Multi‐walled carbon nanotubes (MWNT) were oxidized with nitric acid and resulting carboxy groups were transformed to amino groups with a diamine under microwave irradiation. Grafting of bisphenol‐A‐polycarbonate onto carboxy‐ and amino‐functional MWNT through transesterification or aminolysis resulted in weight increase up to 300%. The morphology of functionalized and grafted MWNTs was investigated with scanning force microscopy (SFM) and transmission electron microscopy (TEM). Depending on the type of functionalisation and the extent of grafting different morphologies were observed. Aminofunctional MWNT‐g‐PCs showed more “ball‐like” or irregular protrusions of grafted PC. Carboxyfunctional MWNT‐g‐PCs were more smoothly covered with PC.
The crystalline structure and crystallization behavior of PLLA crystals in a 1:1 w/w mixture of low‐MW PLLA with high‐MW PDLA were analyzed using WAXD, DSC, and SAXS. Under cold crystallization, homopolymeric PLLA, appearing as a meta crystal, was discovered in the PDLA/LMW‐PLLA blend. The meta‐ and α′ crystal forms of PLLA were found to form on crystallization at a Tcc of 85–95 °C and the α crystal PLLA formed at 100 ≤ Tcc < 120 °C. The meta‐crystal PLLA may be incorporated in the stereocomplexed PDLA/LMW‐PLLA lamellar region. During heating, the meta‐crystal PLLA first partially melted and then repacked directly into the α crystal PLLA without going through the less‐stable α′ form.
Biocompatible hyperbranched polyglycerol (HPG) has been covalently grafted from the surfaces of multiwalled carbon nanotubes (MWNTs) by the “grafting from” method based on in situ anionic ring‐opening polymerization. The macroinitiator of hydroxyl‐functionalized MWNTs (MWNT‐OH) with hydroxyl density of 1.39 mmol per gram of nanotubes was prepared by one‐pot nitrene chemistry in N‐methyl‐2‐pyrrolidone (NMP) at 160 °C for 12 h. The amount of HPG grafted from MWNTs can be readily adjusted in a wide range up to 90.8wt.‐% by tuning the feed ratio of glycidol to MWNT‐OH. The resulting HPG‐grafted MWNTs (MWNT‐g‐HPG) nanohybrids were characterized by TGA, FT‐IR, and NMR spectroscopy, HRTEM, and SEM. The as‐prepared nanohybrids show good dispersibility in polar solvents such as water, DMF, DMSO, and methanol. On the basis of numerous functional hydroxyl groups of the HPG grown on MWNTs, fluorescent molecules of rhodamine 6B were conjugated to the surface of MWNT‐g‐HPG by N, N′‐dicyclohexylcarbodiimide (DCC) coupling, affording fluorescent MWNTs. The multifunctional MWNT‐g‐HPG nanohybrids promise potential applications in drug delivery, cell imaging and bioprobing.
An in situ dispersion polymerization method was adopted to synthesize particulate composites of MWNTs and PMMA, mainly for the investigation of their electrorheological characteristics. The morphology of the PMMA microparticles synthesized in the presence of the MWNTs was examined by both SEM and TEM, showing that the MWNTs were not only grafted onto the surface of the PMMA microbeads, but were also embedded inside the synthesized microbeads. The synthesized MWNT/PMMA particulate composites were also characterized by zeta‐potential measurements and TGA for electric and thermal stability studies, respectively. A suspension of the MWNT/PMMA microparticles dispersed in silicone oil was found to show enhanced electrorheological properties on the increase of shear stresses when subjected to an external electric field, exhibiting high yield stresses despite the tiny amount of the MWNT associated.
Ultra‐fine fiber mats of poly(L ‐lactic acid) containing gallic acid were prepared by electrospinning from gallic acid‐containing PLLA solution in 7:3 v/v dichloromethane (DCM)/N,N‐dimethylformamide (DMF). The amount of the as‐loaded gallic acid was 40% w/w (based on the weight of PLLA in the solution) or 28.6 wt.‐% (based on the weight of the resulting fiber mats). Both the neat and the gallic acid‐loaded PLLA fibers were smooth, with the average diameters of 965 and 843 nm, respectively. No aggregates of gallic acid were observed on the fiber surface and the actual amount of gallic acid in the gallic acid‐loaded PLLA fiber mats, determined in the acetate buffer, the citrate‐phosphate buffer, and the normal saline, was 26.3, 27.1, and 24.6 wt.‐%. The cumulative amount of gallic acid released from the gallic acid‐loaded PLLA fiber mats was greatest in the normal saline, followed by those in the citrate‐phosphate and the acetate buffer, respectively. Lastly, the free radical scavenging activity, based on the 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) assay, of the as‐loaded and the as‐released gallic acid remained active.
PLLA/PDLA blends were crystallized between 120 and 195 °C. The stereocomplex spherulites acquired in equimolar and non‐equimolar blends were compared using POM, WAXD, DSC, and AFM. For equimolar blends, stereocomplex crystals show spherulites with positive birefringence, which is ascribed to the existence of domains made up of tangentially oriented lamellae. For PLLA‐rich (or PDLA‐rich) blends, the signs of the birefringence changed from a positive spherulite to a mixed spherulite and then to a negative spherulite. In negative spherulites, most lamellae orient radially. Radial and tangential cracks were observed in equimolar blends when crystallization took place above 175 °C whereas no cracks formed for non‐equimolar blends.
Well‐defined six‐armed star poly(L ‐lactic acid) (PLLA) with a triphenylene core has been prepared by ring‐opening polymerization of L ‐lactide. As a result of strong π–π interactions between the triphenylene core and the multi‐walled carbon nanotubes (MWCNTs), the polymer was conveniently immobilized on the surface of the as‐received MWCNTs by a simple ultrasonic process while the intrinsic graphitic structure of the pristine MWCNTs is retained. The non‐covalent interaction between the carbon nanotubes and the polymer has been proven by the UV‐vis absorption spectra, the fluorescence spectra, the Raman spectra, and the X‐ray photoelectron spectra.
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.
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.
Novel homoarm and heteroarm star‐shaped inorganic–organic hybrid polymers with a polyhedral oligomeric silsesquioxane (POSS) core are prepared via click chemistry of azide POSS [POSS‐(N3)8], alkynyl poly(L ‐lactide) (PLLA), and alkynyl poly(ethylene oxide) (PEO). The melting and crystallization behaviors of the polymers can be adjusted by altering the PLLA to PEO ratio. The hybrid polymers reveal unique crystalline morphology due to the influence of the star‐shaped structure and the mutual influence of PLLA and PEO. The hybrid polymers show different thermostabilities, owing to the different compositions of the polymers. The hydrophilicity can be adjusted by alternating the composition of the PLLA and PEO segments. In addition, the sizes of the polymer micelles change with the change of the ratio of PLLA and PEO arms in the hybrid polymers.
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.
Equal amounts of poly(L ‐lactide) (PLLA) and poly(D ‐lactide) (PDLA) were mixed with diphenyl ether (DE) at high temperature in DE‐to‐polymer composition from 0 to 80 wt.‐%. Cooling of the ternary mixtures produced white crystallosolvates without deposition of DE. Various analyses revealed that the crystallosolvates consisted of both homo‐chiral (hc) and stereocomplex (sc) crystals of PLLA and PDLA as well as amorphous domains involving DE. The crystallosolvate obtained at a DE content of 80 wt.‐%, comprised only the sc crystals. Atomic force microscopy (AFM) revealed that many granules having a size of 20 nm in diameter were formed from rod‐like hc crystallites and that the DE was slightly phase‐separated to form nano‐sized reservoirs. The stronger sc interaction between the PLLA and PDLA chains excluded DE from the polymer matrix.
The synthesis, thermal, and photoluminescence properties of novel platinum metallopolyynes of electron‐deficient acridone derivatives with electronically tunable bandgaps and their molecular model complexes are described. Polymer P2 has an optical bandgap (Eg) of 2.10 eV which is much lowered than that of P1 (2.60 eV). The incorporation of electron‐accepting dicyanomethylene units on the acridone ring in the main chain creates a strong π‐conjugated system that features unique donor‐acceptor interactions and intramolecular charge‐transfer states.
A novel tertiary amine and amino acid‐based “schizophrenic” pH‐responsive block copolymer, PDEA‐b‐PAP, has been synthesized by RAFT polymerization. By directly dissolving this copolymer in acid or basic aqueous solution block copolymer vesicles with switchable coronas and membranes were prepared. These novel assemblies were characterized using TEM, DLS, zeta potential, and SLS analysis.
Furan‐terminated poly(oxyethylene)‐block‐poly(L‐lactide) (MePEG‐PLLA‐F) and poly(oxyethylene)‐block‐poly(D‐lactide) (MePEG‐PDLA‐F) are synthesized by ring‐opening polymerization of L‐ and D‐lactides, respectively, in the presence of poly(ethylene glycol) monomethyl ether (MePEG) and the following terminal reaction with furfuryl isocyanate. Their mixed micelle solution turns to gel quickly with stereocomplexation of the enantiomeric PLLA and PDLA. When 1,8‐bis(maleimido)diethylene glycol (BMG) is added to the mixed micelle solution, the gelation is promoted by the terminal coupling of the copolymers driven by the Diels–Alder reaction of the furanyl groups and BMG giving a gel having higher strength.
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.
A stereo diblock polylactide di‐sb‐PLA consisting of PDLA and PLLA in a block ratio of 2:8 was prepared and mixed with PDLA to investigate the effect of enantiomer adjustment on the sc crystallinity. Each of these polymer blends was found to have improved stereocomplexibility which was changed with the PDLA compositions in the di‐sb‐PLA/PDLA blend systems. It was also revealed that melt blending is more highly efficient than solution blending in terms of enhancing the sc crystallinity. The blend samples prepared by the former process were found to retain high loss modulus above Tg as well as heat‐stability up to Tm (215 °C) of di‐sb‐PLA. These data hold promise for interesting applications of di‐sb‐PLA and its polymer blends as high‐performance bio‐based materials.
Graft copolyesters with a PCL backbone and PLLA side chains were successfully prepared in three steps avoiding transesterification. First ε‐caprolactone was polymerised with 1,6‐hexane diol as initiator to obtain hydroxytelechelic oligo(ε‐caprolactone)s. These diols were then subjected—in the second step—to polycondensation with L ‐malic acid yielding in linear poly[oligo(ε‐caprolactone)L ‐malate] having secondary hydroxyl functions in the side chain. For both reactions scandium triflate Sc(OTf)3 was used as a catalyst. In the third step various amounts of L ‐lactide were grafted from the polymer backbone using Zn(oct)2 as catalyst. The successful reaction was confirmed by NMR and SEC (size exclusion chromatography) analysis. Further the thermal properties of the graft copolymers with different graft lengths were determined via differential scanning calorimetry.
A series of optically inactive polythiophene derivatives bearing the azobenzene moiety are synthesized in an isotropic toluene solution. The polymers are then dissolved in a cholesteric liquid crystal (Ch*LC) medium within the liquid crystal (LC) temperature range. The dissolution process in Ch*LC produces intermolecular π‐stacking with structural chirality. Although the polymers thus prepared have no chiral center or axial chirality in the primary structure, they do exhibit consistent chiroptical activity derived from three‐dimensional chiral aggregations. Furthermore, photochemical cis–trans isomerization of the substituents allows light‐driven chiroptic modulation of the polymer.
A nonconjugated N‐vinyl monomer, N‐vinylphthalimide (NVPI), was copolymerized with various comonomers via reversible addition‐fragmentation chain transfer (RAFT) process. Two different chain transfer agents (CTAs), O‐ethyl‐S‐(1‐ethoxycarbonyl) ethyldithiocarbonate (CTA 1) and benzyl 1‐pyrrolecarbodithioate (CTA 2), were compared for these copolymerizations with 2,2′‐azobis(isobutyronitrile) as an initiator. The effects of the nature of CTA, the comonomer structure, and solvent on the copolymerization were investigated in terms of the controlled character of the copolymerization and alternating structure. The copolymerization of NVPI and N‐isopropylacrylamide using CTA 2 in DMF or MeOH afforded well‐defined copolymers with predominantly alternating structure, controlled molecular weights, and low molecular mass distributions.
