Nitroxide-mediated radical copolymers

Synthesis of Block Copolymers by Nitroxide-Mediated Radical Polymerization, NMP... 

Nitroxide mediated radical polymerization (NMRP) was pioneered by Riz-zardo and Solomon in the mid-1980s [1]. Their work went unnoticed for almost a decade until Georges et al. reported the preparation of narrow polydispersity (PD) (<1.2) polystyrene using NMRP [2]. This report initiated an explosion of research aimed at both understanding the mechanism of NMRP and also utilizing it to prepare block copolymers. This chapter describes the application and limitations of NMRP for making styrene-containing block copolymers. 

Alternative total solid phase-based strategies for the preparation of polymer-peptide block copolymers were based on the polymerization of the synthetic polymer block from the supported peptide segment using either nitroxide-mediated radical polymerization (NMP) or ATRP (Fig. 15) [64,65]. 

Becker et al. [64] functionalized a peptide, based on the protein transduction domain of the HIV protein TAT-1, with an NMP initiator while on the resin. They then used this to polymerize f-butyl acrylate, followed by methyl acrylate, to create a peptide-functionahzed block copolymer. Traditional characterization of this triblock copolymer by gel permeation chromatography and MALDI-TOF mass spectroscopy was, however, comphcated partly due to solubility problems. Therefore, characterization of this block copolymer was mainly hmited to ll and F NMR and no conclusive evidence on molecular weight distribution and homopolymer contaminants was obtained. Difficulties in control over polymer properties are to be expected, since polymerization off a microgel particle leads to a high concentration of reactive chains and a diffusion-limited access of the deactivator species. The traditional level of control of nitroxide-mediated radical polymerization, or any other type of controlled radical polymerization, will therefore not be straightforward to achieve. 

This polymer was synthesized via NMRP (Nitroxide Mediated Radical Polymerization) (Benoit et al. 1999) by sequential polymerization of 2VP and a mixture of NIPAAm and DMIAAm. Using the macroinitiator method, the preparation of well-defined linear block copolymers consisting of a homo polymer block P2VP (pH-sensitive) and a random copolymer block of PNlPAAm (temperamre sensitive) with DMIAAm (photo crosslinker) was possible. 

LAC Lacroix-Desmazes, P., Andre, P., Desimone, J.M., Ruzette, A.-V., and Boutevin, B., Macromolecular surfactants for supercritical carbon dioxide applications Synthesis and characterization of fluorinated block copolymers prepared by nitroxide-mediated radical polymerization (experimental data by P. Lacroix-Desmazes), J. Polym. Sci. Part A Polym. Chem., 42, 3537, 2004. 

Delplace, V., Harrisson, S., Tardy, A., Gigmes, D., Guillaneuf, Y., Nicolas, J. Nitroxide-mediated radical ring-opening copotymerization Chain-end investigation and block copolymer synthesis. Macromol. Rapid Commun.. 2014, 35,484-491. 

With the development of controlled radical polymerization techniques like nitroxide-mediated radical polymerization (NMRP), atom transfer radical polymerization (ATRP), and reversible addition fragmentation chain transfer (RAFT) polymerization (see Section 3.2), the field of linear glycopolymers has significantly flourished, especially as control of molar mass and monomer sequence has become available, even for functionalized monomers. This enables incorporation of new and more complex glycomonomers as well as allows controlled dispersity, end group functionality, and monomer sequences in block, star-shaped, and graft copolymers, and eventually... 

The DA chck reaction, a [4 + 2] cycloaddition system based on the coupHng of a diene and a dienophile, represents an alternative strategy in chck chemistry [26-28]. This reaction has been applied successfully to the preparation of block copolymers with PEO and PSt or PMMA segments, prepared using AROP and ATRP or nitroxide-mediated radical polymerization (NMRP) [26-28]. Thus, PEO-b-PSt and PEO-h-PMMA block copolymers were synthesized via DA chck reaction of maleimide- and anthracene end-functionahzed polymers. The overall strategy is represented in Scheme 11.3, as the preparation of PEO-h-PSt... 

One of the limitations of anionic polymerization with respect to preparation of block copolymers is the rather limited range of monomers that can be polymerized anionically to form polymers with well-defined stmctures. One solution to this problem is to utilize anionic polymerization to form a well-defined polymer that is functionalized with an end group that can be used to initiate polymerization via another polymerization method, for example, controlled free-radical polymerization. One such functional group is the aminoxy group which can be used to initiate nitroxide-mediated radical polymerization (NMP). °° PSLi has been reacted with 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl (MTEMPO), a stable nitroxide free radical, in THF at -78 °C as shown in eqn [30]. The mechanism of this functionalization was presumed to occur... 

Various synthetic techniques have been used to obtain homopolymers and copolymers with defined chemical compositions and low polydispersity (1) living anionic or cationic polymerization [26,27], (2) controlled ring-opening polymerization (CROP) [28], and (3) controlled radical polymerization (CRP), which includes (a) atom transfer radical polymerization, (b) reversible addition-fragmentation chain transfer polymerization (RAFT), and (c) nitroxide mediated radical polymerization (NMP) [29-31]. 

Becker, M. L., Liu, J., and Wooley, K. L. (2001). Preparation of tritrpticin block copolymer bio-conjugates by fluorinated nitroxide mediated radical polymerization on solid support. Abstracts of Papers, 222nd ACS National Meeting, Chicago, IL, United States, August 26-30, 2001, p. OLY-017. 

Sciannamea, V., Lenoir, S., Cossement, D., Gouttebaron, R., Jerome, R., Jerome, C. 2004. Synthesis of Copolymer Bmshes Endowed with Adhesion to Stainless Steel Surfaces and Antibacterial Properties by Controlled Nitroxide-Mediated Radical Polymerization, 20 10718-10726. 

For nitroxide-mediated radical polymerizations and in the RAFT process, the same synthetic strategy as for ATRP can be used in the synthesis of AB and ABA block copolymers. The first step is coupling a functionalized alkoxyamine with a telechelic or monofunctional nonvinylic polymer to give a macroinitiator. This macroinitiator can be used in standard controlled free-radical polymerization procedures. This approach is best illustrated by the preparation of PEO-based block copolymers [81-84]. One example is the preparation of macroinitiator LMI-7 by the reaction of a monohydroxy-terminated PEO with sodium hydride followed by reaction with the chloromethyl-substituted alkoxy amine as shown in Scheme 3.16. 

There are fewer reports on the preparation of block copolymers via the combination of anionic polymerization with nitroxide-mediated syntheses [132,133]. As shown in Scheme 3.30, the reaction product of sodium with 4-hydroxyl-TEMPO initiated the anionic polymerization of ethylene oxide at 60 °C in THF solution. After treatment with methanol, TEMPO-terminated PEO was obtained, and then used in the nitroxide-mediated radical polymerization of St at 120 °C resulting in block copolymers of type CLB-17 [133]. Another method is the transformation of anionic polymerization into nitroxide-mediated radical polymerization. A poly(butadienyl)lithium solution in... 

Using novel asymmetric difunctional initiators containing TEMPO and 2-bromopropanoate or 2-bromo-2-methylpropanoate groups, block copolymers can be prepared via combination of ATRP and STRP [147,148]. For example, asymmetric difunctional initiator, CLI-25 was used in the ATRP of MM A with CuCl/N, N, N , N ,N -pentamethyldiethylene-triamine (PMDETA) as catalyst. The low initiator efficiency (i.e. 0.8) may be related to the side reactions that occur in the initiation step. Subsequently, the TEMPO-terminated PMMA was used as the macroinitiator in the nitroxide-mediated radical polymerization of St at 125 °C. A series of block copolymers, PMMA-6-PSt [147], PrBA-6-PSt [147] and PtBA-6-PMMA-Zi-PSt [148] have been obtained, an example of which is shown in Scheme 3.36. 

The development of the CRP based on the idea of reversible chain termination decrease the disadvantage of the free-radical polymerization and permits the synthesis of defined block copolymer structures. The growing demand for well-defined and ftinctional soft materials in nanoscale applications has led to a dramatic increase in the development of procedures that combine architectural control with flexibility in the incorporation of ftinctional groups. Thus, there is a strong increase in the elucidation of a variety of controlled polymerization strat es in the past years. " These include nitroxide-mediated radical polymerization (NMRP), atom transfer radical polymerization (ATRP), " and reversible addition-fragmentation chain transfer (RAFT) procedures. Such techniques led to well-defined homo and block copolymers of different architectures whose behavior was investigated in solution and on surfaces. ... 

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