Mechanism of “Autoacceleration” in the Thermal Oxidative Polymerization of α-Methylstyrene

Abstract

Thermal oxidative polymerization of R-methylstyrene (AMS) has been studied at various temperatures (45-70 °C) and pressures (50-400 psi). Due to its high electron dense double bond, it undergoes thermal oxidative polymerization even at low temperatures fairly easily. The major products are poly(R-methylstyrene peroxide) (PMSP), and its decomposition products are acetophenone and formaldehyde. Above 45 °C the rate of polymerization increases sharply at a particular instant showing an "autoacceleration" with the formation of a knee point. The "autoacceleration" is supported from the fact that the plot of Rp vs T shows a rapid rise, and the plot of ln Rp vs 1/T is non-Arrhenius. The occurrence of autoacceleration is explained on the basis of acetophenone-induced cleavage of PMSP during polymerization, generating more initiating alkoxy radicals, which subsequently leads to the rapid rise in the rate of polymerization. The mechanism of autoacceleration is supported by the change in order, activation energy, and activation volume before and after the knee point.

High-Pressure Kinetics of Oxidative Copolymerization of Styrene with -Methylstyrene

“…The saturation pressure of oxygen for styrene (STY) and α ‐methylstyrene (AMS) was found to be 2 and 300 psi, respectively 11. During the oxidative polymerization, STY shows auto‐deceleration with a break point, whereas AMS12 exhibits auto‐acceleration with the formation of a knee point 11. There are no reports on the effect of temperature and oxygen pressure on the oxidative copolymerizations, although some studies on the sequence analysis,10 kinetics and mechanism of their formation have been reported 1.…”

Degradable Polymers Prepared from Alkyl Sorbates and Oxygen under Atmospheric Conditions and Precise Evaluation of Their Thermal Properties

“…For example, a peroxide polymer is formed in a high yield during the oxidative polymerization of styrene, but the simultaneous formation of benzaldehyde and formaldehyde is unavoidable and influences the polymerization kinetics and the reaction mechanism including a radical chain transfer. 8,12,27,28 The accurate evaluation of the thermal properties of peroxide polymers is often hin- dered by contamination with decomposition products despite a large number of studies on the synthesis and characterization of peroxide polymers.…”

Thermally Induced Aerobic Autopolymerization of Methyl Methacrylate in Amide-Type Solvents: Simultaneous Polymerization during Induction via Direct In Situ O2 Activation

“…Interpolymerization of vinylic monomers with O 2 appears to be quite ubiquitous, as no compound containing the vinyl or vinylidene group has been found which does not readily form a peroxide upon exposure to air under ordinary conditions, which have all been found to initiate polymerization . Kishore et al reported the preparation of oligo(peroxide)s with O 2 of typical vinylic monomers, including nonsubstituted, monosubsttituted, 1,1‐disubstituted (vinylidene), 1,2‐disubstituted vinylics, and conjugated dienes form oligo(peroxide)s under the induction of ultraviolet (UV) light, visible light, heat or radicals, or catalysis of Co II complexes, in bulk or organic solvents, while Matsumoto successfully attempted the radical alternating oxidative polymerization of conjugated dienes with O 2 , leading to degradable poly(peroxide)s …”

“…Interpolymerization of vinylic monomers with O 2 appears to be quite ubiquitous, as no compound containing the vinyl or vinylidene group has been found which does not readily form a peroxide upon exposure to air under ordinary conditions, which have all been found to initiate polymerization. [ 7,8,13,14 ] Kishore et al reported the preparation of oligo(peroxide)s with O 2 of typical vinylic monomers, including nonsubstituted, monosubsttituted, 1,1-disubstituted (vinylidene), 1,2-disubstituted vinylics, and conjugated dienes form oligo(peroxide)s under the induction of ultraviolet (UV) light, visible light, heat or radicals, or catalysis of Co II complexes, in bulk or organic solvents, [15][16][17][18][19][20][21][22][23][24][25][26][27] while Matsumoto successfully attempted the radical alternating oxidative polymerization of conjugated dienes with O 2 , leading to degradable poly(peroxide) s. [28][29][30][31][32][33] Although oligo(peroxide)s might be candidates to initiate further polymerization of common vinylics under thermal or UV induction, [34][35][36][37] autopolymerization directly initiated by in situ formed oligo(peroxide)s upon air exposure appears as yet rather diffi cult under ordinary conditions. Due to the low concentration of O 2 in most organic solvents or monomers (≈10 −4 mol L −1 at ambient temperature upon exposure to air atmosphere) [ 38 ] as well as a delicate equivalence between formation and decomposition of peroxides, the build-up concentration of oligo(peroxide)s falls into a very low regime.…”