Sequential polyurethane

In our laboratory, much attention has been devoted to the investigation of in situ sequential polyurethane/poly(methyl methacrylate) interpenetrating polymer networks (SEQ PUR/PAc IPNs) (2- ) in which the elastomeric polyurethane network is completely formed in the presence of the methacrylic monomers before the onset of the radical copolymerization which leads to the second network. To each polymerization process corresponds a typical kinetics, which however is not completely independent from each other ( -8). The results obtained with such SEQ IPNs show that the properties do in... 

The thermal degradation of mixtures of the common automotive plastics polypropylene, ABS, PVC, and polyurethane can produce low molecular weight chemicals (57). Composition of the blend affected reaction rates. Sequential thermolysis and gasification of commingled plastics found in other waste streams to produce a syngas containing primarily carbon monoxide and hydrogen has been reported (58). 

Hyperbranched polyurethanes are constmcted using phenol-blocked trifunctional monomers in combination with 4-methylbenzyl alcohol for end capping (11). Polyurethane interpenetrating polymer networks (IPNs) are mixtures of two cross-linked polymer networks, prepared by latex blending, sequential polymerization, or simultaneous polymerization. IPNs have improved mechanical properties, as weU as thermal stabiHties, compared to the single cross-linked polymers. In pseudo-IPNs, only one of the involved polymers is cross-linked. Numerous polymers are involved in the formation of polyurethane-derived IPNs (12). 

Air (hazardous waste site) (2,3,7,8-TCDD) Collection of sample onto glass fiber filter/polyurethane foam cartridge add [37CI4]2,3,7,8-TCDD and [13C12]2,3,7,8-TCDD Soxhlet extraction with CH2CI2 clean-up with acid/base sequentially on silica gel, modified silica gel, alumina, and carbon HRGC/LRMS No data 0.02 pg/m3 91-112 74-112 Fairless et al. 1987 Harless et al. 1992... 

Ultrasonic nebulizers have also been employed in continuous flow systems as interfaces between sample preparation steps in the analytical process and detection by virtue of their suitability for operating in a continuous mode. Thus, preconcentration devices have commonly been coupled to atomic spectrometers in order to increase the sensitivity of some analytical methods. An enhancement factor of 100 (10 due to USNn and 10 due to preconcentration) was obtained in the determination of platinum in water using a column packed with polyurethane foam loaded with thiocyanate to form a platinum-thiocyanate complex [51]. An enhancement factor of 216 (12 with USNn and 18 with preconcentration) was obtained in the determination of low cadmium concentrations in wine by sorption of metallic complexes with pyridylazo reagents on the inner walls of a PTFE knotted reactor [52]. One special example is the sequential determination of As(lll) and As(V) in water by coupling a preconcentration system to an ICP-AES instrument equipped with a USN. For this purpose, two columns packed with two different resins selective for each arsenic species were connected via a 16-port valve in order to concentrate them for their subsequent sequential elution to the spectrometer [53]. 

An example of a sequential-reaction extractive reaction is the manufacture of 2,4-dinitrotoluene, an important precursor to 2,4-diaminotoluene and toluene diisocyanate (TDl) polyurethanes. The reaction involves nitration of toluene by using concentrated nitric and sulfuric acids which form a separate phase. Toluene transfers into the acid phase where it reacts with nitronium ion, and the reaction product transfers back into the organic phase. Careful control of liquid-liquid contacting conditions is required to obtain high yield of the desired product and minimize formation of unwanted reaction products. A similar reaction involves nitration of benzene to mononitrobenzene, a precursor to aniline used in the manufacture of many products including methylenediphenylisocyanate (MDI) for polyurethanes [Quadros, Reis, and Baptista, Ind. Eng. Chem. Res., 44(26), pp. 9414-9421 (2005)]. 

The first part concludes with a discussion of the similarity between the mechanisms of initiation and chain transfer, the appreciation of which led to the inifer concept, which in turn yielded new telechelics, networks, sequential copolymers, etc. The second part of this presentation focuses on practical consequences of understanding details of the mechanism of initiation. The synthesis of a new family of telechelic linear and tri-arm star polyisobutylenes will be described. Among the new prepolymers are telechelic olefins, epoxides, aldehydes, alcohols, and amines. The preparation of new ionomers and polyisobutylene-based polyurethanes will be outlined and some fundamental properties of these new materials will be discussed. 

Where a step polymerization is used, almost always it is for the first polymer synthesized in a sequential IPN. The reasons involve the slow diffusion into a pre-existing network of most monomers used in step polymerization, and the relatively high glass transition of step polymerized polymers. The latter reason is important because in order for diffusion and concomitant polymerization to occur rapidly, polymer network 1 should be above its glass transition at the temperature of polymerization of monomer mix 11. Table 6.2 presents glycerol as a simple trifunctional crosshnker for step polymerized materials, suitable for polyesters and polyurethanes. 

Figure 6.24. Dependence of log Vg on l/T for, 1, the first network and, 2, the second network in polyurethane/poly-styrene sequential IPNs containing 3, 0.09 4, 0.384 5, 0.483 and 6,0.567 fraction by weight of the second network. Sorbate for sample 1, benzene for the remainder, acetone. ...

Figure 6.25. Polyurethane/polystyrene sequential IPNs. Dependence of 1, the proportion of the intermediate layer, q, and 2, the enthalpy of mixing of the networks, on the concentration of the second network in...

Lipatov and co-workers synthesized sequential IPNs containing a reinforcing silica filler as follows Polyurethane samples based on oligo-ethylene glycol adipate and tolylene diisocyanate were prepared with various levels of Aerosil, a silica filler. Trimethylolpropane was used as the... 

While the dielectric properties of a polymer system clearly have engineering value, changes in dielectric behavior with composition yield fundamental information. The behavior of the dielectric loss factor, tan 5, for the polyurethane/polystyrene sequential IPN was investigated by Lipatov et al Employing a frequency of 300 Hz, they studied the effect of filler over the temperature range -130 to 20°C. In this temperature range, the polystyrene does not exhibit a maximum in tan S however, the polyurethane does, at a temperature just below 0°C. Figure 7.1 shows the effect of Aerosil content on the loss peak. For convenience, the maxima in tan 8 are collected in Table 7.1. 

A curable epoxy resin containing a crosslinked elastomeric latex " yields a special type of sequential IPN. The elastomers mentioned include SBR, EPR, NBR, silicone rubber, and PEA. Hawkins " described an epoxy/polyurethane semi-SIN, and Mendoyanis " revealed an epoxy/liquid rubber SIN. The liquid rubbers were based on polysulfide rubber or polyethylene. The final products could be extended to 400% at... 

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