Microwave-Assisted Polymer Synthesis: State-of-the-Art and Future Perspectives

Surface modification of bulk titanium substrates for biomedical applications via low-temperature microwave hydrothermal oxidation

Micro-to-nanoscale surface topographies of orthopaedic and dental implants can affect fluid wetting and biological response. Nanoscale features can be superimposed on microscale roughness of titanium (Ti) surfaces at high temperatures, resulting in increased osteoblast differentiation. However, high temperatures can compromise mechanical properties of the bulk material. Here, we have developed a novel low-temperature microwave hydrothermal (MWHT) oxidation process for nanomodification of microrough (SLA) Ti surfaces. Nanoscale protuberances (20 -100 nm average diameter) were generated on SLA surfaces via MWHT treatment at 200°C in H₂ O, or in aqueous solutions of H₂ O₂ or NH₄ OH, for times ranging from 1 to 40 h. The size, shape, and crystalline content of the nanoprotuberances varied with the solution used and treatment time. The hydrophilicity of all MWHT-modified surfaces was dramatically enhanced. MG63 and normal human osteoblasts (NHOsts) were cultured on MWHT-treated SLA surfaces. While most responses to MWHT-modified surfaces were comparable to those seen on SLA controls, the MWHT-generated nanotopography reduced osteocalcin production by NHOst cells, suggesting that specific nanotopographic characteristics differentially mediate osteoblast phenotypic expression. MWHT processing provides a scalable, low-temperature route for tailoring nanoscale topographies on microroughened titanium implant surfaces with significantly enhanced wetting by water, without degrading the microscale surface structure of such implants. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 782-796, 2018.

Living cationic ring-opening polymerization of 2-ethyl-2-oxazoline following sustainable concepts: microwave-assisted and droplet-based millifluidic processes in an ionic liquid medium

The synthesis of poly(2-ethyl-2-oxazoline) has been developed in an ionic liquid and performed with microwave-assisted or droplet-based millifluidic processes.

Tailoring degree of esterification and branching of poly(glycerol sebacate) by energy efficient microwave irradiation

A branched poly(glycerol sebacate) prepolymer has been successfully synthesised via single mode microwave irradiation with an improved reaction rate and controllable properties.

Microwave energy assisted synthesis of poly lactic acid via continuous reactive extrusion: modelling of reaction kinetics

The most commonly used batch process to manufacture PLA is ring opening polymerization (ROP) of lactide monomer in a suitable solvent, in the presence of a metallic/bimetallic catalyst (Sn, Zn, and Al) or other organic catalysts.

Microwave-assisted grafting polymerization modification of nylon 6 capillary-channeled polymer fibers for enhanced weak cation exchange protein separations

A weak cation exchange liquid chromatography stationary phase (nylon-COOH) was prepared by grafting polyacrylic acid on to native nylon 6 capillary-channeled polymer (C-CP) fibers via a microwave-assisted radical polymerization. To the best of our knowledge, this is the first study of applying microwave-assisted grafting polymerization to affect nylon material for protein separation. The C-CP fiber surfaces were characterized by attenuated total reflection (ATR) infrared spectroscopy and scanning electron microscope (SEM). The anticipated carbonyl peak at 1722.9 cm^-1 was found on the nylon-COOH fibers, but was not found on the native fiber, indicating the presence of the polyacrylic acid on nylon fibers after grafting. The nylon-COOH phase showed a ∼12× increase in lysozyme dynamic binding capacity (∼12 mg mL^-1) when compared to the native fiber phase (∼1 mg mL^-1). The loading capacity of the nylon-COOH phase is nearly independent of the lysozyme loading concentration (0.05-1 mg mL^-1) and the mobile phase linear velocity (7.3-73 mm s^-1). The reproducibility of the lysozyme recovery from the nylon-COOH (RSD = 0.3%, n = 10) and the batch-to-batch variability in the functionalization (RSD = 3%, n = 5) were also investigated, revealing very high levels of consistency. Fast baseline separations of myoglobin, α-chymotrypsinogen A, cytochrome c and lysozyme were achieved using the nylon-COOH column. It was found that a 5× increase in the mobile phase linear velocity (7.3-to-36.5 mm s^-1) had little effect on the separation resolution. The microwave-assisted grafting polymerization has great potential as a generalized surface modification methodology across the applications of C-CP fibers.

Solid dispersions of efonidipine hydrochloride ethanolate with improved physicochemical and pharmacokinetic properties prepared with microwave treatment

Drug absorption into the body is known to be greatly affected by the solubility of the drug itself. The active pharmaceutical ingredient efonidipine hydrochloride ethanolate (NZ-105) is a novel 1,4-dihydropyridine calcium antagonist that has a very low solubility in water. It is classified as a poorly soluble drug, and improvements in its solubility and higher bioavailability with oral administration are needed. In this study, employing microwave technology as a new means to improve solubility, we established a method for preparing solid dispersions using hydroxypropyl methylcellulose acetate succinate as a polymeric carrier and urea as a third component. This effective method has a treatment time of several minutes (simple) and does not require the use of organic solvents (low environmental impact). The third component, urea, acts to lower the melting point of NZ-105, which promotes amorphization. This greatly improves the solubility compared with the microwave-treated product of NZ-105/HPMC-AS binary system. The solid dispersion prepared with this method, in addition to evaluation in vitro, was tested in vivo using beagle dogs and shown to be effective from the eightfold improvement in absorption compared with NZ-105 alone based on the area under the curve.

A rapid microwave-induced synthesis of polyamides–containing amino acid moieties

5-(2-(9,10-Dihydro-9,10-ethanoanthracene-11,12-dicarboximido)propanoylamino)isophthalic acid as a novel aromatic dicarboxylic acid monomer was prepared in four steps. In the first step, cis-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid anhydride was reacted with l-alanine in acetic acid solution and the resulting imide acid was obtained in high yield. In the second step, treatment of this imide acid with excess thionyl chloride gave acid chloride in good yield. In the last step, this acid chloride was reacted with 5-aminoisophthalic acid to provide novel bulky chiral aromatic dicarboxylic acid. The direct polycondensation reactions of this diacid with several aromatic diamines were carried out under microwave irradiation. In order to compare this technique with classical heating, the polymerization reactions were also performed under solution polycondensation conditions. The polymerization reactions occurred rapidly under microwave conditions and produced a series of novel optically active polyamides (PAs)–containing pendent 9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboximido)propanoylamino group, with good yields and moderate inherent viscosities of 0.27–0.47 dL g−1. The resulting new PAs showed good solubility and are readily soluble in organic solvents. PAs were thermally stable, with 10% weight loss recorded at 411°C and 450°C under nitrogen atmosphere and char yields at 800°C higher than 44% and glass transition temperature above 163°C.

Maleimide-functionalized poly(2-ethyl-2-oxazoline): synthesis and reactivity

Poly(2-ethyl-2-oxazoline)s end-functionalized with a maleimide moiety were prepared from azide-terminated PEtOx_x-N₃viacopper-catalyzed azide–alkyne cycloaddition (CuAAC) with an alkyne-bearing maleimide (MI).

Fabrication of Vertical Array CNTs/Polyaniline Composite Membranes by Microwave-Assisted In Situ Polymerization

A vertical array carbon nanotubes (VACNTs)/polyaniline (PANi) composite membrane was prepared by microwave-assisted in situ polymerization. With microwave assistance, the morphology of PANi revealed a smaller diameter and denser connection. Meanwhile, thermogravimetric analysis showed improved thermal stability of microwave-assisted PANi for higher molecular weight. Focused ion beam thinning method was used to cut the VACNTs/PANi membrane into dozen-nanometer thin strips along the cross-sectional direction, and transmission electron microscopy observation showed seamless deposition of PANi between VACNT gaps, without damaging the vertical status of CNTs. Meanwhile, stronger conjugate interaction between the quinoid ring of PANi and VACNTs of the composite membrane were prompted by microwave-assisted in situ polymerization. By using nanoindentation technology, the VACNTs/PANi composite membrane showed exponential increasing of modulus and hardness. Meanwhile, the elasticity was also improved, which was proved by the calculated plastic index. The results can provide helpful guidance for seamlessly infiltrating matrix into CNT array and also demonstrate the importance of structural hierarchy for getting proper behavior of nanostructures.

Highly efficient microwave-assisted synthesis of photoactive polyamides bearing 5-(3-acetoxynaphthoylamino)benzamide moieties

A novel aromatic dicarboxylic acid monomer, 5-[4-(3-acetoxynaphthoylamino)benzoylamino]isophthalic acid, was prepared in five steps. The direct polycondensation of this dicarboxylic acid with several aromatic diamines was performed under microwave irradiation and conventional heating in the presence of triphenyl phosphite/pyridine/ N-methyl-2-pyrrolidone/calcium chloride. The polymerization reactions were effectively preceded, and the resulting novel photoactive polyamides (PAs) were obtained in high yields and moderate inherent viscosities in the range of 0.32–0.58 dL g−1. Thermogravimetric analysis results showed that polymers were thermally stable, 10% weight loss temperatures were in excess of 430°C and 488°C, and char yields at 800°C under nitrogen atmosphere were higher than 62%. The resulting polymers exhibited ultraviolet–visible absorption bands at 268 and 312 nm in N,N-dimethylformamide (DMF) solution. Their photoluminescence in DMF solution demonstrated fluorescence emission bands maxima around 367 and 429 nm for all of the PAs.

Efficient and rapid adsorption characteristics of templating modified guar gum and silica nanocomposite toward removal of toxic reactive blue and Congo red dyes

The present study highlights the potentiality of sol-gel synthesized guar gum-graft-poly (acrylamide)/silica (g-GG/SiO2) hybrid nanocomposite toward the rapid removal of toxic reactive blue 4 (RB) and Congo red (CR) dyes from aqueous solution. Various physicochemical characterizations support the feasibility of the functionalized guar gum matrix as efficient template for the formation of homogeneous nanoscale silica particles. The composite demonstrates rapid and superior adsorption efficiency of RB (Qmax: 579.01 mg g(-1) within 40 min) and CR (Qmax: 233.24 mg g(-1) within 30 min) dyes from aqueous environment. Here, the pH driven adsorption process depends strongly on the ionic strength of the salt solution. The adsorption kinetics data predicts that pseudo second-order (surface adsorption) and intraparticle diffusion take place simultaneously. The adsorption equilibrium is in good agreement with the Langmuir isotherm, while the thermodynamics study confirms spontaneous nature of the adsorption process. Desorption study predicts the excellent regenerative efficacy of nanocomposite.

Probing the surface-localized hyperthermia of gold nanoparticles in a microwave field using polymeric thermometers

Gold nanoparticles decorated with “polymeric thermometers,” consisting of a polymeric spacer, thermally-labile azo linker, and fluorescent tag, were used to quantify the extent of localized hyperthermia under microwave irradiation.

The surface-localized hyperthermia of gold nanoparticles under microwave irradiation was examined. Gold nanoparticles with a hydrodynamic diameter of ∼6 nm stabilized by polymeric “thermometers” were used to gather information on the extent of heating as well as its spatial confinements. Reversible addition–fragmentation chain transfer polymerization was employed to synthesize well-defined, functional polymers of predetermined molecular weights, allowing for estimation of the distance between the nanoparticle surface and the polymer chain end. The polymers were conjugated with a fluorescent dye separated by a thermally-labile azo linkage, and these polymeric ligands were bound to gold nanoparticles via gold–thiolate bonds. Conventional heating experiments elucidated the relationship between temperature and the extent of dye release from the gold nanoparticle using fluorescence spectroscopy. The local temperature increase experienced under microwave irradiation was calculated using the same methodology. This approach indicated the temperature near the surface of the nanoparticle was nearly 70 °C higher than the bulk solution temperature, but decreased rapidly with distance, with no noticeable temperature increase when the azo linkage was approximately 2 nm away.

A fast track strategy toward highly functionalized dendrimers with different structural layers: an “onion peel approach”

A novel strategy is described for the rapid syntheses of polyhydroxylated dendrimers in which the layer by layer building blocks are different from one another. The resulting dendrimers showed no cytotoxicity.

Preparation of novel biodegradable pHEMA hydrogel for a tissue engineering scaffold by microwave-assisted polymerization

OBJECTIVE

To prepare a novel biodegradable poly(2-hydroxyethylmethacrilate) (pHEMA) hydrogel as tissue engineering scaffold.

METHODS

The pHEMA hydrogel was synthesized by microwave-assisted polymerization using 2-hydroxyethyl methacrylate (HEMA) as the raw material, potassium persulfate as the initiator, and PCLX as the cross-linking additive. The hydrogels was characterized with FTIR and NMR spectroscopy. The physical and chemical properties of the prepared hydrogel were evaluated, and its degradation performance was tested. The cytotoxicity of the optimum composite hydrogel was measured by an MTT assay to confirm the feasibility of its use in tissue engineering.

RESULTS

The optimum conditions under which the hydrogel was prepared by microwave-assisted polymerization are as follows: 1.5 g cross-linking additive, 0.3 g initiator, reaction temperature of 80 °C, and microwave power of 800 W. Degradation studies showed good degradation profiles with 75% in 17 days. Additionally, the hydrogels did not elicit any cytotoxic response in in vitro cytotoxic assays.

CONCLUSION

A biodegradable pHEMA hydrogel was successfully prepared by microwave-assisted polymerization, as confirmed from FTIR and NMR results. The hydrogel shows promising applications in tissue engineering, and its healing ability and biocompatibility will be evaluated in detail in the future.

The microwave adsorption behavior and microwave-assisted heteroatoms doping of graphene-based nano-carbon materials

Microwave-assisted heating method is used to treat graphite oxide (GO), pyrolytic graphene oxide (PGO) and hydrogen-reduced pyrolytic graphene oxide (HPGO). Pure or doped graphene are prepared in the time of minutes and a thermal deoxygenization reduction mechanism is proposed to understand their microwave adsorption behaviors. These carbon materials are excellent catalysts in the reduction of nitrobenzene. The defects are believed to play an important role in the catalytic performance.

Atrazine molecular imprinted polymers: comparative analysis by far-infrared and ultraviolet induced polymerization

Atrazine molecular imprinted polymers (MIPs) were comparatively synthesized using identical polymer formulation by far-infrared (FIR) radiation and ultraviolet (UV)-induced polymerization, respectively. Equilibrium binding experiments were carried out with the prepared MIPs; the results showed that MIP_uv possessed specific binding to atrazine compared with their MIP_FIR radiation counterparts. Scatchard plot’s of both MIPs indicated that the affinities of the binding sites in MIPs are heterogeneous and can be approximated by two dissociation-constants corresponding to the high-and low-affinity binding sites. Moreover, several common pesticides including atrazine, cyromazine, metamitron, simazine, ametryn, terbutryn were tested to determine their specificity, similar imprinting factor (IF) and different selectivity index (SI) for both MIPs. Physical characterization of the polymers revealed that the different polymerization methods led to slight differences in polymer structures and performance by scanning electron microscope (SEM), Fourier transform infrared absorption (FT-IR), and mercury analyzer (MA). Finally, both MIPs were used as selective sorbents for solid phase extraction (SPE) of atrazine from lake water, followed by high performance liquid chromatography (HPLC) analysis. Compared with commercial C₁₈ SPE sorbent (86.4%–94.8%), higher recoveries of atrazine in spiked lake water were obtained in the range of 90.1%–97.1% and 94.4%–101.9%, for both MIPs, respectively.

Microwave-assisted solution polycondensation of l-lactic acid using a Dean–Stark apparatus for a non-thermal microwave polymerization effect induced by the electric field

The solution polycondensation of l-lactic acid (l-LA) in xylene catalyzed by Sc(OTf)₃ was examined using a Dean–Stark apparatus under various microwave power conditions (100–400 W). The results indicate the existence of a non-thermal microwave effect induced by an electric field.

Polymers for electronics and spintronics

This critical review is devoted to semiconducting and high spin polymers which are of great scientific interest in view of further development of the organic electronics and the emerging organic spintronic fields. Diversified synthetic strategies are discussed in detail leading to high molecular mass compounds showing appropriate redox (ionization potential (IP), electron affinity (EA)), electronic (charge carrier mobility, conductivity), optoelectronic (electroluminescence, photoconductivity) and magnetic (magnetization, ferromagnetic spin interactions) properties and used as active components of devices such as n- and p-channel field effect transistors, ambipolar light emitting transistors, light emitting diodes, photovoltaic cells, photodiodes, magnetic photoswitches, etc. Solution processing procedures developed with the goal of depositing highly ordered and oriented films of these polymers are also described. This is completed by the description of principal methods that are used for characterizing these macromolecular compounds both in solution and in the solid state. These involve various spectroscopic methods (UV-vis-NIR, UPS, pulse EPR), electrochemistry and spectroelectrochemistry, magnetic measurements (SQUID), and structural and morphological investigations (X-ray diffraction, STM, AFM). Finally, four classes of polymers are discussed in detail with special emphasis on the results obtained in the past three years: (i) high IP, (ii) high |EA|, (iii) low band gap and (iv) high spin ones.