The Role Of Allylanisole In Metallocene-Catalyzed Propylene Polymerization And Synthesis Of End-Capped Oligomers

Propylene was copolymerized with allylanisole (AA) using Me2Si(Ind)(2)ZrCl2 and Et(Ind)(2)ZrCl2, and the methylaluminoxane MAO cocatalyst at 70 degrees C and a cocatalyst to catalyst (Al:Zr) molar ratio of 1000. It was fed at 8.5 bar(g). The weight-average molecular weight, (M) over bar (w), for both metallocenes decreased as the AA feed concentration increased. Therefore, allylanisole acted as an in situ chain transfer agent. The chain transfer constants, k(tr)/k(P), of AA for Et(Ind)(2)ZrCI2 and Me2Si(Ind)(2)ZrCl2 turned out to be 0.33 and 0.40, respectively. The characterization of the resulting products by (HNMR)-H-1 demonstrated that AA end-capped the isotactic poly(propylene) chains which showed to be low molecular weight oligomers; 4.96 x 10(3) <= (M) over bar (w) <= 9.80 x 10(3). An appropriate chain transfer mechanism for AA has been proposed

Oncological Outcome of Primary versus Secondary Muscle-Invasive Bladder Cancer Is Comparable after Radical Cystectomy

Background: High-risk non-muscle-invasive bladder cancer (NMIBC) progressing to muscle-invasive bladder cancer (MIBC) is associated with adverse tumour biology. It is unclear, however, whether outcome of NMIBC progressing to MIBC is adverse compared to primary MIBC and whether NMIBC of higher risk of progression to MIBC is adverse compared to NMIBC of lower risk. Objective: Our objective was to assess cancer-specific survival (CSS) following radical cystectomy (RC) for primary MIBC and for NMIBC progressing to MIBC in dependence of EORTC risk score. Materials and Methods: Clinical and histopathological characteristics and CSS of 150 patients were assessed. Secondary MIBCs were stratified by EORTC risk score at the last transurethral resection of bladder tumour for NMIBC. Results: CSS did not differ significantly between primary and secondary MIBC (p = 0.521). Secondary MIBC with high EORTC score had significantly shorter CSS compared to secondary MIBC with intermediate EORTC score (p = 0.029). In multivariable analysis, pathological tumour stage (HR = 3.77; p = 0.020) and lymph node stage (HR = 2.34; p = 0.022) were significantly correlated with CSS. Conclusion: While the outcome of secondary MIBC is not generally adverse compared to primary MIBC, the EORTC risk score not only reflects high risk of progression of NMIBC to MIBC, but also worse outcome following RC for secondary MIBC. Timely RC should thus be debated in high-risk NMIBC

Supported ((BuCP)-Bu-N)(2)ZrCl(2)Catalysts: Effects Of Selected Lewis Acid Organotin Silica Surface Modifiers On Ethylene Polymerization

This study investigated the effects of several organotin silica surface modifiers on the ethylene polymerization performance of ((BUCP)-B-n)(2)ZrCl2-based supported catalysts in which MAO and metallocene were sequentially loaded. Each organotin compound acted as a spacer, increasing the catalyst activity. However, the catalyst activity and (M) over bar of the resulting polyethylenes varied as follows: Activity and fractional Sn+ charge: (BuSn)-Bu-n(OH)(2)Cl > MeSnCl3 > (BuSnCl3)-Bu-n > Reference catalyst; and, (M) over bar (w) : Reference catalyst > (BuSnCl3)-Bu-n > MeSnCl3 > (BuSn)-Bu-n(OH)(2)Cl. The above catalyst activity rating was explained considering the influence of the Lewis acidity, that is, the fractional Sn+ charge of the organotin modifiers on the generation, concentration, and electron density at the active [((BUCP)-B-n)(2)ZrMe](+) cation. All the catalysts showed fairly stable kinetic profiles and produced narrow molecular weight distribution resins; 2.8 <= PDI <= 3

Influence of silica calcination temperature on the performance of supported catalyst SiO2–nBuSnCl3/MAO/(nBuCp)2ZrCl2 polymerizing ethylene without separately feeding the MAO cocatalyst

Abstract The effects of support calcination temperature, an important catalyst synthesis parameter, on the overall performance of the supported catalyst [silica ES70–nBuSnCl3/MAO/(nBuCp)2ZrCl2], polymerizing ethylene without separately feeding the MAO cocatalyst, were studied. The silica was calcined at 250, 450, 600, and 800 8C for 4 h. nBuSnCl3 was used to functionalize the silica. Ethylene was polymerized using the synthesized catalysts at 8.5 bar(g) in hexane for 1 h. No reactor fouling was observed. Free-flowing polymer particles with bulk density (0.23–0.27 g/ml) and a fairly spherical morphology similar to that of the catalyst particles were obtained. Also, the particle size distribution of the polymer resembled that of the catalyst. Therefore, the replication phenomenon from catalyst to polymer took place. The narrow PSD span (1.41) indicates that the resulting polyethylenes are suitable for various mixing-intensive polymer applications. The MAO cocatalyst-free ethylene polymerization instantaneously formed a polymer film around the catalyst particle, which coated/immobilized the catalyst constituents; this is how leaching was in situ prevented which favored heterogeneous catalysis to occur. The catalysts showed fairly stable polymerization kinetics. The catalyst activity, as a function of the silica calcination temperature, varied as follows: 250 8C > 600 8C > 800 8C > 450 8C. This finding has been explained considering the relevant surface chemistry phenomena. The calcination temperature did not significantly affect the bulk density and the PDI (3.4 PDI 3.8) of the resulting polyethylenes. The low PDI substantiates the retention of single-site catalytic behavior of the experimental supported catalysts. # 2007 Elsevier B.V. All rights reserved. Keywords: Supported zirconocene catalysts; Silica functionalization; Calcination temperature; Particle size distribution; Bulk densit

Student and Faculty Perceptions of Attendance Policies at a Polytechnic University

Student and Faculty Perceptions of Attendance Policies at a Polytechnic University The goal of an attendance policy is to improve the academic success of students. However,current literature does not provide clear conclusions whether enforcing an attendance policy actually improves student performance. This study explores student and faculty perceptions regarding the utility of attendance policies in undergraduate courses at a polytechnic university.Anonymous surveys were completed by 89 faculty members and 455 responses from five schools (Engineering, Engineering Technology and Management, Computer and Software Engineering, Architecture, and Arts and Sciences) on a single campus. Comparisons between theperceptions of students and faculty members are presented, as are comparisons between theperceptions of lower-level and upper-level students. Variations in perceptions based on major arealso highlighted. Finally, trends in perceptions regarding attendance policies in lower-level versus upper-level undergraduate courses are revealed.Students, regardless of major, class standing, or course level, reported attending more classes in courses that had attendance policies. The most significant impact of an attendance policy on class attendance was observed at the freshman level. While 84% of freshmen reported attending at least 90% of the classes in a course with an attendance policy, only 67% reported attending at that rate in a course without one. Qualitative data containing student and faculty attitudes towards attendance policies are also analyzed and discussed.Even though class attendance appeared to have improved as a result of attendance policies,students’ perceptions about these policies varied significantly. Overall, the majority of students(51%) believed that, for a course with an attendance policy, the policy positively affected final grades. For a course without an attendance policy, the majority (57%) felt that the lack of a policy had no impact of final grades. Faculty members’ perceptions about attendance policy likewise varied. Overall, 61% of the faculty members surveyed reported having an attendance policy in one or more of their courses. The majority of faculty members believed that an attendance policy led to improvements in students’ grades in lower-level courses, but not inupper-level courses. Collectively, this study can help instructors make better informed decisions about the use of attendance policies in their courses

Influence of silica calcination temperature on the performance of supported catalyst SiO2–nBuSnCl3/MAO/(nBuCp)2ZrCl2 polymerizing ethylene without separately feeding the MAO cocatalyst

Abstract The effects of support calcination temperature, an important catalyst synthesis parameter, on the overall performance of the supported catalyst [silica ES70–nBuSnCl3/MAO/(nBuCp)2ZrCl2], polymerizing ethylene without separately feeding the MAO cocatalyst, were studied. The silica was calcined at 250, 450, 600, and 800 8C for 4 h. nBuSnCl3 was used to functionalize the silica. Ethylene was polymerized using the synthesized catalysts at 8.5 bar(g) in hexane for 1 h. No reactor fouling was observed. Free-flowing polymer particles with bulk density (0.23–0.27 g/ml) and a fairly spherical morphology similar to that of the catalyst particles were obtained. Also, the particle size distribution of the polymer resembled that of the catalyst. Therefore, the replication phenomenon from catalyst to polymer took place. The narrow PSD span (1.41) indicates that the resulting polyethylenes are suitable for various mixing-intensive polymer applications. The MAO cocatalyst-free ethylene polymerization instantaneously formed a polymer film around the catalyst particle, which coated/immobilized the catalyst constituents; this is how leaching was in situ prevented which favored heterogeneous catalysis to occur. The catalysts showed fairly stable polymerization kinetics. The catalyst activity, as a function of the silica calcination temperature, varied as follows: 250 8C > 600 8C > 800 8C > 450 8C. This finding has been explained considering the relevant surface chemistry phenomena. The calcination temperature did not significantly affect the bulk density and the PDI (3.4 PDI 3.8) of the resulting polyethylenes. The low PDI substantiates the retention of single-site catalytic behavior of the experimental supported catalysts. # 2007 Elsevier B.V. All rights reserved. Keywords: Supported zirconocene catalysts; Silica functionalization; Calcination temperature; Particle size distribution; Bulk densit

The Charlson Comorbidity Index Predicts Survival after Disease Recurrence in Patients following Radical Cystectomy for Urothelial Carcinoma of the Bladder

Objective: To identify prognostic clinical and histopathological parameters, including comorbidity indices at the time of radical cystectomy (RC), for overall survival (OS) after recurrence following RC for urothelial carcinoma of the bladder (UCB). Materials and Methods: A retrospective multicenter study was carried out in 555 unselected consecutive patients who underwent RC with pelvic lymph node dissection for UCB from 2000 to 2010. A total of 227 patients with recurrence comprised our study group. Cox proportional hazards regression models were calculated with established variables to assess their independent influence on OS after recurrence. Results: The median time from RC to recurrence and the median OS after recurrence was 10.9 and 5.4 months, respectively. Neither the time to recurrence nor the type of recurrence (systematic vs. local) was predictive of the OS. In contrast, age (hazard ratio (HR) 1.53, p = 0.011), lymph node metastasis (HR 1.56, p = 0.007), and positive surgical margins (HR 1.53, p = 0.046) significantly affected the OS after disease recurrence. In addition, the dichotomized Charlson comorbidity index (CCI; dichotomized into >2 vs. 0-2) was the only comorbidity score with an independent prediction of OS (HR 1.41, p = 0.033). We observed a significant gain in the base model's predictive accuracy, i.e. from 68.4 to 70.3% (p < 0.001), after inclusion of the dichotomized CCI. Conclusions: We present the first outcome study of comorbidity indices used as predictors of OS after disease recurrence in patients undergoing RC for UCB. The CCI at the time of RC had no significant influence on the time to recurrence but represented an independent predictor of OS after disease recurrence

Modeling of synthesis and flow properties of propylene-diene copolymers

Copolymerization with nonconjugated dienes offers an attractive route for introducing long-chain branching in polypropylene. From a simplified set of rate equations for such copolymerization with a metallocene catalyst, we derive the probabilities of branch formation at different stages of the reaction in a semibatch reactor. Using these probabilities, we generate an ensemble of molecules via a Monte Carlo sampling. The knowledge of the branching topology and segment lengths allows us to compute the flow properties of the resins from computational rheology. We compare our model predictions with existing experimental data, namely the molar mass distribution and small amplitude oscillatory shear response, for a set of resins with varying diene content. The rheology data suggest that the entanglement time Ï.,e depends sensitively and in a well-defined fashion on the diene content