Influence of Dangling Chains on Molecular Dynamics of Polyurethanes

Abstract

The effect of dangling chains on phaseseparated microstructure and molecular dynamics for polyurethanes (PUs) was investigated. PUs with different dangling chain lengths and polar groups were prepared through changing the types of diol extender. The molecular dynamics was studied by a combination of dynamic mechanical analysis (DMA) and broadband dielectric relaxation spectroscopy (BDRS). Four relaxations (processes), namely, a secondary relaxation (β), the soft phase segmental relaxation (α), the I process associated with hydrogen bond, and Maxwell− Wagner−Sillars (MWS) interfacial polarization process caused by charge accumulation at hard/soft phase interfaces, were detected. The I process occurred in temperatures lower than that of MWS process but higher than α relaxation in general. The β relaxation remains unaffected with changing dangling chain lengths or polar groups. However, the glass transition temperature (T g ) of the soft phase shifts to lower temperature, and the segmental motion becomes faster with increasing dangling chain length, while the introduction of a polar ester group into the dangling chains makes it slow down, corresponding to a higher T g , and results in a higher fragility. On the other hand, there is an absence of I process, and the MWS process shifts to higher frequencies when longer dangling chain is introduced. In the case of increasing the hard segment content, the I process reappears and the MWS process slows down. It is suggested that these results are related to the H-bond interactions within hard segments and the micromorphologies of PUs.

Inner relationship between the damping property and the sand‐fixing durability of polymer materials

“…As a rule, the damping properties of polymer materials are derived from internal friction caused by molecular chain movement and the destruction and regeneration of physical bonds between molecules . Therefore, the dangling chain can increase the internal friction between the molecular chain and improve the damping property of polymer by hindering the motion of main chain of polymer with dangling chain.…”

“…As a rule, the damping properties of polymer materials are derived from internal friction caused by molecular chain movement and the destruction and regeneration of physical bonds between molecules. 41,42 Therefore, the dangling chain can increase the internal friction between the molecular chain and improve the damping property of polymer by hindering the motion of main chain of polymer with dangling chain. Figure 7 gives the dynamic mechanical spectra of PVAc with various dangling chains in a temperature range −100-100 C. As we know, the damping temperature range corresponds to that temperature range when tan δ value is more than or equal to 0.3.…”

Synthesis and adhesion properties of waterborne polyurethane dispersions with long‐branched aliphatic chains

“…The T g of the soft segment was observed in each sample and decreased from −49.6 to −56.5°C with increasing TMPM content. This may have been due to the plasticizing effect of long side chains . The long‐branched aliphatic chains hindered the close aggregation of soft segments and facilitated the movement of the chain segments.…”

Effect of danling chain content on properties of 10-undecenoic acid-based polyurethane

“…There are a lot of researches about polyurethane containing the dangling chain have been reported [2][3][4][5] . Xu et al [6] fabricated segmented PUs with six-carbon dangling chain, they found that the presence of the six-carbon short dangling chain in each repeating unit of the soft segments does not limit the overall bulk properties.…”

“…Xu et al [6] fabricated segmented PUs with six-carbon dangling chain, they found that the presence of the six-carbon short dangling chain in each repeating unit of the soft segments does not limit the overall bulk properties. Yu et al [2] synthesized PUs with different dangling chain lengths and polar groups, their research results show that the Tg of the PU shifted to lower temperature with increasing dangling chain length. When the danling chain is introduced into the polymer, the arrangement regularity between molecules will be disturbed so as to reduce the intermolecular stacking.…”