Research progress on polymer-inorganic thermoelectric nanocomposite materials

A thermoelectric (TE) material is a material where a potential difference is generated as a result of a temperature difference or the corollary of this where a temperature difference is generated when a voltage is applied. These phenomena can be used to generate electricity and/or control temperature. Traditionally, thermoelectric materials are inorganic semiconductors which have been limited in their application by low efficiency and high cost. Since the 1990s, both theoretical and experimental studies have shown that low-dimensional TE materials, such as superlattices and nanowires, can enhance the value of the TE figure of merit (ZT) which is an indicator of TE thermodynamic efficiency. To date it has not been feasible to apply these materials in large-scale energy-conversion processes because of limitations in both their heat transfer efficiency and cost. When compared to inorganic materials, organic conducting polymers possess some unique features, such as low density, low cost, low thermal conductivity, easy synthesis and versatile processability and their use in preparing polymer-inorganic TE nanocomposites appears to have great potential for producing relatively low cost and high-performance TE materials. Recently, an increasing number of studies have reported on polymeric and polymer-inorganic TE nanocomposite materials. The purpose of this paper is to review the research progress on the conducting polymers and their corresponding TE nanocomposites. Its main focus is the TE nanocomposites based on conducting polymers such as polyaniline (PANI), polythiophene (PTH), poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS), as well as other polymers such as polyacetylene (PA), polypyrrole (PPY), polycarbazoles (PC) and polyphenylenevinylene (PPV). Typically, polymer-inorganic TE nanocomposites are produced by physical mixing, solution mixing and in situ polymerization. The key factors that limit the use of these polymers and their polymer-inorganic TE nanocomposites as TE materials are their low ZT values. More recent developments designed to overcome the limitation including, for example, the use of carbon nanotubes and graphenes and the use of computational modelling to accelerate the selection of suitable pairs of conductive polymer and inorganic TE materials to achieve best possible nanocomposites are reviewed.     

Synthesis and thermally responsive characteristics of dendritic poly(ether-amide) grafting with PNIPAAm and PEG

A series of thermally responsive dendritic core-shell polymers were prepared based upon dendritic poly(ether-amide) (DPEA), modified with carboxyl end-capped linear poly(N-isopropylacrylamide) (PNIPAAm-COOH) or both PNIPAAm-COOH and carboxyl end-capped methoxy polyethylene glycol (PEG-COOH) in different ratios via an esterification process to obtain DPEA-PNIPAAm or DPEA-PNIPAAm-PEG. Their molecular structures were verified by gel permeation chromatography, and ¹H NMR and FTIR spectroscopy. The temperature-dependent characteristics study has revealed that DPEA-PNIPAAm exhibits a lower critical solution temperature (LCST) of about 34 °C, whereas DPEA-PNIPAAm-PEG polymers with the PNIPAAm/PEG ratio of about 1.0 and 0.4 possess about 36 °C and 39 °C, respectively, compared with 32 °C for homopolymer PNIPAAm. The critical aggregation temperature was investigated using fluorescence excitation spectrum of pyrene as a sequestered guest molecule based upon the sharp increase of the I₃₃₈/I₃₃₃ value.     

Biodegradable poly(ester amide)s – A remarkable opportunity for the biomedical area: Review on the synthesis,characterization and applications

Poly(ester amide)s have emerged in the last years as an important family of biodegradable synthetic polymers. These polymers present both ester and amide linkages in their structure and they gather in the same entity the good degradability of polyesters with the good thermo-mechanical properties of polyamides. Particularly, poly(ester amide)s containing α-amino acids have risen as important materials in the biomedical field. The presence of the α-amino acid contributes to better cell–polymer interactions, allows the introduction of pendant reactive groups, and enhances the overall biodegradability of the polymers.     

In situ growth of CuInS2 nanocrystals on nanoporous TiO2 film for constructing inorganic/organic heterojunction solar cells

Inorganic/organic heterojunction solar cells (HSCs) have attracted increasing attention as a cost-effective alternative to conventional solar cells. This work presents an HSC by in situ growth of CuInS₂(CIS) layer as the photoabsorption material on nanoporous TiO₂ film with the use of poly(3-hexylthiophene) (P3HT) as hole-transport material. The in situ growth of CIS nanocrystals has been realized by solvothermally treating nanoporous TiO₂ film in ethanol solution containing InCl₃ · 4H₂O, CuSO₄ · 5H₂O, and thioacetamide with a constant concentration ratio of 1:1:2. InCl₃ concentration plays a significant role in controlling the surface morphology of CIS layer. When InCl₃ concentration is 0.1 M, there is a layer of CIS flower-shaped superstructures on TiO₂ film, and CIS superstructures are in fact composed of ultrathin nanoplates as ‘petals’ with plenty of nanopores. In addition, the nanopores of TiO₂ film are filled by CIS nanocrystals, as confirmed using scanning electron microscopy image and by energy dispersive spectroscopy line scan analysis. Subsequently, HSC with a structure of FTO/TiO₂/CIS/P3HT/PEDOT:PSS/Au has been fabricated, and it yields a power conversion efficiency of 1.4%. Further improvement of the efficiency can be expected by the optimization of the morphology and thickness of CIS layer and the device structure.     

Segmented copolymers with monodisperse crystallizable hard segments: Novel semi-crystalline materials

Segmented block copolymers with short monodisperse crystallizable hard segments have interesting structures and properties. In the melt, such short monodisperse segments are miscible with the matrix segments. Moreover, upon cooling, they crystallize fast, demonstrating a very high crystallinity, and only a small crystallization window is needed. The melting temperature of the short segments is high, provided that they can H-bond and/or contain aromatic groups. The melting temperature was found to decrease with increasing matrix segment concentration, due to the solvent effect of the matrix segments. At concentrations of crystallizable segment of 4-35 wt%, good dimensional and solvent stabilities were obtained.The monodisperse segments crystallized into nano-ribbons with uniform thickness and high aspect ratio, and these dispersed nano-ribbon crystallites constituted physical crosslinks, while acting also as reinforcing fillers. At concentrations of the monodisperse segments below 20 wt% no spherulitic ordering took place, and the semi-crystalline polymers were transparent. The monodisperse crystallizable segments can be used in combination with matrix segments of either low or high glass transition temperature, and may even contain (bio)functional units.     

Synthesis and functionalization of nanoengineered materials using click chemistry

The synthesis of nanoengineered materials with precise control over material composition, architecture and functionality is integral to advances in diverse fields, including biomedicine. Over the last 10 years, click chemistry has emerged as a prominent and versatile approach to engineer materials with specific properties. Herein, we highlight the application of click chemistry for the synthesis of nanoengineered materials, ranging from ultrathin films to delivery systems such as polymersomes, dendrimers and capsules. In addition, we discuss the use of click chemistry for functionalizing such materials, focusing on modifications aimed at biomedical applications.     

Interpolymer radical coupling: A toolbox complementary to controlled radical polymerization

The current review focuses on the relevance and practical benefit of interpolymer radical coupling methods. The latter are developing rapidly and constitute a perfectly complementary macromolecular engineering toolbox to the controlled radical polymerization techniques (CRP). Indeed, all structures formed by CRP are likely to be prone to radical coupling reactions, which multiply the available synthetic possibilities. Basically, the coupling systems can be divided in two main categories. The first one, including the atom transfer radical coupling (ATRC), silane radical atom abstraction (SRAA) and cobalt-mediated radical coupling (CMRC), relies on the recombination of macroradicals produced from a dormant species. The second one, including atom transfer nitroxide radical coupling (ATNRC), single electron transfer nitroxide radical coupling (SETNRC), enhanced spin capturing polymerization (ESCP) and nitrone/nitroso mediated radical coupling (NMRC), makes use of a radical scavenger in order to promote the conjugation of the polymer chains. More than a compilation of macromolecular engineering achievements, the present review additionally aims to emphasize the particularities, synthetic potential and present limitations of each system.     

Electrochemically reduced titanocene dichloride as a catalyst of reductive dehalogenation of organic halides

We have studied a reaction between the reduced form of titanocene dichloride (Cp₂TiCl₂) and a group of organic halides: benzyl derivatives (4-XC₆H₄CH₂Cl, X = H, NO₂, CH₃; 4-XC₆H₄CH₂Br, X = H, NO₂, PhC(O); 4-XC₆H₄CH₂SCN, X = H, NO₂) as well as three aryl halides (4-NO₂C₆H₄Hal, Hal = Cl, Br; 4-CH₃O-C₆H₄Cl). It has been shown that the electrochemical reduction of Cp₂TiCl₂ in the presence of these benzyl halides leads to a catalytic cycle resulting in the reductive dehalogenation of these organic substrates to yield mostly corresponding toluene derivatives as the main product. No dehalogenation has been observed for aryl derivatives. Based on electrochemical data and digital simulation, possible schemes of the catalytic process have been outlined. For non-substituted benzyl halides halogen atom abstraction is a key step. For the reaction of nitrobenzyl halides the complexation of Ti(III) species with the nitro group takes place, with the electron transfer from Ti(III) to this group (owing to its highest coefficient in LUMO of the nitro benzyl halide) followed by an intramolecular dissociative electron redistribution in the course of the heterolytic CHal bond cleavage.The results for reduced titanocene dichloride centers immobilized inside a polymer film showed that the catalytic reductive dehalogenation of the p-nitrobenzyl chloride does occur but with a low efficiency because of the partial deactivation of the film due to the blocking of the electron charge transport between the electrode and catalytic centers.     

Complex polymer architectures via RAFT polymerization: From fundamental process to extending the scope using click chemistry and nature's building blocks

Reversible addition fragmentation chain transfer (RAFT) polymerization has made a huge impact in macromolecular design. The first block copolymers were described early on, followed by star polymers and then graft polymers. In the last five years, the types of architectures available have become more and more complex. Star and graft polymers now have block structures within their branches, or a range of different branches can be found growing from one core or backbone. Even the synthesis of hyperbranched polymers can be positively influenced by RAFT polymerization, allowing end group control or control over the branching density. The creative combination of RAFT polymerization with other polymerization techniques, such as ATRP or ring-opening polymerization, has extended the array of available architectures. In addition, dendrimers were incorporated either as star core or endfunctionalities. A range of synthetic chemistry pathways have been utilized and combined with polymer chemistry, pathways such as ‘click chemistry’. These combinations have allowed the creation of novel structures. RAFT processes have been combined with natural polymers and other naturally occurring building blocks, including carbohydrates, polysaccharides, cyclodextrins, proteins and peptides. The result from the intertwining of natural and synthetic materials has resulted in the formation of hybrid biopolymers. Following these developments over the last few years, it is remarkable to see that RAFT polymerization has grown from a lab curiosity to a polymerization tool that is now been used with confidence in material design. Most of the described synthetic procedures in the literature in recent years, which incorporate RAFT polymerization, have been undertaken in order to design advanced materials.     

Synthesis and photoluminescent properties of polymer containing perylene and fluorene units

A new luminescent polymer, F-PTCD, with N,N′-bis-(propenylaniline)-3,4,9,10-perylene tetracarboxylic diimide-emitting segments (PTCD) and 9,9-diphenylfluorene (DIPT) was synthesized by Heck reaction. The structures were characterized by MS, EA, ¹H NMR, IR and the photoluminescent (PL) properties were investigated by UV/vis absorption and fluorescence emission spectra. The fluorescence quantum yield was 0.453 in acetone. Thermogravimetric analysis and differential scanning calorimetry showed that the polymer is thermal stable up to 569 °C with glass-transition temperature higher than 125 °C. They are yellow-red emitting materials with the band gap of 2.33 eV estimated from the onset absorption. In addition, the emission can be quenched by both electron donor (N,N-dimethylaniline) and electron acceptor (Fullerene), where the processes followed the Stern-Volmer equation. Furthermore, the interaction between F-PTCD and carbon nanotubes (CNTs) was also studied by fluorescent quenching.     

Electroactive phases of poly(vinylidene fluoride): Determination,processing and applications

Poly(vinylidene fluoride), PVDF, and its copolymers are the family of polymers with the highest dielectric constant and electroactive response, including piezoelectric, pyroelectric and ferroelectric effects. The electroactive properties are increasingly important in a wide range of applications such as in biomedicine, energy generation and storage, monitoring and control, and include the development of sensors and actuators, separator and filtration membranes and smart scaffolds, among others. For many of these applications the polymer should be in one of its electroactive phases. This review presents the developments and summarizes the main characteristics of the electroactive phases of PVDF and copolymers, indicates the different processing strategies as well as the way in which the phase content is identified and quantified. Additionally, recent advances in the development of electroactive composites allowing novel effects, such as magnetoelectric responses, and opening new applications areas are presented. Finally, some of the more interesting potential applications and processing challenges are discussed.     

Electrocatalytic tandem Knoevenagel–Michael addition of barbituric acids to isatins: Facile and efficient way to substituted 5,5′-(2-oxo-2,3-dihydro-1H-indole-3,3-diyl)bis(pyrimidine-2,4,6-(1H,3H,5H)-trione) scaffold

Electrocatalytic transformation of isatins and barbituric acids in ethanol in an undivided cell in the presence of sodium bromide as an electrolyte results in the formation of substituted 5,5′-(2-oxo-2,3-dihydro-1H-indole-3,3-diyl)bis(pyrimidine-2,4,6(1H,3H,5H)-triones) in 89–95% substance yields and 890–950% current yields. The developed efficient electrocatalytic approach to medicinally relevant 5,5′-(2-oxo-2,3-dihydro-1H-indole-3,3-diyl)bis(pyrimidine-2,4,6(1H,3H,5H)-trione) scaffold is 10 times faster than general chemical method, is beneficial from the viewpoint of diversity-oriented large-scale processes and represents novel example of facile environmentally benign synthetic concept for electrocatalytic tandem reaction strategy.     

New developments in polymer science and technology using combination of ionic liquids and microwave irradiation

The purpose of this review is to provide appropriate details concerning the application of ionic liquids (IL)s associated with microwave-assisted polymer chemistry. From the viewpoint of microwave chemistry, one of the key significant advantages of ILs is their high polarity, which is variable, depending on the cation and anion and therefore can effectively be tuned to a particular application. Hence, these liquids offer a great potential for the innovative application of microwaves for organic synthesis as well as for polymer science. ILs efficiently absorb microwave energy through an ionic conduction mechanism, and thus are employed as solvents and co-solvents, leading to a very high heating rate and a significantly shortened reaction time. Since an IL-based and microwave-accelerated procedure is efficient and environmentally benign, we believe that this method may have some potential applications in the synthesis of a wide variety of vinyl and non-vinyl polymers. This review describes application of combination of ILs with microwave irradiation as a modern tool for the addition and step-growth polymerization as well as modification of polymers and it was compared with ILs alone and conventional polymerization method.     

Investigation of the carbonation front shape on cementitious materials: Effects of the chemical kinetics

Carbonation depth-profiles have been determined by thermogravimetric analysis and by gammadensitometry after accelerated carbonation tests on ordinary Portland cement (OPC) pastes and concretes. These methods support the idea that carbonation does not exhibit a sharp reaction front. From analytical modelling, this feature is explained by the fact that the kinetics of the chemical reactions become the rate-controlling processes, rather than the diffusion of CO₂. Furthermore, conclusions are drawn as to the mechanism by which carbonation of Ca(OH)₂ and C-S-H takes place. Carbonation gives rise to almost complete disappearance of C-S-H gel, while Ca(OH)₂ remains in appreciable amount. This may be associated with the CaCO₃ precipitation, forming a dense coating around partially reacted Ca(OH)₂ crystals. The way in which CO₂ is fixed in carbonated samples is studied. The results indicate that CO₂ is chemically bound as CaCO₃, which precipitates in various forms, namely: stable, metastable, and amorphous. It seems that the thermal stability of the produced CaCO₃ is lower when the carbonation level is high. It is also shown that the poorly crystallized and thermally unstable forms of CaCO₃ are preferentially associated with C-S-H carbonation.     

Supramolecular Coordination Polymers by Self-assembling of Bis-monodentate Ligands with HgI2

Two supramolecular coordination polymers, [HgI₂(L¹)·0.5H₂O]_∞ (1) and [HgI₂(L²)·0.4CH₃OH]_∞ (2), have been prepared by ligands L¹ (L¹ = bis[4-(4- pyridylmethyleneamino)phenyl] ether) and L² (L² = N,N′-bis(3-pyridylmethyl)-diphthalic diimide) with HgI₂, respectively. 1 formed an interestingly infinite cross-linked double helical structure, whereas 2 formed the one-dimensional zigzag chains, which are parallel with each other.     

Telechelic polymers by living and controlled/living polymerization methods

Telechelic polymers, defined as macromolecules that contain two reactive end groups, are used as cross-linkers, chain extenders, and important building blocks for various macromolecular structures, including block and graft copolymers, star, hyperbranched or dendritic polymers. This review article describes the general techniques for the preparation of telechelic polymers by living and controlled/living polymerization methods; namely atom transfer radical polymerization, nitroxide mediated radical polymerization, reversible addition-fragmentation chain transfer polymerization, iniferters, iodine transfer polymerization, cobalt mediated radical polymerization, organotellurium-, organostibine-, organobismuthine-mediated living radical polymerization, living anionic polymerization, living cationic polymerization, and ring opening metathesis polymerization. The efficient click reactions for the synthesis of telechelic polymers are also presented.     

Microwave-assisted polymer synthesis (MAPS) as a tool in biomaterials science: How new and how powerful

Lack of reproducibility, difficult and expensive scale-up and standarization of synthetic processes are the main hurdles towards the industrial production of raw synthetic and semi-synthetic polymers for (bio)pharmaceutical applications. Time- and energy-consuming synthetic pathways that usually involve the use of volatile, flammable or toxic organic solvents are apparently cost-viable and environment-friendly for the synthesis at a laboratory scale. However, they are often not viable in industrial settings especially due to the impact they have on the product cost and the deleterious effect on the environment. This has presented hurdles to the incorporation of many new biomaterials displaying novel structural features into clinics. Nevertheless, owing to unique advantages such as shorter reaction times, higher yields, limited generation of by-products and relatively easy scale-up without detrimental effects, microwave-assisted organic synthesis has become an appealing synthetic tool. Regardless of these features, the use of microwave radiation in biomaterials science has been comparatively scarce. A growing interest in the basic aspects of the synthesis of either ceramic and polymeric biomaterials has been apparent during the last decade. This article reviews the most recent and prominent applications of MW as a versatile tool to synthesize and process organic and inorganic polymeric biomaterials, and discusses the unmet goals and the perspectives for a technology that probably has the potential to make biomaterials more accessible pharmaceutical excipients and the products that involve them more affordable to patients.     

Synthesis, characterization and thermal properties of soluble aromatic poly(amide imide)s

Novel diamines such as N,N′-bis(aminoaryl)terephthalamido-2-carboxylic acids (BATCA), which contain primary amine, amide and carboxylic acid groups and are soluble in dilute aqueous NaOH solution, were synthesized by reacting aromatic diamines with trimellitic anhydride chloride in dimethylformamide. Poly(amide imide)s containing 3:1 ratio of amide:imide groups in the polymer chain were prepared by low temperature solution polymerization of BATCAs with isophthaloyl chloride or terephthaloyl chloride in dimethylformamide at 5-10 °C to form poly(amide amic acid)s, and followed by treating with a mixture of triethylamine and acetic anhydride. The PAIs were soluble in polar aprotic solvents like dimethylformamide, dimethylacetamide, dimethylsulphoxide and N-methylpyrrolidone, and have inherent viscosities in the range of 0.30-0.66 dL/g. The PAIs were characterized by IR, ¹H NMR and ¹³C NMR techniques. Thermogravimetric analysis (TGA) has shown that the initial decomposition temperatures of the polymers are in the range of 250-440 °C, depending upon the structures of diamine and diacid chloride. The glass transition temperatures of the PAIs are in the range of 128-320 °C. The IDT and T_g values of the polymers containing terephthaloyl unit are higher by about 20-40 °C than those of the polymers with isophthaloyl unit. BATCA could be utilized for the preparation of thin film composite membranes having PAA/PAI barrier layer on PES by in situ interfacial polymerization with IPC/TPC/TMC.