ISOTHERMAL THICKENING AND THINNING PROCESSES IN LOW-MOLECULAR-WEIGHT POLY(ETHYLENE OXIDE) FRACTIONS CRYSTALLIZED FROM THE MELT .2. CRYSTALS INVOLVING MORE THAN ONE FOLD

The existence of a non-integral folding chain (NIF) crystal in a poly(ethylene oxide) fraction with molecular weight of 7100 can be proved by differential scanning calorimetry and time-resolved synchrotron small angle X-ray scattering experiments. At this molecular weight, the fraction can crystallize to a final form comprised of integral folding chain (IF) crystals with extended (n = 0), once-folded (n = 1), twice-folded (n = 2), and even triply-folded (n = 3) chain crystals. The fold length of NIF crystals increases with crystallization temperature. When this fold length is between those of IF (n = 2) and IF (n = 1) crystals, the NIF crystal can be thickened into the IF (n = 1) crystal, or thinned into the IF (n = 2) crystal. In the same way, if the fold length of NIF crystal lies between those of IF (n = 1) and IF (n = 0) crystals, similar isothermal thickening and thinning processes can also be observed. Which process occurs depends upon the thermodynamic driving force between the NIF and IF crystals and upon kinetic effects. Detailed kinetic maps of the fold length changes with time will be discussed.