Dendrimers as scaffolds for multifunctional reversible addition-fragmentation chain transfer agents: Syntheses and polymerization

The synthesis and characterization of novel first- and second-generation true dendritic reversible addition-fragmentation chain transfer (RAFT) agents carrying 6 or 12 pendant 3-benzylsulfanylthiocarbonylsulfanylpropionic acid RAFT end groups with Z-group architecture based on 1,1,1-hydroxyphenyl ethane and trimethylolpropane cores are described in detail. The multifunctional dendritic RAFT agents have been used to prepare star polymers of poly(butyl acrylate) (PBA) and polystyrene (PS) of narrow polydispersities (1.4 < polydispersity index < 1.1 for PBA and 1.5 < polydispersity index < 1. 3 for PS) via bulk free-radical polymerization at 60°C. The novel dendrimer-based multifunctional RAFT agents effect an efficient living polymerization process, as evidenced by the linear evolution of the number-average molecular weight (Mn) with the monomer-polymer conversion, yielding star polymers with molecular weights of up to M n = 160,000 g mol-1 for PBA (based on a linear PBA calibration) and up to Mn = 70,000 g mol-1 for PS (based on a linear PS calibration). A structural change in the chemical nature of the dendritic core (i.e., 1,1,1-hydroxyphenyl ethane vs trimethylolpropane) has no influence on the observed molecular weight distributions. The star-shaped structure of the generated polymers has been confirmed through the cleavage of the pendant arms off the core of the star-shaped polymeric materials. © 2004 Wiley Periodicals, Inc.