Relation between liquid-liquid phase separation and crystallization in isotactic and syndiotactic polypropylene solutions

✍ Scribed by Hwan Kwang Lee; Sung Chul Kim

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 123 KB
• Volume: 67
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19980103)67:1<159::aid-app18>3.0.co;2-x

✦ Synopsis

The effects of the stereospecificity of a polymer chain and of the interaction in polypropylene (PP) solutions on the relation between liquid-liquid phase separation and crystallization were investigated by using an isotactic PP (i-PP) and a syndiotactic PP (s-PP) of high stereoregularity and of similar molar mass. Dialkyl phthalate was used as a solvent. A series of dialkyl phthalates with a different number of carbon atoms in the alkyl chain was employed to control the interaction between polymer and solvent. Phase transition temperatures were measured by optical microscopy with a hot stage. Liquid-liquid phase separation temperature ( T L-L ) in the system of i-PP and dihexyl phthalate was located below its melting temperature ( T m ). However, T L-L for the s-PP system in the same solvent was elevated much above its T m due to a decreased T m and increased T L-L . The reduced solubility of s-PP is primarily attributed to enhanced hydrophobicity arising from alternate positioning of the methyl groups along the polymer chain. As the length of the alkyl chain in the phthalate increases, T L-L decreases significantly and T m decreases slightly, resulting in the value of T L-L shifting below that of T m for the solution of s-PP and dinonyl phthalate.