Nucleation Effect of Allyl Sorbitol Nucleating Agents on Isotactic Polypropylene

Isotactic polypropylene (iPP) suffers from slow crystallization rate, inadequate rigidity, and poor optical properties. Adding nucleating agents offers a promising solution; therefore, developing new nucleating agents is significant. In this study, four novel allyl sorbitol nucleating agents 1,3:2,4-bis-O-(benzylidene)-1-allyl-sorbitol (NA-B), 1,3:2,4-bis-O-(4-methylbenzylidene)-1-allyl-sorbitol (NA-BMe), 1,3:2,4-bis-O-(3,4-dimethyldibenzylidene)-1-allyl-sorbitol (NA-B2Me), and 1,3:2,4-bis-O-(4-chlorobenzylidene)-1-allyl-sorbitol (NA-BCl) were synthesized and characterized. Differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD) analyses of nucleated iPP showed that all four compounds were efficient α-nucleating agents, significantly reduced spherulite size, and accelerated crystallization. Mechanical tests exhibited that all nucleating agents enhanced the rigidity of iPP. Specifically, NA-B2Me improved the tensile strength by 16.8%, while NA-BMe enhanced the flexural modulus by 26.9%. These agents also effectively reduced haze, with NA-B2Me reducing by 65.4%. Isothermal crystallization kinetics analysis revealed a decrease in the Avrami exponent for nucleated iPP, supporting the transition toward heterogeneous nucleation induced by the nucleating agents. Molecular dynamics simulations revealed binding energies ranging from 50 to 55 kcal/mol between the nucleating agents and iPP, indicating adsorption interactions that facilitate epitaxial crystallization of iPP. This study presents four effective allyl sorbitol nucleating agents, providing molecular-level guidance for the design of nucleating agents at enhancing rigidity and reducing haze in iPP.