Molecular shape conversion of POSS-(PLLA)x with various arm lengths and its effect on the compatibility of PLLA/POSS-(PLLA)x as a nanofiller blended into PLLA matrix: From spiky ball to panel-like

Abstract

As a nanofiller, the well-defined star POSS-(PLLA)x formed by introducing poly(l-lactide) arms onto an octa(3-hydroxypropyl) polyhedral oligomeric silsesquioxane (POSS) nanocage core was blended into the poly(l-lactide) (PLLA) matrix. Molecular models of the star POSS-(PLLA)x and PLLA hybrids were constructed to investigate the geometrical characteristics of nanofiller and its effect on the compatibility of hybrids by using molecular mechanics (MM) and molecular dynamics (MD). Geometric descriptors and dipole moments demonstrated that the molecular geometry of POSS-(PLLA)x nanofiller converted from a spiky ball to a panel-like shape as the number of l-lactide (LA) units in the arms attached to the POSS core increased from 9 to 12. The highest crystallinity was achieved in blends of PLLA with POSS-(PLLA)12 forming panel-like shape since the longest arms in POSS-(PLLA)12 tended to be parallel, leading to an improved compatibility in hybrid. When blended with the spiky ball-like shape of POSS-(PLLA)9, PLLA hybrid obtained the lowest crystallinity with an apparent plasticization in matrix, due to the steric barrier in adjacent chains resulting from mutually exclusive arms in POSS-(PLLA)9. Moreover, consistent with the experimental results, analysis of the mean square displacement (MSD) and radial distribution function (RDF) confirmed that POSS-(PLLA)x nanofiller acted as a nucleating core for crystallization due to its limited mobility compared to the PLLA chain.