Morphology of crystallized spherulites in poly(nonamethylene terephthalate) (PNT) in bulk forms, instead of thin‐film forms, was investigated using scanning electron microscopy (SEM), polarized‐optical microscopy (POM), and transmission electron microscopy (TEM). Ring textures were found to exist on the fractured surfaces or microtomed films from bulk PNT samples. By further SEM and TEM examinations, the fracture surfaces and microtomed films from the interior of the bulk display similar ring‐banded patterns as those in thin films cast on glass slides. Although the cast PNT thin films in two‐dimensional growth are known to display both Type‐1 ring bands as majority and Type‐2 ring bands as minority, this study further shows that the interior of PNT bulk exhibits mainly Type‐1 (single rings with narrower spacing than Type‐2) ring bands, and Type‐2 spherulites exist sporadically in three‐dimensional forms. From these analyses on the ring bands in the interiors of bulk‐form PNT crystallized at several specific temperatures, it can be proposed that the growth of spherulites in three dimensions is layer‐by‐layer, packing into a multi‐shells structure in three‐dimensional ring‐banded spheres.
The curing of a mesomorphic epoxy has been studied by polarized light microscopy (PLM) and differential scanning calorimetry. PLM in combination with wide‐angle X‐ray diffraction proves the formation of a liquid crystalline (LC) structure. An advanced isoconversional method reveals that the formation of the LC structure is accompanied by a dramatic decrease in the effective activation from ∼60 to ∼10 kJ · mol−1. A kinetic model of the phenomenon has been discussed.
The dependence of the activation energy on the extent of conversion for isothermal curing of the diglycidyl ether of 4,4′‐dihydroxybiphenyl/2,6‐diaminopyridine (diamonds) and DGEBA/2,6‐diaminopyridine (circles) systems. 相似文献
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 1H 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.
Dispersion polymerization of n‐butyl acrylate has been performed in a mixture of ethanol and water in the presence of poly(N‐acryloylmorpholine) (polyNAM). These hydrophilic polymer chains are synthesized by the RAFT process and thus incorporate well‐defined chain ends. The dithioester ω‐end group is used as an efficient chain transfer agent under dispersion polymerization conditions to produce hairy poly(n‐butyl acrylate) latex particles. Moreover, pre‐functionalization of the polyNAM chains on the α‐end by a carbohydrate derivative is also achieved to obtain directly functionalized particles according to the same strategy.
Poly(2‐alkyl‐2‐oxazoline)s can be regarded as pseudo‐peptides or bioinspired polymers, which are available through living/controlled cationic polymerization and polymer (“click”) modification procedures. Materials and solution properties may be adjusted via the nature of the side chain (hydrophilic‐hydrophobic, chiral, bio‐functional, etc.), opening the way to stimulus‐responsive materials and complex colloidal structures in aqueous environments. Herein, we give an overview over the macromolecular engineering of polyoxazolines, including the synthesis of biohybrids, and the “smart”/bioinspired aggregation behavior in solution.
Micro‐Raman spectroscopy has been used to investigate the chemical micro‐heterogeneity of multiphase‐separated poly(ether urethanes) (PETU). Analysis of PETU cross‐sections by means of micro‐Raman spectroscopy revealed the nearly complete absence of soft segments in AI aggregates (called globules). These aggregates are in the order of a few micrometers in size. The composition of the matrix and the AII aggregates (spherulites) was comparable.
Example of an AFM image (sample 706, scan size 25 μm, converted to monochromatic image). 相似文献
The proteins of eggshell membranes, an industrial waste product, are dissolved by reductive cleavage with aqueous 3‐mercaptopropionic acid and acetic acid. The soluble protein preparation is cast into a thin film, and its bioactivity is investigated by cell culture.
Photomicrograph of NIH3T3 fibroblasts cultured on SEP film for 3 days. 相似文献
Atomic force microscopy characterization has been conducted to reveal the morphological difference between single‐ring bands in poly(butylene adipate) (PBA). Furthermore, morphological features of the ring‐less Maltese‐cross spherulites are compared to the ring‐band spherulites. Periodic changes in height seem to be common for either the ring‐band or ring‐less (Maltese‐cross) crystal domains; however, the steepness in height change is greater for the ring‐band crystal, while height change in the ring‐less crystal exhibits a terrace‐like layer pattern. In the ring‐band crystal region, the lamellar stalks, which taper off to pointed needle‐like stalks, monotonously protrude out of the layers of softer materials, with no signs of twisting, bending, or turning. In contrast, all lamellae in the ring‐less (Maltese‐cross) crystal region are uniform platelets arranged like flower petals in a layered pattern.
Reactions between the ethylene groups in the backbone of conjugated polymers under UV illumination and heat treatment result in the cross‐linking of the main polymer chains. The cross‐linking leads to two simultaneous results in the polymer: excellent solvent resistance and increased bandgap. Using this reaction, three‐color polymer light‐emitting diodes (PLEDs) with a multi‐layer structure can be easily realized by a dry photo‐pattern in an active‐gas‐free environment. Multi‐layer blue devices with dramatically enhanced efficiency can also be achieved conveniently.
FTIR microspectrometry with in situ temperature variation and IR‐peak‐mapping capability, and POM characterization were used to study the crystal distribution in dual spherulites in poly(heptamethylene terephthalate). By tracing the crystalline IR bands of the α‐crystal and β‐crystal to get the crystal distribution, the techniques resolve that the ringed and ringless spherulites comprise α‐ and β‐crystals, respectively. In addition, temperature‐dependent IR analyses on the spots related to the two crystals also reveal the α‐ and β‐crystals melt at 98 and 104 °C, respectively. The ringed and ringless spherulites were proven to be correlated with the α‐ and β‐crystal forms, respectively.
A single stage electrospinning process can give rise to preferentially oriented induced dipoles in poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)] nanofibers. The piezoelectricity of as‐electrospun P(VDF‐TrFE) nanofiber webs opens up new possibilities for their use as a flexible nanogenerators and nano‐pressure sensors. In this work, the origin of the piezoelectricity has been spotlighted by randomization of the induced dipoles at the Curie temperature and analyzed by polarized FT‐IR spectroscopic techniques as well as by detecting the piezoelectric signal from a nano‐pressure sensor.
The coherent dynamic structure factor of a single polymer chain is calculated based on the model of a Rouse polymer chain constrained (confined) by a harmonic radial potential and its behavior in different limiting cases is analyzed. The strength of confinement is characterized using an effective diameter of the harmonic radial potential as a model parameter. The method provides a reliable model to study the crossover between unconstrained (Rouse) and constrained dynamics.
A functional coil–rod–coil triblock copolymer containing a terfluorene unit as the rigid segment and poly(N‐isopropylacrylamide) (PNIPAAm) as the flexible block was successfully synthesized via reversible addition–fragmentation chain‐transfer (RAFT) polymerization using terfluorene‐based dithioester as the RAFT agent. The temperature‐responsive optical properties were investigated with the aid of dynamic light scattering and fluorescence techniques. Additionally, the relationship between the optical properties and the reversible phase transition of the doping system formed by blending the copolymer with tetraphenylporphine tetrasulfonic acid was studied. Above the lower critical solution temperature, the energy transfer efficiency decreased as a result of the globule–to–coil transition from PNIPAAm segments. The result indicates that these copolymers have a potential to be used as responsive fluorescent probes in facile detection of dye‐labeled biopolymers.
Summary: A new method for the preparation of poly(ester amide)s derived from glycolic acid units has been developed. Glycolic acid units can be incorporated with a high yield into a nylon‐n or a nylon‐n,m. The synthesis is based on a final thermal polycondensation with the formation of a metal halide salt as a driving force. New poly(ester amide)s have high molecular weights, good mechanical behaviour, and variable thermal properties, giving rise to a group of materials with potential interest as biodegradable materials in applications like surgical sutures.
Results of the differential scanning calorimeter heating runs for the sodium (a) and potassium (b) salts of N‐chloroacetyl‐6‐aminohexanoic acid. 相似文献
Summary: The influence of architecture on ink‐jet printability of polymer solutions is investigated by comparing linear and 6‐arm star PMMA. At comparable concentration and molecular weight, filament formation is much more pronounced for linear PMMA than for star PMMA. Visual examination of filament stretching allows estimation of the involved elongation rates, which are at high voltages sufficiently large for coil‐stretch transition of the chains, suggesting its role in filament formation.
The results obtained in this study suggest a possible role of the coil‐stretch transition of the polymer chains in filament formation. 相似文献
The morphological evolution of poly(butylene succinate) (PBS) solution‐grown single crystals during annealing was studied using hot‐stage atomic force microscopy. Their morphology changed with increasing temperature and annealing time. The annealing behavior and melting temperature were found to be affected by the substrate. Morphological changes occurred at a much lower temperature on an amorphous carbon film than that on a mica surface. Moreover, the pattern of morphological evolution of the single crystals on a carbon film was different from that on a mica surface. Since the PBS melt had a larger contact angle on the mica surface, these differences in the melting behavior were ascribed to the different interfacial interactions between the chain‐folded surface of the single crystal and the substrate.
Recently, it has been recognized the shape of particles plays an essential role in the design of materials with unique properties. In this study, PLGA non‐spherical microarchitectures, rods and fibers, were fabricated successfully in high yield by single emulsion‐solvent evaporation method in the presence of sodium tripolyphosphate. The assay of PVA residue was carried out and the hydrogen bonds formation was verified as well. The presented data show that viscosity and coagulation agent have a synergistic effect on forming the rod‐ and fiber‐like microarchitectures in the shear response and the formation mechanisms were proposed accordingly.
A continuum model is developed to investigate the microstructure‐dependent AC properties of MWCNT/polymer nanocomposites. The AC conductivity of the composite is increased by a higher curl ratio of MWCNTs. At a critical frequency ω0, the AC conductivity switches to a frequency‐dependent region. For high MWCNT content, the curl curliness of MWCNTs has only a weak influence on the AC conductivity. For medium MWCNT content, the AC conductivity became frequency‐dependent for low frequencies with decreasing curl ratio of MWCNTs, which cannot be explained by correlation length theory. An interpretation based on the linear circuit theory is given. With increasing size of MWCNT clusters, the critical frequency ω0 increases. It is also affected significantly by the crystallinity the polymer.
