Monomer activity measurement examined

An examination of reported reactivity ratios (Table 6) shows that the behaviour rj > 1, r2 1 or vice versa is a common feature of anionic copolymerization. Only in copolymerizations involving the monomers 1,1-diphenylethylene and stilbene, which cannot homopolymerize, do we find <1, r2 <1 [212—215], and hence the alternating tendency so characteristic of many free radical initiated copolymerizations. Normally one monomer is much more reactive to either type of active centre in the order acrylonitrile > methylmethacrylate > styrene > butadiene > isoprene. This is the order of electron affinities of the monomers as measured polarographically in polar solvents [216, 217]. In other words, the reactivity correlates well with the overall thermodynamic stability of the product. Variations of reactivity ratio occur with different solvents and counter-ions but the gross order is predictable. 

The tendency toward alternation is not the only pattern in terms of which copolymerization can be discussed. The activities of radicals and monomers may also be examined as a source of insight into copolymer formation. The reactivity of radical 1 copolymerizing with monomer 2 is measured by the rate constant kj2. The absolute value of this constant can be determined from copolymerization data (rj) and studies yielding absolute homopolymerization constants (ku) ... 

McGarrity and Ogle examined the aggregation of BuLi in THF by using H and Li NMR spectroscopy and determined that BuLi exists as a tetramer in equilibrium with a dimer in THF. Activation and equilibrinm parameters were measured for the tetramer-dimer equilibrium (equation 2). No evidence was obtained for a monomer at concentrations of BuLi down to 0.1 mM. ... 

Tewari and Srivastava published the results on interaction between atactic polyCvinyl acetate) and poly(acrylonitrile), and poly(methyl methacrylate) and poly(methacrylic acid). On the basis of viscometric measurements of DMF solutions of mixtures of the pair of polymers mentioned above, the authors concluded that for all the systems examined complex formation occurs. This observation explains the results published earlier by the authors about template polymerization of acrylonitrile, methacrylic acid, and methyl methacrylate carried out in the presence of poly(vinyl acetate). It was found that polymerization of acrylonitrile in DMF in the presence of atactic poly(vinyl acetate) (mol. weight 47,900) takes place much faster than without poly(vinyl acetate), especially, when concentration of the monomer is equimolar to the concentration of template repeat units. The overall energy of activation was found to be 55.76 kJ/mol for template polymerization and 77.01 kJ/mol for polymerization in the absence of the template. 

A study of benzocyclobutene polymerization kinetics and thermodynamics by differential scanning calorimetry (DSC) methods has also been reported in the literature [1]. This study examined a series of benzocyclobutene monomers containing one or two benzocyclobutene groups per molecule, both with and without reactive unsaturation. The study provided a measurement of the thermodynamics of the reaction between two benzocyclobutene groups and compared it with the thermodynamics of the reaction of a benzocyclobutene with a reactive double bond (Diels-Alder reaction). Differential scanning calorimetry was chosen for this work since it allowed for the study of the reaction mixture throughout its entire polymerization and not just prior to or after its gel point. The monomers used in this study are shown in Table 3. The polymerization exotherms were analyzed by the method of Borchardt and Daniels to obtain the reaction order n, the Arrhenius activation energy Ea and the pre-exponential factor log Z. Tables 4 and 5 show the results of these measurements and related calculations. 

Glusker (37, 38) attempted to prove that these processes are absent by an estimation of active chains by reaction with C14 labelled C02 or H8(T) labelled acetic acid, followed by measurements of the radioactivity of the polymer isolated. Most of the experiments were carried out with fluorenyllithium as initiator in toluene containing 10% diethyl-ether at —60°. At —78° at least 80% of the polymer chains were found to be active at the end of polymerization. The lowest fraction was appreciably less active. Similar results were obtained at —60° although no examination was made of the fractions of lowest molecular weight. Kinetic experiments indicated a first order decay of monomer concentration after an initial rapid consumption of about 3 molecules of monomer per initiator molecule. The mechanism suggested to explain these results involves rapid addition of fluorenyllithium across the vinyl double bond followed by the rapid addition of three monomer units. At this stage it is... 

These basic concepts and techniques were further extended in the fifties and sixties by Russell and coworkers [8] to structure reactivity relationships for aromatic compounds, by Mayo et al. [9] to copolymerization of oxygen with many vinyl monomers, and by Ingold and Howard to extensive measurements of absolute rate coefficients for peroxy and alkoxy radicals [10]. During this same period, an active group in the Soviet Union including Emanuel et al. [11] examined many complex oxidation systems. 

The primary structure of rat lysozyme has been determined and compared with those of human and other mammalian lysozymes. Lysozyme activity has been detected in the gastric mucosa of a prosimian mammal Perodicticus potto) The dependence on pH of the binding of 2-acetamido-2-deoxy-D-glucopyranose and methyl 2-acetamido-2-deoxy-a- and -P-D-glucopyranosides to turkey and hen egg-white lysozymes has been examined with the aid of c.d. measurements. The similarity of the pH-dependence curves suggested that aspartic acid-48, as well as aspartic acid-66 and -52 and glutamic acid-35, is perturbed on binding a monomer. 

---