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  • 1
    ISSN: 0887-624X
    Keywords: fotopolymerization ; free radical polymerization ; furfuryl acrylate ; furfuryl methacrylate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect and the participation of the furfuryl ring, in particular the hydrogen at position C-5 in the free radical polymerization are analyzed following the polymerization of furfuryl acrylate (FA) and furfuryl methacrylate (FM) initiated by AIBN under photochemical activation. The results obtained indicate that the polymerization of FA deviates from the classical free radical kinetic scheme, giving rise to crosslinked polymers even at a degree of conversion lower than 7%. This behavior is well explained taking into consideration the participation of the furfuryl ring which acts as a degradative transfer agent. This was demonstrated by the kinetic analysis of the free radical polymerization of MMA initiated by the thermal decomposition of AIBN in the presence of different concentrations of furfuryl acetate. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 2
    ISSN: 0887-624X
    Keywords: copolymers ; furfuryl acrylate ; hydroxyethyl methacrylate ; biomaterials ; glass transition temperature ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copolymers of furfuryl acrylate (F) and 2-hydroxyethyl methacrylate (H) were prepared by free radical polymerization in DMF solution at 50°C, using 2,2′-azobisisobutyronitrile (AIBN) as initiator. The reactivity ratios of both monomers were calculated according to the general copolymerization equation using the Fineman-Ross and Kelen-Tüdös linearization methods, as well as the Tidwell and Mortimer nonlinear least-squares treatment. The reactivity ratios obtained were rF = 0.93 and rH = 1.42. The microstructure of copolymer chains is described on the basis of first-order Markov statistics, and the copolymer glass transition temperatures were determined calorimetrically. The variation of Tg with the copolymer composition is discussed according to modern methods, considering the sequence distribution of monomeric units along the copolymer chains. Also the Tg of the corresponding homopolymers was determined giving the values Tg(F) = 321 K and Tg(H) = 358 K, whereas the Tg of the corresponding alternating diad has an average value of TgFH = 326 K. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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  • 3
    ISSN: 0887-624X
    Keywords: photopolymerization ; copolymers ; hydrogels ; biocompatible polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The study of the homo- and copolymerization of furfuryl methacrylate (F) and vinylpyrrolidone (P) in bulk, initiated by the photoactivation of AIBN at low temperatures (0 and 40°C), is described. The kinetic diagrams for the homopolymerization of F and P were obtained following the evolution of the heat of reaction by DSC, and revealed the autoacceleration and the vitrification effects on the polymerization rate. The influence of oxygen in the photoinitiated polymerization was analyzed by determining the steady-state concentration of oxygen from the kinetic data obtained for polymerizations performed out in the presence and absence of oxygen. The results obtained indicate that P is more sensitive than F to the presence of oxygen in free radical polymerization. The photoinitiated copolymerization process is little affected by the concentration of monomers, giving similar Rp and θm values for both systems. However, at low polymerization temperature 0°C non-crosslinked copolymers are obtained, whereas at a temperature of 40°C, the copolymers prepared at conversion higher than 20 mol % become crosslinked as a result of the active participation of the furfuryl ring in the polymerization process at this temperature. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 4
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The thermal degradation of poly(N-vinyl-2-pyrrolidone) (PVP) was studied by dynamic thermogravimetric analysis (TGA) in the range 200-600°C under nitrogen and oxygen atmospheres at various heating rates. The apparent activation energy of the degradative process was determined by the application of kinetic treatments, giving an average value of 242 kj/mol in N2, whereas in the presence of oxygen, two trends may be considered: At relatively low temperatures (200-400°C) and degrees of conversion, α, lower than 0.5, we obtained an average value of 199 kj/mol, whereas in the temperature interval 400-600°C with degrees of conversion higher than 0.5, the value of Ea was 306 kj/mol. Isothermal experiments carried out in N2 in the interval 350-400°C gave an average value of Ea = 231 kj/mol, in good agreement with that obtained from dynamic treatments. The FTIR spectra of the volatile compounds evolved in degradation experiments carried out in N2 as well as in the presence of oxygen suggest that PVP is thermally degraded, predominantly, by the release of the pyrrolidone side group and the subsequent decomposition of polyenic sequences. © 1993 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 5
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The thermal behaviour of random copolymers of furfuryl methacrylate (F) and N-vinylpyrrolidone (P) was studied by means of dynamic thermogravimetric analysis (TGA) in the range 100-600°C. The dynamic experiments show that these copolymers exhibit two degradation steps in the intervals 260-320°C and 350-520°C, respectively. The normalized weight loss in the low temperature interval increases as the mole fraction of F in the copolymer mF increases, whereas an inverted trend in the high temperature interval is observed. The apparent activation energy Ea of the first degradation step for copolymers prepared with different composition, was obtained according to the treatment suggested by Broido. A plot of the values of Ea versus the F diad molar fraction in the copolymer chains mFF gave a straight line that indicates that there is a direct relationship between the thermogravimetric behaviour of these systems and their corresponding microstructure, that is, the distribution of comonomeric units along the copolymers chains. The first decomposition step was also studied by isothermal TGA and a good linearity for the variation of the weight loss percentage ΔW versus mF at least during the first 30 min of treatment was obtained. These results also indicate that from a kinetic point of view the isothermal degradation in these conditions follows a first order behaviour and the corresponding reaction rate constants increase linearly with mFF. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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  • 6
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Hydrogels of biomedical interest were prepared by the free redical copolymerization of 2-hydroxyethylmethacrylate, H, with furfuryl acrylate, A, at low and high conversion. The microstructural analysis of the copolymer system was carried out by nuclear magnetic resonance (NMR) spectroscopy, taking into consideration statistical perameters according to the Mayo-Lewis copolymerization model. The hydration process in physsiological conditions was studied gravimetrically at 37°C, following the kinetics of swelling of homogeneous thin films. A diffusion mechanism based on the stress relaxation model of copolymer chains accounts satisfactorily for the expermental data obtained. The diffusion coefficents determined according to the classical to the Fickian uptake kinetics are very sensitive to the copolymer's composition. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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