摘要:

AbstractThe kinetics of styrene (St) copolymerization with maleic anhydride (MA) initiated by light (at λ = 365 nm) was studied in acetone, acetonitrile, chloroform, andN,N‐dimethyl formamide at 30°C. With the exception of the chloroform containing system, the copolymerizations took place in homogeneous reaction media. The copolymerization rateRp= −d([St] + [MA])/dt was found to be a function of the mole ratio of the comonomers in the reaction mixture. For a given ratio of comonomersRpand the molecular weight of the resulting copolymer were found to be a function of the donor number of the solvent used for a given rate of initiation. Due to the dependence ofRpon the concentration of an equimolar mixture of both comonomers in acetone on [St] (at constant [MA]), and on [MA] (at constant [St]) the participation of the exciplex {St…acetone}*in the initiation reaction can be expected. The ratio of the overall rate constants for the propagation (k̄p) and termination (k̄t) reactions, k̄p/2k̄t, determined by a rotating sector technique, was found to depend on the composition of the comonomer mixture. The copolymerization rate is proportional to the square root of the intensity of incident light, which, together with the observed inhibition effect of oxygen points to a radical mechanism of the photoinitiated copolymerization of St with MA. In the presence of the photosensitizer benzophenone in the system St/MA/acetone an increase inRpwas observed, accompanied by a decrease in molecular weight of the copolymer in comparison with the system without b

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810121

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractThe effect of UV light (λ>300 nm) on the system styrene/maleic anhydride/solvent (acetone or chloroform) in the presence and/or absence of the alternating styrene/maleic anhydride copolymer was studied by the ESR method at −196°C. It was found that the concentration of paramagnetic species increased with the time of irradiation. The intensity of the ESR spectra at −196°C did not change when the light was cut off. By analysis of the ESR spectra of the systems studied the methyl (aH= 2,3 mT), dichloromethyl (aH= 1,66 mT), and acetyl (aH= 0,52 mT) radicals as well as the radicalsAandD(aHα= 2,25 mT,aHβ= 3,19 mT) and (aHβ= 1,1 mT), respectively, were i

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810122

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractThe interaction between alternating styrene/maleic anhydride copolymer as polymeric acceptor and styrene as low molecular weight donor in acetone and/or tetrahydrofuran was investigated by UV spectroscopy and polymerization technique. The equilibrium constant for the complex formation between styrene and the maleic anhydride structural unit of the styrene/maleic anhydride copolymer at 20°C was found to be 0,02 ± 0,001 dm3·mol−1in acetone and 0,06 ± 0,003 dm3·mol−1in tetrahydrofuran. The results of the thermally initiated polymerization of styrene in acetone in the presence of the alternating styrene/maleic anhydride copolymer indicate that the copolymer or the products of the interaction between the monomeric units of maleic anhydride in the copolymer and styrene do not initiate a radical polymerization of

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810123

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractProducts with>90% of 1,4‐cis‐units in the grafted chains are obtained by employing suitable concentrations of cobalt complexes as an initiator component in the grafting of butadiene onto chlorinated polycyclopentadiene. Grafting efficiencies>90% can be achieved. In contrast to grafting without using cobalt complexes the reaction rate is faster. Suitable solvents are chlorobenzene, 1,2‐dichloroethane, or dichloromethane. Grafting efficiency, degree of grafting, and the molecular weights of the grafted chains are obtained by selective extraction of the grafts with pentane. The results suggest a cationic‐coordinative mechanism, in most cases accompanied by a “pure” cation

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810124

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractThe low‐frequency viscoelastic behaviour of three stereoregular samples of poly(ethyl methacrylate) (PEMA) in the main transition region was investigated. The main effect of tacticity in the transition from the syndiotactic sample to the isotactic one consists in a shift of the main transition region (or of the glass transition temperatures,Tg) to lower temperatures by ≈ 70 K. The temperature dependence of the shift factor of all samples could not be adequately described by the single Williams‐Landel‐Ferry (WLF) equation within the whole range of temperatures; in the rangeT>Tg+60K, isotactic PEMA exhibited the largest departures from the WLF equation. In all cases, departures from the WLF equation could be quantitatively described in terms of the temperature dependence of the Andreade coefficient β. The temperature dependence of the Andreade compliance,JA, was also most pronounced for the isotactic sample. Vertical correction of the complex modulusG*, with WLF horizontal shifts preserved, led to the lowest activation energy ΔHfor the isotactic sample, which means the highest magnitude of secondary relaxation mechanism in this sample. The birefringence measurement showed that the molecular nature of the deformational birefringence is independent of the tacticity of the sample and does not vary in the rangeTg+25K

ISSN:0025-116X    

DOI:10.1002/macp.1980.021810125

出版商:Hüthig&Wepf Verlag    

年代:1980

数据来源: WILEY