Kinetics of Formation of Many Armed Stars With Dendrimer Cores as a Model of Crosslinking
Barry J. Bauer, B D. Viers
Many armed star molecules were formed by endlinking monofunctional vinyl sulfone endcapped PEG to the terminal amines dendrimers. Gel permeation chromatography was used to separate the stars from the unreacted arms and to measure the conversion. The PEG and dendrimer were mixed in a GPC vial and were repeatedly injected over a period of several days. Conversions up to 80% could be followed and the results were fit to kinetic models. The reaction slows down as the conversion increases, presumably due to crowding of the reaction sites on the dendrimer. The kinetics that are fit can be used to calculate the polydispersity of the number of arms per star and result in a very narrow distribution. Networks made from difunctional PEG and dendrimers should therefore produce networks with high functionality and low polydispersity.