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Published in Joseph C. Salamone, Polymeric Materials Encyclopedia, 2020
Studies of phenyl isocyanate and methanol by Baker et al. found that the catalytic activity of certain tertiary amines (quinoline, pyridine, α-picoline, and triethylamine) increased with amine basicity.10,12 They also found, however, that dialkylanilines with a basicity comparable with that of pyridine and α-picoline were not effective catalysts. This latter finding points to the importance of steric considerations in the formation of transition states. In addition, it was found that urethane itself catalyzes the formation of urethane and indicates that this reaction does not proceed in a truly uncatalyzed fashion. The data in Table 1, obtained for the reaction of phenyl isocyanate and n-butanol in toluene, as well as that obtained for other systems, illustrate the importance of steric hindrance on catalytic activity.18,19 A. Farkas and P. F. Strohm suggest that basicities determined potentiometrically in ethyl acetate yield a better correlation with catalytic activity than do pKa values.21
Tracking Microwave-Assisted Sample Preparation Through the Last Years
Published in Banik Bimal Krishna, Bandyopadhyay Debasish, Advances in Microwave Chemistry, 2018
Mónica B. Alvarez, Anabela Lorenzetti, Carolina C. Acebal, Adriana G. Lista, Claudia E. Domini
An on-line method for the assisted microwave derivatization of aliphatic and Chávez et al. [312] developed polyethoxylated alcohols with phenyl isocyanate or benzyl chloride reagents. The solution containing the alcohols and the reagents (phenyl-isocyanate and benzoyl chloride) in acetonitrile medium was inserted into acetonitrile carrier stream and driven to a spiral Teflon coil reactor placed into a household microwave (450 W). The sample was irradiated at 400 W for 60 s and the derivatization reaction took place. After derivatization process, the reactions products were loaded in the loop of an injection valve and injected into a HPLC system with photodiode array detection for separation. Compared to the conventional conditions, the proposed method presented high sensitivity, and analysis time has been drastically reduced (10 times), as has the number of reagents used.
Reactivity and Accessibility of Cellulose, Hemicelluloses, and Lignins
Published in David N.-S. Hon, Chemical Modification of Lignocellulosic Materials, 2017
Cellulose can be esterified by reacting with acids, acid chloride, anhydrides, or unsaturated agents [5,73] such as CS2, phenyl isocyanate [128,145] and urea. Model Glucosides. The esterification of simple glycoside in homogeneous system generally indicated [84,141] that the 6-OH group is more reactive than the secondary OH groups. The relative reactivity of the 2-OH and 3-OH groups depends appreciably on the reagent used [146] and on the nature of the glycosides [147–149]. Acetylation with acetic chloride favored reaction at the 2-OH site whereas it occurred preferentially at the 3-OH with acetic anhydride. The reaction of methyl a-D-glucopyranoside with 1 M equivalent of acetic anhydride in pyridine [147] indicated that the DS was essentially identical for the C2, C3, and C4 positions (0.2) and higher (0.4) for the C6.
A review: can waste wool keratin be regenerated as a novel textile fibre via the reduction method?
Published in The Journal of The Textile Institute, 2022
A recent example reported by Cao (Cao et al., 2020) extracted keratin from wool via a reduction method, and blended with hydroxypropyl cellulose (H-HPC). This blend was then spun via a wet spinning method, and cross-linked with glutaraldehyde (GA) and subsequently with 4,4′-methylenebis- (phenyl isocyanate) (MDI). Filaments containing 10 wt% H-HPC as-spun, had a tensile strength of around 0.7 g/den. Cross-linking with just glutaraldehyde offered only some increase in strength (tenacity), but also cross linking with 4,4′-methylenebis- (phenyl isocyanate) imparted a favourable tenacity of around 1.04 g/den (Cao et al., 2020), an almost 1.5 fold increase. The effect on the keratin chain arrangement is seen in Figure 14. The cross linking imparts a favourable tensile strength within the range of the minimum application requirement of wool fibres in the industry (Cao et al., 2020).
Synthesis of helical branched carbodiimide polymers with liquid crystalline properties
Published in Liquid Crystals, 2022
Enosha Harshani De Silva, Bruce M. Novak
4.59 g (0.047 mol) of 5-hexyn-1-amine and 5.64 g (0.047 mol) of phenyl isocyanate were combined and allowed to react 8 h in dichloromethane. The obtained, white-coloured urea was recrystallised in ethanol. The corresponding white-coloured crystals were separated by filtration and dried under vacuum. To a round bottom flask, 100 mL of dichloromethane was combined with 2.50 g (5.78 mmol) of triphenylphosphine dibromide, 1.60 mL (11.57 mmol) triethylamine, and the 1.00 g (4.63 mmol) of synthesised urea at 0°C. The reaction was allowed to reach room temperature and monitored by IR (Infrared) spectroscopy, monitoring the appearance of a strong carbodiimide stretching peak at ~2140 cm−1. The reaction was quenched by adding n-hexane, and the solution was filtered to remove the byproducts of triphenylphosphine oxide and triethylammonium bromide salt. The filtrate was evaporated by rotary evaporation. The monomer was further purified by performing silica gel chromatography with dichloromethane as the mobile phase. Colourless thick liquid yield 90%. 1H NMR (500 MHz, CDCl3): δ (ppm) 7.32 (2H, d, Ar-H),7.13 (3 H, d, Ar-H), 3.49 (2 H, t, NCH2), 2.29 (2 H, td, CH2), 2.00 (H, t, CH),1.83 (2 H, p, CH2), 1.70 (2 H, p, CH2).
Glove permeation of chemicals: The state of the art of current practice—Part 2. Research emphases on high boiling point compounds and simulating the donned glove environment
Published in Journal of Occupational and Environmental Hygiene, 2020
Diisocyanates (isocyanates), including methylene diphenyl diisocyanate (MDI), are the primary reactive components of spray polyurethane foam (SPF) insulation. Five common disposable garment materials (disposable latex gloves [0.07 mm thickness], nitrile gloves [0.07 mm], vinyl gloves [0.07 mm], polypropylene coveralls [0.13 mm], and Tyvek coveralls [0.13 mm]) were tested by Mellette et al. (2018). These materials were cut into small pieces and assembled into a permeation test cell system and coated with a two-part slow-rise SPF insulation. Glass fiber filters (GFF) pretreated with 1-(9-anthracenylmethyl)piperazine) were used underneath the garment to collect permeating isocyanates. GFF filters were collected at specific time intervals between 0.75 and 20.00 min and subsequently analyzed using liquid chromatography-mass spectrometry (LC-MS). The cumulative permeated concentration of total isocyanate, including phenyl isocyanate and three MDI isomers, was measured over the test time. The estimated BT, average permeation rate, and standardized breakthrough time (SBT) at the estimated 0.1 µg/cm2/min permeation rate were also determined. Typical isocyanate loadings were in the range of 0.900–15 µg MDI/cm2. Each type of glove material had an observed average permeation rate well below the ASTM F739 SBT. Disposable latex gloves displayed the greatest total isocyanate permeation rate (4.11 ng/cm2/min), followed by the vinyl and nitrile gloves, respectively. Nitrile gloves also showed the lowest cumulative permeation.