This is an editorial article. It has no abstract.
Nanostructures of diglycidyl ether of bisphenol-A epoxy/poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) (PMMA-b-PnBA-b-PMMA) triblock copolymer (BCP) blends were studied in relation to their mechanical properties. Three types of self-assembled nanostructures, such as spheres, random cylinders, and curved lamella, were controlled in phenol novolac-cured epoxy blends with a wide range of BCP content. Three types of nanostructures were observed using two-dimensional and three-dimensional transmission electron microscopy (TEM). The 3D-TEM, dynamic viscoelastic analyses, and theoretical model on the elastic modulus clarified that the spheres and the random cylinders, consisted of epoxy-immiscible PnBA phases, were discontinuously dispersed in the epoxy matrix. In contrast, the curved lamella formed co-continuous nanostructure, in which both the PnBA and epoxy phases formed continuous channels. The fracture toughness (critical strain energy release rate, GIC) and the flexural moduli of elasticity (E) of the cured blends were evaluated for various amounts of BCP content. The highest GIC was obtained from the random cylindrical nanostructured blends in the three types of nanostructures with the same PnBA content. The lowest E was obtained for the curved lamella with co-continuous nanostructures. The details of deformation and fracture events were observed using optical and electron microscopy, and the mechanical properties are discussed in relation to the nanostructures.
This article surveys recent and not so recent literature in the field of rotational molding. The mechanisms of heat transfer, sintering and bubble removal are evaluated; as are degradation and dimensional stability. The parameters that affect the surface finish are highlighted and a number of the control systems available to the rotational molding process are mentioned. Improvements in molds and machinery, and the extent to which they reduce cycle times are also described. Finally, the range of materials available to the rotational molding process is examined and recent developments are highlighted. Of particular interest is the rotational molding of liquid polymer systems; which are shown to possess great potential for fulfilling many of rotational molding’s surface quality requirements while simultaneously reducing cycle times.
Various sugar-based methacrylate monomers have been prepared and randomly copolymerized with methyl methacrylate (MMA) using classical atom transfer radical polymerization (ATRP). Firstly, four different sugar-based methacrylates are synthesized by two-step method: (i) etherification of protected monosaccharides with epichlorohydrin and (ii) following ring-opening reaction of obtained epoxides with methacrylic acid (MAA) in the presence of triethylamine. Next, these monomers are copolymerized with MMA via ATRP at 90 °C to obtain corresponding random copolymers. The molecular weights of the copolymers are determined by both GPC (gel permeation chromatography) and 1H-NMR (nuclear magnetic resonance spectroscopy) analyses and found as 10600~16800 and 12200~18500 g/mol, respectively. Moreover, the copolymer compositions are also determined by 1H-NMR analysis using characteristic signals of the monomers and found as about 94.1~97.8%, which are good agreement with feeding ratio. In addition, the glass transition temperatures of copolymers are found as 101.2~102.9 °C by changing type and composition of sugar-based methacrylate monomers. Overall, a series of well-defined random copolymers comprising different sugar-based methacrylates and methyl methacrylates were successfully synthesized by classical ATRP method.
Chitosan, a derivative of chitin, is a biodegradable polymer known of its favorable properties, applicable in medicine and industry. Commonly obtained chitosan hydrogels are of various swelling capacity, and may bind only anions losing their susceptibility to biodegradation. Hydrogels are mostly obtained using toxic crosslinkers, which pollute environment due to waste generation during their synthesis. In the present article a novel, waste-free method for obtaining chitosan hydrogels under microwave irradiation, is described. Their chemical and morphological structure, swelling properties, sorption capability of a model dye and cadmium ions are described, and kinetic studies, were carried out. Biodegradability of the obtained hydrogels was investigated with the Sturm Test method. As a result, multifunctional chitosan hydrogels with both negative and positive surface charges and increased ability of anions and cations binding, were obtained. Materials were fully biodegradable, capable to absorb high amounts of water, as well as to remove various water contaminants.
Creep deformation of polymers results from their inherent viscoelastic nature that changes polymer’s shape with time. Creep response represents an important property of thermoplastic composites that affects their dimensional stability, especially in applications requiring the material ability to support relatively high loads for long periods. This work examines the creep behavior of self-reinforced recycled poly(ethylene terephthalate) (srrPET) composites, which were produced by film stacking from fabrics composed of double covered uncommingled yarns with recycled PET homopolymer filaments (serving as the reinforcements) and copolymerized PET (mPET) filaments (serving as the matrix). The short-term creep behavior of both srrPET and mPET was studied in the single cantilever mode below and above the glass transition temperature, and the obtained data were analyzed using the Findley’s viscoelastic and Burgers four-element models. The long-term creep behavior of srrPET specimens with and without open circular holes was described using an Arrhenius-type time–temperature superposition principle.
A pH-triggered drug delivery system of degradable core cross-linked (CCL) prodrug micelles was prepared by click chemistry. Doxorubicin conjugated block copolymers of azido functional poly(ethylene oxide)-b-poly(glycidyl methacrylate) were synthesized by the combination of RAFT polymerization, epoxide ring-opening reaction, and acid-cleavable hydrazone linkages. The CCL prodrug micelles were produced by the reaction of dipropargyl 3,3′-dithiodipropionate and dipropargyl adipate cross-linking agents with the azido groups of the micellar core via alkyne-azide click reaction, which were denoted as CCL/SS and CCL/noSS, respectively. The TEM images of CCL/SS prodrug micelles showed a spherical shape with the average diameter of 61.0 nm from water, and the shape was maintained with an increased diameter upon dilution with 5-fold DMF. The high DOX conjugation efficiency was 88.4%. In contrast to a very slow DOX release from CCL/SS prodrug micelles under the physiological condition (pH 7.4), the drug release is much faster (90%) at pH 5.0 and 10 mM of GSH after 96 h. The cytotoxicity test and confocal laser scanning microscopy analysis revealed that CCL/SS prodrug micelles had much enhanced intracellular drug release capability in HepG2 cells than CCL/noSS prodrug micelles.
Electrochemical preparation of a composite consisting of poly[2,2′-bis(3,4-ethylenedioxythiophene)-alt-fluorene] and hydroxypropyl cellulose (PEFE/HPC) was carried out. We conducted electrochemical polymerization of poly[2,2′-bis(3,4-ethylenedioxythiophene)-alt-fluorene] (EFE) as a monomer in a lyotropic liquid crystal of HPC. We used an organic solvent instead of water for lyotropic liquid crystal medium to expand the possibility of the range of monomers, although water is usually employed as a solvent for HPC for showing liquid crystallinity. Here, we employed N,N-dimethylformamide (DMF) as a solvent for HPC. Electrochemical polymerization in the polymer liquid crystal was carried out to obtain a polymer film with liquid crystal order. The polymer film thus prepared exhibited optical activity. Fourier transfer infrared (FT-IR) absorption spectroscopy reveals that the film is a composite consisting of HPC and polymer. The composite PEFE/HPC thus prepared in HPC/DMF system showed electrochromism.