Synthesis and ring-opening (co)polymerization of lactones derived from the cotelomerization of isoprene, butadiene, and CO ₂

Herein, we report ring-opening polymerizations and copolymerizations of substituted δ-lactones derived from isoprene, butadiene, and CO₂. While the telomerization of CO₂ with butadiene to form a disubstituted δ-lactone is well-established, the similar telomerization of isoprene with CO₂-or cotelomerization of isoprene and butadiene with CO₂-has been less studied. Our initial efforts focused on identifying the factors that govern yield and selectivity in the cotelomerization of isoprene, butadiene, and CO₂. The most effective cotelomerization/hydrogenation reaction sequence was scaled-up, leading to mixtures of two isoprene-butadiene coupled lactones, 3-ethyl-6-(prop-1-en-2-yl)tetrahydro-2<i>H</i>-pyran-2-one (EtPeP), and 3-ethyl-6-methyl-6-vinyltetrahydro-2<i>H</i>-pyran-2-one (EtVMeP) and the butadiene homocoupled lactone, 3-ethyl-6-vinyltetrahydro-2<i>H</i>-pyran-2-one (EtVP). The ratios of these three lactones varied depending on the telomerization conditions and purification methods employed. Stepwise syntheses of pure EtVMeP and EtPeP<i>via</i> alternate routes were also carried out. The pure lactones as well as lactone mixtures were subjected to organocatalyzed ring-opening (co)polymerization (ROP) using triazabicyclodecene (TBD), yielding CO₂-based copolymers with molar masses (<i>M</i>_n) ranging from 5.5 to 12.7 kDa and narrow dispersities (<i>Đ</i> = 1.3). Increasing the proportion of EtPeP relative to EtVP led to a notable increase in the glass transition temperature (<i>T</i>_g) of the copolymers, reaching -20.5 °C. While EtPeP underwent successful ring-opening polymerization, reactions with EtVMeP resulted in termination of the polymerization owing to the formation of a non-nucleophilic tertiary alkoxide chain end. Thus, small amounts of EtVMeP can have a deleterious effect on copolymerizations of lactone mixtures derived from cotelomerization. These results motivate further development in the selective synthesis of EtPeP<i>via</i> cotelomerization of butadiene and isoprene with CO₂.