Chain copolymerization temperature effect

Counterion effects similar to those in ionic chain copolymerizations of alkenes (Secs. 6-4a-2, 6-4b-2) are present. Thus, copolymerizations of cyclopentene and norbomene with rhenium- and ruthenium-based initiators yield copolymers very rich in norbomene, while a more reactive (less discriminating) tungsten-based initiator yields a copolymer with comparable amounts of the two comonomers [Ivin, 1987]. Monomer reactivity ratios are also sensitive to solvent and temperature. Polymer conformational effects on reactivity have been observed in NCA copolymerizations where the particular polymer chain conformation, which is usually solvent-dependent, results in different interactions with each monomer [Imanishi, 1984]. 

Entropy, enthalpy, and free energy of reversible polymerization Arrhenius relationship for rate constants Subcritical damped oscillations during thermal polymerization Polyrate of terpolymerization of AMS-AN-Sty Enthalpy of random copolymers Effect of chain sequence distribution Entropy and free energy of copolymerization Copolymer composition with and without ceiling temperature effect... 

Absent from Table 10 are the comonomers carbon monoxide, carbon dioxide, and sulfur dioxide. These comonomers are not included because their copol mieiization does not obey the normal copolymer model illustrated by reactions (vix—xvii) and hence cannot be described by kinetic parameters which take into account only these reactions. For example. Furrow (/28) has i own that caibon dioxide will react with growing polyethylene chains in a free-radical reaction, but that it terminates the chains giving carboxylic acids. It does not copolymerize in the usual sense (which would give polyesters). Carbon monoxide and sulfur dioxide appear not to obey the normal cppol3nner curve of feed composition versus polymer composition and it has been reported that these materials form a complex with ethylene whidi is more reactive than free CO or SOg, perhaps a 1 1 complex. Copolymerization of both CO and SO is further complicated by a ceiling temperature effect. Cppolymerization has been carried out with ethylene and these monomers, however, and poly-ketones and pol3Tsufones are the resultant products. 

Copolymerization of NIPAAM with NTBAAM proved to be an effective method for producing material with an LCST that was lowered in direct and apparently linear proportions to the amount of NTBAAM added (Figure 5). The poor water solubility of NTBAAM was apparently not a problem. Likewise NNBAAM demonstrated a similar dependence of LCST on co-monomer input ratio up to a point. Copolymers containing 40% or more NNBAAM, however, would not redissolve in PBS at any of several temperatures including -2 and -4 C. Thus it was not possible to produce copolymers of NIPAAM and NNBAAM that precipitate between 0 and 17 C. Beyond a critical number of n-butyl side chains per polymer molecule water solubility virtually disappears. 

The solution thus consists of different particles denoted as contact ion pairs, solvent-separated ion pairs and free ions. The fraction of the individual particles depends on the type of salt, type of solvent, polymerization system, temperature, and salt concentration. The catalytic effect of these particles may be very different as is evident in anionic polymerization of vinyl monomers. For instance, free polystyryl anion is 800times more reactive than its ion pair with the sodium counterion 60 . From this fact it follows that, although the portion of free ions is small in the reaction system, they may play an important role. On the other hand, anionic polymerization and copolymerization of heterocycles proceeds mostly via ion pairs. This is due to a strong localization of the negative charge on the chain-end heteroatom which strongly stabilizes the ion pair itself62. Ionic dissociation constants and ion contributions to the reaction kinetics are usually low. This means that for heterocycles the difference between the catalytic effect of ion pairs and free ions is much weaker than for the polymerization of unsaturated compounds. This is well documented by the copolymerization of anhydrides with epoxides where the substi-... 

After investigating the effect of comonomer composition on the chain association as well as the effect of comonomer distribution on the chain folding, Siu et al. [141] extended their study to the effect of comonomer distribution on the chain association. They copolymerized NIPAM and vinyl pyrroli-done (VP) at temperatures, respectively, higher and lower than the LCST, which resulted in segmented and random VP distributions on the PNIPAM chain backbone. The synthesis characterization of these PNIPAM-co-VP amphiphilic copolymers with a similar chain length and comonomer composition, but different comonomer distributions, were described in previous sections. 

Catalysts of the Ziegler type have been used widely in the anionic polymerization of 1-olefins, diolefins, and a few polar monomers which can proceed by an anionic mechanism. Polar monomers normally deactivate the system and cannot be copolymerized with olefins. However, it has been found that the living chains from an anionic polymerization can be converted to free radicals in the presence of peroxides to form block polymers with vinyl and acrylic monomers. Vinylpyridines, acrylic esters, acrylonitrile, and styrene are converted to block polymers in good yield. Binary and ternary mixtures of 4-vinylpyridine, acrylonitrile, and styrene, are particularly effective. Peroxides are effective at temperatures well below those normally required for free radical polymerizations. A tentative mechanism for the reaction is given. 

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