Molare Masse

Gray G W 1990 Low-molar-mass thermotropio liquid orystals Phil. Trans. R. Soc. A 330 73... 

As can be seen from equation 8.14, we may improve a method s sensitivity in two ways. The most obvious way is to increase the ratio of the precipitate s molar mass to that of the analyte. In other words, it is desirable to form a precipitate with as large a formula weight as possible. A less obvious way to improve the calibration sensitivity is indicated by the term of 1/2 in equation 8.14, which accounts for the stoichiometry between the analyte and precipitate. Sensitivity also may be improved by forming precipitates containing fewer units of the analyte. 

The product s molar mass, coupled with the temperature range, suggests that this represents the loss of H2O. The residue is CaC204. 

Be careful to use the necessary number of significant figures for the molar masses.) For... 

The wide variety of ketomethylene and amino ketone monomers that could be synthesized, and the abiUty of the quinoline-forming reaction to generate high molar mass polymers under relatively mild conditions, allow the synthesis of a series of polyquinolines with a wide stmctural variety. Thus polyquinolines with a range of chain stiffness from a semirigid chain to rod-like macromolecules have been synthesized. Polyquinolines are most often prepared by solution polymerization of bis(i9-amino aryl ketone) and bis (ketomethylene) monomers, where R = H or C H, in y -cresol with di-y -cresyl phosphate at 135—140°C for a period of 24—48 h (92). 

The next approach to incorporate the 12F-diol into a polyurethane matrix was reaction of the y -12F-diol with aUphatic diacid chlorides (where a = 3 or 4) to give low molar mass polyesters (141) ... 

Polarity Parameter. Despite their appareat simplicity, these parameters, ( ), show a good correlatioa with plasticizer activity for nonpolymeric plasticizers (10). The parameter is defiaed 2ls (j) = [M A j Po)]/1000 where M = molar mass of plasticizer, = number of carboa atoms ia the plasticizer excluding aromatic and carboxyHc acid carbon atoms, and Pg — number of polar (eg, carbonyl) groups present. The 1000 factor is used to produce values of convenient magnitude. Polarity parameters provide useful predictions of the activity of monomeric plasticizers, but are not able to compare activity of plasticizers from different families. 

The Flory-Huggins Interaction Parameter. These ideas, based on a study of polymer miscibility, have been appHed to plasticizers according to the foUowiag equation ia which is the molar volume of the plasticizer, obtaiaed from molar mass figures and density values at T, and represents the iateraction parameter (11). 

Mechanistic studies on the formation of PPS from polymerization of copper(I) 4-bromobenzenethiolate in quinoline under inert atmosphere at 200°C have been pubUshed (91). PPS synthesized by this synthetic procedure is characterized by high molar mass at low conversions and esr signals consistent with a single-electron-transfer mechanism, the Sj l-type mechanism described earlier (22). 

Chemical Grafting. Polymer chains which are soluble in the suspending Hquid may be grafted to the particle surface to provide steric stabilization. The most common technique is the reaction of an organic silyl chloride or an organic titanate with surface hydroxyl groups in a nonaqueous solvent. For typical interparticle potentials and a particle diameter of 10 p.m, steric stabilization can be provided by a soluble polymer layer having a thickness of - 10 nm. This can be provided by a polymer tail with a molar mass of 10 kg/mol (25) (see Dispersants). 

Third, picking the point on the cui ve of retention versus molar mass where 90 percent falls is inexacl . The retention cui ve usually bends in a way that makes picking the 90 percent point somewhat arbitraiy. 

The UF-resin itself is formed in the acid condensation step, where the same high molar ratio as in the alkaline methylolation step is used (F/U = 1.8 to 2.5) the methylolureas, urea and the residual free formaldehyde react to form linear and partly branched molecules with medium and even higher molar masses, forming polydispersed UF-resins composed of oligomers and polymers of different molar m.asses. Molar ratios lower than approx. 1.7-1.8 during this acid condensation step might cause resin precipitation. 

Molecules with higher molar masses, which are resin molecules in the closer sense of the word. 

The condensation reaction and the increase of the molar mass can also be monitored by GPC [25], With longer duration of the acid condensation step, oligomers of higher molar masses are progressively formed. 

PMDI is produced on an industrial scale by the phosgenation of diamin-odiphenylmethane. Structure and molar mass of PMDI depend on the number of aromatic rings in the molecule. For PMDI the distribution of the three monomeric isomers has a great influence on the quality, because the reactivities of the various isomers (4,4 -, 2,4 - and 2,2 -MDI) differ significantly. The greater the portion of the 2,2 - and 2,4 -isomers, the lower is the reactivity. This can lead to different bonding strengths as well as to residual isomers in the produced wood-based panels. 

PMDI also contains isocyanates with higher molar masses (triisocyanates, tetraisocyanates, polyisocyanates), whereby the structure and the molar mass depend on the number of phenyl groups. This distribution influences, to a great extent, the reactivity, but also the usual properties like viscosity, flowing and wetting behavior as well as the penetration into the wood surface. 

Polymer. The polymer determines the properties of the hot melt variations are possible in molar mass distribution and in the chemical composition (copolymers). The polymer is the main component and backbone of hot-melt adhesive blend it gives strength, cohesion and mechanical properties (filmability, flexibility). The most common polymers in the woodworking area are EVA and APAO. 

---