Decomposition of Stable Free Radicals as “Self-Regulation” in Controlled Radical Polymerization

Abstract

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.

Novel Telechelic 2-Methyl-2-Bromopropionate Terminated Polyurethane Macroinitiator for the Synthesis of ABA type Tri-block Copolymers through Atom Transfer Radical Polymerization of Methyl Methacrylate

“…This may be due to the poor deactivation by CuBr 2 which lead to the unavoidable radical-radical termination as side reactions. Similar types of results have been discussed thoroughly by Steenbock et al 5 and large deviation of experimental M n with theoretical M n has also been reported in the polymerization of MMA through ATRP mechanism. 50 However the initiator efficiency, f, is more or less high in all the cases.…”

“…But the increase of M n with conversion is not linear. Due the presence of inevitable radicalradical termination reactions, 5 it leads to the loss of linearity in the curves. Similar type curves have been reported in case of ATRP.…”

“…2 Indeed different types of CRP techniques have been reported which facilitated the synthesis of broad variety of polymeric materials with predetermined molecular weight, narrow MWD and desired chain end groups. CRP was achieved through iniferter (initiation transfer termination), 3 stable nitroxide radicals, 4 triazolinyl radicals, 5 organo-bismuthine, 6 organotellurium, 7 organo-cobalt, 8 organo-stilbene, 9 alkyl-9-BBN, 10 reversible addition-fragmentation-chain transfer (RAFT), 11 degenerative chain transfer by alkyl iodide, 12 and atom transfer radical polymerization (ATRP). 13,14 All the CRP methods include activation and deactivation steps with their respective rate constants, k act and k deact respectively and k deact is higher in all the cases to get controlled radical polymerization of monomers.…”

N-tert-Butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide as counter radical in the controlled free radical polymerization of styrene: kinetic aspects

“…Such side reactions could be of particular interest. For example, Klapper et al 34) have recently shown that the slow decomposition of some triazolinyl radicals makes it possible to effectively control the polymerization of monomers with no spontaneous initiation such as methyl methacrylate. The values of the rate constants determined herein, based on an ideal kinetic scheme, could be altered by the occurrence of the above mentioned side reactions.…”

Recent advances in controlled/living radical polymerization in emulsion and dispersion

“…A number of persistent radicals have been examined as mediators in the SFRP process. They include 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), [103][104][105] other nitroxides including N-t-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)nitroxide (called SG1) [106][107][108] and 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO) and its derivatives 109,110 as well as triazolinyl 111,112 and verdazyl 113,114 stable radicals, employed with free radical initiators to initiate polymerization (Fig. 3).…”