Synthesis and characterization of β-myrcene/styrene and β-ocimene/styrene copolymers

The objective of this work is to study the structure-property relationships of two new classes of sustainable materials, obtained using monomers derived from biomass. Hybrid styrene-based copolymers with terpene molecules such as β-myrcene and β-ocimene, were studied. The copolymers have a blocky microstructure. Myrcene and ocimene are olefinic monomers obtained from biomass. They are combined with styrene, an aromatic monomer, to produce copolymers with a wide range of adjustable properties, depending on the composition and conditions of polymerization. Samples with myrcene/styrene and ocimene/styrene ratios 30/70, 50/50, 70/30 and 80/20 mol/mol were synthesized using a titanium complex as catalyst activated with MAO. Polymerizations were carried out at 70 ºC in a nitrogen atmosphere. [1] For both series the glass transition temperature (Tg) increases as the styrene content increases. Differential scanning calorimetry thermograms show relaxation phenomena close Tg, attributed to the presence of long styrene sequences, as highlighted by annealing experiments at different temperatures. All samples are amorphous. They show X-ray powder diffraction profiles characterized by a double halo typical of polystyrene, and remain amorphous even after annealing treatments. Copolymers based on myrcene with styrene content greater than or equal to 30 mol% show a high rigidity and experience viscous flow upon stretching at 70°C. The sample with 20 mol% appears as a soft material, able to flow even at 40 °C. The samples based on ocimene shows the same characteristics. Exceptions occur for the samples with 70 and 80 mol% of ocimene, which show double Tg,, due to phase separation of styrene rich and styrene poor domains. From the SAXS analysis, recorded at different temperatures, the size ζ of heterogeneities at nanometric scale was estimated using the Debye-Bueche equation. The oscillations of the ζ parameter value are probably due to tendency of alike comonomers to form small aggregates, the size of which are subjected to changes depending on the comonomer content, the temperature, and the thermal history in general. The present study has enabled the identification of new classes of terpene-based hybrid systems, with potential applications for surface coating and with properties that can be adjusted according to composition.