Peroxide radical treatments of a perfluorinated ionomer used in polymer electrolyte membrane (PEM) fuel cells and its small molecule analogues were carried out, along with analysis of the resultant products. Molecules containing terminal carboxylic acids degraded at least 1 order of magnitude faster than noncarboxylate materials; all of the systems did show peroxide-initiated degradation nonetheless. Product analysis suggests that terminal carboxylic acids react according to a sequential chain shortening, consistent with previous studies. Cleavage of side chains from both polymer and model compounds was also observed to be important and in fact may be the dominate pathway in low carboxyl content commercial PEM membranes, based on the following comparison of reactivity and concentration. The relative reactivities of carboxylic chain ends and ether linkages is approximately 500, as calculated using model compounds fluoride generation rates. Commercial perfluorosulfonic acid (PFSA) products contain minimal carboxylic acid end groups, and the side chain concentrations are of 2−3 orders of magnitude higher than carboxylic acid end groups.

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Objective To evaluate the feasibility and results of prosthetic venous replacement, as inferior vena cava (IVC) and iliofemoral vein resection and replacement are sometimes necessary when they are extensively involved by a large and fixed tumour thrombus from renal cell carcinoma (RCC) or other urological malignancies. Patients and methods Five men and two women (age range 41-75 years) were treated over a 10-year period (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001) by aggressive venous surgery to achieve complete tumour resection, with prosthetic graft replacement to re-establish venous flow. The tumours included RCC of the right kidney (two), retroperitoneal liposarcoma (two), bladder cancer (one), retroperitoneal fibrosarcoma (one) and inguino-pelvic lymphoma (one). Two patients had a vena caval replacement, of whom one had a circular reinforced PTFE and one a Dacron silver graft; five patients had either an iliofemoral or an ilio-iliac circular reinforced PTFE graft. The prosthetic diameter was 18-20 mm for the IVC grafts and 8-10 mm for the iliac grafts. In all the patients, graft patency was evaluated during the follow-up by colour flow duplex imaging, and in one it was determined by angio-computed tomography scan and venography. Results One patient died 30 days after surgery; of the remaining six patients one had no evidence of regional recurrence or metastatic disease at 12 months, and five died from recurrent tumour 8-30 months after surgery. The mean time to death was 23 months. At 3 months all six prosthesis were patent; at 6 months four were patent and at 12 months three of five prostheses were patent. Conclusion Resecting and replacing the IVC allows complete tumour resection and avoids renal failure, providing durable relief from the symptoms of venous obstruction. Iliofemoral prosthetic reconstruction for urological-related malignancies represents a viable option to avoid venous engorgement and lower extremity swelling, at least in the early postoperative period. The mean time to death for the present patients must be considered the limit for these aggressive operations.

Inorg. Chem.between the two closest distances to the nickel atom, and it can be seen that the charge (+l.5) is consistent with the Mulliken population analysis on the nickel atom found in the present EHMO calculations.Certainly this method involves the appearance of two new parameters that could be avoided if we apply a charge iteration scheme using the results of a Kohn-Sham calculation instead of the usual iteration parameters. Work on this line is in progress 1987, 26, 357-363 357 and will be presented elsewhere.

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