Kinetic Study of Radical Polymerization VIII. A Comprehensive Study of Solution Copolymerization of Vinyl Acetate and Methyl Acrylate by 1H‐NMR Spectroscopy

Radical copolymerization reaction of vinyl acetate (VA) and methyl acrylate (MA) was performed in a solution of benzene‐d₆ using benzoyl peroxide (BPO) as the initiator at 60°C. Kinetic studies of this copolymerization reaction were investigated by on‐line ¹H‐NMR spectroscopy. Individual monomer conversions vs. reaction time, which was followed by this technique, were used to calculate the overall monomer conversion, as well as the monomer mixture and the copolymer compositions as a function of time. Monomer reactivity ratios were calculated by various linear and nonlinear terminal models and also by simplified penultimate model with r _2(VA)=0 at low and medium/high conversions. Overall rate coefficient of copolymerization was calculated from the overall monomer conversion vs. time data and k _p  . k _t ^?0.5 was then estimated. It was observed that k _p  . k _t ^?0.5 increases with increasing the mole fraction of MA in the initial feed, indicating the increase in the polymerization rate with increasing MA concentration in the initial monomer mixture. The effect of mole fraction of MA in the initial monomer mixture on the drifts in the monomer mixture and copolymer compositions with reaction progress was also evaluated experimentally and theoretically.     

Design,Synthesis, and Properties of Substituted Polyacetylenes

This article reviews recent topics on the polymerization of substituted acetylenes, focusing on the synthesis of poly(diphenylacetylenes) and the living polymerization of phenylacetylenes. Diphenylacetylene (DPA) polymerizes with TaCl_s-n-Bu₄Sn to give a polymer which is thermally very stable but insoluble in any solvents. DPAs with various groups (e.g.,p-Me₃Si,m-Me₃Ge, p-t-Bu,and_p-PhO) polymerize similarly. These polymers are soluble and their M¯_w's reach 1 × 10⁶ to 3 × 10⁶. Some of them are more gas-permeable than poly(dimethylsiloxane). Several acetylenes (e.g., ClC -n-C₆H₁₃ and HCUC-t-Bu) have been found to undergo living polymerization with MoOCl₄-n-Bu₄Sn-EtOH. Whereas phenylacetylene (PA) does not polymerize in a living fashion, ortho-substituents in PA more or less suppress termination and chain transfer. PAs with bulky ortho groups (e.g., CF₃ and Me₃Ge) especially undergo virtually ideal living polymerization.     

Effect of Membrane Preparation Methods on the Release of Theophylline through CA Membranes at In-Vitro Conditions

In this study the effect of the membrane preparation methods on the release of theophylline through cellulose acetate (CA) membranes was studied at in vitro conditions. CA/acetone binary and CA/acetone/water ternary systems were used as casting solutions and poly(ethylene glycol) (PEG) was used as the pore forming, plasticizing agent in the study. Membranes were characterized by FTIR, SEM, and DSC analysis. It was determined that pH, temperature and drug concentration affected the release of theophylline. A decrease in pH, increase in temperature and drug concentration increased the permeated amount of theophylline through the membranes. In addition, receiver solution circulation at a capillary blood rate increased the permeation of theophylline. As a result of the study, it was concluded that the release of theophylline could be controlled for a prolonged period of time and modified CA membranes prepared in the study could be as an advisable membrane material for potential release of theophylline at transdermal conditions.     

Synthesis of novel poly(aminophosphonate ester)s flame retardants and their applications in EVA copolymer

Novel oligomeric intumescent flame retardants, poly(amino phosphonate ester)s (PAPEs), containing both phosphorous and nitrogen, were synthesized by reacting diethyl phosphite with two different polyschiff bases obtained from the reaction of diamines with dialdehyde. The target PAPEs (designated as PAPE‐d and PAPE‐e, respectively) were characterized by ¹H NMR, ³¹P NMR, Fourier Transform infrared spectroscopy, elemental analysis, gel permeation chromatography and thermogravimetric analysis (TGA) techniques. Thermal stability and flammability of ethylene‐vinyl acetate copolymer (EVA)/PAPE blends with various PAPE content were investigated by TGA, limited oxygen index (LOI), vertical burning test (UL‐94) and microscale combustion colorimeter (MCC). The results indicate that PAPEs effectively improve the flame retardancy of EVA. The EVA/30%PAPE‐e blend has a LOI value of 28, and its peak heat release rate (PHRR) value in MCC measurement is reduced by 36%. At the same time, the EVA/PAPE blends also have high yield of residual char, indicating that PAPEs are effective charring agents. Scanning electron microscopy observations of the residues of the EVA/PAPE blends show the existence of compact char layer on the surface of the residues, which is responsible for the improvement of the flame retardancy of EVA. Copyright © 2012 John Wiley & Sons, Ltd.     

PEROXIDASE,HEMATIN, AND PEGYLATED-HEMATIN CATALYZED VINYL POLYMERIZATIONS IN WATER

Horseradish peroxidase-, hematin- and pegylated-hematin mediated polymerization of sodium styrene sulfonate and sodium acrylate in water is reported. Molecular weight and yields were influenced by the concentrations of hydrogen peroxide and initiator, 2,4-pentanedione. Hematin and pegylated-hematin were studied in lieu of peroxidase at pH 11.0 and 7.0 in aqueous solution, respectively. Polymer with a high molecular weight (Mn = 223,520) was formed when the pegylated-hematin was used as the catalyst. The results demonstrate vinyl polymerizations in an all aqueous process in high yield and molecular weight catalyzed by peroxidase as well as biomimetic catalysts.     

Stereoselective Synthesis of (Z)‐ and (E)‐Allyl Aryl Sulfides and Selenides from Baylis?Hillman Acetates under Neutral Conditions Using β‐Cyclodextrin in Water

The first example of the stereoselective synthesis of (Z)‐ and (E)‐allyl aryl sulfides and selenides from Baylis? Hillman acetates under neutral conditions in H₂O by supramolecular catalysis involving β‐cyclodextrin is reported. β‐Cyclodextrin can be recovered and reused. The reaction is very efficient in providing allyl aryl sulfides and selenides in good‐to‐excellent yields with clean reaction profiles under mild reaction conditions.     

Studies towards the Synthesis of Alkyl N‐(4‐Nitrophenyl)‐3/2‐oxomorpholine‐2/3‐carboxylates

The syntheses of methyl 4‐(4‐nitrophenyl)‐3‐oxomorpholine‐2‐carboxylate ( 3a ) and ethyl 4‐(4‐nitrophenyl)‐2‐oxomorpholine‐3‐carboxylate ( 5b ), important building blocks for the synthesis of factor Xa inhibitor rivaroxaban analogs with potential dual antithrombotic activity, via Rh₂(OAc)₄‐catalyzed O? H and N? H carbene insertion reactions are described.     

Aryl vinyl cyclopropane Cope rearrangements

While the divinyl cyclopropane Cope rearrangement is well-known, and has been broadly applied in synthesis, examples of the aryl vinyl cyclopropane Cope rearrangement are less common and generally limited in scope or reaction yield. The aryl vinyl cyclopropane Cope rearrangement gives access to the benzocycloheptene scaffold, which is present in a variety of naturally occurring and medicinally relevant products. Herein we report a method to obtain either of two regioisomeric benzocycloheptene products via an aryl vinyl cyclopropane Cope rearrangement, featuring additive-controlled regioselectivity. Mechanistic studies indicate a dynamic equilibration of cyclopropane stereoisomers, followed by rearrangement of the cis diastereomer.