We report the synthesis of a novel pH‐responsive amphiphilic block copolymer poly(dimethylaminoethyl methacrylate)‐block‐poly(pentafluorostyrene) (PDMAEMA‐b‐PPFS) using RAFT‐mediated living radical polymerization. Copolymer micelle formation, in aqueous solution, was investigated using fluorescence spectroscopy, static and dynamic light scattering (SLS and DLS), and transmission electron microscopy (TEM). DLS and SLS measurements revealed that the diblock copolymers form spherical micelles with large aggregation numbers, Nagg ≈ 30 where the dense PPFS core is surrounded by dangling PDMAEMA chains as the micelle corona. The hydrodynamic radii, Rh of these micelles is large, at pH 2–5 as the protonated PDMAEMA segments swell the micelle corona. Above pH 5, the PDMAEMA segments are gradually deprotonated, resulting in a lower osmotic pressure and enhanced hydrophobicity within the micelle, thus decreasing the Rh. However, the radius of gyration, Rg remains independent of pH as the dense PPFS cores predominate.
Well‐defined diblock copolymers, poly(ethylene glycol)‐block‐poly(glycidyl methacrylate)s (PEG‐b‐PGMAs), with different poly(glycidyl methacrylate) (PGMA) chains, were prepared via atom transfer radical polymerization (ATRP) from the same macromolecular initiator 2‐bromoisobutyryl‐terminated poly(ethylene glycol) (PEG). Ethyldiamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), and polyethyleneimine (PEI) with an of 400 (PEI400) were used to decorate PEG‐b‐PGMAs to get the cationic polymers PEG‐b‐PGMA‐ oligoamines. These cationic polymers possessed high buffer capability and could condense plasmid DNA (pDNA) into nanoscaled complexes of 125–530 nm. These complexes showed the positive zeta potential of 20–35 mV at N/P ratios of 10–50. Most of them exhibited very low cytotoxicity and good transfection efficiency in 293T cells. The presence of the serum medium did not decrease the transfection efficiency due to the steric stabilization of the PEG chains.
This paper aims to report the fabrication of biodegradable thin films with micro‐domains of cylindrical nanochannels through the solvent‐induced microphase separation of poly(L ‐lactide)‐block‐poly(ethylene glycol)‐block‐poly(L ‐lactide) (PLA‐b‐PEG‐b‐PLA) triblock copolymers with different block ratios. In our experimental scope, an increase in each of the block lengths of the PLA and PEG blocks led to both a variation in the average number density (146 to 32 per 100 µm2) and the size of the micro‐domains (140 to 427 nm). Analyses by atomic force microscopy (AFM) and fluorescence microscopy indicated that the hydrophilic PEG nanochannels were dispersed in the PLA matrix of the PLA‐b‐PEG‐b‐PLA films. We demonstrated that the micro‐domain morphology could be controlled not only by the block length of PEG, but also by the solvent evaporation conditions.
Summary: Amphiphilic triblock copolymers (PEOx‐b‐PDMSy‐b‐PEOx) with different block lengths were synthesized and multi‐morphological complex crew‐cut, star‐like, and short‐chain aggregates were prepared by self‐assembly of the given copolymers. The morphologies and dimensions of the aggregates can be well controlled by variation of the preparation conditions. TEM, SEM, FFR‐TEM, and LLS studies show the resulting morphologies range from LCMs, unilamellar or multilayer vesicles, LCVs, porous spheres to nanorods.
TEM images of the vesicles formed from PEO‐b‐PDMS‐b‐PEO. 相似文献
Summary: Tetraaniline‐block‐poly(L ‐lactide) diblock oligomers are synthesized via ring‐opening polymerization. The diblock oligomers cast from an L ‐lactide selective solvent (chloroform) show spherical aggregates for the leucoemeraldine state, and ring‐like structures that are composed of much smaller spherical aggregates for the emeraldine state. The formation mechanisms of the two different surface morphologies are discussed in detail.
Surface morphology changes induced by oxidation of the aniline segment of tetraaniline‐block‐poly(L ‐lactate) and drying effects. 相似文献
Summary: Plasma‐initiated controlled/living radical polymerization of methyl methacrylate (MMA) was carried out in the presence of 2‐cyanoprop‐2‐yl 1‐dithionaphthalate. Well‐defined poly(methyl methacrylate) (PMMA), with a narrow polydispersity, could be synthesized. The polymerization is proposed to occur via a RAFT mechanism. Chain‐extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA‐block‐PSt copolymer.
Dependence of ln([M]0/[M]) on post‐polymerization time (above), and \overline M _{\rm n} and PDI against conversion (below) for plasma initiated RAFT polymerization of MMA at 25 °C. 相似文献
Well‐defined diblock copolymers composed of poly(N‐octylbenzamide) and polystyrene were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization of styrene with a polyamide chain transfer agent (CTA) prepared via chain‐growth condensation polymerization. Synthesis of a dithioester‐type macro‐CTA possessing the polyamide segment as an activating group was unsatisfactory due to side reactions and incomplete introduction of the benzyl dithiocarbonyl unit. On the other hand, a dithiobenzoate‐CTA containing poly(N‐octylbenzamide) as a radical leaving group was easily synthesized, and the RAFT polymerization of styrene with this CTA afforded poly(N‐octylbenzamide)‐block‐polystyrene with controlled molecular weight and narrow polydispersity.
A PFS/PLA block copolymer was studied to probe the effect of strong surface interactions on pattern formation in PFS block copolymer thin films. Successful synthesis of PFS‐b‐PLA was demonstrated. Thin films of these polymers show phase separation to form PFS microdomains in a PLA matrix, and ultrathin films (<5 nm) formed SINPATs on silicon and mica. The SINPATs consisted of strongly surface‐adsorbed PLA blocks on top of which the PFS blocks dewetted into sphere‐like features. The lateral spacing between these features was regular, and was typically much larger than the length scale associated with regular block copolymer phase separation.
Well‐defined PEO‐b‐PMMA was prepared, initiated by macroinitiator PEO‐Br, by means of ATRP, where esterification of the terminal hydroxyl group of PEO with 2‐bromoisobutyryl bromide yielded a macroinitiator PEO‐Br. Highly ordered microporous films (hexagonal pattern) were constructed by emulsion micelles of such amphiphilic diblock copolymer formed from a solution with CHCl3/H2O/THF = 100:5:10 (v/v). We also constructed the microporous films using diblock copolymer by the current water‐assisted method.
Ferrocenylmethyl methacrylate (FMMA) is one of the very few metallocene‐based monomers that are promising candidates for truly living anionic polymerization. Nevertheless, FMMA homopolymers with a narrow polydispersity, or block copolymerization studies that result in satisfying blocking efficiencies, are unknown so far. Here we describe a procedure that leads to highly regular FMMA‐based polymers for the first time, characterized by polydispersity indices (PDI) of less that 1.05 and very high blocking efficiencies (>95%) in sequential copolymerization with styrene. Some of the obtained poly[styrene‐block‐(ferrocenylmethyl methacrylate)]s show unusual microphase morphologies, presumably the consequence of high Tgs causing ‘frustrated’ non‐equilibrium states.
In this communication, polyanionic poly(potassium 3‐sulfopropyl methacrylate) (PSPM) brushes were switched from hydrophilic to hydrophobic by exchange of the counter cations. First, poly(potassium 3‐sulfopropyl methacrylate) brushes were grown by means of atom transfer radical polymerization (ATRP) from thiol monolayers of initiating ω‐mercaptoundecyl bromoisobutyrate and mixed monolayers of thiol initiator and 1‐undecanothiol (blank thiol) attached to gold surfaces. The kinetics of the polymerization reaction were followed by means of the quartz microbalance technique with dissipation (QCM‐D). The collapse of PSPM brushes in the presence of cationic surfactants like quaternary ammonium salts (tetraethylammonium bromide, hexadecyltrimethylammonium bromide) and imidazolium salts (1‐dodecyl‐3‐methylimidazolium bromide, 1H,1H,2H,2H‐perfluoro‐1‐decyl‐3‐methylimidazolium bromide) was shown by QCM‐D. Water contact angle measurements proved that the wettability of the surface could be tuned reversibly from hydrophilic values (<30 °) to hydrophobic ones (>85 °).
The use of a bisaminooxy compound as initiator for nitroxide‐mediated radical polymerization (NMRP) of styrene or n‐butyl acrylate allows the synthesis of α,ω‐nitroxide‐capped polymers. At high temperatures and with the addition of acetic anhydride, it was found that these polymers could be applied as macroinitiators in the free‐radical polymerization of methyl methacrylate. This enables the synthesis of block copolymers with only minor contents of homopolymer.
The structure of bis‐TIPNO, the bisaminooxy compound used as an initiator for the nitroxide‐mediated radical polymerization of styrene or n‐butyl acrylate. 相似文献
We report first results on the controlled radical polymerization of 2,3‐epithiopropyl methacrylate (ETMA) also known as thiiran‐2‐ylmethyl methacrylate. Reversible addition‐fragmentation chain transfer (RAFT) of ETMA was carried out in bulk and in solution, using AIBN as initiator and the chain transfer agents: cyanopropyl dithiobenzoate (CPDB) and cumyl dithiobenzoate (CDB). A linear increase of the number‐average molecular weight and decrease of the polydispersity with monomer conversion were observed using CPDB as transfer agent, indicating a controlled process. Atom transfer radical polymerization (ATRP) of ETMA was performed under different reaction conditions using copper bromide complexed by tertiary amine ligands and ethyl 2‐bromoisobutyrate (EBiB) or 2‐bromopropionitrile (BPN) as initiator. All experiments lead to a crosslinked polymer. Preliminary studies in the absence of initiator showed that the CuBr/ligand complex alone initiates the ring‐opening polymerization of thiirane leading to a poly(propylene sulfide) with pendant methacrylate groups.
Novel poly(2‐(3‐sulfo)benzoyl‐1,4‐phenylene)‐block‐polynaphthalimide (PSP‐b‐PI) copolymers were successfully synthesized by Ni(0)‐catalyzed copolymerization of 2,5‐dichloro‐3′‐sulfo‐benzophenone and dichloro‐terminated naphthalimide oligomer. The membranes exhibited a microphase‐separated structure and good hydrolytic stability at 130 °C. They showed a fairly strong anisotropy of membrane swelling with much smaller in‐plane swelling, but a rather weak anisotropy of proton conductivity. The membranes had a fairly high through‐plane conductivity in water and even under low relative humidity. The PSP‐b‐PI copolymer with an IEC of 1.5 meq · g−1 showed high PEFC performance due to the high through‐plane conductivity.
Novel luminescent electrospun (ES) fibers have been successfully prepared from a conjugated rod–coil block copolymer, poly[2,7‐(9,9‐dihexylfluorene)]‐block‐poly(methyl methacrylate) (PF‐b‐PMMA) using a single‐capillary spinneret. Experiment results indicate that PF‐b‐PMMA ES fibers prepared from THF, THF/DMF (50/50), and DMF contain PF block aggregated structures of dot‐like (5–10 nm), line‐like (10–20 nm), and ellipse‐like structure (25–50 nm), respectively. Such variation of aggregation size leads to a red‐shift of the absorption or luminescence spectra. In addition, the fiber diameters decrease upon enhancing the DMF content. The present study demonstrates that blue light‐emitting ES fibers are successfully prepared from conjugated rod–coil diblock copolymers and their aggregate morphology and photophysical properties could be tuned through use of selective solvent.
A clickable alkyne monomer, PgMA, was successfully polymerized in a well‐controlled manner via single electron transfer initiation and propagation through the radical addition fragmentation chain transfer (SET‐RAFT) method. The living nature of the polymerization was confirmed by the first‐order kinetic plots, the linear relationships between molecular weights and the monomer conversions while keeping relatively narrow (≤1.55), and the successful chain‐extension with MMA. The better controllability of SET‐RAFT than other CRP methods is attributed to the less competitive termination in view of the presence of the CTA as well as the Cu(II) that is generated in situ. Moreover, a one‐pot/one‐step technique combining SET‐RAFT and “click chemistry” methods has been successfully employed to prepare the side‐chain functionalized polymers.
New multifunctional copoly(2‐oxazoline) nanoparticles were prepared for cell studies. The polymer contains double‐bond side chains as potential reaction sites for “thio”‐click reactions as well as a fluorescein label covalently bound to the polymer backbone. Using the nanoprecipitation technique, spherical nanoparticles of 200–800 nm were obtained. Confocal laser scanning microscopy measurements revealed the cellular uptake of the nanoparticles.
Summary: Nitroxide‐mediated dispersion polymerization of styrene in supercritical carbon dioxide has been performed successfully at 110 °C using a new polymeric so‐called inistab species, which fulfils the dual functions of an initiator and a colloidal stabilizer. The inistab species comprised a poly(dimethylsiloxane) block and a polystyrene block end‐capped with the nitroxide N‐tert‐N‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] nitroxide (SG1). The dispersion polymerization resulted in sub‐micron sized polymer particles and polymers of narrow polydispersity.
TEM micrograph of PS particles prepared in the dispersion polymerization of S in scCO2 in the presence of PDMS(\overline M _{\rm n} = 6 500)‐b‐PS(\overline M _{\rm n} = 4 500)‐SG1 at 110 °C. 相似文献
The use of the reversible addition fragmentation chain transfer—hetero Diels–Alder (RAFT‐HDA) click reaction for the modular construction of block copolymers is extended to the generation of high molecular weight materials. Cyclopentadienyl end‐functionalized polystyrene (PS‐Cp) prepared via both atom transfer radical polymerization (ATRP) and the RAFT process are conjugated to poly(isobornyl acrylate) (PiBoA) (also prepared via RAFT polymerization) to achieve well‐defined block copolymers with molecular weights ranging from 34 000 to over 100 000 g · mol−1 and with small polydispersities (PDI < 1.2). The conjugation reactions proceeded in a very rapid fashion (less than 10 min in the majority of cases) under ambient conditions of temperature and atmosphere. The present study demonstrates—for the first time—that RAFT‐HDA click chemistry can provide access to high molecular weight block copolymers in a simple and straight‐forward fashion.
A novel approach is employed to produce core–corona nanospheres, which introduces a stereoregular hydrophilic part to an amphiphilic block copolymer. The resultant morphology is reported using isotactic‐poly(methacrylic acid)‐block‐poly(butyl acrylate). Infrared spectroscopy revealed a supramolecular interaction, and X ray diffraction revealed the crystallization of the outer isotactic‐poly(methacrylic acid) part. The nanostructure, which looks like a nanosized ‘grape’, was formed when nanospheres and nanofibers coexisted simultaneously and partially fused.
