Thermoreversible gelation in polymer systems—I: The sol-gel transition in dilute poly(vinyl chloride) gels

✍ Scribed by M.A. Harrison; P.H. Morgan; G.S. Park

• Publisher: Elsevier Science
• Year: 1972
• Tongue: English
• Weight: 691 KB
• Volume: 8
• Category: Article
• ISSN: 0014-3057
• DOI: 10.1016/0014-3057(72)90024-9

✦ Synopsis

The gel to sol transition temperature (Tin) has been obtained at several concentrations between 25 g1-1 and 140 g 1-1 for six different samples of poly(vinyl chloride) in dioxan and at concentrations of 63 g l-1 and 92 g 1-1 for a particular sample of poly(vinyl chloride) in several solvents.

For the dioxan solutions, the Ferry and Eldridge relationships

In l~Iw = Const + AH,,/RT~,,

and In C = Const + AHm/RT,,,, approximate to the data and give junction point energies (AHm) of about 35 kJ mol-1.

Two "regular" polymers, made at low temperatures, give higher values of Tm as would be expected for gel networks linked by "fringed micelle" crystallites; AHm values of only about 27 kJ mol-1 for these two polymers suggest other complications such as microsyneresis.

Changes in T, with solvent type are related to the Flory-Huggins interaction parameter X and the solvent molar value V by a form of the Flory depressed melting point expression:

The low values of 438 K for T°c, the ultimate melting point of pure poly(vinyl chloride), and of 73 J cm-a for AHo, the enthalpy of melting per unit volume of pure poly(vinyl chloride), given by this expression are attributed to the minuteness of the crystallites that have to melt at the sol-gel transition temperature.