Single chain self‐assembly of well‐defined heterotelechelic polymers generated by ATRP and click chemistry revisited

Well‐defined heterotelechelic poly(styrene) carrying thymine/diaminopyridine (DAP) (M_n,SEC = 9300, PDI = 1.04) and Hamilton wedge (HW)/cyanuric acid (CA) (M_n,SEC = 8200, PDI = 1.04) bonding motifs are prepared via a combination of controlled/living radical polymerization and copper catalyzed azide/alkyne “click” chemistry and are subsequently self‐assembled as single chains to emulate—on a simple level—the self‐folding behavior of natural biomacromolecules. Hydrogen nuclear magnetic resonance (¹H NMR) in deuterated dichloromethane and dynamic light scattering analyses provides evidence for the hydrogen bonding interactions between the α‐thymine and ω‐DAP as well as α‐CA and ω‐HW chain ends of the heterotelechelic polymers leading to circular entropy driven single chain self‐assembly. This study demonstrates that the choice of NMR solvent is important for obtaining well‐resolved NMR spectra of the self‐assembled structures. In addition, steric effects on the HW can affect the efficiency of the self‐assembly process. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Fabrication of Supramolecular Semiconductor Block Copolymers by Ring‐Opening Metathesis Polymerization

ω‐Telechelic poly(p‐phenylene vinylene) species (PPVs) are prepared by living ring‐opening metathesis polymerization of a [2.2]paracyclophane‐1,9‐diene in the presence of Hoveyda–Grubbs 2nd generation initiator, with terminating agents based on N¹,N³‐bis(6‐butyramidopyridin‐2‐yl)‐5‐hydroxyisophthalamide (Hamilton wedge), cyanuric acid, Pd^II–SCS‐pincer, or pyridine moieties installing the supramolecular motifs. The resultant telechelic polymers are self‐assembled into supramolecular block copolymers (BCPs) via metal coordination or hydrogen bonding and analyzed by ¹H NMR spectroscopy. The optical properties are examined, whereby individual PPVs exhibit similar properties regardless of the nature of the end group. Upon self‐assembly, different behaviors emerge: the hydrogen‐bonding BCP behaves similarly to the parent PPVs whereas the metallosupramolecular BCP demonstrates a hypsochromic shift and a more intense emission owing to the suppression of aggregation. These results demonstrate that directional self‐assembly can be a facile method to construct BCPs with semiconducting networks, while combating solubility and aggregation.     

A “plug and play” polymer through biocomplementary hydrogen bonding

This article describes a DNA‐like polymer that exhibits the ability to self‐assemble through hydrogen bonding. We synthesized poly[1‐(4‐vinylbenzyl)thymine] (PVBT) and 9‐hexadecyladenine (A‐C16) through an atom transfer radical polymerization (ATRP) and alkylation, respectively. Biocomplementary PVBT/A‐C16 hierarchical supramolecular complexes formed in dilute DMSO solution through nucleobase recognition, that is, hydrogen bonding interactions between the thymine (T) groups of PVBT and the adenine (A) group of A‐C16; evidence for this molecular recognition was also gained from dynamic light scattering studies. ¹H NMR titration studies in CDCl₃ showed that T–A complexes formed rapidly on the NMR time scale with high association constants (up to 534 M^?1). Moreover, FTIR spectroscopic, differential scanning calorimetry, wide‐angle X‐ray diffraction, and small‐angle X‐ray scattering analyses provided further details into the nature of the self‐assembly of these systems. In the bulk state, these complexes self‐assemble into well‐ordered lamellar structures; the changing d‐spacing distance (ranging from 4.98 to 2.32 nm) at different A‐C16 loadings reveals that the molecular structures of the PVBT/A‐C16 complexes are readily tailored. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6416–6424, 2008     

Atom transfer radical polymerization of methyl methacrylate via reversibly supported catalysts on silica gel via self‐assembly

A reversible catalyst immobilization system via self‐assembly of hydrogen bonding between thymine anchored on silica gel support and 2,6‐diaminopyridine functionalized with a catalyst (copper bromide‐N,N,N′,N′‐tetraethyldiethylenetriamine (TEDETA) complex) was developed for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). At elevated temperatures, the hydrogen bonding disassociated and released the catalyst as free small molecules for catalysis, which effectively mediated a living polymerization of MMA, producing PMMA with controlled molecular weight and narrow molecular weight distribution (<1.3). At room temperature, the catalyst assembled on the silica gel support by hydrogen bonding, and thus could be recovered and reused for a second run of ATRP. The recovered catalyst still mediated a living polymerization of MMA with reduced activity (54–64%), but had much improved control of the polymerization. The resulting PMMA had molecular weights very close to theoretical vales. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 22–30, 2004     

Self-assembly with block copolymers through metal coordination of SCS-Pd(II) pincer complexes and pseudorotaxane formation

Poly(norbornene)-based block copolymers containing side chains of palladated pincer complexes/dibenzo[24]crown-8 or palladated pincer complexes/dibenzylammonium salts were synthesized. Noncovalent functionalization was accomplished with their corresponding recognition units through simple 1:1 addition with association constants (Ka) greater than 10(5) m(-1). The self-assembly processes were monitored by using both 1H NMR spectroscopy and isothermal titration calorimetry. In all cases, we found that the self-assembly of the recognition units along each polymer block does not preclude the self-assembly processes along the other block.     

Bioinspired core‐crosslinked micelles from thymine‐functionalized amphiphilic block copolymers: Hydrogen bonding and photo‐crosslinking study

Bioinspired core‐bound polymeric micelles, based on hydrogen bonding and photo‐crosslinking, of thymine have been prepared from poly(vinylbenzylthymine)‐b‐poly(vinylbenzyltriethylammonium chloride). The amphiphilic block copolymer was synthesized by 2,2‐tetramethylpiperidin‐1‐oxyl‐mediated living radical polymerization in water/ethylene glycol solution. Micelle characterization and critical micelle concentration measurements demonstrated that the hydrogen bonding of the attached thymine units stabilizes the micelles. Further, core‐crosslinked polymeric micelles were formed by ultraviolet (UV) radiation showing that the stability of the micelle could be controlled by the UV crosslinking of the attached thymines. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Chain center‐functionalized amphiphilic block polymers: Complementary hydrogen bond self‐assembly in aqueous solution

Hydrogen bonding self‐assemblies were formed in an aqueous medium from a pair of an amphiphilic ABA triblock copolymer and a hydrophobic homopolymer, both with a triple hydrogen bonding site that was complementary to each other and precisely placed at the main‐chain center: (PEGMA)_m–(MMA)_n– ADA –(MMA)_n–(PEGMA)_m and (MMA)_p– DAD –(MMA)_p ( A = hydrogen acceptor; D = hydrogen donor; PEGMA: PEG methacrylate; MMA: methyl methacrylate). The polymers were synthesized by the ruthenium‐catalyzed living radial polymerization with bifunctional initiators (Br– ADA –Br and Cl– DAD –Cl) aiming at pinpoint chain center functionalization to give a symmetric segmental sequence; ADA and DAD initiators were derived from 2,6‐diaminopyridine and thymine, respectively. On mixed equimolar in tetrahydrofuran (THF), both polymers spontaneously associated, and the apparently 1:1 assembly further grew into higher aggregate particles on subsequent addition of water. The aggregates in water/THF were relatively stable and uniform in size, which most likely stems from the intermolecular complementary hydrogen bond interaction at polymer chain centers. In sharp contrast, an equimolar mixture of ADA ‐block polymer and DAD ‐free poly(MMA) in water/THF resulted in larger and irregular particles, and thus short‐lived to eventually collapse. These results indicate that, however structurally marginal, precise pinpoint functionalization of macromolecular chains allows stable self‐assemblies via complementary hydrogen bond interaction even in aqueous media. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4498–4504     

Construction of different supramolecular polymer systems by combining the host–guest and hydrogen‐bonding interactions

Poly(ethylene glycol) (PEG) can form either the inclusion complex with α‐cyclodextrins (α‐CDs) through host–guest interactions or the interpolymer complex with poly(acrylic acid) (PAA) through hydrogen‐bonding interaction. Mixing α‐CD, PEG, and PAA ternary components in an aqueous solution, the competition between host–guest and hydrogen‐bonding interactions occurs. Increasing feed ratio of α‐CD:EG:AA from 0:1:1 to 0.2:1:1 (molar ratio), various interesting supramolecular polymer systems, such as hydrogen‐bonding complex, dynamic polyrotaxane, crystalline inclusion complex, and thermoresponsive hydrogel, are successively obtained. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1114–1120, 2008     

End‐Functionalized Palladium SCS Pincer Polymers via Controlled Radical Polymerizations

A direct and facile route toward semitelechelic polymers, end‐functionalized with palladated sulfur–carbon–sulfur pincer (Pd^II‐pincer) complexes is reported that avoids any post‐polymerization step. Key to our methodology is the combination of reversible addition‐fragmentation chain‐transfer (RAFT) polymerization with functionalized chain‐transfer agents. This strategy yields Pd end‐group‐functionalized materials with monomodal molar mass dispersities (Đ ) of 1.18–1.44. The RAFT polymerization is investigated using a Pd^II‐pincer chain‐transfer agent for three classes of monomers: styrene, tert‐butyl acrylate, and N‐isopropylacrylamide. The ensuing Pd^II‐pincer end‐functionalized polymers are analyzed using ¹H NMR spectroscopy, gel‐permeation chromatography, and elemental analysis. The RAFT polymerization methodology provides a direct pathway for the fabrication of Pd^II‐pincer functionalized polymers with complete end‐group functionalization.

     

Second‐Generation Supramolecular Dendrimer with a Defined Structure due to Orthogonal Binding

A second‐generation supramolecular dendrimer has been prepared by orthogonal multiple hydrogen bonding. In the first (inner) recognition domain, the interaction of one bis‐isocyanuric acid ( 25 ) with two branching units ( 21 ) that carry complementary Hamilton receptors has been exploited. In the second (outer) generation, the two ADDA (A=hydrogen‐bond acceptor, D=donor) receptors of each branching unit ( 21 ) have bound complementary DAAD units ( 4 ). The problem of limited solubility of the building blocks has been overcome by the introduction of branched ethylhexyl residues and by the use of flexible alkylene or oligo(ethylene glycol) linking chains. The orthogonal binding of the two hydrogen‐bonding pairs was elucidated by chemical induced shift NMR titrations, which proved that the two pairs, isocyanuric acid with the Hamilton receptor and ADDA with DAAD, bind preferentially. The formation of the supramolecular self‐assembled 1:2:4 dendrimer with a molecular weight of 5065 g mol^?1 was investigated by diffusion NMR spectroscopy.     

Supramolecular poly(ether ketone)–polyisobutylene pseudo‐block copolymers

The association behavior of telechelic hydrogen‐bonded poly(ether ketone) (PEK) and polyisobutylene (PIB) polymers and the formation of a new class of pseudo‐block copolymers is reported. The attachment of complementing hydrogen bonds (thymine/2,6‐diaminotriazine and cytosine/2,6‐diaminotriazine) onto the respective PIB and PEK polymers leads to a dramatic increase in the miscibility between the normally immiscible PEK and PIB polymers. The structure formation in the liquid state was studied by dynamic NMR spectroscopy as well as in the solid state via solid‐state NMR‐spectroscopy, DSC, and TEM methods. The polymers form a nanophase structure with a periodicity of 70 nm with the microphase separation occurring specifically within the donor–acceptor pair with the higher binding constant (thymine/2,6‐diaminotriazine) and not within the weaker bonded cytosine/2,6‐diaminotriazine pair. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 162–172, 2004     

Synthesis of polyamides from diols and diamines with liberation of H2

The amidation reaction based on catalytic coupling of alcohols with amines previously reported by us, using the pincer complexes 1 and 2 as catalysts, was applied to the generation of polyamides from nonactivated diols and diamines. A range of polymers was prepared, with M_n up to 26.9 kDa. Unlike the traditional syntheses of polyamides based on carboxylic acid derivatives, which require the use of toxic reagents and generate stoichiometric amounts of waste, this process generates only molecular hydrogen as byproduct. Both aromatic and aliphatic diols and diamines were used. Gel permeation chromatography measurements of the dimethylformamide‐soluble polymers and thermal studies of the polyamides were performed. Matrix assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) spectra are also reported. Thermogravimetric analyses studies indicate that the aromatic polyamides (with the exception of the pyridine‐based polyamide) are more thermally stable than the aliphatic ones. This general, environmentally benign method for the synthesis of polyamides is homogeneously catalyzed under neutral conditions by dearomatized ruthenium‐pincer complexes 1 and 2 and proceeds in 1,4‐dioxane under an inert atmosphere. Conditions for polyamidation in the absence of solvent are also reported, using the pincer complex 2 as catalyst. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Thymine‐based,water‐soluble phototerpolymers: Their preparation and synthesis

Terpolymers of vinylbenzylthymine, vinylbenzyltriethylammonium chloride, and N‐butyl‐N,N‐dimethyl‐(4‐vinylbenzyl)ammonium chloride with different monomer ratios have been prepared, and the effect of the monomer ratios on the properties of the terpolymers has been investigated. These polymers are water‐soluble and, when irradiated with low levels of UV light, undergo a 2π+2π photodimerization reaction of thymine. This photodimerization significantly reduces the water solubility, immobilizing the polymer to the substrate, and shows potential for water‐soluble photoresists. Thermogravimetric analysis has revealed that the terpolymers have two degradation stages corresponding to the quaternary ammonium pendant groups and to the thymine. An evaluation of the contact‐angle measurements has shown that the surface properties and hydrophobicity can be controlled by the variation of the monomer ratios. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1296–1303, 2007     

A conjugated hydrogen bond receptor for attachment to gold

A fully conjugated host molecule (in order to allow conductivity) with a hydrogen bonding motif for molecular recognition (six hydrogen bonds in the Hamilton receptor array) on one end and a sulfur unit for immobilization on gold at the other end has been synthesized and its binding to gold clusters has been investigated by fluorescence spectroscopy.     

Interpolymer complexation between polyacrylic acid and cellulose ethers: Formation and properties

The interaction between polyacrylic acid and two water‐soluble cellulose ethers (methylcellulose and hydroxyethylcellulose) was studied. Viscometry, velocity sedimentation, small‐angle neutron scattering, and potentiometric titration methods show the formation of stable water‐soluble interpolymer complexes due to hydrogen bonding between nondissociated groups of polyacrylic acid and proton‐acceptor groups of the cellulose ether. Both complexes exhibit polyelectrolyte properties and keep the conformation of the semirigid chain component. The hydrophobic groups in the methylcellulose macromolecule are responsible for the absence of complexes at temperatures greater than 60 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1323–1330, 2000     

Spectroscopic studies of interactions in poly(N‐acryloyl‐N′‐methylpiperazine)/acidic polymer complexes

Poly(N‐acryloyl‐N′‐methylpiperazine) (PAMP) forms complexes with four strong acidic polymers, namely, poly(styrenesulfonic acid), poly(vinylphosphonic acid), poly(acrylic acid) and poly(methacrylic acid) in ethanol/water (1:1) solution. The nature of interpolymer interactions in various complexes was studied by Fourier transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS). Both the carbonyl oxygen and the amide nitrogen of PAMP are involved in hydrogen‐bonding interactions. Some of the amine nitrogens of PAMP are protonated and therefore PAMP also interacts with the acidic polymers through ionic interactions. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 501–508, 2000     

Density Functional Theory Study of the Interaction between Thymine and Luteolin

The density function B3LYP method has been used to optimize the geometries of the luteolin, thymine and luteolin‐thymine complexes at 6‐31+G?? basis. The vibrational frequencies have been studied at the same level to analyze these seventeen complexes, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) have been utilized to investigate the hydrogen bonds involved in all the systems. The interaction energies of the complexes corrected by basis set superposition error are between ?93.00–?76.69 kJ/mol. The calculating results indicate that strong hydrogen bonding interactions have been found in the luteolin‐thymine complexes.     

Polyampholyte terpolymers of amphoteric,amino acid‐based monomers with acrylamide and (3‐acrylamidopropyl)trimethyl ammonium chloride

Low‐charge‐density amphoteric copolymers and terpolymers composed of acrylamide, (3‐acrylamidopropyl)trimethyl ammonium chloride, and the amino acid derived monomers (e.g., N‐acryloyl valine, N‐acryloyl alanine, and N‐acryloyl aspartate) were prepared via free‐radical polymerization in aqueous media to yield terpolymers with random charge distributions and homogeneous compositions. Sodium formate (NaOOCH) was employed as a chain transfer agent during the polymerization to suppress gel effects and broadening of the molecular weight distribution. Terpolymer compositions were determined by ¹³C and ¹H NMR spectroscopy. Terpolymer molecular weights and polydispersity indices were obtained via size exclusion chromatography/multi‐angle laser light scattering, and hydrodynamic diameter values were obtained via dynamic light scattering. The solution properties of low‐charge‐density amphoteric copolymers and terpolymers have been studied as a function of solution pH, ionic strength, and polymer concentration. The low‐charge‐density terpolymers display excellent solubility in deionized (DI) water with no phase separation. The charge‐balanced terpolymers exhibit antipolyelectrolyte behavior at pH values ≥(6.5 ± 0.2). As solution pH is decreased, these charge‐balanced terpolymers become increasingly cationic because of the protonation of the anionic repeat units. Charge‐imbalanced terpolymers generally demonstrate polyelectrolyte behavior, although the effects of intramolecular electrostatic interactions (e.g., polyampholyte effects) on the hydrodynamic volume are evident at certain values of solution pH and salt concentration. The aqueous solution behavior (i.e., globule‐to‐coil transition at the isoelectric point in the presence of salt and globule elongation with increasing charge asymmetry) of the terpolymers in the dilute regime correlates well with that predicted by the polyampholyte solution theories of Dobrynin and Rubinstein as well as Kantor and Kardar. Examination of comonomer charge density, hydrogen‐bonding ability, and spacer group (e.g., the moiety separating the ionic group from the polymer chain) indicates that conformational restrictions of the amino acid comonomers result in increased chain stiffness and higher solution viscosities in DI water and brine solutions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4479–4493, 2006     

Cross-linked and functionalized ‘universal polymer backbones’ via simple, rapid, and orthogonal multi-site self-assembly

A novel route to cross-linked and functionalized random copolymers using a rapid, one-step, and orthogonal copolymer cross-linking/functionalization strategy has been developed. Random terpolymers possessing high concentrations of pendant alkyl chains and either (1) palladated-pincer complexes and diaminopyridine moieties (DAD hydrogen-bonding entities) or (2) palladated-pincer complexes and cyanuric wedges (ADAADA hydrogen-bonding entities) have been synthesized using ring-opening metathesis polymerization. Non-covalent cross-linking of the resultant copolymers using a directed functionalization strategy leads to dramatic increases in solution viscosities for cross-linked polymers via metal-coordination while only minor changes in viscosity were observed when hydrogen-bonding motifs were employed for cross-linking. The cross-linked materials could be further functionalized via self-assembly by employing the second recognition motif along the polymeric backbones giving rise to highly functionalized materials with tailored cross-links. This novel non-covalent polymer cross-linking/functionalization strategy allows for rapid and tunable materials synthesis by overcoming many difficulties inherent to the preparation of covalently cross-linked polymers.     

High modulus ratio shape‐memory polymers achieved by combining hydrogen bonding with controlled crosslinking

A new type of poly(methyl acrylate)‐co‐(acrylic acid) (PMA‐AA) networks obtained by combining hydrogen bonding with controlled crosslinking exhibit full and rapid shape‐memory recovery. The structure, thermal properties, dynamical mechanical properties and shape‐memory effects of these networks were presented. High modulus ratios were achieved for the series of PMA‐AA networks based on intense self‐complementary hydrogen bonding in poly(acrylic acid) (PAA) segments. This lead to excellent shape‐memory effects with strain‐recovery ratio above 99%. Meanwhile, faster recovery speed was achieved by the synergistic effect of hydrogen bonding and controlled crosslinking compared to the linear PMA‐AA copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1241–1245, 2011