Estimation of the rate constant of termination by the monomer in the anionic polymerization of methyl methacrylate

Abstract

S U M M A R Y :Based on the assumption that the termination reaction in the anionic polymerization of methyl methacrylate in T H F with cumyl cesium as initiator is exclusively caused by the monomer, the termination rate constant k,, + ) for the ion-pairs of polymethylmethacrylcesium is estimated by analyzing the molecular weight distribution (MWD) of polymer samples prepared at different temperatures under otherwise identical reaction conditions. The activation energy of the termination reaction of the ion-pairs is found to be about 11 kcal/mol (46 kJ/mol). -The relatively broad MWD of the non-deactivated chains (the so called internal nonuniformity) reveals the existence of ion-pairs with different reactivity. Z U S A M M E N F A S S U N G :Unter der Voraussetzung, daI3 der Abbruch bei der anionischen Polymerisation von Methylmethacrylat in Tetrahydrofuran mit Cumylcasium als Initiator ausschlieDlich durch das Monomere verursacht wird, wird die Abbruchsgeschwhdigkeitskonstante E,(+) fur die Ionenpaare des Polymethylmethacrylcasiums aus der Molekulargewichtsverteilung von Polymeren, die bei verschiedenen Temperaturen unter sonst gleichen Bedingungen hergestellt wurden, abgeschatzt. Die Abbruchreaktion hat eine Aktivlerungsenergie von etwa 11 kcal/mol (46 kJ/mol). -Die relativ groRe Breite der Verteilung der nicht desaktivierten Ketten (,,interne Uneinheitlichkeit") zeigt deutlich die Existenz von verschieden reaktiven Ionenpaararten.

Specific Salt Effect of Lithium Perchlorate in Living Anionic Polymerization of Methyl Methacrylate and tert-Butyl Acrylate

“…At higher temperatures the termination reaction predominates, as evidenced by the deviation from the first-order kinetics, broadening of the MWD, and the generation of alkali metal methoxide. 16 Recent kinetic studies indicate that polymerization of MMA proceeds from more than one kind of species. 17,18 The nature of solvent and the size of cation influences the course of MMA polymerization.…”

“…It was shown by Löhr and Schulz , and Mita et al that anionic polymerization of MMA proceeds with insignificant or with no termination in THF at −78 °C using cesium as a counterion, leading to narrow MWD PMMA. At higher temperatures the termination reaction predominates, as evidenced by the deviation from the first-order kinetics, broadening of the MWD, and the generation of alkali metal methoxide , The nature of solvent and the size of cation influences the course of MMA polymerization …”

The Organometallic Polymerization of (Meth)acrylates: An Overview

“…The propagating enolate endgroup of the ketone is not as reactive as the enolate anion of the (meth)acrylate, and also gives lowered and broadened molecular weight distributions since the overall polymerization rate is slowed. Schreiber (15) and Korotkov (27) and Lohr et al (28) have proposed similar termination steps involving 1,2-addition at either the monomer or backbone carbonyl groups by the enolate propagating species; however, no evidence has been found for the existence of these mechanisms. Extremely bulky methacrylates, such as tert-butyl methacrylate (*BMA), are the only monomers which have been thought to be immune to terminating side reactions (29)(30)(31).…”