Amphiphilic ABCBA pentablock copolymers based on PVP, PS, and PDMS were synthesized using a combination of ATRP and RAFT polymerizations. The PVP‐block‐PS‐block‐PDMS‐block‐PS‐block‐PVP pentablock copolymer was characterized using a variety of chromatography and spectroscopic methods which showed that a high degree of end group and molecular weight control can be achieved. Preliminary analysis of the aqueous solution behavior of the pentablock copolymer showed that it self‐assembles in water in order to shield the PDMS and PS segments from the water.
A series of amphiphilic graft copolymers of poly(ethylene glycol)‐co‐glycidol‐graft‐(ε‐caprolactone) (PEG‐co‐PGL‐g‐PCL) with PEG as the hydrophilic backbone chain and hydrophobic PCL as side chains have been synthesized by living anionic polymerization and ring‐opening polymerization. By changing the composition of the PEG‐co‐PGL backbone chains, and the molar ratio of CL monomer to PEG‐co‐PGL in the feed, copolymers with well‐defined architecture and controllable numbers and length of graft chains can be obtained. The micellization and drug release of the PEG‐co‐PGL‐g‐PCL graft copolymers have been studied in terms of dependence on graft numbers and length, and the results indicate that the micelles with shorter PCL side chains have more compact cores and a relatively small size which are favorable for drug loading and controlled release.
Terpyridine‐modified hydrophobic poly(dimethylsiloxane) and hydrophilic poly(ethylene oxide) were combined to new metallo‐supramolecular AB‐diblock copolymers by utilizing Ru(II) ions. The polymers were synthesized by hydrosilylation of heteroleptic allyloxy‐functionalized Ru(II) complexes. The amphiphilic AB‐diblock copolymers were used to prepare micelles in an aqueous environment, which were subsequently characterized by dynamic light scattering and cryogenic transmission electron microscopy.
Multi‐arm poly(THF)‐b‐polyglycerol linear‐hyperbranched copolymers consisting of a linear hydrophobic poly(THF) block and a hyperbranched hydrophilic polyglycerol block were synthesized by ring opening polymerization of tetrahydrofuran with silver trifluoromethane sulfonate as a catalyst and the consecutive polymerization of glycidol. Initiators with different geometries that propagated into different numbers of arms (e.g., 1, 2 or 4) were used to investigate the dependence of the micelle properties of the copolymers on the number of arms. The critical micelle concentration (CMC) first decreased and then increased with increasing numbers of arms showing a minimum CMC at an arm number of 2. A minimum CMC was difficult to obtain using multi‐arm block copolymers composed of linear polymers with the small number of arms investigated in this study. DLS showed that the 4‐arm poly(THF)‐b‐polyglycerol copolymer had a micelle size of approximately 83 nm under aqueous conditions, and the micelle size of the copolymers with different numbers of arms was similar. Unimolecular micelles could eventually be obtained using this system by increasing the number of arms, they are considered an ideal drug delivery carrier due to the concentration‐independent stability in the blood stream.
The synthesis of a novel amphiphilic block copolymer containing a photodegradable linker as a junction point between hydrophilic and hydrophobic chains is presented. PmCL–ONB–PAA block copolymers were synthesized via a combination of ROP and ATRP from a difunctional photoresponsive initiator (ONB). The copolymers are biodegradable and biocompatible, they can self‐assemble into different structures, including micelles and vesicles which are photoresponsive. When polymer solutions were exposed to UV we observed significant changes in size and number of particles. We are currently investigating the promising potential of this system as photosensitive nanocarrier.
The amphiphilic triblock copolymer PLA‐b‐PLL‐b‐MPEG is prepared in three steps through acylation coupling between the terminal amino groups of PLA‐b‐PZLL‐NH2 and carboxyl‐terminal MPEG, followed by the deprotection of amines. The block copolymers are characterized via FT‐IR, 1H NMR, DSC, GPC, and TEM. TEM analysis shows that the triblock polymers can form polymeric micelles in aqueous solution with a homogeneous spherical morphology. The cytotoxicity assay indicates that the final triblock polymer micelles after deprotection show low cytotoxicity against Bel7402 human hepatoma cells. MPEG and PLL were introduced into the main chain of PLA affording a kind of ideal bioabsorbable polymer materials, which is expected to be useful in drug and gene delivery.
A novel approach to amphiphilic polymeric Janus micelles based on the protonation/deprotonation process of poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) (P2VP‐b‐PEO) diblock copolymers in THF is presented. It is found that addition of HCl to the micelles solution of P2VP‐b‐PEO copolymers leads to the formation of vesicles. Subsequently mixing a small amount of hydrazine monohydrate with the vesicle solution can induce the dissociation and reorganization of the vesicles into Janus micelles. When HCl is replaced by HAuCl4 precursors, composite Janus particles containing gold in P2VP blocks are obtained.
Amphiphilic poly(2‐alkyl‐2‐oxazoline) diblock copolymers of 2‐methyl‐2‐oxazoline (MOx) building the hydrophilic block and either 2‐nonyl‐2‐oxazoline (NOx) for the hydrophobic or 2‐(1H,1H′,2H,2H′‐perfluorohexyl)‐2‐oxazoline (FOx) for the fluorophilic block were synthesized by sequential living cationic polymerization. The polymer amphiphiles form core/shell micelles in aqueous solution as evidenced using small‐angle neutron scattering (SANS). Whereas the diblock copolymer micelles with a hydrophobic NOxn block are spherical, the micelles with the fluorophilic FOxn are slightly elongated, as observed by SANS and TEM. In water, the micelles with fluorophilic and lipophilic cores do not mix, but coexist.
The phase behavior of PCH‐b‐PtBA‐b‐PCH triblock copolymers has been studied. Measurements in the wide‐angle region probed the existence of microphase segregation through variation of block mobility and thermal expansion coefficients. SAXS experiments pointed out that most copolymers present ordered nanostructures, mostly hexagonally packed cylinders, the morphology being confirmed by AFM. An unusual disorder‐to‐order transition is observed in one copolymer synthesized from a macroinitiator with intermediate length and the highest outer‐block molecular weight, whereas none of the copolymers shows an order‐to‐disorder transition upon heating over the temperature range analyzed.
Isoconversional methods were applied to DSC data to determine the effective activation energy, ΔE, for the glass transition in a series of PEBN random copolymers. It was revealed that ΔE varies rather significantly throughout the process, decreasing with temperature as well as with the amount of BN units in the copolymer chain. Moreover, the dynamic fragility, m, of PEBN copolymers was evaluated. Employing the scanning rate dependency of Tg it was found that as the amount of BN units in the copolymer increases, m gets lower values denoting more strong materials, while the inverse was concluded by applying the extrapolation of configurational entropy to zero method. Results of the later method were verified by tensile mechanical property measurements of the copolymers.
Well‐defined sulfonated block copolymers were prepared by direct thermolysis with block copolymers of n‐butyl acrylate (nBA) and neopentyl styrene sulfonated (NSS), which were synthesized by Cu‐based living radical polymerization ( <1.20). A simple thermal process for 10 min at 150 °C completely deprotected the neopentyl groups in the poly(NSS) block segment to give fully sulfonated polystyrene backbone. SAXS profile of the block copolymer with 47 wt.‐% of poly(NSS) showed lamella structure, which appeared more clearly with long ranged order after sulfonation of the block copolymer.
Water soluble poly[2‐(diisopropylamino)ethyl methacrylate]‐block‐poly[2‐(dimethylamino) ethyl methacrylate]‐block‐poly[2‐(N‐morpholino)ethyl methacrylate] triblock copolymers are synthesized via group transfer polymerization. They are molecularly soluble in acidic solution but give PDPA‐core three‐layer “onion‐like” micelles in alkaline solution. They also give two types of micelles in hexane depending on whether a cosolvent is used: i) PMEMA‐core “onion‐like” reverse micelles are formed with a cosolvent, or, ii) [PDMA‐b‐PMEMA]‐core core–shell micelles without. In addition, novel shell cross‐linked micelles and reverse SCL micelles are also synthesized by cross‐linking the inner PDMA shell of both PDPA‐core micelles in water and PMEMA‐core reverse micelles in hexane.
Biodegradable supermacroporous PHEMA cryogels were produced by combining two crosslinkers, poly(ethylene glycol) diacrylate and a newly developed disulfide water soluble crosslinker, N,N′‐bis(methacryloyl)‐L ‐cystine. The biodegradable PHEMA cryogels were prepared with gel fraction yields up to 70% and were characterized by highly interconnected pores of micrometer size and good mechanical stability. When subjected to reductive agents like DTT, the biodegradable PHEMA cryogels disintegrated into small pieces. The rate of disintegration was controlled by the crosslinking density in the cryogels and the DTT concentration.
The influence of the support architecture (structure and pore size) on the activity of MAO/(nBuCp)2ZrCl2 heterogeneous catalysts in the polymerization of ethylene and 1‐hexene is studied through the characterization of the polymers' microstructure. SBA‐15 silica‐based mesostructured materials are synthesized with different pore sizes and compared with commercial silica. All SBA‐15 supported catalysts lead to higher catalytic activities than amorphous silica and give rise to ethylene/1‐hexene copolymers with bimodal CCD, which suggests that the carrier structure plays an important role not only in the global rate of the process but also in the copolymer composition. The structures and pore sizes of the support show a marked influence on the polymer CCD shape.
The syntheses of PODA‐b‐PMA and PODA‐grad‐PMA copolymers using NMP are reported for the first time. The gradient copolymerization of ODA and MA was performed in a semi‐batch system with a continuous addition of MA during ODA polymerization. The results showed that the semi‐batch NMP proceeded in a living fashion, producing well‐defined copolymers with narrow polydispersities and controlled molecular weights. The potentially semicrystalline copolymers were characterized by techniques such as 1H NMR, SEC and DSC. Their surface crystallization has also been studied by AFM.
This report describes a facile route to prepare the vesicles and large compound micelles (LCMs) from a series of poly(ε‐benzyloxycarbonyl L ‐lysine)‐block‐poly[diethylene glycol bis(3‐amino propyl) ether]‐block‐poly(ε‐benzyloxycarbonyl L ‐lysine) (PZLL‐DGBE‐PZLL) in their water solution, depending on molecular weight of the polypeptides. A pyrene probe is used to demonstrate the aggregate formation of PZLL‐DGBE‐PZLL in solution, and also to measure their critical micelle concentration as a function of molecular weight of the polymer. Transmission electron microscopy, atomic force microscopy, dynamic light scattering and confocal laser scanning microscopy are used to observe their aggregate morphologies. Rhodamine B is used as a fluorescent probe to confirm the structure of large compound micelles composed of many reverse micelles with aqueous cores. These polypeptides are prepared by ring‐opening polymerization of α‐amino acid N‐carboxyanhydrides with a small molecule as the initiator. Their structures are confirmed by NMR and SEC‐MALLS. These vesicles and large compound micelles are extremely expected to be used in drug delivery.
The micellization on surfaces of two series of quasi‐diblock copoly(2‐oxazoline)s consisting of 2‐phenyl‐2‐oxazoline (PhOx) segments linked to either 2‐methyl‐2‐oxazoline (MeOx) or 2‐ethyl‐2‐oxazoline (EtOx) segments is investigated in detail. Those micelles are not pre‐existing in the initial ethanol solution but are formed during the spin‐coating process by the evaporation of the solvent inducing the precipitation of the less soluble PhOx segments. The morphology and size of the surface micelles vary according to the fraction of PhOx in the copolymers. Moreover, it is demonstrated that the chemical nature of the more soluble MeOx or EtOx segments also has an influence on the morphology of the resulting surface micelles.
A facile approach to the preparation of functionalized polymeric nanoparticles with UV‐crosslinkable core and bromine‐bearing shell has been developed from the polymerization‐induced self‐assembly of the block copolymers PBNBE‐b‐PCONBI and PBNBE‐b‐PCONBI‐b‐PONBDM. The block copolymers were characterized by means of 1H NMR and GPC. The polymeric nanoparticles with a fixed shell length and varied core lengths were obtained through the control of the molar ratio of monomers in the feed. The micelles were crosslinked using UV‐irradiation, and the characteristics of the polymeric nanoparticles in toluene, THF, or CHCl3 before and after UV irradiation were investigated by means of DLS, UV‐Vis, GPC, AFM, and TEM.
A series of amphiphilic random copolymers with MPC as the hydrophilic segment, SMA as the hydrophobic segment and GMA as the reactive segment were synthesized. Polymeric micelles with different sizes were obtained through tuning the hydrophilic/hydrophobic segment ratios in the copolymers. The formation and properties of these micelles were investigated using 1H NMR spectroscopy, fluorescence probe techniques and DLS. The reactive polymeric micelles were crosslinked with a di‐functional reagent. The crosslinked micelles showed improved stability and thiol reactivity. Cell viability tests indicated that the bioinspired phosphorylcholine‐based micelles showed excellent biocompatibility, thus promising great potential for applications in the field of nanocarrier systems.
Six new bifunctional bis(trithiocarbonate)s were explored as RAFT agents for synthesizing amphiphilic triblock copolymers ABA and BAB, with hydrophilic “A” blocks made from N‐isopropylacrylamide and hydrophobic “B” blocks made from styrene. Whereas the extension of poly(N‐isopropylacrylamide) by styrene was not effective, polystyrene macroRAFT agents provided the block copolymers efficiently. End group analysis by 1H NMR spectroscopy supported molar mass analysis and revealed an unexpected side reaction for certain bis(trithiocarbonate)s, namely a fragmentation to simple trithiocarbonates while extruding ethylenetrithiocarbonate. The amphiphilic block copolymers with short polystyrene blocks are directly soluble in water and self‐organize into thermoresponsive micellar aggregates.
