Termination In Copolymerization Research Articles

An investigation on chain transfer to monomers and initiators, termination of radicals in EVA copolymerization process based on DFT and microkinetic simulation

Chain transfer and termination in copolymerization between ethylene and vinyl acetate (VAc) were investigated with DFT method. Chain transfer becomes more active in copolymerization than homopolymerization due to an incorporation between low propagation reactivity of alkyl radical and high chain transfer reactivity of VAc. Competition between combination and disproportionation were detailed for self-termination and cross-termination, and most radical chains terminate through combination. Combination involving alkyl radical or tail radical shows much lower energy barrier than combination involving head radical. Effect of head-to-head defect on termination and chain transfer is also clarified. Chain transfer to initiators and termination of primary radicals were studied for BPO and AIBN. The both, especially AIBN, shows reactivity in direct addition of radicals to initiators, which is revealed by this work at first time. Based on kinetics from DFT, a microkinetic simulation was conducted to extend the research from electron scale to micro scale. Relationship between copolymerization conditions (including temperature, monomer composition and concentration, and initiator concentration) and rates of elemental reactions, radical concentrations, DP and PDI was discussed.

New Degradable Alternating Copolymers from Naturally Occurring Aldehydes: Well-Controlled Cationic Copolymerization and Complete Degradation

Three naturally occurring conjugated aldehydes, (1R)-(−)-myrtenal, (S)-(−)-perillaldehyde, and β-cyclocitral, were cationically copolymerized with isobutyl vinyl ether using the EtSO3H/GaCl3 initiating system in the presence of 1,4-dioxane as an added Lewis base. Alternating copolymerization proceeded exclusively via 1,2-carbonyl addition of the aldehydes. In addition, controlled alternating copolymerization was achieved under appropriate reaction conditions, producing copolymers with controlled molecular weights and narrow molecular weight distributions. The relationships between the copolymerization behaviors and the cyclic side group structures of the aldehydes suggested that conjugated and bicyclic structures were important factors for controlled alternating copolymerization. However, too much bulkiness around the carbonyl group resulted in termination of copolymerization. The resulting alternating copolymers were stable under neutral and basic conditions. In sharp contrast, mild acidic conditions deg...

Living carbocationic copolymerizations. I. Synthesis and characterization of isobutylene/p‐methylstyrene copolymers

AbstractThe isobutylene (IB)–p‐methylstyrene (pMeSt) monomer pair readily produces by living copolymerization nearly random copolymers with up to M̄n ≈ 50,000 g mol−1 and M̄w/M̄n ≈ 1·4. The livingness of the copolymerization process and the compositional homogeneity of the copolymers have been demonstrated by the following four diagnostic plots: (A) M̄n (number‐average molecular weight) and corresponding N (number of moles of copolymer formed) vs Wp (weight of copolymer formed) for the diagnosis of chaintransfer; (B) −ln (1 – C) (C = conversion of monomers) vs time for the diagnosis of termination; (C) copolymer composition vs molecular weight; and (D) cumulative copolymer composition vs conversion for the diagnosis of true homogeneous copolymers. The theory for the use of the −ln(1 – C) vs time plot for the quantitation of irreversible termination in copolymerization has been developed. The exact conditions (i.e. nature of reagents, reagent concentrations, temperature, etc.) which lead to desirable products in terms of conversion, molecular weight, molecular weight distribution (MWD) and copolymer composition, were developed systematically by analyzing the results of a large number of experiments. The following combination of chemicals was found to lead to living copolymerization, and uniform high molecular weight, narrow MWD copolymers: IB–pMeSt 97 : 3 mol/mol with 5‐tert‐butyl‐1,3‐dicumyl methyl ether (5‐tBu‐1,3‐DiCumOMe) initiator, TiCl4 coinitiator, ethyl chloride (EtCl) solvent, triethylamine (TEA) electron pair donor (ED) and 2,6‐di‐tert‐butylpyridine (DtBP) proton trap at −52, −65 and −85°C.

Copolymerization with Depropagation. II. Rate of Copolymerization of Styrene α - Methylstyrene

Abstract Styrene and α-methylstyrene have been copolymerized at 60°C. At this temperature depropagation of the latter monomer must be considered. The rate of copolymerization and the chain length of the polymer formed are quantitatively interpreted by an extension of the theory previously used to describe the copolymer composition. It is postulated that rapid termination of copolymerization occurs because of the presence in the systems of low molecular weight free radicals of poly(α-methylstyrene) of chain length 3 cr less.