Core–shell nanogels by RAFT crosslinking polymerization: Synthesis and characterization

A synthetic methodology is described for the preparation of core–shell nanogels by reversible addition‐fragmentation chain transfer. Well‐defined macro chain transfer agents (macro‐CTA's) were prepared in a first step using monomers that yield sensitive polymers. In the second step, a crosslinker alone or with the addition of a functionalized comonomer were used to form a crosslinked core. The ratio of crosslinker to macro‐CTA is crucial to yield nanogels. Furthermore, the polymerization time has an impact in the architecture of the nanomaterial obtained: it evolves from a core‐crosslinked star to a core–shell nanogel. Controlling the molecular weight of the macro‐CTA and the type of comonomer in the core forming step, core–shell nanogels with hydrodynamic diameters from 22 to 168 nm and a core that represents from 35 to 77% of the size, were prepared containing functional groups in the core which could be used as catalytic scaffolds. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.     

Amphiphilic micro- and nanogels: Combining properties from internal hydrogel networks,solid particles,and micellar aggregates

Polymeric micro- and nanogels are defined by their water-swollen hydrophilic networks that can often impart outstanding biocompatibility and high-colloidal stability. Unfortunately, this highly hydrophilic nature limits their potential in areas where hydrophobic or amphiphilic interactions are required, for example, the delivery of hydrophobic cargoes or tailored interactions with amphipathic (bio-)surfaces. To overcome this limitation, amphiphilic micro−/nanogels are emerging as new colloidal materials that combine properties from hydrogel networks with hydrophobic segments, known from solid hydrophobic polymer particles or micellar cores. The ability to accurately adjust the balance of hydrophobic and hydrophilic components in such amphiphilic colloidal systems enables new tailored properties. This opens up new applications ranging from the controlled and sustained delivery of hydrophobic drugs, over carriers for catalytic moieties, to their assembly at hydrophilic/hydrophobic interfaces, for example, as advanced stabilizers in Pickering emulsions. While promising, the synthetic realization of such amphiphilic materials remains challenging since hydrophobic and hydrophilic moieties need to be combined in a single colloidal system. As a result, adjusting the micro−/nanogel amphiphilicity often changes the colloidal features too. To overcome these limitations, various strategies have been reported. The aim of this review is to give a brief overview of important synthetic tools, considering both advantages and disadvantages, thus critically evaluating their potential in different research fields.     

Synthesis of biocompatible and thermally sensitive poly(N‐vinylcaprolactam) nanogels via inverse miniemulsion polymerization: Effect of the surfactant concentration

The goal of this study was to develop a new route to prepare thermally responsive polymer nanogels. Poly(N‐vinylcaprolactam) nanogels were prepared via inverse miniemulsion polymerization (W/O) at 70 °C using n‐hexadecane as a nonpolar continuous phase, potassium persulfate as an initiator, and N,N′‐methylenebisacrylamide as a crosslinker. Sorbitan monooleate (Span 80) was used as surfactant and its influence on the polymerization kinetics and on the colloidal characteristics of the nanogels were principally investigated. It was observed that the addition of a strong “lipophobe” is required to stabilize the resulting miniemulsion. The nanogels were characterized in terms of morphology, size, zeta potential, and thermoproperties using transmission electron microscopy and dynamic light scattering. It was observed that all the nanogels obtained collapsed when the lower critical solution temperature (LCST) was raised. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3932–3941, 2010     

Recent advances in conjugated polymer energy storage

This review covers recent advances in conjugated polymers and their application in energy storage. Conjugated polymers are promising cost-effective, lightweight, and flexible electrode materials. The operating principles of conjugated polymers are presented within the framework of their potential for energy storage. Special focus is given to polyaniline electrodes. Recent advances are reviewed including new methods of synthesis, nanostructuring, and assembly. Also, covered are applications that take full advantage of the mechanical properties of conjugated polymers and future applications of these novel materials. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Inverse miniemulsion ATRP: a new method for synthesis and functionalization of well-defined water-soluble/cross-linked polymeric particles

A new methodology for the synthesis and functionalization of nanometer-sized colloidal particles consisting of well-defined, water-soluble, functional polymers with narrow molecular weight distribution (M(w)/M(n) < 1.3) was developed, utilizing atom transfer radical polymerization (ATRP) of water-soluble monomers in an inverse miniemulsion. The optional introduction of a disulfide-functionalized cross-linker allowed for the synthesis of cross-linked (bio)degradable nanogels. Dynamic light scattering (DLS) and atomic force microscopy (AFM) measurements indicated that these particles possessed excellent colloidal stability. ATRP in inverse miniemulsion led to materials with several desirable features. The colloidal particles preserved a high degree of halogen chain-end functionality, which enabled further functionalization. Cross-linked nanogels with a uniformly cross-linked network were prepared. They were degraded to individual polymeric chains with relatively narrow molecular weight distribution (M(w)/M(n) < 1.5) in a reducing environment. Higher colloidal stability, higher swelling ratios, and better controlled degradability indicated that the nanogels prepared by ATRP were superior to their corresponding counterparts prepared by conventional free radical polymerization (RP) in inverse miniemulsion.     

Biodegradable nanogels prepared by self-assembly of poly(L-lactide)-grafted dextran: entrapment and release of proteins

We showed previously that poly(L-lactide)-grafted dextran could form biodegradable nanogels in water. In this paper, various properties of Dex-g-PLLA nanogels were compared with Dex-Chol (dextran-cholesterol conjugate) nanogels to investigate the effects of hydrophobic units. Dex-g-PLLA nanogels exhibited significantly lower CAC and higher colloidal stability, indicating a strong tendency to form nanogels. We prepared lysozyme-loaded Dex-g-PLLA nanogels, and they exhibited a sustained release of lysozyme for 1 week without denaturation in PBS at 37 degrees C. The Dex-g-PLLA nanogels therefore have great potential as a delivery vehicle for therapeutic protein.     

Cyclic polymers: Synthetic strategies and physical properties

Syntheses of cyclic polymers including cyclic homopolymers, cyclic block copolymers, sun‐shaped polymers, and tadpole polymers are discussed on the basis of a differentiation between synthetic methods and synthetic strategies (e.g., polycondensation, ring–ring equilibration, or ring‐expansion polymerization). Furthermore, all synthetic methods are classified as kinetically or thermodynamically controlled reactions. Characteristic properties of cyclic polymers such as smaller hydrodynamic volume, lower melt viscosities, and higher thermostabilities are compared to the properties of their linear counterparts. Furthermore, the nanophase separation of cyclic diblock copolymers is discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 251–284, 2010     

Recent progress on the synthesis of cyclic polymers via ring-expansion strategies

Cyclic polymers are the simplest topological isomers of linear macromolecules, but exhibit properties that differ from linear chains in ways that remain imperfectly understood. The difficulty of synthesizing appropriately pure and high molecular weight cyclic samples has hindered experimental studies. Ring-closure methods, while versatile, are inherently limited in the range of molecular weights that can be achieved. Ring-expansion methods are a much more promising strategy toward obtaining high molecular weight cyclic polymers. The current review focuses on recent developments in ring-expansion polymerization strategies toward the synthesis of high molecular weight cyclic polymers. Significant progress in the last decade has made the synthesis of cyclic polymers possible by a variety of methods, such as ruthenium- and tungsten-catalyzed ring-expansion metathesis polymerization, organocatalytic and Lewis acid-catalyzed zwitterionic polymerization, RAFT and nitroxide-mediated radical polymerization, among many others. While the study of cyclic polymers has long been hampered by synthetic challenges, the recent resurgence of interest in this field presents an exciting opportunity for chemists. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2892–2902     

Polypeptoids: A perfect match for molecular definition and macromolecular engineering?

Precision synthesis of polymers has been a hot topic in recent years. While this is notoriously difficult to address for polymers with a C? C backbone, Merrifield has discovered a way many decades ago for polypeptides. Using a similar approach, N‐substituted polypeptides, so‐called polypeptoids have been synthesized and studied for about 20 years. In contrast, the living ring‐opening polymerization (ROP) of N‐substituted N‐carboxyanhydrides was among the first living polymerizations to be discovered. More recently, a surge in new synthetic approaches led to the efficient synthesis of cyclic or linear multiblock copolypeptoids. Thus, polypeptoids can be synthesized either by solid phase synthesis to yield complex and exactly defined oligo‐ and small polymers or by ROP of appropriately N‐substituted N‐carboxyanhydrides (NNCA) to give linear, cyclic, or star‐like polymers. Together with an excellent biocompatibility, this polymer family may have a bright future ahead as biomaterials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2731–2752     

Responsive core–shell microgels: Synthesis,characterization, and possible applications

Core–shell microgels are of increasing interest as smart carriers of catalysts, as sensors, or as building blocks for colloidal superstructures. In the context of colloidal assemblies, photonic applications are probably the most promising ones. This progress report presents and discusses the most recent results in this area focusing on the last 2–3 years, and also gives some background information. In addition, potential perspectives of this area will be outlined. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1073–1083     

Biomedical applications of biodegradable polymers

Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. To fit functional demand, materials with desired physical, chemical, biological, biomechanical, and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Biological–synthetic hybrid block copolymers: Combining the best from two worlds

Although biopolymers and synthetic polymers share many common features, each of these two classes of materials is also characterized by a distinct and very specific set of advantages and disadvantages. Combining biopolymer elements with synthetic polymers into a single macromolecular conjugate is an interesting strategy for synergetically merging the properties of the individual components and overcoming some of their limitations. This article focuses on a special class of biological–synthetic hybrids that are obtained by site‐selective conjugation of a protein or peptide and a synthetic polymer. The first part of the article gives an overview of the different liquid‐phase and solid‐phase techniques that have been developed for the synthesis of well‐defined, that is, site‐selectively conjugated, synthetic polymer–protein hybrids. In the second part, the properties and potential applications of these materials are discussed. The conjugation of biological and synthetic macromolecules allows the modulation of protein binding and recognition properties and is a powerful strategy for mediating the self‐assembly of synthetic polymers. Synthetic polymer–protein hybrids are already used as medicines and show significant promise for bioanalytical applications and bioseparations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1–17, 2005     

Understanding of nanogels swelling behavior through a deep insight into their morphology

A thorough understanding of the morphology of the environmental sensitive nanogels was indispensable to obtain a deeper insight on their stimuli‐responsive behavior. Therefore, in this work the colloidal characterization and the study of the inner morphology were related by using light scattering technique and ¹H‐nuclear magnetic resonance transverse relaxation measurements combined with the Flory–Rehner theory. Different biocompatible and dual‐stimuli‐sensitive nanogel particles based on poly(2‐diethylaminoethyl) methacrylate were synthesized using three different crosslinkers: two bifunctional and one multifunctional. All the nanogels obtained had a core–shell type heterogeneous morphology, but they presented completely different swelling behaviors due to their different crosslinking points’ distribution and polymeric chains’ microstructure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2017–2025     

Cyclic polymers: Methods and strategies

Cyclic polymers have different physical properties compared to their linear counterparts of the same molecular weight. These different properties could have potential impact in the production of new and exciting polymer products. For industry to commercialize such materials, cyclic polymers need to be made on large scales, have controlled molecular weight distributions, and have versatile chemical composition. This highlight article describes many of the synthetic methods and strategies for obtaining highly pure cyclic polymers, and presents kinetic attributes for some of the processes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Control of cationic nanogel PEGylation in heterogeneous ARGET ATRP emulsion polymerization with PEG macromonomers

Crosslinked cationic nanoscale networks with hydrophobic cores are an environmentally robust alternative to self‐assembled polymeric drug delivery carriers with respect to therapeutic encapsulation and stability to dilution. However, the ability to tune the degree of PEG incorporated into nanogels during synthesis is more challenging. In this work, biodegradable cationic nanogels were synthesized by ARGET ATRP emulsion polymerization in a single step. The density of PEG in the final nanogels ranged from zero to 40 wt % and was dependent on the feed concentration of PEG monomer, surfactant concentration, surfactant hydrophilic–lipophilic balance, and the ratio of cationic to nonionic surfactant. A comprehensive analysis of nanogel material properties as a function of PEG graft density is presented including analysis of composition, monomer conversion, thermal properties, size, surface charge, and degradation. This study provides a robust analysis for the synthesis of degradable cationic nanogels via a controlled radical polymerization with predictable degrees of PEGylation. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1536–1544     

Preparation of thermosensitive nanogels by photo-cross-linking

 A novel method to prepare thermosensitive nanogels from photocross-linkable copolymers of N-isopropylacrylamide and dimethyl maleinimido acrylamide (DMIAAm) was developed. The colloidal nanogels were formed by UV irradiation of solutions of thermosensitive polymers in water at 45 °C. The compositions of the photopolymer solutions were varied by changing the amount of DMIAAm in the photopolymer chains (2–10 mol%) or by varying the sodium dodecyl sulfate (SDS) concentration. The resultant nanogel particles were rather spherical and showed large changes in hydrodynamic diameters in the vicinity of the phase transition temperature of the corresponding linear photopolymers. The particle sizes of the nanogels and their swellability could be controlled through the UV irradiation time, the chromophore content and the SDS concentration. An increase in the chromophore content and the SDS concentration resulted in nanogels with smaller dimensions. The hydrodynamic diameters of the nanogels decreased significantly from 2 to 10 min UV irradiation time but not significantly after that. The phase transition of the photopolymer solutions and the respective nanogels could be adjusted by the chromophore content or the SDS concentration. An increase in the chromophore content leads to lower phase-transition temperatures, whilst an increase in the SDS concentration elevated them. Pulsed-field-gradient NMR proved a useful tool to investigate the network formation in the nanogels by determining changes in the diffusion coefficients. Received: 14 May 2001 Accepted: 1 June 2001     

New developments in hyperbranched polymers

In the last 12 years the field of hyperbranched polymers has been well established with a large variety of synthetic approaches and fundamental studies on structure and properties of these unique materials. However, new developments involving hyperbranched materials appeared recently, for example, different synthetic strategies, new reaction mechanisms, formation of more complex architectures, a deeper understanding of the branched structure and their kinetic development, and intensive studies on the material properties and possible applications. This demonstrates the high versatility and the possibilities that are still involved in hyperbranched polymers and render it one of the most active fields in polymer science with a very promising future. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2505–2525, 2000     

Lignin‐based polymers via graft copolymerization

Lignin is an important source of synthetic materials because of its abundance in nature, low cost, stable supply, and no competition to the human food supply. Lignin, a cross‐linked phenolic polymer, contains a large number of aromatic groups that can be used as a substitute for petroleum‐based aromatic fine chemicals. However, modification of lignin is necessary for its application in advanced materials due to its chemically inert nature and structural complexity. Polymeric modification of lignin via graft copolymerization represents an important avenue for modification because this method forms stable covalent bond linkages between lignin and synthetic functional polymers. In this review, we discuss recent synthetic strategies toward polymeric modification of lignin using graft copolymerization and the special properties and applications of the produced lignin copolymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3515–3528     

Preparation of Ag nanoparticles termini‐protected side‐chain liquid crystalline azobenzene polymers by RAFT polymerization

A new synthetic approach to prepare Ag nanoparticles protected side‐chain liquid crystalline (LC) azobenzene polymers was reported. It is based on the reduction of silver ions in presence of a LC polymer polymerized by RAFT. The formation of Ag colloidal nanoparticles was confirmed by TEM and UV analysis. At the same time, according to the results of DSC, XPS, and FTIR spectra, Ag nanoparticles were protected by the side‐chain LC azobenzene polymers through surface attachment interactions between thiol groups and Ag. The out‐plane orientation of side‐chain LC is confirmed by surface‐enhanced Raman spectra analysis and scanning near‐field optical microscope, resulting from the large electromagnetic field arising from the excitation of surface plasmon polariton of Ag nanoparticles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5380–5386, 2007