Jiří Horský

Quantification in MALDI-TOF mass spectrometry of modified polymers

MALDI-TOF mass spectrometry quantification is hampered by the poor reproducibility of the signal intensity and by molecular-mass and compositional discrimination. The addition of a suitable compound as an internal standard increases reproducibility and allows a calibration curve to be constructed. The concept was also verified with synthetic polymers but no instructions for practical implementation were given [H. Chen, M. He, J. Pei, H. He, Anal. Chem. 75 (2003) 6531-6535.], even though synthetic polymers are generally non-uniform with respect to molecular mass and composition and access to the polymer of the same molecular mass distribution and composition as that of the quantified one is thus the exception rather than rule. On the other hand, relative quantification of polymers e.g., the content of the precursor polymer in a batch of a modified polymer, is usually sought. In this particular case, the pure precursor is usually available and the modified polymer can serve as an internal standard. However, the calibration curve still cannot be constructed and the use of the internal standard has to be combined with the method of standard addition in which the precursor polymer is added directly to the analyzed sample. The experiments with simulated modified polymers, mixtures of poly(ethylene glycol) (PEG) and poly(ethylene glycol) monomethyl ether (MPEG) of similar molecular-mass distribution, revealed a power dependence of the PEG/MPEG signal-intensity ratio (MS ratio) on the PEG/MPEG concentrations ratio in the mixture (gravimetric ratio). The result was obtained using standard procedures and instrumentation, which means that the basic assumption of the standard-addition method, i.e., the proportionality of the MS and gravimetric ratios, generally cannot be taken for granted. Therefore, the multi-point combined internal-standard standard-addition method was developed and experimentally verified for the quantification of the precursor in modified polymers. In this method, the two parameters of the power-type calibration curve - the proportionality constant and the exponent-are assumed. If the exponent strongly deviates from unity the minority component can be significantly underrepresented in the spectrum. Therefore, the absence of the precursor polymer signals in the MALDI-TOF mass spectrum of a modified polymer sample does not prove the absence of the precursor in the sample. Such a conclusion has to be corroborated by the standard-addition method.

Thickening of butyl acrylate/styrene/2-hydroxyethyl methacrylate/acrylic acid latices with an HEUR associative thickener

Thickening of acrylate copolymer latices containing various amount of 2-hydroxyethyl methacrylate (HEMA) by commercial associative thickener SER-AD FX 1070 (CONDEA Servo BV), based on hydrophobic ethoxylated urethane (HEUR), showed that the thickening efficiency decreases with the HEMA content in the latex copolymer. The strongest increase in viscosity occurred in the latex without HEMA comonomer suggesting formation of the network space structure due to the bridging of the latex particles by adsorption of hydrophobic ends of the thickener. When HEMA was incorporated into the latex copolymers, the particle surface became more hydrophilic and the association of the thickener was more significant. In this case thickening was much lower and was only a result of the hydrodynamic interaction between swollen latex particles and the thickener macromolecules or their aggregates (clusters, micelles).

Effect of alkalinization on carboxylated latices prepared with various amount of a non-ionogenic hydrophilic comonomer 2-hydroxyethyl methacrylate

Abstract Six latices of carboxylated styrene/butyl acrylate copolymers with 0–25% of 2-hydroxyethyl methacrylate (HEMA) were prepared by semicontinuous non-seeded emulsion polymerization and investigated by photon correlation spectroscopy and viscometry. Although HEMA is non-ionogenic, it profoundly affects the latex behavior after alkalinization: both methods revealed that HEMA promotes an increase in hydrodynamic dimensions of dispersed particles. The increase in viscosity due to incorporation of 10% of HEMA into the copolymers can make more than one order of magnitude at high volume fractions.

Thickening of butyl acrylate/styrene/2-hydroxyethyl methacrylate/acrylic acid lattices with dispersion of crosslinked ethyl acrylate/methacrylic acid copolymer

Abstract Thickening of lattices of styrene–acrylic copolymers containing a small amount of acrylic acid and various amounts of 2-hydroxyethyl methacrylate (HEMA) with alkali-swellable dispersion of crosslinked ethyl acrylate/methacrylic acid copolymer has been studied using capillary viscometry and dynamic and steady shear measurements. The higher the amount of HEMA incorporated into the latex copolymers, the stronger the thickening effect is. A comparison of flow behavior of thickened systems with those of neat lattices confirmed a significant influence of the effective volume fraction of alkalinized swollen latex particles on the thickening process. Under these conditions, to obtain the same rheological properties, the necessary amount of thickener was lower for the latex copolymers with higher amounts of HEMA because a part of the thickener volume fraction was replaced by an increased volume fraction of swollen latex particles. These findings indicate weakly interacting dispersion systems without strong compression of particle domains.

The effect of (2-hydroxypropyl)-β-cyclodextrin on rheology of hydrophobically end-capped poly(ethylene glycol) aqueous solutions

(2-Hydroxypropyl)-β-cyclodextrin (HPBCD), a modified cyclic oligosaccharide, changes the flow behavior of aqueous solutions of a model telechelic associative polymer, hydrophobically end-capped poly(ethylene glycol) (ODU-12), because the inclusion complexation of HPBCD and octadecyl end-capping groups interferes with aggregation of the polymer end groups. The HPBCD-induced decrease in the high-frequency modulus can be well described assuming a 1:1 binding isotherm, but cannot fully explain the decrease in the low shear rate Newtonian viscosity, because HPBCD also strongly decreases the relaxation time. Consequently, besides decreasing low shear rate Newtonian viscosity, HPBCD also extends the Newtonian behavior to higher shear rates as predicted by the free-path version of the transient network theory [Marrucci et al., Macromolecules 26, 6483–6488 (1993)].(2-Hydroxypropyl)-β-cyclodextrin (HPBCD), a modified cyclic oligosaccharide, changes the flow behavior of aqueous solutions of a model telechelic associative polymer, hydrophobically end-capped poly(ethylene glycol) (ODU-12), because the inclusion complexation of HPBCD and octadecyl end-capping groups interferes with aggregation of the polymer end groups. The HPBCD-induced decrease in the high-frequency modulus can be well described assuming a 1:1 binding isotherm, but cannot fully explain the decrease in the low shear rate Newtonian viscosity, because HPBCD also strongly decreases the relaxation time. Consequently, besides decreasing low shear rate Newtonian viscosity, HPBCD also extends the Newtonian behavior to higher shear rates as predicted by the free-path version of the transient network theory [Marrucci et al., Macromolecules 26, 6483–6488 (1993)].

Synthesis of C 3 -symmetric tri(alkylamino) guests and their interaction with cyclodextrins

The synthesis of a series of star-shaped C3-symmetric amines and their inclusion complexation properties toward α-, β-, γ-cyclodextrins and their permethylated derivatives has been described. The star molecules comprise of 1,3,5-trisubstited benzene core and the points formed by (alkylamino)methyl or 4-((alkylamino)methyl)phenyl groups. The modes of host–guest interaction were studied by UV–Vis spectroscopy, ITC, 1H NMR and 2D-NMR (NOESY). It was found that star molecules containing (tert-butylamino)methyl, (adamantan-1-ylamino)methyl, 4-((isopropylamino)methyl)phenyl, 4-((tert-butylamino)methyl)phenyl and protonated 4-((adamantan-1-ylamino)methyl)phenyl points form strong host–guest complexes with β-cyclodextrin. It was also proved that the largest C3-symmetric guest can form complexes with β-cyclodextrin with stoichiometry 3 which is required for construction of dendrimer supramolecular structures. None of the investigated amines forms a strong complex with permethylated cyclodextrins.

Thickening Effect of Commercial Associative Thickeners on the Latices of Copolymers of Acrylic Monomers Carrying Hydrophilic Reactive Groups

Abstract Investigation of flow properties of butyl acrylate/styrene/2‐hydroxyethyl methacrylate/acrylic acid latices thickened by commercial associative thickeners based on hydrophobic ethoxylated urethane (HEUR) or hydrophobically modified alkali‐soluble emulsions (HASE) showed that the apparent viscosity, at a constant medium shear rate, increased with the increasing content of 2‐hydroxyethyl methacrylate (HEMA). In contrast, the relative change in latex viscosity after the thickener addition (thickening efficiency), expressed as the ratio of viscosities of the thickened and untreated latices, decreased. This indicates that the increase in viscosity of the thickened latex with a higher HEMA content is caused by the increasing viscosity of the untreated latices due to rising hydrodynamic volume of alkalinized latex particles and not by higher particle bridging with the thickener macromolecules. The HEMA monomer clearly increases hydrophilicity of the particle surface which reduces adsorption of hydrophobic ends of the thickener on latex particles and the thickening efficiency decreases.

Remarks on the Dondos‐Benoit plot of the intrinsic viscosity and its combination with the Mark‐Houwink‐Kuhn‐Sakurada plot

The theoretical analysis of the Dondos-Benoit plot of intrinsic viscosity data and its modification by Dondos and Staikos not only reveals limitations of these methods as tools for determining the conformational characteristics of polymers but – more importantly – removes a previously reported contradiction between experimental data and the Yamakawa-Fujii theory of the intrinsic viscosity of worm-like chains.

Synthesis and supramolecular properties of regioisomers of mononaphthylallyl derivatives of γ-cyclodextrin

Monosubstituted derivatives of γ-cyclodextrin (γ-CD) are suitable building blocks for supramolecular polymers, and can also serve as precursors for the synthesis of other regioselectively monosubstituted γ-CD derivatives. We prepared a set of monosubstituted 2I-O-, 3I-O-, and 6I-O-(3-(naphthalen-2-yl)prop-2-en-1-yl) derivatives of γ-CD using two different methods. A key step of the first synthetic procedure is a cross-metathesis between previously described regioisomers of mono-O-allyl derivatives of γ-CD and 2-vinylnaphthalene which gives yields of about 16–25% (2–5% starting from γ-CD). To increase the overall yields, we have developed another method, based on a direct alkylation of γ-CD with 3-(naphthalen-2-yl)allyl chloride as the alkylating reagent. Highly regioselective reaction conditions, which differ for each regioisomer in a used base, gave the monosubstituted isomers in yields between 12–19%. Supramolecular properties of these derivatives were studied by DLS, ITC, NMR, and Cryo-TEM.

Effect of cyclodextrins on pH-induced conformational transition of poly(methacrylic acid)

A pH-induced conformational transition of atactic poly(2-methylprop-2-enoic acid) (poly(methacrylic acid), PMMA) from the contracted to expanded conformation was investigated by viscometry, potentiometric titration, and anthracene solubilisation in the presence of low-molecular-mass non-ionogenic co-solutes-glucose, α-cyclodextrin (αCD), and γ-cyclodextrin (γCD), respectively. No effect of glucose and αCD on the conformational transition was observed with either of the methods used. On the other hand, the characteristic features of the conformational transition were absent in the presence of γCD. The different effects of the co-solutes indicate that the interaction between PMAA and γCD corresponds to the partial inclusion of the PMAA chain into the γCD cavity. The viscometry and anthracene solubilisation imply that γCD promotes the expanded conformation of PMAA at low pH. The potentiometric titration does not support this conclusion. Even though there is no break on the Henderson-Hasselbalch plot, a characteristic of the conformational transition, the potentiometric behaviour corresponds to that of the contracted PMMA conformation. Thus the results suggest the hierarchical picture of the PMAA conformation at low pH in which the local arrangement of the PMAA chain is a prerequisite for clustering on a larger scale.