Influence of the reaction medium on the composition and the microstructure of styrene–acrylic acid copolymers

Two series of acrylic acid-styrene copolymers of various composition have been prepared in benzene and dimethylformamide in order to study their sequence distribution by using ¹³C NMR spectroscopy. The reactivity ratios in benzene were r_A = 0.13, r_A = 0.30 and in dimethylformamide r_A = 0.05, r_S = 1.60. Copolymers with the same overall composition but prepared in different media display marked differences in sequence distribution, the copolymers obtained in dimethylformamide always having longer sequences. For the series of copolymers prepared in dimethylformamide, the experimental percentages of acrylic acid-centered triads (SAS, SAA, AAA) disagree with the values calculated from the monomer reactivity ratios.     

Synthesis and micellar behavior of poly(acrylic acid-b-styrene) block copolymers

Poly(acrylic acid-b-styrene) (PAA-b-PS) amphiphilic block copolymers were synthesized by consecutive telomerization of tert-butyl acrylate, atom transfer radical polymerization (ATRP) of styrene, and hydrolysis. The resulting block copolymers were characterized by ¹H NMR and GPC. These amphiphilic block copolymeric micelles were prepared by dialysis against water. Transmission electron micrograph (TEM) and laser particle sizer measurements were used to determine the morphology and size of these micelles. The results showed that these amphiphilic block copolymers formed spherical micelles with average size of 140–190?nm. The critical micelle concentration (CMC) and the kinetic stability of these micelles were investigated by fluorescence technique, using pyrene as a fluorescence probe. The observed CMC value was in the range of 0.075–0.351?mg/L. Kinetic stability studies showed that the stability of micelles increased with the decrease of the pH value of the solution.     

Influence of metal ions on the alkali-swelling behavior of carboxylated acrylic polymer latexes

The alkalization of carboxylated acrylic polymer latexes by sodium hydroxide gives rise to swelling of the particles. For a poly(n-butyl acrylate) latex copolymerized with 15 wt % methacrylic acid (MAA) and 7 wt % acrylonitrile the particle volume increases by a factor of 30. The alkali-swelling does not depend on the type of monovalent cation used in the base (LiOH, NaOH, KOH, NH₄OH). In contrast, when bivalent cation bases such as Ca(OH)₂ are employed no latex swelling is observed during neutralization because of ionic crosslinking of the copolymer chains. Crosslinking also takes place when the bivalent cations (Ca²⁺, Zn²⁺, Mg²⁺) are added as chlorides to dispersions with latexes previously swollen by sodium hydroxide. In these experiments the original size of the latexes is reached again at a molar ratio MAA: bivalent metal ion of 2:1, i.e. at charge compensation of the carboxyl groups. The shrinking behavior is almost independent of the type of bivalent metal ion used. On the other hand, it is more pronounced when trivalent cations such as Fe³⁺ are added. In general, the experiments demonstrate that the alkali swelling of acrylic latexes is dominated by electrostatic forces. Received: 18 August 1998 Accepted in revised form: 26 October 1998     

Synthesis of glycolide/trimethylene carbonate copolymers: Influence of microstructure on properties

Copolymers of glycolide and trimethylene carbonate with different compositions and microstructures (i.e. random, blocky and segmented) were synthesized by two-step ring opening polymerization.NMR analyses revealed that transesterification reactions took place during the first step, which corresponded to the synthesis of soft segments, and mainly when the trimethylene carbonate content of the reaction medium was high. The transesterification percentage did not significantly change with the addition of hard blocks in the second reaction step. Infrared spectroscopy was a complementary, highly effective tool to evaluate the hard segment length, crystallinity and glycolide percentage incorporated into the crystalline phase for all studied samples.Calorimetric analyses showed dependency of properties on the length of the polyglycolide hard segment and also good miscibility between glycolide and trimethylene carbonate rich phases. Crystalline morphologies attained with segmented and random copolymers were significantly different, although in all cases a positive birefringence was detected.Thermogravimetric analyses indicated that all studied copolymers had a similar degradation behavior, which was intermediate between those observed in the corresponding homopolymers. Samples with a significant glycolide unit content showed a stabilizing effect for the degradation of poly(trimethylene carbonate) blocks.     

Influence of oxycycloaliphatic groups in the relaxation behavior of acrylic polymers

A comparative study on the mechanical and dielectric relaxation behavior of poly(5‐acryloxymethyl‐5‐methyl‐1,3‐dioxacyclohexane) (PAMMD), poly(5‐acryloxymethyl‐5‐ethyl‐1,3‐dioxacyclohexane) (PAMED), and poly(5‐methacryloxymethyl‐5‐ethyl‐1,3‐dioxacyclohexane) (PMAMED) is reported. The isochrones representing the mechanical and dielectric losses present prominent mechanical and dielectric β relaxations located at nearly the same temperature, approximately −80°C at 1 Hz, followed by ostensible glass–rubber or α relaxations centered in the neighborhood of 27, 30, and 125°C for PAMMD, PAMED, and PMAMED, respectively, at the same frequency. The values of the activation energy of the β dielectric relaxations of these polymers lie in the vicinity of 10 kcal mol⁻¹, ∼ 2 kcal mol⁻¹ lower than those corresponding to the mechanical relaxations. As usual, the temperature dependence of the mean‐relaxation times associated with both the dielectric and mechanical α relaxations is described by the Vogel–Fulcher–Tammann–Hesse (VFTH) equation. The dielectric relaxation spectra of PAMED and PAMMD present in the frequency domain, at temperatures slightly higher than T_g, the α and β relaxations at low and high frequencies, respectively. The high conductive contributions to the α relaxation of PMAMED preclude the possibility of isolating the dipolar component of this relaxation in this polymer. Attempts are made to estimate the temperature at which the α and β absorptions merge together to form the αβ relaxation in PAMMD and PAMED. Molecular Dynamics (MD) results, together with a comparative analysis of the spectra of several polymers, lead to the conclusion that flipping motions of the 1,3‐dioxacyclohexane ring may not be exclusively responsible for the β‐prominent relaxations that polymers containing dioxane and cyclohexane pendant groups in their structure present, as it is often assumed. The diffusion coefficient of ionic species, responsible for the high conductivity exhibited by these polymers in the α relaxation, is semiquantitatively calculated using a theory that assumes that this process arises from MWS effects, taking place in the bulk, combined with Nernst–Planckian electrodynamic effects, due to interfacial polarization in the films. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2486–2498, 1999     

Influence of the microstructure of acrylic acid-n-butyl acrylate copolymers prepared by pseudoliving radical polymerization by the reversible addition-fragmentation chain transfer mechanism on their surface activity in aqueous solutions

The influence of the microstructure of acrylic acid-n-butyl acrylate copolymers prepared by pseudoliving radical polymerization by the reversible addition-fragmentation chain transfer mechanism on their surface activity in aqueous solutions was studied. The mechanisms of adsorption of polymer macromolecules on the phase boundary, accounting for the difference in the behavior of the random and block copolymers, were suggested. The dependence of the surface activity on the chain flexibility was elucidated. This dependence is very significant for the random copolymers and insignificant for the block copolymers.     

Modelling the microstructure of emulsion copolymers

A simple model for predicting the microstructure of emulsion copolymers is presented. The model, which is based on the Markov processes, allows the prediction of the copolymer sequence distribution as accurately as the previous complex model.     

Blends of styrene/acrylic acid copolymers and acrylic polymers

The miscibility of a series of styrene/acrylic acid copolymers with various polyacrylate and polymethacrylate homopolymers, as well as a series of styrene/methyl methacrylate copolymers, has been investigated. According to the binary interaction model, the miscibility diagram for styrene/acrylic acid copolymers with styrene/methyl methacrylate copolymers indicates that acid and ester groups interact endothermically. The phase behavior of the homopolymers also implies this. The analysis ignores the association and self-association observed for the polymer blends and the low-molecular-weight analogs used to model them. The heat of mixing of low-molecular-weight analogs depended greatly on both composition and acid structure.     

Influence of the draw ratio on the tensile and fracture behavior of NMMO regenerated silk fibers

The tensile properties and fracture surfaces of N‐methylmorpholine‐N‐oxide (NMMO) regenerated silk fibroin fibers produced with a range of draw ratios has been characterized and related to their microstructure with data obtained from Raman spectroscopy and birefringence measurements. The spinning process allows control of two different draw ratios, coagulation, and postspinning, and it has been found that the microstructure and the properties of the fibers can be modified by the proper combination of both draw ratios. NMMO regenerated silk fibroin fibers subjected to postspinning drawing yield tensile properties comparable to other regenerated fibers and strain at breaking comparable to natural Bombyx mori silk fibers. Tensile strength; however, is still significantly lower than that of natural fibers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2568–2579, 2007     

Influence of microstructure on the hydrodynamic behavior of poly-α-methylstyrene

The theta temperature of poly-α-methylstyrene in cyclohexane has been found to vary with the stereostructure of the polymer. The observed values range from 305.5°K. for highly syndiotactic material (0.95 syndiotactic diads) to 310.0°K. for anio ically polymerized samples (0.67 syndiotactic diads). Results indicate that the unperturbed dimensions of the polymer increase with increasing isotacticity of the chain, whereas the entropy parameter ψ₁, measured in cyclohexane, decreased as the structure became more isotactic. Measurements of the second virial coefficient in toluene showed an increasing interaction with the solvent as the polymer became more syndiotactic.     

Evaluation of molecularly imprinted membranes based on different acrylic copolymers

Polyacrylonitrile and its copolymers with different functional monomers (itaconic acid, acrylic acid and acrylamide) were synthesized via water-phase precipitation polymerization in order to prepare molecularly imprinted polymer (MIP) membranes with recognition properties for the flavonoid naringin (NR). Membranes were prepared by phase inversion technique using dimethylformamide (DMF) as the solvent and adding naringin as template molecule to the casting solution. For comparison, membranes without template (blank) were prepared and tested. All MIP membranes showed high specific binding capacity; among them, the membrane prepared with the copolymer containing acrylamide as functional group, showed the highest binding capacity. Blank membranes only showed non-specific binding. The bound template was totally recovered and regenerated membranes maintained their initial binding capacity after reuse.     

Glass-transition in donor and acceptor acrylic copolymers

Tg vs. composition studies on acrylic(methacrylic) copolymers of donor 2-(9-carbazolyl)ethyl acrylate(methacrylate) and of acceptor 2(3,5-dinitrobenzoyloxy)ethyl acrylate(methacrylate) have evidenced specific T_g vs. composition dependences. The acrylic(methacrylic) copolymers of the donor show always positive deviations from additivity of the T_g suggesting reduced mobility do to donor acceptor-like interactions. The T_g behaviour of the acceptor copolymers is much more complex showing an inversion from reduced to increased mobility of the copolymeric chain as the acceptor content is increased.     

Thermosensitive behavior of amphiphilic triblock copolymers based on poly(acrylic acid) and poly(propylene oxide)

Self‐association in aqueous solution of amphiphilic poly(acrylic acid)‐b‐poly(propylene oxide)‐b‐poly(acrylic acid) (PAA‐b‐PPO‐b‐PAA) copolymers having various outer PAA block lengths are presented. These copolymers show two thermosensitive behaviors. The first one, due to hydrogen bonds between PAA and PPO resulting in large aggregates, was observed by visible spectroscopy. The second one, due to the association of PPO middle block into aggregates, was evidenced by dynamic light scattering and pyrene fluorescence. These critical temperatures both depend on the ionization and the length of PAA blocks. The characterization of the aggregates above the critical aggregation concentration by fluorescence quenching experiments showed a very low aggregation number corresponding to dimers or trimers association depending on the conditions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1507–1514     

Influence of various series of additives on the clouding behavior of aqueous solutions of triblock copolymers

The cloud point (CP) studies on aqueous solutions of two ethylene oxide-propylene oxide triblock copolymers (EO)_2.5(PO)₃₁(EO)_2.5 and (EO)₁₃(PO)₃₀(EO)₁₃ with varying number of ethylene oxide (EO) units were carried out in the presence of series of additives, such as alkali, acids, ionic surfactants, alcohols, salts, and hydrotropes. The results of this study show that sodium hydroxide decreases the CP of the two copolymers. Acids increase the CP in the order hydrochloric acid > acetic acid > formic acid for both the triblock copolymers. Hydrotropes increase the CP, whereas salts decrease or increase the CP based on their salting-out/salting-in nature. Alcohols, which are polar organic additives, affect the CP of the two copolymers differently. The change in the CP of the triblock copolymers depends upon the structure and concentration of the additives and on the number of EO units of the two triblock copolymers.     

Effect of butyl lactate methacrylate content on the properties of acrylic acid copolymers

In the present work, the effect of butyl lactate methacrylate (BLM) content on the properties of acrylic acid (AA) copolymers was investigated. The BLM monomer was synthesized by reacting butyl lactate with methacrylic acid through azeotropic distillation method, which was confirmed by Mass spectrometric technique. Copolymers were synthesized by free-radical solution polymerization technique to obtain poly(BLM-co-AA). BLM monomer and copolymers were characterized by Fourier transform infrared (FTIR), ¹H-nuclear magnetic resonance (¹H-NMR) and proton decoupled ¹³C-NMR spectroscopic techniques. The Finemann-Ross method was used to determine the reactivity ratio of AA and BLM and the values were found to be 0.79 and 0.39, respectively. The wide angle X-ray scattering (WAXS) studies exhibited that the increase in BLM content in copolymers, shifted the amorphous halo from 21.34° to 15.39° and also increased the average molecular interchain spacing (〈R〉) from 5.20 to 7.18 Å, which was calculated from 2θ values of amorphous halo of copolymers. Moisture absorption of polymers followed Fickian absorption. Depending upon the copolymer composition, relative humidity and time, the moisture absorption of copolymers can be tuned to a wide range from 11 to 35% (wt/wt). Glass transition temperature of copolymers decreased from 106 to 72.1°C with increase in BLM content. Copolymers were thermally stable up to 150°C and thereafter exhibited three-step thermal degradation in nitrogen atmosphere. Thermal stability of copolymers can be explained on the basis of 〈R〉 value.