Molecular weight cellulose nitrate

FIGURE A3.29 Solubility of medium-molecular-weight cellulose nitrate, half second grade. Source Hansen (2007). 

Interpret the slope and intercept values of the line in Fig. 10.12 in terms of the molecular weight and radius of gyration of cellulose nitrate in this solution. At 436 nm the refractive index of acetone is 1.359. 

Benoit et al.f prepared a mixture of two different fractions of cellulose nitrate and determined the molecular weight of the mixture by light scattering. The mixture was 25.8% by weight fraction A and 74.2% fraction B, where the individual fractions have the following properties ... 

Nitrocellulose, of the resins used in these end uses and in car refinishing, is the nitrate ester of cellulose. The structure is linear and a wide range of (high) molecular weights is available as well as various degrees of nitration ... 

Tape >System of Analysis. A tape system which is used widely for analysis in the Pediatric Laboratory is a system whose principle was developed by the author. A reagent is placed on a paper tape. The paper is covered with a membrane, such as cellophane, cellulose nitrate or cellulose acetate, porous to low molecular weight substances. Finally, the serum is placed above the porous membrane, so that diffusion of the components of serum take place and a stain is produced on the paper (60). This principle has been incorporated for example, with glucose oxidase, in the conmercially available Dextro-Sticks. In addition, a similar principle is being applied by some for the analysis of components in urine (Ames Co., South Bend, Indiana). 

Polyamide, collodion (cellulose nitrate), ethylcellulose, cellulose acetate butyrate or silicone polymers have been used for preparation of permanent microcapsules. This method offers a double specificity due to the presence of both the enzyme and a semipermeable membrane. Moreover, it allows simultaneous immobilization of many enzymes in a single step and the surface area for contacting the substrate and the catalyst is large. The need of high protein concentration and the restriction to low molecular weight substrates are the main limitations of enzyme microencapsulation. 

Whereas GALDI-MS detects low molecular weight synthetic resins, common synthetic polymers, such as various acrylic polymers, polystyrene, and cellulose nitrate, did not produce any mass spectra using this method. 

Meyerhoff (14-16) has also observed similar blocking of the gel column using cellulose trinitrate fractions with molecular weight above 1.4 x 10, while fractions with molecular weight 4.2 X 10° could not be separated. It is obvious from these results that he did not, however, realize the presence of the hemlcellulose derivatives in the wood-pulp based cellulose nitrate and its role in blocking of the high porosity column as shown in this study. 

Various molecular weight fractions of cellulose nitrate were dissolved in acetone and the intrinsic viscosity was measured at 25°C ... 

EXAMPLE 5.3 The Use of Zimm Plots Determination of Molecular Weight, Second Virial Coefficient, and Radius of Gyration of Cellulose Nitrate in Acetone. The following are the values of the intercept and slope from Figure 5.9 ... 

Nitrocellulose with a decreased molecular weight may be obtained as the result of depolymerization (degradation) of the cellulose before nitration, e.g. by keeping it at a temperature of 150-170°C or by treating it with acids. The resultant hydrocellulose, which usually possesses a lower molecular weight than cellulose, is then subjected to nitration to produce a more soluble substance as compared with the nitration product of a non-depolymerized raw material. 

Recently, the effect on the nitration product of beating the cellulose prior to nitration has been studied by Ellefsen [97] who confirmed the well-known view that beating of cellulose was accompanied by partial degradation to soluble substances. However, the molecular weight was unchanged in those fractions of cellulose that did not dissolve in water. 

Using the ultracentrifuge sedimenting method, Gralen and Svedberg [40] have determined the molecular weight of nitrocellulose prepared from various types of cellulose. The nitration was carried out at 0°C by means of a mixture composed of 40% of nitric acid, 40% of phosphoric acid, and 20% of phosphorus pentoxide. The results are collected in Table 79. 

VI. Molecular Weight Averages and Molecular Weight Distribution of Cellulose Nitrate... 

Gel permeation chromatography (GPC) of poly(methyl methacrylate) and cellulose nitrate showed elution volume peaks at 62.5 ml for PMMA and at 87.5 for cellulose nitrate (Figure 5), due to their difference in molecular weight. A mixture of poly(methyl methacrylate) and cellulose nitrate of the same ratio as that of the graft copolymer was recorded and two peaks in elution volume at almost identical positions were observed. This shows that the constituent homopolymers retain their identity in a physical mixture. The isolated graft copolymer showed a single peak in elution volume at 80.0 ml. The second peak in elution volume is absent in spite of poly(methyl methacrylate) attached to cellulose nitrate as revealed by infrared spectrum. Hence, these results indicate that GPC can be used as a technique to differentiate between homopolymer, physical mixture, and graft copolymer. 

Table IV. Effect of Cellulose Nitrate on Percentage Grafting and Molecular Weight...

Fig. IS. Molecular-weight dependence of sedimentation constant (rc) and intrinsic viscosity ( ), for various degrees of draining and coil expansion. Full line is for coiled polymers without draining. Dotted curve is for rigid ellipsoids of revolntion at various axial ratios p. Experimental points a, cellulose nitrate in ethyl acetate 729) b, cellulose nitrate in acetone (181) c, cellulose acetate in acetone (125) d., ethyl cellulose in ethyl acetate 223 ) e, ethyl bydroxyethyl cellulose in water (772)...

From another point of view, it can be seen that approximate conformity of cellulose nitrates to both of the asymptotic relations (63) and (89) for [ /] and (SF), respectively, implies that the number 0 should remain essentially constant at its asymptotic value 0, given by Eq. (57). Since it is difficult to assess the polydispersity of cellulose nitrate fractions, the constancy of 0, rather than its numerical value, should be of prime importance in testing the consistency of our conclusions. Doty, Schneider and Holtzer (59) and Newman and Flory (198) both originally reported, that 0 decreased systematically with decreasing molecular weight. Later Holtzer, Benoit and Doty (726) preferred to regard 0 as essentially constant at about 1.9 1021, somewhat smedler... 

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