Thermoresponsive PNIPAAM bottlebrush polymers with tailored side-chain length and end-group structure

Abstract

We explore the phase behaviour, solution conformation, and interfacial properties of bottlebrush polymers with side-chains comprised of poly(N-isopropylacrylamide) (PNIPAAM), a thermally responsive polymer that exhibits a lower critical solution temperature (LCST) in water. PNIPAAM bottlebrush polymers with controlled side-chain length and side-chain end-group structure are prepared using a "grafting-through" technique. Due to reduced flexibility of bottlebrush polymer side-chains, side-chain end-groups have a disproportionate effect on bottlebrush polymer solubility and phase behaviour. Bottlebrush polymers with a hydrophobic end-group have poor water solubilities and depressed LCSTs, whereas bottlebrush polymers with thiol-terminated side-chains are fully water-soluble and exhibit an LCST greater than that of PNIPAAM homopolymers. The temperature-dependent solution conformation of PNIPAAM bottlebrush polymers in D2O is analyzed by small-angle neutron scattering (SANS), and data analysis using the Guinier-Porod model shows that the bottlebrush polymer radius decreases as the temperature increases towards the LCST for PNIPAAM bottlebrush polymers with relatively long 9 kg mol(-1) side-chains. Above the LCST, PNIPAAM bottlebrush polymers can form a lyotropic liquid crystal phase in water. Interfacial tension measurements show that bottlebrush polymers reduce the interfacial tension between chloroform and water to levels comparable to PNIPAAM homopolymers without the formation of microemulsions, suggesting that bottlebrush polymers are unable to stabilize highly curved interfaces. These results demonstrate that bottlebrush polymer side-chain length and flexibility impact phase behavior, solubility, and interfacial properties.

Atomistic Structure of Bottlebrush Polymers: Simulations and Neutron Scattering Studies

“…This implies that solubility and the side chain length play important roles in determining the conformation of bottlebrush polymers. 45 It is interesting to note that such nonmonotonic relation between the side chain length and the size of the bottlebrush polymer was also found from Figure 4 and 5 in ref 6, although the polymer is different. In CGMD with HSP potential, however, R g showed monotonic changes with increase side chain length.…”

Polymer‐coated nanoparticles for enhanced oil recovery

“…It should be noted that the reduction in interfacial tension by PNPs and star polymers is at most by one order of magnitude (from roughly 25 to 1 mN/m) . By comparison, surfactant additives can lead to much greater reductions in oil‐water interfacial tension, down to 0.001 mN/m 2 and below.…”

“…More recently, Saigal et al reported stable oil‐in‐water emulsions using silica nanoparticles coated with a pH responsive polymer, and they found that the most stable emulsions were formed at lower polymer chain grafting densities . Related studies on star polymers, bottlebrush polymers, and paramagnetic particles with adsorbed amphiphilic polymers found stable emulsions and reductions in the oil‐water interfacial tension at relatively low (0.1 wt %) particle contents . Alvarez et al evaluated the dynamic reduction in interfacial tension of air and water in the presence of PNPs while changing the grafting density of the polymer brushes and showed that the polymer coating is a key factor in reducing the interfacial tension of air and water using PNPs .…”

Cationic Bottlebrush Polymers from Quaternary Ammonium Macromonomers by Grafting‐Through Ring‐Opening Metathesis Polymerization

“…Due to steric effects, initiation and propagation can be challenging with less reactive polymerizable end‐groups such as methacrylates 31,32. As a result, ring‐opening metathesis polymerization (ROMP) of high strained cyclic olefins has successfully produced well‐defined bottlebrush polymers due to its wide functional group tolerance,33–37 fast polymerization rate, high MM conversion, high molecular weights (MW), and a narrow molecular weight distribution (MWD), typically, by using the fast initiating third‐generation Grubbs catalyst (G3) 38. Different polymerizable terminal norbornene or anchor groups of MMs influence the ROMP propagation rate due to steric and electronic effects 39–41.…”