Molar mass water content

The copolymer can be further fractionated by precipitation from acetone solution to n-hexanc at room temperature. In each case, only the first fraction should be used to obtain narrowly distributed high molar mass copolymer chains for LLS measurement, ll NMR can be used to characterize the copolymer composition. The ratio of the peak areas of the methine proton of the isopropyl group in NIPAM and the two protons neighboring the carbonyl group in VP can be used to determine the VP content. The composition of each NIPAM-co-VP copolymer was found to be close to the feeding monomer ratio prior to the copolymerization. The nomenclature used hereafter for these copolymers is NIPAM-co-VP/x/y, where x andy are the copolymerization temperature (°C) and the VP content (mol%), respectively. The solution with a concentration of as low as 3.0 x 10-6 g/mL can be clarified with a 0.45 cm Millipore Millex-LCR filter to remove dust before the LLS measurement. The resistivity of deionized water used should be close to 18 M 2 cm. The chemical structure of poly(NIPAM-co-VP) is as follows (Scheme 2). 

Abstract This paper proposes new ways of preparation of hybrid silicones, i.e. an alternated multiblock seqnence of silicone and alkyl spacers, via a polycondensation process catalyzed by the tris(pentaflnorophenyl)borane, a water-tolerant Lewis acid, between methoxy and hydrogeno fnnctionalized silanes and siloxanes at room temperature and in the open air. The protocol was first developed with model molecules which led to polydimethylsiloxane (PDMS) chains, in order to seize the best experimental conditions. Several factors were studied such as the contents of each reactants, the nature of the solvent or the rate of addition. The best conditions were then adapted to the synthesis of hybrid silicones, condensing alkylated oligo-carbosiloxanes with methoxy or hydrogeno chain-ends and complementary small molecules. A systematic limitation in final molar masses of hybrid silicones was observed and explained by the formation of macrocycles, which cannot redistribnte or condense further while formed. 

Figure 2 and Table 1 show the content of polymer formed and the molar masses obtained using different solvents of different polarity. In solvents of moderate to high dielectric constants (typically C HjOC Hj and CH Cy, the content of cycles is too high for the experiment to be worth, whereas experiments in bulk or toluene reached a good conversion in polymer of low molar masses. The case of water as a solvent has already been treated in a separate study, and will not be further described here [15]. 

In the absence of L H, the condensation of silanol groups is slow and inefficient, since after three days the molar masses slightly shifted (note that the reactions qnoted in Table 1 were carried out only during 24h, unless otherwise stated). In the presence of L H, the reaction is much faster and larger molar masses are reached, which seems to indicate that the SiH/SiOH condensation is competitive with the SiH/SiOMe one. Snch result may explain the double distribution found in some rnns of Table 1, where both fast L H addition and fair content of water present the best conditions for this co-condensation reaction to occur. 

Another study [54] considers the molar mass dependence of droplet size fluctuations in a water-n-octane-AOT-PEO system by small-angle neutron scattering. The polydispersity increases upon increasing the molar mass and the polymer content. Usually [44], this is accompanied by larger shape fluctuations, which would make this a case 2 system. Unfortunately, shape fluctuations were not considered here. 

FIGURE 8.9 Effective diffusion coefficient (Deff) of molecules in systems of various water contents, (a) Diffusivity of solutes of various molar mass as a function of mass fraction water (w). (b) Diffusivity of water at some temperatures as a function of w. (c) Diffusivity of water in two systems as a function of water activity. Very approximate, only to illustrate trends. 

Fig. 1 Glycerolysis of soybean using various lipases. Conditions 7 =40°C, substrate molar ratio glycerol/oil=4, 10% enzyme load (wt% of oil mass), 3.5% water content (wt% of glycerol mass), 24 h of reaction...

Azeotropic dehydration and condensation polymerization (route 2 in Figure 8.2) yields directly high molar mass polymers. The procedure, patented by Mitsui Toatsu Chemicals [13, 14], consists of the removal of condensation water via a reduced pressure distillation of lactic acid for 2-3h at 130°C. The catalyst (in high amounts) and diphenyl ester are added and the mixture is heated up to reflux for 30-40 h at 103°C. Polycondensated PLA is purified to reduce residual catalyst content to the ppm range [5,10,15]. 

Later, the influence of diverse experimental parameters such as the macroinitiator length, its concentration, the initial free nitroxide concentration, the solids content, and the concentration of an added electrolyte was evaluated and exploited to propose a mechanism for particle formation and growth of polymer chains [135]. For instance, it was demonstrated that the molar mass of the so-formed amphiphilic block copolymers and the particle diameter could be tuned by varying the initial macroalkoxyamine concentration (Fig. 14). Narrower molar mass distribution could also be reached (PDI = 1.3 at 90% conversion), although complete and/or fast initiation could still not be achieved. To explain this, the importance of water-phase kinetics and slow initiation by the polyAA-based macroinitiator was pointed out [135, 137]. 

The most convenient unit of concentration for use in equilibrium calculations is the molarity, and it is the most frequently used unit of concentration in this book. Using molarity has certain disadvantages, however. First, to calculate the exact amount of solvent present in the solution, it is necessary to obtain the density of the solution at the temperature desired. Since the density of the solution varies with temperature, the molarity will also vary. To obtain the water content in a 0.1000 M NaCl solution, for example, we need to know the density of the solution at 20° C (from the Handbook of Chemistry and Physics (CRC Press), P = 1.0028 g/mL). The mass of a liter of the solution is 1002.8 g. Of this, 5.845 g (corresponding to 0.1000 mole) is NaCl. Hence, 997.0g is the mass of water. Five degrees higher, at 25°C, this solution occupies a volume of 1.0018 L, but the amount of salt has not changed, which means that the molarity has dropped by 0.1%. (With more concentrated solutions, this temperature effect is more pronounced.) For most purposes, however, such changes do not introduce any appreciable error in equilibrium calculations. 

Protein Humidity/water content Hydrocarbons Carboxylic acids Amines Oil/fat Sucrose/glucose Additives in fuels Density Digestibility Viscosity Motor fuel octane number Reid vapor pressure of gasoline Seed germination Distillation parameters Fruit ripeness Total dissolved solids Particle size/fiber diameter Temperature Mechanical properties Thermal and mechanical pretreatment Molar masses of polymers... 

A chemical equilibrium between condensation and chain scission is established when a polymer melt receives a given amount of water. The actual water content after equihbration depends on the temperature, pressure, time and the types of end groups [8,16,30]. If more H2O is added to the equUibrated mixture, a new equilibrium sets in with a more pronounced degradation through hydrolytic chain scission with reduction of the molar mass and consequent deterioration of the final properties [30]). The reverse direction is taken (i.e. polycondensation) if H2O is removed from the equihbrium melt [16]. 

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