Stabilization of Polystyrene by Friedel-Crafts Chemistry: Effect of Position of Alcohol and the Catalyst

Polystyrene has been copolymerized with 4-vinylbenzyl alcohol, 4-(2-hydroxyethyl)styrene, and 4-(3-hydroxypropyl)styrene and it has been shown that thermal cross-linking of these copolymers is dependent upon the alcohol content. When the alcohol content is low, no thermal cross-linking is observed. When various phosphate esters are present as catalysts with these low alcohol content copolymers, cross-linking is observed at temperatures of about 250°C but not at lower temperatures. Cross-linking enhances the thermal stability of the copolymers. Studies of the thermal stability of the copolymers and their blends with the catalysts have been performed using thermogravimetric analysis and thermogravimetric analysis coupled to Fourier transform infrared spectroscopy. There is little difference in the thermal stability of all three copolymers and their blends with the catalysts

Polybutadiene Cross-Linked With Various Diols – Effect On Thermal Stability

The relationship between cross-linking and thermal stability as related to polybutadiene is the focus of current research. Cross-linked polybutadienes have been prepared using various diols as the cross-linking agent. Cross-linked polymers have been characterized by gel content, swelling ratios, infrared spectroscopy, and thermal analysis. These polymers are not highly cross-linked, as seen by gel content and swelling ratios, and cross-linking does not have a large effect on the onset temperature of the degradation. Nonetheless, extensive formation of a non-volatile residue occurs

Cross-linking of Polystyrene by Friedel–Crafts Chemistry to Improve Thermal Stability

Copolymers which contain either alcohol or chloride functionalized polystyrene units have been prepared and they participate in Friedel–Crafts chemistry to give cross-linked polymers by the evolution of either hydrogen chloride or water. Proof of cross-linking comes from the identification of the evolved gas, the insolubility of the product, and the thermal resistance of the newly formed polymer. The onset temperature for the degradation is raised by about 100°C relative to that of polystyrene and the fraction which is not volatile at 800°C ranges from 10% for the alcohol copolymers to 20% for the chloride copolymers

TGA/FTIR Studies on the Thermal Degradation of some Polymeric Sulfonic and Phosphonic Acids and Their Sodium Salts

The thermal degradation of poly(vinyl sulfonic acid) and its sodium salt, poly(4-styrenesulfonic acid) and its sodium salt, and poly(vinylphosphonic acid) was studied by a combination of techniques, including TGA/FTIR, to identify the volatile products which were evolved during the degradation as well as analysis of the residues which were obtained in order to propose a mechanism for the degradation. The motivation for the work was to attempt to identify new monomers which could be graft copolymerized onto a polymer in order to improve the thermal stability of that polymer

Chronic Nicotine Selectively Enhances α4β2* Nicotinic Acetylcholine Receptors in the Nigrostriatal Dopamine Pathway

These electrophysiological experiments, in slices and intact animals, study the effects of in vivo chronic exposure to nicotine on functional α4β2* nAChRs in the nigrostriatal dopaminergic (DA) pathway. Recordings were made in wild-type and α4 nicotinic acetylcholine receptor (nAChR) subunit knock-out mice. Chronic nicotine enhanced methyllycaconitine citrate hydrate-resistant, dihydro-β-erythroidine hydrobromide-sensitive nicotinic currents elicited by 3–1000 µM ACh in GABAergic neurons of the substantia nigra pars reticulata (SNr), but not in DA neurons of the substantia nigra pars compacta (SNc). This enhancement leads to higher firing rates of SNr GABAergic neurons and consequently to increased GABAergic inhibition of the SNc DA neurons. In the dorsal striatum, functional α4* nAChRs were not found on the neuronal somata; however, nicotine acts via α4β2* nAChRs in the DA terminals to modulate glutamate release onto the medium spiny neurons. Chronic nicotine also increased the number and/or function of these α4β2* nAChRs. These data suggest that in nigrostriatal DA pathway, chronic nicotine enhancement of α4β2* nAChRs displays selectivity in cell type and in nAChR subtype as well as in cellular compartment. These selective events augment inhibition of SNc DA neurons by SNr GABAergic neurons and also temper the release of glutamate in the dorsal striatum. The effects may reduce the risk of excitotoxicity in SNc DA neurons and may also counteract the increased effectiveness of corticostriatal glutamatergic inputs during degeneration of the DA system. These processes may contribute to the inverse correlation between tobacco use and Parkinson's disease

Habitat Characteristics Associated with the Distribution and Abundance of \u3cem\u3eHistrionicus histrionicus\u3c/em\u3e (Harlequin Ducks) Wintering in Southern New England

Histrionicus histrionicus (Harlequin Ducks) that winter along the east coast of North America are listed as a population of special concern in Canada, and they use several coastal wintering sites in southern New England that are subject to varying degrees of urbanization. We studied patterns of habitat use by Harlequin Ducks at 12 known wintering sites in southern New England. An average of 327 ± 114 Harlequin Ducks were found at the sites during the winters of 2001–2003. More Harlequin Ducks wintered at sites south of Cape Cod, MA that had greater mollusk (709,133 ± 504,568 versus 97,154 ± 72,427 kcal ha−1) and crustacean (27,907 ± 16,312 versus 1412 ± 1675 kcal ha−1) prey energy density, and a higher index of hunting activity (2.4 ± 1.2 versus 1.4 ± 0.5) than sites to the north. We used logistic regression analysis at 12 sites inhabited by Harlequin Ducks and 12 nearby sites of similar geomorphology that did not support Harlequin Ducks to identify habitat characteristics that best explained their distribution in southern New England. Our analysis identified two habitat characteristics that affected the likelihood a site was used by Harlequin Ducks: 1) the proportion of residential, commercial, and industrial land use within a 100-m radius of the perimeter of the site; and 2) distance to the nearest Harlequin Duck wintering site. However, other factors, including those related to their extremely low population size, need to also be considered as recommendations are developed for the conservation of east coast Harlequin Ducks

Online learning: Examining instructional design strategies in leisure curriculum

An assessment of the park and recreation-related educational programs and departments within the United States indicates an increasing presence of web-based distance learning (WBDL) environments. According to a voluntary listing posted on NRPA’s official website, over 35 courses are offered within a WBDL environment with almost 20 U.S. colleges and universities participating. In addition, some programs currently offer a 100% WBDL baccalaureate and/or master degree. These numbers are also somewhat conservative as additional programs offered by universities continue to emerge as evident by the dialogue and postings on the online discussion forum of the Society of Park and Recreation Educators (SPREnet). With this increase in instructional technologies there has been a growing concern in the educational community regarding the effectiveness of these tools to meet the needs of the learners (Lukow & Ross, 2003; Van Dusen & Worthen, 1995). Despite this concern, many of the issues surrounding the effective implementation of WBDL programs have not been explored sufficiently. Grounded within social cognitive theory, this study examined the instructional design of a WBDL about pay-for-performance systems in parks and recreation. The effects of two instructional methods, online discussion groups and multiple formats, are assessed on cognitive outcomes. The moderating role of experience with technology, technology selfefficacy, and several individual characteristic variables were also examined

The Development of a Pay-for-Performance Appraisal System for Municipal Agencies: A Case Study

Well-designed employee performance appraisal instruments assume great importance by providing agencies with information that can guide administrative and developmental decision-making about their most important asset—their human resources. Administratively, performance appraisals serve as the formal evaluation tool used by managers when making decisions about the distribution of pay increases and the promotion and demotion of an employee. Developmentally, performance appraisals assist agencies in identifying issues such as employee training needs and cross training opportunities.1 Despite its importance, both employees and management often view the performance appraisal process as frustrating and unfair. These frustrations are largely attributed to a reliance on performance appraisal instruments that: are not job related; have confusing or unclear rating levels, and; are viewed as subjective and biased by staff.2 This study was undertaken to identify steps for creating a more effective pay-for-performance system for public agencies. Specifically, this case study: (1) identified a systematic procedure for creating performance appraisal instruments; (2) described the appropriate training for those conducting an appraisal interview; (3) implemented performance reviews using the developed instruments and appraisal interview/review training, and; (4) evaluated employee attitudes toward the newly developed system. Survey results identified significant mean differences between employee attitude toward the original pay-forperformance instrument and appraisal interview process and the newly developed system. Results of the case study are analyzed and discussed