There are many polymers formed of acrylate monomers in existence. Here we interrogate four commonly-used examples and study how their solution properties are pH dependent, or how their state of ionisation can affect their solution properties. Poly(acrylic acid) and poly(methacrylic acid) are both polyelectrolytes, with ionisable functional groups that make them stimuli responsive, changing their hydrodynamic volume. Poly(acrylamide) is a mass-produced material used in a variety of industrial applications, often with an anionic and cationic co-monomer, which dictates both its efficacy and impact on the environment. Poly(N-isopropyl acrylamide) is a thermally responsive material with applications in smart bioengineering. In solution, these materials can interact with each other due to competing hydrogen bonding interactions. However, this interpolymer complexation is dependent on both the ionisation, and the conformational state, of the polymers involved. This review focuses on the results from fluorescence tagging and turbidimetric techniques.
- poly(acrylic acid)
- poly(methacrylic acid)
- stimuli responsive
- interpolymer complexation
- hydrodynamic volume
- solution properties
A common feature of the many polymer systems formed from acrylate monomers is their hydrophilicity; apparent either from their increased absorbency, wettability or increased solubility. Whilst the latter is often overlooked in materials science, it is of vital importance to a range of industries, as a multitude of polyacrylates form vital components in commercial products too varied to list, but including dispersants, adhesives, emulsifiers, lubricants, flocculants, thickeners, surfactants, sensors, delivery agents, coatings, chromatographic phases, grouting, passivation and many more. As of 2018, the multi-million tonne polyacrylate global market is still rising with an annual growth greater than 6% . Research over the last 20 years into controlled radical polymerisation, and copolymerisation, has provided increased insight into the distinct properties of these materials. However, even 50 years after the initial patenting of poly(acrylic acid) , new discoveries about its fundamental properties are still being made .
In solution many, but not all, acrylate copolymers act as polyelectrolytes, containing ionisable repeat units; and thus show some form of stimuli-response to pH. The solution forces that govern these properties are the same that give function to biological macromolecules (i.e., peptides, proteins, DNA) and so many polyelectrolytes have been used as simple models for these more complex systems. However, due to their applications are so widespread and varied, it is essential to any chemist or engineer working with these sensitive materials to acquire some understanding of the need to control their pH.
Depending on the nature of these ionisable repeat units, a polymer can be classified as a ‘weak’ or ‘strong’ polyelectrolyte, governed by the p
and the dissociation constant (α) can be described by the Henderson-Hasselbalch equation
This chapter will discuss recent advances in the study of pH dependent polyacrylate solution behaviour, examining our improvements in understanding of weak polyelectrolyte systems. Critically this review limits itself to studies of linear polymer systems, as the properties of branched, or crosslinked, macromolecules are fundamentally different [15, 16] and warrant further, separate discussion.
2. Poly(carboxylic acids)
The two most comprehensively studied synthetic poly(carboxylic acid)s within the literature are poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) respectively. Both contain a carboxylic acid repeat unit that dissociated to form a negatively charged anion in low pH aqueous solutions. The additional methyl group on the methacrylic acid functional group gives PMAA a degree of amphiphilic behaviour  depending on the degree of ionisation (Figure 1).
This additional hydrophobicity dominates the solution properties of PMAA, leading to the aforementioned ‘anomalous’ Henderson Hasselbalch titration behaviour [4, 5, 7, 9], whilst PAA has long been considered a more ‘ideal’ system  as it does not undergo as dramatic a macroscopic switch. As the carboxylic acid group can only be classed as hydrophilic when the functional monomer is protonated, PMAA undergoes a rapid swelling as the pH is increased, becoming an entirely hydrophobic material with increasing anionic charge along the backbone. Extensive investigations have been carried out into its behaviour using diverse methods and techniques: pontentiometry [4, 5, 7, 10, 19], viscometry [8, 11], Raman spectroscopy , scattering methods [21, 22, 23] and fluorescence probe interrogation techniques [3, 24, 25, 26]. The combined research has shown that PMAA undergoes a dramatic conformational change between pH 4 and 6, (corresponding to an α (degree of ionisation) between 0.1 and 0.3), whilst PAA adopts a relatively smooth swelling process in the same pH range (initiating at the same degree of ionisation). In acidic media, due to the increased hydrophobicity, PMAA adopts a globular, contracted structure designed to minimise unfavourable interactions between the hydrophobic backbone and side chain and the aqueous solution, whilst PAA has been described as a random, statistical coil [6, 7, 9]. The PMAA shows significantly increased compaction due to the hydrophobic methyl backbone [8, 13, 22, 24, 25, 26, 27, 28, 29], that has been shown to induce
As the degree of ionisation is increased from pH 4 to 6 the PMAA anionic units begin populating the macromolecule backbone, resulting in a transition between pH 5 and 6 where repulsive units between these charges initiate a macroscopic switch from the compact to the water swollen (described in multiple places as ‘rod like’ [30, 31]) state. Due to the increased initial compaction in PMAA, this macromolecular swelling results in dramatically changed properties between the compact/swollen polymer. Compared to this, the equivalent deprotonation and subsequent anionic charge drive PAA to adopt an extended state with a relatively smooth transition, with only small changes to polymer physical properties save additional anionic potential. These conformational responses to external stimuli can be viewed as ‘smart behaviour’ and have led to the incorporation of acrylic acid and methacrylic acid monomers being incorporated into a range of copolymer systems to act as triggers and solvating groups in a range of applications.
Due to the increased compaction, and hydrophobicity, of its globular state, PMAA can solubilise low molar mass organic compounds in solution [12, 17, 32], which is a property not shared by PAA [17, 32, 33]. This is particularly evidenced by the fluorescence emission vibrational fine structure of the aromatic label pyrene. The pyrene excited state emits multiple emission bands, and the relative intensity of bands 1 and 3 vary with different solvents, thus when dispersed in a solution it can give an indication of system polarity [34, 35]. For example, the I3/I1 ratio is known to vary between 0.55 (water) and 1.7 (n-pentane) . This feature has been used in the study of many polymer systems, and commonly used by spectroscopists to study macromolecular aggregate structures such as colloids , microemulsions , micelles  and microgels [39, 40]. For example when a 10−6 M solution of pyrene was dispersed in an aqueous solution of PAA, the I3/I1 ratio did not shift from ≈0.55 between pH 3 and 10, identical to the ratio seen for a dispersion in water. This reflects the fact that any interaction between the fluorophore and the polymer does not alter the microenvironment of the label, and confirms the existence of PAA in a water-swollen conformation across the entire pH range. In PMAA at low pH, however, a I3/I1 ratio of 1.1 is commonly observed , indicating the compact hypercoiled polymer provides hydrophobic shielding from the aqueous solvent. When the pH of pyrene/PMAA solution is increased, this ratio begins to decrease at pH 5, indicating the conformational rearrangement of the polymer, until at pH 6 the probe is released into the solution, returning the fluorescence emission ratio to the state seen in both pure water and PAA. This experiment confirms both the increased solubilisation potential of PMAA over PAA and also the fact that the transition occurs over a broad pH range.
However, the electrostatic potential of these polyelectrolytes cannot be so simply described as indicating that the swollen/collapsed state is neutral/charged as there is an evident near neighbour effect present in polymers that is not seen in comparative small molecule systems . This has been evidenced by the different acid dissociation titration behaviours seen in PMAA when comparing different polymer tacticities . In dilute solutions intrachain interactions across the macromolecule tend to dominate its properties—the molecule can be considered a single long chain surrounded by counter ions, and their solution properties are thus governed by their corresponding electrostatic interactions, which are well described by a range of mathematical theories [43, 44]. To summarise: due to electrostatic repulsion ionisation of acrylate polyelectrolytes occurs over a much wider pH range than observed in the equivalent small molecule, and at the ‘stated’ p
More recent data indicates that the length scale of the chain plays a role in this transition. For instance, whilst in 0.1 M NaCl the hydrodynamic radii of PAA scales with molar mass  the conformational rearrangement of the chai non ionisation in low ionic strength liquids only occurs above a known molar mass lower limit . Current results suggest this is a salt dependent phenomenon [41, 47] and has not been observed in PMAA (although increasing polymer size does slow the kinetics of polymer reconfiguration ). As such differences in behaviour between low and high molar mass PAA materials have been observed, such as stark changes in the polymer behaviour at oil-water interfaces [27, 48].
Not all polyacrylates demonstrate electrolyte properties, and one of the most common non-ionisable acrylate materials produced today is acrylamide copolymers. This chapter concerns itself specifically with two specific materials of particular interest with divergent properties, although there are a range of further examples. These polymers are poly(acrylamide) (PAM) and the hydrophobically modified poly(
Random copolymers of acrylamide (both anionic, cationic and neutrally charged) have been extensively used in the water industry for many years [51, 52, 53, 54]. They are extensively employed to remove dissolved organic matter (DOM) for water clarification purposes. Flocculation of fine particles can occur
Polyacrylamide is used in a range of other scenarios including erosion control [51, 57, 58, 59], medical implants [60, 61, 62, 63], and reduction of water seepage via increasing aqueous viscosity to both stabilise soil and dust prevention . Poly(acrylamide) was one of the first polymers used to reduce soil losses in furrow irrigation  and the polymer has been sold commercially for this purpose since at least 1995 . Large quantities of this material are therefore escaping into the environment [59, 65] and a body of research is being built up regarding its effect on the ecosystem . Generally, the polymer is considered non-toxic, with most concerns around its use arising due to its close association from the potent neurotoxin monomer from which it is formed. Since Swedish researchers discovered that acrylamide can be found in heated foodstuffs [67, 68, 69, 70, 71, 72], there has been low level public concern about the use of polyacrylamides in a range of industries.
However, studies of polyelectrolyte flocculants of all types have been carried out and consistently poly(acrylamide) is identified as being the primary ‘toxicant’ . Within much of the poly(acrylamide) literature, there has been a lot of emphasis placed on the toxicity of the monomer, resulting in studies discounting the effects of the polymer and only focusing on residual monomer spread . However, some studies have shown that poly(acrylamide) is unlikely to degrade into residual monomers, or any other toxic compounds , and this has only been observed under specific harsh conditions . Therefore, a complete study of the environmental impact of these polymers should include the raw polymeric product. Testing of poly(acrylamide) interaction with the gill tissues of several aquatic species including fish [66, 73, 75, 76, 77], crustaceans [66, 73, 77], algae [66, 77] and insects  have been carried out. In many studies of adult fish, the anionic and non-ionic form of the poly(acrylamide) cause only low levels of damage to the fish, with effects increasing at higher concentrations . However, sustained exposure of organisms over a 40 day period has shown that low levels of these polymers are intrinsically toxic to almost all aquatic fauna . Environmental exposure is unlikely to be sustained over long periods due to the polymer desorption to organic matter but few studies have been undertaken into the metabolic rate at which they are removed from living organisms. Even in tests where fish survival was not impacted, the general activity and swimming behaviour of the fish were sub normal . Conversely the cationic form of the polymer is known to be far more toxic, causing pathological issues at sub mg ml−1 concentrations, as the polymer builds up on negatively charged gill surfaces [75, 77]. Reduced gill functionality impairs oxygen uptake in the fish and results in death. Further studies have shown that polyelectrolytes can cause adverse changes in fish organ cells (liver and kidneys) , decrease animal locomotion and greatly increase respiratory rate. This suggests that the presence of dissolved flocculants may not be lethally toxic but suggests it is capable of causing the fish elevated levels of distress. In invertebrates, their mechanical action was reduced as polyelectrolytes adsorbed onto their body surfaces, reducing their vital functions , and again the cationic form of the polymer is far more toxic than the anionic form.  In microcosms tests, it has been shown that high polyelectrolyte concentration can reduce algal growth [66, 77]. This in turn can increase the potential toxicity of the polymer as the algae acts as a neutralising agent towards the polymer. To algae, even the anionic and non-ionic polymer is toxic, negatively affecting both cell growth and O2 production . It has been observed that addition of combinations of both anionic and cationic polymer can reduce toxicity  and several patents have been issued suggesting that anionic polymers can be used to detoxify cationic polyelectrolytes [78, 79]. In conclusion, the discrepancy between anionic and cationic polymers in regard to aquatic toxicity must be considered in the application of these polymers [75, 77]. The cationic form of the polymer is regarded as generally more toxic but the anionic form has also been shown to cause chronic, sub-lethal responses even at low concentrations .
Although it has some larger applications, PNIPAM is not produced or utilised in such great quantities. It is mainly of interest due to a thermally induced conformation the polymer exhibits at 32°C, caused by the hydrophobic isopropyl groups . This ‘smart’ response has led to great interest in the polymer, both to understand its properties and apply them in a range of fields, specifically in Bioengineering . In essence, the polymer has a lower critical solution temperature (LCST), a conformational change that occurs
The LCST of PNIPAM can be affected by the addition of hydrophobic or hydrophilic end groups , or the molecular weight and concentration of the sample . Due to the LCST is reasonably close to body temperature, there has been much work to manipulate PNIPAM to act as a drug-delivery agent or trigger or apply it in other bio-engineering circumstances [86, 87].
4. Acrylate interpolymer complexes
Interactions between multiple polymers in a formulation are almost inevitable, and there has been plenty of studies of specific driving factors undertaken over the last 50 years to build a strong picture of inter-polymer interactions. This phase separation phenomena is observed in even the most dilute solutions, as it is driven by a mixture of electrostatic, hydrogen bonding and hydrophobic interactions, all dependent on pH, salt concentration and temperature [88, 89]. To our knowledge this type of complex was first patented in 1966 , with much of the following fundamental measurements carried out over the following decades [14, 91, 92, 93, 94]. Since then, the system has been described as a
The interactions between PAA and PAM are one of the more studied systems of interpolymer complex formation (IPC) [93, 96, 97, 98, 99, 100, 101], and in both solution and solid state the interaction has been shown to be pH dependant [14, 96]. Mixed solutions of PAA and PAM form a turbid solution that precipitates when cooled . This phase separation follows the formation of complexes between PAA and PAM that varies in structure depending on the concentration, medium and the ionisation constant . For complexes between PAA and a proton-acceptor polymer it has been shown that IPCs will only form below a critical value of pH (pHcrit) [14, 99], the structure dependent point above which any partial neutralisation of the polyacid inhibits complex formation [14, 100].
Early work within this field required high molecular weight materials to detect complex formation [99, 102], however, modern instrumentation has facilitated detection of smaller complexes down at the parts per million loading level . The structure of the resultant IPC (whether in a gel or a compact solvated complex) depends on the relative molecular weight of complexing partners,  but as this is a multivalent effect of repeated binding sites, larger molecular weight materials demonstrate stronger interactions. Furthermore, it has been indicated that very large molecular weight polyacids have been seen to raise pHcrit .
When dissolved in high ionisation solutions, both polymers have rapid segmental motion, existing as random polymeric coils. If the solution ionisation is decreased, this deprotonates the acidic polyelectrolytes and reduces its affinity for inter-polymer complexation. This occurs as can now form both intramolecular H-bonds internally across the chain backbone or intermolecularly forming H-bonds with other polymers , leading to a rigid polymer mixture with restricted chain motions. PAA forms stronger complexes to PAM than some other polymers (i.e., poly(ethylene oxide) or poly(vinyl acetate)) due to additional ion-dipole interaction of the partially protonated amide groups and the C═O dipoles of PAA . In ambient conditions the peak aqueous interaction between PAA and PAM occurs ≈ pH 2.69  but this is affected by many environmental factors including temperature [89, 101], ionic strength [93, 107, 108] and the addition of inorganic binders . The complex polymer/polymer/solvent ratio of interactions is temperature sensitive causing PAM-PAA copolymers to become upper-critical solution temperature materials (an inversion of the LCST seen in PNIPAM where they become only soluble above a specific temperature ). These combined external factors deteriorate the thermodynamic quality of the solvent, strengthening polymer-polymer interactions by weakening polymer-water solvation . However, below pHcrit, only small portions of the PAM form into ‘multimacroion clusters’, indicating that in an equivalent system with 1:1 acid/acrylamide repeat units, a large percentage of acrylamide will be free in solution unbound to PAA . This was the first result of several which have cast doubt on the ladder model, and computational modelling software of polymer/polymer ionic interactions has proposed a range of complexing structures ranging from ladders to scrambled egg structures . Further experimental evidence has shown that a PAA coil does not unwind or swell on addition of a PAM polymer but potentially contracts into a smaller co-globule , and an explanation for this can be found when considering the difference between the pHcrit of IPC formation and p
Other acrylate materials, such as PNIPAM, demonstrate similar responses to polyacids, and exhibit their own IPC potential . Whilst PAM-PAA interactions are dominant at lower temperatures, PAA-PNIPAM show increased interactions at high temperatures, indicating that the complex formation is driven by hydrophobic interactions not seen in the base acrylamide structure . Studies using dissolved pyrene indicated these lead to stronger interactions between PAA and PNIPAM than PAA-PAM [115, 116]. Furthermore, the hydrophobic isopropyl side chain causes PNIPAM to alter its response to ionic strength. Whereas PAM-PAA complexes are strengthened by increasing ionic strength, PNIPAM complexes show decreased critical pH reducing their bond forming potential . As the initial critical pH for IPC formation was larger than 3, Khutoryanskiy theorised that the increasing ionic strength partially dissociates the polyacid. As only non-ionised carboxylic groups are able to form hydrogen bonds, this impedes IPC formation and reduces the p
For PAA-PAM, pHcrit was found to be 2.7, whilst for increasing hydrophobic additions to the acrylamide unit (poly(ethyl acrylamide), poly(dimethyl acrylamide), poly(diethyl acrylamide), the pHcrit was found to increase to 3, 4, 5 respectively . It is interesting to note that the most hydrophilic acrylamide polymers (including a hydrophilic-functionalised poly(hydroxyl ethyl acrylamide)) show lower pHcrit, indicating that their IPC with the polyacid are less tolerant of deprotonation. The PAA-PAM complex appears to separate when the first acid repeat unit along the chain is deprotonated whilst more hydrophobically modified polymers are more tolerant to partial ionisation when complexing with PAA. Computational modelling of the solvation energy of each repeat unit shows a clear correlation between solvation potential and pHcrit .
Clearly the polyacid dictates the potential of IPC with receptive polymers , and in this mind, it is worth revisiting the PAA-PAM IPC structure. As the p
We suggest that compacted PAA has no entropic or enthalpic reason to uncoil or swell prior to complexation. Given the combined evidence from two separate sources that (1) most PAM chains are not binding to partners and (2) PAA chains do not swell further apart on PAM binding (in fact there is some evidence of contraction), it seems reasonable to propose that the PAA-PAM complex is not amorphous in nature, and certainly not an extended ribbon/ladder structure.
This chapter reviews some of the recent developments in polyacrylate properties and interactions, and delves deeply into their industrial applications to provide both further context and understanding. During the early study many assumptions were made due to the difficulty to analyse these large macromolecules, particularly in dilute solutions, and our understanding of these systems has slowly evolved as more advanced technology with greater sensitivity has facilitated deeper interrogation of these systems . This chapter only touches on a few choice themes of polymer-responsiveness and ignored many of the more challenging aspects of the field. The state of ionisation of all of these polymers has clearly been shown to have an effect on their solution properties, and although the field is still under development after several decades of work, common themes can be seen across the subject dictating macromolecular conformational changes.
This book chapter is both an update, summation of, and substantial revision to my Ph.D., work area carried out at the University of Sheffield, originally under Dr. Linda Swanson, who has published extensively on the photophysical analytical techniques described in this paper. For further reference on the application of those techniques in these systems, particularly in the study of polyelectrolytes, please see her book chapter ‘Optical Properties of Polyelectrolytes’ .
Conflict of interest
There are no conflicts of interest to declare.
Written following the arrival of, and dedicated to, Jonathan Swift, born in 2017.
|IPC||interpolymer complex formation|
|DOM||dissolved organic matter|
Polyacrylate Market - Segmented by Product Type, Application, and Geography - Trends and Forecast (2018-2023). Hyderabad: Mordor Intelligence; 2018
Harper BG, Niles Bashaw R, Leroy Atkins B. Absorbent Product Containing a Hydrocellodal Composition. Patent US3670731; 1966
Swift T, Swanson L, Geoghegan M, Rimmer S. The pH-responsive behaviour of poly(acrylic acid) in aqueous solution is dependent on molar mass. Soft Matter. 2016; 12:2542-2549
Katchalsky A, Spitnik P. Potentiometric titrations of polymethacrylic acid. Journal of Polymer Science. 1947; 2:432-446
Leyte JC, Mandel M. Potentiometric behavior of polymethacrylic acid. Journal of Polymer Science, Part A: General Papers. 1964; 2:1879-1891
Crescenzi V. Some recent studies of polyelectrolyte solutions. Advances in Polymer Science. 1968; 5:358-386
Arnold R. The titration of polymeric acids. Journal of Colloid Science. 1957; 12:549-556
Katchalsky A. Solutions of polyelectrolytes and mechanochemical systems. Journal of Polymer Science, Part A: General Papers. 1951; 7:393-412
Mandel M. The potentiometric titration of weak polyacids. European Polymer Journal. 1970; 6:807-822
Přádný M, Holata J, Ševčík S. The use of low-molecular-weight model compounds in an investigation of polyelectrolytes, 1. Potentiometric properties of poly(methacrylic acid) and its 2-dimethylaminoethyl ester. Macromolecular Chemistry and Physics. 1989; 190:1079-1088
Eisenberg H. Conductance of partially neutralized polymethacrylic and polyacrylic acids, using a polarization compensated twin cell. Journal of Polymer Science, Part A: General Papers. 1958
Chen TS, Thomas JK. Influence of the conformational state of polymethacrylic acid on the photophysical properties of pyrene in aqueous solution: A fluorescent probe and laser photolysis study. Journal of Polymer Science, Part A: Polymer Chemistry. 1979; 17:1103-1116
Soutar I, Swanson L. Luminescence studies of polyelectrolyte behaviour in solution-I. Accessibility of naphthalene-based labels of poly(methacrylic acid) to mobile low molar mass species in aqueous media. European Polymer Journal. 1993; 29:371-378
Swift T, Seaton CC, Rimmer S. Poly(acrylic acid) interpolymer complexes. Soft Matter. 2017; 14:8736-8744
Alves L, Lindman B, Klotz B, Böttcher A, Haake HM, Antunes FE. Rheology of polyacrylate systems depends strongly on architecture. Colloid and Polymer Science. 2015; 239:3285-3293
Shallcross L, Roche K, Wilcock CJ, Stanton KT, Swift T, Rimmer S, et al. The effect of hyperbranched poly(acrylic acid)s on the morphology and size of precipitated nanoscale (fluor)hydroxyapatite. Journal of Materials Chemistry B. 2017; 5:6027-6033
Barone G, Crescenzi V, Liquori AM, Quadrifoglio F. Solubilization of polycyclic aromatic hydrocarbons in poly(methacrylic acid) aqueous solutions. The Journal of Physical Chemistry. 1967; 71:2341-2345
Morawetz H. Macromolecules in Solution. Wiley; 1975
Nekrasova TN, Anufriyeva YV, Yel’yashevich AM, Ptitsyn OB. Potentiometric titration of polyacrylic acid, polymethacrylic acid and poly-L-glutamic acid. Polymer Science USSR. 1965; 7:1008-1018
Koenig JL, Angood AC, Semen J, Lando JB. Laser-excited Raman studies of the conformational transition of syndiotactic polymethacrylic acid in water. Journal of the American Chemical Society. 1969; 91:7250-7254
Heitz C, Rawiso M, François J. X-ray scattering study of a poly(methacrylic acid) sample as a function of its neutralization degree. Polymer (Guildf). 1999; 40:1637-1650
Pleštil J, Ostanevich YM, Bezzabotonov VY, Hlavatá D, Labský J. Small-angle scattering from polyelectrolyte solutions: Dimensions of poly(methacrylic acid) chains in salt-free solutions. Polymer (Guildf). 1986; 27:839-842
Moussaid A, Schosseler F, Munch JP, Candau SJ. Structure of polyacrylic acid and polymethacrylic acid solutions: A small angle neutron scattering study. Journal of Physics B Atomic and Molecular Physics. 1993; 3:573-594
Ruiz-Pérez L, Pryke A, Sommer M, Battaglia G, Soutar I, Swanson L, et al. Conformation of poly(methacrylic acid) chains in dilute aqueous solution. Macromolecules. 2008; 41:2203-2211
Olea AF, Thomas JK. Fluorescence studies of the conformational changes of poly(methacrylic acid) with pH. Macromolecules. 1989; 22:1165-1169
Swanson L. Optical properties of polyelectrolytes. In: Photochemistry and Photophysics of Polymer Materials. Hoboken, New Jersey: John Wiley & Sons inc.; 2010. pp. 41-92
Olea AF, Rosenbluth H, Thomas JK. Effect of the molecular weight on the dynamics of the conformational transition of poly(methacrylic acid). Macromolecules. 1999; 27:8077-8083
Chu DY, Thomas JK. Photophysical studies of a water-soluble copolymer of methacrylic acid and 1-pyreneacrylic acid. Macromolecules. 1984; 17:2142-2147
Bednar B, Morawetz H, Shafer JA. Kinetics of the conformational transition of poly(methacrylic acid) after changes of its degree of ionization. Macromolecules. 1985; 18:1940-1944
Katchalksy A, Eisenberg H. Molecular weight of polyacrylic and polymethacrylic acid. Journal of Polymer Science. 1951; 6:145-154
Soutar I, Swanson L. Luminescence studies of polyelectrolyte behavior in solution. 3. Time-resolved fluorescence anisotropy measurements of the conformational behavior of poly(methacrylic acid) in dilute aqueous solutions. Macromolecules. 1994; 27:4304-4311
Tan KL, Treloar FE. Solubilization of 9-methylanthracene by the hypercoiled form of poly(methacrylic acid) in water: Fluorescence decay and rotational diffusion measurements. Chemical Physics Letters. 1980; 73:234-239
Treloar FE. Conformational transition in poly(methacrylic acid) in aqeous-solution-dye binding and fluorescence depolarization. Chemica Scripta. 1976; 10:219-224
Akira N, Hiroaki B. Fluorescence spectrum of pyrene vapor: Emission from the second excited singlet state. Bulletin of the Chemical Society of Japan. 1970; 43:967-967
Kalyanasundaram K, Thomas JK. Environmental effects on vibronic band intensities in pyrene monomer fluorescence and their application in studies of micellar systems. Journal of the American Chemical Society. 1977; 99:2039-2044
Soutar I, Swanson L, Annable T, Padget JC, Satgurunathan R. Luminescence techniques and characterization of the morphology of polymer latices. 3. An investigation of the microenvironments within stabilized aqueous latex dispersions of poly(n-butyl methacrylate) and polyurethane. Langmuir. 2006; 22:5904-5910
Lianos P, Lang J, Zana R. Fluorescence probe study of oil-in-water microemulsions. 2. Effect of the nature of alcohol, oil, and surfactant on the surfactant aggregation number in the aggregates. The Journal of Physical Chemistry. 1982; 86:4809-4814
Jay J, Johnston L, Scaiano JC. Quenching of pyrene fluorescence by cupric ions in micellar solution: Effect of quenching on the polarity reported by the prob. Chemical Physics Letters. 1988; 148:517-522
Pankasem S, Thomas JK, Snowden MJ, Vincent B, Snowden MJ. Photophysical studies of poly( N-isopropylacrylamide) microgel structures. Langmuir. 1994; 10:3023-3026
Flint NJ, Gardebrecht S, Swanson L. Fluorescence investigations of “smart” microgel systems. Journal of Fluorescence. 1998;8:343-353
Dolce C, Mériguet G. Ionization of short weak polyelectrolytes: When size matters. Colloid & Polymer Science. 2017
Loebl EM, O’Neill JJ. Solution properties of isotactic polymethacrylic acid. Journal of Polymer Science, Part A: General Papers. 1960; 45:538-540
Dobrynin AV, Rubinstein M. Theory of polyelectrolytes in solutions and at surfaces. Progress in Polymer Science. 2005; 30:1049-1118
Kuhn W, Künzle O, Katchalsky A. Verhalten polyvalenter Fadenmolekelionen in Lösung. Helvetica Chimica Acta. 1948; 31:1049-118
Anghel DF, Alderson V, Winnik FM, Mizusaki M, Morishima Y. Fluorescent dyes as model “hydrophobic modifiers” of polyelectrolytes: A study of poly(acrylic acid)s labelled with pyrenyl and naphthyl groups. Polymer (Guildf). 1998; 39:3035-3044
Reith D, Müller B, Müller-Plathe F, Wiegand S. How does the chain extension of poly (acrylic acid) scale in aqueous solution? A combined study with light scattering and computer simulation. The Journal of Chemical Physics. 2002; 116:9100
Geoghegan M. The swelling of weak polyelectrolytes at low salt concentrations in dilute solution. Polymer (United Kingdom). 2017; 112:414-417
Zaibudeen AW, Philip J. A spectroscopic approach to probe macromolecular conformational changes at interface under different environmental conditions: A case study with PAA adsorbed at oil-water interface. Journal of Molecular Liquids. 2018;252:30-39
Pelton R. Poly( N-isopropylacrylamide) (PNIPAM) is never hydrophobic. Journal of Colloid and Interface Science. 2010; 348:673-674
Shepherd J, Sarker P, Rimmer S, Swanson L, MacNeil S, Douglas I. Hyperbranched poly(NIPAM) polymers modified with antibiotics for the reduction of bacterial burden in infected human tissue engineered skin. Biomaterials. 2011; 32:258-267
Sojka RE, Bjorneberg DL, Entry JA, Lentz RD, Orts WJ. Polyacrylamide in agriculture and environmental land management. Advances in Agronomy. 2007; 92:75-163
Yongrui P, Zheng Z, Bao M, Li Y, Zhou Y, Sang G. Treatment of partially hydrolyzed polyacrylamide wastewater by combined Fenton oxidation and anaerobic biological processes. Chemical Engineering Journal. 2015; 273:1-6
Bolto B, Gregory J. Organic polyelectrolytes in water treatment. Water Research. 2007; 41:2301-2324
Aguilar MI, Sáez J, Lloréns M, Soler A, Ortuño JF. Nutrient removal and sludge production in the coagulation-flocculation process. Water Research. 2002; 36:2910-2919
Nasser MS, James AE. The effect of polyacrylamide charge density and molecular weight on the flocculation and sedimentation behaviour of kaolinite suspensions. Separation and Purification Technology. 2006; 52:241-252
Griot O, Kitchener JA. Role of surface silanol groups in the flocculation of silica suspensions by polyacrylamide: Part 2—Surface changes of silica suspensions on ageing. Transactions of the Faraday Society. 1965; 61:1026-1031
Kang J, Sowers TD, Duckworth OW, Amoozegar A, Heitman JL, McLaughlin RA. Turbidimetric determination of anionic polyacrylamide in low carbon soil extracts. Journal of Environmental Quality. 2013; 42:1902-1907
Trout TJ, Sojka RE, Lentz RD. Polyacrylamide effect on furrow erosion and infiltration. American Society of Agricultural and Engineers. 1995; 38:761-765
Lentz RD, Sojka RE, Foerster JA. Estimating polyacrylamide concentration in irrigation water. Journal of Environmental Quality. 1996; 25:1015-1024
Christensen LH, Breiting VB, Aasted A, Jørgensen A, Kebuladze I. Long-term effects of polyacrylamide hydrogel on human breast tissue. Plastic and Reconstructive Surgery. 2003; 111:1883-1890
Cheng NX, Liu LG, Hui L, Chen YL, Xu SL. Breast cancer following augmentation mammaplasty with polyacrylamide hydrogel (PAAG) injection. Aesthetic Plastic Surgery. 2009; 33:563
Davis BK. Control of diabetes with polyacrylamide implants containing insulin. Experientia. 1972; 28:348
Altman D, Hjern F, Zetterström J. Transanal submucosal polyacrylamide gel injection treatment of anal incontinence: A randomized controlled trial. Acta Obstetricia et Gynecologica Scandinavica. 2016; 95:528-533
Lentz RD, Sojka RE, Carter DL, Shainberg I. Preventing irrigation furrow erosion with small applications of polymers. Soil Science Society of America Journal. 1992; 56:1926-1932
Touzé S, Guerin V, Guezennec AG, Binet S, Togola A. Dissemination of acrylamide monomer from polyacrylamide-based flocculant use—Sand and gravel quarry case study. Environmental Science and Pollution Research. 2015; 22:6423-6430
Harford AJ, Hogan AC, Jones DR, van Dam RA. Ecotoxicological assessment of a polyelectrolyte flocculant. Water Research. 2011; 45:6393-6402
Yaylayan VA, Wnorowski A, Perez Locas C. Why asparagine needs carbohydrates to generate acrylamide. Journal of Agricultural and Food Chemistry. 2003; 51:1753-1757
Tareke E, Rydberg P, Karlsson P, Eriksson S, Törnqvist M. Acrylamide: A cooking carcinogen? Chemical Research in Toxicology. 2000; 13:517-522
Becalski A, Lau BPY, Lewis D, Seaman SW. Acrylamide in foods: Occurence, sources and modelling. Journal of Agricultural and Food Chemistry. 2003; 51(3):802-808
Zyzak DV, Sanders RA, Stojanovic M, Tallmadge DH, Eberhart BL, Ewald DK, et al. Acrylamide formation mechanism in heated foods. Journal of Agricultural and Food Chemistry. 2003; 51:4782-4787
Ahn JS, Castle L, Clarke DB, Lloyd AS, Philo MR, Speck DR. Verification of the findings of acrylamide in heated foods. Food Additives and Contaminants. 2002; 19:1116-1124
Rydberg P, Eriksson S, Tareke E, Karlsson P, Ehrenberg L, Törnqvist M, et al. Investigations of factors that influence the acrylamide content of heated foodstuffs. Journal of Agricultural and Food Chemistry. 2003; 51:7012-7018
Beim AA, Beim AM. Comparative ecological—toxicological data on determination of maximum permissible concentrations (mpc) for several flocculants. United Kingdom: Environmental Technology; 1994; 15:195-198
Aksberg R, Wågberg L. Hydrolysis of cationic polyacrylamides. Journal of Applied Polymer Science. 1989; 38:297-304
Kerr JL, Lumsden JS, Russell SK, Jasinska EJ, Goss GG. Effects of anionic polyacrylamide products on gill histopathology in juvenile rainbow trout ( Oncorhynchus mykiss). Environmental Toxicology and Chemistry. 2014; 33:1552-1562
Liber K, Weber L, Lévesque C. Sublethal toxicity of two wastewater treatment polymers to lake trout fry ( Salvelinus namaycush). Chemosphere. 2005; 61:1123-1133
Biesinger KE, Stokes GN. Effects of synthetic polyelectrolytes on selected aquatic organisms. Journal Water Pollution Control Federation. 1986; 58:207-213
Furuno Method of rendering cationic polymers harmless to fish. 1976
Furuno. Process for the Detoxification of Water Treated with Polymer Cationic Flocculation Agents. 1980
Chee CK, Rimmer S, Soutar I, Swanson L. Fluorescence investigations of the thermally induced conformational transition of poly( N-isopropylacrylamide). Polymer (Guildf). 2001; 42:5079-5087
Wang X, Qiu X, Wu C. Comparison of the coil-to-globule and the globule-to-coil transitions of a single poly( N-isopropylacrylamide) homopolymer chain in water. Macromolecules. 1998; 31:2972-2976
Schmaljohann D. Thermo- and pH-responsive polymers in drug delivery. Advanced Drug Delivery Reviews. 2006; 58:1655-1670
Kammer H-W, Inoue T, Ougizawa T. Upper and lower critical solution temperature behaviour in polymer blends and its thermodynamic interpretation. Polymer (Guildf). 1989; 30:888-892
Kujawa P, Aseyev V, Tenhu H, Winnik FM. Temperature-sensitive properties of poly( N-isopropylacrylamide) mesoglobules formed in dilute aqueous solutions heated above their demixing point. Macromolecules. 2006; 39:7686-7693
Plunkett KN, Zhu X, Moore JS, Leckband DE. PNIPAM chain collapse depends on the molecular weight and grafting density. Langmuir. 2006; 22:4259-4266
Ward MA, Georgiou TK. Thermoresponsive polymers for biomedical applications. Polymers (Basel). 2011; 3:1215-1242
Gandhi A, Paul A, Sen SO, Sen KK. Studies on thermoresponsive polymers: Phase behaviour, drug delivery and biomedical applications. Asian Journal of Pharmaceutical Sciences. 2015; 10:99-107
Bailey FE, Lukdberg RD, Callard RW. Some factors meeting the molecular association of poly(ethy1ene oxide) and poly (acrylic acid) In aqueous solution. Journal Polymer Science PART A. 1964; 2:845-851
Sudre G, Tran Y, Creton C, Hourdet D. PH/Temperature control of interpolymer complexation between poly(acrylic acid) and weak polybases in aqueous solutions. Polymer (Guildf). 2012; 53:379-385
Smith KL, Winslow AE, Seltzer EC. Chemical reaction product of polycarboxylic acid and a polymeric polyether. Patent US3387061A; 1966
Ikawa T, Abe K, Honda K, Tsuchida E. Interpolymer complex between poly(ethylene oxide) and poly(carboxylic acid). Journal of Polymer Science, Polymer Chemistry Edition. 1975; 13:1505-1514
Tsuchida E, Osada Y, Ohno H. Formation of interpolymer complexes. Journal Macromolecular Science Part B. 1980; 17:683-714
Sivadasan K, Somasundaran P, Turro NJ. Fluorescence and viscometry study of complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide). Colloid & Polymer Science. 199; 269:131-137
Abe K, Koide M, Tsuchida E. Selective complexation of macromolecules. Macromolecules. 1977; 10:1259-1264
Baranovsky VY, Kazarin LA, Litmanovich AA, Papisov IM. Thermochemical reactions in polycomplexes. European Polymer Journal. 1984; 20:191-194
Garces FO, Sivadasan K, Somasundaran P, Turro NJ. Interpolymer complexation of poly(acrylic acid) and polyacrylamide: Structural and dynamic studies by solution- and solid-state NMR. Macromolecules. 1994; 27:272-278
Klenina OV, Fain EG. Phase separation in the system polyacrylic acid-polycrylamide-water. Polymer Science USSR. 1981; 23:1439-1446
Swift T, Swanson L, Rimmer S. Poly(acrylic acid) interpolymer complexation: Use of a fluorescence time resolved anisotropy as a poly(acrylamide) probe. RSC Advances. 2014; 4:57991-57995
Mun GA, Nurkeeva ZS, Khutoryanskiy VV, Sarybayeva GS, Dubolazov AV. pH-effects in the complex formation of polymers I. Interaction of poly(acrylic acid) with poly(acrylamide). European Polymer Journal. 2003; 39:1687-1697
Staikos G, Bokias G, Tsitsilianis C. The viscometric methods in the investigation of the polyacid-polybase interpolymer complexes. Journal of Applied Polymer Science. 1993; 48:215-217
Staikos G, Karayanni K, Mylonas Y. Complexation of polyacrylamide and poly( N-isopropylacrylamide) with poly(acrylic acid). The temperature effect. Macromolecular Chemistry Physics. 1997; 198:2905-2915
Eustace DJ, Siano DB, Drake EN. Polymer compatibility and interpolymer association in the poly(acrylic acid)-polyacrylamide-water ternary system. Journal of Applied Polymer Science. 1988; 35:707-716
Swift T, Swanson L, Bretherick A, Rimmer S. Measuring poly(acrylamide) flocculants in fresh water using inter-polymer complex formation. Environmental Science: Water Research & Technology. 2015; 1:332-340
Staikos G, Tsitsilianis C. Viscometric investigation of the poly(acrylic acid)—Polyacrylamide interpolymer association. Journal of Applied Polymer Science. 1991; 42:867-872
Dong J, Ozaki Y, Nakashima K. Infrared, Raman, and near-infrared spectroscopic evidence for the coexistence of various hydrogen-bond forms in poly(acrylic acid). Macromolecules. 1997; 30:1111-1117
Tsuchida E, Abe K. Interactions between macromolecules in solution and intermacromolecular complexes. In: Interactions between Macromolecules in Solution and Intermacromolecular Complexes. Berlin, Heidelberg: Springer; 1982. p. 88
Moharram MA, Balloomal LS. Infrared study of the complexation of poly(acrylic acid) with poly(acrylamide). Journal of Applied Polymer Science. 1996; 59:987-990
Nurkeeva ZS, Mun GA, Khutoryanskiy VV, Sergaziev AD. Complex formation between poly(vinyl ether of diethyleneglycol) and polyacrylic acid I. Effect of low molecular salts and phenols additives. European Polymer Journal. 2001; 37:1233-1237
Khutoryanskiy VV, Mun GA, Nurkeeva ZS, Dubolazov AV. pH and salt effects on interpolymer complexation via hydrogen bonding in aqueous solutions. Polymer International. 2004; 53:1382-1387
Deng L, Wang C, Li ZC, Liang D. Re-examination of the “zipper effect” in hydrogen-bonding complexes. Macromolecules. 2010; 43:3004-3010
Lazutin AA, Semenov AN, Vasilevskaya VV. Polyelectrolyte complexes consisting of macromolecules with varied stiffness: Computer simulation. Macromolecular Theory and Simulations. 2012; 21:328-339
Swift T, Paul N, Swanson L, Katsikogianni M, Förster RS. Resonance energy transfer across interpolymer complexes of poly(acrylic acid) and poly(acrylamide). Polymer (United Kingdom). 2017; 123:10-20
Garay MT, Alava C, Rodriguez M. Study of polymer-polymer complexes and blends of poly( N-isopropylacrylamide) with poly(carboxylic acid). 2. Poly(acrylic acid) and poly(methacrylic acid) partially neutralized. Polymer (Guildf). 2000; 38:5091-5096
Khutoryanskiy VV, Nurkeeva ZS, Mun GA, Dubolazov AV. Effect of temperature on aggregation/dissociation behavior of interpolymer complexes stabilized by hydrogen bonds. Journal of Applied Polymer Science. 2004; 93:1946-1950
Staikos G. Interpolymer complexes of poly(acrylamide) and poly( N-isopropylacrylamide) with poly(acrylic acid): A comparative study. Polymer International. 1996; 41:345-350
Koussathana M, Lianos P, Staikos G. Investigation of hydrophobic interactions in dilute aqueous solutions of hydrogen-bonding interpolymer complexes by steady-state and time-resolved fluorescence measurements. Macromolecules. 1997; 30:7798-7802
Khutoryanskiy VV, Smyslov RY, Yakimansky AV. Modern methods for studying polymer complexes in aqueous and organic solutions. Polymer Science, Series A. 2018; 60(5):553-576