Analyzing the real advantages of bifunctional initiator over monofunctional initiator in free radical polymerization

Monofunctional initiators are extensively used in free radical polymerization. To enhance productivity, a higher temperature is usually used; however, this leads to lower molecular weights. Bifunctional initiators can increase the polymerization rate without decreasing the average molecular weight and this can be desirable. A bifunctional initiator is an important issue to be investigated, and it is of great interest to industries. The objective of this work is to study polymerization reactions with mono‐ and bi‐functional initiators through comprehensive mathematical models. Polystyrene is considered as case study. This work collects and presents some experimental data available in literature for polymerization using two different types of bifunctional initiators. Model prediction showed good agreement with experimental data. It was observed that the initial initiator concentration has a huge impact on the efficiency of initiators with functionality bigger than one and high concentrations of bifunctional initiator make the system behave as if it were a system operating with monofunctional initiator. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Perceived reciprocity, social support, and stress at work: The role of exchange and communal orientation.

Perceived reciprocity regarding support in relationships at work was examined among employees of a psychiatric hospital (Study 1) and in a study of employees of the Dutch National Railway Company (Study 2). Relationships with colleagues were more often perceived as reciprocal than relationships with superiors, and in relationships with superiors individuals more often felt overbenefited. Lack of reciprocity (being underbenefited or being overbenefited) was in general associated with negative affect, and these effects were independent of the effect of perceived job stress. In Study 2 it was also found that these effects were moderated by the individual-differences variables exchange orientation (the general expectation of immediate reciprocity) and communal orientation (a positive regard for the needs and feelings of others). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Oxidation of methionine residues of food proteins and nutritional availability of protein-bound methionine sulphoxide

The extent of oxidation of methionine residues has been determined in food proteins submitted to various oxidative treatments.The nutritional value of oxidised casein, in which 98% of the methionine residues were converted to the corresponding sulphoxide, was assessed both by proteolysis in vitro and on rats.The nutritional availability of residues of methionine sulphoxide appears to be only slightly inferior to that of methionyl residues.     

Contribution to the study of the vasculature of submandibular and sublingual glands and lymph nodes of rats by corrosion cast technique combined with scanning electron microscopy

The study of anatomical structures in their normal state allows the identification of pathological changes that can occur in them. Angiogenesis and the vasculature have been widely studied, mainly because of their association with the development of neoplasms. One of the methods applied for such purposes is the corrosion cast technique, which provides a copy of the vessels with normal as well as pathological structures. The replica of the vasculature provided by this technique allows the three-dimensional analysis of vessels by means of scanning electron microscopy. The aim of the present study was to demonstrate, by means of corrosion casts, the angioarchitecture of the submandibular and sublingual glands and lymph nodes. Scanning electron microscopy showed that the three structures have distinct vascular patterns. The corrosion cast technique can be employed in the study of the angioarchitecture of the submandibular and sublingual glands and lymph nodes, but requires specific precautions. The removal of the structures en bloc and the handling of the replicas with the aid of a stereoscopic magnifier reduce the risk of fractures.     

Artificial Neural Networks Associated to Calorimetric Measurements Used as a Method to Predict Polymer Composition of High Solid Content Emulsion Copolymerizations

Summary: Inspired by biological systems, artificial neural networks (ANN) have demonstrated to be powerful tools to model non‐linear systems, such as high solid content latexes produced by emulsion polymerization which have a great importance in the polymeric industry, essentially for environmental reasons, since they usually have water as a continuous phase. The quality of the produced polymer is closely related to the structure of the polymeric chain. In order to propose technical and economically feasible alternatives to control a polymeric structure, this work is aimed to develop a new methodology based on ANN associated with calorimetry to predict the polymeric structure. The designed ANN presented excellent results when tested with process condition variations (such as temperature and reaction time) as well as when they were submitted to test concerning the variation on the proportion of monomers in the latex formulation. Hence, it was possible to conclude that ANN, associated to calorimetry, lead to an efficient method to predict the polymer composition in emulsion copolymerizations.

     

Effect of fruit load on maturity and carotenoid content of clementine (Citrus clementina Hort. ex Tan.) fruits

BACKGROUND: Citrus fruits contain many secondary metabolites displaying valuable health properties. There is a lot of interest in enhancing citrus quality traits, especially carotenoid contents, by agronomic approaches. In this study the influence of carbohydrate availability on maturity and quality criteria was investigated in clementine fruits during ripening. Fruiting branches were girdled and defoliated after fruit set to obtain three levels of fruit load: high (five leaves per fruit), medium (15) and low (30). RESULTS: Considering the soluble solid content/titratable acidity (SSC/TA) ratio, it was found that fruits of the high and medium fruit load treatments reached maturity 1.5 months later than fruits of the control. At the time of maturity the SSC/TA ratio of fruits of all treatments was about 13.6. At harvest, fruits were 23% smaller and total sugar concentration of the endocarp was 12.6% lower in the high fruit load treatment than in the control. In contrast, the concentrations of organic acids and total carotenoids were 55.4 and 93.0% higher respectively. Total carotenoids were not positively correlated with either soluble sugars or total carbohydrates. CONCLUSION: Taken together, the results do not support the common view that carbohydrate availability directly determines carotenoid synthesis by influencing precursor availability. Copyright © 2012 Society of Chemical Industry     

Functionalization of styrene-butadiene-styrene (SBS) triblock copolymer with maleic anhydride

Summary The thermoplastic elastomers have been widely used in polymer blends to improve their mechanical properties. This work is about the study of chemical modification of styrene-butadiene-styrene (SBS) with maleic anhydride (MA) by radical reaction. The functionalization reaction was carried out in a mixer Haake Rheomix 600 and the torque variation was monitored during the process. The products were characterized by Infrared Spectroscopy (FTIR) and crosslinking was evaluated by extraction. A calibration curve was plotted to determine the functionality. The results showed that it is possible to accomplish the functionalization reaction avoiding the crosslinking. Received: 26 February 2001/Revised version: 25 June 2001/Accepted: 25 June 2001