< Back to previous page
Rheokinetics and network formation in crosslinking step-growth polymerization
Book - Dissertation
Since the discovery of polyurethane reaction consisting out of isocyanates and polyols, in 1937 up until today, this material has been studied and applied. By combining different monomers and reaction environments several different materials can be made with varied applications like foams, fiber composites matrix, paints, coatings and adhesives. Like in other polymers there is an intimate relation between the structure-processing-property relationships, starting from the monomers building up the network, viscous and the mechanical properties, but due to the fast reaction kinetics of polyurethanes is not well-known and therefore less controllable The goal of this work was to gain in-depth knowledge and insight in the reaction kinetics of polyurethane resins and to link it to the changing rheological properties, consequently gaining insight in the use of these resins to produce polyurethane materials. To accomplish this, first the reaction mechanism behind the urethane formation, which is still up for debate, was investigated. Using the concentration profiles obtained from this reaction mechanism and knowing the structure of the monomers, the molecular structure development, such as the average molar mass and crosslink density, can be predicted using a recursive algorithm. Using the average molar mass, the viscosity evolution, gelation and mechanical properties can be predicted. To help facilitate this, a software was developed for simulating and optimizing reaction kinetic mechanisms in a first step and calculate the structure development in a second step. The developed methods and rheokinetic models are useful for industry as their application can aid in improving the design and process conditions of existing processed and help create and develop new ones.