The homopolymerization of methyl methacrylate (MMA) in the presence of 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO) is described and compared to the TEMPO-mediated polymerization of styrene. Furthermore, the formation of block copolymers between MMA and styrene from polystyrene chains with TEMPO fragments as end groups is examined. The degree ofblock formation is estimated by GPC analyses. ESRexperiments are performed on the polystyrene chains to study the scission behavior of the TEMPO fragments.

The triazoline derivative 1 was used as an additive in the chain-growth controlled radical polymerization of vinylic monomers to afford narrowly distributed polymers. This new system is applicable to styrene as well as to methacrylates. The monomer consumption and the variation of the molar mass were monitored with time. Thermal properties of the obtained polymers were also studied. After isolation of the polymers, the growth of the chains was re-initiated in the presence of a second monomer and yielded block copolymers.

A new concept for controlled radical polymerization in the presence of stable free radicals is presented. Due to irreversible side reactions of free polymer radicals, the amount of dead polymer chains and, consequently, the concentration of stable free radicals increases during the polymerization reaction ( Figure 1). Therefore, only monomers with the ability to constantly thermally initiate radical polymerization (e.g., styrene) to capture the excess counter radicals are susceptible to this type of polymerization. In contrast, we present a self-regulating process in controlled radical polymerization, which allows controlled radical polymerization of monomers with no spontaneous initiation. The increase of stable free radicals in our approach is prevented by slow decomposition of the counter radicals and by simultaneous formation of new initiating species. To prove this concept, two triazolinyl radicals (4 and 7) with different thermal stabilities have been studied. Their difference in stability shows a remarkable effect on their use as additives for the controlled radical bulk polymerization of styrene and MMA. The procession of the polymerization in the presence of spirotriazolinyl 7, a stable radical, again strongly depends on the initiating properties of the monomer. While the polymerization of styrene is very well controlled, polymerization of MMA in the presence of spirotriazolinyl 7 could only be accomplished to very low conversions. In contrast, triazolinyl 4, a less stable radical, is additionally able to effectively control the polymerization of MMA at comparably low temperatures.

No abstract

The effect of the addition of the triazoline derivative 1 on the radical polymerization of styrene and some methacrylates is discussed. The polymerization of styrene in the presence of 1 exhibits the characteristics of a controlled radical polymerization such as a linear time-conversion development and increasing molecular weights versus conversion. Additionally, even monomers other than styrene, namely methacrylates, can be polymerized in a controlled fashion. Furthermore, the properties of the isolated PS and PMMA samples were studied. It will be shown, that polymers obtained by controlled radical polymerization in the presence of 1 possess triazolinyl end-groups and the degree of end-functionalisation will be estimated. To demonstrate the ability of the polymers to reinitiate, chain extension experiments were performed on our PSsamples.