New reaction for the preparation of liquid rubber

Abstract

The article reports on the noncatalytic transformation of a polybutadiene (number‐average molecular weight = 128,000) into a functionalized liquid rubber via the carboxidation of the polymer CC bonds by nitrous oxide. The reaction was conducted in a benzene solution at 160–230 °C and a pressure of 3–6 MPa. The carboxidation mechanism was determined. The main route (95%) of the reaction proceeded without cleavage of CC bonds and led to the formation of ketone groups in the polymer backbone. A minor route (5%) of the reaction proceeded with the cleavage of CC bonds, yielding two smaller fragments containing aldehyde and vinyl end groups. The availability of the cleavage route could lead to a dramatic decrease in the molecular weight, which, depending on the carboxidation degree, could be 1–2 orders of magnitude less than that of the initial material. Thus, the carboxidation of more than 15% of the polybutadiene CC bonds transformed it into a CO‐functionalized liquid rubber with a narrow molecular weight distribution. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2510–2520, 2006

Synthesis of functionalized liquid rubbers from polyisoprene

“…The rubbers were carboxidized with nitrous oxide in a high‐pressure Parr reactor of 100 cm 3 capacity equipped with a manometer and stirrer. The setup used in these experiments was described in detail earlier 17. After loading 5 g rubber and 60 cm 3 benzene, air was evacuated from the reactor for 1 min with a vacuum pump.…”

“…After termination of the reaction, the reactor was cooled to room temperature, and the gas phase composition (N 2 O, N 2 , O 2 , CO, CO 2 , low hydrocarbons) was analyzed using the GC method 17. In all cases, molecular nitrogen was a sole reaction product detected in the gas phase, and CO x concentration did not exceed 0.01 mol %.…”

“…This makes it possible to apply the carboxidation for functionalizing such unsaturated polymers by converting some CC bonds into carbonyl groups. Earlier, this approach has been demonstrated with a low‐molecular polyethylene containing terminal CC bonds,23 and cis ‐1,4‐polybutadiene (poly‐BD) rubber having a high concentration of internal double bonds 17. In the latter case, especially interesting results were obtained.…”

“…A remarkable feature of N 2 O is its ability to react solely with the alkene CC bonds, being inert toward all other bonds 15. Since the carbonyl groups are formed by an oxidation process, this reaction type was called the “carboxidation.”12, 16, 17 The carboxidation proceeds by a nonradical mechanism via the 1,3‐dipolar cycloaddition of N 2 O to the alkene double bond with intermediate formation of 1,2,3‐oxadiazoline cycle (reaction 1)13, 14, 18: where R 1 and R 2 are the alkyl radicals or hydrogen atoms. This mechanism was convincingly supported by the quantum‐chemical modeling of the N 2 O interaction with some alkenes 19–21.…”

Ketonization of 1,5‐Cyclooctadiene by Nitrous Oxide

“…In particular, ketonization of polydiene rubbers makes it possible to obtain a new type of material, that is, unsaturated liquid polyketones. [10] Recently, the opportunities of N 2 O chemistry have been explored in relation to unsaturated renewable resources like fatty esters and triacylglycerols. [11] The corresponding keto products were obtained with a selectivity 95-99%, the volume-time yield being one order of magnitude higher than that provided by the conventional Wacker process.…”