Rheological characterization and modeling of end-functionalized polybutadienes |
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Authors: | Manuel García-Leiner Octavio Manero Rafael Herrera |
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Institution: | (1) Departamento de Ingeniería Química, Ed. E, Facultad de Química, UNAM, Circuito Exterior, C. U., México, D. F. 04510, México,;(2) Instituto de Investigaciones en Materiales, UNAM, A.P. 70–360, México, D. F. 04510, México, |
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Abstract: | The rheological characterization and modeling of a series of polybutadienes obtained by anionic solution polymerization is
presented in this work. The polybutadienes are synthesized using two different initiators: R,R′,R′′-silyloxyalkyllithium (F1)
and R,R′,R′′-silylalkyllithium (F3). In addition, a polybutadiene obtained with a conventional alkyllithium initiator (n-butyllithium) is used as a reference.
The rheological characterization is carried out under small amplitude oscillatory shear in the stress-controlled mode. Microstructure,
molecular weight, and molecular weight distribution are determined by FTIR and GPC. The vinyl content of the polybutadienes
synthesized using the functionalized initiators is similar to that obtained with n-butyllithium (8–11%). Materials obtained with F1 show a relatively low polydispersity within a narrow molecular weight range
(250,000–300,000 g/mol), while samples obtained with F3 cover a wider range of molecular weights (65,000–670,000 g/mol) and
display higher values of polydispersity. In all cases, a parallel reaction using propylene oxide in the termination step is
done to place a functional group at the chain ends. The effect of this group on the rheological behavior appears to be negligible.
Three rheological models are used and their predictions of the experimental data are compared. The models include the Doi
and Edwards reptation model, expressions using a discrete spectrum of relaxation times based in the rubber-like liquid constitutive
equation and the fractional Maxwell equation in which a given analytical relaxation-spectrum is used. Relevant relations are
obtained between the models' parameters and the molecular properties of these systems, which in turn are related to the presence
of functional groups at the polymer chain ends. |
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Keywords: | Polybutadiene Anionic polymerization Functionalized initiators Small amplitude oscillatory shear Rheological modeling |
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