Breathing New Life into Living Anionic Polymerisation:
The Anionic Polymerisation and Selective Functionalisation of Myrcene-Containing Polymers

Abstract

The bio-available monomer myrcene is a highly interesting and increasingly researched chemical within the polymer chemistry community. However, many recent articles about the polymerisation of myrcene and its functionalisation have been published which have been factually incorrect. This has led to many misconceptions about what myrcene can be used for and has slowed the progression of further research. Within this report several erroneous studies reported in the literature have repeated in order to correct our understanding of the polymerisation of myrcene.
Along with reporting the homopolymerisation of myrcene, it’s copolymerisation with butadiene and styrene, and the effect that polar additives – such as N,N,N’,N’-tetramethylethylenediamine – have on the polymerisation kinetics, a system was devised to allow for the living anionic polymerisation of liquid monomers to be performed in a nuclear magnetic resonance tube (without the requirement of a glove box). This setup allows for the direct mapping of the incorporation of different monomers into a copolymer in real time. This approach was used for the accurate determination of the reactivity ratios of the copolymerisation of myrcene and styrene, in the presence of N,N,N’,N’-tetramethylethylenediamine, to be calculated in an attempt to show that this copolymerisation is not random despite previous claims of a couple of recently published articles.
A method for the selective functionalisation of butadiene-containing polymers has also been devised, whereby it has been shown that the same bio-available monomer, myrcene, can be incorporated into butadiene containing polymers and then be used as a selective site to functionalise the polymer. It was shown that the trisubstitued pendant double bond of myrcene, which is not involved in the polymerisation reaction, can be selectively epoxidised using m-CPBA, in preference to any other double bonds present within the copolymerisation with butadiene. This effect, which can be enhanced by the addition of TMEDA during the copolymerisation through the increase in vinyl microstructure content, culminated in the synthesis of a model randomised styrene-butadiene rubber with 5 molar % myrcene that was epoxidised and shown to still selectively epoxidise the myrcene units.
Finally, a new method of multi-chain end functionalisation was proposed using epoxidised myrcene, whereby it was shown that due to the relatively high tolerance of the myrcene epoxide towards nucleophilic attack, that the epoxidised myrcene could added at the end of anionic polymerisations to install 3-4 functionalised monomer units (compared to the standard 1 or 2 of traditional chain-end functionalisation methods). These epoxides can then be ring opened selectively using LiAlH4 to yield the corresponding hydroxylated polymer.