Formation of the extended chain crystals and once folded crystals of linear chain molecules

Assuming that initial transient crystals with nonintegral folding (NIF) chain lengths immediately transform into once folded crystals (F1C) or extended chain crystals (ECC), a simple equation was derived for the rate of overall crystallization as a function of crystallization temperature. This equation shows a maximum at a given crystallization temperature. Assuming that the activation energy, E(d) for the sliding diffusion in the crystal is different between the thinning and the thickening, the two maxima in the crystallization (and crystal growth) rate versus temperature curve were predicted, corresponding to the formation of F1C and ECC, respectively. Two maxims were really found when plotting the crystallinity obtained at prolonged times of isothermal crystallization against the crystallization temperature for two low molecular weight poly(ethylene glycol) (PEG)samples. Making use of this result including more detailed data on the crystallization rate for low molecular weight PEG and n-alkane, relative values of E(d) could be obtained from the two maximum temperatures. it was concluded that the lager E(d) values for the thickening than for the thinning were attributed to the fact that the chains in the NIF crystals reached F1C faster than ECC, whose thickness was two times longer than that of F1C.