Mechanism of low‐profile behavior in single‐phase unsaturated polyester systems

Abstract

Abstract The mechanism of the low profile behavior in certain single‐phase polyester systems has been examined. It appears that as polymerization occurs, crosslinked beads (< 1μ) of polymer separate from the bulk solution. As the temperature rises, liquid monomer expands, counteracting polymerization shrinkage. As shrinkage surpasses expansion towards the end of polymerization, stresses are induced in the system. These are relieved internally by a series of micro cracks in the continuous matrix of the polymer rather than, as in ordinary systems, through macroscopic shrinkage of the molded part.