Acid–base Properties of Ion-exchange Resins. Dissociation and Swelling of Resin Copolymers of Methacrylic Acid,Methyl Methacrylate,Divinylbenzene, and Ethylvinylbenzene

The dissociation, capacity, swelling, and water content of crosslinked methacrylic acid—methyl methacrylate resins have been measured. Resins were prepared with different degrees of crosslinking for the same carboxylate content, and vice versa. The ionic strength of the external solution was also varied, and the behavior of commercial resins compared with that of the laboratory resins. Potentiometric titration curves were obtained, and curves were also obtained by back-titration of the salt form of the resins with acid. The capacities showed that almost all carboxyl groups are accessible in resins containing 2.5% or 4.0% divinylbenzene, but not in those containing 8% or 12%. For these highly crosslinked resins the back-titration curves differed from the forward curves. Apparent dissociation constants pK′_a = pH + n log [(1 ? α)/α] decreased with increased ionic strength, increased with increased crosslinking, and showed no trend with carboxylate content. Swelling is decreased by increased salt concentration, particularly for lightly crosslinked resins. Maximum swelling is achieved at about 80% dissociation. The reciprocal of the swollen volume is proportional to the per cent of divinylbenzene. Commercial resins showed much lower swelling than laboratory prepared resins ostensibly having the same composition. The Gibbs-Donnan theory of resin dissociation was applied to calculate the intrinsic dissociation constant (pK′₀). Assuming a model of randomly kinked chains dissolved in the sorbed solution, good agreement with the expected value of 4.85 was found (calcd. pK′₀ = 4.81 = 0.14), except for the most highly crosslinked resins. For polyampholyte resins, agreement was found by using a model having a uniform potential distribution throughout the resin (pK′₀ = 4.9).     

Following cellulose depolymerization in paper: comparison of size exclusion chromatography techniques

The study focuses on the comparison of the results obtained by size exclusion chromatography (SEC) detection systems using multiangle laser light scattering (MALLS) and/or ultraviolet–visible (UV/VIS) detectors in analyses of cellulose in paper-based heritage objects. The commonly applied parameter for the evaluation of paper degradation stage and kinetics is weight (M _w ) average molar mass measured by SEC. The main problems addressed here are whether the parameters obtained by various techniques and calibration strategies and in various laboratories can be treated universally and what the sources of the discrepancies can be. The SEC-UV/VIS technique proved to give reproducible results as demonstrated by the interlaboratory correlations. Using various data processing methods and SEC techniques it was also shown that molar masses should only be treated relatively. The differences between the kinetic curves based on the M _w values obtained from various techniques and processed with various calibration procedures question the reliability of kinetic equations derived using the SEC results to describe the paper degradation.     

Solution properties of semirigid polyquinolines. I. Size-exclusion chromatography with light-scattering detection of poly[2,2′-(P,P′-oxydi-P-phenylene) 6,6′-oxybis(4-phenylquinoline)]

An aromatic semirigid polyquinoline, poly[2,2′-(p,p′-oxydi-p-phenylene) 6,6′-oxybis(4-phenylquinoline)], has been studied in dilute solution using viscometry, light scattering, and size-exclusion chromatography coupled with low-angle light-scattering detection (SEC/LALS). The SEC/LALS technique permits determination of the intrinsic viscosity and absolute molecular weight for a series of narrow fractions without preparative fractionation. Aggregation that was observed in dilute chloroform solutions was found to be related to protonation of the polyquinoline by HCI present in chloroform. Unperturbed dimensions calculated from the SEC/LALS results show the chain to have nearly freely rotating dimensions, as expected for a chain composed of long (12-Å) rigid segments connected by ether linkages.     

Synthesis by ATRP of triblock copolymers with densely grafted styrenic end blocks from a polyisobutylene macroinitiator

A macroinitiator was prepared from a triblock copolymer of polyisobutylene (PIB) with end blocks of poly(p‐methylstyrene) (P(p‐MeS)) by bromination to obtain initiating bromomethyl groups for atom transfer radical polymerization (ATRP). Controlled polymerization of styrene and p‐acetoxystyrene yields new triblock copolymer structures with densely grafted end blocks. Simultaneously, however, thermally initiated polymerizations can be observed by size exclusion chromatography (SEC) which were also controlled yielding low molecular weight polymers with narrow distributions. A tendency to crosslinking can be suppressed by selection of the polymerization conditions.     

Kinetics Characterization of Ion Release under Dynamic and Batch Conditions. I. Weak Acid and Weak Base Ion Exchange Resins

The aim of the present work is concerned with a study of the kinetics of release of both Ca²⁺ and F⁻ from the corresponding loaded ion-exchange resins (weak acid and weak base character for Ca²⁺ for F⁻, respectively), using both dynamic and batch experimental conditions with an artificial saliva solution as the ion-exchange media at 293 and 310 K. The influence of resin particle size and the temperature were evaluated by the kinetics parameters for the effective rate of release (B) and diffusion coefficient (D). The rate of ion release increases with temperature and decreases with particle size. The experimental data were well fitted by models based on intraparticle diffusion-controlled processes. In dynamic studies, the linear dependence of −log ₁₀(B) with the diameter of the resin particles can be applied for the estimation of B values when resins of low particle size are considered. In batch processes, although resins of low particle size can be studied, a linear relationship was only attained for the case of slow ion-exchange kinetic systems.     

SIZE EXCLUSION CHROMATOGRAPHIC COLUMN PACKED WITH REGENERATED CELLULOSE GELS*

Microporous regenerated cellulose gel particles were prepared by mixing cellulose cuoxam with silk fibroin aspore former, and the mean pore size and pore volume of the pallicles were 525 nm and 7.27 mL g~(-1), respectively. Apreparative size-exclusion chromatography (SEC) column (550 mm×20 mm) packed with the cellulose gel particles wasused for the fractionation of two polysaccharides Dextran 07 (M_w = 7.14×10~4, d= 1.7) and Dextran 50(M_w = 50.5×10~4,d = 3.8) in water phase. The fractionation range of the stationary phase covered M_w from 3×10~3 to 1.1×10~6. The dailythroughput was 2.9 g for Dextran 07 (D07) and 4.3 g for Dextran 50 (D50) with a flow-rate of 1.5 mL min~(-1). The fractionsobtained by using the SEC were analyzed by an analytical SEC combined with laser light scattering (LLS), and thepolydispersity indices of fractions for Dextran 07 and Dextran 50 were determined to be 1.34-1.57 and 1.53-3.36,respectively. The preparative SEC is a simple, rapid, and suitable means not only for the fractionation of polysaccharides inwater but also for other polymers in organic solvents.     

Elution Behavior of Oligomers on a Polyvinyl Alcohol Gel Column with Chloroform,Methanol, and Their Mixtures

Abstract

Elution phenomena of size exclusion chromatography (SEC) plus superimposed adsorption effects for oligostyrenes, epoxy resins, methylated melamine-formaldehyde resin prepolymers, p-cresolformaldehyde resin prepolymers, and phenol-formaldehyde resin prepolymers were investigated. SEC and superimposed adsorption effects could be elucidated from a concept of solubility parameter. Minimum retention volumes of these oligomers were obtained with the mobile phases of chloroform/methanol, 80/20 or 60/40 (v/v), and separation was expected to be mostly performed by SEC. The solubility parameter of polyvinyl alcohol gels was estimated to be between 21 and 23 from the above results. Elution for normal phase chromatography was in the order of increasing molecular weight and that for reversed-phase chromatography was in the order of decreasing molecular weight. These are reversed phenomena to those for low-molecular weight compounds. Solubility of sample solutes to mobile phase must be considered. Methanol mobile phase-polyvinyl alcohol gel system might be exception.     

Molecular weight characterization of soluble high performance polyimides. 2. Validity of universal SEC calibration and absolute molecular weight calculation

Six different soluble high-performance aromatic polyimides, each prepared by solution imidization to three controlled average molecular weights, were analyzed by size exclusion chromatography (SEC) using on-line parallel coupled refractometric and viscometric detectors. N-methylpyrrolidone (NMP) with 0.06 M LiBr and NMP stirred over P₂O₅ were used as mobile phase for four of the polyimides; NMP with 0.06 M LiBr and NMP stirred over P₂O₅ were used as mobile phases for four of the polyimides; NMP with 0.06 M LiBr tetrahydrofuran (THF) and chloroform served as mobile phases for the other two polyimides. For all the samples the stationary phase in the SEC columns was cross-linked polystyrene beads. Molecular weight averages of the polyimides were calculated using universal SEC calibration with polystyrene standards in each solvent. The agreement of the calculated molecular weight averages in the different solvents confirms that the universal SEC calibrations are valid for these semiflexible polymers. There was good agreement with weightaverage molecular weights obtained by low-angle laser light scattering (LALLS) performed in pure NMP. Intrinsic viscosity and molecular weight data for a series of nine samples of one polyimide covering a M_w = 20,000–70,000 g mol^–1 interval were treated to obtain Mark-Houwink-Sakurada constants. Unperturbed chain dimensions of this polyimide were obtained by application of the Stockmayer-Fixman extrapolation procedure to these data. ©1995 John Wiley & Sons, Inc.     

Possibilities and pitfalls in analyzing (upgraded) pyrolysis oil by size exclusion chromatography (SEC)

The applicability of size exclusion chromatography (SEC) to analyze (upgraded) pyrolysis oil samples has been studied using model compounds, pyrolysis oils and hydrodeoxygenated pyrolysis oils. The assumptions needed for the conversion of the chromatogram to the M_w-distribution were validated. It was shown that the conversion of elution volume to molecular weight (based on polystyrene calibration curves) can introduce substantial errors in the prediction of the molecular weight. The conversion of RID response to W(log M) (as plotted on the y-axis of the M_w-distribution) is based on the assumption of a compound independent RID response factor and linear response to concentration. While the latter was shown to be true within the concentration range studied, the former was not true: the RID response factor depends on the type of (upgraded) pyrolysis oil. It was shown that within a single pyrolysis oil sample, the RID response for the low molecular weight fraction was a factor 3 lower than the high molecular weight fraction. Furthermore long term column fouling can influence SEC results that cannot be corrected with regular polystyrene recalibrations.Based on the results we recommend SEC not to be used as a quantitative method for characterization (upgraded) pyrolysis oil samples, but as a tool to compare (upgraded) pyrolysis oil samples, preferably prepared using incremental operating conditions and expected to have similar molecular composition. This work has further shown that (i) the ∫UVDdv/∫RIDdv ratio can be used as an indication of the sum of the relative aromaticity and conjugated double bond content for (upgraded) pyrolysis oil, and (ii) the negative peak area appearing in the low molecular weight part of the chromatogram can be used to estimate the water content of (upgraded) oil samples.     

Semimicro Size Exclusion Chromato-Graphy For Oligomers. II. Separation of Oligomers and Comparison With Conventional Columns

Abstract

Sixteen columns of 1.5 mm i.d. × 25 cm length packed with polystyrene gels of a particle diameter 10 ± 2 μm and having the exclusion limit of 8000 molecular weight as polystyrene were connected in series and used for the separation of oligomers such as oligostyrenes, epoxy resins, methylated melamine-formaldehyde resins, and phenol-formaldehyde resins of novolac and resol types. The observed overall value of the number of theoretical plates was 103000 plates/4 m. Separation results were compared with the conventional SEC which used two SEC columns of 8 mm i.d. × 30 cm length packed with PS gels of a particle diameter 6 ± 2 μm and having the same exclusion limit of the semimicro SEC. The value of N of this column was 17500 plates/30 cm. Oligostyrenes up to n = 11 (undecamer) were separated. Methyl ether derivatives of polynuclear methylol melamines up to penta-nuclear methylol melamine were separated. The possibility for separation of overlapping peaks by SEC having clearly higher efficiency was discussed.     

pH‐Responsive ampholytic terpolymers of acrylamide,sodium 3‐acrylamido‐3‐methylbutanoate,and (3‐acrylamidopropyl)trimethylammonium chloride. I. Synthesis and characterization

Low-charge-density ampholytic terpolymers composed of acrylamide, sodium 3-acrylamido-3-methylbutanoate (NaAMB), and (3-acrylamidopropyl)trimethylammonium chloride were prepared via free-radical polymerization in 0.5 M NaCl to yield terpolymers with random charge distributions. NaOOCH was used as a chain-transfer agent during the polymerization to eliminate the effects of the monomer feed composition on the degree of polymerization (DP) and to suppress gel effects and broadening of the molecular weight distribution. The terpolymer compositions were obtained via ¹³C NMR spectroscopy, and the residual counterion content was determined via elemental analysis for Na⁺ and Cl⁻. The molecular weights (MWs) and polydispersity indices (PDIs) were determined via size exclusion chromatography/multi-angle laser light scattering (SEC–MALLS); the terpolymer MWs ranged from 1.3–1.6 × 10⁶ g/mol, corresponding to DPs of 1.6–1.9 × 10⁴ repeat units, with all terpolymers exhibiting PDIs of less than 2.0. Intrinsic viscosities determined from SEC–MALLS data and the Flory–Fox relationship were compared to intrinsic viscosities determined via low-shear dilute-solution viscometry and were found to agree rather well. Data from the SEC–MALLS analysis were used to analyze the radius of gyration/molecular weight (R_g–M) relationships and the Mark–Houwink–Sakurada intrinsic viscosity/molecular weight ([η]–M) relationships for the terpolymers. The R_g–M and [η]–M relationships revealed that most of the terpolymers exhibited little or no excluded volume effects under size exclusion chromatography conditions. Potentiometric titration of terpolymer solutions in deionized water showed that the apparent pK_a value of the poly[acrylamide-co-sodium 3-acrylamido-3-methylbutanoate-co-(3-acrylamidopropyl)trimethylammonium chloride] terpolymers increased with increasing NaAMB content in the terpolymers and increasing ratios of anionic monomer to cationic monomer at a constant terpolymer charge density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3236–3251, 2004     

三嵌段共聚物PS-PHB-PS的原子转移自由基聚合

为了克服聚β-羟基丁酸酯(PHB)的弱点, 得到性能良好的新材料, 本文利用原子转移自由基聚合方法, 以Br-PHB-Br为大分子引发剂, 苯乙烯为单体, 在CuBr/N,N,N′,N″,N″-五甲基–二乙基三胺(PMDETA)催化体系作用下合成了一种新的三嵌段共聚物聚苯乙烯-聚β-羟基丁酸酯-聚苯乙烯(PS-PHB-PS). 共聚物的链结构利用¹H NMR和¹³C NMR进行了表征, 分子量特性和链段组成利用凝胶渗透色谱(SEC)方法进行了测定. 聚合物的分子量随单体转化率的增加而线性增加, 分子量分布指数相对较窄. 这些特征都满足原子转移自由基活性聚合的理想要求. 所得到的共聚物PS-PHB-PS具有较好的生物相容性, 与PHB相比具有良好的耐热性.     

Effect of tacticity on conformation of p-tert-butylphenol acetaldehyde resins as studied by molecular simulation

p-tert-Butylphenol acetaldehyde resins can have isotactic, syndiotactic, and atactic sequences. Structural characteristics of the p-tert-butylphenol acetaldehyde resin with different tacticities were studied using molecular mechanics and molecular dynamics. Trimer–decamer isotactic and syndiotactic resins and 12 stereoisomers of a hexamer were calculated. In the p-tert-butylphenol acetaldehyde resin, the hydroxyl groups cluster in the center of the molecule through intramolecular hydrogen bonding and the tert-butyl groups are extended out. It has been found that the energy-minimized structures of the isotactic resin are more stable than those of the syndiotactic resin by 7–17 kcal/mol. From the results of molecular dynamics at 303, 373, 474, and 573 K for 300 ps, the isotactic resin was also found to be more stable than the syndiotactic resin. For atactic resins, the closer to isotactic their structures are, the more stable they are. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1355–1361, 1998     

Free‐Radical Propagation Rate Coefficients via n‐Pulse Periodic Polymerization

Aspects of applying n‐pulse periodic initiation in pulsed laser polymerization/size‐exclusion chromatography (PLP/SEC) experiments are studied via simulation of molecular weight distributions (MWDs). In n‐pulse periodic PLP/SEC, sequences of n laser pulses at successive time intervals Δt₁ up to Δt_n are periodically applied. With the dark time intervals being suitably chosen, n‐modal MWDs with n well separated peaks occur. The n‐pulse periodic PLP/SEC method has the potential for providing accurate propagation rate coefficients, k_p. Among several measures for k_p, the differences in molecular weights at the MWD peak positions yield the best estimate of k_p under conditions of medium and high pulse laser‐induced free‐radical concentration. Deducing k_p from n dark time intervals (corresponding to n regions of free‐radical chain length) within one experiment at otherwise identical PLP/SEC conditions allows addressing in more detail a potential chain‐length dependence of k_p. Simulations are compared with experimental data for 2‐pulse periodic polymerization of methyl methacrylate.

Measured MWD (solid line) and associated first derivative curve (dotted line) for a 2‐pulse periodic bulk polymerization experiment of MMA at 20 °C.     

Molecular weight characterization of soluble high performance polyimides. 1. Polymer-solvent-stationary phase interactions in size exclusion chromatography

Soluble, fully cyclized m-amino phenyl acetylene terminated polyimides based on several anhydride/diamine monomers were prepared in N-methylpyrrolidine (NMP) and cyclized by solution imidization to controlled molecular weight. The polyimides and a polyamic acid precursor were successfully analyzed by size exclusion chromatography (SEC) utilizing online parallel coupled refractive index and differential viscometer detectors. The calculated M _nvalues were varied from 3,000 to 20,000 daltons. N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and chloroform served as mobile phases for the cross-linked polystyrene gel packings. Normal retention behavior of the polyimides was observed in chloroform, THF, and NMP containing LiBr, or in NMP stirred over P₂O₅ before use. Values of Mark-Houwink-Sakurada exponents for narrow distribution linear polystyrene indicate that pure NMP and NMP with 0.06 M LiBr are good solvents for polystyrene standards at 60°C. In contrast, SEC behavior of polyimides in pure NMP leads to splitting of the peaks with the major portion observed to pass through the columns at the exclusion limit. In contrast to strong polymeric chain expansion of the polyamic acid in dilute solution, presumably due to a polyelectrolyte effect, no increase of intrinsic viscosity of polyimide samples in pure NMP was observed. This exclusion effect of polyimides analyzed in NMP is discussed in terms of possible ion-exclusion from pores of the stationary phase. Differences in polystyrene calibration in NMP with or without additives and the temperature dependence of calibration curves in these mobile phases is discussed as well. ©1995 John Wiley & Sons, Inc.     

Aqueous phase size exclusion chromatography of polyvinylalcohols of different degrees of hydrolysis

The aqueous-phase size exclusion chromatography (SEC) represents a suitable method for the analysis of molecular weight distribution (MWD) of polyvinylalcohols (PVOHs) of different degree of hydrolysis ranging from 72 to 98 mol-% applying the Suprema columns. Eluents of different composition were used consisting of either a mixture of water and acetonitrile for the lower degrees of hydrolysis (72 - 88 mol-%) or 0.1 M LiNO₃ solution for the higher degrees of hydrolysis (88 - 98 mol-%). By knowing the M̄_w̄ values of commercially available PVOHs samples of a given degree of hydrolysis and using the commercial water soluble narrow distribution standards, a principle of the constant hydrodynamic equivalence ratios was applied to obtain the absolute values of the molecular weights of PVOHs of different degree of hydrolysis. The effect of a various number of extrusion cycles on MWD of different PVOHs was used to demonstrate the sensitivity of the selected SEC conditions.     

Ethylene/1‐pentene copolymers synthesized using the metaloxycarbene complex catalyst system [(CO)5W=C(Me)OZr(Cp)2Cl]/MAO

Ethylene/1‐pentene copolymers were prepared using a [(CO)₅W= C(Me)OZr(Cp)₂Cl] (1)/MAO catalyst system. 1‐Pentene incorporation in the copolymer was monitored using ¹³C‐NMR spectroscopic methods. The weight average molecular weights (M_w) of the copolymers were between 142,000 and 629,000 g/mol, with polydispersity indexes (PDIs) ranging from ≈ 2 to 90, as analyzed by size exclusion chromatography (SEC). Melting and crystallization temperatures, determined using differential scanning calorimetry (DSC) and crystallization analysis fractionation (CRYSTAF), decreased linearly as the amount of 1‐pentene in the copolymer increased. SEC‐FTIR revealed that the 1‐pentene is predominantly incorporated in the low molecular weight fraction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5121–5133, 2004     

On the Quantitative Click Conjugation of Molecular Weight Distributions: What Can Theoretically Be Expected?

The assessment of the success of a click conjugation for block copolymer formation often occurs via ill‐defined criteria based on the qualitative shape of the size exclusion chromatography (SEC) distribution as well as unsuitable characteristics of these molecular weight distribution such as the peak molecular weight, M_p. The data presented herein illustrate that from the shape of the SEC distribution, w(log M) versus log M, of the click product—under the assumption of a 100% efficient conjugation reaction—a conclusion about the effectiveness of the click conjugation cannot be derived. It is demonstrated that under certain conditions multi‐modal molecular weight distributions are obtained from two well‐defined monomodal initial distributions. Similarly, the comparison of peak maxima between the conjugate and the initial SEC distributions is a poorly defined criterion to assess the success of a conjugation. The only reliable assessment for the success of the click coupling reaction is the true number average molecular weight, , of the SEC distribution of the click product, as well as a plot of the concentration or number distributions, c versus M, of the precursors and product polymer.

     

Study of the Degradation of High Molecular Weight Polystyrene in the Course of Size Exclusion Chromatography (SEC)

Abstract

The possibility of degradation of large macromolecules in their motion through a porous medium in the course of SEC decreases considerably the range of application of this highly productive and highly selective analytical method for the determination of the MWD of polymers. In fact, the MWD determined by SEC with the existence of degradation is mainly the distribution according to degradation fragments and does not reflect the initial molecular characteristics of the polymer.

The dependence of the degree of degradation of maccromolecules on the main parameters of the chromatographic experiment: the rate of the eluent flow, the size and shape of sorbent particles and the size of their pores was studied in detail. A non-monotonic change in the degree of degradation with increasing flow rate of the eluent was detected.

It is shown that the degree of degradation increases with decreasing particle size and the size of their pores. A new concept of the degradation of high polymers in SEC is formulated. It is related mainly not to the existence of local rate gradients in the interparticle volume but, rather, to the entire combination of hydrodynamic and adsorption effects accompanying the process of interaction between the macromolecules and the surface of sorbeiit particles. Practical recomendations are given for carrying out SEC, including that of super-high molecular weight samples under “non-degrada- tive” condritions.     

Large‐scale extrusion processing and characterization of hybrid nylon‐6/SiO2 nanocomposites

Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide‐6 (PA‐6) is achieved using a twin‐screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6 kg h^?1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA‐6 showed higher amounts of γ‐phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E‐modulus increased from 2.7 to 3.9 GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E′ and E″) increased and tan δ decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd.