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.
Well‐defined amphiphilic PLA‐b‐PMPC diblock copolymers were synthesized. Bimimetic micelles were prepared and applied for release of anti‐cancer drugs (DOX). TEM and DLS analysis revealed a regular spherical shape with small diameter (less than 50 nm) of the micelle. The biocompatibility of PLA‐b‐PMPC micelles was studied, and it was found that the micelles possessed excellent cytocompatibility due to the zwitterionic phosphorylcholine group. DOX could be efficiently loaded into the micelles with a loading efficiency of 44–67%. The DOX‐loaded micelles showed lower cytotoxicity than free drugs and efficiently delivered and released the drug into cancer cells. With these properties, the PLA‐b‐PMPC polymer micelles are attractive as drug carriers for pharmaceutical application.
Synthesis and solution morphologies of four new heteroarm star polystyrene‐block‐poly(4‐vinylpyridine) were studied. As the water content increased, a morphological transformation of heteroarm PS4‐P4VP4 from spheres to cylinders, vesicles, and large compound vesicles was observed. The morphology of PS4‐P4VP4 in the solvent mixture of DMF/water or 1,4‐dioxane/water was spherical, but changed to large compound micelles in THF/water. As the P4VP molar ratio decreased, the morphology changed from spherical mixed with cylindrical to vesicles, giant vesicles, and then to LCMs. The present study demonstrated the formation of multiple morphologies through manipulating solvent polarity and block ratio in dilute solution.
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.
Temperature‐ and pH‐sensitive diblock copolymers PAANa75‐b‐PNIPAMm are prepared by a combination of reverse and normal ATRP in aqueous solution at room temperature. The block copolymer is also stimuli‐sensitive with respect to salt in the aqueous solution, and forms spherical star‐like micelles with a PNIPAM core and an expanded PAANa shell for PAANa75‐b‐PNIPAM76 as well as spherical crew‐out micelles with a PNIPAM core for PAANa75‐b‐PNIPAM5110, as indicated by a fluorescence probe technique and TEM. A three‐stage model mechanism of phase transition driven by small molecule salt is proposed.
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.
Homopolypeptides of linear and star‐like architectures were prepared by polymerizing benzylic‐protected L ‐glutamic acid and L ‐aspartic acid N‐carboxyanhydrides (Glu NCA, Asp NCA) in DMF. The polymerization rate of the Glu NCA is faster than that of Asp NCA. Using a simple monoamino initiator, its hydrochloride, di‐, tri‐, and tetraamino functional initiators, homopolypeptides with well‐defined structures and molar masses were obtained. The molar‐mass averages of the poly(γ‐benzyl‐L ‐glutamate)s lie very close to calculated values, according to the initial [M]:[I] ratios, while those of the linear poly(β‐benzyl‐L ‐aspartate)s were lower than the predicted ones. PBAs had somewhat broader molar‐mass distributions than PBGs.
The effect of sonication on the size and structure of polymeric aggregates formed by amphiphilic block copolymers was studied by the combination of dynamic and static light scattering. Poly(ethylene oxide)‐block‐polyisoprene, poly(ethylene oxide)‐block‐polystyrene diblock copolymers, and poly(ethylene oxide)‐block‐polyisoprene‐block‐poly(ethylene oxide) triblock copolymer were used as typical polymeric amphiphiles. Sonication was found to be an effective method to break up inter‐micellar associations and split large polymeric aggregates, present initially in the aqueous solutions, into monodisperse micelles. The content and type of hydrophobic block, copolymer solution‐preparation protocol, and copolymer concentration were also investigated as co‐factors in conjunction to the effect of sonication time.
Polymerization of NVPI was carried out by a RAFT process using five xanthate‐type, a dithiocarbamate‐type, and a dithioester‐type CTA. The xanthate‐type [O‐ethyl‐S‐(1‐ethoxy carbonyl) ethyl dithiocarbonate and O‐ethyl‐S‐(1‐ethoxycarbonyl‐1‐methyl)ethyl dithiocarbonate] and the dithiocarbamate‐type CTA (benzyl‐1‐pyrrolecarbodithioate) were the most efficient to obtain poly(NVPI) with controlled molecular weights ( = 4 100–13 000) and low polydispersities ( = 1.29–1.38). The effects of parameters such as solvent, temperature, and CTA‐to‐initiator molar ratio, were examined in order to determine the conditions leading to optimal control of the polymerization.
Organic field‐effect transistors (OFETs) are a promising cost‐effective alternative to silicon‐based field‐effect transistors, and possess low‐cost, light‐weight, and flexibility advantages. Conjugated polymers based on fused‐thiophene building blocks have received considerable attention in the emerging field of organic electronics. In this review the most recent developments in conjugated polymers based on fused‐thiophene rings for high‐performance OFETs are summarized. The focus is on correlations of polymer chemical structures with properties, such as energy levels, film‐forming property, film morphology, and OFET performance. This structure–property relationship analysis may guide rational structural design and evaluation of organic semiconductors.
Oriented films of miscible polymer blends of poly(vinylidene fluoride) and poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] were prepared using a flow‐orientation technique. The lamellar structure and crystal orientation depended upon composition and flow temperature (Tflow). An interlamellar exclusion structure was induced in the blend flow‐oriented below 150 °C, whereas an interlamellar inclusion structure was developed above 150 °C. The crystal orientation of PHBHV was affected by the lamellar structures because the PHBHV chains crystallized in the pre‐existing crystalline morphology of PVDF. Crystallization of PHBHV was markedly restricted at lower PHBHV contents.
The new complex 25,27‐dipropyloxy‐26,28‐dioxocalix[4]arene titanium (IV) dichloride ( 1 ) was evaluated as an ethylene polymerization catalyst. Activation with methylalumoxane resulted in an active system producing ultrahigh‐molecular‐weight polyethylene. As expected for a Ziegler‐Natta catalyst, the polymerization reaction follows first‐order kinetics. The most striking feature of the catalytic system ( 1 /MAO) is its remarkably high thermal stability. This peculiarity probably relies on the electronic stabilization of the metal center by the two coordinating propoxy groups.
P2VN‐b‐PAA is a novel diblock copolymer which has potential as a self‐assembled nanoscale patterning material. Thin spin cast P2VN‐b‐PAA films rapidly reorganize to vertical lamellar with exposure to acetone vapor. P2VN‐b‐PAA lamellar morphology was aligned by electric field under acetone vapor at a significantly faster rate and at lower electric field strengths than other polymer systems. Observed dry etching selectivity for P2VN to PAA were comparatively high for a variety of etch gases, consistent with estimations from Ohnishi and ring parameters. Block copolymer self assembled patterns were transferred to silicon via two‐step CF4 and SF6 etching.
A new poly(3‐butylthiophene) derivative with one terminus functionalized with a 1H,1H,2H,2H,3H,3H‐perfluoroundecyl group (P3BT‐F17) is synthesized by Ni‐catalyzed quasi‐living polymerization and the subsequent quenching of living ends by allyl‐Grignard reagent and the attachment of a fluoroalkyl chain. The quantitative introduction of fluoroalkyl chain ends is confirmed by matrix‐assisted laser desorption/ionization time‐of‐flight–mass spectrometry (MALDI‐TOF‐MS), gel‐permeation chromatography (GPC), 1H NMR spectroscopy, and X‐ray photoelectron spectroscopy (XPS). The electronic properties of P3BT‐F17 in solution and its crystalline structure in the solid state are investigated by UV–vis spectroscopy and cyclic voltammetry (CV), and by DSC and X‐ray diffraction (XRD) analyses.
The PLP technique in combination with MALDI‐ToF‐MS was used to determine the Arrhenius plots for the propagation rate coefficients of THFA and ADBL, which polymerize much faster than alkyl acrylates. It is demonstrated that this is not due to higher propagation rate coefficients. It is shown that the temperature at which the PLP experiment brakes down increases in the order ADBL > THFA > alkyl acrylates, indicating a high extent of transfer to polymer for these monomers. Although kp decreases in the same order, the decrease of the corresponding overall polymerization rate is much larger. Therefore, the high polymerization rates of ADBL and THFA cannot be accounted for by fast propagation rates but more likely are linked to a low rate of termination.
The effect of inorganic salt at concentrations typical of a biological environment on the micellar morphology of semicrystalline PCL‐b‐PEO in aqueous solution is investigated. The salt is introduced either by dialysis of a THF solution against an aqueous solution of the salt or by adding it into an aqueous solution containing preformed micelles. The inorganic salt can induce sphere‐to‐rod or sphere‐to‐lamella transformations of the PCL‐b‐PEO micelles in aqueous solution, depending on the length of the PCL block. The inorganic salt induces “salting‐out” of the PEO block, leading to a decrease in the reduced tethering density of the corona in the micelles.
Cationic ring‐opening polymerization techniques are very sensitive to nucleophiles, which make it difficult to introduce different functional groups into these polymers. Clickable poly(2‐oxazoline)s were synthesized and functionalization was performed by the copper(I)‐catalyzed 1,3‐dipolar cycloaddition between alkynes and azides. Therefore, an alkyne function is introduced into the polymer backbone by utilizing alkyne toluene‐4‐sulfonates as an initiator. The polymerization kinetics were investigated for four different 2‐substituted‐2‐oxazolines and well‐defined acetylene‐functionalized poly(2‐ethyl‐2‐oxazoline)s with different lengths were synthesized having ≈100% functionality. One of these polymers was used to demonstrate its applicability in the azide‐alkyne click reaction by reaction with different azide compounds.
This paper reports a novel synthetic process to obtain poly(ethylene glycol)‐coated magnetite nanoparticles. Magnetite nanoparticles were synthesized by a chemical co‐precipitation of Fe2+ and Fe3+ ions under alkaline conditions, which were then coated with poly(ethylene glycol) diacrylate via UV‐curing in water. The nanoparticles were characterized by means of DLS, FT‐IR spectroscopy, TGA, TEM, and XPS. The magnetic properties of the magnetic nanoparticles at room temperature were also characterized by the measurement of hysteresis curves using a vibrating‐sample magnetometer.
The preparation of poly[2,6‐(1,4‐phenylene)‐benzobisimidazole] (PPBI) nanofibers was examined using the crystallization of oligomers during isothermal polymerization of self‐polymerizable 2‐(1,4‐carbophenoxyphenyl)‐5,6‐diaminobenzimidazole. The polymerization was carried out at 350 °C at a concentration of 1wt.‐% for 6 h in three kinds of solvent. The solvent influenced the morphology of PPBI precipitates significantly, and PPBI nanofiber networks were successfully formed in DBT, of which the width ranged from 30 to 110 nm. Molecules were aligned along the long axis of nanofibers. A fibrillar morphology with molecular orientation is ideal for high performance materials such as reinforcements, non‐woven fabrics and so on. The nanofiber networks exhibit the highest thermal stability.
The self‐assembly of PVPh‐b‐PS in different solvents was studied. Upon replacing toluene by THF as the solvent, the morphology of the resulting aggregates change from core‐shell spheres, rod‐like micelles and vesicles to onion‐like aggregates. With increasing block copolymer concentration, morphologies such as honeycomb‐like films, surfaces of aggregated large porous spheres, or pincushion‐like spheres with protruding tubular vesicle aggregates are observed. These surface‐patterned films show significantly enhanced hydrophobicity. The results suggest that a superhydrophobic behavior can be achieved, with a maximum contact angle of 158°, by using the pincushion‐like micellar structure.
