Chetna Khosla, Andrew B. Jackson, Peter S. White,
Isocyanate - Wikipedia
/ Khosla, Chetna; Jackson, Andrew B.; White, Peter S.
The polyols used are either hydroxyl-terminated polyethers (in about 90% of total polyurethane manufacture) or hydroxyl-terminated polyesters. They have been developed to have the necessary reactivity with the isocyanate that will be used and to produce polyurethanes with specific properties.
It is expensive to produce this mixture in different proportions. It means purifying the mixture of the nitromethylbenzenes, NMB, by very careful distillation.
Cookies are used by this site. To decline or learn more, visit our
Soya bean oil contains triglycerides of long chain saturated and unsaturated carboxylic acids, which, after hydrogenation, can, on reaction with epoxypropane, form a mixture of polyols suitable for the manufacture of a wide range of polyurethanes. The use of these biopols means that at least part of the polymer is derived from renewable sources.
If the polyol has two hydroxyl groups and is mixed with either TDI or MDI, a linear polymer is produced. For example, a linear polyurethane is produced by reaction with a diisocyanate and the simplest diol, ethane-1,2-diol, a occurs:
The mixture of diisocyanates known as TDI consists of two isomers:
If the polyol has more than two reactive hydroxyl groups, adjacent long-chain molecules become linked at intermediate points. These crosslinks create a stiffer polymer structure with improved mechanical characteristics which is exploited in the development of 'rigid' polyurethanes. Thus a diisocyanate, such as MDI or TDI which reacts with a polyol with three hydroxyl groups, such as one derived from propane-1,2,3-triol and epoxyethane, undergoes crosslinking and forms a rigid .
An example of a polyol with two hydroxyl groups (ie a long chain diol) is one made from (propylene oxide), by interaction with propane-1,2-diol, (which itself is formed from epoxypropane, by hydrolysis):
which may be represented as this idealised structure:
1155 Sixteenth Street N.W.Washington, DC 20036
Date last amended: 24th April 2017
1155 Sixteenth Street N.W.Washington, DC 20036
It’s easy to organize your research with our built-in tools.
Citation data is made available by participants in Cited-by Linking service. For a more comprehensive list of citations to this article, users are encouraged to perform a search in.
All the latest content is available, no embargo periods.
A shoe sole, for example, may be 'blown' to double the volume of solid polymer. This process is so versatile that the expansion can be taken much further. In low-density foams for upholstery or thermal insulation less than 3% of the total volume is polyurethane. The gas has expanded the original volume occupied by the liquid by 30 to 40 times. In the case of cushions, only just enough solid polymer is needed to ensure that we can sit comfortably.
Instant access to the journals you need!
The synthesis of rigid-rod, helical isocyanate-based macromonomers was achieved through the polymerization of hexyl isocyanate and 4-phenylbutyl isocyanate, initiated by an -norbornene functionalized half-titanocene complex. Sequential ruthenium-mediated ring-opening metathesis polymerization of these macromonomers readily afforded well-defined brush block copolymers, with precisely tunable molecular weights ranging from high (1512 kDa) to ultrahigh (7119 kDa), while maintaining narrow molecular weight distributions (PDI = 1.08–1.39). The self-assembly of these brush block copolymers to solid thin-films and their photonic properties were investigated. Due to the rigid architecture of these novel polymeric materials, they rapidly self-assemble through simple controlled evaporation to photonic crystal materials that reflect light from the ultra-violet, through the visible, to the near-infrared. The wavelength of reflectance is linearly related to the brush block copolymer molecular weight, allowing for predictable tuning of the band gap through synthetic control of the polymer molecular weight. A combination of scanning electron microscopy and optical modeling was employed to explain the origin of reflectivity.
Read and print from thousands of top scholarly journals.
In thermal insulation, it is the gas trapped in the cells which insulates. The polymer that encloses the cells reduces the insulation efficiency, so it makes sense to have as little of it as possible.
Bookmark this article. You can see your Bookmarks on your .
A tiny amount of air is dispersed through the mixture of polyisocyanate and polyol. This provides nucleation seeds for the multitude of gas bubbles that are produced throughout the polymer. Heat makes the bubbles expand until the chemical reaction changes the liquid to solid polymer, and the available gas pressure cannot create any further expansion.
"I have always been impressed by the quick turnaround and your thoroughness. Easily the most professional essay writing service on the web."
"Your assistance and the first class service is much appreciated. My essay reads so well and without your help I'm sure I would have been marked down again on grammar and syntax."
"Thanks again for your excellent work with my assignments. No doubts you're true experts at what you do and very approachable."
"Very professional, cheap and friendly service. Thanks for writing two important essays for me, I wouldn't have written it myself because of the tight deadline."
"Thanks for your cautious eye, attention to detail and overall superb service. Thanks to you, now I am confident that I can submit my term paper on time."
"Thank you for the GREAT work you have done. Just wanted to tell that I'm very happy with my essay and will get back with more assignments soon."