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Polymers density values

Examples of various reduction treatments are listed in Table 63. Cr/silica-titania, activated at 800 °C in dry air, was treated with reducing agents at various temperatures and then flushed with N2 at the same temperature. These catalysts were tested with 5 ppm of BEt3 cocatalyst added to the reactor, and the polymer was recovered and analyzed. The polymer density values are listed in Table 63. CO at 340 °C produced polymer with the lowest density. [Pg.512]

The three models presented have been used for the calculations however, for the sake of brevity the results explicitly presented in Figure 2.6a and b refer to NE-PHSC-SW for the PMMA-CO2 system and NELF for the AFI6OO-CO2 mixtures. As in the previous case, the model results obtained with a constant polymer density value have also been included in the two figures and are represented by a dashed line once again, one can... [Pg.56]

As a good first approximation (187), the heat conduction of low density foams through the soHd and gas phases can be expressed as the product of the thermal conductivity of each phase times its volume fraction. Most rigid polymers have thermal conductivities of 0.07-0.28 W/(m-K) and the corresponding conduction through the soHd phase of a 32 kg/m (2 lbs/fT) foam (3 vol %) ranges 0.003-0.009 W/(m-K). In most cellular polymers this value is deterrnined primarily by the density of the foam and the polymer-phase composition. Smaller variations can result from changes in cell stmcture. [Pg.414]

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). [Pg.124]

Crystal Structure. The crystal stmcture of PVDC is fairly well estabhshed. Several unit cells have been proposed (63). The unit cell contains four monomer units with two monomer units per repeat distance. The calculated density, 1.96 g/cm, is higher than the experimental values, which are 1.80—1.94 g/cm at 25°C, depending on the sample. This is usually the case with crystalline polymers because samples of 100% crystallinity usually cannot be obtained. A dkect calculation of the polymer density from volume changes during polymerization yields a value of 1.97 g/cm (64). If this value is correct, the unit cell densities may be low. [Pg.430]

With the availability of the higher density polymers the value of the melt flow index as a measure of molecular weight diminishes. For example, it has been found that with two polymers of the same weight average molecular weight (4.2 X 10 ), the branched polymer (density = 0.92 g/cm ) had only 1/50 the viscosity of the more or less unbranched polymer (density = 0.96 g/cm ). This is due to long chain branches as explained above. [Pg.216]

Monomer and Polymer Densities. Liquid density values at the relevant taiperature have been used (L5) a constant value for the polymer density, Pp, is assumed, indepandent of polymer c qposltlon and correspondent to the average of the homopalymer density values. [Pg.389]

Vc crystalline Va, amorphous). The densities of the pure crystalline (pc) and pure amorphous (pa) polymer must be known at the temperature and pressure used to measure p. The value of pc can be obtained from the unit cell dimensions when the crystal structure is known. The value of pa can be obtained directly for polymers that can be quenched without crystallization, polyfethylene terephtha-late) is one example. However, for most semi-crystalline polymers the value of pa is extrapolated from the variation of the specific volume of the melt with temperature [16,63]. [Pg.261]

Little is known about the variation of the critical stress ", with structure and temperature. For the polyethylene discussed abovedecreased from 620 psi at 22X to 39general trend with all polymers. Turner (84) found that the value of (r(. for polyethylenes increased by a factor of about 5 in going from a polymer with a density of 0.920 to a highly crystalline one with a density of 0.980. Reid (80,81) has suggested that for rigid amorphous polymers. ", should be proportional t° (Tt - T) For brittle polymers, the value of ", may be related to the onset of crazing. [Pg.86]

The density of the polymer clearly shows the formation of a foamed polymer. The density values for selected foams together with the polyimide homopolymers are shown in Table 11. The density values for the ODPA/FDA and PM-DA/FDA polyimides were both 1.28 g/cm and 3FDA/PMDA is 1.34, while most of the propylene oxide-based copolymers showed substantially lower values. The densities of the foamed copolymers derived from these copolymers ranged from 1.09 to 1.27 g/cm, which is 85-99 % of that of the polyimide homopolymers. This is consistent with 1-15 % of the film being occupied by voids. From these data (i.e., the comparison of Tables 10 and 11), it appears that the volume fraction of voids or the porosity is substantially less than the volume fraction of propylene oxide in the copolymer (i.e., 70 % or less). Thus the efficiency of foam formation is poor. Conversely, the propylene oxide-based copolymers with PMDA/ODA as the imide component did not show the expected density drop, and the values were essentially identical to that of the homopolymer. In PM-DA/ODA-based systems, molecular ordering and orientation were found to be critical in determining the stability of the foam structure. Where the character-... [Pg.97]

Here Bd is a dimensionless constant of order unity43, q being the polymer density f ( 0.025) is the fractional free volume at the glass transition temperature Tg, with the latter taking its maximum value T at infinite molecular weight. VE denotes the... [Pg.12]

I, the extremely low concentration of polymer in the fractions collected reduced the precision in the ultraviolet optical density values measured, the influence of which is amplified in the figures in the last column. Therefore, the average styrene content was used as the composition of the peak point to calculate the MW of the polymer by Equation 5. The MW of the styrene homopolymer which is present in small amounts was taken as the MW of the first block, as explained above. In this manner the molecular structure of the polymer was found to be S( 15,000) B(61,000)S( 14,000) the figures given in parentheses being the MW s of the successive blocks. [Pg.168]

It appears that for these cyclic polymers the values of the specific refraction and the specific parachor are almost constant, though the refractive index, the density and the surface tension vary notably. The specific refraction and the specific parachor are independent of the degree of polymerization. [Pg.84]

In Figure 5 the results obtained by rapid density gradient centrifugation of a polymer latex of unknown composition are shown. The gradient system consists of pure H2O and D2O. The density distribution of the particles has two broad peaks at the density values... [Pg.245]

Plastics compare more favourably with other materials if the stiffness per unit mass is considered, or the modulus of elasticity divided by the specific mass. This is demonstrated by the right hand side of Figure 7.3 as a result of the lower density of polymers the values are closer to each other an advanced composite now amply exceeds steel ... [Pg.118]

The studies of Rg as well as Rrl and Rh of a number of dendrimer systems establish a transition from v=0.45+0.05 to v=0.25+0.05 dependence on MW as shown in Figs. 4 and 5. This result is qualitatively consistent with the simulation results and has several consequences. Because [q] -R- /M, the value of [q] will increase with the MW of the dendrimer when v>l/3, be independent of MW when v=l/3,and decrease with MW when v< 1/3. This last, unusual, behavior of high MW dendrimers has been pointed out [48]. The maximum in the value of [q] at intermediate MW resembles the behavior of star polymers when values of [q] are plotted against f, the arm functionality at constant arm MW [62,81]. It is also observed in comb and graft copolymers with increasing grafting density, other variables being kept constant [82]. [Pg.199]

Figure 8 Locus of the critical values of a at which the interaction between the grafted monolayers becomes attractive for different bulk free polymer densities pfOf3 = 0.6 ( ) and pfOf3 =0.75 ( ). Ng—101 and cg — Cf—c. Figure 8 Locus of the critical values of a at which the interaction between the grafted monolayers becomes attractive for different bulk free polymer densities pfOf3 = 0.6 ( ) and pfOf3 =0.75 ( ). Ng—101 and cg — Cf—c.

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See also in sourсe #XX -- [ Pg.583 , Pg.884 ]




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Density values

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