One-step multifunctionalization of random copolymers via self-assembly

A novel methodology for random copolymer functionalization based on a noncovalent, one-step, multifunctionalization strategy has been developed. Random copolymers possessing both palladated-pincer complexes and diaminopyridine moieties (hydrogen-bonding entities) have been synthesized using ring-opening metathesis polymerization. Noncovalent functionalization of the resultant copolymers is accomplished via (1) directed self-assembly, (2) multistep self-assembly, and (3) one-step orthogonal self-assembly. This system shows complete specificity of each recognition motif for its complementary unit, with no observable changes in the association constants regardless of the degree of functionalization.     

Reactive, multifunctional polymer films through thermal cross-linking of orthogonal click groups

The ability to produce robust and functional cross-linked materials from soluble and processable organic polymers is dependent upon facile chemistries for both reinforcing the structure through cross-linking and for subsequent decoration with active functional groups. Generally, covalent cross-linking of polymeric assemblies is brought about by the application of heat or light to generate highly reactive groups from stable precursors placed along the chains that undergo coupling or grafting reactions. Typically, these strategies suffer from a general lack of control of the cross-linking chemistry as well as the fleeting nature of the reactive species that precludes secondary chemistry. We have addressed both of these issues using orthogonal chemistries to effect both cross-linking and subsequent functionalization of polymer films by mild heating, which results in exacting control of the cross-link density as well as the density of the residual stable functional groups available for subsequent, stepwise functionalization. This methodology is exploited to develop a strategy for the independent and orthogonal triple-functionalization of cross-linked polymer thin-films through microcontact printing.     

Orthogonally functionalizable copolymers based on a novel reactive carbonate monomer

A novel N‐hydroxy succinimide‐based carbonate monomer that allows direct synthesis of polymers incorporating a reactive carbonate group in the side chain was synthesized. This new monomer was copolymerized with methyl methacrylate and poly(ethylene glycol) methylether methacrylate using free‐radical polymerization to obtain organo‐ and water‐soluble reactive copolymers. Copolymerization of the activated carbonate monomer with an azide‐containing monomer and N‐hydroxy succinimide‐containing activated ester monomer provided orthogonally functionalizable copolymers. The pendant reactive carbonate groups of the copolymers were functionalized with amines to obtain carbamates. Polymers capable of orthogonal functionalization could be selectively functionalized as desired using subsequent 1,3‐dipolar cycloaddition or amidation reactions. The novel monomer and the copolymers were characterized by ¹H‐NMR, ¹³C‐NMR, and infrared spectroscopy. The efficient stepwise orthogonal functionalization of the copolymers were examined via ¹H‐NMR spectroscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Towards Targeted Drug Delivery by Covalent Ligand-Modified Polymeric Nanocontainers

Here we present a novel strategy for specific cellular targeting of polymeric nanocontainers by using self-assembly of block copolymers consisting of either Polydimethoxysiloxane-b-Polymethyloxazoline-b-Polydimethoxysiloxane (PDMS-b-PMOXA-b-PDMS) or functionalized PDMS-b-PMOXA-b-PDMS. Covalent functionalization of the above copolymer was accomplished using either the fluorescent dye sulforhodamine B or a poly-guanosin ligand, the latter by using the Huisgen 1,3-dipolar cycloaddition. The success of the covalent modification of the block copolymer has been determined by studying functionalized sulforhodamine B by NMR and fluorescence correlation spectroscopy. The covalent click chemistry approach leads to efficiently functionalized polymeric nanocontainers which enables specific uptake by activated macrophages overexpressing the scavenger receptor A1.     

Recent progress in coordination chemistry,photo-physical properties,and applications of pyridine-based Cu(I) complexes

Abstract

Copper(I) [Cu(I)] complexes offer cheap and alternative materials for several real-life applications. Pyridine (Py), bipyridine (Bpy), and related analogues have strong donating ability with propensity to ease functionalization via modern synthetic protocols. A large number of Cu(I) complexes/clusters/polymers bearing functionalized Py-based ligands have emerged with rich coordination chemistry, fascinating structures, and intriguing photo-physical properties. This article sheds light on recent advances in the coordination chemistry and photophysical properties of Cu(I) complexes/clusters/polymers and their applications in the areas of optoelectronics (OE) (light emitting devices [LEDs] and dye-sensitized solar cells [DSSCs]) and sensing (aliphatic and aromatic gases).     

From NMP to RAFT and Thiol‐Ene Chemistry by In Situ Functionalization of Nitroxide Chain Ends

A straightforward, novel strategy based on the in situ functionalization of polymers prepared by nitroxide‐mediated polymerization (NMP), for the use as an extension toward block copolymers and post‐polymerization modifications, has been investigated. The nitroxide end group is exchanged for a thiocarbonylthio end group by a rapid transfer reaction with bis(thiobenzoyl) disulfide to generate in situ reversible addition–fragmentation chain transfer (RAFT) macroinitiators. Moreover, not only have these macroinitiators been used in chain extension and block copolymerization experiments by the RAFT process but also a thiol‐terminated polymer is synthesized by aminolysis of the RAFT end group and subsequently reacted with dodecyl vinyl ether by thiol‐ene chemistry.     

Modification of perfluorinated polymers by high-energy irradiation

This review surveys about the possibilities for the modification of perfluorinated polymers using high-energy irradiation: degradation, functionalization, branching, and cross-linking. The reaction mechanisms for the different reaction conditions are discussed. Electron irradiation of polytetrafluoroethylene (PTFE) with a very high dose leads to a complete degradation of the macromolecules to low-molecular products. In the presence of oxygen perfluorocarboxylic acids and in an inert atmosphere, mixtures of perfluorinated olefins and paraffins can be obtained. Virgin PTFE is disintegrated by high-energy irradiation in air with a lower dose into a micropowder modified with COOH groups. This powder can be homogeneously incorporated in other polymers. So, the special properties of PTFE can be made effective in these polymers. Micropowders functionalized with COOH groups and polyamides (PA) form by reactive extrusion PTFE-PA blockcopolymers which can be used as slide bearing materials. The copolymers poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) and poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) irradiated in air show a significantly higher degree of COOH functionalization compared with PTFE. Irradiation of molten PTFE in an inert atmosphere leads to formation of different kinds of double bonds, CF₃ side groups, long-chain branches as well as cross-links. Irradiation of PFA in vacuum results in the generation of COF and COOH groups; in molten state also branches and cross-links are formed.The focus of the present paper is on the work that has been carried out at the Institute of Polymer Research Dresden.     

Novel polyaminoacidic copolymers as nonviral gene vectors

 Human gene therapy is one of the most promising methods developed in recent years, providing great potential for the treatment of a variety of diseases. Complexes formed between DNA and cationic polymers are attracting increasing attention as novel synthetic vectors for the delivery of genes. We have synthesized polycations with quaternary ammonium groups in their side chains for self-assembly with calf thymus DNA. This paper describes the functionalization of α,β-polyasparthydrazide (PAHy), a synthetic macromolecule having many potential applications in the field of biomedical sciences, with glycidyltrimethylammonuim chloride (GTA) in order to introduce positive charges into their chains. Derivatized PAHy with various GTA contents have been obtained and characterized. Highly functionalized copolymers have been used for condensing DNA, yielding discrete complexes. The complex formation has been confirmed by gel electrophoresis and the surface charge of interpolyelectrolyte complexes has been assessed by the zeta potential. Received: 22 June 1999/Accepted in revised form: 17 August 1999     

An overview of synthetic modification of nitrile group in polymers and applications

The physicochemical properties of polymers are mainly dependent on the nature of polymer backbone and/or pendant groups linked to the main chain. Therefore, synthetic modification of these functional groups via post functionalization is an important approach for obtaining novel polymeric systems with improved properties and targeted applications. In this context, the synthetic modifications of nitrile group in polymers into various useful functionalities have received considerable attention and several interesting applications of the resulting polymers have been identified. The majority of the studies are based on Polyacrylonitrile (PAN), and some isolated examples of nitrile functionalization in copolymers such as Poly (Styrene-co-Acrylonitrile) (SAN), Poly (Acrylonitrile-co-Butadiene-co-Styrene (ABS) and Nitrile Rubber (NBR) are available. These synthetic modifications are mainly accomplished by the reactions such as Nucleophilic addition, cycloaddition, reduction, and hydrolysis using various reagents. These studies describing the post-polymerization modifications of nitrile group in polymers reported during the last three decades are covered in this review.     

Approach to formation of multifunctional polyester particles in controlled nanoscopic dimensions

We present the synthesis of discrete functionalized polyester nanoparticles in selected nanoscale size dimensions via a controlled intermolecular chain cross-linking process. The novel technique involves the controlled coupling of epoxide functionalized polyesters with 2,2'-(ethylenedioxy)bis(ethylamine) to give well-defined nanoparticles with narrow size distribution and selected nanoscopic size dimensions. Diverse functionalized polyesters, synthesized with pendant functionalities via ring-opening copolymerization of delta-valerolactone with alpha-allyl-delta-valerolactone, alpha-propargyl-delta-valerolactone and 2-oxepane-1,5-dione, were prepared as linear precursors which facilitated 3-D nanoparticles with functionalities such as amines, keto groups, and alkynes for post modification reactions. We found that the nanoparticle formation and the control over the nanoscopic dimension is primarily influenced by the degree of the epoxide entity implemented in the precursor polymers and the amount of 2,2'-(ethylenedioxy)bis(ethylamine) as cross-linking reagent. The other functionalities in the linear polyester do not participate in the nanoparticle formation and particles with defined functionalities can be prepared from batches of identical linear polymers containing various functionalities or by mixing different polyester materials to achieve controlled amounts of specific functional groups. The utilization of integrated functionalities was demonstrated in one post-modification reaction with N-Boc-ethylenediamine via reductive amination. This work describes the development of a novel methodology to prepare functionalized well-defined 3-D nanoparticle polyester materials in targeted nanoscopic ranges with amorphous morphologies or tailored crystallinities that offer a multitude of utilizations as a result of their unique properties and control in preparation.     

Functionalized poly(oxanorbornene)‐block‐copolymers: Preparation via ROMP/click‐methodology

Block copolymers on basis of poly(oxanorbornenes) bearing functional moieties in their side‐chains are prepared via a combination of ROMP‐methods and 1,3‐dipolar‐“click”‐reactions. Starting from N‐substituted‐ω‐bromoalkyl‐oxanorbornenes and alkyl‐/perfluoroalkyl‐oxanorbornenes, block copolymers with molecular weights up to 25,000 g mol^?1 were generated. Subsequent nucleophilic exchange‐reactions yielded the block‐copolymers functionalized with ω‐azidoalkyl‐moieties in one block. The 1,3‐azide/alkine‐“click” reactions with a variety of terminal alkynes in the presence of a catalyst system consisting of tetrakis(acetonitrile)hexafluorophosphate copper(I) and tris(1‐benzyl‐5‐methyl‐1H‐ [1,2,3]triazol‐4‐ylmethyl)‐amine furnished the substituted block copolymers in high yields, as proven by NMR‐spectroscopy. The resulting polymers were investigated via temperature‐dependent SAXS‐methods, revealing their microphase separated structure as well as their temperature‐dependent behavior. The presented method offers the generation of a large set of different block‐copolymers from only a small set of starting materials because of the high versatility of the “click” reaction, thus enabling a simple and complete functionalization after the initial polymerization reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 485–499, 2007     

Ketene functionalized polyethylene: control of cross-link density and material properties

The functionalization and cross-linking of polyethylene is synthetically challenging, commonly relying on highly optimized radical based postpolymerization strategies. To address these difficulties, a norbornene monomer containing Meldrum's acid is shown to be effectively copolymerized with polyethylene using a nickel α-iminocarbaxamidato complex, providing high-melting, semicrystalline polymers with a tunable incorporation of the functional comonomer. Upon heating the copolymer to common polyethylene processing temperatures, the thermolysis of Meldrum's acid to ketene provides the desired reactive group. This simple and versatile methodology does not require small molecule radical sources or catalysts, and the dimerization of the in situ generated ketenes is shown to provide tunable cross-linking densities in polyethylene. Subsequent rheological and tensile experiments illustrate the ability to tune cross-linked polyethylene properties by comonomer incorporation and elucidate valuable structure/property relationships in these materials. This study illustrates the power of well-defined and synthetically accessible functional groups in polyolefin synthesis and functionalization.     

Stimuli-responsive polymeric materials functioning via host–guest interactions

Molecular recognition is essential for realizing functional supramolecular materials. Non-covalent host–guest interactions are an effective tool to introduce switching and functional properties into materials. This review focuses on the achievement of selective molecular adhesion, self-healing, toughness, and actuation properties. These functions have been achieved by reversible bond formation with cyclodextrins (CDs). Self-healing materials with host–guest interactions involving CDs have been used to achieve redox-responsive healing properties and healing efficiency. Furthermore, the materials, which undergo self-healing by chemical and physical mechanisms, exhibit rapid and efficient self-healing properties under semi-dry conditions. To prepare a supramolecular actuator using host–guest complexes, two approaches have been introduced. The first is the functionalization of a supramolecular gel actuator by changing the cross-linking density, and the second is the functionalization of a topological gel actuator by changing distances between the cross-linking points. Both actuators exhibit contractive bending behavior. This review summarizes advancements within the past 10 years in supramolecular materials that function via the chemical mechanism of host–guest interactions and the physical mechanism of the sliding motion of ring molecules.     

Functioning via host–guest interactions

Molecular recognition is essential for realizing functional supramolecular materials. Non-covalent host–guest interactions are an effective tool to introduce switching and functional properties into materials. This review focuses on the achievement of selective molecular adhesion, self-healing, toughness, and actuation properties. These functions have been achieved by reversible bond formation with cyclodextrins (CDs). Self-healing materials with host–guest interactions involving CDs have been used to achieve redox-responsive healing properties and healing efficiency. Furthermore, the materials, which undergo self-healing by chemical and physical mechanisms, exhibit rapid and efficient self-healing properties under semi-dry conditions. To prepare a supramolecular actuator using host–guest complexes, two approaches have been introduced. The first is the functionalization of a supramolecular gel actuator by changing the cross-linking density, and the second is the functionalization of a topological gel actuator by changing distances between the cross-linking points. Both actuators exhibit contractive bending behavior. This review summarizes advancements within the past ten years in supramolecular materials that function via the chemical mechanism of host–guest interactions and the physical mechanism of the sliding motion of ring molecules.     

Hetero and homo α,ω-chain-end functionalized polyphosphazenes

The control of chain-ends is fundamental in modern macromolecular chemistry for directed one-to-one bioconjugation and the synthesis of advanced architectures such as block copolymers or bottlebrush polymers and the preparation of advanced soft materials. Polyphosphazenes are of growing importance as elastomers, biodegradable materials and in biomedical drug delivery due to their synthetic versatility. While controlled polymerization methods have been known for some time, controlling both chain-ends with high fidelity has proven difficult. We demonstrate a robust synthetic route to hetero and homo α,ω-chain-end functionalized polyphosphazenes via end-capping with easily accessible, functionalized triphenylphosphine-based phosphoranimines. A versatile thiol-ene “click”-reaction approach then allows for subsequent conversion of the end-capped polymers with various functional groups. Finally, we demonstrate the utility of this system to prepare gels based on homo α,ω-chain-end functionalized polyphosphazenes. This development will enhance their progress in various applications, particularly in soft materials and as degradable polymers.     

Facile syntheses of surface-functionalized micelles and shell cross-linked nanoparticles

Block copolymer micelles and shell cross-linked nanoparticles (SCKs) presenting Click-reactive functional groups on their surfaces were prepared using two separate synthetic strategies, each employing functionalized initiators for the controlled radical polymerization of acrylate and styrenic monomers to afford amphiphilic block copolymers bearing an alkynyl or azido group at the α-terminus. The first route for the synthesis of the azide-functionalized nanostructures was achieved via sequential nitroxide-mediated radical polymerization (NMP) of tert-butyl acrylate and styrene, originating from a benzylic chloride-functionalized initiator, followed by deprotection of the acrylic acids, supramolecular assembly of the block copolymer in water and conversion of the benzylic chloride to a benzylic azide. In contrast, the second strategy utilized an alkynyl-functionalized reversible addition fragmentation transfer (RAFT) agent directly for the RAFT-based sequential polymerization of tetrahydropyran acrylate and styrene, followed by selective cleavage of the tetrahydropyran esters to give the α-alkynyl-functionalized block copolymers. These Click-functionalized polymers, with the functionality located at the hydrophilic polymer termini, were then self-assembled using a mixed-micelle methodology to afford surface-functionalized “Clickable” micelles in aqueous solutions. The optimum degree of incorporation of the Click-functionalized polymers was investigated and determined to be ca. 25%, which allowed for the synthesis of well-defined surface-functionalized nanoparticles after cross-linking selectively throughout the shell layer using established amidation chemistry. Functionalization of the chain ends was shown to be an efficient process under standard Click conditions and the resulting functional groups revealed a more “solution-like” environment when compared to the functional group randomly inserted into the hydrophilic shell layer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5203–5217, 2006     

Synthesis and characterization of an isocyanate functionalized polyhedral oligosilsesquioxane and the subsequent formation of an organic-inorganic hybrid polyurethane

Organic-inorganic hybrids are an important class of new materials that offer improved thermal and mechanical properties over normal polymers. They may be produced by either the sol-gel route or through the use of inorganic compounds possessing reactive functional groups. Polyhedral oligosilsesquioxanes (POSS) are completely defined molecules of nanoscale dimensions that may be functionalized with reactive groups suitable for the synthesis of new organic-inorganic hybrids. Here we report the synthesis and characterization of a novel POSS possessing eight isocyanate groups via the hydrosilylation of octakis(hydridodimethylsiloxy)octasilsesquioxane (Q8M8H) and m-isopropenyl-alpha,alpha'-dimethylbenzyl isocyanate (m-TMI). The suitability of this new macromer to the synthesis of a organic-hybrids has been explored by forming a new type of highly cross-linked polyurethane elastomer via reaction of the macromer with poly(ethylene glycol) using dibutyltin dilaurate catalyst.     

Supramolecular polymers as dynamic multicomponent cellular uptake carriers

Supramolecular synthesis represents a flexible approach to the generation of dynamic multicomponent materials with tunable properties. Here, cellular uptake systems based on dynamic supramolecular copolymers have been developed using a combination of differently functionalized discotic molecules. Discotics featuring peripheral amine functionalities that endow the supramolecular polymer with cellular uptake capabilities were readily synthesized. This enabled the uptake of otherwise cell-impermeable discotics via cotransport as a function of supramolecular coassembly. Dynamic multicomponent and multifunctional supramolecular polymers represent a novel and unique platform for modular cellular uptake systems.     

A facile route to ureidopyrimidinone‐functionalized polymers via RAFT

Three new ureidopyrimidinone(UPy)‐functionalized chain‐transfer agents (CTAs) have been synthesized for use in reversible addition‐fragmentation chain transfer (RAFT) polymerization. These UPy‐CTAs are able to polymerize a wide variety of vinyl monomers to yield UPy‐functionalized polymers, including homopolymers, block copolymers, and amphiphilic block copolymers. These polymers have been characterized via ¹H and ¹³C NMR spectroscopy, gel permeation chromatography (GPC), UV/visible spectroscopy and differential scanning calorimetry (DSC) to demonstrate end‐group fidelity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Non‐Covalent Functionalization of Carbon Nanotubes with Surfactants and Polymers

Carbon nanotubes (CNTs) possessing unique structure and properties are attractive building blocks for novel materials and devices of important practical interest. However, the insolubility or poor dispersibility of pristine CNTs in common solvents poses a serious obstacle to their further development. To effectively utilize CNTs as building blocks for nanotechnology, CNTs have been covalently and noncovalently functionalized in a number of ways to render them soluble in aqueous or organic solutions. Here, we review recent progress and advances that have been made on dispersion of carbon nanotubes in aqueous and organic media by non‐covalent functionalization with surfactants and polymers.