Polyurethane preparation

Write the structure of a representative segment of polyurethane prepared by reaction of ethylene glycol with MDI (Problem 31.29). 

Owing to their improved stability towards hydrolysis and oxidation, dimer diol polyethers (and dimer diol polycarbonates) are used as soft segments in the preparation of thermoplastic polyurethanes. Polyurethanes prepared from such oleo-chemical building blocks are very hydrophobic and show the expected stability. 

Polyurethanes prepared via the use of renewable carbon sources are a relatively recent introduction to the commercial market. The opportunity is driven primarily by the high and volatile cost of petroleum, and by societal concerns over the... 

Woodhouse described a degradable polyurethane prepared with a novel amine chain extending agent. As with the insertion of lactic acid into the backbone, bio-degradability was achieved, but the fragments appeared problematic. Thus, while biodegrading polyurethanes are fairly simple to prepare, one must be aware of the product to which a polyurethane degrades. The use of TDI as the isocyanate would clearly raise concerns from the FDA. 

In a recent patent, Reuter (110) describes a polyurethane prepared from PTHF (mol. wt. 1000 to 3000), 1,4-butanediol, and OCN(CH2)6CN0. In another case Murbach and Adicoff (67) interrupted the regularity of PTHF by copolymerization with ethylene oxide before chain extension with diphenyl-methane-4,4 -disiocyanate. Dickinson (99) prepared a series of polyurethane elastomers from THF-PO copolymer diols and 2,4-tolylene diisocyanate. He found that the use of copolymers with approximately 75 wt.-% THF led to polyurethanes with very good properties relative to the use of propylene oxide homopolymer. 

Furthermore, Wall reviewed the fluorinated polyurethanes prepared from polyesters of fluorinated diols [79], from fluorinated polyethers [80] and detailed their properties [81]. 

The value of a for poly(propylene oxide) was obtained from the data of Moacanin 189) for polyurethanes prepared by condensation of toluene-2,4-diisocyanate with atactic polypropylene glycols of molecular weights about 1000 and 2000. The small quantity of diisocyanate present in these compositions can make only a negligible effect on the chain dimensions (less than one per cent on the freely rotating chain, as is... 

Spindler, R., and Frechet, J. M. J. 1993. Synthesis and characterization of hyper-branched polyurethanes prepared from blocked isocyanate monomers by step-growth polymerization. Macromolecules, 26, 4809 1813. 

The viscoelastic properties of carbon nanotube/polymer composites have both practical importance related to composite processing and scientific importance as a probe of the composite dynamics and microstructure. The viscosity for CNT/PU dispersion at mixing is also very important for in-situ formation of polyurethane nanocomposite. Lower viscosity means a better flow ability and more homogenous mixing with isocyanate. Furthermore, low viscosity is very helpful to remove the bubbles before curing, which is a key step for polyurethane preparation. 

T.J0- Write the structure of n repreaentative se.gmcnt of polyurethane prepared hy reaction of ethylene idycol with MI>I (Probltrni 31-29.1. 

Polyurethanes have frequently been prepared in the laboratory from diamines and bis-chloroformates, using interfacial or solution techniques. The processes have not been widely used in industry, however. The general considerations of interfacial and solution processes described in Section 3 apply to polyurethane preparations by these methods. Specific... 

Test Methods. Prior to testing, the polyurethane preparations were sheeted out on a 4 inch plastics mill at 120° - 140°C and samples for tests or molding were taken from this sheet. 

Isocyanate Content Isocyanate levels in polyurethane preparations were measured on 2g samples taken from the polym-erizate and immediately cut into small pieces which were then promptly immersed in excess 0.05 N di(n-butyl)amine solution in dry tetrahyrofuran which was contained in an iodine flask. The gross weight of reagent plus flask was very accurately determined ahead of time to enable the exact weight of the added polyurethane sample to be subsequently determined by difference. Excess di(n-butyl)amine was titrated with 0.05N hydrochloric acid to the bromcresol green endpoint to enable calculation of the sample isocyanate concentration. 

It can be seen from Table XIII data that control Polymer 7 is a high molecular weight and high quality polyurethane whereas the modified polymerization yielded lower molecular weight Polymer 19 with good but lesser properties. The lowest final (16 minute) [NCO] was obtained in the polyurethane prepared with a diisocyanate deficiency in the charging recipe. 

Typical polyamides and polyurethanes prepared from aminosugars, both from anhydroalditols and protected monosaccharides, are shown in Figures 1.8 and 1.9, respectively. 

Starch polyurethane foams could be converted into sorbents for water when starch-acrylonitrile or starch-methacrylonitrile graft copolymers were crosslinked with diisocyanates.2655 2656 Such polyurethanes have been proposed as occlusive wound dressings,2657 as well as sizes for cotton yams.2658 Starch polyurethanes for reinforced paper were produced in reaction of iV-chlorocarbamoylethyl starch with cresol or thiolignin.2659 The addition of mineral salts to polyurethanes prepared from starch and urea improved their performance as adhesives.570... 

Petrovic, Z.S. W. Zhang I. Javni. Structure and properties of polyurethanes prepared from triglyceride polyols by ozonolysis. Biomacromolecules 2005b, 6, 713—719. 

L. Chan-Chan, R. Solis-Correa, R. Vargas-Coronado, J. Cervantes-Uc, J. Cauich-Rodriguez, P. Quintana, P. Bartolo-Perez, Degradation studies on segmented polyurethanes prepared with HMDI, PCL and different chain extenders, Acta Biomater. 6 (6) (2010) 2035-2044. 

Okieimen, F.E., Bakare, I.O. and Pavithran, C. (2009) Network stmctures, flexibility and stability in thermal and chemical environments of polyurethane prepared from mbber seed oil. Advanced Materials Research (Zuerich, Switzerland), 62-64, 324-334. 

CALORIMETRIC STUDY OF OLIGO/ETHYLENE ADIPATES/ AND LINEAR AND CROSSLINKED POLYURETHANES PREPARED FROM THEM. 

Key words vegetable oil-based polyurethane, preparation of polyurethane, curing of polyurethane, stmcture-property relationships of polyurethane, application of polyurethane. 

Various catalysts are used to prepare polyurethane at a relatively low temperature and with a much faster rate of polymerisation than would be the case with an uncatalysed reaction. Catalysts may be classified into two broad categories namely, amine (basic) compounds and organometalhc complex compounds. Tertiary amine is stiU one of the most frequently used urethane catalysts. Commonly used amine catalysts are triethylenedi-amine (TEDA), l,4-diazabicyclo[2.2.2]octane (DABCO), triethylamine (TEA), dimethylethanolamine (DMEA) and dimethylcyclohexylamine (DMCHA). The catalysis mechanism of tertiary amine catalysed urethane reaction involves complexation of the amine with isocyanate groups, followed by reaction of the complex with alcohol to produce polyurethane. A list of catalysts used in polyurethane preparation is given in Table 6.4. 

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