Renewable Terpene Derivative as a Biosourced Elastomeric Building Block in the Design of Functional Acrylic Copolymers.

In order to move away from traditional petrochemical-based polymer materials, it is imperative that new monomer systems be sought out based on renewable resources. In this work, the synthesis of a functional terpene-containing acrylate monomer (tetrahydrogeraniol acrylate, THGA) is reported. This monomer was polymerized in toluene and bulk via free-radical polymerizations, achieving high conversion and molecular weights up to 278 kg·mol-1. The synthesized poly(THGA) shows a relatively low Tg (-46 °C), making it useful as a replacement for low Tg acrylic monomers, such as the widely used n-butyl acrylate. RAFT polymerization in toluene ([M]0 = 3.6 mol·L-1) allowed for the well-controlled polymerization of THGA with degrees of polymerization (DP n) from 25 to 500, achieving narrow molecular weight distributions ( D̵ ≈ 1.2) even up to high conversions. At lower monomer concentrations ([M]0 = 1.8 mol·L-1), some evidence of intramolecular chain transfer to polymer was seen by the detection of branching (arising from propagation of midchain radicals) and terminal double bonds (arising from β-scission of midchain radicals). Poly(THGA) was subsequently utilized for the synthesis of poly(THGA)- b-poly(styrene)- b-poly(THGA) and poly(styrene)- b-poly(THGA)- b-poly(styrene) triblock copolymers, demonstrating its potential as a component of thermoplastic elastomers. The phase separation and mechanical properties of the resulting triblock copolymer were studied by atomic force microscopy and rheology.