Direct and indirect effects of POSS on the molecular mobility of polyurethanes with varying segment M

The influence of POSS nanoparticles on selected thermal properties of polyurethane-based hybrids

“…In our investigation, we have observed that POSS bonded to the chain as pendent groups, using urethane linkages [79] did not impose any significant change in the temperature of the transition, but its enthalpy was moderately suppressed, indicating that the quality of the hard domains did not change, i.e., the POSS likely did not penetrate the hard domains. However, urea bonds were used for the covalent attachment, the hydrogen bonding increased and led to hard domains with higher dissolution temperature.…”

“…In our work, we have observed that POSS pendent on a PTMG-based polyurethane affect crystallinity in a way very much dependent on the nature of the chemical bond used for their incorporation on the chain [79]. The PU chain in this case contained a PTMEG chain of M w * 2000, which in bulk form crystalized 25 K below the melting temperature of the bulk PTMEG.…”

“…In addition, the role of the chemistry of the bonding was demonstrated in [79]. In this work, POSS were bonded with urea bonds as opposed to urethane.…”

“…In this series of investigations, the POSS substituents have been incorporated covalently in three distinctively different chain architectures. Namely, they have been bonded as (1) pendent groups on the hard domains, using the POSS substituents with one bifunctional ligand [34,79] (2,3-Propanediol)propoxy-heptaisobutyl POSS), (2) as part of the main chain, forming a bead-like copolymer, using an open cage with OH groups attached to the two ''disconnected'' Si atoms [35] (disilanol octaisobutyl POSS), and (3) as crosslinks, forming a polyurethane network, using an octafunctional moiety [45] (octa(3-hydroxy-3-methylbutyldimethylsiloxy) POSS). Note that all inert vertex groups in these cases are isobutyl, which in principle drives to strong crystallization.…”

“…5) by a few degrees. A comparative study of the specific heat increase at T g as well as dielectric and morphological properties [79] showed that both direct and indirect effects drove this slowing of dynamics. For polyurethane with shorter segments (PU1000), POSS increased miscibility of the hard domains in the soft phase, while at larger segment lengths, POSS crystallites, suppressed the chains which were anchored on them and even formed a rigid amorphous fraction.…”