Complex macromolecular structures from stable radical containing block copolymers

A novel synthetic strategy for the synthesis of graft copolymers is reported. Block copolymers containing segments with stable nitroxyl radicals side groups were first prepared by anionic polymerization, which were then used as a precursor for the subsequent nitroxide-mediated radical polymerization (NMRP) of styrene. This way, block–graft copolymers with polystyrene side chains grafted from one of the blocks were successfully synthesized in a controlled manner. In addition, block–graft copolymers with grafted polystyrene chains and a poly(tert-butyl methacrylate) block were subjected to hydrolysis to yield the corresponding amphiphilic polymers. The structures and the molecular weight characteristics of the polymers were characterized by spectral and chromatographic analyses. The surface morphology of thus obtained polymers was also investigated by microscopic techniques. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 62–69     

Microwave-assisted nitroxide-mediated radical polymerization of styrene

The first single-mode microwave-assisted nitroxide-mediated radical polymerizations (NMRP) of styrene in bulk were successfully performed. The results showed that the polymerization proceeded in a controlled way. The power of microwave irradiation has considerable effect on the polymerization rate. The polymerization rates under appropriate power of microwave irradiation were faster than that under conventional heating (CH) at the same polymerization temperature. The living nature of the polymer was proved by successful chain extension polymerization and ¹H NMR spectrum analysis.     

Kinetics of Nitroxide Mediated Radical Polymerization of Styrene with Unimolecular Initiators

Summary: This study examined the kinetics of nitroxide-mediated radical polymerization of styrene with unimolecular (alkoxyamine) initiators. Control of polymerization rate and polymer molecular weight in unimolecular nitroxide-mediated radical polymerization was studied by looking at the effects of the three main factors: initiator concentration, temperature, and initiator molecular weight on polymerization rate, molecular weight and polydispersity. In addition, the behavior of the unimolecular initiating systems was compared to that of the corresponding bimolecular system. The effective TEMPO concentration and degree of self-initiation of styrene were proved to be significant in dictating magnitudes of molecular weight averages and widths of molecular weight distribution.     

“Living” free radical copolymerization of styrene and N-vinylcarbazole

Poly[styrene-co-(N-vinylcarbazole)] copolymers with controlled molecular weights and narrow polydispersities were synthesized by nitroxide-mediated “living” free radical copolymerization using an initiator/capping agent system consisting of benzoyl peroxide (BPO) and the stable nitroxyl radical 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO). The copolymerization behaves in a “living” fashion and allows the synthesis of poly[styrene-co-(N-vinylcarbazole)]/polystyrene block copolymers via a controlled chain-extension reaction of the prepared copolymers with styrene.     

Design and synthesis of trivalent Tn glycoconjugate polymers by nitroxide-mediated polymerization

A new synthetic method for preparing Tn glycoconjugate polymers, containing tumor-associated carbohydrate antigens, by controlled living radical polymerization is reported. To mimic the authentic structures of Tn glycopeptide antigens and to explore the controlled living radical polymerization, three tumor-associated carbohydrate antigens (GalNAc, GalNAcα1-O-Ser, and GalNAcα1-O-Thr) were attached to a styrene-type monomer through a diethylene glycol spacer. Under nitroxide-mediated polymerization, controlled living radical polymerization proceeded to afford defined glycopeptide polymers with different Tn densities and compositions. The polydispersity index (PDI) and molecular weights were increased and conversions were decreased upon increasing the concentration of Tn glycoconjugate monomers. The resulting Tn glycoconjugate polymers were characterized by NMR and IR. The spectral data indicate that the Tn glycoconjugate moiety did attach to the polymer chain and Tn glycoconjugate density could be adjusted through the nitroxide-mediated polymerization conditions. The number of Tn units containing in the polymer chains could be estimated by NMR integration. This synthetic approach provides a new and efficient tool for constructing novel Tn glycoconjugate polymers.     

Tailoring macromolecular architecture with imidazole functionality: A perspective for controlled polymerization processes

Controlled radical polymerization (CRP) allows for the design and synthesis of functional polymers with tailored composition and unique macromolecular architectures. Synthetic methods that are readily available for controlled radical polymerization include nitroxide-mediated polymerization, reversible addition–fragmentation chain transfer polymerization, and atom transfer radical polymerization. N-Vinyl monomers that are typically amenable to free radical methods are often difficult to synthesize in a controlled manner to high molecular weight due to the lack of resonance stabilization of the propagating radical. However, recent advances in the field of CRP have resulted in successful controlled polymerization of various N-vinyl heterocyclic monomers including N-vinylcarbazole, N-vinylpyrrolidone, N-vinylphthalimide, and N-vinylindole. The incorporation of the imidazole ring into homopolymers and copolymers using conventional free radical polymerization of N-vinylimidazole monomer is particularly widespread and advantageous due to facile functionalization, high thermal stability, and the relevance of the imidazole ring to many biomacromolecules. Copolymers prepared with methyl methacrylate displayed random incorporation according to differential scanning calorimetry and amorphous morphologies according to X-ray scattering. Imidazole- and imidazolium-containing monomers have shown recent success for CRP; however, the controlled polymerization of N-vinylimidazole has remained relatively unexplored. Future efforts focus on the development of tailored imidazole-containing copolymers with well-defined architectures for emerging biomedical, electronic and membrane applications.     

Synthesis of Poly （styrene-b-isoprene-b-styrene） via Nitroxide-mediated Radical Polymerization by a Novel Alkoxyamine

Bifunctional alkoxyamine bis-TIPNO derived from 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxyl （TIPNO） and α, ω-alkyl bromide by atom transfer radical addition（ATRA） was employed as “biradical initiator” for nitroxide-mediated radical polymerization（NMRP） of isoprene and styrene. The kinetics study for the polymerization of styrene at different time showed living features. The poly（styrene-b-isoprene-b-styrene） （SIS） copolymers have two glass transition temperatures, indicating the immiscibility of the corresponding blocks.     

丙烯腈可控/"活性"自由基聚合研究进展

可控/"活性"自由基聚合能有效控制聚合物的分子量及其分布,并且能调控其微观拓扑结构。聚丙烯腈及其共聚物具有良好的成纤成膜性能,是一类应用十分广泛的聚合物。本文综述了可控/"活性"自由基聚合法合成聚丙烯腈及其共聚物的研究现状与进展,从氮氧自由基法(NMP)、引发转移终止剂法(iniferter)、原子转移自由基聚合(ATRP)和可逆加成-断裂链转移(RAFT)聚合等方面对丙烯腈均聚物和共聚物的合成研究作了全面的总结,提出了存在的问题,并且对今后的研究方向作了展望。     

Synthesis of star polymers via nitroxide mediated free‐radical polymerization: A “core‐first” approach using resorcinarene‐based alkoxyamine initiators

The synthesis of new octafunctional alkoxyamine initiators for nitroxide‐mediated radical polymerization (NMRP), by the derivatization of resorcinarene with nitroxide free radicals viz TEMPO and a freshly prepared phosphonylated nitroxide, is described. The efficiency of these initiators toward the controlled radical polymerization of styrene and tert‐butyl acrylate is investigated in detail. Linear analogues of these multifunctional initiators were also prepared to compare and evaluate their initiation efficiency. The favorable conditions for polymerization were optimized by varying the concentration of initiators and free nitroxides, reaction conditions, etc., to obtain well‐defined star polymers. Star polystyrene thus obtained were further used as macro‐initiator for the block copolymerization with tert‐butyl acrylate. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5559–5572, 2007     

Nitroxide-mediated styrene polymerization initiated by an oxoaminium chloride

An oxoaminium chloride that is prepared by reacting 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) with chlorine in carbon tetrachloride initiates radical polymerization of styrene at 120°C. In the early stages of polymerization, a monomeric adduct, 2,2,6,6-tetramethyl-1-(2-chloro-1-phenylethoxy)piperidine, is formed. Thereafter, styrene polymerization exhibiting the characteristics of living polymerization proceeds. High molecular weight polymers with relatively narrow molecular weight distributions are obtained by this polymerization. ¹H-NMR spectra of the polymers reveal that a chlorine atom and a TEMPO group are present at the α- and ω-termini, respectively. The monomeric adduct was prepared by heating the oxoaminium chloride and styrene in carbon tetrachloride at 65–70°C, and was characterized by ¹H- and ¹³C-NMR spectroscopy. It was found to be suitable as an initiator for nitroxide-mediated radical polymerization of styrene to make polymers with chlorine on the chain end. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2555–2561, 1998     

Synthesis of New Graft Copolymers by Combining the DPE Technique and Cationic Polymerization

The synthesis of a new macroinitiator for cationic polymerization via radical polymerization is presented. The macroinitiator, consisting of poly(methyl methacrylate)‐block‐poly[styrene‐co‐(4‐chloromethylstyrene)], was synthesized by heating poly(methyl methacrylate), prepared in the presence of 1,1‐diphenylethylene, in a mixture of styrene and 4‐chloromethylstyrene to 85°C without any additional initiator. The resulting macroinitiator could be used for the cationic polymerization of isobutylene yielding graft copolymers.     

Novel dinitroxide mediating agent for stable free‐radical polymerization

A novel dinitroxide mediating agent that was suitable for stable free‐radical polymerization was synthesized and used in the block copolymerization of styrene and t‐butyl styrene. Quantitative yields of a novel dinitroxide based on 1,6‐hexamethylene diisocyanate and 4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy were obtained. Various experimental parameters, including the nitroxide‐to‐initiator molar ratio, were examined, and it was determined that the polymerization was most controlled under conditions similar to those of conventional 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐mediated stable free‐radical polymerization. Moreover, the dinitroxide mediator proved to be a viable route for the facile two‐step synthesis of triblock copolymers of styrene and t‐butyl styrene. However, the dinitroxide mediation process resulted in a higher than expected level of nitroxide decomposition, which resulted in polymers possessing a terminal alkoxyamine and an adjacent hydroxylamine rather than a preferred internal bisalkoxyamine. This decomposition resulted in the formation of diblock copolymer species during the triblock copolymer synthesis. Gel permeation chromatography was used to monitor the chain‐end decomposition kinetics, and the determined observed rate constant (5.89 × 10^?5 s^?1) for decomposition agreed well with previous studies for other dinitroxide mediating agents. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1547–1556, 2004     

Relevance of a prereaction for the in situ NMP of styrene using the C‐Phenyl‐N‐tert‐butylnitrone/2,2′‐azobis(isobutyronitrile) pair

In this article, we compare two routes for carrying out in situ nitroxide‐mediated polymerization of styrene using the C‐phenyl‐N‐tert‐butylnitrone (PBN)/2,2′‐azobis(isobutyronitrile) (AIBN) pair to identify the best one for an optimal control. One route consists in adding PBN to the radical polymerization of styrene, while the other approach deals with a prereaction between the nitrone and the free radical initiator prior to the addition of the monomer and the polymerization. The combination of ESR and kinetics studies allowed demonstrating that when the polymerization of styrene is initiated by AIBN in the presence of enough PBN at 110 °C, fast decomposition of AIBN is responsible for the accumulation of dead polymer chains at the early stages of the polymerization, in combination with controlled polystyrene chains. On the other hand, PBN acts as a terminating agent at 70 °C with the formation of a polystyrene end‐capped by an alkoxyamine, which is not labile at this temperature but that can be reactivated and chain‐extended by increasing the temperature. Finally, the radical polymerization of styrene is better controlled when the nitrone/initiator pair is prereacted at 85 °C for 4 h in toluene before styrene is added and polymerized at 110 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1085–1097, 2009     

Living free radical donor-acceptor copolymerization of styrene and N-cyclohexylmaleimide and the synthesis of poly[styrene-co-(N-cyclohexylmaleimide)]/polystyrene block copolymers

Styrene/N-cyclohexylmaleimide copolymers with small polydispersities and controlled molecular weights were synthesized by a free radical copolymerization using an iniferter system consisting of benzoyl peroxide and 2,2,6,6-tetramethylpiperidine-N-oxyl. Due to the interactions of the electropositive (styrene) and electronegative (N-cyclohexylmaleimide) monomers the brutto polymerization rates are higher than for other living polymerizations initiated with the same iniferter system. The prepared copolymers were used as macroiniferters for bulk polymerization of styrene.     

水介质中可控/活性自由基聚合的研究进展

综述了均相水溶液体系和分散，悬浮，乳液及微乳液等非均匀相水溶液体系中的可控／活性自由基聚合的研究现状，对一些最常见的可控自由基聚合方法，如氮氧调控聚合，原子转移自由基聚合和可逆加成－继裂链转移聚合方法的聚合情况进行了详细的介绍，展望了水介质中可控／活性自由基聚合的发展方向及前景。     

“点击”反应在制备环状聚合物中的应用

环状聚合物具有不同于线性高分子的独特性质,是一类具有应用前景的新型聚合物材料,但复杂的结构导致其合成过程复杂繁琐.＂点击＂化学由于其高效、可靠、高选择性的特点已成为拓扑高分子合成的新方法,活性自由基聚合（ATRP、RAFT和NMP）具有聚合物结构可控等特点,二者联用为环状聚合物的合成拓宽了思路.本文就近几年＂点击＂反应、＂点击＂反应与活性自由基聚合联用以及其他方法联用在环状聚合物中的应用进行综述.＂点击＂反应与这些方法的结合将在功能性环状聚合物的设计与合成中发挥积极的作用.     

Micelle formation of polystyrene-<Emphasis Type="Italic">block</Emphasis>-poly(4-<Emphasis Type="Italic">tert</Emphasis>-butoxystyrene) in hexane

A new type of hexane-soluble polymeric surfactant based on poly(4-tert-butoxystyrene) (P ^t BSt) was prepared by the nitroxide-mediated living radical polymerization, and their self-assemblies in hexane were explored. Polystyrene-block-P ^t BSt diblock copolymers with six different P ^t BSt block lengths were obtained by the sequential living radical polymerization of styrene followed by 4-tert-butoxystyrene using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator; Mn(P ^t BSt block) = 13,500, 21,700, 26,600, 47,500, 91,300, and 108,000 at the constant length of the PSt block (Mn = 12,900). Dynamic light-scattering studies demonstrated that the copolymers self-assembled into monodispersed spherical micelles in hexane. The hydrodynamic diameter of the micelles increased with an increase in the P ^t BSt block length. The micellar size also increased as the copolymer concentration increased. However, the size decreased as a result of the increasing temperature due to a decrease in the aggregation number. The ¹H NMR analysis confirmed that the copolymers formed micelles with PSt cores.     

Steric and electronic effects in cyclic alkoxyamines--synthesis and applications as regulators for controlled/living radical polymerization

The synthesis of new six- and seven-membered cyclic alkoxyamines bearing ethyl groups at the alpha-N position of the alkoxyamines is described. The key step in the synthesis of the sterically hindered six-membered cyclic alkoxyamines is a Wadsworth-Horner-Emmons olefination with bisphosphonate 1. The seven-membered cyclic alkoxyamines were prepared from the corresponding six-membered keto alkoxyamines by ring-enlargement with trimethylsilyl(TMS)-diazomethane. The use of the new alkoxyamines as regulators/initiators for radical polymerization is discussed. Efficient controlled and living polymerization of styrene and n-butyl acrylate was obtained with the six-membered tetraethyl alkoxyamine 13. Controlled polymerizations can be conducted even at 90 degrees C. In addition, alkoxyamine 13 can be used for the preparation of AB diblock and ABA triblock copolymers with narrow polydispersities. The influence of the replacement of methyl groups in the alpha-position of the N atom in cyclic alkoxyamines by larger ethyl groups on the styrene polymerization (reaction time, PDI, kinetics of the C-O bond homolysis) is discussed. In addition, thermal decomposition of the new alkoxyamines was studied. Furthermore, the synthesis of N,N-bissilylated alkoxyamines is described. The silylated alkoxyamines are not suitable as regulators/initiators for the controlled/living radical polymerization. The C-O bonds in silylated alkoxyamines are stronger than the C-O bonds in analogous N,N-dialkylated alkoxyamines. The experimental results are verified by calculations with Gaussian 98 (A. 9).     

A New Sterically Highly Hindered 7‐Membered Cyclic Nitroxide for the Controlled Living Radical Polymerization

The synthesis of a new sterically highly hindered 7‐membered alkoxyamine, 2,2,7,7‐tetraethyl‐1‐(1‐phenylethoxy)‐1,4‐diazepan‐5‐one ( 4 ), starting from known 2,2,6,6‐tetraethyl‐1‐(1‐phenylethoxy)piperidin‐4‐one ( 3 ) via a Beckmann‐type rearrangement is presented. It is shown that ring‐enlargement by insertion of an NH moiety in going from 3 to 4 leads to a more efficient regulator for nitroxide‐mediated controlled living radical styrene (= ethenylbenzene) and butyl acrylate (= butyl prop‐2‐enoate) polymerization. In addition to the polymerization experiments, kinetic data on the reversible C? O bond homolysis of alkoxyamines 3 and 4 are presented.     

Relationship between one-electron transition-metal reactivity and radical polymerization processes

Controlled radical polymerization has come along in leaps and bounds following the development of efficient transition-metal catalysts for atom-transfer radical polymerization. Another type of controlled radical polymerization process, namely organometallic radical polymerization, uses the reversible formation of metal-carbon bonds. Metals are also implicated in catalytic chain transfer, a process that involves the abstraction of hydrogen atoms. This Minireview discusses the importance of one-electron transition-metal reactivity in metal-mediated controlled radical polymerization processes.