Why delta-valerolactone polymerizes and gamma-butyrolactone does not

Area of Science:

• * Computational Chemistry
• * Polymer Science
• * Organic Chemistry

Background:

• * Cyclic lactones are monomers for polyester synthesis.
• * Gamma-butyrolactone (GBL) and delta-valerolactone (DVL) are common lactones with differing polymerizability.
• * GBL's inability to polymerize, despite significant ring strain, presents a scientific anomaly.

Purpose of the Study:

• * Investigate the reasons behind GBL's lack of polymerization compared to DVL.
• * Utilize quantum mechanical methods to analyze the thermochemistry and conformational preferences related to polymerizability.
• * Determine the factors influencing the ring-opening reactions and enthalpy variations in these cyclic lactones.

Main Methods:

• * Applied quantum mechanical calculations.
• * Studied thermochemistry of ring-opening reactions for GBL and DVL.
• * Analyzed conformational preferences of model molecules for poly-4-hydroxybutyrate and related polyesters.

Main Results:

• * GBL exhibits lower ring strain and less geometric distortion in its ester group compared to DVL.
• * Model compounds for poly-4-hydroxybutyrate show stable coiled conformations.
• * Enthalpy variations indicate differing polymerizability between GBL and DVL.

Conclusions:

• * GBL's lack of polymerizability is attributed to its low ring strain and the stability of its polyester's conformations.
• * Quantum mechanical insights clarify the distinct polymerization behaviors of GBL and DVL.
• * The findings provide a deeper understanding of factors governing cyclic lactone polymerization.