Photo‐initiated thiol–ene “click” hydrogels from RAFT‐synthesized poly(N‐isopropylacrylamide)

Despite the efficiency and robustness of the widely used copper‐catalyzed 1,3‐dipolar cycloaddition reaction, the use of copper as a catalyst is often not attractive, particularly for materials intended for biological systems. The use of photo‐initiated thiol‐ene as an alternative “click” reaction to synthesize “model networks” is investigated here. Poly(N‐isopropylacrylamide) precursors were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization and were designed to have trithiocarbonate moieties as end groups. This structure design provides opportunity for subsequent end‐group modifications in preparation for thiol‐ene “click.” Two reaction routes have been proposed and studied to yield thiol and ene moieties. The advantages and disadvantages of each reaction path were investigated to propose a simple but efficient route to prepare copper‐free “click” hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4626–4636     

A “self‐pinning” adhesive based on responsive surface wrinkles

Surface wrinkles are interesting since they form spontaneously into well‐defined patterns. The mechanism of formation is well‐studied and is associated with the development of a critical compressive stress that induces the elastic instability. In this work, we demonstrate surface wrinkles that dynamically change in response to a stimulus can improve interfacial adhesion with a hydrogel surface through the dynamic evolution of the wrinkle morphology. We observe that this control is related to the local pinning of the crack separation pathway facilitated by the surface wrinkles during debonding, which is dependent on the contact time with the hydrogel. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

“Synthetic Metals”: A Novel Role for Organic Polymers (Nobel Lecture)

Since the initial discovery in 1977, that polyacetylene (CH)_x, now commonly known as the prototype conducting polymer, could be p‐ or n‐doped either chemically or electrochemically to the metallic state, the development of the field of conducting polymers has continued to accelerate at an unexpectedly rapid rate and a variety of other conducting polymers and their derivatives have been discovered. Other types of doping are also possible, such as “photo‐doping” and “charge‐injection doping” in which no counter dopant ion is involved. One exciting challenge is the development of low‐cost disposable plastic/paper electronic devices. Conventional inorganic conductors, such as metals, and semiconductors, such as silicon, commonly require multiple etching and lithographic steps in fabricating them for use in electronic devices. The number of processing and etching steps involved limits the minimum price. On the other hand, conducting polymers combine many advantages of plastics, for example, flexibility and processing from solution, with the additional advantage of conductivity in the metallic or semiconducting regimes; however, the lack of simple methods to obtain inexpensive conductive polymer shapes/patterns limit many applications. Herein is described a novel, simple, and cheap method to prepare patterns of conducting polymers by a process which we term, “Line Patterning”.     

Synthesis and functionalization of dendron‐polymer conjugate based hydrogels via sequential thiol‐ene “click” reactions

Fabrication and functionalization of hydrogels from well‐defined dendron‐polymer‐dendron conjugates is accomplished using sequential radical thiol‐ene “click” reactions. The dendron‐polymer conjugates were synthesized using an azide‐alkyne “click” reaction of alkene‐containing polyester dendrons bearing an alkyne group at their focal point with linear poly(ethylene glycol)‐bisazides. Thiol‐ene “click” reaction was used for crosslinking these alkene functionalized dendron‐polymer conjugates using a tetrathiol‐based crosslinker to provide clear and transparent hydrogels. Hydrogels with residual alkene groups at crosslinking sites were obtained by tuning the alkene‐thiol stoichiometry. The residual alkene groups allow efficient postfunctionalization of these hydrogel matrices with thiol‐containing molecules via a subsequent radical thiol‐ene reaction. The photochemical nature of radical thiol‐ene reaction was exploited to fabricate micropatterned hydrogels. Tunability of functionalization of these hydrogels, by varying dendron generation and polymer chain length was demonstrated by conjugation of a thiol‐containing fluorescent dye. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 926–934     

“Click” chemistry for in situ formation of thermoresponsive P(NIPAAm‐co‐HEMA)‐based hydrogels

The strategy for in situ chemical gelation of poly(N‐isopropylacrylamide‐co‐hydroxylethyl methacrylate) [P(NIPAAm‐co‐HEMA)]‐based polymers was demonstrated. Two types of new P(NIPAAm‐co‐HEMA) derivatives with alkyne and azide pendant groups, respectively, were prepared. When the solutions of the two derivatives were mixed together, a crosslinking reaction, a type of Huisgen's 1,3‐dipolar azide‐alkyne cycloaddition, in the presence of Cu(I) catalyst occurs. The morphology, equilibrium swelling ratio, swelling kinetics, and temperature response kinetics of the in situ gelated hydrogels were studied. In comparison with the conventional PNIPAAm hydrogel, because of the spatial hindrance of polymeric chains, the resulted hydrogels had a macroporous structure as well as a fast shrinking rate. The strategy described here presents a potential alternative to the traditional synthesis techniques for the in situ formation of thermoresponsive hydrogels. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5263–5277, 2008     

An “Ingredients” Approach to Functional Self‐Synthesizing Materials: A Metal‐Ion‐Selective,Multi‐Responsive,Self‐Assembled Hydrogel

New methodology for making novel materials is highly desirable. Here, an “ingredients” approach to functional self‐assembled hydrogels was developed. By designing a building block to contain the right ingredients, a multi‐responsive, self‐assembled hydrogel was obtained through a process of template‐induced self‐synthesis in a dynamic combinatorial library. The system can be switched between gel and solution by light, redox reactions, pH, temperature, mechanical energy and sequestration or addition of Mg^II salt.     

CF3: An Electron‐Withdrawing Substituent for Aromatic Anion Acceptors? “Side‐On” versus “On‐Top” Binding of Halides

The ability of multiple CF₃‐substituted arenes to act as acceptors for anions is investigated. The results of quantum‐chemical calculations show that a high degree of trifluoromethyl substitution at the aromatic ring results in a positive quadrupole moment. However, depending on the polarizability of the anion and on the substitution at the arene, three different modes of interaction, namely Meisenheimer complex, side‐on hydrogen bonding, or anion–π interaction, can occur. Experimentally, the side‐on as well as a η²‐type π‐complex are observed in the crystal, whereas in solution only side‐on binding is found.     

On the Origin of the “Giant” Electroclinic Effect in a “De Vries”‐Type Ferroelectric Liquid Crystal Material for Chirality Sensing Applications

W415 is a chiral smectic compound with a remarkably weak temperature dependence of its giant electroclinic effect in the liquid crystalline smectic A* phase. Furthermore it possesses a high spontaneous polarization in the smectic C* phase. The origin of this striking electroclinic effect is the co‐occurrence of a de Vries‐type ordering with a weak first‐order tilting transition (see the synchroton X‐ray scattering profiles).

     

“Cell adhesion resistant,UV curable,polymer zinc oxide nanocomposite materials for intraocular lens application”

Foldable acrylic lenses are used for surgical replacement of diseased intraocular lens in treatment of cataract. One of the main postsurgical complications of this treatment method is postcapsular opacification caused by proliferating epithelial cells. The most common approach taken by research community to address this issue has been modification of lens surface with hydrophobic or hydrophilic moieties to manipulate surface cell interaction. In the present study, inherently cell repellent photopolymer resins are presented. Taking advantage of zinc oxide antiproliferative properties, its nanocomposite resins were made and investigated. Hydrophobically modified zinc oxide nanoparticles and poly(phenylethylacrylate‐co‐phenylethyl methacrylate) were made, and their nanocomposite films were prepared by UV polymerization. Films made with 5 wt% ZnO nanoparticles in them resisted fibroblast attachment substantially. In addition, these films filtered harmful UV light and showed other necessary properties like visible light transparency, glass transition temperatures, mechanical strength, and biocompatibility necessary for making intraocular lenses.     

(Ge4Bi14)4−: A Case of “Element Segregation” on the Molecular Level

Extraction of a solid with the nominal composition “K₂GeBi” with 1,2‐diaminoethane (en) in the presence of 4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane (crypt‐222) afforded the salt [K(crypt‐222)]₄(Ge₄Bi₁₄). The 18‐atom Zintl anion (Ge₄Bi₁₄)⁴⁻ has a heretofore unknown molecular topology, which can be thought of as the formal condensation product of two E₁₁³⁻ cages along a shared Ge₄ waist. In this way, (Ge₄Bi₁₄)⁴⁻ represents the largest and most structurally complex Bi‐containing polyanion. We describe its stepwise formation, its geometric and electronic structure, and comment on relative stabilities of isomers with different distributions of the four Ge atoms on the 18 positions that were investigated using DFT calculations.     

Hydrogels from Amorphous Calcium Carbonate and Polyacrylic Acid: Bio‐Inspired Materials for “Mineral Plastics”

Given increasing environmental issues due to the large usage of non‐biodegradable plastics based on petroleum, new plastic materials, which are economic, environmentally friendly, and recyclable are in high demand. One feasible strategy is the bio‐inspired synthesis of mineral‐based hybrid materials. Herein we report a facile route for an amorphous CaCO₃ (ACC)‐based hydrogel consisting of very small ACC nanoparticles physically cross‐linked by poly(acrylic acid). The hydrogel is shapeable, stretchable, and self‐healable. Upon drying, the hydrogel forms free‐standing, rigid, and transparent objects with remarkable mechanical performance. By swelling in water, the material can completely recover the initial hydrogel state. As a matrix, thermochromism can also be easily introduced. The present hybrid hydrogel may represent a new class of plastic materials, the “mineral plastics”.