Changes in Molecular Weight

At 300°C and in the presence of KOH an increase in the molecular weight is observed, i.e., the reaction of macropolymerization is realized [38,39]. Potassium hydroxide is effectively inhibiting thermal destruction of polyethylene at temperatures from 350-375°C. The per cent change in molecular weight is half or one-third as high as that without the use of an inhibitor. At 400°C the efficiency of inhibition is insignificant. Potassium hydroxide with an ABC carrier is effective up to the temperature of 440°C due to the increased contact surface of the inhibitor with macroradicals. 

For r-BuCl/Et2AlCl/MeX a change in AEjj from -1.8 to —4.6 kcal/mole brought about by changing the solvent from MeCl to MeBr suggests a change in molecular weight control from termination to a combination of termination and transfer to monomer. 

Changes in molecular weight and carbohydrate composition of cell wall polyuronide and hemicellulose during ripening in strawberry fruit... 

The molecular weight distributions obtained for polymers prepared with these catalysts have a polydispersity close to 2, over a fivefold change in molecular weight. This is shown in Table XXII. 

By the ideal gas law, assuming no change in molecular weight, p = pRT/M, or density must also be constant. Consequently, Equation (10.68) becomes... 

NMR DETERMINATION OF SCISSION AND CROSSLINKING. The methods described above using changes in molecular weight, soluble fraction or mechanical properties are related indirectly to the rates of scission and crosslinking. They give no information about the nature of the crosslinks or the new chain ends. 

The A and B peptide chains in insulin are linked through disulfide bridges. Their presence was suspected from the change in molecular weight which followed the reduction of insulin. For quantitative analyses the S-S bridges had to be broken. Sanger, following the approach used by Toennies and Homiller (1942), oxidized the protein with performic acid, so that the half-cystines were converted to cysteic acid. After oxidation, insulin could be separated into its A and B chains, the A peptide with 20 amino acid residues and the B with 30. 

Figure 36. Effect of change in molecular weight at constant dispersity on the e-beam sensitivity of poly (chloromethylstyrene), PCMS. (Reproduced with permission from Ref 47 J...

Table 8.2 Changes in molecular weights and molecular weight distributions in radical crossover reactions of 43...

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