The development of a high clarity polyurethane adhesive from a crystalline soft-phase capable of bonding untreated and ethanolamine surfaced-treated polycarbonate is described.A series of polyurethanes were prepared, based on poly(caprolactone diol), selected as the soft-phase as its ester-functionalised backbone structure will assist the adhesive performance.A high crystallinity soft-phase, however, will have an adverse effect on the adhesive's clarity.However, through careful design of the hard-phase architecture, it is possible to address this issue. Eight formulations were synthesised each with a subtly different hard-phase architecture, created using a combination of methylene diphenyl diisocyanate or isophorone diisocyanate with trimethylol propane only or by including the chain-extenders 2,2-diethyl-1,3-propane diol, 1,3-butane diol and 1,2-propane diol. DSC and FTIR data show that having trimethylol propane alone is not sufficient in disrupting soft-phase crystallisation in the methylene diphenyl diisocyanate formulations, and that for total removal of soft-phase crystallisation a diol chain-extender is required to promote phase mixing within the microphase structure. This reduces peel strengths but values remain above 3 N mm -1 on both untreated and ethanolamine treated polycarbonate after 18 months. More importantly, the change to the morphology markedly improves clarity. In contrast, isophorone diisocyanate systems show poor phase mixing even in the presence of the chain-extenders and, although offering good peel strengths, have low clarity. cured MCPU-Us, the biphasic morphology consists of a hard-segment and a soft-phase. The soft-phase is normally a polyether or polyester which possesses a low temperature glass transition, making it responsible for the flexibility and softness of the matrix. These properties can be adjusted via careful selection of the molecular weight, functionality and structure of the soft-phase. 11,12 The hard-phase of the copolymer is responsible for the cohesive strength within the MCPU-U matrix and is constructed using diisocyanates and chain-extenders. The properties of the hard-phase can be modified by the hard-segment content, diisocyanate, chain-extender and curing conditions. 11,13-15 MCPU-Us are commonly obtained by application of a polyurethane (PU) prepolymer which moisture cures via diffusion of water from the atmosphere. As moisture diffuses, nucleophilic attack of isocyanate groups by water occurs producing an amine and carbon dioxide. 16 Reaction of these amine groups with a further isocyanate groups leads to the formation of urea linkages yielding the final MCPU-U material (figure 1) 17 In coating applications, moisture diffusion occurs initially at the adhesive -air interface. As the coating beings to cure a "skin" forms at the interface, with this process altering the rate of further moisture diffusion to the bulk. The rate at which full cure is obtained will be determined by the rate of diffusion through the cured interface and the thickness of coating laye...

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The behavior of gelatin hydrogels is influenced by the charges located on the amino acid side chains throughout the gelatin molecules. The presence and distribution of ionisable side chains influences the surface activity of gelatin and ultimately determines the material properties. Herein, we report the influence of pH on mechanical properties as studied by texture analysis supported by data from polarimetry, zeta potential, pH titrations and NMR experiments. When adjusted to more extreme pH values (pH 2 and 12), softer gelatin blocks were observed. However, at pH values close to the isoelectric point (pH 5–10), the material is firmer. This behavior is related to the helical content. At pH 2 and pH 12 the surface of the gelatin carries a net charge, positive and negative, respectively, that inhibits the formation of tight helices and lowers the physical crosslink network density. Chemical shift perturbations were observed for the acidic amino acids glutamic and aspartic acid, under acidic pH, where their peaks shifted to higher ppm. Intense amide signals were observed at acidic pH but diminished with increasing pH. This was due to an increase in the rate of chemical exchange between the solvent and peptide amide protons as the pH increases.

Polystyrene and poly(4-methylstyrene) have very similar chemical structures with the only differences being the para methyl group of poly(4-methylstyrene). This methyl group is susceptible to oxidation at elevated temperatures. Here we demonstrate that it is possible to introduce oxidative cross-links to poly(4-methylstyrene), via the para methyl group, by thermal oxidative treatment at 230 °C, 250 °C and 270 °C in the absence of catalyst, leading to a material with markedly modified thermal degradation chemistry. Thermal gravimetric analysis and differential scanning calorimetry were used to characterise and compare untreated and post-oxidised materials and established that as the temperature of pre-treatment was increased, the subsequent thermal stability of the material increased. FTIR, NMR and microanalysis indicated that after the thermal oxidative pre-treatment ether cross-links are present alongside new oxygen containing functional groups such as aldehydes, carboxylic acids and hydroxyl groups. Finally, data obtained from pyrolysis combustion flow calorimetry confirmed that as the number of oxidative cross-links increase, a reduction in the polymer's flammability as assessed by heat release data is observed