Sternpolymere mittels RAFT-Polymerisation

Abstract

The goal of the work presented was the synthesis of star polymers with a defined number of arms, narrow molecular weight distribution and high degree of polymerization from controlled radical polymerization of different monomers. In order to reach this goal 2, 3, 4, 6 and 8 arm addition fragmentation chain transfer (RAFT)-agents were synthesized. In all cases the core of the stars was the stabilizing group (Z-group approach). Poly styrene, poly methylacrylate, poly butylacrylate, poly dodecylacrylate, and poly vinylacetate star polymers were produced and analyzed. For styrene polymerizations investigations regarding the RAFT pre equilibrium in star polymerizations were carried out via NMR measurements, Monte-Carlo simulations and the analysis of the conversion dependence of the apparent number of arms. It was shown that the rate in which the RAFT main equilibrium is reached depends on the leaving group of the RAFT agent. Thus, the RAFT leaving group has a significant influence on the topology of star polymers produced via RAFT star polymerization. Restrictions for the synthesis of styrene star polymers given by the high rate of termination were limited using high pressure. Esters of acrylic acid are known to have a high reactivity regarding intra and inter molecular transfer to polymer. During the polymerization of the above mentioned acrylates star-star coupling was observed, which is exclusively due to inter molecular transfer to polymer. By analysis of the molecular weight distributions in combination with modelling it was possible to determine the rate coefficients of the transfer to polymer reaction step for butyl acrylate and dodecyl acrylate for the first time directly. During the RAFT star polymerizations of vinyl acetate star-star coupling was observed also. Transfer reaction to monomer and polymer were identified as the limiting factors in the production of well defined vinyl acetate star polymer with a controlled molecular weight. A method to estimate the absolute number average of the molecular weight distribution of star polymers was developed using a mixture of linear and star like RAFT agents. A conventional SEC setup calibrated against linear polymer standards is sufficient for the method developed.