Polyurethane crystal structure

The addition of small amounts (ca 0,6%) of cellulose esters removes exudate by absorption, and also reduces the tendency to crack (Ref 17) polyurethanes remove exudate and double the compressive strength of the case (Ref 8), or impart finer crystal structure to the TNT matrix (Ref 33). Exudation is also, discussed in a limited-access report (Ref 11)... 

On the other hand, there are data suggesting that amides have a rather high value for association as pure liquids. Trifan and Terenzi measured IR spectra of several polyamides and polyurethanes from 25°C to 300°G. They deduce an average —AH of 8.5 1.2 kcal/mole for the polymers. Until more data are available we must draw the provisional conclusion that —AH for amide N—bonds in crystals (and possibly in pure liquids) may be much larger than in solutions. Under any circumstances, however, we arc reminded that the data of Davies establish empirically the substantial contribution of the amide groups to the stability of the amide crystal structures. 

Two crystalline structures have been found for MDI-BD hard segments in the unoriented state with another distinct form found in the oriented state (Briber and Thomas, 1983,1985). Other studies have examined the effect of chain extender length on the crystal structure (Blackwell et al., 1982). The differences between polyurethanes with chain-folded and chain-extended hard segment crystallites have been extensively studied by Eisenbach and Stadler (1995). 

A model for the chain conformation and packing of diphenyl methane 4,4 -di-isocyanate butane diol (M) hard segments in polyurethane elastomers" has been made based on the single crystal structure of the monomer unit, Me-M-Me in which... 

Sebastian Munoz-Guerra completed his Ph.D in Organic Chemistry in 1974 at the University of Seville. After postdoctoral work on crystal structure and morphology of non-conventional nylons, he initiated research on synthesis and characterization of bio-based polymers and copolymers. Since 1987, he is full Professor in Chemical Engineering at the Technical University of Catalonia in Barcelona. His current research is focussed on the development of polyesters, polyamides and polyurethanes derived from carbohydrates with special attention paid to industrial aromatic polyesters, as well as on modification of microbial biopolymers with therapeutic interest. He has authored more than 200 peer reviewed papers and several book chapters, and has been granted more than 15 patents on these issues. 

The crystal structure and three-dimensional network prevent cellulose from behaving as a polyol for PU syntheses. To overcome this problem a liquefaction process in the presence of organic solvents was developed and resulted in products suitable for PU synthesis. Yan and co-workers (2008) liquefied corn stalk, an agricultural by-product, and tested it for the synthesis of PU foams blown by water. The report revealed that such polyurethane foams had excellent mechanical and thermal properties and could be used as heat insulating materials. 

BOURIDAH A, DALARD F, DEROO D, CHERADAME H, LE NEST J F (1985), Poly(dimethlsilo-xane)-poly(ethylene oxide) based polyurethane networks used as electrolytes in lithium electrochemical solid state batteries . Solid State Ionics, 15,233-240. CHADWICK B M, JONES D w, WILDE H J, YERKESS J (1985), X-ray and neutron diffraction studies of the crystal structures of the dicesium lithium hexacyanometallates of iron(III) and cobalt(III) , J Cryst Spectrosc, 15,133-146. 

T.L. Boggs et al, AIAA J 8 (2), 370-72 (1970) CA 72, 113371 (1970) Scanning electron microscopy is used to study the surface structure of solid proplnts, prepd from AP (1) and polyurethane or caiboxylated polybutadiene. Polyurethane proplnts are self-extinguish-ing at high pressure due to the flow of molten binder over I crystals. I crystals formed a thin surface melt with gas liberation in the molten phase... 

URETHANE. [CAS 51-79-6], CO(NH2)OC2H5, also referred to as ethyl carbamate or ethyl urethane. Its structure is typical of the repeating unit in polyurethane resins. Colorless crystals or white powder, odorless, saltpeterlike taste. D 0.9862. mp 49C, bp 180C solutions neutral to litmus, soluble in w ater, alcohol, ether, glycerol, and chloroform slightly soluble in olive oil. Formed by the heating of ethanol and urea nitrate to 120-130% or by the action of ammonia on ehtyl carbonate or ethyl chloroformate. 

The formation of cellular products also requires surfactants to facilitate the formation of small bubbles necessary for a fine cel] structure. The most effective surfactants are polyoxyalkylene-polysiloxane copolymers. The physical properties of polyurethanes are derived from their molecular structure and determined by the choice of building blocks as well as the suprainolecular structures caused by atomic interaction between chains. The ability to crystallize, the flexibility of the chains, and spacing of polar groups are of considerable importance, especially in linear thermoplastic materials. In rigid cross-linked systems, e.g., polyurethane foains, other factors such as density determine the final properties. 

The variation of Tg of the soft matrix in segmented polyurethanes as a function of composition or segmental chemical structure has been monitored and used as an indicator of the degree of microphase separation. Factors influencing the phase-separation process in these MDI-based polyurethanes have been summarized by Aitken and Jeffs (69) as follows (a) crystallization of either component, (b) the steric hin-... 

As mentioned in the previous section, hollow zeolite spheres of LTA, FAU, BEA, MFI can be prepared in the presence of polystyrene beads as templates by using an LBL self-assembly technique. Recently, several research groups have tried to adopt similar methods to synthesize zeolite-template composites on the surfaces of templates with various shapes and sizes, properties, and structures through self-assembly or in situ-crystallization approaches. Subsequent removal of the templates forms zeolite materials with analogical skeletons of the templates. Up to now, the reported templates include microspheres, carbon fibers, polyurethane foams, and microbe structures,[144,145] as well... 

Sepiolite was subjected to a thermal treatment which removes crystallization water at 500 C and constitution water at 850°C. When these changes occur, they are accompanied by crystal folding which introduce substantial changes in the structure and interaction capabilities of sepiolite. Treated and untreated sepiolites were used in the preparation of a polyurethane adhesive to determine if the modification impacts the properties of the adhesive such as its interaction with polymer essential for its performance in adhesive. Figure 19.1 shows the effect of treatment... 

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