Controlled Radical Polymerization of Myrcene in Bulk: Mapping the Effect of Conditions on the System

Abstract

Solvent-free reversible deactivation radical polymerization of myrcene, a naturally occurring terpenoid monomer, with high regioselectivity was developed recently. Here, this green polymerization system is further improved to reach increased yields and produce polymers with high molar mass but still low dispersity and regioregular microstructure. To this end, two initiators (dibenzoyl peroxide, DBPO; azobis­(isobutyro­nitrile), AIBN) at 65, 90, and 130 °C were applied, and it was demonstrated that these varying conditions have a huge effect not only on the monomer conversion and the molar mass of the product, but also on the microstructure of the resulting polymyrcene. The polymerizations utilized two trithio­carbonate chain-transfer agents, and were similar in yields, molar masses, and dispersity of the produced polymyrcene, but progressed differently for the diverse initiator–temperature pairs. Generally, in all systems, pseudo-first-order kinetics, linear increase of molar mass with conversion, and low Đ values were found as a result of controlled polymerization. The systems using AIBN and DBPO initiators at 90 and 130 °C, respectively, have rate constants of propagation (k p app) lower than the decomposition rates (k d) of initiators, likewise important to control the polymerizations. At 130 °C, also branching occurred at the higher stage of the reaction, and lower regioregularity developed during the polymerization as a consequence of the favorable junction formation at elevated temperature and increased viscosity. Generally, compared to the previous study on the reversible deactivation radical polymerization of myrcene via reversible addition–fragmentation chain-transfer polymerization process, significantly higher conversions (30 → 65%) and increased chain length (9 → 40 kDa) were reached. The dispersity values for these polymerizations remained as low as 1.3–1.6, and also regioregular microstructures (up to 94%) were detected.

Strategies for the production of biochemicals in bioenergy crops

“…Due to the complexity of plant biomass, it is difficult to isolate pure macromolecules; however, biosynthesis and purification of bio-based monomers for functionalization and copolymerization are simpler and cheaper. Unlike ring-opening polymerization processes, terpenes can be polymerized using radical initiators [300].…”

Green Engineered Polymers: Solvent Free, Room‐Temperature Polymerization of Monomer From a Renewable Resource, Without Utilizing Initiator.

“…Myrcene is a common polymerizable monoterpene which was only recently polymerized by controlled radical polymerizations, such as reversible addition‐fragmentation chain transfer polymerization (RAFT), or nitroxide‐mediated radical polymerization (NMP) . The most significant advantage of these methods beyond their simplicity is that the produced polymers are not only controlled regarding molar mass or dispersity but also concerning regioselectivity, which was achieved previously only by non‐controlled polymerization using coordinative catalysts …”

“…The controlled polymerizations of Myrcene were carried out at high temperatures (up to 130 °C) mostly using azo‐ or peroxo‐initiators. Applying such high temperature does not fit into the rules of green chemistry, just like the application of several components with various reaction and dissociation rates . Also, these kinds of initiators are explosive ones, which conflicts with safety regulations besides green terms.…”

“…Applying such high temperature does not fit into the rules of green chemistry, just like the application of several components with various reaction and dissociation rates. [14] Also, these kinds of initiators are explosive ones, which conflicts with safety regulations besides green terms. Here in this paper, the controlled polymerization of myrcene is carried out using the RAFT technique, via the iniferter (initiatortransfer-terminator) [19] method, where the mediator also plays the role of the initiator.…”

Bio‐based β‐myrcene‐modified solution‐polymerized styrene–butadiene rubber for improving carbon black dispersion and wet skid resistance

“…Early work by David presented emulsion copolymerization of styrene/methyl methacrylate and myrcene initiated by 2,2‐azobisisobutyronitrile, wherein a higher molecular weight (20 000 Da) but a lower conversion rate (5–13%) was obtained. In the last 3 years, additional works initiated by free radicals have been investigated . However, those studies revealed that free radical polymerization did not produce ideal results as they encountered issues such as longer reaction time (>15 h), uncontrollable microstructure, and unsatisfactory conversion rate (only up to 80%) .…”