Georgios Bokias

Solution properties and phase behaviour of copolymers of acrylic acid with N-isopropylacrylamide: the importance of the intrachain hydrogen bonding

Abstract The solution properties and the phase behaviour of random copolymers of N -isopropylacrylamide (NIPAM) with acrylic acid (AA) have been investigated. The mole fraction of NIPAM in these copolymers ( x ) varies from 0 to 0.29. At pH=3.00, i.e. when the AA groups are in the undissociated form, the intrinsic viscosity decreases substantially as x increases. This chain shrinkage is attributed to the formation of intrachain hydrogen bonds between the two complementary groups, AA and NIPAM. The weakening of the hydrophilic character and the appearance of hydrophobic properties with increasing x is further supported by fluorescence probing studies and potentiometric measurements of the aqueous copolymer solutions. Moreover, the phase behaviour of these copolymers in salt solution changes dramatically with x . The copolymer with x =0.10 presents, like the homopolymer poly(acrylic acid), an Upper Critical Solution Temperature (UCST) behaviour. On the contrary, the copolymer with x =0.29 presents, similar to the homopolymer poly( N -isopropylacrylamide), a Lower Critical Solution Temperature (LCST) behaviour. Finally, the copolymer with the intermediate NIPAM content, x =0.17, presents both an UCST and an LCST behaviour.

Formation of hybrid wormlike micelles upon mixing cetyl trimethylammonium bromide with poly(methyl methacrylate-co-sodium styrene sulfonate) copolymers in aqueous solution.

The association of cetyltrimethylammonium bromide, CTAB, with a series of P(MMAx-co-SSNa) random copolymers of sodium styrene sulfonate (SSNa) with methyl methacrylate (MMA) was explored in aqueous solution as a function of the MMA molar content, x, of the copolymers. The polyelectrolyte/surfactant complexation in aqueous solution was verified through pyrene fluorescence probing. In addition, turbidimetry studies in dilute or more concentrated aqueous solutions elucidated the phase separation behavior of the P(MMAx-co-SSNa)/CTAB systems as a function of the copolymer composition x and the surfactant to polyelectrolyte mixing charge ratio. It is found that practically phase separation is completely suppressed within the studied mixing range when the MMA content of the copolymers is ∼30-40 mol%. For lower MMA contents the polyelectrolyte/surfactant complex separates out from water, while for higher x values the solubility limits of the copolymers in water are attained. For the intermediate MMA contents, viscoelastic systems are obtained in more concentrated polymer/surfactant solutions provided that the polyelectrolyte is fully complexed with the cationic surfactant ((1)H NMR results). Moreover, the (1)H NMR studies indicate that hybrid P(MMAx-co-SSNa)/CTAB wormlike micelles are formed in water under these conditions. Finally, it is shown that addition of salt prevents syneresis problems and facilitates the rheological investigation.

Rheological study of semidilute aqueous solutions of a thermoassociative copolymer

In this paper, the linear and nonlinear rheological behavior of semidilute aqueous solutions of a recently synthesized thermoassociative graft copolymer was investigated, as a function of temperature and polymer concentration. The polymer, namely CMC–g–PNIPAM, is based on a carboxymethylcellulose (CMC) backbone bearing thermosensitive poly(N-isopropylacrylamide) (PNIPAM) sidechains. The samples have been submitted to steady shear, oscillatory shear, and step-strain experiments, mainly at temperatures above the threshold temperature Tassoc to observe thermothickening. The linear and nonlinear rheological data clearly show the existence of two temperature regimes, separated by a transition temperature T′ > Tassoc. At temperatures below T′, the solutions behave like a soft critical gel, corresponding to weak PNIPAM segregation. At temperatures above T′, the solutions behave like a stiff critical gel, corresponding to strong PNIPAM segregation.

Template copolymerisation of N-isopropylacrylamide with a cationic monomer: influence of the template on the solution properties of the product

A copolymer containing 91 mol% N-isopropylacrylamide (NIPAM) units and 9 mol% N,N-(dimethylaminopropyl)methacrylamide (MADAP) units, copolymer II, was prepared using polyacrylate chains as a template for the positively charged MADAP units. The properties of this product were compared to the properties of a similar copolymer (copolymer I) prepared in the absence of the template. The molar mass of copolymer II was found much higher than that of copolymer I. Moreover, the cloud point of copolymer II is closer to the cloud point of the homopolymer poly(N-isopropylacrylamide) at various pH conditions, indicating that copolymer II contains longer NIPAM-sequences than copolymer I. This explanation is further supported by the fact that copolymer II forms stronger, more compact and more hydrophobic hydrogen-bonding interpolymer complexes with polyacrylic acid at low pH, as it was revealed by viscometry, fluorescence and turbidity studies.

Association of hydrophobically modified positively charged N-isopropylacrylamide copolymers with the nonionic surfactant Triton X-100

The association in dilute aqueous solution of the nonionic surfactant t-octylphenoxy polyoxyethanol (Triton X-100) with hydrophobically modified copolymers based on an N-isopropylacrylamide (NIPAM) backbone is presented. The NIPAM-based copolymers contain also N,N-[(dimethylamino)propyl] methacrylamide (MADAP), the content x of MADAP varying from 0 up to 25 mol%, completely alkylated with dodecylbromide or octadecylbromide. The highly hydrophobic copolymers are characterised by a compact conformation in aqueous solution, due to the formation of intrachain hydrophobic aggregates. Association with Triton X-100 leads to the destruction of these intrachain aggregates and to their replacement by mixed alkyl/surfactant ones, revealed macroscopically by a gradual viscosity increase upon addition of surfactant. Fluorescence probing studies and dialysis equilibrium experiments confirmed that polymer/surfactant association starts in the vicinity of the critical micelle concentration (CMC) of Triton X-100.

Polymeric Quaternary Ammonium-Containing Coatings with Potential Dual Contact-Based and Release-Based Antimicrobial Activity

In the present work, reactive blending of copolymers with complementary functional groups was applied to control their antimicrobial activity and antifouling action in real conditions. For this purpose, two series of copolymers, poly(4-vinylbenzyl chloride-co-acrylic acid), P(VBC-co-AAx), and poly(sodium 4-styrenesulfonate-co-glycidyl methacrylate), P(SSNa-co-GMAx), were synthesized via free radical copolymerization and further modified by the incorporation of biocidal units either covalently (4-vinyl benzyl dimethylhexadecylammonium chloride, VBCHAM) or electrostatically bound (cetyltrimethylammonium 4-styrenesulfonate, SSAmC16). The cross-linking reaction of the carboxylic group of acrylic acid (AA) with the epoxide group of glycidyl methacrylate (GMA) of these two series of reactive antimicrobial copolymers was explored in blends obtained through solution casting after curing at various temperatures. The combined results from the ATR-FTIR characterization of the membranes, solubility tests, turbidimetry, and TEM suggest that the reaction occurs already at 80 °C, leading mostly to graft samples, while at higher curing temperatures (120 or 150 °C) insoluble cross-linked samples are usually obtained. Controlled release experiments of selected membranes were performed in pure water and aqueous 1 M NaCl solutions for a period of two months. The released material was followed through gravimetry and TOC/TN measurements, while the evolution of the integrity and the morphology of the membranes were followed visually and through SEM, respectively. Antimicrobial tests also revealed that the cross-linked membranes presented strong antimicrobial activity against S. aureus and P. aeruginosa. Finally, a specific blend combination was applied on aquaculture nets and cured at 80 °C. The modified nets, emerged in the sea for 15 and 35 days, exhibited high antifouling action as compared to blank nets.

A quantitative description of the viscometric behaviour of partially neutralized poly(acrylic acid) in aqueous solutions studied by the isoionic dilution method

Abstract The intrinsic viscosity, [η], and the Huggins constant, κ′, of a poly(acrylic acid) (PAA) sample have been measured at different degrees of neutralization, i, ranging from i=0.25 to i=1.00 and different ionic strengths, I, in the region 1.0 × 10−4 M

Multifunctional Polymeric Platform of Magnetic Ferrite Colloidal Superparticles for Luminescence, Imaging, and Hyperthermia Applications

Adequately designed multiresponsive water-soluble graft copolymers were used to serve as a multifunctional polymeric platform for the encapsulation and transfer in aqueous media of hydrophobic magnetic nanoparticles (MNPs). The backbone of the graft copolymers was composed of hydrophilic sodium methacrylate units, hydrophobic dodecyl methacrylate units, and luminescent quinoline-based units, while either the homopolymer poly(N-isopropylacrylamide) or a poly(N,N-dimethylacrylamide-co-N-isopropylacrylamide) copolymer was used as thermosensitive pendent side chains. The polymeric platform forms micellar-type assemblies in aqueous solution, and exhibits pH-responsive luminescent properties and a lower critical solution temperature behavior in water. Depending on the design of the side chains, the cloud point temperatures were determined at 38 and 42 °C, close or slightly above body temperature (37 °C). Above the critical micelle concentration (CMC), both graft copolymers can effectively stabilize in aqueous media as magnetic colloidal superparticles (MSPs), oleylamine-coated MnFe2O4 MNPs, as well as 1:1 mixture of oleylamine-coated MnFe2O4 and CoFe2O4 MNPs. When CoFe2O4 particles were mixed with MnFeO4 in equal amounts, the specific loss power increased significantly, while an opposite trend was observed in the magnetic resonance imaging (MRI) studies, probably due to the anisotropy of cobalt. As a consequence, fine-tuning of the chemical structure of the copolymers and the composition of the MSPs can lead to materials that are able to act simultaneously as luminescent, hyperthermia, and contrast MRI agents.

Micellar copolymerisation of N,N-dimethylacrylamide and t-butylacrylamide

A copolymer of the water-soluble hydrophilic monomer N,N-dimethylacrylamide and of the practically water-insoluble hydrophobic t-butylacrylamide was synthesised in aqueous solution in the presence of sodium dodecylsulfate (SDS) micelles. Its behaviour in dilute aqueous solution was compared to the behaviour of its respective counterpart with practically the same composition, prepared under homogeneous conditions in tetrahydrofuran. The product synthesised under micellar conditions exhibits a pronounced hydrophobic character, as it phase separates in water by increasing temperature at about 46°C, i.e. 29°C lower than the copolymer prepared under homogeneous conditions and associates much stronger with SDS.

Temperature-Sensitive Water-Soluble Hybrid Organic/Inorganic Nanoparticles Formed through Complexation of Cu2+ Ions with Poly(sodium acrylate)-g-poly(N-isopropylacrylamide) Comb-Type Copolymers in Aqueous Solution

The preparation of temperature-sensitive water-soluble hybrid organic/inorganic nanoparticles, exploiting the complexation of Cu2+ ions with PANa-g-PNIPAMx comb-type copolymers, is presented. These copolymers consist of a Cu2+-complexing poly(sodium acrylate) backbone, PANa, and thermosensitive poly(N-isopropylacrylamide), PNIPAM, side chains. UV-vis spectrophotometry verified that the polymer/Cu2+ complexation follows a charge neutralization process, while turbidimetry revealed that the complexes formed can indeed be stabilized in water, provided that copolymers with a sufficiently high PNIPAM content (x approximately 80 mol % in monomer units) are used. Dilute solution viscometry and dynamic light scattering indicated that the hydrodynamic dimensions of the hybrid polymer/Cu2+ nanoparticles decrease substantially upon heating, reflecting the lower critical solution temperature behavior of the PNIPAM side chains. However, when the net negative charge of the hybrid polymer/Cu2+ nanoparticles decreases, interparticle aggregation and, eventually, phase separation may take place. In semidilute aqueous solution, the complexation of the polymer backbone with Cu2+ ions effectively controls the thermothickening properties of the thermosensitive comb-type PANa-g-PNIPAM copolymers. Finally, the temperature-induced formation of a compartmentalized hydrophilic-hydrophobic nanocontainer, where the hydrophilic and the hydrophobic compartments can be loaded with Cu2+ ions and hydrophobic substances, respectively, was evidenced through pyrene fluorescence probing.