The grafting of functional groups onto polymers is a suitable approach applied to achieve specific properties not intrinsic of starting materials. However, the classical radical post-reactor modification does not guarantee the structural preservation of the pristine macromolecular architecture. Indeed, the macroradical possibility/capability to react with the functionalizing monomer or to undergo to side reactions (degradation by ?-scission and crosslinking/branching by coupling) determines the probability of success of the process. Moreover, propagation and chain transfer steps increase the amount of free radicals, raising the occurrence of collateral reactions1. In this scenario different chemicals were employed to control the stability of macroradicals and to lead their reactivity towards the desired grafting reaction. First, chemicals able to quickly react with macroradicals by generating new resonance-stabilized macroradicals were used. The butyl-3(2 furanyl) propenoate (BFA, or thiofene derivatives)2,3 was proved to be effective in hindering side reactions, even if a certain detriment of the grafting efficiency was noticed. This result was due to the inhibition of propagation and transfer reactions thus promoting a better control over the macromolecular structure and, if anything, promoting inter/intramacromolecular coupling reactions4. From the mechanism point of view, this moved the whole grafting trial towards a stoichiometric process. Afterwards, chemicals able to effectively decrease the instantaneous concentration of macroradicals, by quenching them, were employed. In particular 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) derivatives were used as functionalizing molecules. This approach allowed inserting selected functionalities by a one-step procedure and mostly addressed the process mechanism towards a stoichiometric reaction, avoiding the macroradical reactions not producing the target products. This approach made possible to achieve a good control of the grafting degree and of the macromolecular architecture5,6. This lecture reports the main results collected in our group in this field with particular emphasis to mechanistic aspects in modulating the chemistry to fully control the radical functionalization of polymers. References 1.E. Passaglia, S. Coiai, S. Augier, Prog. Polym. Sci. 34: 911-947 (2009) 2.S. Coiai, S. Augier, C. Pinzino, E. Passaglia, Polym Degrad Stab, 95: 298-305 (2010) 3.I. Domenichelli, S. Coiai, F. Cicogna, C. Pinzino, E. Passaglia Polym. Int. 64, 631-640 (2015). 4.F. Cicogna, S. Coiai, D. Moliterni G. Ruggeri, M.-B. Coltelli, A. Lazzeri, E. Passaglia, Polym. Int,; 65: 621-630 (2016) 5.F. Cicogna, S. Coiai, E. Passaglia, I. Tucci, L. Ricci, F. Ciardelli, A. Batistini J. Polym. Sci., Part A: Polym. Chem. Polym. Chem.49: 781-795 (2011) 6.F. Cicogna, S. Coiai, P. Rizzarelli, S. Carroccio, C. Gambarotti, I. Domenichelli, C. Yang, N. Tz. Dintcheva, G. Filippone, C. Pinzino, E. Passaglia, Polym. Chem., 5 (19), 5656 - 5667 (2014)
Controlled radical post-reactor functionalization of polymers"
2017
Abstract
The grafting of functional groups onto polymers is a suitable approach applied to achieve specific properties not intrinsic of starting materials. However, the classical radical post-reactor modification does not guarantee the structural preservation of the pristine macromolecular architecture. Indeed, the macroradical possibility/capability to react with the functionalizing monomer or to undergo to side reactions (degradation by ?-scission and crosslinking/branching by coupling) determines the probability of success of the process. Moreover, propagation and chain transfer steps increase the amount of free radicals, raising the occurrence of collateral reactions1. In this scenario different chemicals were employed to control the stability of macroradicals and to lead their reactivity towards the desired grafting reaction. First, chemicals able to quickly react with macroradicals by generating new resonance-stabilized macroradicals were used. The butyl-3(2 furanyl) propenoate (BFA, or thiofene derivatives)2,3 was proved to be effective in hindering side reactions, even if a certain detriment of the grafting efficiency was noticed. This result was due to the inhibition of propagation and transfer reactions thus promoting a better control over the macromolecular structure and, if anything, promoting inter/intramacromolecular coupling reactions4. From the mechanism point of view, this moved the whole grafting trial towards a stoichiometric process. Afterwards, chemicals able to effectively decrease the instantaneous concentration of macroradicals, by quenching them, were employed. In particular 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) derivatives were used as functionalizing molecules. This approach allowed inserting selected functionalities by a one-step procedure and mostly addressed the process mechanism towards a stoichiometric reaction, avoiding the macroradical reactions not producing the target products. This approach made possible to achieve a good control of the grafting degree and of the macromolecular architecture5,6. This lecture reports the main results collected in our group in this field with particular emphasis to mechanistic aspects in modulating the chemistry to fully control the radical functionalization of polymers. References 1.E. Passaglia, S. Coiai, S. Augier, Prog. Polym. Sci. 34: 911-947 (2009) 2.S. Coiai, S. Augier, C. Pinzino, E. Passaglia, Polym Degrad Stab, 95: 298-305 (2010) 3.I. Domenichelli, S. Coiai, F. Cicogna, C. Pinzino, E. Passaglia Polym. Int. 64, 631-640 (2015). 4.F. Cicogna, S. Coiai, D. Moliterni G. Ruggeri, M.-B. Coltelli, A. Lazzeri, E. Passaglia, Polym. Int,; 65: 621-630 (2016) 5.F. Cicogna, S. Coiai, E. Passaglia, I. Tucci, L. Ricci, F. Ciardelli, A. Batistini J. Polym. Sci., Part A: Polym. Chem. Polym. Chem.49: 781-795 (2011) 6.F. Cicogna, S. Coiai, P. Rizzarelli, S. Carroccio, C. Gambarotti, I. Domenichelli, C. Yang, N. Tz. Dintcheva, G. Filippone, C. Pinzino, E. Passaglia, Polym. Chem., 5 (19), 5656 - 5667 (2014)I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
