End-functionalized polymers by controlled/living radical polymerizations: synthesis and applications

This review focuses on end-functionalized polymers synthesized by controlled/living radical polymerizations and the applications in fields including bioconjugate formation, surface modification, topology construction, and self-assembly.

Molecular Weight Distribution of Two Types of Living Chains Formed during Nitroxide-Mediated Polymerization of Styrene

Different types of polymer chains generated during the nitroxide-mediated polymerization of styrene are separated for the first time, and their molecular weight distribution (MWD) is investigated. Living and dead chains are monitored during the reaction; specifically, two types of living chains derived from the initiation of the alkoxyamine (RT) and the self-initiation of styrene and dead chains present in the as-prepared polystyrene (PS). To distinguish between each polymer species, different numbers of hydroxyl groups are introduced onto the T and R groups of the alkoxyamine (one and two groups, respectively). Each living and dead chains is resolved according to the distinct number of hydroxyl groups on its chain-end using high-performance liquid chromatography. Molecular structures of the fractionated PS are characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and ¹ H nuclear magnetic resonance spectroscopy, and the results of which show two distinct initiation paths: one originating from RT and the other from the self-initiation of styrene. Molecular weight and MWD are measured using size-exclusion chromatography and reveal a narrow MWD for the living chains derived from RT. Contrastingly, a broad and skewed MWD is observed for the other living chains derived from the self-initiation of styrene and the dead chains.

Metal Free Reversible-Deactivation Radical Polymerizations: Advances, Challenges, and Opportunities

A considerable amount of the worldwide industrial production of synthetic polymers is currently based on radical polymerization methods. The steadily increasing demand on high performance plastics and tailored polymers which serve specialized applications is driven by the development of new techniques to enable control of polymerization reactions on a molecular level. Contrary to conventional radical polymerization, reversible-deactivation radical polymerization (RDRP) techniques provide the possibility to prepare polymers with well-defined structures and functionalities. The review provides a comprehensive summary over the development of the three most important RDRP methods, which are nitroxide mediated radical polymerization, atom transfer radical polymerization and reversible addition fragmentation chain transfer polymerization. The focus thereby is set on the newest developments in transition metal free systems, which allow using these techniques for biological or biomedical applications. After each section selected examples from materials synthesis and application to biomedical materials are summarized.

C-ON bond homolysis in alkoxyamines. Part 12: the effect of the para-substituent in the 1-phenylethyl fragment

The application of alkoxyamines as initiators/controllers in nitroxide mediated polymerization and as agents for theranostics requires the development of switchable (from stable one to labile one) alkoxyamines. One way to achieve this is to tune the polarity of various groups carried by either the alkyl fragment or the nitroxyl fragment. Thus, the effect of protonation/deprotonation of the para-functionalized aryl moiety carried by the alkyl fragment in diethyl(2,2-dimethyl-1-((1,1-dimethylethyl)(1-para-subsitutedphenylethoxy)amino)propyl)phosphonate is investigated. An increase in kd is observed with increasing localized electrical effect, i.e., in the presence of electron withdrawing groups at the para position of the phenyl ring. A striking effect of the intimate ion pair on kd is also observed.

Nitroxides: applications in synthesis and in polymer chemistry

This Review describes the application of nitroxides to synthesis and polymer chemistry. The synthesis and physical properties of nitroxides are discussed first. The largest section focuses on their application as stoichiometric and catalytic oxidants in organic synthesis. The oxidation of alcohols and carbanions, as well as oxidative C-C bond-forming reactions are presented along with other typical oxidative transformations. A section is also dedicated to the extensive use of nitroxides as trapping reagents for C-centered radicals in radical chemistry. Alkoxyamines derived from nitroxides are shown to be highly useful precursors of C-centered radicals in synthesis and also in polymer chemistry. The last section discusses the basics of nitroxide-mediated radical polymerization (NMP) and also highlights new developments in the synthesis of complex polymer architectures.

Rapid Synthesis of Block and Cyclic Copolymers via Click Chemistry in the Presence of Copper Nanoparticles

A new method for the rapid and efficient coupling of homopolymers to yield di- and triblock copolymers as well as cyclic polymers using the 3 + 2 π Huisgen copper catalyzed cyclo-addition reaction has been developed. This facile method utilizes commercially available Cu nanoparticles that are tolerant to O(2), easily removable and recyclable.