Molecular weight determination elastomers

Much work has been done on the incorporation of castor oil into polyurethane formulations, including flexible foams [64], rigid foams [65], and elastomers [66]. Castor oil derivatives have also been investigated, by the isolation of methyl ricinoleate from castor oil, in a fashion similar to that used for the preparation of biodiesel. The methyl ricinoleate is then transesterified to a synthetic triol, and the chain simultaneously extended by homo-polymerization to provide polyols of 1,000, 000 molecular weight. Polyurethane elastomers were then prepared by reaction with MDl. It was determined that lower hardness and tensile/elongation properties could be related to the formation of cyclization products that are common to polyester polyols, or could be due to monomer dehydration, which is a known side reaction of ricinoleic acid [67]. Both side reactions limit the growth of polyol molecular weight. 

Figure 2.11 Fluids, resins, and elastomers. Silicone fluids are linear chains where molecular weight determines viscosity, silicone resins are branched polymers and thus glass-like solids and silicone elastomers are composed of long, linear polysiloxane chains reinforced with an inorganic filler and cross-linked. (From Plastics Handbook, Modern Plastics Magazine, McGraw-Hill, New York, 1994, p. 86.)...

The bulk viscosity control parameter for CSM, as with other elastomers, is molecular weight M and molecular-weight distribution (MWD). Mooney viscosity for CSM is determined by selection of the polyethylene precursor. 

Hergenrother W.L. and Doshak J.M., Determination of entanglement molecular weight of thermoplastic elastomers by tensile retraction measurement, J. Appl. Polym. Sci., 40, 989, 1990. 

Recent Trends in the Determination of Molecular Weights and Branching in Elastomers... 

Bahary, W. S. (1973). Recent trends in the determination of molecular weights and branching in elastomers. In Polymer Molecular Weight Methods, Gould, R. F. (Ed.), pp. 85-97. Am. Chem. Soc., Washington, DC. 

The characterization of surface activity of fillers is obtained by use of several analytical techniques [1]. Examples of them are inverse gas chromatography [1, 2], the adsorption of a low molecular weight analog of elastomers [3], the adsorption of elastomer chains fi om dilute solutions [4], the wettability, viscosity of PDMS fluids in the boundary layer at the surface of solids [5], the determination of the specific surface area, and the analysis of surface groups [1]. It should, however, be mentioned that the results obtained by these methods do not provide direct information on the elastomer behavior at the interface, due to the use of small probe molecules or the presence of a solvent in the systems studied. 

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