Refined Continuous Thermodynamic Treatment for the Liquid-Liquid Equilibrium of Copolymer Solutions

Based on an improved calculation of activity coefficients, continuous thermodynamics using a generalized divariate Stockmayer distribution is applied to the liquid-liquid equilibrium of random copolymer solutions. The effects of the chemical polydispersity on the cloud-point curve, the shadow curve, the spinodal, and the critical point are discussed. The theory can account for the occurrence of three-phase equilibria as well as for the phase separation in pure copolymers.     

Cloud-Point Curve for the System Copoly(Ethylene-Vinyl Acetate) Plus Methyl Acetate. Measurement and Prediction by Continuous Thermodynamics

The cloud-point curve for the system copoly(ethylene-vinyl acetate) plus methyl acetate has been measured by a simple visual method. The critical point was determined by using the phase volume ratio method. The method of continuous thermodynamics was applied for thermodynamic treatment. The composition of the copolymer is described by a divariate distribution function assumed as a generalized Stockmayer distribution. The activity coefficients were obtained with the aid of the Huggins Chi -parameter concept assuming Chi to be a quadratic polynomial with respect to the weight-average chemical composition of the copolymer. The three model parameters were calculated from the critical point and the slope of the cloud-point curve at the critical point. The cloud-point curve and the shadow curve were predicted from these parameters. The cloud-point curve shows qualitative agreement with experimental data.     

Thermoreversible UCST-type phase behavior of comb-like poly(N-phenyl maleimide-co-n-octadecyl vinyl ether) in organic media

Comb-like copolymer of N-phenyl maleimide and n-octadecyl vinyl ether was synthesized by conventional free radical solution polymerization. The molecular weight and molecular weight distribution were measured by GPC. The chemical composition of copolymer was characterized by FT-IR, ¹H NMR and ¹³C NMR, and the results indicated that the obtained copolymer contained much more content of N-phenyl maleimide rather than equal molar ratio of monomer unit. The comb-like copolymer can exhibit upper critical solution temperature thermoresponsive phase behavior reversibly in N,N-dimethylformamide and some proper alcohols such as 1-butanol, 1-hexanol, etc. The effect of polymer concentration and co-solvent on thermoresponsive behavior of polymer solution was investigated, and the cloud point of polymer solution can be tuned conveniently. The high resolution ¹H NMR method was used to comprehend the reversible thermoresponsive behavior in molecular level, and the results revealed that as temperature decreased the pendent long alkyl side chain aggregated and phase separation occurred at cloud point temperature; however, the mobility of main polymer chain decreased at lower temperature.     

Copolymerization of Ethylene and Propylene Using Silicon Tetrachloride‐Modified Silica/MAO with Et[Ind]2ZrCl2 Metallocene Catalyst

For the copolymerization of ethylene with propylene or a higher α‐olefin, using Et[Ind]₂ZrCl₂ metallocene catalyst, modification of silica with silicon tetrachloride prior to MAO adsorption can increase the activity, which is more pronounced for ethylene/1‐hexene copolymerization at higher pressure and temperature. The molecular weight of the copolymer produced was lower and the polydispersity tends to be decreased. No significant effect of SiCl₄ addition on the microstructure and the chemical composition distribution of the copolymer produced was observed.     

Determination of composition distribution of acrylonitrile-styrene copolymers by thin-layer chromatography

Determination of chemical composition distribution of acrylonitrile-styrene copolymers was carried out by thin-layer chromatography (TLC). A mixture of benzene and methyl ethyl ketone gave the most suitable calibration curve of R_f values versus acrylonitrile (AN) contents, where a concentration gradient technique was applied for development. Average AN contents obtained by TLC are coincident with those found by elemental analysis. The copolymers extracted from ABS resins are sufficiently arranged in the order of breadth of composition distribution by using the data from TLC. The agreement between the composition distribution curve and that from the theory of copolymerization is good.     

Calculation of critical points not requiring the derivatives of the Gibbs energy demonstrated for a mixture of two homopolymers with the corresponding copolymer

The method for the calculation of phase diagrams (spinodal, binodal and tie lines) exclusively on the basis of the Gibbs energy of mixing, ΔG, with no need of calculating its derivatives with respect to the composition variables was extended to determine the critical conditions and the condition of the stability of the critical points. The method is applied to a ternary mixture of two homopolymers with a copolymer consisting of the same monomers. The sequence distribution of the copolymer is kept constant between random and purely alternating, and phase diagrams are calculated for different chemical compositions of the copolymer. Three critical lines were found within a very small interval of the copolymer composition.     

Column fractionation of acrylonitrile-styrene copolymers

An acrylonitrile-styrene copolymer having 51.4 wt % acrylonitrile content was fractionated using dimethylformamide and a toluene–n-propanol mixture as solvent and nonsolvent, respectively. From characterization of the fractions, it is shown that the copolymer was fractionated principally in accordance with composition. The weight distribution curve of the copolymer was expressed as a function of both molecular weight and chemical composition on a two-dimensional contour map. The same plotting technique was applied to a copolymer having nearly the azeotropic composition.     

Liquid-Liquid Equilibrium of Polydisperse Copolymer Solutions. Multivariate Distribution Functions in Continuous Thermodynamics

In addition to the usual polydispersity with respect to molar mass, copolymers show chemical polydispersity. Thus, the species present may not be adequately characterized by a single variable, and a divariate distribution function has to be applied for describing the composition of the copolymer. In continuous thermodynamics, such continuous distribution functions are used directly (without splitting into pseudocomponents) for describing the composition of complex multicomponent systems. Whereas until now usually only one distribution variable has been used in continuous thermodynamics, consideration of copolymers requires an extension to divariate distribution functions. Continuous thermodynamics is generalized to divariate distribution functions in this paper. The liquid-liquid equilibrium of copolymer solutions is considered as a specific example.     

Quantifying and Controlling the Composition and ‘Randomness’ Distributions of Random Copolymers

The effect of disparity in the reactivity ratios of monomer pairs on the composition distribution and microstructure of the resultant copolymer formed through free‐radical polymerization is quantified computationally. This correlation has been determined for the monomer pairs of styrene/methyl methacrylate and styrene/2‐vinyl pyridine for a variety of monomer feed ratios. These monomer pairs were chosen as they represent systems that have been utilized to experimentally examine the importance of copolymer architecture on its ability to compatibilize an immiscible polymer blend. Moreover, their respective random copolymers show conflicting results for this examination. The results of this work show that the difference in the reactivity ratios of styrene and 2‐vinyl pyridine copolymer (r₁ = 0.5, r₂ = 1.3) significantly broadens the composition and randomness distribution of the resultant copolymer. This breadth is not easily avoided as it evolves even in the early stages of the copolymerization. Conversely, for the styrene/methyl methacrylate pair, the reactivity ratios are similar (r₁ = 0.46, r₂ = 0.52) and this results in a copolymer with a narrow composition distribution and sequence distribution dispersion. Stopping the polymerization at early conversion further narrows both distributions. The presented results, therefore, provide fundamental information that must be considered when planning an experimental procedure to evaluate the relative importance of sequence distribution and composition distribution of a random on its application.     

Synthesis of thermo- and pH-sensitive star-shaped poly(2-alkyl-2-oxazoline) and its properties in aqueous its properties in aqueous solutions with varying medium acidity

Abstract

pH-sensitive eight-arm star-shaped polymer with calix[8]arene core and block copolymer of poly(2-methoxycarbonylethyl-2-oxazoline) and poly(2-isopropyl-2-oxazoline) arms was synthesized for the first time. The block composition was 1:1 and molar mass was 24000?g?mol^?1. The behavior of synthesized star in aqueous solutions was analyzed by turbidity and light scattering at the pH values from 2 to 12.2. It is shown that in an organic solvent, the polymer molecule has a low shaped asymmetry. In aqueous solutions, the synthesized star exhibits thermosensitivity with a lower critical solution temperature. It was found that at low temperature in solutions, there were macromolecules and aggregates which were formed due to interaction of hydrophobic cores. The phase separation temperatures did not depend on pH in basic media and decreased strongly at pH <5.     

Copolymerisation a l'etat cristallise des acides acrylique et methacrylique

Acrylic acid (A Ac) and methacrylic acid (MA Ac) form a eutectic mixture for the equimolecular composition; its melting point is ?30°. Most polymerization experiments were carried out at ?37° with gamma-ray initiation. The irradiation of the eutectic mixture generates a random copolymer with a narrow distribution of compositions and containing 80% MA Ac. In solid mixtures which contain an excess of MA Ac with respect to the eutectic, the reaction product is essentially the same copolymer as generated in the eutectic, the rate of polymerization in MA Ac crystals being negligible as compared with the reaction in the eutectic. When A Ac is in excess, the phenomena are more complex. A pronounced minimum is observed in the rate vs composition curve at ca 20 mole % MA Ac. Fractionation of the reaction product demonstrates the presence of a block copolymer built by sequences of A Ac and of random copolymer. An interpretation is suggested to account for the various results.     

Phase behaviour and miscibility window in UCST-type blends of poly(styrene-co-acrylonitrile) and tetramethylbisphenol A oligosulfones

The pressure–volume–temperature (PVT) behaviour of styrene–acrylonitrile (SAN) random copolymers and of tetramethylbisphenol A oligosulfones (TMOS) was studied using the Flory–Orwoll–Vrij (FOV) as well as the Sako–Wu–Prausnitz (SWP) equation-of-state (EOS). It was found that the SWP EOS is superior to the FOV theory in describing the PVT behaviour of the polymers, especially in the high-pressure range. Furthermore, blends comprising TMOS and SAN copolymers of varying acrylonitrile content were studied by means of cloud point measurements and differential scanning calorimetry. The system shows pronounced miscibility-window behaviour, i.e. the miscibility depends strongly on the copolymer composition. At the edges of the miscibility window, UCST (upper critical solution temperature) behaviour was observed and discussed in terms of the FOV EOS. The cloud point curves were exceptionally broad and could be reproduced neither by the Flory–Huggins nor by the FOV theory. However, taking the polydispersity of both components into account, the calculation of correct phase diagrams was possible using the FOV theory. Exchange energy parameters between the polymers, X_AB, were obtained from fitting the critical points of the phase diagrams. Additionally, segmental exchange energy parameters X_i/j of the components were calculated.     

Brush macro‐RAFT agent mediated dispersion polymerization of styrene in the alcohol/water mixture

Dispersion RAFT polymerization of styrene in the alcohol/water mixture mediated with the brush macro‐RAFT agent of poly[poly(ethylene oxide) methyl ether vinylphenyl‐co‐styrene] trithiocarbonate [P(mPEGV‐co‐St)‐TTC] with similar molecular weight but different chemical composition is investigated. Well‐controlled RAFT polymerization including an initial slow homogeneous polymerization and a subsequent fast heterogeneous polymerization at almost complete monomer conversion is achieved. The molecular weight of the synthesized block copolymer increases linearly with the monomer conversion, and the polydispersity is relatively narrow (PDI < 1.3). The RAFT polymerization kinetics is dependent on the chemical composition in the brush macro‐RAFT agents, and those with high content of hydrophobic segment lead to fast RAFT polymerization. The growth of the block copolymer nano‐objects during the RAFT polymerization is explored, and various block copolymer nano‐objects such as nanospheres, worms, vesicles and large‐compound‐micelle‐like particles are prepared. The parameters such as the chemical composition in the brush macro‐RAFT agent, the chain length of the solvatophobic block, the concentration of the feeding monomer and the solvent character affecting the size and morphology of the block copolymer nano‐objects are investigated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3177–3190     

The Fractionation of Copolymers by Chemical Composition

Abstract

Phase diagrams for the system of methyl ethyl ketone, cyclo-hexane, and styrene-acrylonitrile copolymer were determined. The phase diagrams indicate that the copolymer may be fractionated by chemical composition in this system. Discussions of the thermodynamics are also presented, to show that copolymers can effectively be fractionated into fractions of different compositions if a system can be found in which the difference between the Flory interaction parameters (x parameters) of two constituents of the copolymer with solvent is sufficiently large. Theoretically, the fractionation of copolymer must always occur to a certain extent, depending both on chemical composition and molecular weight. The composition fractionation results of styrene-acrylonitrile copolymers are given to confirm the discussions.     

Dynamic Monte Carlo Simulation of ATRP in a Batch Reactor

A dynamic MC model was developed to simulate the polymerization kinetics and the detailed microstructure of copolymers made with ATRP in a batch reactor. The model was used to predict monomer conversion, average molecular weight, polydispersity index, and copolymer composition as a function of polymerization time. The model can also predict the distribution of molecular weight, chemical composition, and comonomer sequence length at any polymerization time or comonomer conversion. The simulation was used to explore the effects of rate constants and reactant stoichiometry on the microstructure of chains. Two copolymerization systems were chosen to demonstrate the effect of reactivity ratios and comonomer feed compositions on the final chemical composition distribution.

     

The mechanism of chemical degradation of polymers: Part III—The anomaly in the hydrolysis of glycolide copolymers

The data published on the chemical and enzymatic degradation of polyesters and some other polymers is analysed. Earlier studies on copolymers have shown that chemical stability changes monotonously with change in composition if the corresponding homopolymers differ in their sensitivity to the action of a degrading agent. The present work shows that anomalous dependence of chemical stability on copolymer composition is observed for a copolymer based on the isomeric monomers, glycolide and ethylene glycol oxalate. In this case the minimum in the chemical stability versus copolymer composition curve corresponds to the minimum in the copolymer melting temperature versus copolymer composition curve. A possible interpretation of the observed phenomenon is given.     

GPC Analysis of Ethylene-Propylene Copolymers

Abstract

Determination of the values of K and alpha of the Mark-Houwink equation by applying the universal calibration curve and using a trial and error method was performed with samples of ethylene-propylene copolymers with broad MW distributions and different intrinsic viscosities. The following equation was obtained, correlating K with composition of ethylene-propylene copolymer and alpha: logK = log(5.755-4.65C3)-5.75 alpha where C3 is the mole percent of propylene in the copolymer, alpha is a value within the range of 0.73 and 0.755 (i.e., K and alpha are dependent upon each other). Values of intrinsic viscosity or molecular weight determined by means of the universal calibration curve agree well with those determined by solution viscosity, light scattering, and osmometry.     

Aqueous solution properties of amphiphilic triblock copolymer poly(p-dioxanone-co-l-lactide)-block-poly(ethylene glycol)

A poly(ethylene glycol) (PEG)-based new amphiphilic block copolymer bearing the poly(p-dioxanone-co-l-lactide) (PPDO/PLLA) hydrophobic moieties was prepared. Depending on the copolymer composition and molecular weights, solubility of the polymeric samples in water was varied. Its diluted aqueous solution properties were studied by viscometry, dye solubilization, ¹H-NMR and dynamic light scattering. 1,6-Diphenyl-1,3,5-hexatriene solubilization and ¹H-NMR spectra carried out in CDCl₃ and D₂O were used to prove the existence of hydrophobic domains as the core of micelle. Average particle size of 60-165 nm with low polydispersity and lower negative zeta (ξ) potential of −3 to −14 mV were observed on the aqueous copolymer dispersion.     

Cross Fractionation of Styrene-Butadiene Copolymer

A sample of styrene-butadiene copolymer was fractionated by successive precipitation (one-direction fractionation) in cyclohexane/isooctane and benzene/methyl ethyl ketone systems. The chemical composition and molecular weight distributions of the sample were constructed from the fractionation data. The results obtained in both systems were nearly identical for the chemical composition distribution, but were different for the molecular weight distribution. The same sample was fractionated by cross fractionation using both solvent/nonsolvent systems. Comparing the results of cross fractionation with the results of one-direction fractionation, the first gave broader molecular weight and chemical composition distribution curves than the second. However, only cross fractionation showed that the chemical composition distribution curve has a long tail not only at the right side but also at the left side of the distribution maximum.

The superiority of cross fractionation over one-direction fractionation seems clear from the present work. It is also clear that even if the chemical composition distribution curves obtained by one-direction fractionation in different systems are identical with one another, the curves do not always show the true distribution.     

Use of a Programmable Pocket Calculator for Data Reduction in GPC: Calculation of Molecular Weights and Molecular Weight Distribution

Abstract

A short program was written for a pocket programmable calculator (HP-29C), to reduce data from a Gel Permeation Chromatogram. The output of this program consists of weight-and number-average molecular weights, polydispersity, and normalized weight distribution. All were uncorrected for dispersion. Mathematical approximation of the GPC calibration curve was made by exponential fit, also performed on the programmable calculator. The program and its application to NBS 706 and one narrow-molecular weight distribution (NMWD) polystyrene standards are presented. With slight modification, the program can be used on newer, more powerful calculators such as the HP-41C, on which dispersion correction subroutines could be performed.