Tadpole-Shaped Amphiphilic Block−Graft Copolymers Prepared via Consecutive Atom Transfer Radical Polymerizations

Grafting PMMA onto P(VDF-TrFE) by CF Activation via a Cu(0) Mediated Controlled Radical Polymerization Process

In the present work, poly(methyl methacrylate) (PMMA) is successfully grafted onto poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) side chains via directly activated CF bonds using Cu(0)/2,2'-bipyridine as catalyst. The reaction mechanism and the initiating sites can be confirmed by the structure of the graft copolymer. The graft copolymerization exhibits first-order kinetics, and reaction conditions can affect the chemical composition of the graft copolymer, including reaction time, reaction temperature, solvents, the amount of catalyst, and monomer. The introduction of rigid PMMA side chains onto P(VDF-TrFE) can effectively tune the displacement-electric field hysteresis behaviors of P(VDF-TrFE) from normal ferroelectric to anti-ferroelectric, even linear-like dielectric, under high electric field, resulting in dramatically reduced energy loss while maintaining the discharged energy density. This work may provide an effective strategy to introduce functional groups into P(VDF-TrFE) copolymer via activation of CF bonds.

Experiments and Simulations of Complex Sugar-Based Coil-Brush Block Polymer Nanoassemblies in Aqueous Solution

In this work, we investigated the fundamental molecular parameters that guide the supramolecular assembly of glucose-based amphiphilic coil-brush block polymers in aqueous solution and elucidated architecture-morphology relationships through experimental and simulation tools. Well-defined coil-brush polymers were synthesized through ring-opening polymerizations (ROP) of glucose carbonates to afford norbornenyl-functionalized poly(glucose carbonate) (NB-PGC) macromonomers, followed by sequential ring-opening metathesis polymerizations (ROMP) of norbornene N-hydroxysuccinimidyl (NHS) esters and the NB-PGC macromonomers. Variation of the macromonomer length and grafting through ROMP conditions allowed for a series of coil-brush polymers to be synthesized with differences in the brush and coil dimensions, independently, where the side chain graft length and brush backbone were used to tune the brush, and the coil block length was used to vary the coil. Hydrolysis of the NHS moieties gave the amphiphilic coil-brush polymers, where the hydrophilic-hydrophobic ratios were dependent on the brush and coil relative dimensions. Experimental assembly in solution was studied and found to yield a variety of structurally dependent nanostructures. Simulations were conducted on the solution assembly of coil-brush polymers, where the polymers were represented by a coarse-grained model and the solvent was represented implicitly. There is qualitative agreement in the phase diagrams obtained from simulations and experiments, in terms of the morphologies of the assembled nanoscopic structures achieved as a function of coil-brush design parameters ( e.g., brush and coil lengths, composition). The simulations further showed the chain conformations adopted by the coil-brush polymers and the packing within these assembled nanoscopic structures. This work enables the predictive design of nanostructures from this glucose-based coil-brush polymer platform while providing a fundamental understanding of interactions within solution assembly of complex polymer building blocks.

A twin-tailed tadpole-shaped amphiphilic copolymer of poly(ethylene glycol) and cyclic poly(ε-caprolactone): synthesis, self-assembly and biomedical applications

A tadpole-shaped amphiphilic copolymer containing cyclic PCL and two PEG tails, PEG-b-(c-PCL)-b-PEG, was rationally designed and synthesized.

Dissipative particle dynamics study on self-assembled platycodin structures: the potential biocarriers for drug delivery

Platycodin, as a kind of plant based biosurfactants, are saponins which derived from the root of Platycodon grandiflorum A. DC. It has been confirmed that platycodin have the potential to enhance the solubility of hydrophobic drugs and function as the drug carrier, which depends on their micellization over critical micelle concentration (CMC) in aqueous solutions. With the purpose of investigating the effects of influencing factors on the micellization behavior of platycodin and obtaining the phase behavior details at a mesoscopic level, dissipative particle dynamics (DPD) simulations method has been adopted in this study. The simulations reveal that a rich variety of aggregates morphologies will appear with changes of structure or the concentration of saponins, including spherical, ellipse and oblate micelles and vesicles, multilamellar vesicles (MLVs), multicompartment vesicles (MCMs), tubular and necklace-like micelle. They can be formed spontaneously from a randomly generated initial state and the result has been represented in the phase diagrams. Furthermore, deeper explorations have been done on the concentration-dependent structure variation of spherical vesicles as well as the formation mechanism of MLVs. This work provides insight into the solubilization system formed by platycodin, and may serve as guidance for further development and application in pharmaceutical field of platycodin and other saponins.

Synthesis and Direct Visualization of Dumbbell-Shaped Molecular Brushes

Dumbbell-shaped triblock molecular brushes were synthesized by ring-opening metathesis polymerization (ROMP) of poly(lactide) macromonomers with terminal norbornene groups (NB-PLA) in a sequential addition manner. By changing the macromonomer size and the feed ratio of Grubbs' catalyst to macromonomer, the dimensions of the "ball" and "bar" of the dumbbell-shaped molecular brushes were controlled. The growth and production of well-defined structures were verified by gel permeation chromatography (GPC), and the final dumbbell-shaped architectures were visualized by atomic force microscopy (AFM). This synthetic methodology represents a rapid and convenient route to unique macromolecular topologies.

Amphiphilic Block-Graft Copolymers with a Degradable Backbone and Polyethylene Glycol Pendant Chains Prepared via Ring-Opening Polymerization of a Macromonomer

Well-defined amphiphilic block-graft copolymers PCL-b-[DTC-co-(MTC-mPEG)] with polyethylene glycol methyl ether pendant chains were designed and synthesized. First, monohydroxyl-terminated macroinitiators PCL-OH were prepared. Then, ring-opening copolymerization of 2,2-dimethyltrimethylene carbonate (DTC) and cyclic carbonate-terminated PEG (MTC-mPEG) macromonomer was carried out in the presence of the macroinitiator in bulk to give the target copolymers. All the polymers were characterized by (1) H NMR and gel permeation chromatography (GPC). The polymers have unimodal molecular weight distributions and moderate polydispersity indexes. The amphiphilic block-graft copolymers self-assemble in water forming stable micelle solutions with a narrow size distribution.

Synthesis and self-assembly of brush-type poly[poly(ethylene glycol)methyl ether methacrylate]-block-poly(pentafluorostyrene) amphiphilic diblock copolymers in aqueous solution

Well-defined fluorinated brush-like amphiphilic diblock copolymers of poly[poly(ethylene glycol)methyl ether methacrylate] (P(PEGMA)) and poly(pentafluorostyrene) (PPFS) have been successfully synthesized via atom transfer radical polymerization (ATRP). The self-assembly behavior of these polymers in aqueous solutions was studied using (1)H NMR, fluorescence spectrometry, static and dynamic light scattering and transmission electron microscopy techniques. The micellar structure comprised of PPFS as the core and brush-like (hydrophobic main chain and hydrophilic branches) polymers as the coronas. The hydrodynamic radius (R(h)) of the micelles in aqueous solution was in the nanometer range, independent of the polymer concentration, consistent with a closed association model. Diblock copolymers with a longer P(PEGMA) block formed micelles with smaller R(h) and lower aggregation numbers consistent with an improved solubilization of the core. The micelles possessed a thick hydration layer as verified by the ratio of the radius of gyration, R(g) to the hydrodynamic radius, R(h). The aggregation number and ratio of R(g) to R(h) were observed to increase with temperature (20-50 degrees C), while the R(h) of the micelle decreased slightly over the same temperature range. An increase in temperature induced the brush-like PEG segments in the corona to dehydrate and shrink while forming micelles with larger aggregation numbers.