Synthesis of Polymers Containing Potassium Acyltrifluoroborates (KATs) and Post‐polymerization Ligation and Conjugation

We report the synthesis of monomers for atom‐transfer radical polymerization (ATRP) and a reversible addition‐fragmentation chain transfer (RAFT) agent bearing trifluoroborate iminiums (TIMs), which are quantitatively converted into potassium acyltrifluoroborates (KATs) after polymerization. The resulting KAT‐containing polymers are suitable for rapid amide‐forming ligations for both post‐polymerization modification and polymer conjugation. The polymer conjugation occurs rapidly, even under dilute (micromolar) aqueous conditions at ambient temperatures, thereby enabling the synthesis of a variety of linear and star‐shaped block copolymers. In addition, we applied post‐polymerization modification to the covalent linking of a photocaged cyclic antibiotic (gramicidin S) to the side chains of the KAT‐containing copolymer. Cellular assays revealed that the polymer–antibiotic conjugate is biocompatible and provides efficient light‐controlled release of the antibiotic on demand.     

多力响应基团聚合物合成的研究进展

多力响应基团聚合物(MMPs)的设计与合成为高灵敏地观察和定量力化学转变及高效利用机械能提供了新机遇, 推动了聚合物力化学的发展. 本文主要介绍了后聚合改性、 逐步聚合、 开环易位聚合和活性/可控自由基聚合等4种MMPs的合成方法, 分别对这些方法的特点、 优势和适用体系进行了论述, 期望为新型机械力响应性聚合物的制备和应用提供新思路.     

Organoborane-mediated synthesis of functional polymers: A review

This article reviews recent advances in the synthesis of polar functional polymers via the mediation of organoborane monomers and polymers. Both direct polymerization and post-polymerization functionalization processes are described. Organoborane-assisted Ziegler–Natta, metathesis, and hydroboration (haloboration) polymerizations are presented. Moreover, the special problems and opportunities of polymer modification of olefin containing homo and copolymers by organoboranes are discussed.     

Amphiphilic block copolymers by a combination of anionic polymerization and selective post-polymerization functionalization

Anionic polymerization is the oldest known living/controlled polymerization methodology that leads to well defined macromolecules. It has been also used, with considerable success, for the synthesis of amphiphilic block copolymers (AmBC), a class of functional copolymers having interesting self-assembling properties and high potential for applications in various technological fields. The use of mild and effective post-polymerization functionalization/chemical modification reactions on block copolymers has substantially increased the synthetic capabilities of anionic polymerization methodologies, toward the creation of a variety of AmBC. In this feature article we review work done on these directions in the last ten years. Some perspectives and future work on this particular field of polymer science are also discussed.     

Recent advances in the preparation of glycopolymer bioconjugates

The significant progress made in understanding the role of carbohydrates and carbohydrates based therapeutics at molecular level has highlighted the importance of carbohydrate bioconjugates in the field of biology, chemistry and therapeutics. The glycosylation of biomolecules is a nature-inspired approach, to impart structural and functional properties to the biomolecules. The availability of facile techniques to synthesize well-defined glycopolymers of varying molecular weights, compositions and shape and their facile conjugation with biomolecules of interest have helped researchers in understanding many aspects of their biological functions at the molecular level. This review focuses on the development of glycopolymer-bioconjugates and provides a comprehensive overview of the present bioconjugation tools for their synthesis. The glycosylation of biomolecules is achieved by either pre or post-polymerization modification approaches. The review highlights the potential of living radical polymerization for the facile synthesis of glycopolymer bioconjugates using both pre and post-polymerization bioconjugation approaches, and without disrupting the native structure and functions of the biological molecules. Non-covalent carbohydrate–carbohydrate and carbohydrate–protein interactions play a significant role in many biological and pathological events. The non-covalent interactions of synthetic glycopolymers with biomolecules are also discussed in this review.     

Orthogonal synthesis and modification of polymer materials

In this review, we detail the progress throughout the years toward developing truly orthogonal polymerization mechanisms and modification procedures en route to complex macromolecular structures built from synthetic polymer materials. The orthogonal modifications of polymer side-chains and end-groups via sequential click reactions is described providing post-polymerization routes to functional materials and unique polymer topologies. Further, historical and modern orthogonal polymerization methodologies are thoroughly reviewed showing the evolution of the field through the decades long study of selective polymerization mechanisms that provide unique copolymer structures that are typically difficult to achieve. These include the combinations of reversible deactivation radical polymerization mechanisms with a variety of polymerization mechanisms including ring opening polymerizations, ring opening metathesis polymerizations, and cationic polymerizations, to name a few.     

Poly(Lactic Acid)-Based Graft Copolymers: Syntheses Strategies and Improvement of Properties for Biomedical and Environmentally Friendly Applications: A Review

As a potential replacement for petroleum-based plastics, biodegradable bio-based polymers such as poly(lactic acid) (PLA) have received much attention in recent years. PLA is a biodegradable polymer with major applications in packaging and medicine. Unfortunately, PLA is less flexible and has less impact resistance than petroleum-based plastics. To improve the mechanical properties of PLA, PLA-based blends are very often used, but the outcome does not meet expectations because of the non-compatibility of the polymer blends. From a chemical point of view, the use of graft copolymers as a compatibilizer with a PLA backbone bearing side chains is an interesting option for improving the compatibility of these blends, which remains challenging. This review article reports on the various graft copolymers based on a PLA backbone and their syntheses following two chemical strategies: the synthesis and polymerization of modified lactide or direct chemical post-polymerization modification of PLA. The main applications of these PLA graft copolymers in the environmental and biomedical fields are presented.     

Non-activated Esters as Reactive Handles in Direct Post-Polymerization Modification

Non-activated esters are prominently featured functional groups in polymer science, as ester functional monomers display great structural diversity and excellent compatibility with a wide range of polymerization mechanisms. Yet, their direct use as a reactive handle in post-polymerization modification has been typically avoided due to their low reactivity, which impairs the quantitative conversion typically desired in post-polymerization modification reactions. While activated ester approaches are a well-established alternative, the modification of non-activated esters remains a synthetic and economically valuable opportunity. In this review, we discuss past and recent efforts in the utilization of non-activated ester groups as a reactive handle to facilitate transesterification and aminolysis/amidation reactions, and the potential of the developed methodologies in the context of macromolecular engineering.     

Post-synthetic ‘Click’ Synthesis of RAFT Polymers with Pendant Self-immolative Triazoles

Self-immolative linkers offer efficient mechanisms for deprotecting ‘caged’ functional groups in response to specific stimuli. Herein we describe a convenient ‘click’ chemistry method for introducing pendant self-immolative linkers to a polymer backbone through post-polymerization modification. The introduced triazole rings serve both to anchor the stimuli-cleavable trigger groups to the polymer backbone, while also forming a functional part of the self-immolation cascade. We investigate the polymerization kinetics, post-synthetic modification, and self-immolation mechanism of a model polymer system, and discuss avenues for future studies on poly-pendant self-immolative triazoles as a modular, stimuli-responsive macromolecule platform.     

Synthesis of thiol functionalized poly(meth)acrylates through enzymatic catalysis and a subsequent one pot reaction process

The synthesis and modification of thiol functionalized poly(meth)acrylates using a straightforward reaction concept that consists of an enzymatically catalyzed monomer synthesis, free radical polymerization and post-polymerization modification is presented. The well-known enzymatic transacylation of methyl acrylate and methyl methacrylate that runs under mild and environmentally friendly conditions was used to synthesize thiol protected acrylic and methacrylic monomers. Upon free radical polymerization and subsequent removal of protection groups, polymers with pendant thiol groups are obtained, which, in turn, can react in situ with Michael acceptors to form thiol-ene reaction products. The exceptional advantage of the proposed method is that upon removal of the enzyme from the monomer mixture, the polymerization, deprotection of thiols and subsequent Thio-Michael-type addition reaction can be conducted in one pot without purification of the intermediate products. Furthermore, the different reactivities of acetyl and benzoyl protection groups in lipase catalyzed reactions are discussed.     

Solid-phase synthesis of polymers using the ring-opening metathesis polymerization

We report a general method for the solid-phase synthesis of polymers via the ring-opening metathesis polymerization (ROMP). The method involves polymerization in solution to form a block copolymer, immobilization of the polymer via reaction of one block with a resin-bound functional group, modification of the other block, and liberation of the polymer from the resin. We demonstrated the utility of this approach by generating a block copolymer with an N-hydroxysuccinimidyl ester-substituted block (for on-resin functionalization) and a maleimide-substituted block (for conjugation to the resin). We showed that the Diels-Alder reaction can be employed to immobilize the polymers and that amines of diverse structure can be used to modify the resin-bound polymers. The reversibility of the furan-maleimide Diels-Alder adduct was exploited to liberate the polymer from the support. Specifically, treatment of the resin with cyclopentadiene resulted in complete polymer release. The resulting polymers are functional: they were as potent in assays with the lectin concanavalin A as polymers generated by traditional solution routes. We anticipate that this method can be used for the rapid synthesis of diverse polymers via ROMP.     

Facilitating polymer conjugation via combination of RAFT polymerization and activated ester chemistry

The synthesis of block copolymers via polymer conjugation of well‐defined building blocks offers excellent control over the structures obtained, but often several coupling strategies need to be explored to find an efficient one depending on the building blocks. To facilitate the synthesis of polymers with adjustable functional end‐groups for polymer conjugation, we report on the combination of activated ester chemistry with RAFT polymerization using a chain transfer agent (CTA) with a pentafluorophenyl ester (PFP‐CTA), which allows for flexible functionalization of either the CTA prior to polymerization or the obtained polymer after polymerization. Different polymethacrylates, namely PMMA, P(t‐BuMA) and PDEGMEMA, were synthesized with an alkyne‐CTA obtained from the aminolysis of the PFP‐CTA with propargylamine, and the successful incorporation of the alkyne moiety could be shown via ¹H and ¹³C NMR spectroscopy and MALDI TOF MS. Further, the reactive α‐end‐groups of polymers synthesized using the unmodified PFP‐CTA could be converted into azide and alkyne end‐groups after polymerization, and the high functionalization efficiencies could be demonstrated via successful coupling of the resulting polymers via CuAAC. Thus, the PFP‐CTA allows for high combinatory flexibility in polymer synthesis facilitating polymer conjugation as useful method for the synthesis of block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Training the old dog new tricks: the applications of the Biginelli reaction in polymer chemistry

Recently, the Biginelli reaction, one of the most famous multicomponent reactions, has been introduced into the polymer chemistry to highly efficiently synthesize some interesting functional polymers. In this mini-review, several applications of the Biginelli reaction in polymer chemistry have been summarized, including polycondensation, post-polymerization modification, one-pot synthesis of well-defined polymer, etc. Meanwhile, the utilization of the Biginelli reaction in material science and chemical biology, and the future development of the Biginelli reaction in polymer chemistry have also been discussed.     

Self-repairing polymers: poly(dioxaborolane)s containing trigonal planar boron

The molecular weight of poly(dioxaborolane)s can be controlled during the polymerization reaction or through post-polymerization processing in such a manner that hydrolytic damage to these materials may be repaired, thereby regenerating the polymer.     

Double Modification of Polymer End Groups through Thiolactone Chemistry

A straightforward synthetic procedure for the double modification and polymer–polymer conjugation of telechelic polymers is performed through amine‐thiol‐ene conjugation. Thiolactone end‐functionalized polymers are prepared via two different methods, through controlled radical polymerization of a thiolactone‐containing initiator, or by modification of available end‐functionalized polymers. Next, these different linear polymers are treated with a variety of amine/acrylate‐combinations in a one‐pot procedure, creating a library of tailored end‐functionalized polymers. End group conversions are monitored via SEC, NMR, and MALDI‐TOF analysis, confirming the quantitative modification after each step. Finally, this strategy is applied for the synthesis of block copolymers via polymer–polymer conjugation and the successful outcome is analyzed via LCxSEC measurements.

     

Access to Hydroxy-Functionalized Polypropylene through Coordination Polymerization

Preparation of polyethylenes containing hydroxy groups has been already industrialized through radical copolymerization under harsh conditions followed by alcoholysis. By contrast, hydroxy-functionalized polypropylene has proven a rather challenging goal in polymer science. Propylene can't be polymerized through a radical mechanism, and its coordination copolymerization with polar monomers is frustrated by catalyst poisoning. Herein, we report a new strategy to reach this target. The coordination polymerization of allenes by rare-earth-metal precursors affords pure 1,2-regulated polyallenes, which are facilely transformed into poly(allyl alcohol) analogues by subsequent hydroboration/oxidation. Strikingly, the copolymerization of allenes and propylene gives unprecedented hydroxy-functionalized polypropylene after post-polymerization modification. Mechanistic elucidation by DFT simulation suggests kinetic rather than thermodynamic control.     

Post-polymerization modification of aromatic polyimides via Diels-Alder cycloaddition

We report a facile post-polymerization modification route to functionalized aromatic polyimides via Diels-Alder cycloaddition. Aromatic polyimides are important, versatile high-performance polymers; however, their structural diversity is restricted by the requirements of the step-growth polymerization. We prepared polyimides with alkynes in their main-chain as macromolecular dienophiles and quantitatively grafted tetraphenylcyclopentadienone based dienes. The resulting solution-processable, wholly aromatic polyimides show a considerable increase in surface area due to the induced conformational changes and bulky, rigid, and contorted molecular structures. The orthogonality of the reaction is exploited to insert functional groups, namely bromine and sulfonates, along the polymer backbone. In a further extension, the phenylene segments undergo cyclodehydrogenation to form nanographene segments within the polymer chains. The Diels-Alder cycloaddition onto polyimides is therefore demonstrated to be an effective, widely applicable route to tunable high-performance polymers with value-added functionality and thus considerable potential in a wide range of advanced materials.     

Influence des solvants sur les associations moleculaires et sur la cinetique de polymerisation de l'acrylonitrile. Precisions supplementaires sur l'“effet de matrice”

The polymerization of acrylonitrile is auto-accelerating in bulk and in solvents which do not dissolve the polymer. The “auto-acceleration indexes” remain almost constant in these systems. Trichloracetic acid, a very polar solvent, leads however to linear conversion curves. An earlier assumption is confirmed according to which auto-acceleration is not caused by non-stationary conditions but by an oriented association complex between the monomer and the polymer arising at the beginning of the reaction (“matrix effect”). DMF, a solvent for polyacrylonitrile, seems to produce a similar effect. The disappearance of auto-acceleration in DMF solutions was explained until now by the disappearance of the perturbation of the reaction connected with polymer precipitation (“occlusion effect”). Linear conversion curves were obtained, however, in 60% DMF solutions in which the polymer still precipitates. A detailed study of post-polymerization confirms the above interpretation. It is shown that auto-acceleration remains unaltered in the presence of solvents which swell polyacrylonitrile, such as acetonitrile or small amounts of DMF, whereas post-polymerization (caused by occluded chains) is strongly reduced. Moreover, a marked post-polymerization is observed in the presence of trichloracetic acid, demonstrating the presence of long-living chains in a system which gives rise to linear conversion curves. The association of acrylonitrile with numerous solvents is investigated; it is shown by swelling measurements that polyacrylonitrile associates with its monomer.     

Triple Click Reaction Strategy for Macromolecular Diversity

This Feature Article focuses on the rapidly emerging concept of the “triple click reactions” towards the design and synthesis of macromolecules with well‐defined topology and chemical composition, and also precise molecular weight and narrow molecular weight distribution. The term “triple click reaction” used in this feature article is based on the utilization of three chemically and mechanistically different click reactions for polymer–polymer conjugation and post‐modification of the polymers. Three sequential click reactions of which two are identical should not be considered to be triple click reactions. The triple click reaction strategy for polymer conjugation and post‐modification of polymers is classified in this article based on the resultant architectures: linear and non‐linear structures.