Polyurethanes (PUs) are a class of versatile materials with great potential for use in different applications, especially based on their structure–property relationships. Their specific mechanical, physical, biological, and chemical properties are attracting significant research attention to tailoring PUs for use in different applications. Enhancement of the properties and performance of PU-based materials may be achieved through changes to the production process or the raw materials used in their fabrication or via the use of advanced characterization techniques. Clearly, modification of the raw materials and production process through proper methods can produce PUs that are suitable for varied specific applications. The present study aims to shed light on the chemistry, types, and synthesis of different kinds of PUs. Some of the important research studies relating to PUs, including their synthesis method, characterization techniques, and research findings, are comprehensively discussed. Herein, recent advances in new types of PUs and their synthesis for various applications are also presented. Furthermore, information is provided on the environmental friendliness of the PUs, with a specific emphasis on their recyclability and recoverability.

https://ir.unikl.edu.my/jspui/bitstream/123456789/15237/1/Polyurethane%20types%2c%20synthesis%20and%20applications%20%e2%80%93%20a%20review.pdf

Polyurethane types, synthesis and applications – a review

Here we describe the application of dendrimer-encapsulated Pd nanoparticles to fluorous biphasic catalysis. 1 Complexation of Pd/dendrimer composites with perfluorinated carboxylic acids renders the resulting nanocomposites preferentially soluble in fluorinated hydrocarbons. These new catalysts show high activity and selectivity for biphasic hydrogenation of alkenes and conjugated dienes. Moreover, the catalysts can easily be recovered and used for multiple reactions. Reactions in biphasic fluorous/organic systems were suggested by Horvath and Rabai in 1994 2 to facilitate recovery and recycling of soluble catalysts. The general approach to biphasic catalysis is illustrated in Scheme 1. 3 The system consists of organic and fluorous layers. The catalyst is selectively soluble in the fluorous phase, while the reactants are preferentially soluble in the organic solvent. Stirring, sonicating, and/or heating of the mixture leads to formation of a fine emulsion and partial homogenization (with some solvents, complete homogenization is obtained at elevated temperatures), and the catalytic reaction proceeds at the interface between the two liquids. When the reaction is over, the liquid phases are separated, the product is isolated from the organic phase, and the catalyst-containing fluorous layer is recycled. Such easy separation and recycling are particularly attractive in terms of “green chemistry”, and a number of fluorous phase-soluble catalysts have been reported in the literature, including some based on metal complexes. 4,5 Preparation of fluorous phase-soluble metal nanoparticles, however, has not previously been reported. Catalytic properties of metal nanoparticles have been explored since the pioneering studies of Rampino and Nord in the early 1940s. 6 Over the past decade research in this area intensified, 7

/pdf/dendrimer-encapsulated-pd-nanoparticles-as-fluorous-phase-3j3klgyqid.pdf

Dendrimer-Encapsulated Pd Nanoparticles as Fluorous Phase-Soluble Catalysts

2.6. Microencapsulated Cu(acac)2 [MC Cu(acac)2] 606 2.7. Microencapsulated Palladium [MC Pd] 607 2.8. Microencapsulated Methathesis Catalyst 609 3. Polymer Incarcerated Catalysts 611 3.1. Polymer Incarcerated Palladium [PI Pd] 611 3.2. Polymer-Micelle Incarcerated (PMI) Palladium 617 3.3. Polymer Incarcerated Ruthenium Catalyst 619 3.4. Polymer-Micelle Incarcerated Scandium Trifluoromethanesulfonate [PMI Sc(OTf)3] and Ruthenium Catalyst [PMI Ru] 621

https://pubs.acs.org/doi/pdf/10.1021/cr900066n

'Microencapsulated' and related catalysts for organic chemistry and organic synthesis

This chapter describes composite materials composed of dendrimers and metals or semiconductors. Three types of dendrimer/metal-ion composites are discussed: dendrimers containing structural metal ions, nonstructural exterior metal ions, and nonstructural interior metal ions. Nonstructural interior metal ions can be reduced to yield dendrimer-encapsulated metal and semiconductor nanoparticles. These materials are the principal focus of this chapter. Poly(amidoamine) (PAMAM) and poly(propylene imine) dendrimers, which are the two commercially available families of dendrimers, are in many cases monodisperse in size. Accordingly, they have a generation-dependent number of interior tertiary amines. These are able to complex a range of metal ions including Cu2+, Pd2+, and Pt2+. The maximum number of metal ions that can be sorbed within the dendrimer interior depends on the metal ion, the dendrimer type, and the dendrimer generation. For example, a generation six PAMAM dendrimer can contain up to 64 Cu2+ ions. Nonstructural interior ions can be chemically reduced to yield dendrimer-encapsulated metal nanoparticles. Because each dendrimer contains a specific number of ions, the resulting metal nanoparticles are in many cases of nearly monodisperse size. Nanoparticles within dendrimers are stabilized by the dendrimer framework; that is, the dendrimer first acts as a molecular template to prepare the metal nanoparticles and then as a stabilizer to prevent agglomeration. These composites are useful for a range of catalytic applications including hydrogenations and Heck chemistry. The unique properties of the interior dendrimer microenvironment can result in formation of products not observed in the absence of the dendrimer. Moreover the exterior dendrimer branches act as a selective gate that controls access to the interior nanoparticle, which results in selective catalysis. In addition to single-metal nanoparticles, it is also possible to prepare bimetallic nanoclusters and dendrimer-encapsulated semiconductor nanoparticles, such as CdS, using this same general approach.

Dendrimer-Encapsulated Metals and Semiconductors: Synthesis, Characterization, and Applications

Composite colloids of gold and polypyrrole were prepared using two different methods: 1, using pyrrole colloid, created by the oxidation of pyrrole by ferric chloride, to subsequently reduce chlorauric acid and, 2, oxidizing pyrrole monomer with chlorauric acid in a sodium dodecylbenzene sulfonate solution. In each case, the polypyrrole colloid consisted of irregularly shaped particles approximately 500 nm in diameter. The gold produced in each case was in the form of irregular spheres, approximately 407 nm in diameter in method 1 and 13 nm in method 2. X-ray photoelectron spectroscopy was used to determine the oxidation state of the species present. Transmission electron microscopy and light scattering data were used to determine the particle sizes of both gold and polypyrrole colloids. Energy dispersed spectrum X-ray analysis and electron diffraction were used to confirm the presence of metallic gold in the composite colloids. The second-order rate constant for the reaction of chlorauric acid with pyrrole in dilute solution was found to he 13 M -1 s -1 . Aqueous solutions of palladium, platinum, rhodium, cobalt, tin, silver, zinc, nickel, titanium, cadmium, mercury, arsenic, and selenium were also examined for their potential to act as oxidants to produce composite polypyrrole colloids. Palladium, platinum, and rhodium salts were suitable oxidants, producing polypyrrole in less than 12 h.

https://iopscience.iop.org/article/10.1149/1.1405802/pdf

Reaction of Pyrrole and Chlorauric Acid A New Route to Composite Colloids

A new class of polyhydrazides having aromatic as well as aliphatic units has been synthesized by low-temperature solution polycondensation from equimolar amounts of diacid chloride and dihydrazides in HMPT as solvent. These polyhydrazides have poor solubilities and their intrisnsic viscosities ranged from 0.2 to 0.6 dl/g. X-ray diffractograms of these polyhydrazides show that the polymers having terephthalic acid dihydrazide unit were more crystalline and all the polymers have densities in the range of 1.2-1.8 g/cm3. Thermogravimetric analysis of these polyhydrazides showed initial weight losses commencing at 220–300°C in both air and nitrogen.

Preparation and properties of novel polyhydrazides

Copolymerization of 2-hydroxyethyl methacrylate (HEMA) with eight acrylic monomers and vinyl acetate using redox initiators was carried out in DMF and in aqueous medium. Reactivity ratios were calculated according to the general copolymerization equation using Fineman-Ross, Kelen-Tudos and the YBR methods. The results indicate that reactivity of the methacrylates towards growing HEMA radicals decreased in the order, methyl methacrylate > 2-dimethylaminoethyl methacrylate > 2,3-epoxypropyl methacrylate. Reactivity of the acrylates decreased in the order butyl acrylate > ethyl acrylate > methyl acrylate. In the HEMA-acrylate systems, the intrinsic viscosity of the copolymers decreased with increasing content of the acrylates in the copolymer. On the other hand, the intrinsic viscosity of the copolymers of HEMA-MMA showed an increasing trend with increasing content of MMA in the copolymer. Changing the polymerization medium from DMF to water resulted in copolymers having a higher HEMA content.

Redox‐initiated radical polymerization of 2‐hydroxyethyl methacrylate, 3. Copolymerization with nine monomers, effect of structure and media on the reactivity of monomers

The kinetics of oxidation of dimethyl sulfoxide by tervalent manganese was investigated in sulfuric and perchloric acid media at 40–45°C. A mechanism involving prior complexation between reactants followed by a reversible electron-transfer step was shown to be consistent with the kinetics. The radical ion thus produced initiates polymerization of acrylonitrile, the termination being effected by the oxidant. Rates of polymerization vary directly as the sulfoxide concentration and are proportional to the square of the monomer concentration and being independent of the oxidant. Oxidation as well as polymerization is retarded by Mn(II). Average degrees of polymerization lend support to the proposed mechanism. Rate parameters have been evaluated in the two media, and their significance is discussed.

V. Mahadevan

Papers

Preparation and properties of novel polyhydrazides

Redox‐initiated radical polymerization of 2‐hydroxyethyl methacrylate, 3. Copolymerization with nine monomers, effect of structure and media on the reactivity of monomers

Redox polymerization of acrylonitrile‐kinetics of the reaction initiated by the redox system dimethyl sulfoxide–Mn(III)

Poly(maleimide-amine)s and poly(maleimide-amine)ethers

Synthesis of some low glass transition temperature polytetrahydrofuran polymers