ISOTHERMAL THICKENING AND THINNING PROCESSES IN LOW-MOLECULAR-WEIGHT POLY(ETHYLENE OXIDE) FRACTIONS CRYSTALLIZED FROM THE MELT .2. CRYSTALSINVOLVING 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 b y differential scanning calorimetry and time-resolved synchrotron smal l angle X-ray scattering experiments. At this molecular weight, the fr action can crystallize to a final form comprised of integral folding c hain (IF) crystals with extended (n = 0), once-folded (n = 1), twice-f olded (n = 2), and even triply-folded (n = 3) chain crystals. The fold length of NIF crystals increases with crystallization temperature. Wh en this fold length is between those of IF (n = 2) and IF (n = 1) crys tals, 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 len gth of NIF crystal lies between those of IF (n = 1) and IF (n = 0) cry stals, similar isothermal thickening and thinning processes can also b e observed. Which process occurs depends upon the thermodynamic drivin g force between the NIF and IF crystals and upon kinetic effects. Deta iled kinetic maps of the fold length changes with time will be discuss ed.