Chain-End Effects on Supramolecular Poly(ethylene glycol) Polymers

Abstract

In this work we present a fundamental analysis based on small-angle scattering, linear rheology and differential scanning calorimetry (DSC) experiments of the role of different hydrogen bonding (H-bonding) types on the structure and dynamics of chain-end modified poly(ethylene glycol) (PEG) in bulk. As such bifunctional PEG with a molar mass below the entanglement mass Me is symmetrically end-functionalized with three different hydrogen bonding (H-bonding) groups: thymine-1-acetic acid (thy), diamino-triazine (dat) and 2-ureido-4[1H]-pyrimidinone (upy). A linear block copolymer structure and a Newtonian-like dynamics is observed for PEG-thy/dat while results for PEG-upy structure and dynamics reveal a sphere and a network-like behavior, respectively. These observations are concomitant with an increase of the Flory–Huggins interaction parameter from PEG-thy/dat to PEG-upy that is used to quantify the difference between the H-bonding types. The upy association into spherical clusters is established by the Percus–Yevick approximation that models the inter-particle structure factor for PEG-upy. Moreover, the viscosity study reveals for PEG-upy a shear thickening behavior interpreted in terms of the free path model and related to the time for PEG-upy to dissociate from the upy clusters, seen as virtual crosslinks of the formed network. Moreover, a second relaxation time of different nature is also obtained from the complex shear modulus measurements of PEG-upy by the inverse of the angular frequency where G’ and G’’ crosses from the network-like to glass-like transition relaxation time, which is related to the segmental friction of PEG-upy polymeric network strands. In fact, not only do PEG-thy/dat and PEG-upy have different viscoelastic properties, but the relaxation times found for PEG-upy are much slower than the ones for PEG-thy/dat. However, the activation energy related to the association dynamics is very similar for both PEG-thy/dat and PEG-upy. Concerning the segmental dynamics, the glass transition temperature obtained from both rheological and calorimetric analysis is similar and increases for PEG-upy while for PEG-thy/dat is almost independent of association behavior. Our results show how supramolecular PEG properties vary by modifying the H-bonding association type and changing the molecular Flory–Huggins interaction parameter, which can be further explored for possible applications.

Printable Electrolytes: Tuning 3D‐Printing by Multiple Hydrogen Bonds and Added Inorganic Lithium‐Salts

“…We thus conducted DSC measurements of polymer-UPy samples and electrolyte mixtures with different lithium concentrations in a temperature range of -10 to 150 °C with a heating rate of 10 K•min -1 (Figure 3). In the case of pure PEG-1500-UPy 1 in Figure 3a, the melting peak at 5 and 102 °C is indicative for a phase separation between the EO-parts and the UPyend groups, also demonstrated previously with SAXS by Brás et al [21] These melting peaks shift for PEG-1500-UPy 2 and 3 closer together to 15 °C and 64 °C (2), as well as 50 °C (3). Samples with higher lithium concentrations, PEG-1500-UPy 5 (10:1) and PEG-1500-UPy 8 (5:1), suggested a purely amorphous material.…”

“…In the case of pure PEG‐1500‐UPy 1 in Figure 3a, the melting peak at 5 and 102 °C is indicative for a phase separation between the EO‐parts and the UPy‐end groups, also demonstrated previously with SAXS by Brás et al. [ 21 ] These melting peaks shift for PEG‐1500‐UPy 2 and 3 closer together to 15 °C and 64 °C (2), as well as 50 °C (3). Samples with higher lithium concentrations, PEG‐1500‐UPy 5 (10:1) and PEG‐1500‐UPy 8 (5:1), suggested a purely amorphous material.…”

Influence of Polymer Polarity and Association Strength on the Properties of Poly(alkyl ether)-Based Supramolecular Melts

“…Interestingly, this slowest process characteristic times are very close to the relaxation times of the PPO-UPY network τ d , determined using the shear rate at the maximum viscosity (Figure 4), which basically indicates the detachment relaxation time of the PPO chains from the network junctions, i.e., from the UPY clusters, 18,64,71 as shown in Figure 8c. However, looking to Figure 6c and Figure 7c, the dielectric strength, Δε, is on the order of 10 3 (see Table S8 in Section V of the Supporting Information), higher than the values found for typical dipolar relaxations but rather typical of electrode polarization or the Maxwell−Wagner−Sillars mechanism.…”

“…In the case of PPO-UPY, shear thickening is only observed at the two lowest temperatures, 283 and 293 K, on the contrary to PEO-UPY, where this effect is observed at the full measured temperature range. 18 Above T = 293 K, shear thinning is detected for PPO-UPY, where the viscosity decreases under shear strain.…”

“…In fact, a lower value and an overestimation of the plateau modulus are also found for PEO-UPY and for systems that also form cluster-like structures due to H-bonding interactions. 18,39,63,72 Even though H-bonding can create cross-links that built the network, it also introduces defects formed due to loops existence, lowering G N 0 . Indeed, the possibility of PPO chains to form loops within the same cluster instead of bridges to different clusters has to be considered and can explain the lower f e (see further in the text).…”