Blocked isocyanates:from analytical and experimental considerations to non-polyurethane applications

In this review we aim to provide an introductory guide to blocked isocyanates, through discussion on different examples of blocking groups, along with experimental considerations for their application. The review brings together updated examples of functionalities used and places specific emphasis on the analytical techniques used for the determination of deblocking temperature, updating previous reviews with the newly applied technique of X-ray photoelectron spectroscopy (XPS). Additionally, we put forward a brief update on the use of blocked isocyanates for other non-traditional polyurethane based polymer applications. We also highlight the importance of matching the analytical technique to the application of the blocked isocyanate, with differences in material state and experimental parameters having a great impact on the deblocking temperature reported

Fluoride degradable and thermally debondable polyurethane based adhesive

We report the one-pot, solvent free synthesis of a stimuli-responsive polyurethane (PU) adhesive. The hard domains within the supramolecular PU network contain a silyl protected phenol ‘degradable unit’ (DU). The DU undergoes rapid decomposition (<30 minutes) upon treatment with fluoride ions which causes depolymerisation of the linear PU adhesive. The mechanism of depolymerisation was investigated in solution using 1H NMR spectroscopy by following the degradation of the polymer in the presence of tetra-butylammonium fluoride (TBAF). In the absence of fluoride ions, the material behaves as a typical thermoplastic adhesive, and underwent four adhesion/separation cycles without loss of strength. The fluoride initiated depolymerisation of the PU adhesive in the solution state was verified by GPC analysis, showing reduction in Mn from 26.1 kg mol−1 for the pristine PU to 6.2 kg mol−1 for the degraded material. Degradation studies on solid samples of the PU which had been immersed in acetone/TBAF solution for 30 minutes exhibited a 91% reduction in their modulus of toughness (from 27 to 2 MJ m−3). Lap shear adhesion studies showed the fluoride responsive PU was an excellent material to join metallic, plastic, glass and wood surfaces. Pull adhesion tests confirmed that immersing the adhesive in TBAF/acetone solution resulted in a reduction in strength of up to 40% (from 160 N to 95 N at break) after drying

Anion complexation properties of thiophene-2,4-and-2,5-biscarboxamides

Thiophene-2,4- and -2,5-biscarboxamides have been synthesised and shown to act as anion receptors in DMSO-d(6)/water solution. The crystal structure of the fluoride complex of a N,N'-diphenylthiophene-2,5-biscarboxamide derivative has been solved and reveals the involvement of the thiophene CH protons in anion complexation in the solid state

Pentapyrrolic calix[4]pyrrole

A new calix[4]pyrrole has been synthesised that contains a 3,4,5-trisbromopyrrole appended to one meso-position which shows enhanced anion affinity as compared to the parent meso-octamethylcalix[4]pyrrole macrocycle

2,5-Diamidofuran anion receptors

3,4-Diphenylfuran-2,5-dicarboxylic acid bis-N-phenylamide 1 and 3,4-biphenyl-furan-2,5-dicarboxylic acid bis-N-butylamide 2 have been synthesised and shown to act as fluoride selective anion receptors in DMSO-d6/0.5% water solution

Anion complexation and electrochemical behaviour of ferrocene-appended amido-pyrrole clefts

Two amido-pyrrole cleft anion receptors bearing two ferrocene reporter groups have been synthesised and crystallographically characterised; the receptors contain either a non-conjugated or conjugated link between the anion-binding amido-pyrrole unit and the ferrocene reporter groups. The anion binding a?nities and electrochemical behaviour of the receptors in the absence and presence of anions have been studied by 1H NMR titration techniques and cyclic voltammetry using a Pt microdisc working electrode, respectively

Crystallographic and solution anion binding studies of bis-amidofurans and thiophenes

A variety of furan and thiophene amide and thioamide cleft type anion receptors have been synthesised and crystallographically characterised. Unlike 2,5-diamidopyrrole anions, analogous 2,5-diamidofurans and thiophenes do not interlock in the solid state. The anion binding properties of these receptors have been investigated in DMSO/0.5% water solution using H-1 NMR titration techniques. Solution studies and solid-state evidence suggests that the thiophene receptors may utilise a thiophene CH hydrogen atom for hydrogen bond formation to anions with a 2,4-diamidothiophene showing similar anion binding affinities to a 2,5-diamidopyrrole

Mono- and bis-ferrocene 2,5-diamidopyrrole clefts: solid-state assembly, anion binding and electrochemical properties.

Four amido-pyrrole cleft anion receptors bearing one or two ferrocene reporter groups have been synthesised and crystallographically characterised. The receptors contain either a non-conjugated (1 and 3) or conjugated (2 and 4) link between the anion binding amido-pyrrole unit and the ferrocene reporter groups. The anion binding affinities and electrochemical behaviour of the receptors in the absence and presence of anions have been studied by 1H NMR titration techniques and cyclic voltammetry using a Pt microdisc working electrode, respectively

Ferrocene substituted calix[4]pyrrole: a new electrochemical sensor for anions involving CH...anion hydrogen bonds

A new calix[4]pyrrole 1 containing a ferrocene moiety attached to one of the meso-positions has been synthesised by co-condensation of pyrrole, cyclohexanone and acetylferrocene. The crystal structure of 1 has been elucidated whilst 1H NMR titration studies in acetonitrile-d3/DMSO-d6 9:1 v/v have revealed that 1 binds fluoride, chloride, and dihydrogen phosphate in this solvent mixture. Electrochemical studies using cyclic voltammetric and square-wave voltammetric techniques show cathodic shifts of up to 100 mV (approx.) with dihydrogen phosphate anions

Carborane-induced excimer emission of severely twisted bis-o-carboranyl chrysene

\u3cp\u3eThe synthesis of a highly twisted chrysene derivative incorporating two electron deficient o-carboranyl groups is reported. The molecule exhibits a complex, excitation-dependent photoluminescence, including aggregation-induced emission (AIE) with good quantum efficiency and an exceptionally long singlet excited state lifetime. Through a combination of detailed optical studies and theoretical calculations, the excited state species are identified, including an unusual excimer induced by the presence of o-carborane. This is the first time that o-carborane has been shown to induce excimer formation ab initio, as well as the first observation of excimer emission by a chrysene-based small molecule in solution. Bis-o-carboranyl chrysene is thus an initial member of a new family of o-carboranyl phenacenes exhibiting a novel architecture for highly-efficient multi-luminescent fluorophores.\u3c/p\u3