The anionic polymerisation of styrene-based monomers has been studied very extensively. Polymerisation conditions, such as the solvent, initiator and temperature, have an influence on the properties of the polymers. The interesting properties are, for example, tacticity, molar mass and molar mass distribution. These properties have an effect on the crystallinity and rheology of the polymer. Anionic polymerisation is an excellent method to control the molar mass of the synthesised polymer. When
THEORY OF FIELD-FLOW FRACTIONATION (FFF)
Since s.e.c. and LS are familiar methods to the polymer chemist, only the principle of ThFFF is presented briefly here. Field-flow fractionation (FFF) is a family of analysis techniques covering a wide range of molecular size from a few thousand Daltons of molar mass to a particle size of ca. 100 μm. Many types of external field can be utilised in FFF including gravitational, centrifugal, electrical and magnetic fields. Also, a thermal gradient and another perpendicular flow can affect the
Styrene (Merck-Schuchardt; > 99%), p-methoxystyrene (Aldrich; > 97%), p-methylstyrene (Aldrich; > 97%) and p-chlorostyrene (Aldrich; > 97%) were dried over CaH2 and purified by fractional distillation in vacuo. The monomers were stored in ampoules sealed with Young's Teflon stopcocks at − 25°C. p-Cyanostyrene was prepared by one-pot reaction of 4-vinylbenzaldehyde with the hydroxylammonium chloride/pyridine/toluene system followed by azeotropic separation of water in 74% yield11, 12, 13.
RESULTS AND DISCUSSION
The repeatabilities of two different FFF runs are listed in Table 1. The calibration accuracy was estimated by calculating the molar mass averages of one individual standard in the standard series used for calibration. The standard deviations, calculated and nominal molar mass averages are in Table 2. The long-term stability of the system was estimated by calculating molar mass averages of one single run using 10 different calibrations carried out during 21 days (Table 3). Since the relative
R. Dammert and M. Jussila thank Neste Ltd. Foundation for financial support. The authors are indebted to E. Aitola for his technical assistance in course of the s.e.c. analysis and to K. Muje for her help in the polymerisations of poly(p-cyanostyrene)s.
Field-flow fractionation: New and exciting perspectives in polymer analysis
2016, Progress in Polymer Science
Citation Excerpt :
It has been demonstrated that the value of DT is unique for a given homopolymer and it is constant above a certain molar mass . Unfortunately, the low value of DT in water makes it an unfeasible technique for polymer analysis in water as carrier liquid . Therefore, ThFFF is mainly used for simultaneous chemical composition and molar mass analysis of polymers in organic solvents.
The development of advanced polymeric materials requires state-of-the-art synthesis and molecular characterization protocols. Only the precise knowledge of molecular structure–property correlations allows achieving optimum performance properties of novel materials. The analysis of the molecular composition of a complex polymeric material requires the determination of its molar mass, chemical composition, functionality and molecular topology among other (less important) parameters.
A number of column-based fractionation methods, including size exclusion chromatography (SEC) and high performance interaction chromatography (HPLC) are the standard techniques for the analysis of complex polymers. These methods work well as long as the molar mass is not too high and/or the macromolecules do not exhibit undesired interactions with the stationary phase (column). Certain polymers form large aggregates or other entities (micelles, liposomes) in solution that typically cannot be analyzed by column-based fractionation methods.
One alternative for the fractionation of such complex materials is field-flow fractionation (FFF), an open-channel technique which does not use a stationary phase. In FFF, all problems related to the stationary phase such as undesired adsorption, shear degradation of large macromolecules, co-elution of linear and branched macromolecules, can be avoided. Different sub-techniques of FFF render the fractionation of complex polymer systems according to molecular size, chemical composition or molecular topology.
In this review article, most recent developments of FFF in polymer analysis are addressed. Natural and synthetic polymers, polyolefins and polymeric nanocomposites are embraced. The most important FFF sub-techniques in polymer analysis include asymmetric flow field-flow fractionation (AF4) and thermal field-flow fractionation (ThFFF). Major developments in these very topics since 2008 are critically discussed following a previous review article that summarized earlier work (see Prog. Polym. Sci. 2009; 34: 351–68). The potentials and limitations of the different FFF sub-techniques for polymer analysis are elaborated and most recent methods of hyphenating FFF with other techniques are highlighted.
An overview on field-flow fractionation techniques and their applications in the separation and characterization of polymers
2009, Progress in Polymer Science (Oxford)
Field-flow fractionation (FFF) is a family of analytical techniques developed specifically for separating and characterizing macromolecules, supramolecular assemblies, colloids and particles. It combines the effects of a laminar flow profile with an exponential concentration profile of analyte components caused by their interactions with a physical field applied perpendicular to the flow of a carrier liquid. FFF is undergoing increasingly widespread use as researchers learn of its potential and versatility. This overview underlines the basic principle and theory behind FFF and reviews recent research efforts incorporating flow and thermal FFF methods to characterize natural, biological, and synthetic polymers. These FFF techniques will be discussed in terms of theory and practice. Selected applications of FFF and their coupling capability with other chromatographic techniques or spectrometric detection for the separation and characterization of polymers in organic and aqueous media are presented.
2014, Analytical and Bioanalytical Chemistry
2014, Monitoring Polymerization Reactions: From Fundamentals to Applications
Asymmetrical flow field-flow fractionation as a novel technique for the analysis of PS-b-PI copolymers
2013, Analytical and Bioanalytical Chemistry
2013, Macromolecular Rapid Communications
Enhanced electrochemical stimuli multilayers based on a ferrocene-containing polymer
Science Bulletin, Volume 60, Issue 10, 2015, pp. 936-942
Based on the noncovalent functionalization of ferrocene-grafted polyethylenimine (PEI-Fc) and carbon nanotubes (CNTs), CNT bundles are exfoliated by PEI-Fc solution and thus form stable compounds [emailprotected], which is used to construct the [emailprotected]/DNA multilayers through layer-by-layer assembly. The multilayers show a highly uniform and homogeneous characteristic, which significantly improve the electrical property of the multilayers. Upon the oxidation electrical potential, the ferrocene groups are switched from reduction state ([Fe(C5H5)2]) to oxidation state ([Fe(C5H5)2]+), leading to change of microenvironments’ charge density, resulting in swelling of the multilayers and a final degree of swelling of 37% and the decrease of multilayer stiffness. We maintain that electrochemical control over the swelling behavior of multilayers could have important implications for responsive coatings of nanoscale devices, including mechanically tunable surfaces which are used to modulate cellular activities and control drug delivery.
Synthesis of organic-inorganic polymer hybrids utilizing in-situ anionic hydrogen-transfer polymerization of acrylamide
Polymer, Volume 92, 2016, pp. 13-17
Homogeneous polymer hybrid consisting of poly(β-alanine) and silica gel was synthesized by an in-situ anionic polymerization method. Acrylamide (AAm) as an organic monomer was introduced into a sol–gel reaction of tetramethoxysilane (TMOS). The polymerization of AAm was initiated by potassium tert-butoxide (t-BuOK), while sol–gel reaction of TMOS proceeded to generate a silica gel matrix. The obtained polymer hybrid was optically transparent and no phase separation was observed by SEM measurement. From the 1H and 13C NMR analysis, the anionic polymerization of AAm proceeded via a hydrogen-transfer process under in-situ hybridization conditions.
Interpolyelectrolyte complex formation: From lyophilic to lyophobic colloids
Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 498, 2016, pp. 112-120
Interpolyelectrolyte complexes (IPEC) have been used in different fields, ranging from biomedicine to oil exploration. Particle dimension is a key parameter for the use of an IPEC for a particular application. In this work, dynamic and static scattering (in the form of optical DLS and SAXS, respectively) were used to follow particle growth as a function of anionic/cationic polyelectrolyte mass ratio, , coupled to turbidimetry, conductometry, viscometry, and zeta potential measurements. Turbidimetry, conductometry, and viscometry showed that at the IPEC dispersions presented changes that were associated to a massive production of IPEC particles. At the same value, zeta potential measurements indicated an apparent isoelectric point, showing that this must be related to a stoichiometric point for IPEC formation. Double KWW equation was adjusted to data from DLS intensity correlation functions, and parameters related to the distribution of relaxation rates presented characteristic changes at the same value of . SAXS was used to follow particle growth until massive IPEC production. It showed that particles firstly were in the form of small, globular particles, tending to unfolded chain geometry, which can be related to the occurrence of flocculation, just at the point of massive IPEC production.
A novel method for hydrogel nanostructuring
European Polymer Journal, Volume 52, 2014, pp. 137-145
Nanostructured hydrogels tailor-made for specific applications are new grounds for the creation of novel soft materials. The current research presents a new method for hydrogel nanostructuring involving the incorporation of Pluronic® F127 micelles mixed with acrylated blockcopolymer molecules, which enable the attachment of these micelles to the hydrogel matrix through their endgroups. This design impacts the hydrogel nanostructure as well as its swelling and mechanical properties. Small Angle X-ray Scattering (SAXS) and Cryogenic Transmission Electron Microscopy (cryo-TEM) revealed that photochemical crosslinking of the hydrogel caused immobilization of the nanostructured micelles. Mechanical and weight gain experiments demonstrated a significant impact of these nanostructures on the hydrogel’s elastic modulus as well as the transient and equilibrium weight gain ability of the material.
Self-assembly of homopolymers through strong dipole–dipole interaction in their aqueous solutions
Polymer, Volume 97, 2016, pp. 1-10
This study reveals the critical importance of dipole–dipole interaction for homopolymers to form self-assembled microspheres in solutions. For the polymers with different side-groups, the self-assembly is induced by gradually adding deionized water into their solutions in N, N-dimethylformamide (DMF). Three of the polymers containing side-groups with the strong dipoles form uniform colloidal spheres in the processes. Beyond the critical water content (CWC), the aggregate sizes first increase and then decrease with the increasing water content before forming the final assemblies. In the intermediate states, the aggregates possess a microgel-like structure in the swollen form. On the other hand, no such self-assembling behavior is observed for the other polymer without the dipolar side-groups, which precipitates from the DMF-H2O solution with the increase in the water content. The strong dipolar groups acting as associating groups are necessary to avoid polymer molecules forming dense aggregates and precipitating from the solutions after phase separation.
Fabrication of highly cross-linked reversed-phase monolithic columns via living radical polymerization
Journal of Chromatography A, Volume 1367, 2014, pp. 90-98
New monolithic reversed-phase liquid chromatography (RPLC) stationary phases based on single multi-acrylate/methacrylate-containing monomers [i.e., 1,12-dodecanediol dimethacrylate (1,12-DoDDMA), trimethylolpropane trimethacrylate (TRIM) and pentaerythritol tetraacrylate (PETA)] were synthesized using organotellurium-mediated living radical polymerization (TERP), which was expected to produce more efficient monolithic columns than conventional free-radical polymerization. The rationale behind selection of porogens, relative concentrations of reagents and polymerization conditions are described. The new monolithic columns were applied to the separation of small molecules (i.e., alkylbenzenes) under isocratic conditions. Chromatographic efficiencies as high as 60,200plates/m (71,300plates/m when corrected for extra-column variance) were obtained, showing a general improvement over previous RPLC monoliths.
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