A General Model for the Kinetics of Self-Condensing Vinyl Polymerization

The kinetic model of the self-condensing vinyl polymerization (SCVP) with nonequal molar concentrations of stimulus and monomer was developed in this work. The molecular size distribution function and other molecular parameters of the resulting hyperbranched polymers were derived. The feed ratio of stimulus to monomer significantly affects the molecular parameters of the products. The residual monomer and inimer in the reaction system have an important influence on the molecular parameters of the hyperbranched polymers obtained even at a high double-bond conversion. Similarly to the SCVP with nonequal reactivities and self-condensing vinyl copolymerization, the maximum of the degree of branching is 0.5 for the SCVP with nonequal molar concentrations of stimulus and monomer. In other words, when the molar ratio of stimulus to monomer approaches 0.627 and the vinyl conversion reaches 1, we can get the hyperbranched polymers with the highest degree of branching

Real-Time Membrane Fusion of Giant Polymer Vesicles

Membrane fusion is very important for the formation of many complex organs in metazoans throughout evolution, such as muscles, bones, and placentae. Lipid vesicles (liposomes) are frequently used as model membranes to study the fusion process. This work demonstrates for the first time the real-time membrane fusion of giant polymer vesicles by directly displaying a series of high-resolution and real-time transformation images of individual vesicles. The fusion process includes the sequential steps of membrane contact, forming the center wall, symmetric expansion of fusion pore and complete fusion, undergoing the intermediates of “8” shape with a protruding rim at the contact site, peanut (pear) shape, and oblate sphere. The vesicle swells during fusion, and the fusing vesicle only deforms in the neck domain around the fusion pore in the lateral direction, which verifies the importance of the lateral tension on the fusion pore at the vesicle deformation level. The successful fusion of the synthetic and protein-free polymer vesicles reported here also supports that vesicle proximity combined with membrane perturbation suffices to induce membrane fusion, and that the protein is not necessary for the fusion process

Crystal Structure of Novel Polyamides with Long Diacid Segment: Polyamides 2 16, 4 16, 6 16, 8 16, 10 16, and 12 16

The morphologies of a series of novel polyamides with a long diacid segment were carefully studied using transmission electron microscopy (TEM), while their crystal structure was investigated using both TEM and wide-angle X-ray diffraction (WAXD). It was seen that the solution-grown crystals of all polyamides in this work were lath-like and crystallized as chain-folded, hydrogen-bonded sheet lamellae from 1,4-butanediol. The electron diffraction of these samples reveals that two crystalline phases are present including both αp and βp in all polyamides under consideration except for polyamide 2 16, which only consists of one crystal form, αp. In addition, sedimented mats of these polyamide crystals and stretched film samples were examined by WAXD. The unit cell parameters for these crystals were calculated thereinafter

Synthesis and Size-Controllable Self-Assembly of a Novel Amphiphilic Hyperbranched Multiarm Copolyether

A series of novel hyperbranched multiarm copolyethers of PEHO-star-PPO with different molar ratios of PPO arms to PEHO cores (RA/C) were synthesized. NMR and SEC measurements confirm the molecular structure of PEHO-star-PPOs. Both glass transition temperature (Tg) and decomposition temperature (Td) of PEHO-star-PPO decrease with increasing RA/C. The self-assembly behavior of PEHO-star-PPO copolymers was investigated by TEM, SEM, DLS, etc. The results indicate that the ill-defined PEHO-star-PPO molecules could aggregate into large spherical micelles (over 100 nm) with controlled sizes, and the micelle size decreases as RA/C increases. The structure of the large micelles was explored by FT-IR, NMR, etc. Accordingly, a possible self-assembly process is put forward, and a new aggregate model termed as multimicelle aggregate (MMA) (Figure C) is suggested to explain the formation of the large micelles. In MMA model, the large micelles are the aggregates of small micelles associated by intermicellar interactions such as hydrogen bonds

Sulfonated Poly(arylene ether sulfone)s with Phosphine Oxide Moieties: A Promising Material for Proton Exchange Membranes

Sulfonated poly(arylene ether sulfone)s with phosphine oxide moieties (sPESPO) were achieved by polycondensation of bis(4-hydroxyphenyl)phenylphosphine oxide with 3,3′-disulfonate-4,4′-difluorodiphenyl sulfone (SFDPS) and 4-fluorophenyl sulfone (FPSF). Sulfonated poly(arylene ether sulfone)s (sPES) were also synthesized by polymerization of 4,4′-sulfonyldiphenol with SFDPS and FPSF for comparison. The comparative study demonstrates that the sPESPO ionomers exhibit strong intermolecular interactions and high oxidative stability because of the phosphine oxide groups. Furthermore, the sPESPO membrane and the sPES membrane with an equal ion exchange capacity show much different nanophase separation morphology. As a result, the former shows better properties than the latter. The sPESPO membranes exhibit excellent overall properties. For instance, the sPESPO membrane, with a disulfonation degree of 45%, exhibits high thermal and oxidative stability. Moreover, it shows a water uptake of 30.8% and a swelling ratio of 15.8% as well as a proton conductivity of 0.087 S/cm at 80 °C

Controlled Functionalization of Multiwalled Carbon Nanotubes by in Situ Atom Transfer Radical Polymerization

The in situ ATRP (atom transfer radical polymerization) “grafting from” approach was successfully applied to graft poly(methyl methacrylate) (PMMA) onto the convex surfaces of multiwalled carbon nanotubes (MWNT). The thickness of the coated polymer layers can be conveniently controlled by the feed ratio of MMA to preliminarily functionalized MWNT (MWNT-Br). The resulting MWNT-based polymer brushes were characterized and confirmed with FTIR, 1H NMR, SEM, TEM, and TGA. Moreover, the approach has been extended to the copolymerization system, affording novel hybrid core−shell nanoobjects with MWNT as the core and amphiphilic poly(methyl methacrylate)-block-poly(hydroxyethyl methacrylate) (PMMA-b-PHEMA) as the shell. The approach presented here may open an avenue for exploring and preparing novel carbon nanotubes-based nanomaterials and molecular devices with tailor-made structure, architecture, and properties

Sulfonated Polybenzothiazoles: A Novel Candidate for Proton Exchange Membranes

Sulfonated polybenzothiazoles (sPBT) with high molecular weight as well as excellent solubility were synthesized for the first time, which was achieved by attaching the phenylsulfonyl pendant groups or incorporating the hexafluoroisopropylidene moieties to the polymer backbone. Such sulfonated polybenzothiazoles thus could be cast into homogeneous membranes and could be further evaluated as proton exchange membranes. These sPBTs showed high thermal stability and high proton conductivity as well as low swelling. For instance, the hexafluoroisopropylidene-containing sPBT with a disulfonation degree of 65% exhibited a Td5 of 380 °C, a proton conductivity of 0.11 S/cm, and a swelling of 15.5% at 80 °C. In addition, the sPBT membranes showed excellent oxidative and hydrolytic stability. In comparison with the phenylsulfonyl pendant-group-containing sPBT membranes, the hexafluoroisopropylidene-containing sPBT membranes with an equivalent ion exchange capacity showed much narrower ionic channels because of the hydrophobic hexafluoroisopropylidene moieties. This made the latter display better dimensional stability, oxidative stability, and hydrolytic stability than the former. This investigation illustrated that sulfonated polybenzothiazoles are a novel candidate for proton exchange membranes

Synergistic Supramolecular Encapsulation of Amphiphilic Hyperbranched Polymer to Dyes

A novel synergistic effect during supramolecular host−guest encapsulations of core−shell amphiphilic hyperbranched polymers to two kinds of dyes was reported. Two kinds of palmityl chloride-modified hyperbranched polymer, polyamidoamine (HPAMAM10K-C16) and poly(sulfone−amine) (HPSA11K-C16), were used as the hosts of supramolecular encapsulations, and water-soluble dyes such as methyl orange (MO) and methyl blue (MB) were selected as the corresponding guests. In cases of single-dye encapsulations, each host can extract one kind of guest from water phase into chloroform phase with a certain loading capacity (Cload). In the double-dye encapsulations, a pair of dyes, MO and MB, was employed as the guests. The Cload increased significantly for one or both of the pair dyes with the Cload of the single-dye encapsulation as the reference. This is defined as synergistic encapsulation in this paper. For the HPAMAM10K-C16, Cload of MO can be increased by about 100% with the cooperation of MB. For HPSA11K-C16, Cload of MB can be raised to a 40−100-fold level of single-dye encapsulation without loss of MO. Experiments with different encapsulating sequence showed that the synergistic encapsulation for HPAMAM10K-C16 is a parallel-type process because the sequence has no significant impact on the Cload of each dye, while the case of HPSA11K-C16 is a cascade-type process since the results with different encapsulating order were different. The synergistic encapsulation phenomenon was confirmed by the measurements of 1H NMR, DSC, and TGA on the resulting dye-encapsulated hyperbranched polymers. In addition, investigations on the guest−host supramolecular systems with different pH indicated that the pH value has certain influence on the synergistic encapsulation Cload, but it was not the dominating factor for the synergistic encapsulation. The synergistic effect was found simultaneously in the supramolecular encapsulation of two hosts, indicating this effect is not limited to a peculiar dendritic polymer. The phenomenon presented here will trigger further application of dendritic and other complex polymeric materials in the supramolecular host−guest chemistry

Molecular Parameters of Hyperbranched Polymers Made by Self-Condensing Vinyl Polymerization. 2. Degree of Branching^†

Using a modified definition, the average degree of branching, , the fraction of branchpoints, , as well as the fractions of various structural units are calculated as a function of conversion of double bonds for hyperbranched polymers formed by self-condensing vinyl polymerization (SCVP) of monomers (or “inimers”) with the general structure AB*, where A is a vinyl group and B* is an initiating group. The results are compared to those for the polycondensation of AB2-type monomers. At full conversion, is somewhat smaller for SCVP ( ∞ ≈ 0.465) than for AB2 systems ( ∞ = 0.5). There are two kinds of linear groups in SCVP whereas there is only one kind in AB2 systems. Since there are two different active centers in SCVP, i.e., initiating B* and propagating A* centers, the effect of nonequal reactivities on is also discussed. At a reactivity ratio of the two kinds of active centers, r = kA/kB ≈ 2.59, a maximum value of ∞ = 0.5 is reached. For the limiting case r << 1, a linear polymer resembling a polycondensate will be formed whereas for r >> 1 a weakly branched vinyl polymer is expected. NMR experiments allow for the determination of reactivity ratio r

Supramolecular and Biomimetic Polypseudorotaxane/Glycopolymer Biohybrids: Synthesis, Glucose-Surfaced Nanoparticles, and Recognition with Lectin

A new class of supramolecular and biomimetic glycopolymer/poly(ε-caprolactone)-based polypseudorotaxane/glycopolymer triblock copolymers (poly(d-gluconamidoethyl methacrylate)−PPR−poly(d-gluconamidoethyl methacrylate), PGAMA−PPR−PGAMA), exhibiting controlled molecular weights and low polydispersities, was synthesized by the combination of ring-opening polymerization of ε-caprolactone, supramolecular inclusion reaction, and direct atom transfer radical polymerization (ATRP) of unprotected d-gluconamidoethyl methacrylate (GAMA) glycomonomer. The PPR macroinitiator for ATRP was prepared by the inclusion complexation of biodegradable poly(ε-caprolactone) (PCL) with α-cyclodextrin (α-CD), in which the crystalline PCL segments were included into the hydrophobic α-CD cavities and their crystallization was completely suppressed. Moreover, the self-assembled aggregates from these triblock copolymers have a hydrophilic glycopolymer shell and an oligosaccharide threaded polypseudorotaxane core, which changed from spherical micelles to vesicles with the decreasing weight fraction of glycopolymer segments. Furthermore, it was demonstrated that these triblock copolymers had specific biomolecular recognition with concanavalin A (Con A) in comparison with bovine serum albumin (BSA). To the best of our knowledge, this is the first report that describes the synthesis of supramolecular and biomimetic polypseudorotaxane/glycopolymer biohybrids and the fabrication of glucose-shelled and oligosaccharide-threaded polypseudorotaxane-cored aggregates. This hopefully provides a platform for targeted drug delivery and for studying the biomolecular recognition between sugar and lectin