1. Polymer Chain Length and Branching Effects on the Viscoelastic Bulk Modulus and Structural Recovery at High Pressure Sindee L. Simon, Texas Tech University, DMR 0606500 The principal aim of this project is to measure the time-dependent bulk modulus as a function of polymeric architecture in polymers. We have recently examined two polycyanurate samples of differing crosslink density. Results from the polycyanurate with 10 mol% monofunctional monomer are shown. Crosslink density was found to have no impact on the breadth of the bulk dispersion for the system studied, rather the bulk response simply shifts to longer times as T g increases. The results are important, for example, for modeling residual stress development in thermosetting composites used in aerospace applications. Comparison of the bulk and shear retardation spectra for the polycyanurate systems indicates that the two responses arise from similar molecular mechanisms at short times but that long time chain mechanisms available to the shear response are not available to the bulk response. This corroborates our previous results on polysytrene. We are continuing our studies by examining the effect of branching using star polystyrene polymers. Pressure relaxation response for a polycyanurate containing 10 % monofuntional monomer measured at temperatures from 136 to 180 °C. On the left, the raw data are shown after application of small vertical shifts; on the right is the time-temperature superposed curve.

2. Education: Two graduate students, Fatema Begum and Jiaxi Guo, both finishing their second year, are being supported by the grant. The students are measuring the volumetric response after pressure and temperature jumps using pressurizable and conventional dilatometry, respectively. Two additional students supported by the grant, Prashanth Badrinarayanan and Yan Meng, successfully defended their dissertations in 2007; Prashanth is working as postdoctoral researchers at another institution, wheresa Yan has begun an academic position in China. Four refereed journal articles have been published to date, with a fifth accepted for publication. 1-5 Outreach and Broader Impact: In addition to publications, outreach has included presentations by the PI and the graduate students at various local, national, and international meetings. Broader impacts include the hosting of a young female professor supported by a Danish L'Oreal Women in Science grant in our laboratory, as well as an upgrade of the conventional dilatometer with an optical system for measuring volume changes. Jiaxi Guo in the laboratory with the pressurizable dilatometer. 1.J. Guo and S. L. Simon, J. Polym. Sci.: Part B: Polym. Phys., accepted for publication. 2.Y. Meng, P. Bernazzani, P. O'Connell, G. B. McKenna, and S. L. Simon, Rev. Scientific Instr., 80, 053903 (2009). 3.P. Badrinarayanan, W. Zheng, and S. L. Simon, Thermochimica Acta, 468, 87-93 (2008). 4.Y. Meng and S. L. Simon, J. Polym. Sci.: Part B: Polym. Phys., 45, 3375-3385 (2007). 5.P. Badrinarayana, W. Zheng, Q. X. Li, and S. L. Simon, J. Non-Cryst. Solids, 353, 2603 - 2612 (2007). Sindee L. Simon, Texas Tech University, DMR 0606500