Activation energy ring-opening polymerization

Kinetic measurements of the ring-opening polymerization of trimethylene carbonate (TMC) versus the enchainment of oxetane and CO2 to provide poly (TMC) reveal that these processes in the presence of (salen)CrCl and an ammonium salt have similar free energies of activation (AG ) at 110°C. This similarity in reactivity coupled with the observation that in situ infrared studies of the copolymerization of oxetane and CO2 showed the presence of TMC during the early stages of the reaction has led to the overall mechanism for copolymer production shown in... 

The kinetics of anionic ring opening polymerization of caprolactam initiated by iso-phthaloyl-bis-caprolactam and catalyzed by caprolactam-magnesium-bromide satisfactorily fit Malkin s autocatalytic model below 50 percent conversion. The calculated value of the overall apparent activation energy for this system is 30.2kJ/mol versus about 70kJ/mol for Na/hexamethylene-l,6,-bis-carbamidocaprolactam as the initiator/catalyst system. 

It was found that the ring-opening polymerization of D4 by KOH proceeds according to first order kinetics, with a square root dependence on the catalyst concentration. The square root dependence on the catalyst concentration Is believed to be due to the existence of an equilibrium between an active Ion pair and a an Inactive associated form (-S10M)2 Rate constants were determined at different catalyst levels and temperatures. An activation energy of about 18 kcal/mole was determined by an Arrhenius plot, in agreement with other workers In the field ( ). 

Polymerization efficiencies for the initiator systems hexamethylene di-isocyanate and 7V-acetyl caprolactam have been evaluated and the di-isocyanate found to be the more active. Studies on -caprolactam in closed systems have been made and the main polymerization processes for the system, caprolactam, water, and a viscosity stabilizer (acetic acid or butylamine), were evaluated. These are ring-opening polymerizations by hydrolysis, polycondensation of amine and carboxyl ends, and polyaddition of caprolactam to amino end-groups. Apparent activation energies were determined for these main reactions and it was suggested that addition occurred in preference to polycondensation. Post-polymerization of E-caprolactam under reduced pressure in the presence of water vapour and phosphoric acid has been kinetically analysed and the rate of increase of the degree of polymerization was derived theoretically as a function of reaction variables. 

The nature and concentration of the initiator play a cmcial role in the nonactivated anionic polymerization, where the growing centers are formed in the slow reaction [46] between the monomer and the lactam anion bringing about the presence of some induction periods. On the other hand, the evaluation of the specific action of a given initiator in the activated lactam polymerization is more complex, since it cannot be taken in consideration apart from the activator used. It is necessary to consider here the dual system initiator/activator. It seems that the activation energy for the anionic ring-opening polymerization of CL is almost independent of the activator used, " whilst it is probably a fimction of the initiator nature. 

Nucleophilic bimolecular ring-opening of ethylene oxide by the hydride anion has been investigated theoretically. Molecular orbital calculations of the interaction energy (a combination of coulomb, exchange, delocalization, and polarization interaction terms) were carried out. The kinetics and stereochemistry of base-catalysed polymerization of epoxides have been studied using optically active epoxide monomers. 

Block copolymer systems have aroused interest with reviews of the synthesis of nylon elastomers, thermoplastic polyether-polyamide elastomers, and thermoplastic cross-linked polyamides of 3,3 -bis(hydroxymelhyl) glutaric add. Block copolymers were also reported from poly(/n-phenylene isophthalamidc) and poly(ethylene oxide) or poly(dimethylsiloxane). The polycondensation of oco -dicarboxylic-poly(amide 11) and x -dihydroxy-polyoxyethylene has also been studied and rate constants and activation energies evaluated for the process. The polycondensation of axo -diacid and e9o> -diester-poly(amide 11) oligomers with cuco -dihydroxy-polyether oligomers has similarly been reported. Lactam Rli -opening Polymerization Routes.—The effects of ring size, substitution and the presence of heteroatoms on the polymerizability of lactams has been the subject of reviews. - In the field of lactam polymerization, two systems have evoked major interest, namely caprolactam and 2-pyrrolidone. Studies on caprolactam have reported the effect of water on the mechanism of polymerization and polymerization rate, where it was found that the process was... 

Ring opening of 2-ethylsilirane formed from addition of H2Si to 1-butene led to the formation of n-butyl- and sec-butylsUylene . It was deduced that sec-butylsUylene undergoes ring closure to 2,3-dimethylsilirane by intramolecular H—C insertion with an activation energy of 11.6 2.6 kcalmol . From this work a silylene-mediated polymerization of olefins can be envisioned (equation 82). 

In a fashion similar to ring-opening reactions of epoxides [44], 1,2-siloxacycloalkanes are polymerized in the presence of Lewis acids or bases [Eq. (18)] [45]. Zero-order kinetics and an activation energy of about 12kcal/mole are typical for the 1,2-siloxacycloalkane polymerization. 

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