Hydration changes of poly(2-(2-methoxyethoxy)ethyl methacrylate) during thermosensitive phase separation in water

Hydration changes of poly(2-(2-methoxyethoxy)ethyl methacrylate) (PMoEoEMa) during thermosensitive phase separation in water have been investigated by infrared spectroscopy. The C=O stretching band can be separated into three components assigned to non-hydrated carbonyl groups and singly and doubly hydrogen-bonded carbonyl groups (1728, 1709, and 1685 cm-1, respectively). Relatively large parts of the carbonyl groups (50% in 30 wt % solution) do not form hydrogen bonds even below the transition temperature (Tp) probably because they possess crowded positions near the backbone. The fraction of hydrogen-bonding carbonyl groups decreased during phase separation by approximately 0.2. Among five nu(C-H) bands, the highest- and the lowest-frequency bands (nu(C-H)A and nu(C-H)E) exhibited relatively large red shifts of 8 and 11 cm(-1), respectively. DFT calculations indicate that the formation of a H-bond between the ether oxygen and water leads to blue shifts of nu(C-H) of adjacent alkyl groups and has a larger effect than a direct H-bond to the alkyl groups, namely, C-H...O H-bonds. The fraction of hydrogen-bonding methoxy oxygens estimated from the position of the nu(C-H)A is 1 at Tp. This result indicates that the methoxy oxygens and the carbonyl are more favorably hydrated than the other at Tp, respectively.     

Temperature- and pH-responsive behaviour of poly(2-(2-methoxyethoxy)ethyl methacrylate-co-N,N-dimethylaminoethyl methacrylate) hydrogels

Hydrogels with pH/temperature responsiveness and high water uptake have been synthesized by the free radical polymerization of 2-(2-methoxyethoxy)ethyl methacrylate (MEO₂MA) with N,N-dimethylaminoethyl methacrylate (DMAEMA) in a low proportion. The amphiphilic character of the biocompatible MEO₂MA provides thermo-sensitivity at low temperature. On the other hand, DMAEMA units incorporate ionisable amino groups and hydrophobic moieties, leading by themselves to a dual pH and thermo-sensitive system. Therefore, the combination of both monomers yields an interesting system with tuneable pH/temperature responsiveness and swelling capacity, which depends on composition and ionic strength. Thus, the volume transition temperature (VTT) is suppressed at low pH due to the basic character of DMAEMA. However, at basic pH, where amino groups are not charged, lower swelling capacities and narrow thermal volume transitions were obtained. At neutral pH, higher modulation of both the swelling achieved and VTT was observed.     

Superhelices of poly[2-(acetoacetoxy)ethyl methacrylate

Poly[2-(acetoacetoxy)ethyl methacrylate] (PAEMA) homopolymers were found to self-assemble into hierarchical superstructures, that is, double-stranded helical tubes of either screw sense (scanning force microscopy). Both the diameter and the pitch of the superhelices are approximately 12 nm, and their length is 200-500 nm. It is proposed that PAEMA chains first organize into ribbons, the width of which determines the pitch of the helix, and then coil up into the helical superstructure. The formation of these structures is driven by the establishment of hydrogen-bridging interactions between adjacent acetoacetoxy groups (NMR and dielectric relaxation spectroscopy) and compensation of dipole moments.     

Thermally triggered assembly of cationic graft copolymers containing 2-(2-methoxyethoxy)ethyl methacrylate side chains

Thermoresponsive copolymers continue to attract a great deal of interest in the literature. In particular, those based on ethylene oxide-containing methacrylates have excellent potential for biomaterial applications. Recently, some of us reported a study of thermoresponsive cationic graft copolymers containing poly(N-isopropylacrylamide), PNIPAm, (Liu et al., Langmuir, 24, 7099). Here, we report an improved version of this new family of copolymers. In the present study, we replaced the PNIPAm side chains with poly(2-(2-methyoxyethoxy)ethylmethacrylate), PMeO(2)MA. These new, nonacrylamide containing, cationic graft copolymers were prepared using atom transfer radical polymerization (ATRP) and a macroinitiator. They contained poly(trimethylamonium)-aminoethyl methacrylate and PMeO(2)MA, i.e., PTMA(+)(x)-g-(PMeO(2)MA(n))(y). They were investigated using variable-temperature turbidity, photon correlation spectroscopy (PCS), electrophoretic mobility, and (1)H NMR measurements. For one system, four critical temperatures were measured and used to propose a mechanism for the thermally triggered changes that occur in solution. All of the copolymers existed as unimolecular micelles at 20 °C. They underwent reversible aggregation with heating. The extent of aggregation was controlled by the length of the side chains. TEM showed evidence of micellar aggregates. The thermally responsive behaviors of our new copolymers are compared to those for the cationic PNIPAm graft copolymers reported by Liu et al. Our new cationic copolymers retained their positive charge at all temperatures studied, have high zeta potentials at 37 °C, and are good candidates for conferring thermoresponsiveness to negatively charged biomaterial surfaces.     

Water soluble polyperoxides from 2-(2-methoxyethoxy)ethyl methacrylate: influence of molecular oxygen on thermoresponsive properties and thermal degradation

The 2-(2-methoxyethoxy)ethyl methacrylate and molecular oxygen react at 50 °C under high pressure in the presence of a radical initiator to give water soluble, thermoresponsive poly(2-(2-methoxyethoxy)ethyl methacrylate) peroxide (PMEO(2)MAP), which degrades highly exothermically. The polymer structure has been confirmed by spectroscopy, elemental analysis, calorimetry and mass spectrometry.     

Transformations of poly(methoxy hexa(ethylene glycol) methacrylate)-b-(2-(diethylamino)ethyl methacrylate) block copolymer micelles upon metalation

Micelle transformations upon metalation (i.e., incorporation of metal compounds and metal nanoparticle formation) in poly(methoxy hexa(ethylene glycol) methacrylate)-block-poly((2-(diethylamino)ethyl methacrylate)), PHEGMA-b-PDEAEMA, solutions have been studied using transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS). Three different methods for the formation of metalated micelles are compared: (A) dissolution of the block copolymers in pure water followed by incorporation of platinic acid (H(2)PtCl(6).6H(2)O), (B) micellization in acidic molecular solutions of block copolymers induced by interaction of the protonated amino groups with the PtCl(6)(2)(-) ions, and (C) incorporation of metal species in pH-induced micelles. The latter method leads to well-defined metalated micelles of 22-25 nm diameter containing nanoparticles with diameters of 1.3-1.5 nm. No nanoparticle aggregation is observed. Good agreement is obtained for the sizes of the platinic acid-containing micelles assessed by TEM and PCS.     

Synthesis and characterization of semi-interpenetrating polymer network based on poly(dimethylsiloxane) and poly[2-(dimethylamino)ethyl methacrylate]

A semi-interpenetrating polymer network (semi-IPN) based on poly(dimethylsiloxane) and poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) was prepared. The material obtained was characterized by infrared spectrometry, differential scanning calorimetry, thermogravimetric analysis and scanning electronic microscopy. The results indicated the presence of PDMAEMA into the semi-IPNs. Only the network with the highest amount of crosslinker [(3-chloropropyl)trimethoxysilane] was stable in water. To evaluate the hydrophilic/hydrophobic character of the obtained material, swelling measurements were performed for the stable network in water and in toluene. The semi-IPN was able to adsorb about 34 % in mass of water, indicating that an appropriate hydrophylic/hydrophobic balance was obtained. That behavior is desirable since the material was designed for metal adsorption from aqueous medium, without a lost in the ability to swell in less polar solvents.     

Terephthalic acid esterification kinetics: 2-(2-methoxyethoxy)ethyl terephthalates

The process of esterification of terephthalic acid is characterized by a mechanism that involves three equilibrium reactions. Two are esterification-hydrolysis equilibria entailing the reactions of the two terephthalic acid carboxyl groups with alcoholic hydroxyl groups, whereas the third one is a transesterification-acidolysis equilibrium that is concerned with the reaction between two terminal terephthalic acid moieties. The products of these three interrelated equilibria are terephthalic acid, its monoester and diester, the particular alcohol, and water. The alcohol used in the present study was 2-(2-methoxyethoxy)ethanol. Equilibrium constants and rate constants were developed from experimental data obtained at 230°C. The esterification-hydrolysis reactions were found to be catalyzed by carboxyl groups, and the rate of transesterification was found to be a function of the terephthalic acid concentration. With the constants developed, the system of nonlinear differential equations, as derived from the mechanism postulated, was integrated numerically using the Runge-Kutta method. Good agreement between calculated and experimental values was observed.     

Target grafting of poly(2-(dimethylamino)ethyl methacrylate) to biodegradable block copolymers

A series of copolymers composed of methoxy poly(ethylene glycol) and a hydrophobic block of poly(ɛ-caprolactone-co-propargyl carbonate) grafted with poly(2-[dimethylamino]ethyl methacrylate) was synthesized by combining ring opening polymerization, azide-alkyne click reaction, and atom transfer radical polymerization (ATRP). Well-defined copolymers with a target composition and a tailored structure were achieved via the grafting from approach by using a single catalytic system for both click reaction and ATRP. Kinetic studies demonstrated the controlled/living character of the employed polymerization methods. The thermal properties and self-assembly in aqueous medium of the graft copolymers were dependent on their composition. The resulting polymeric materials showed low cytotoxicity toward L929 cells, demonstrating their potential for biomedical applications. This type of materials containing cationic side chains tethered to biocompatible and biodegradable segments could be the basis for promising candidates as drug and gene delivery systems.     

Micellization and applications of narrow-distribution poly[2-(dimethylamino)ethyl methacrylate]

Oxyanion-initiated polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA), initiated by potassium benzyl alcoholate (BzOK), produced a number of well-defined, water-soluble benzyloxy end-capped homopolymers of various molecular weights. The structure of these homopolymers was confirmed by FTIR and ¹H NMR. The molecular weights of the polymers were estimated by comparing the ¹H NMR peak integrals for phenyl protons of the benzyloxy group with those of the dimethylamino protons of the monomeric unit. GPC analysis showed that these homopolymers possess a narrow molecular weight distribution ( ) in the range of 1.15–1.28. Under acidic or neutral conditions, the polymers exhibit the behavior of polymeric surfactants bearing protonized tertiary amines in their pendants, with critical micelle concentration (CMC) between 0.5 to 1 g/L and surface tension dropping below 40 mN/m. It was also found that the lower critical solution temperature (LCST) of the polymeric surfactants (as determined by UV-visible spectroscopy) varied with properties such as molecular weight, concentration, and pH in aqueous media. The polymeric surfactants showed excellent pH-response and emulsifier properties when used in the emulsion polymerization of styrene.     

Synthesis and characterization of original 2-(dimethylamino)ethyl methacrylate/poly(ethyleneglycol) star-copolymers

Novel synthetic transfection vectors with linear triblock and star-shaped diblock copolymer architectures have been synthesized by atom transfer radical polymerization (ATRP). Based on 2-(dimethylamino)ethyl methacrylate (DMAEMA) and copolymerization with poly(ethyleneglycol) α-methoxy, ω-methacrylate (MAPEG), the synthesis was realized using CuBr ligated with 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) as catalytic complex and either ethyl 2-bromoisobutyrate (EBⁱB) or bis(α-bromoisobutyryl) N-methyl diethanolamine (DEA) or tris(α-bromoisobutyryl) triethanolamine (TEA) as (multifunctional)initiator. The polymers were characterized by GPC and NMR. The solution properties of these homopolymers and palm-tree-like copolymers were investigated by viscometry either in pure water or in buffered aqueous solutions. Interestingly, all the synthesized polymers show polyelectrolyte effect in Millipore water (25 °C) and in Hepes (20 mM) buffer solution (pH 7.4, NaCl 155 mM, 25 °C). Fitting of these viscometric data according to either Fuoss or Fedors equation allows for calculating the intrinsic viscosity of the polymers. These results are compared with dynamic light scattering (DLS) experiments to determine absolute masses. Finally, DEA based palm-tree-like copolymer is investigated to AFM measurement and micelles were observed at pH 8.     

Dielectric study of low-temperature relaxations in poly(isobutyl methacrylate), poly(n-butyl methacrylate), poly(isopropyl methacrylate), and poly(4-methylpentene-1)

Isochronal measurements of dielectric constant and loss are made for poly(isobutyl methacrylate) (PiBMA), poly(n-butyl methacrylate) (PnBMA), poly(isopropyl methacrylate) (PiBMA), and poly(4-methylpentene-1) (P4MP1) at temperatures ranging from 4°K to 250°K. Loss peaks are found around 120°K (10–100 Hz) for PiBMA, PnBMA, and P4MP1. By comparing the activation energy with the calculated potential barrier for the internal rotation of alkyl group in the side chain, the motion responsible for the 120°K peak is concluded to be essentially the rotation of the isopropyl group as a whole for PiBMA and P4MP1 but, for PnBMA, the rotation of n-propyl group accompanied by the rotation of the end ethyl group. Multiple paths of internal rotation are involved with the 120°K peaks of PiBMA and, in particular, PnBMA, which explain differences between PiBMA and PnBMA in the broadness and the temperature location of the 120°K peak. The 120°K peak is in general assigned to a side chain including a sequence? O? C? C? C or ? C? C? C? C. PiPMA without this sequence in the side chain does not show the 120°K peak, but it exhibits the 50°K peak (1 kHz) like poly(ethyl methacrylate). The 50°K peak is assigned to the rotation of ethyl or isopropyl group attached to COO group. Poly-L-valine in which the isopropyl group is directly attached to carbon does not have the 50°K peak. An additional loss peak at 20°K (1 kHz) for P4MP1 is also discussed on the basis of the calculated potential.     

Thermal degradation of poly(ethyl methacrylate) and its copolymer with poly(ethyl acrylate)

The thermal degradation behaviour of poly(ethyl methacrylate) homopolymers and poly(ethyl methacrylate) and poly(ethyl acrylate) copolymers synthesized by using the benzoyl peroxide-di-methyl aniline redox pair at different temperatures (18–35C) was investigated. Contrary to some reports in the literature, the thermal degradation of PEMA was observed to take place in multi steps. These are assigned to be loss of labile end groups, side chain scission, anhydride formation and main chain degradation steps. Dominating chemical formations at the end of these steps were characterized by FTIR spectroscopy.The homopolymer samples synthesized at 18C showed a greater thermal stability against degradation. Copolymerization with small amounts of ethyl acrylate was observed to impart thermal stability to PEMA by stabilizing mainly the end groups against degradations.     

Intermolecular excimer formation in poly(2-naphthyl methacrylate) solutions

Efficient intermolecular excimer emission is observed for solutions of poly(2-naphthyl methacrylate) and copolymers of 2-naphthyl methacrylate and methyl methacrylate, only above a critical concentration. From analysis of the dependence of this concentration upon the polymer molecular weight and the thermodynamic character of the solvent, it is concluded that the results cannot be explained only in terms of an excluded volume effect, and that the different behaviour for dilute and concentrated regions is mainly a consequence of a change in the factors which control the rate of intermolecular excimer formation. The efficient excimer formation in the concentrated solutions is attributed to the contribution of migration of the excited energy to the formation of the excimeric pair.     

Sorption of light gases in glassy poly(ethyl methacrylate)

Although gas sorption in glassy polymers is a well‐studied phenomenon, no general microscopical model is developed which is able to describe the gas sorption in a wide temperature range using only characteristics of polymer and gas molecule. In this work, sorption isotherms and desorption kinetics of O₂, Ar, and N₂ for glassy poly(ethyl methacrylate) have been measured in the temperature range from 160 to 308 K. To describe both the phenomena, the model is developed which postulates that, in the frozen structure of glassy polymer, any cavities between macromolecules are the sorption sites for small molecules. The cavities of small size can expand elastically to accommodate a gas molecule. The sorption sites are considered to be the potential wells and their depths are distributed according to Gaussian law. The concentration of sorption sites, their mean depth and depths dispersion, and the frequency of molecules oscillations in the sorption sites are the only parameters which determine both the gas transport and sorption. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 288–296     

Insight into the origin of the thermosensitivity of poly[2-(dimethylamino)ethyl methacrylate].

We investigate the effects of pH and temperature on the conformational changes of poly[2-(dimethylamino)ethyl methacrylate] (PDEM) chains at the air/water interface by using Langmuir balance and sum frequency generation vibrational spectroscopy. At pH 4, the tertiary amine groups are fully charged and the PDEM chains are so hydrophilic that they completely enter into the water phase and do not exhibit thermosensitivity. At pH 7, these groups are only partially charged, and the accompanying hydration/dehydration--followed by repartitioning into the water and air phases--gives rise to a marked thermosensitivty. Finally, at pH 10, the tertiary amine groups become uncharged and thus preferentially stay in the hydrophobic air phase, devoid of associated water molecules, which results in the surface-pressure change (DeltaPi) being nearly independent of the temperature. Our Langmuir-balance experiments, coupled with surface-sensitive spectroscopy, demonstrate that: 1) the thermosensitivity of the PDEM chains relates to the hydration/dehydration of the tertiary amine groups, 2) the phase transition of thermosensitive polymers is most likely initiated by the dehydration of the chains, and 3) the phase transition of thermosensitive polymers at the air/water interface is markedly different from that in aqueous solution because of the redistribution of the macromolecular segments induced by the asymmetric forces at the air/water interface.     

Kinetic study of swelling of rubbery poly(ethyl methacrylate) networks in 2-hexanone

The kinetics of the swelling of cross-linked poly(ethyl methacrylate) gels in 2-hexanone was studied at temperatures varying from 70.0 to 85.0 °C. The sorption curves exhibit the characteristic features of transport processes, apparently the Fickian diffusion of fast rates. The data were analyzed successfully by the contemporary model of Li and Tanaka, resulting in the cooperative diffusion coefficient, D_c, and the ratio of the shear modulus to the longitudinal osmotic modulus. It has been established empirically that the D_c is a composite function consisting of an Arrhenius expression and two simple power laws of the number-average molecular weight between cross-links and the equilibrium volume fraction of the gel. On the basis of the present findings, the quality of the swelling agent is discussed.     

Fluorescence depolarization studies of micro-brownian relaxations of poly (methyl methacrylate) in solution

Fluorescence depolarization and quenching measurements have been used to study motions of poly(methyl methacrylate) in toluene at 298 K. Data concerning segmental motion of the polymer chain have been obtained using both an “ideal” label which cannot move independently of the macromolecule and a label in which independent motion should not result in depolarization of radiation. The results compare favourably. Motions affecting the ester group and terminal macromolecular segments also have been studied. The use of naphthalene derivatives as labels of limited bulk has been made possible by the use of dynamic quenching.