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 well‐defined, high‐density poly(N‐isopropylacrylamide) (PNIPAM) brush was fabricated through a novel and reliable strategy by the combination of the self‐assembly of a monolayer of dendritic photoinitiator and surface‐initiated photopolymerization. The whole fabrication process of the PNIPAM brush was followed by water contact angles, X‐ray photoelectron spectroscopy, and atomic force microscopy. Characterization of the PNIPAM brush, such as molecular weight and thickness determination, were measured by gel permeation chromatography, and ellipsometry, and the graft density was estimated. The temperature response of the PNIPAM brush was further investigated and the result verified the coil‐to‐globule transition of the PNIPAM chains in water from low to high temperature.
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 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.
The formation of complexes between Cu2+ ions and graft copolymers built from a PANa backbone and non‐ionic hydrophilic PDMAM side chains is investigated by means of turbidimetry, viscometry, DLS, ζ‐potential measurements, and UV‐vis spectrophotometry. The macroscopic phase separation which accompanies complexation is gradually depressed with increasing PDMAM content x, and water‐soluble complexes are formed for x = 70 mol‐%. The polymer/Cu2+ complexation is a charge neutralization process that leads to the formation of water‐soluble, compact, hybrid polymer/metal ion nanostructures. UV‐vis data indicate that this graft copolymer could possibly serve as a water‐soluble sensor for Cu2+ ions.
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.
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.
Isothermal crystallization of the poly(ferrocenyl dimethylsilane) (PFDMS) segments in a poly[styrene‐block‐(ferrocenyl dimethylsilane)] (PS‐b‐PFDMS) diblock copolymer of lamellar micro‐morphology has been investigated. The PFDMS is shown to crystallize in a confined and grain‐by‐grain fashion. Here a ‘grain’ is defined as an ensemble of stacked lamellae wherein the PFDMS crystallization spreads quickly but stops at its surroundings. Such crystallization propagates not only along the PFDMS lamellae but across the amorphous PS layers as well. We suggest that conformational changes in the PS as induced by the PFDMS crystallization (‘squeezing transfer’) are responsible for the latter pathway of the crystallization's spread.
Three polymers of pharmaceutical/medical relevance are synthesized: poly(glycidol) (PG), poly(glycidol)‐g‐L ‐lactide (PG‐g‐La), and poly(glycidol)‐g‐glycolide (PG‐g‐Gly). Because the thermal stability of these polymers is an essential factor of their processing and practical application, the study focuses on kinetic and mechanistic aspects of non‐oxidative thermal degradation. The study is conducted by combining thermogravimetry, Fourier transform infrared spectroscopy, and isoconversional kinetic analysis. It is found that PG degrades in a single mass loss step, whereas, PG‐g‐La and PG‐g‐Gly in two. It is demonstrated that the first step in degradation of PG‐g‐La and PG‐g‐Gly is associated with decomposition of the pendant groups and the second is due to degradation of the PG backbone.
Star‐shaped, star‐block‐linear, and hyperbranched poly(1,3‐cyclohexadiene) (PCHD) (co)polymers were synthesized through a convergent living anionic polymerization process or via addition of divinylbenzene. Chemical modification of star‐shaped PCHDs, including aromatization, hydrogenation, fluorination, and sulfonation, was carried out in order to manipulate the physical and thermal properties of these materials. The obtained (co)polymers were characterized by gel permeation chromatography, 1H NMR, DSC, and thermal gravimetric analysis in order to elucidate their molecular weights, molecular weight distributions, chemical nature, and physical and thermal properties. The synthetic approaches described herein offer routes to novel structure and functionality in PCHD‐based materials.
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.
Biocomposite PP‐g‐PAAc‐CS films based on PP were generated and utilized as support of methylene blue, a thiazidic dye. Using a photograft polymerization of acrylic acid, the PP film was functionalized with carboxyl groups (PP‐g‐PAAc), which attached chitosan by electrostatic bond. A longer poly(acrylic acid) chain or a higher CS immobilization temperature led to a higher chain interpenetration and crosslinking reaction. Immobilized MB confirmed to possess redox activity from its reaction with ascorbic acid, where the dye decomposition rate ( ) increases together with the chain interpenetration, then decreasing with the increase in the crosslinking degree.
PPP derivatives with high molecular weights were synthesized and characterized by FT‐IR, 1H, 13C NMR and GPC. The decomposition temperatures of 2a–2c were above 300–400 °C. DSC analysis indicated their nature to be crystalline as all of them exhibited a melt temperature on controlled heating. Optical and electrochemical band gaps was determined using UV/Vis spectroscopy and CV. Single‐layer PLEDs fabricated with 2a–2c displayed high threshold voltages due to high potential barrier for holes. Their EL spectra reveal a small shift in blue peak and the emission form higher wavelength shoulder peak is enhanced.
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.
MWs are explored as the driving force for an SMP based on chemically crosslinked moist PVA networks. The samples show rapid shape recovery under MW irradiation, whereas dry samples experience no shape changes when irradiated. This effect is attributed to the heat created by vibrating water molecules inside the samples that supplies the energy required for shape recovery. The rate of recovery rate is affected not only by the water content in the material but also by the applied MW power output. Automatic network analysis, DSC, and DMA are used to study the dielectric, thermal and mechanical properties of the samples. MW‐induced shape recovery offers advantages such as high and variable recovery rate and the absence of direct contact between the heating source and the material.
The molecular characteristics of poly(N‐isopropylacrylamide) (PNIPA), prepared by free‐radical polymerization using an aqueous redox initiator and reaction conditions comparable to those used in the synthesis of nanocomposite gels, were investigated by altering the monomer concentration ([NIPA]) and the polymerization temperature (Tp) across the transition temperature (LCST). When Tp<LCST, there is a critical [NIPA] (=n*) above which PNIPA partially forms gels in the absence of a chemical crosslinker, and the gel fraction increases with increasing [NIPA] and decreasing Tp. In the range of n<n*, the molecular weight of soluble PNIPA correlated well with [NIPA]. When Tp>LCST, gels were not formed regardless of [NIPA]. The structure and mechanism of formation of self‐crosslinked PNIPA gels are discussed.
Graft‐type anion‐conducting polymer electrolyte membranes (AEMs) are prepared by the radiation‐induced graft polymerization of chloromethylstyrene into poly(ethylene‐co‐tetrafluoroethylene) (ETFE) films and subsequent quaternization with trimethylamine. AEMs in the hydroxide form (AEM‐OH) are prepared by immersing the chloride form (AEM‐Cl) in 1 M potassium hydroxide (KOH) solution, followed by KOH and washing with nitrogen‐saturated water to prevent bicarbonate formation (AEM‐HCO3). The AEM‐OH shows conductivity and water uptake four and two times higher than AEM‐Cl and ‐HCO3 and is thermally and chemically less stable, resulting in the tendency to absorb water and to convert to the bicarbonate form.
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.
A series of supramolecular degradable inclusion complex (IC) films were formed by threading α‐cyclodextrin (α‐CD) molecules over poly(ε‐caprolactone) (PCL) according to the designed ratio of α‐CD–PCL. Due to containing both α‐CD–PCL inclusion crystallites and uncovered PCL crystallites, the resulting supramolecular α‐CD–PCL IC partial films displayed a shape memory effect. The properties of the materials were investigated by 1H NMR, X‐ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and swelling measurement. It was found that the casting temperature and solvent have great influence on the formation and properties of the α‐CD–PCL partial ICs. The modes of complexes on different conditions were proposed. In addition, the introduction of inclusion structure accelerates the degradation of materials strongly.
The possibility of introducing hydrolytically cleavable ester linkages onto the poly(N,N‐dimethylaminoethyl methacrylate) for the formation of less toxic and degradable polycations is shown in this work. For achieving this aim, the copolymerization behavior of 5,6‐benzo‐2‐methylene‐1,3‐dioxepane (BMDO), with N,N‐dimethylaminoethyl methacrylate (DMAEMA) is studied by free radical ring‐opening polymerization. Structural characterization is performed using 1D and 2D NMR techniques. Under optimized reaction conditions, quantitative ring‐opening of BMDO took place during the copolymerizations leading to the formation of poly(DMAEMA‐co‐ester)s. Blocky random copolymers were further quaternized by alkyl bromide to generate degradable cation containing polymers. Cytotoxicity results were highly encouraging and showed less cytotoxicity as compared to polyethyleneimine, which was used as a positive control. The formation and characterization of highly stable copolymer/DNA polyplexes is also shown here.
