Thermosetting powder coating is an important coating material, and polyester resin is one of its core components. The molecular weight and distribution characteristics of polyester resin have an important influence on the performance and quality of the coating. In the analysis of its molecular weight and distribution, the end group chemical determination and molecular weight distribution SEC method are often used. These two methods provide us with an in-depth understanding of the structural characteristics and performance of polyester resins.

Molecular weight and distribution characteristics range and determination description

Molecular weight and distribution characteristics of polyester resin in thermosetting powder coatings

The saturated polyester resin used in thermosetting powder coatings usually has a low molecular weight, generally below 3X10^4. The end groups of these resins can be hydroxyl or carboxyl groups, and their hydroxyl or acid values can be determined chemically. Most of these saturated polyester resins are linear or linear polycondensation followed by end-group structure, and their molecular weight can be calculated by end-group chemical determination. The molecular weight distribution describes the proportion of polymers of different molecular weights in the mixture, and its determination requires separating these homologues and determining the proportion on a grade-by-grade basis. Today, volume exclusion chromatography (SEC) or gel permeation chromatography (GPC) is widely used to determine molecular weight distribution, and is often represented by cumulative mass distribution curves or differential mass distribution curves.

Principle and instrument of molecular weight distribution SEC method

The SEC method is achieved by using a column of stationary phase porous gels. The sample is injected into the column as a dilute solution, and the solvent is then used as a mobile phase to flush the column. In the column, the polyester resin is washed down one by one according to the order of molecular size, and the detector records and determines the different molecular weights of the polyester resin. SEC instruments mainly include sample and solvent injection systems, gel columns, detection systems (refractive index and volume measurement), data acquisition and processing systems, and heating and constant temperature systems.

Molecular weight and distribution characteristics of polyester resin in thermosetting powder coatings

Determination method and result analysis

The molecular weight of the polyester resin can be obtained by end-group chemical determination, according to the acid value or hydroxyl value, and combined with the chemical structure of the polyester resin, its molecular weight can be calculated. However, it is important to note that the calculated molecular weights are usually only meaningful on an order of magnitude basis, and smaller values may not be of practical significance. The molecular weight distribution curves are usually characterized by high peaks and low dispersion, and these curves provide important information about the cumulative or differential mass distribution of the sample.

Therefore, the molecular weight and distribution characteristics have an important influence on the application of polyester resin in thermosetting powder coatings. The end group chemical assay and the molecular weight distribution SEC method provide us with an in-depth understanding of the structure and properties of polyester resins, which helps to optimize coating formulations and improve coating properties to meet the needs of different fields.