Weight relationships

The molecular weight of SAN can be easily determined by either intrinsic viscosity or size-exclusion chromatography (sec). Relationships for both multipoint and single point viscosity methods are available (18,19). Two intrinsic viscosity and molecular weight relationships for azeotropic copolymers have been given (20,21) ... 

Fig. 2. Glass-transition temperature—molecular weight relationship for poly(ethylene oxide) (-) represents classical T —mol wt relationship Q, data from...

Fig. 15. Polymerization rate vs molecular weight relationship for spontaneous bulk styrene polymerization under neutral and acidic conditions.

The dilute solution properties of copolymers are similar to those of the homopolymer. The intrinsic viscosity—molecular weight relationship for a VDC—AN copolymer (9 wt % AN) is [77] = 1.06 x 10 (83). The characteristic ratio is 8.8 for this copolymer. 

Intrinsic viscosity—molecular weight relationships have been obtained for copolymers in methyl ethyl ketone. The value for a 15 wt % ethyl acrylate (EA) copolymer is [77] = 2.88 x 10 . ... 

Table 3. Intrinsic Viscosity—Viscosity Average Molecular Weight Relationships as a Function of Hydrolysis...

The study of the peak temperature sensitivity to the reactor operating parameters and the construction of sensitivity boundary curves for stable reactor operation were previously reported ( l). This paper presents a computer study on conceptual relationships between the conversion-product properties and the reactor operating parameters in a plug flow tubular reactor of free radical polymerization. In particular, a contour map of conversion-molecular weight relationships in a reactor of fixed size is presented and the sensitivity of its relationship to the choice of initiator system, solvent system and heat transfer system are discussed. 

This work particularly emphasizes the importance of selecting the initiator system for optimum reactor operation and reveals general concepts which specify the desired properties and operational modes of an optimum initiator system. In addition, the effects of the system heat transfer and the CTA (chain transfer agent) level on the conversion-molecular weights relationships are presented. 

Equation (8) provides a general relationship between the reactor temperature profile and the operating parameters. In relating the system heat transfer to the conversion-molecular weights relationship for a reactor of fixed size, the heat transfer coefficient emerges as the correlating parameter. 

Fig. 50.—Intrinsic viscosity-molecular weight relationship for polyisobutylene in diisobutylene (DIB) at 20° and in cyclohexane at 30°C. Open circles from Ref. 7 filled circles, Ref. 8.

The viscosity average molecular weight depends on the nature of the intrinsic viscosity-molecular weight relationship in each particular case, as represented by the exponent a of the empirical relationship (52), or (55). However, it is not very sensitive to the value of a over the range of concern. For polymers having the most probable distribution to be discussed in the next chapter, it may be shown, for example, that... 

The calibration technique used in conventional SEC does not always give the correct MWD, however. The molecular size of a dissolved polymer depends on its molecular weight, chemical composition, molecular structure, and experimental parameters such as solvent, temperature, and pressure ( ). If the polymer sample and calibration standards differ in chemical composition, the two materials probably will feature unequal molecular size/weight relationships. Such differences also will persist between branched and linear polymers of identical chemical composition. Consequently, assumption of the same molecular weight/V relation for dissimilar calibrant and sample leads to transformation of the sample chromatogram to an apparent MWD. 

The hydrodynamic volume separation mechanism of SEC, along with the different molecular size/weight relationships of branched and linear polymers of identical chemical composition, can be exploited with the SEC/LALLS method to gain information about polymer branching. In the studies described in this paper both conventional SEC and SEC/LALLS are used to obtain data about branching in samples of poly(vinyl acetate) (PVA) and polychloro-prene (PCP). 

For illustration consider SEC chromatograms obtained for two polymers on the same chromatographic system. One sample is a linear homopolymer while the other is a branched polymer with the same chemical composition. In the latter sample assume that the polymer components of different molecular weight have uniform branching characteristics so that all have similar molecular size/weight relationships. 

We, therefore, propose an indirect method for obtaining the variation of the intrinsic viscosity and number average molecular weight across the chromatogram. First the intrinsic viscosity-molecular weight relationship for a polymer with long chain branching (LCB) is assumed to be expressable in a form similar to that used by Ram and Milts (6),... 

Kurata, M., Tsunashima, Y., Iwama, M., and Kamada, K., Viscosity-molecular weight relationships and unperturbed dimensions of linear chain molecules, in Polymer Handbook, 2nd ed., Brandrup, J. and Immergut, E. H., Eds, John Wiley Sons, New York, 1975, iv, 1-60. 

Figure 2 shows the time-conversion and time-molecular weight relationships in the photopolymerization of St and MMA with 13 at 30°C [16, 76,157]. The yields and molecular weight of the polymer increased with polymerization time. From the analysis of the end groups of the polymer chain, it was confirmed that the number of the DC groups remained at two during polymerization (Table 2) [76,156]. 

The time-conversion and time-molecular weight relationships in the photopolymerization of St with 7 and 8 are shown in Fig. 3, in which the concentration of the DC group as an iniferter site in these iniferters was identical, i.e., [7]/2-[8]. 

The resulting AEGL-3 values are shown in Table 3-11. Conversion of animal exposure data to human equivalent concentrations based upon minute volume and body weight relationships was not appropriate. Such a conversion predicted that monkeys and dogs would be more sensitive than rodents, a contention that is not supported by the animal data. Furthermore, the conversion to human equivalent concentrations assumes 100% absorption of inhaled monomethylhydrazine such absorption efficiency has not been verified. 

Fig Intrinsic viscosity-Molecular weight relationships for polyisobutylene in disobutylene and cyclohexane. 

Kurata, M. and Tsunashima, Y., Molecular weight relationships and unper-turbated dimensions of linear chain molecules, In Polym. Handbook, 4th Edn, Wiley-Interscience, New York, 1999, p. VII-35. 

The original poly(vinyl alcohol) was studied in both aqueous and DMSO solutions. Viscosity-molecular weight relationships have been reported for each of these solutions at 30°C as shown in Equations 19 and 20 (3). 

Uemitsu N, Nishimura C, Nakayoshi H. 1986. Evaluation of liver weight changes following repeated administration of carbon tetrachloride in rats and body-liver weight relationship. Toxicology 40 181-190. 

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