HEAD-TO-HEAD POLYMERS .2. DILUTE-SOLUTION PROPERTIES OF HEAD-TO-HEAD POLYPROPYLENE

The behaviour in dilute solution of head-to-head (H-H) polypropylenes, covering the range Mn = 0.22 to 4.19 × 104, has been studied in cyclohexane as solvent at 303 K. The data could be represented by two distinct Mark-Houwink equations describing the low and the high molecular weight regions. The unperturbed dimensions of (H-H) polypropylenes were found to be less than those for conventional atactic polypropylene in agreement with theoretical predictions. The theta temperature for (H-H) polypropylene in isoamylacetate was found to be 316 K. At this temperature the characteristic ratio was estimated to be 4.5 compared with 6.4 for atactic and syndiotactic polypropylene. The conclusion is that (H-H) placements in polypropylene increase the flexibility of the chain. © 1979.