = 0.92 to 0.51 are the same. However, the rates for the more dilute mixtures, V2 = 0.04 and 0.30 are lower. For poly(decamethylene adipate)-dimethyl formamide mixture the rates for the pure polymer and V2 = 0.80 are the same.(77) The mixture of isotactic poly(propylene) with dotricontane shows interesting behavior.(81) At all undercoolings studied, the crystallization rate initially decreases with dilution, reaches a minimum in the range V2 — 0.7 (a maximum in ti/2) and then slowly increases with further dilution, up to V2 = 0.10. 

When ethylene and the catalyst and a diluent are fed continuously into the reactor. Polyethylene gets formed as a powder of granules which is insoluble in the reaction mixture. After the reaction gets completed, the catalyst is destroyed by adding water or methanol or ethanol. Finally, the polymer gets centrifuged, dried, extruded and granulated. 

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