A competitividade no minibasquete: estudo em equipas do escalão de mini-12 das associações de basquetebol do Porto, Aveiro e Lisboa

Chain transfer to polymer is a significant process in the polymerization of acrylate-type monomers.1??4 It is well accepted that intramolecular chain transfer to polymer (socalled backbiting) is favored over intermolecular chain transfer to polymer. It has been reported that chain transfer to polymer occurs primarily via a 1,5-hydrogen shift (Scheme S1, Supporting Information).5??7 It is important to note that intramolecular chain transfer to remote positions is also possible, though not favored. The result of chain transfer to polymer is an interesting situation in which two distinct transient radicals coexist in the system. The complexity and challenges posed by the coexistence of two distinct transient radicals in n-butyl acrylate (BA) polymerization becomes apparent in the kinetic description of its controlled radical polymerization. The prime focus of this Communication is to probe the kinetics of BA polymerization mediated by nitroxides, especially the implications on kinetics of the reversible deactivation of the tertiary mid-chain radicals (MCRs)

Terminal monomer units in dormant and active copolymer chains

NatuurwetenskappeChemie & PolimeerwetenskapPlease help us populate SUNScholar with the post print version of this article. It can be e-mailed to: [email protected]

In situ 1H NMR studies of high-temperature nitroxide-mediated polymerization of n -butyl acrylate

This paper presents results on the independence of the rate of polymerization of n-butyl acrylate (n-BA) toward initial concentration of the alkoxyamine initiator. The alkoxyamine, 2-methyl-2-[N-tert-butyl-N-(1- diethoxyphosphoryl-2,2-dimethylpropyl)aminooxy]propionic acid (MAMA-DEPN), was used to initiate and mediate the polymerization of n-BA in the temperature range 90-120 °C. In situ1H NMR spectroscopy was used to follow the consumption of the monomer and monitor other related reactions. Intra- and intermolecular chain transfer processes are well-known phenomena in the polymerization of n-BA that result in the transformation of secondary propagating radicals (SPRs) into tertiary midchain radicals (MCRs). At high polymerization temperature (T ≥ 110 °C), the MCRs undergo β-fragmentation. The concentrations of the products of the β-fragmentation process (in the form of chains bearing 1,1-disubstituted alkene end group) were measured as a function of polymerization time. The independence of rate of polymerization of n-BA initiated by MAMA-DEPN can be explained in terms of thermal autoinitiation in the case where free [DEPN] 0 is no larger than 1 mol % relative to [MAMA-DEPN]0. © 2011 American Chemical Society.Articl

RAFT–mediated ab initio emulsion copolymerization of 1,3-butadiene with acrylonitrile

The successful RAFT-mediated ab initio emulsion copolymerization of acrylonitrile and 1,3-butadiene using 2-(((dodecylsulfanyl)carbonothioyl)sulfanyl)propanoic acid (DoPAT) is reported at 45-55 degrees C. The number-average molecular weight exhibits a linear evolution as a function of monomer conversion (5000 40% was tentatively attributed to branch formation. The current study evidences that RAFT mediated ab initio emulsion polymerization of 1,3-butadiene and acrylonitrile is a viable polymerization protocol for the synthesis of well-defined next generation nitrile-butadiene rubbers including in industrial context

Mechanistic insights into the UV-induced radical copolymerization of 1,3-butadiene with acrylonitrile

An in-depth mechanistic study into the solution based initiator-free UV-induced radical copolymerization of 1,3-butadiene with acrylonitrile is reported. The light induced constant radical flux leads to moderate monomer conversions within 4 to 24 h. The number-average molecular weights of the prepared nitrile butadiene rubber (NBR) range from 2500 to 50 000 g mol -1 (1.7 ≤ PDI ≤ 2.4), while the achievable monomer conversion ranged from close to 7 up to 31% depending on the polymerization temperature, reaction time and UV light intensity. The rate coefficient for the generation of primary radicals, determined as the coupled parameter k1 *k3, showed a dependence on the UV light intensity with values between 6.0 s-2 and 34.6 s-2 deduced for the UV light intensity range of 280 to 700 W. The estimated values of the lower limit average termination rate coefficient displayed no dependence on the UV light intensity, with lower limit values between 2.6 × 108 L mol-1 s-1 and 6.3 × 108 L mol -1 s-1 for the UV light intensity range of 280 to 700 W. The deduced values for the average termination rate coefficient were above the expected values for comparable average termination rate coefficients. © 2013 American Chemical Society