Aqueous Solutions of Poly[2‐(N‐morpholino)ethyl methacrylate]: Learning about Macromolecular Aggregation Processes from a Peculiar Three‐Step Thermoresponsive Behavior

Abstract

Aqueous solutions of narrowly distributed poly[2‐(N‐morpholino)ethyl methacrylate], a biocompatible multiple stimuli‐responsive polymer, show a peculiar three‐step aggregation behavior upon heating, an effect which has hitherto barely been reported for other polymers. The phenomenon is discussed in terms of mesoglobule formation (first step) as well as by an unusual distinct disruption of hydrophobic hydration (second step) and hydrogen bonding to the hydrophilic aggregate surface (third step). Macroscopic precipitation only takes place after the third step, a behavior which resembles the denaturation and limited aggregation of proteins. Furthermore, the influence of different anions along the Hofmeister series is investigated, identifying salting‐out (kosmotropic) and salting‐in (chaotropic) effects. As an experimental tool to monitor the thermally induced aggregate growth, dynamic light scattering is used. The reported findings might lead to a more detailed understanding of both aggregation behavior of (biological) macromolecules and mechanistic processes involved in thermoresponsivity and salt‐responsivity of water soluble polymers.

Solubility behaviour of random and gradient copolymers of di- and oligo(ethylene oxide) methacrylate in water: effect of various additives

“…In a conventional free radical polymerization, the chains can present a strong chain-to-chain deviation of composition, which results in different phase transitions. 1,37 The synthesis route of this research is an optimized work based on the research of Lutz et al 55 and Matyjaszewski et al 6 Lutz et al reported a well-controlled ATRP of OEOMAs in pure ethanol. The polarity of ethanol establishes fast polymerization kinetics, 55 but since OEOMA monomers have a slight polarity, their polymerization can also be successfully done in apolar solvents like anisole as reported by Matyjaszewski's group.…”

“…34,[72][73][74][75] Salts are well-known to have a high impact on the behavior of thermoresponsive polymers in solution. 37 Both the cation and anion in the salt are considered to influence the solubility behavior of the macromolecules. 71 To study the effect of different anions on the solubility behavior of gradient and random copolymers, sodium salts of these anions are used.…”

“…This characteristic makes such gradient copolymers a great potential in biomimetic applications. [21][22][23][24][25][26][27][28][29] Various studies are done on the effect of additives on the solubility behavior of thermoresponsive polymers [30][31][32][33][34][35][36][37][38][39] including POEOMAs, [40][41][42][43][44] but so far there is no comprehensive study to compare the effect of different additives on the phase transition of thermoresponsive copolymers with different structure.…”

“…Knowledge of the copolymer's responsivity towards different additives is essential for in vivo applications, as well as separation and membrane technology. 37,45 While adjusting the phase transition behavior of POEOMAs by changing the structure seems to be expensive, time consuming and complicated, an easier way to alter the dynamic thermal transition is by addition of small amounts of additives to the system.…”

Double thermoresponsive block–random copolymers with adjustable phase transition temperatures: From block‐like to gradient‐like behavior

“…Furthermore, the large variety and complexity of still regularly unpredictable stimuli‐related behavior makes fundamental research on the underlying mechanisms very important to date. Just to name a few, ongoing debates are held on cononsolvency phenomena, salting‐in and salting‐out effects, stimuli‐triggered aggregation mechanisms, and on the origins of upper and lower critical solution temperature‐type (UCST‐ and LCST‐type, respectively) behavior . Further remarkable research goes into the direction of time‐programmed stimuli‐responsive self‐assembly and superfast actuation …”