2,2-dinitropropyl acrylate (DNPA), 2,2-dinitrobutyl acrylate (DNBA) and 2,2-dinitrobutyl methacrylate (DNBMA) were synthesized
and the kinetics of their free-radical polymerization in the presence of 2,2′-azobisisobutyronitrile (AIBN) were investigated
by DSC in the non-isothermal mode. The kinetics of the free-radical polymerization as estimated by the Kissinger and Ozawa
methods showed that the reaction is disfavoured by increasing steric hindrance around the acrylyl double bond. The rate constants
calculated from the activation parameters showed the structural dependency. The polymerization kinetics revealed that the
polymerizability of three monomers decreased due to the presence of substituent methyl groups on the acrylyl double bond and
2,2-dinitrobutyl on ester group. Thus, the polymerization tendency increased in the order DNPA>DNBA>DNBMA.
Authors:S. Du, G. Zhang, H. Li, P. Wang, and X. Wang
The free-radical bulk polymerization of 2,2-dinitro-1-butyl-acrylate (DNBA) in the presence of 2,2′-azobisisobutyronitrile
(AIBN) as the initiator was investigated by DSC in the non-isothermal mode. Kissinger and Ozawa methods were applied to determine
the activation energy (Ea) and the reaction order of free-radical polymerization. The results showed that the temperature of exothermic polymerization
peaks increased with increasing the heating rate. The reaction order of non-isothermal polymerization of DNBA in the presence
of AIBN is approximately 1. The average activation energy (92.91±1.88 kJ mol −1) obtained was smaller slightly than the value of Ea=96.82 kJ mol−1 found with the Barrett method.
Authors:R. Radičević, D. Stoiljković, and J. Budinski-Simendić
The free radical polymerizations of higher n-alkyl methacrylates were not investigated in detail until now. In this work, the courses of the isothermal free radical bulk
polymerization of dodecyl, quatrodecyl and hexadecyl methacrylates were investigated by differential scanning calorimetry.
The effects of the polymerization temperature and the alkyl group length in the esters on the monomer conversions during polymerization
were studied. It was found that the polymerization rate vs. time curves have two maxima. The free radical polymerizations of above-mentioned monomers proceed with slightly expressed
gel effect at the temperatures below 90°C, at initiator concentration 1 mass% in monomer.
Authors:G. Maschio, J. Feliu, J. Ligthart, I. Ferrara, and C. Bassani
Adiabatic calorimetry is a technique that has been introduced as an important approach to hazard evaluation of exothermically reactive systems. In this paper the free radical polymerization of methyl methacrylate (MMA) has been studied. One of the most important aspects of MMA polymerization is its exothermicity and autoaccelerating behaviour, these characteristics can generate the occurrence of a runaway reaction.In a runaway situation the reacting system is close to adiabatic behaviour because it is unable to eliminate the heat that is being generated. An even worse situation can be reproduced in the laboratory with the Phi-Tec pseudo-adiabatic calorimeter. Process design parameters that are usually calculated from thermodynamic data or using semiempirical rules, such as adiabatic temperature rise or maximum attainable pressure, can be directly determined.The existence of the ceiling temperature has been experimentally demonstrated.
Authors:R. Radičević, D. Stoiljković, and J. Budinski-Simendić
It is well known that the free radical bulk polymerization of lower n-alkyl methacrylates is characterized by autoacceleration after definite conversions of the monomers. The conversion vs.time curves of polymerization have a typical 'S' shape. There are several characteristic points in these curves: the onset
of autoacceleration (point M), the maximum in the polymerization rate (point S) and the end of the polymerization (point K).
We have observed points P and R (maximum and minimum of autoacceleration) as inflection points in the derived polymerization
rate vs. time curve.
In this work, the free radical bulk polymerizations of methyl, ethyl and butyl methacrylates were investigated by differential
scanning calorimetry. The effects of the polymerization temperature and the alkyl group length in the esters on the monomer
conversions at the points M, P, S, R and K were studied. By regression analysis of the experimental results, relations were
developed with which it is possible to predict the positions of the characteristic points, depending on the polymerization
temperature and the alkyl group length.
Authors:Taís Vanessa Gabbay Alves, Eraldo José Madureira Tavares, Fauze Ahmad Aouada, Charles Alberto Brito Negrão, Marcos Enê Chaves Oliveira, Anivaldo Pereira Duarte Júnior, Carlos Emmerson Ferreira da Costa, José Otávio Carréra Silva Júnior, and Roseane Maria Ribeiro Costa
Synthesis of PAAm- co -MC hydrogels
The PAAm- co -MC hydrogels were synthesized by freeradicalpolymerization. They were prepared in the following sequence: aqueous solutions are prepared, consisting of AAm and MC 1.0% (w/v); MBAAm (8.55 μmol mL
Acrylonitrile-styrene /AN-St/ copolymers of different compositions were prepared, with and without ferric chloride by free radical polymerization. It was found using Mössbauer spectroscopy that reduction of Fe3+ to Fe2+ takes place during the polymerization. The addition of ferric chloride and the reduction of Fe3+ was found to influence the thermal stability of the copolymers.
In this study NMR and DSC are used to probe the structure, thermal characteristics and morphology of a network formed from a diepoxide/acrylate system. Separate chemistries are employed to polymerize the diepoxide and acrylate components. The cationic polymerization of the diepoxide exhibits excellent selectivity in producing a crosslinked polyether network without affecting the acrylate monomer. Subsequent photoinitiated free-radical polymerization of the acrylate produces a phase separated, semi-interpenetrating polymer network (SIPN).
Polyethyl methacrylate /PEMA/ containing ferric chloride was prepared by free radical polymerization at 70°C. Mössbauer studies of the polymer heated at 150°C, 300°C and 500°C for 1 h showed that during the thermal degradation the Fe3+ species are reduced to Fe2+ and the final form is -Fe2O3. TGA studies showed that the addition of ferric chloride during the polymerization of ethyl methacrylate increased the thermal stability of PEMA by 40°C. The final decomposition temperature /FDT/ increased by 75°C.
Methyl methacrylate /MMA/-n-butyl methacrylate /nBuMA/ copolymer containing anhydrous ferric chloride was prepared by free radical polymerization at 70 °C. TGA studies showed that the addition of ferric chloride increases the thermal stability of copolymer by 90 °C. Mössbauer studies of the copolymer were carried out to determine the oxidation state and environments of iron in the copolymer. Mössbauer studies of the copolymer heated at 150 °C, 300 °C and 500 °C for 1 h showed that during the thermal degradation, no reduction of Fe3+ takes place.