Thermosetting powder coating is an important coating material, in which polyester resin is one of its core components. The molecular weight of polyester resin and its distribution characteristics have an important impact on the performance and quality of the coating. When analyzing its molecular weight and distribution, end-group chemical determination and molecular weight distribution SEC methods 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 measurement instructions
The saturated polyester resin used in thermosetting powder coatings usually has a lower molecular weight, generally below 3X10^4. The end groups of these resins can be hydroxyl or carboxyl groups, and their hydroxyl value or acid value can be determined chemically. Most of these saturated polyester resins have a linear or linear polycondensation first and then end-grouping structure, and their molecular weight can be calculated by end-group chemical determination. Molecular weight distribution describes the proportions of polymers of different molecular weights in a mixture, and its determination requires the separation of these homologues and the determination of the proportions level by level. Nowadays, size exclusion chromatography (SEC) or gel permeation chromatography (GPC) are widely used to determine molecular weight distribution, and are often represented by cumulative mass distribution curves or differential mass distribution curves.
Principles and instruments of molecular weight distribution SEC method
The SEC method is implemented using a chromatographic column using porous gel as a stationary phase. The sample is injected into the column as a dilute solution, and the solvent is then used as the mobile phase to flush the column. In the chromatographic column, the polyester resin is washed down one by one according to the order of molecular size, and the Detector records and measures the polyester resin with different molecular weights. SEC instruments mainly include sample and solvent injection systems, gel chromatography columns, detection systems (refractive index and volume size detection), data acquisition and processing systems, and heating and constant temperature systems.
Determination methods and result analysis
The molecular weight of polyester resin can be obtained by end-group chemical determination. According to the acid value or hydroxyl value, combined with the chemical structure of the polyester resin, its molecular weight can be calculated. However, it is important to note that calculated molecular weights are usually only meaningful in orders of magnitude and may not be of practical significance at smaller values. Molecular weight distribution curves usually exhibit higher peaks and less dispersion. These curves provide important information about the cumulative mass distribution or differential mass distribution of the sample.
Therefore, molecular weight and distribution characteristics have an important impact on the application of polyester resin in thermosetting powder coatings. The end group chemical determination method and the molecular weight distribution SEC method provide us with a deep understanding of the structure and performance of polyester resin, which helps to optimize coating formulations and improve coating performance to meet the needs of different fields.