Ability of nitrones of various structures to control the radical polymerization of styrene mediated by in situ formed nitroxides

Abstract

The ability of several nitrones to control the radical polymerization of styrene at 110 °C has been investigated by high-throughput experimentation. The nitrone/free radical initiator pair dictates the structure of the nitroxide and the alkoxyamine formed in situ, which determines the position of the equilibrium between the active and the dormant species operating in the nitroxide-mediated polymerization. For the styrene polymerization to be controlled, the nitrone must be reacted with 2,2′-azo-bis-isobutyronitrile (AIBN) at 85 °C, prior to addition of styrene and polymerization at 110 °C. The effect of the nitrone structure on the kinetics of the styrene polymerization has been emphasized. Amongst all the nitrones tested, those of the C-phenyl-N-tert-butylnitrone (PBN) type are the most efficient in terms of polymerization rate, control of molecular weight and polydispersity. Electrophilic substitution of the phenyl group of PBN by either an electrodonor or an electroacceptor group has only a minor effect on the polymerization kinetics. Importantly, the polymerization rate is not governed by the thermal polymerization of styrene but by the alkoxyamine formed in situ during the pre-reaction step. The initiation efficiency is, however, very low, consistent with a limited conversion of the nitrone into nitroxide and alkoxyamine.

Formation Efficiency of ABA Blockcopolymers via Enhanced Spin Capturing Polymerization (ESCP): Locating the Alkoxyamine Function

“…11 Nitrones have been used previously in radical polymerization systems, most notably by Detrembleur and Jêrome, who employed these species to form macronitroxides in situ for subsequent NMP reactions. [12][13][14] The findings of these colleagues during the in situ macronitroxide formation phase are in excellent agreement with recent results from our group.…”

Kinetics and electron spin resonance study of the radical polymerization of n‐butyl acrylate mediated by a nitroxide precursor: C‐phenyl‐N‐tert‐butylnitrone

“…To get rid of the uncontrolled formation of PnBuA during the prereaction step, only PBN and AIBN were prereacted in toluene at 85 °C for 4 h. The [PBN]/[AIBN] ratio was fixed to 1/0.5 because it was previously demonstrated to be the optimal one for the styrene radical polymerization with this in situ system 58. After toluene elimination and nBuA addition, the reaction medium was heated at 110 °C.…”

“…Very recently, we demonstrated that two specific nitrones, that is, N ‐ tert ‐butyl‐α‐isopropylnitrone and PBN (Fig. 3), were able to control the radical polymerization of styrene 57, 58. In contrast to NMP carried out with preformed alkoxyamines, the in situ NMP process based on nitrones is strongly dependent on the experimental conditions, such as the prereaction of the nitrone with a radical initiator before polymerization or not, the prereaction in the presence of the monomer or not, the structures of both the nitrone and the initiator, the nitrone/initiator molar ratio, the time, and the temperature.…”

Parallel Synthesis of Polymer Libraries Using Atom Transfer Radical Polymerization (ATRP)

“…In the literature there are reports that have demonstrated that automated parallel synthesizers can provide fast and reliable screening possibilities and are well suited for the investigation of various polymerization systems 49. Some of the reported polymerizations are ATRP,50 RAFT,51 NMP,43, 52 cationic ring‐opening polymerization,53 and the synthesis of photocrosslinkable and degradable materials 54. Using ATRP, the polymerization of MMA has been studied after monomer purification 50, 55.…”