Polyethylene theta solvent

According to the statistical-mechanical theory of rubber elasticity, it is possible to obtain the temperature coefficient of the unperturbed dimensions, d InsjdT, from measurements of elastic moduli as a function of temperature for lightly cross-linked amorphous networks [Volken-stein and Ptitsyn (258 ) Flory, Hoeve and Ciferri (103a)]. This possibility, which rests on the reasonable assumption that the chains in undiluted amorphous polymer have essentially their unperturbed mean dimensions [see Flory (5)j, has been realized experimentally for polyethylene, polyisobutylene, natural rubber and poly(dimethylsiloxane) [Ciferri, Hoeve and Flory (66") and Ciferri (66 )] and the results have been confirmed by observations of intrinsic viscosities in athermal (but not theta ) solvents for polyethylene and poly(dimethylsiloxane). In all these cases, the derivative d In sjdT is no greater than about 10-3 per degree, and is actually positive for natural rubber and for the siloxane polymer. 

Although the unperturbed dimensions of many addition polymers have been obtained by means of theta-solvent experiments, there are some important exceptions, for which the present method leads to useful results. A notable member of this group is polyethylene. From the... 

NA2 Nakajima, A., Hamada, F., and Hayashi, S., Unpertuibed dimensions of polyethylene in theta solvents, J. Polym. Sci. Part C, 15, 285, 1966. 

Hre butterfly patterns were observed at various tempera-mres and concentrations and for various solvents such as DOP, tydohexane, and diethyl malonate, which are theta solvents for PS at 35°C, as wdl as dibutyl phthalate and tricresyl phosphate, which are good solvents for PS. The patterns were also observed for semidilute solutions of polyethylene with paraflin as the solvent (athermal solution) and for sheared colloidal srrspensions. They are thus quite general for sheared dynamically asymmetric systems. The butterfly pattern was also formd for PS/PVME mixtures by Mani et and Gerard et and for other polymer mixtures. ... 

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