Some implications of the gel point concept to the chemistry of alkyd resins

Abstract

Abstract This study explored the effects of chemical composition, extent of polyesterification and possible side‐reactions upon the rheological behavior of a variety of oil‐modified, glyceryl phthalate alkyds in both melt and in dilute solutions with several solvents. Correlative data were obtained on molecular weight and on other aspects of solubility and drying properties important to paint technology. Viscometric data proved very useful in relating variances of reaction degree with usage properties of these polymeric materials. Those data suggest a viewpoint of the gel point mechanism which enhances practical utility of polyesterification theory. This hypothesis proposes that alkyd synthesis is not a homogeneous reaction throughout, and that phase separation creates a colloidal dispersion in the reacting mass long before gelatification occurs. Classical polyesterification theory can predict the event of initial phase separation; other process variables affect the relative stability of the transition colloid which ultimately coalesces into the final gel structure. Practical properties of alkyds in paint vehicles can be adjusted to satisfy varying requirements by arresting the reaction at different levels before or in the transition region. Measurements of melt viscosity and intrinsic viscosity are especially sensitive and convenient probes for control of process and product in terms of this concept.