Phenolic Functionality of Polyhedral Oligomeric Silsesquioxane Nanoparticles Affects Self-Assembly Supramolecular Structures of Block Copolymer Hybrid Complexes

We prepared polyhedral oligomeric silsesquioxane (POSS) nanoparticles (NPs) presenting one, two, and eight phenolic OH units (MP-POSS, BP-POSS, and OP-POSS, respectively) and investigated their blends with poly­(styrene-<i>b</i>-4-vinylpyridine) (PS-<i>b</i>-P4VP) diblock copolymer. We prepared MP-POSS, BP-POSS, and OP-POSS each through a simple two-step synthesis including the hydrosilylation of 4-acetoxystyrene (AS) with H-POSS, DDSQ, and Q₈M₈^H, respectively, and then subsequent hydrolysis of acetoxyl groups with N₂H₄. Fourier transform infrared spectra and differential scanning calorimetry revealed that the hydrogen bonding strengths in the three hybrid complexes follow the order of P4VP/OP-POSS > P4VP/BP-POSS > P4VP/MP-POSS. Small-angle X-ray scattering and transmission electron microscopy revealed that the self-assembly nanostructures formed by PS-<i>b</i>-P4VP were strongly dependent on the nature of the POSS NPs. The weakly hydrogen bonded PS-<i>b</i>-P4VP/MP-POSS hybrid formed a disordered structure at MP-POSS contents greater than 10 wt %. The moderately hydrogen bonded PS-<i>b</i>-P4VP/BP-POSS hybrid self-assembled into structures ranging from lamellar to cylindrical upon increasing the BP-POSS concentration higher than 50 wt %. The strongly hydrogen bonded PS-<i>b</i>-P4VP/OP-POSS hybrid underwent a full sequence of order–order morphological transitionfrom lamellar, bicontinuous double gyroid, cylindrical, and finally to body-centered cubic spherical structureswith the increase of OP-POSS concentrations. The number of phenolic OH functionalities presented by the POSS NPs was the key factor affecting the nature of these self-assembled structures

Water-Soluble Fluorescent Nanoparticles from Supramolecular Amphiphiles Featuring Heterocomplementary Multiple Hydrogen Bonding

We describe a facile strategy, involving bio-inspired noncovalent molecular recognition, for fabricating water-dispersible luminescent polymer dots without any ionic groups. We first synthesized the thymine-functionalized conjugated polymers PC-T and PTC-T through conventional Suzuki coupling polymerization and copper­(I)-catalyzed alkyne/azide cycloaddition (CuAAC). These multiple-hydrogen-bonding materials exhibited distinct luminescent properties in protic and aprotic solvents as well as attractive thermal properties and stabilities; most importantly, they had the ability to pair with complementary base units. Next, we prepared the hydrophilic polymer PEG-A and examined its molecular recognition with PC-T and PTC-T through DNA-like adenine–thymine (A–T) base pairing. We used transmission electron microscopy (TEM) and dynamic light scattering (DLS) to determine the size distributions and dispersibilities of the resulting supramolecular micelles, which appeared as polymeric dots with high signal-to-background ratios through fluorescence microscopy. The PEG shells of these micelles functioned as biomimetic surfaces that sustained the biocompatibility for practical usage. Our results suggest that supramolecular self-assembly through specific nucleobase recognition appears to be a reliable process with which to apply conjugated polymers into, for example, modern biological analysis

Highly Thermally Stable, Transparent, and Flexible Polybenzoxazine Nanocomposites by Combination of Double-Decker-Shaped Polyhedral Silsesquioxanes and Polydimethylsiloxane

In this study a new type of bifunctional phenolic compound based on a double-decker silsesquioxane (DDSQ-BP) was synthesized from phenyltrimethylsilane and then reacted (Mannich condensation) with allylamine and CH₂O to form a bis-allyl benzoxazine DDSQ derivative (DDSQ-BZ). The structures of these DDSQ derivatives were confirmed using Fourier transform infrared and nuclear magnetic resonance spectroscopy and MALDI-TOF mass spectrometry. Highly thermally stable, transparent, and flexible polybenzoxazine prepolymers were obtained after hydrosilylation of DDSQ-BZ with polydimethyl­siloxane (PDMS) as the flexible segment; these materials were characterized using differential scanning calorimetry, thermogravimetric analysis, microtensile testing, and UV–vis spectroscopy. The char yield of DDSQ-BZ-PDMS was 73 wt %, significantly higher than that of a typical polybenzoxazine; in addition, DDSQ-BZ-PDMS displayed high flexibility and transparency after thermal curing

From Microphase Separation to Self-Organized Mesoporous Phenolic Resin through Competitive Hydrogen Bonding with Double-Crystalline Diblock Copolymers of Poly(ethylene oxide-<i>b</i>-ε-caprolactone)

A series of immiscible crystalline–crystalline diblock copolymers, poly(ethylene oxide)-<i>b</i>-(ε-caprolactone) (PEO-<i>b</i>-PCL), were synthesized through ring-opening polymerization and then blended with phenolic resin. FT-IR analyses demonstrate that the ether group of PEO is a stronger hydrogen-bond acceptor with the hydroxyl group of phenolic resin than is the carbonyl group of PCL. Phenolic, after being cured with hexamethylenetetramine (HMTA), results in the excluded and confined PCL phase based on analyses by differential scanning calorimetry (DSC). This effect leads to the formation of a variety of composition-dependent nanostructures, including disorder, gyroid and short-cylinder structures. The self-organized mesoporous phenolic resin was found only at 40–60 wt % phenolic content by an intriguing balance of the contents of phenolic, PEO, and PCL. In addition, the mesoporous structure was destroyed at higher PCL/PEO ratios in the block copolymers, as determined by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) experiments. In addition, the large and long-range order of bicontinuous gyroid-type mesoporous carbon was obtained from mesoporous gyroid phenolic resin calcined at 800 °C under nitrogen

Complementary Multiple Hydrogen Bonding Interactions Induce the Self-Assembly of Supramolecular Structures from Heteronucleobase-Functionalized Benzoxazine and Polyhedral Oligomeric Silsesquioxane Nanoparticles

We prepared octuply adenine (A)-functionalized polyhedral oligomeric silsesquioxane [(octakis­(vinylbenzyladenine-siloxy)­silsesquioxane, OBA-POSS] nanoparticles through the reaction of A with octakis­(benzyl chloride) POSS (OVBC-POSS), itself prepared through hydrosilylation of octakis­(dimethylsiloxy)­silsesquioxane (Q₈M₈^H) with vinyl benzyl chloride. We observed the self-assembly of lamellar structures from the complexation of a thymine (T)-functionalized polybenzoxazine (PA-T) with OBA-POSS, stabilized through complementary multiple hydrogen bonding interactions between the T groups of PA-T and the A groups of OBA-POSS. In addition, incorporating POSS presenting multiple, strong, complementary hydrogen bonding A units into the PA-T matrix significantly enhanced the thermal stability of this polymer, as evidenced using differential scanning calorimetry and thermogravimetric analysis

Competitive Hydrogen Bonding Interactions Influence the Secondary and Hierarchical Self-Assembled Structures of Polypeptide-Based Triblock Copolymers

A new biocompatible triblock copolymer, poly­(ε-caprolactone-<i>b</i>-ethylene oxide-<i>b</i>-γ-benzyl l-glutamate) (PCL-<i>b</i>-PEO-<i>b</i>-PBLG), has been prepared through sequential ring-opening polymerizations, with two degrees of polymerization for the PBLG block segment when using an amino-terminated PCL-<i>b</i>-PEO diblock copolymer as the macroinitiator. The hydrogen bonding strengths (interassociation equilibrium constants) followed the order of phenolic/PEO (<i>K</i>_A = 264.8) > phenolic/PCL (<i>K</i>_C = 116.8) > phenolic/PBLG (<i>K</i>_D = 9.0), indicating that the phenolic OH groups preferred to interact with the C–O–C units of PEO block, then the CO units of PCL block, and finally with the CO units of PBLG block. The hydrogen bonding behavior of these four competing functional units could be predicted accurately using the Painter–Coleman association model. These competitive hydrogen bonding interactions induced various miscibility behaviors and self-assembled hierarchical structures, ranging from the hexagonally packed cylinder structure of α-helical conformation of PBLG block segment in the crystalline lamellar structure of the PCL block segment to a miscible ordered structure upon increasing phenolic concentrations in the phenolic/PCL-<i>b</i>-PEO-<i>b</i>-PBLG blend system

Mediated Competitive Hydrogen Bonding Form Mesoporous Phenolic Resins Templated by Poly(ethylene oxide‑<i>b</i>‑ε-caprolactone‑<i>b</i>‑l‑lactide) Triblock Copolymers

A series of immiscible triple crystalline triblock copolymers, poly­(ethylene oxide-<i>b</i>-ε-caprolactone-<i>b</i>-l-lactide) (PEO-<i>b</i>-PCL-<i>b</i>-PLLA), synthesized through sequential ring-opening polymerization, have been blended with phenolic resin. FTIR spectra revealed that the ether groups of the PEO blocks were stronger hydrogen bond acceptors for the OH groups of phenolic resin than were the CO groups of the PCL and PLLA blocks. Curing of phenolic with the templates and hexamethylenetetramine resulted in excluded and confined PCL or PLLA phases, depending on the phenolic content. This effect led to the formation of various composition-dependent nanostructures, including disordered structures, bicontinuous gyroids, hexagonally packed cylinders, and spherical micelle structures. Small-angle X-ray scattering and transmission electron microscopy revealed that self-organized mesoporous phenolic resin formed at phenolic contents of only 30–50 wt % as a result of an intriguing balance among the contents of phenolic and the PEO, PCL, and PLLA blocks. An interesting closed-loop mesoporous structure existed in the phase diagram of the mesoporous phenolic resins templated by the PEO-<i>b</i>-PCL-<i>b</i>-PLLA triblock copolymers

Complexation of Fluorescent Tetraphenylthiophene-Derived Ammonium Chloride to Poly(<i>N</i>‑isopropylacrylamide) with Sulfonate Terminal: Aggregation-Induced Emission, Critical Micelle Concentration, and Lower Critical Solution Temperature

Amphiphilic polymers with hydrophilic poly­(<i>N</i>-isopropylacylamide) (PNIPAM) shell connecting hydrophobic tetraphenylthiophene (TP) core, which has the novel aggregation-induced emission (AIE) property, by ionic bonds were prepared to explore the AIE-operative emission responses toward critical micelle concentration (CMC) and lower critical solution temperature (LCST). To exercise the idea, ammonium-functionalized TP2NH₃⁺ and sulfonate-terminated PNIPAM were separately prepared and mixed in different molar ratios to yield three amphiphilic TP-PNIPAM<i>n</i> complexes for the evaluations of CMC and LCST by fluorescence responses. The nonemissive dilute aqueous solutions of TP-PNIPAM<i>n</i> became fluorescent when increasing concentrations above CMC. Heating micelles solution to temperatures above LCSTs causes further enhancement on the emission intensity. The fluorescence responses are explained by the extent of aggregation in the micelles and in the globules formed at room temperature and at high temperatures, respectively

Functional Supramolecular Polypeptides Involving π–π Stacking and Strong Hydrogen-Bonding Interactions: A Conformation Study toward Carbon Nanotubes (CNTs) Dispersion

New supramolecular polypeptides have been prepared through simple ring-opening polymerization and “click” reactions. Postfunctionalization with diamino­pyridine (DAP) moieties, capable of multiple hydrogen bonding, was an efficient approach toward forming α-helical-dominant polypeptides. The physically cross-linked networks produced upon self-organization of the DAP units increased the glass transition temperature (<i>T</i>_g) of the polymers and sustained the secondary structures of the polypeptides. Additional thermal responsivity resulted from dynamic noncovalent bonding on the polymer side chains. Molecular recognition through heterocomplementary DAP···thymine (T) base pairs was revealed spectroscopically and then used to construct poly­(γ-propargyl-l-glutamate)-<i>g</i>-<i>N</i>-(6-acetamido­pyridin-2-yl)-11-undecan­amide/thyminyl­pyrene (PPLG-DAP/Py-T) supramolecular complexes. Transmission electron microscopy images revealed that this complex was an efficient dispersant of carbon nanotubes (CNTs). Indeed, it could disperse CNTs in both polar and nonpolar media, the direct result of combining two modes of secondary noncovalent bonding: multiple hydrogen bonding and π–π interactions. Furthermore, CNT composites fabricated with biocompatible polymers and high value of <i>T</i>_g should enable the development of bio-inspired carbon nanostructures and lead the way toward their biomedical applications

Trilayered Single Crystals with Epitaxial Growth in Poly(ethylene oxide)-<i>block</i>-poly(ε-caprolactone)-<i>block</i>-poly(l‑lactide) Thin Films

Manipulation of crystalline textures of biocompatible block copolymers is critical for the applications in the medical field. Here, we present the control of multiple-crystalline morphologies with flat-on chain orientation in biocompatible poly­(ethylene oxide)-<i>block</i>-poly­(ε-caprolactone)-<i>block</i>-poly­(l-lactide) (PEO–PCL–PLLA) triblock copolymer thin films using melt and solvent-induced crystallizations. Only single-crystalline morphologies of the first-crystallized blocks can be obtained in the melt-crystallized thin films due to the confinement effect. With solvent annealing by PCL-selective toluene, single-crystalline PLLA to double-crystalline PLLA/PCL and to triple-crystalline PLLA/PCL/PEO layered crystals in sequence are observed for the first time. With the control of solvent selectivity, different sequential crystallization involving first-crystallized PCL transferring to double-crystalline PCL/PLLA is obtained using PEO-selective <i>n</i>-hexanol for annealing. Surprisingly, the crystalline growth of the trilayered single crystal exhibits specific layer-by-layer epitaxial relationship. As a result, the multiple-crystalline textures of the PEO–PCL–PLLA thin films can be carried out by controlling solvent and polymer interaction