Polyethylene chain length

Fig. 6. A primary means of regulating polyethylene chain length is through control of reactor temperature. Increasing the temperature enhances termination, probably by destabilizing the Cr-chain bond, resulting in shorter chains.

Shin, M., Umebayashi, Y., Kanzaki, R., andlshiguro, S. I. (2000). Formation of copper(II) thiocyanato and cadmium(II) iodo complexes in micelles of nonionic surfactants with varying polyethylene chain length. J. Colloid Interface Sci. 225(1), 112-118. 

The PIT (with water and a given oil phase, i.e., hexadecane) was first correlated with the cloud point, i.e., the temperature at which a surfactant phase separates from u low concentration, c.g., 3%. surfactant solution (48). It is worth noting that the cloud point indicates a property of the surfactant, somehow the HLB. while the PIT takes into account the interaction with both the aqueous and oil phase. Early experimental evidence indicated that the PIT increased as the nonionic surfactant polyethylene chain length increased, increased as the hydrocarbon oil chain length increa.sed, and decreased as the salt concentration increased in the aqucou.s phase. Since the PIT is actually the physicochemical situation in which Winsor = I, and since an increase in temperature tends to reduce the Aiw interaction, the interpretation of the previously mentioned trends is siraighiforward when the numerator and denominator of Winsor R are equated. 

Another subclass of substituted amides that is of great commercial value is the ethoxylated amides. They can be synthesized from alkanolamides by chain extending with ethylene or propylene oxide or by ethoxylation directly from the primary amide (46—48). It was originally beheved that the stepwise addition of ethylene oxide (EO) would produce the monoethano1 amide and then the diethanolamide when sufficient ethylene oxide was added (49), but it has been discovered that only one hydrogen of the amide is substituted with ethylene oxide (50—53). As is typical of most ethylene oxide adducts, a wide distribution of polyethylene oxide chain length is seen as more EO is added. A catalyst is necessary to add ethylene oxide or propylene oxide to a primary or an ethoxylated amide or to ethoxylate a diethoxy alkanolamide synthesized from diethanolamine (54). 

Fig. 11. Newtonian viscosity vs chain length in terms of the number of carbon atoms for a series of molten polyethylenes. To convert Pa-s to P, multiply...

Fig. 22.1. (a) The ethylene molecule or monomer (b) the monomer in the activated state, ready to polymerise with others (<)-(f) the ethylene polymer ("polyethylene") the chain length is limited by the addition of terminators like —OH. The DP is the number of monomer units in the chain. 

Both investigated systems are melts of polybead chains at a temperature of 473 K. Configurations of chain length ranging from 24 beads to 100 beads at a density of 0.75 g/cm3 (this corresponds to a comparable real system of polyethylene at a pressure of 1 bar) have been successfully embedded. The hard-sphere radius was 2.2 A, corresponding approximately to a van-der-Waals ra-... 

Figures 8 and 9 show the dependence of the self-diffusion constant and the viscosity of polyethylene melts on molecular weight [47,48]. For small molecular weights the diffusion constant is inversely proportional to the chain length - the number of frictional monomers grows linearly with the molecular weight. This behavior changes into a 1/M2 law with increasing M. The diffusion...

Strain-induced crystallization would presumably further improve the ultimate properties of a bimodal network. It would therefore obviously be of considerable importance to study the effect of chain length distribution on the ultimate properties of bimodal networks prepared from chains having melting points well above the very low value characteristic of PDMS. Studies of this type are being carried out on bimodal networks of polyethylene oxide) (55), poly(caprolactone) (55), and polyisobutylene (56). 

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