SynopsisA 1:l hydrogen-bonded complex was formed between acrylic acid (AA) or methacrylic acid (MA) and the pyridine group of poly(4-vinylpyridine) (P4VP) in dilute solutions. A shift of infrared absorption of the hydrogen-bonded acid 0-H to a lower energy direction and an upfield shift of acid proton in the NMR were observed when the monomers were added with pyridine. The equilibrium constants of the 1:l complexation with P4VP measured by using a semipermeable membrane were 0.58 and 0.26 for AA and MA, respectively, at 25'C in methanol. The bromometrically measured initial rate of radical polymerization showed only a slight enhancement in the presence of P4VP, the rate being maximum at the 4VP unitmonomer mole ratio of 0.25 and 0.5 for AA and MA, respectively, in dilute methanol solution at 60°C.
EXPERIMENTAL MaterialsReagent-grade chemicals were used. AA (Tokyo Kasei), MA (Fluka), and 4-vinylpyridine (4VP) (Fluka) were fractionally distilled before use. 2,2'-Azobisisobutyronitrile (AIBN) (British Drug House) was recrystallized from
The composition of the copolymers of maleic anhydride (MA) with ethyl cinnamate (EC) and with anethole (ANE) polymerized in chloroform solutions with a radical initiator is reported. A strong alternating tendency is observed in the ANE-MA copolymer but EC is incorporated dominantly into the EC-MA copolymer. Both ANE and EC form 1 : 1 charge-transfer complexes with MA with the equilibrium constants determined to be 0,0845 and 0,026 L/mol, respectively. Applicability of the terminal, the penultimate and the complex participation models of the copolymerization mechanism is examined by non-linear least-square minimization technique using the most general forms of the composition equations. The complex participation model is found to be slightly in favor for both EC-MA and ANE-MA copolymerizations in CHC1,. 0 1991, Huthig & Wepf Verlag, Base1 CCC 0025-1 16X/91/$03.00
SYNOPSISThe Comppen model for the mechanism of free-radical copolymerization has been developed to account for both penultimate effects and the participation of 1 : 1 electron donor-acceptor complexes during chain propagation. This was achieved by incorporating penultimate effects into the existing complex participation model of Cais, Farmer, Hill, and O'Donnell, using probability theory to derive new copolymer composition and sequence distribution equations that are solely functions of the reactivity ratios, the composition of the comonomer feed, and the equilibrium constant for 1 : 1 electron donor-acceptor complex formation. The model was applied to experimental data from styrene/maleic anhydride copolymers prepared in methyl ethyl ketone a t 50°C over a wide range of comonomer feed compositions, using nonlinear least-squares curve fitting techniques to determine best estimates of the reactivity ratios. Copolymer compositions and sequence distributions for copolymers in this comonomer system were then predicted using the Comppen model and compared to those determined experimentally via 13C-NMR spectroscopy.
The monomer unit triad sequence distribution and the cidtrans linkage configurations at the cyclic maleic anhydride (MA) units in the copolymers of styrene (ST) and MA prepared in CCI, with AIBN at 50°C were quantitatively determined by 13C DEPT NMR spectroscopy. So much as 61 % of the linkages at the MA units were found to be in cis configuration, which was considered to be formed by a participation of the 1 : 1 electron donor-acceptor complex formed between ST and MA in the propagation step. The mole fraction of the cis configuration was found to be proportional to the mole fraction of alternating triad sequences when the monomer unit sequences approach to be completely alternating. This supported the proposal that, in alternating and semi-alternating copolymerizations, the alternating sequences were formed mainly by the addition of the complex. The equilibrium constant of the complexation in CCI, at 23°C was determined to be 0,21 L/mol.
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