Polyethylene oxide crystallization kinetics

Research in this field is ongoing aiming to understand the mechanism of action of kinetic inhibitors. Lee and Englezos (2005) showed that inclusion of polyethylene oxide (PEO) to a kinetic inhibitor solution was found to enhance by an order of magnitude the performance of the hydrate inhibitor. Binding of inhibitor molecules to the surface of hydrate crystals was considered to be the key aspect of the mechanism of kinetic inhibition (Anderson et al.,... 

Kim rr, Lee JH, Shofner ML, Jacob K, Tannenbaum R. Crystallization kinetics and anisotropic properties of polyethylene oxide/magnetic carbon nanotubes composites films. Polymer 2012 53 2402-11. 

Figure 32 Crystallization kinetics for the poly(ethylene oxide) block in triblock terpolymers with a rubbery end biock (poiybutadiene-Wocfr-polystyrene-b/oc/f-poly(ethylene oxide)) or a crystalline end block (polyethylene-b/oc/f-polystyrene-Wock -poiy(ethylene oxide)) (a) deveiopment of the relative crystallinity with crystallization time during isothermal crystallization at 49.5 °C, and (b) inverse of experimentai crystaiiization haif-time as a function of crystallization temperature. Reprinted with permission from Boschetti-de-Fierro, A. etal. Macromol. Chem. Phys. 2008,209,476- 87. ...

Again, the influences of nucleants or additives on crystallization behavior have made considerable inroads in the scientific and patent literature (39), but the importance of shear rates (40,41) on crystallization kinetics is beginning to receive more attention in the literature (42). In the field of single crystal growth many new results have been added to older kinetic data (43,44) tabulated in previous editions of Polymer Handbook . The most recent are concerned with the crystallization of oligomers of polyethylene, polyethylene oxide and so on. Many aspects of crystallization are reported in some recent reviews (45,45a,45b) and later in this article. 

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. 

A previously described kinetic model for polyethylene radical chain oxidation is tentatively extended to include the conditions relevant to embrittlement behavior in the case of thermal oxidation at 90°C. The important roles of chemi-crystallization and morphology as a follow-up to initial chemical changes are discussed. The philosophy of how chemical reactions will ultimately lead to physical polymer changes apparent in Mw and lamellar properties, and how these processes could be discussed in terms of advanced modeling strategies is briefly reviewed. 

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