Separation of branched polystyrene by comprehensive two-dimensional liquid chromatography

Branched polystyrenes (PS) featuring a bivariate distribution in the molecular weight and in the number of branches were characterized by comprehensive two-dimensional liquid chromatography (2D-LC). The branched PS were prepared by anionic polymerization using n-butyl Li as an initiator and a subsequent linking reaction with p-(chlorodimethylsilyl)styrene (CDMSS). The n-butyl Li initiator yields polystyryl anions with broad molecular weight distribution (MWD) and the linking reaction with CDMSS yields branched PS with different number of branches. For the first dimension (1st-D) separation, reversed-phase temperature gradient interaction chromatography (RP-TGIC) was employed to separate the branched polymer according to mainly the molecular weight. In the second dimension (2nd-D) separation, the effluents from the RP-TGIC separation are subjected to liquid chromatography at chromatographic critical conditions (LCCC), in which the separation was carried out at the critical condition of linear homo-PS to separate the branched PS in terms of the number of branches. The 2D-LC resolution of RP-TGICxLCCC combination worked better than the common LCCCxsize-exclusion chromatography (SEC) configuration due to the higher resolution of RP-TGIC in molecular weight than SEC. Furthermore, by virtue of using the same eluent in RP-TGIC and LCCC (only the column temperature is different), RP-TGICxLCCC separation is free from possible 'break through' and large system peak problems. This type of 2D-LC separation could be utilized efficiently for the analysis of branched polymers with branching units distinguishable by LC separation.     

Synthesis of hyperbranched polymers by self‐addition free radical vinyl polymerization of photo functional styrene

The hyperbranched polystyrenes are prepared by the self‐addition free radical vinyl polymerization of N,N‐diethylaminodithiocarbamoylmethylstyrene (DTCS). DTCS monomers play an important role in this polymerization system as an inimer that is capable of initiating living radical polymerization of the vinyl group. The compact nature of the hyperbranched macromolecules is demonstrated by viscosity measurements compared to the linear analogues.     

Structure characterization of hyperbranched poly(ether amide)s. I. Preparative fractionation

The focus of our investigation lies on the separation of typically broadly distributed hyperbranched poly(ether amide)s into narrow fractions of various molar masses. Their exact molar mass found via size-exclusion chromatography (SEC) with light uttering detection allows us to use these fractions for sample specific calibration in the SEC investigation of other hyperbranched samples. The analysis of the degree of branching, molar mass and viscosity behavior of the fractions gives a first indication about their molecular shape and the contribution of that shape to the overall viscosity. We determined the Mark-Houwink exponent for a hyperbranched sample using a number of narrow fractions which showed that an increase of molar mass leads to an increased molecular density.     

Combined techniques for the characterization of linear–hyperbranched hybrid poly(butylene adipate) copolymers

Linear–hyperbranched hybrid poly(butylene adipate) (HPBA) copolymers were synthesized through a branching reaction between the linear tailored prepolymer terminated with methyl ester groups and different mol percents of the 1,1,1‐tris(hydroxymethyl) propane (TMP) as branching agent, using the titanium(IV) isopropoxide as catalyst, at 180 °C under vacuum for different times. All samples were characterized by NMR and matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI‐TOF MS). In particular, MALDI‐TOF mass spectra of the unfractionated and size exclusion chromatography (SEC)‐fractionated hyperbranched (HB) samples gave information on their composition, on the end groups as well as on the TMP units present in each family of HB macromolecules. HB chains containing cyclic branches and ether bonds formed by intermolecular transesterification and intramolecular and intermolecular transetherification side reactions, respectively, were also revealed by MALDI‐TOF MS analysis. All samples were also investigated by SEC. The average molar masses (MMs) evaluated by SEC calibrated with the polystyrene (PS) narrow standards were overestimated with respect to those calculated by the SEC/MALDI‐TOF MS self‐ calibration method, which gave reliable values. Moreover, it also showed that the hydrodynamic volume of the HPBA polymers was higher than that of the linear PSs with similar MMs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of a new hyperbranched‐linear‐hyperbranched triblock copolymer and its use as a chemical modifier for the cationic photo and thermal curing of epoxy resins

A new hyperbranched‐linear‐hyperbranched polymer was prepared in a one pot process by reaction of 4,4‐bis(4‐hydroxyphenyl)valeric acid and poly(ethylene glycol) (HPH). After characterization by ¹H and ¹³C NMR, SEC, DSC, and TGA, this polymer was used, in proportions of 5, 10, and 15 phr, as a chemical modifier in the UV and thermal cationic curing of 3,4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexyl carboxylate epoxy resin. The curing process was studied by calorimetry, demonstrating the accelerating effect of the hydroxyl groups present in HPH's structure. The morphology of the resulting thermosets depended on the curing system used, as demonstrated by FE‐SEM microscopy, but in both cases phase separation occurred. Thermosets obtained by thermal curing presented lower thermal stability than UV‐cured materials. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Electrically driven capillary size exclusion chromatography

Summary Electrically driven size exclusion chromatography (ED-SEC) of polystyrenes in packed capillaries using dimethylformamide as solvent is demonstrated. The efficiency and retention behaviour of polystyrenes under pressure and electro drive were investigated. Under pressure drive the plate height (H) increases steadily with increasing linear velocity (u) whereas under electro drive the H-u curves largely coincide and are very flat. At higher velocities the plate heights are about 50% smaller with electro drive than with pressure drive. Calculations show that with increasing ionic strength, the flow through the particles may increase causing a clear diminishing of the elution window.     

Kinetic topology‐selective encapsulation and mixture separation by a nanocapsule with hyperbranched polyethylenimine as core and polystyrene as shell

Topology‐selective encapsulation of a guest is generally exclusively achieved by a well‐defined host. In this article, a macromolecular reverse micelle (PEI@PS), with a hyperbranched polyethylenimine (PEI) as core and polystyrenes (PSs) as shell, is prepared and shown with excellent encapsulation and separation abilities. It is found that the encapsulation and phase transfer is kinetically dependent on the size of the dyes, creating a time window for the separation of dyes. All the experimental results show that the thickness and density of shell plays the most important roles in guest selectivity. In addition, highly size‐selective release is also found. This macromolecular reverse micelle (PEI@PS) can find useful applications in the liquid–liquid or solid–liquid extraction separation, especially for the latter.© 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1273–1281     

Rapid determination of molecular parameters of synthetic polymers by precipitation/redissolution high‐performance liquid chromatography using “molded” monolithic column

Rapid high‐performance liquid chromatography (HPLC) of polystyrenes, poly(methyl methacrylates), poly(vinyl acetates), and polybutadienes using a monolithic 50 × 4.6 mm i.d. poly(styrene‐co‐divinylbenzene) column have been carried out. The separation process involves precipitation of the macromolecules on the macroporous monolithic column followed by progressive elution utilizing a gradient of the mobile phase. Depending on the character of the separated polymer, solvent gradients were composed of a poor solvent such as water, methanol, or hexane and increasing amounts of a good solvent such as THF or dichloromethane. Monolithic columns are ideally suited for this technique because convection through the large pores of the monolith enhances the mass transport of large polymer molecules and accelerates the separation process. Separation conditions including the selection of a specific pair of solvent and precipitant, flow rate, and gradient steepness were optimized for the rapid HPLC separations of various polymers that differed broadly in their molecular weights. Excellent separations were obtained demonstrating that the precipitation‐redissolution technique is a suitable alternative to size‐exclusion chromatography (SEC). The molecular weight parameters calculated from the HPLC data match well those obtained by SEC. However, compared to SEC, the determination of molecular parameters using gradient elution could be achieved at comparable flow rates in a much shorter period of time, typically in about 1 min. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2767–2778, 2000     

Preparation of Functional Long-Subchain Hyperbranched Polystyrenes via Post-polymerization Modification: Study on the Critical Role of Chemical Stability of Branching Linkage

Post-polymerization modification (PPM) is one of the most powerful strategy for preparing polymers with functional groups that cannot be synthesized by direct polymerization. So far, numerous experimental efforts have been devoted to the stability issue of monomer structures during the PPM process, but little attention was paid to chemical linkages. However, for hyperbranched polymers, a minor change of linkage unit could lead to a significant influence on the overall stability and performance of polymer materials. In this work, we investigated the chemical stability of long-subchain hyperbranched polystyrenes with ester, aryl ether, and carbon-carbon bonds as branching linkages under a few most popular PPM conditions, including NaOH hydrolysis reaction, TFA-promoted hydrolysis reaction, BBr₃-catalyzed methoxy-hydroxyl conversion reaction, and LiAlH₄ carbonyl reduction reaction. Related results are summarized into a synthetic route map that can provide practical and intuitive guidance for preparing functional long-subchain hyperbranched polystyrenes and other type of polymers by PPM for future applications.     

Synthesis of novel well-defined chain-end-functionalized polystyrenes with dendritic chiral ephedrine moieties and their applications as highly enantioselective diethylzinc addition to N-diphenylphosphinoyl arylimines

A series of novel well-defined chain-end-functionalized polystyrenes having 2, 4, 8, and 16 chiral ephedrine moieties dendritically distributed at their hyperbranched chain-ends were quantitatively synthesized. Their well-defined architectures were fully confirmed by elemental analysis, FTIR, SEC as well as by ¹H and ¹³C NMR spectroscopies. These polymers were precisely controlled in the molecular weight and molecular weight distribution as well as well-defined in chain-end-functionalities. These dendritic chiral polymers serve as highly enantioselective chiral ligands in the enantioselective addition of diethylzinc to a series of N-diphenylphosphinoyl arylimines. Among them, chiral dendrimer having eight ephedrine moieties at the chain-ends afforded the corresponding enantiomerically enriched phosphinoylamides in good to high yields with enantioselectivities up to 93% ee. The obtained enantioselectivities are comparable with those obtained by using N-benzylephedrine and its corresponding copolymer as chiral ligands.     

Control of polymer topology through transition-metal catalysis: synthesis of hyperbranched polymers by cobalt-mediated free radical polymerization

A novel approach was demonstrated for the synthesis of hyperbranched polymers by direct free radical polymerization of divinyl monomers controlled by a cobalt chain transfer catalyst (1). By controlling the competition between propagation and chain transfer with 1, the free radical polymerization of ethylene glycol dimethacrylate (3) afforded soluble hyperbranched polymers in one pot. The structure of the hyperbranched polymers was confirmed by (1)H and (13)C NMR. The molecular weight and intrinsic viscosity of the hyperbranched polymers were measured by matrix-assisted laser desorption ionization (MALDI) mass spectrometry and size exclusion chromatography (SEC) equipped with triple detectors. The intrinsic viscosities of the hyperbranched polymers are much lower than those of their linear analogues and do not show molecular weight dependence. The unique structure and properties of these hyperbranched polymers combined with the commercial availability of many divinyl monomers and the robustness of free radical polymerization make this new approach attractive for the preparation of new functional materials.     

Strategies in two‐dimensional liquid chromatographic separation of complex polymer systems

Complex synthetic polymer systems as for example copolymers exhibit distributions in at least two of the three basic molecular characteristics which are molar mass, chemical structure/composition and molecular architecture. Size exclusion chromatography (SEC) separates macromolecules according to their size in solution which simultaneously depends on all molecular characteristics. Therefore, multi‐dimensional liquid chromatographic techniques are to be applied to independently assess all different distributions present in the sample. So far, two‐dimensional separations have been attempted. In the first dimension separation column, selected liquid chromatographic mechanisms are intentionally combined to suppress effects of all but one molecular characteristic. Consequently, polymer species are separated exclusively or at least predominantly according to one single parameter. In the second dimension separation column, macromolecules are separated according to another molecular characteristic. In this contribution the methods are briefly reviewed in which effect of polymer molar mass on polymer retention is suppressed. The resulting ”one parameter separation systems” can be on‐line or off‐line connected to another separation system such as SEC to provide more detailed characterization of complex polymers. Besides, selected procedures for the re‐concentration of diluted polymer solutions are concisely treated. These may be utilized for increasing the concentration of sample(s) leaving the first dimension separation column. Eventually, some arrangements for controlled sample re‐introduction into the second dimension separation column are outlined.     

Studies on high-performance size-exclusion chromatography of synthetic polymers. I. Volume of silica gel column packing pores reduced by retained macromolecules

Macromolecules, which stay adsorbed within the active size-exclusion chromatography (SEC) column packings may strongly reduce effective volume of the separation pores. This brings about a decrease of retention volumes of the non-retained polymer samples and results in the increased apparent molar mass values. The phenomenon has been demonstrated with a series of poly(methyl methacrylate)s (PMMA) and a polyethylenoxide (PEO) fully retained by adsorption within macroporous silica gel SEC column from toluene or tetrahydrofuran, respectively. The non-retained probes were polystyrenes (PS) in toluene and both PS and PMMA in THF eluents. The errors in the peak molar mass values determined for the non-retained polymer species using a column saturated with adsorbed macromolecules and considering calibration curves monitored for the original "bare" column packing assumed up to several hundreds of percent. Errors may appear also in the weight and number averages of molar masses calculated from calibration dependences obtained with columns saturated with adsorbed macromolecules. Moreover, the SEC peaks of species eluted from the polymer saturated columns were broadened and in some cases even split. These results demonstrate a necessity not only to periodically re-calibrate the SEC columns but also to remove macromolecules adsorbed within packing in the course of analyses.     

星形聚苯乙烯的玻璃化转变温度和液1-液2松弛

用扭辫仪(TBA)和线膨胀仪测定了一组规则的星形聚苯乙烯的玻璃化转变温度T_g和T_ll松弛。两种实验方法的结果表明:支链分子量相同的星形结构聚合物的T_g随着支化度增加而升高,但也发现星形聚苯乙烯的T_g却低于具有相同分子量的线形聚苯乙烯的T_g·液₁-液₂松弛温度T_ll和损耗峰的强度也依赖其支化度。与以二乙烯基苯为凝胶核的星形结构相比较,证实了后者的双T_g转变。     

一种新型超支化聚酯物理吸附涂层毛细管电泳柱的制备及其对碱性蛋白质的分离

采用一步法和准一步法合成了以季戊四醇为核的两个系列的超支化聚酯,利用红外光谱、羟值测定等手段对分子结构进行了表征。利用超支化聚合物低粘度的特点,用物理吸附方法将其涂于毛细管电泳柱内壁,使其在毛细管内壁上形成稳定的超支化聚酯涂层。该涂层在pH 3.0~7.0范围内能够有效地抑制电渗流和蛋白质在毛细管壁上的吸附,在pH 5.0的缓冲液中分离碱性蛋白质时,分离柱效可达105塔板/m,具有良好的分离效果。     

One‐Step Synthesis of Dendritic Highly Branched Polystyrenes by Organotellurium‐Mediated Copolymerization of Styrene and a Dienyl Telluride Monomer

Dendritic highly branched polystyrenes (HB‐PSts) were prepared by a one‐step copolymerization of dienyl telluride 6 and St in the presence of organotellurium chain transfer agent 2 . The molecular weight (MW), dendritic generation, and branching density were easily controlled by the ratio of 2 to 6 to styrene (St) with maintaining monodispersity. The branching efficiency estimated by a deuterium‐labeling experiment showed that 6 quantitatively (>95 %) served as the branching point. The end group fidelity was high (ca. 90 %) as determined by the end group transformation to pyrene‐derivative. Intrinsic viscosity of the HP‐polystyrenes was significantly lower than that of linear polystyrenes and were easily tuned by the branching number and branching density. The method is compatible of various functional groups and chloro and acetoxy‐substituted styrenes were also used as a comonomer. A tadpole block copolymer was also synthesized starting from linear PSt as a macroinitiator.     

超支化聚合物化学键合毛细管电泳柱的制备及其对蛋白质的分离行为

分别合成了以三羟甲基丙烷和季戊四醇为核的超支化聚(胺-酯),并对其进行了红外测定、羟值测定、粘度测定等表征。采用化学键合方法将其涂于毛细管内壁,并测定涂层柱的电渗流以及对碱性蛋白质的分离能力,结果表明,涂层柱能有效地抑制碱性蛋白质在毛细管内壁上的吸附,大大降低电渗流;以三羟甲基丙烷为核的超支化聚(胺-酯)涂层柱的塔板数达105/m,而以季戊四醇为核的超支化聚(胺-酯)涂层柱的分离柱效更高,塔板数达107/m。实验结果表明这两类涂层柱都具有较好的分离效果和稳定性。     

Nanopattern formation on polymer substrate using star-hyperbranched nanospheres

Hyperbranched polystyrenes (PS) were prepared by living radical photopolymerization of 4-vinylbenzyl N,N-diethyldithiocarbamate as an inimer under UV irradiation. These hyperbranched PS exhibited large amounts of photofunctional dithiocarbamate groups on their outside surfaces. Subsequently, we derived the star-hyperbranched copolymers by grafting from hyperbranched macroinitiator with t-butyl methacrylate. We obtained poly(methacrylic acid) star-hyperbranched PS nanospheres by hydrolysis of poly(t-butyl methacrylate) grafted chains. We studied in detail two-dimensional nanopattern formation on poly(4-vinylpyridine) (P4VP) or partially quaternized P4VP substrate using such nanospheres by electrostatic interaction.     

Two-dimensional liquid chromatography analysis of synthetic polymers using fast size exclusion chromatography at high column temperature

In recent years, two-dimensional liquid chromatography (2D-LC) has been used increasingly for the analysis of synthetic polymers. A 2D-LC analysis provides richer information than a single chromatography analysis at the cost of longer analysis time. The time required for a comprehensive 2D-LC analysis is essentially proportional to the analysis time of the second dimension separation. Many of 2D-LC analyses of synthetic polymers have employed size exclusion chromatography (SEC) for the second-dimension analysis due to the relatively short analysis time in addition to the wide use in the polymer analysis. Nonetheless, short SEC columns are often used for 2D-LC analyses to reduce the separation time, which inevitably deteriorates the resolution. In this study, we demonstrated that high temperature SEC can be employed as an efficient second-LC in the 2D-LC separation of synthetic polymers. By virtue of high temperature operation (low solvent viscosity and high diffusivity of the polymer molecules), a normal length SEC column can be used at high flow rate with little loss in resolution.     

Off‐Lattice Monte Carlo Simulation of Hyperbranched Polymers, 2. Effect of the Reactivity Ratio of Linear to Terminal Unit on the Microstructure of Hyperbranched Polymers Based on AB2 Monomers

The polycondensation of hyperbranched polymers was simulated using an off‐lattice Monte Carlo method in order to investigate the effect of reactivity ratio (x) of linear to terminal unit on the microstructure of hyperbranched polymers based on AB₂ type monomers. The polydispersity index (PI) shows a maximum when the reactivity ratio is 1.0 and decreases as the reactivity ratio deviates from unity. Fractions of dendritic, linear and terminal units were determined from simulation and compared with theoretical predictions. As the reactivity ratio increases, the formation of the dendritic unit is more favored. The relative Wiener indices, free from the polydispersity effects, were newly defined in this simulation. The relative Wiener indices increases with increasing the reactivity ratio, indicating that the more branched structures are formed as the reactivity ratio increases.