Understanding the effect of chain entanglement on the glass transition of a hydrophilic polymer

Abstract

In this article, we report an interesting phenomenon of the glass transition temperature (T g ) deviation of a hydrophilic polymer. Polyacrylamide (PAL) samples with different extents of chain entanglement were prepared by spray drying and solution casting. We found that the glass transition temperature increases as the extent of chain entanglement decreases upon the sub-T g annealing. The water content in the PAL matrix is found with no direct correlation to T g . However, the observation of a faster diffusion process of water in the disentangled PAL matrix offers an evidence of a faster relaxation process of disentangled PAL molecules. The T g increase of the disentangled PAL samples is believed to be associated with the increased molecular interaction during the chain relaxation process upon the sub-T g annealing. A macroscopic evidence is the fact that the density of the hot-laminated samples increases as the extent of chain entanglement decreases. A thermodynamic analysis suggests that enthalpy more than entropy favors an elevated T g of a disentangled hydrophilic polymer upon the sub-T g annealing. We believe that this research provides new understanding of T g of the hydrophilic polymers, which are being extensively used in bio-related studies.

Molecularly Engineered Intrinsically Healable and Stretchable Conducting Polymers

“…When cast from the 30 vol % methanol/THF solvent mixture, the graft copolymers showed a T g of −3.9 °C that was significantly lower than the T g of those cast from THF (13.6 °C). The significant decrease in T g , which is an effect of the solvent mixture, suggests the increased entanglement 53 of grafted PAUs in the graft copolymer films.…”

The Entanglements of Macromolecules and Their Influence on the Properties of Polymers

“…A much smaller decrease of only 2–5 °C was reported by Bernazzani et al The change of glass transition temperature for PS depended not only on the concentration, but also on the kind of solvent used . The decrease of T g is interpreted in the literature as an enhanced degree of freedom of the bond rotation by a reduction of the entanglements, affecting the chain relaxation process . It can be cohesional entanglements, resulting from local nematic interactions between neighboring chain segments.…”

“…Sometimes an increase of T g is observed for the disentangled polymer instead of a decrease. A hydrophilic polyacrylamide (PAM) prepared by spray drying showed an elevated T g compared to its bulk state . The spray‐dried particles and the bulk PAM were formed in films and annealed at 180 °C (i.e., near, but below T g ) for 2–16 h .…”

“…A hydrophilic polyacrylamide (PAM) prepared by spray drying showed an elevated T g compared to its bulk state . The spray‐dried particles and the bulk PAM were formed in films and annealed at 180 °C (i.e., near, but below T g ) for 2–16 h . The authors found that T g (≈194 °C) increased as the extent of the chain entanglement decreased.…”

Chain entanglement and molecular dynamics of solution-cast PMMA/SMA blend films affected by hydrogen bonding between casting solvents and polymer chains

“…Lu et al found that a hydrophilic polymer polyacrylamide (PAL) presented an increased T g with decreasing chain entanglement and they attributed it to the strong molecular interaction formed between an amino group and a carbonyl group in PAL. 56 However, the PMMA/SMA system differs from the PAL one. It is a hydrophobic one and there is no intermolecular interaction between PMMA and SMA molecular, because the hydrogen bonding only occurs between the polymer and the casting solvents during sample preparation.…”