Experimental and theoretical investigations on petroleum-based elastomers with two cross-linking systems of different lengths viewed as bimodal networks.pdfVIP

Polymer 47 (2006) 415–423 /locate/polymer Experimental and theoretical investigations on petroleum-based elastomers with two cross-linking systems of different lengths viewed as bimodal networks Tarek M. Madkour *, Rasha A. Azzam College of Arts and Sciences, ABTI-American University of Nigeria, Lamido Zubairu Way, P.M.B. 2250, Yola, Adamawa State, Nigeria Received 10 October 2005; received in revised form 13 November 2005; accepted 15 November 2005 Available online 28 November 2005 Dedicated to his Excellency, Alhaji Atiku Abubakar, the founder of the ABTI-American University of Nigeria, as the ?rst published research article of AAUN. Abstract A review with 36 references discussing the chemistry and the structure–property relationship of elastomers cured with two cross-linking systems of different chain lengths such as sulfur and the polymerization products of p-benzoquinone and viewed as bimodal networks. These exceptional networks have shown remarkable improvements in the overall mechanical properties which are anticipated to be due to the nonGaussian effects known for bimodal networks and evident by the anomalous upturn in the modulus values in Mooney–Rivlin stress–strain data representations. Proton and 13C NMR as well as energy minimization calculations were used to study the chemical structures and single chain contributions of polyquinones. Nuclei bending of these oligomers have shown to be greatly in?uenced by the restricted torsional behavior due to the presence of the hydrogen bonds between the benzenoid nuclei. Intrinsic atomic-level forces for the networks were evaluated using molecular dynamics techniques and showed that while the forces acting on the junction points of the cross-linking segments and the elastomeric chains had no apparent change as a consequence of the networks’ bimodal formation, forces acting on the short chains of the bimodal networks are of much higher values as compared to those of unimodal networks. The presence of the relatively