Mechanism of low profile behavior in unsaturated polyester systems

Abstract

SynopsisThe mechanism by which low profile character is achieved in unsaturated polyester systems has been investigated. Using techniques of microscopy, data are developed that support a model in which micro stress cracking is induced to relieve stress promoted by polymerization shrinkage. Thus the strain is accommodated internally in a molded part, rather than through macroscopic shrinkage of the article.

Effects of poly(vinyl acetate) and poly(vinyl chloride‐ co‐vinyl acetate) low‐profile additives on properties of cured unsaturated polyester resins. I. Volume shrinkage characteristics and internal pigmentability

“…Pattison et al 25,26 have proposed that, as the crosslinking of LPA-containing UP resins proceeds, strain due to polymerization shrinkage develops in the system, * The values in parentheses represent the estimated standard errors for the experimental averages.…”

Effects of reactive low‐profile additives on the volume shrinkage and internal pigmentability for low‐temperature cure of unsaturated polyester

“…3,4,13,14 This is, however, different from the viewpoint proposed for the ST/UP/ reactive LPA system in this work.…”

“…Pattison et al 3,4 have proposed that as the crosslinking of LPA-containing UP resins proceeds, strain due to polymerization shrinkage develops in the system, particularly at the interface of LPA phase (phase R) and crosslinked UP phase (phase P). This strain can increase to the point that stress cracking propagates through the weak LPA phase, relieving this strain, forming microcracks or microvoids or both, and compensating for the overall volume shrinkage by the microcrack or microvoid space.…”

“…1 For the past 35 years, extensive studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14] have been devoted to the employment of nonreactive LPAs, such as thermoplastic polyurethane (PU), poly(vinyl acetate) (PVAc), poly(methyl methacrylate) (PMMA), and polystyrene (PS), aimed at the compensation of volume shrinkage by effective microviod and/or microcrack formation, 3,4 to which the phase separation between LPA and crosslinked UP phases during the cure is a prerequisite. It is straightforward that the other approach to the volume shrinkage control during the cure would be reducing the intrinsic polymerization shrinkage since the total volume change is the summation of volume shrinkage and volume compensation.…”

Thermosetting polymer blends of unsaturated polyester resin and poly(ethylene oxide). II. Hydrogen-bonding interaction, crystallization kinetics, and morphology

“…The mechanism of low profile behavior in polyester systems is the the increasing number of papers in literatures, but there are only few papers concerned with polymain topic in the early research work. Pattison 9,10 indicated that in either single-phase or two-phase mer blends where one component is crystallizable and another is highly crosslinked.…”