The Thermal Degradation of Poly-Tert.-Butyl Methacrylate

Grant, Douglas H (1959) The Thermal Degradation of Poly-Tert.-Butyl Methacrylate. PhD thesis, University of Glasgow.

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Thermal degradation reactions of vinyl polymers can be classified into chain scission and non chain scisson reactions. Previous work on poly-tert-butyl methacrylate had indicated that the only reaction to occur with this substance was of the latter type; a "classical" decomposition of the substituent ester groups into an acid, polymethacrylie, and an olefine, iso-butene. Further evidence had shown that this reaction displayed unexpected auto-catalytic features. The theme of the present investigation was a more complete study of the thermal degradation of poly-tert-butyl methacrylate with the aim of elucidating the mechanism of decomposition and accounting for this autocatalysis. Because some polymer degradation reactions often show a close analogy with polymer synthesis reactions, it was thought logical to make a full investigation using established technique into the mechanism and kinetics of the polymerisation of tert-butyl methacrylate. The results of these investigations show clearly that tert-butyl methacrylate polymerises by a radical mechanism whose general features resemble closely those of other methacrylate esters which have been investigated. The measured values of the kinetic rate constants for the primary processes contribute to the body of information which is being accumulated about the effects of structure on reactivity of monomers. In the course of this work it was possible to confirm that one of the decomposition products of the polymerisation initiator alphaalpha' azo-di-isobutyronitrile is methacrylonitrile, by the isolation and identification of polymethacrylonitrile. The thermal degradation of poly-tert-butyl methacrylate was elucidated by kinetic measurements in high vacuum supplemented by investigations into the products of the reaction mainly by infra-red and gas chromatographic techniques. These sensitive methods revealed that the degradation process is considerably more complex than had been reported previously. It is possible to distinguish at least four constituent reactions. 1. Depolymerisation. It has been shown that poly-tert-butyl methacrylate undergoes a chain scission reaction with production of monomer. In the initial stages this reaction resembles the depolymerisation of polymethylmethacrylate, but it is retarded by the accompanying ester decomposition reaction. In the course of this investigation it has been demonstrated that a copolymer of methyl methacrylate and methacrylic acid is more stable towards depolymerisation than is polymethyl methacrylate. 2. Olefine production. It has been confirmed that iso-butene production is auto-catalysed. Evidence has been obtained that this decomposi tion has a non-radical chain mechanism showing a close resemblance to the acid catalysed hydrolyses of esters which are encountered in reactions in polar solutions. 3. Anhydride formation. It has been found that polymethacrylic acid is unstable at temperatures above 150

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Polymer chemistry
Date of Award: 1959
Depositing User: Enlighten Team
Unique ID: glathesis:1959-79390
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 05 Mar 2020 10:28
Last Modified: 05 Mar 2020 10:28

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