Rodrigo Navarro

Preparation of Surface-Attached Polymer Layers by Thermal or Photochemical Activation of α-Diazoester Moieties

We report on the attachment of polymer monolayers or surface-attached, polymer networks onto SiO2 and/or polymer surfaces using thermo- and photoreactive α-diazoester groups. In the prior case, the α-diazoester groups are introduced into the system in the form of self-assembled monolayers of appropriately functionalized silanes. The monolayer decorated substrates are coated by polymer films and the α-diazoester groups in the monolayer are activated by heat or irradiation with UV-light. Upon activation, they cleave off nitrogen and the resulting carbene intermediates insert into C-H bonds of neighboring polymer chains. As a result of this binding process, surface-attached monolayers of the deposited polymer are obtained. When the polymers themselves carry such reactive moieties, the photo- or thermal activation leads to cross-linking of the polymers and thin surface-attached polymer networks result from the same process. The formation of the surface-attached layer is studied as a function of activation conditions, especially the temperature and the wavelength of the light used in the process.

Opening New Gates for the Modification of PVC or Other PVC Derivatives: Synthetic Strategies for the Covalent Binding of Molecules to PVC

Several synthetic strategies based on the use of substituted aromatic and hetero-aromatic thiols for the covalent binding of modifier compounds to PVC are described. A variety of aliphatic alcohols and amines are linked to the aromatic or heteroaromatic rings via highly active functionalities as the isocyanate, acidchloride, or chlorosulfonyl group, and the three chlorine atoms of trichlorotriazine. The first three pathways lead to protected aromatic disulfides obtaining the substituted aromatic thiols by reduction as a final step of an unprecedented synthetic route. The second approach, in a novel, extremely efficient, and scalable process, uses the particular selectivity of trichlorotriazine to connect aliphatic amines, alcohols, and thiols to the ring and creates the thiol via nucleophilic substitution of a heteroaromatic halogen by thiourea and subsequent hydrolysis. Most of the modifier compounds were linked to the polymer chains with high degrees of anchorage. The presented approaches are highly versatile as different activations of aromatic and heteroaromatic rings are used. Therefore, many types of tailored functional nucleophiles may be anchored to PVC providing non-migrating materials with a broad range of applications and properties.

Potential of prodendronic polyamines with modulated segmental charge density as novel coating for fast and efficient analysis of peptides and basic proteins by CE and CE-MS

In this work, the suitability of a new polymer family has been investigated as capillary coatings for the analysis of peptides and basic proteins by CE. This polymer family has been designed to minimize or completely prevent protein–capillary wall interactions and to modify the EOF. These coating materials are linear polymeric chains bearing as side cationizable moiety a dentronic triamine derived from N,N,N’,N’‐tetraethyldiethylenetriamine (TEDETA), which is linked to the backbone through a spacer (unit labeled as TEDETAMA). Four different polymers have been prepared and evaluated: a homopolymer which comprised only of those cationizable repetitive units of TEDETAMA, and three copolymers that randomly incorporate TEDETAMA together with neutral hydrosoluble units of N‐(2‐hydroxypropyl) methacrylamide (HPMA) at different molar percentages (25:75, 50:50 and 75:25). It has been demonstrated that the composition of the copolymers influences the EOF and therefore the separation of the investigated biopolymers. Among the novel polymers studied, poly‐(TEDETAMA‐co‐HPMA) 50:50 copolymer was successfully applied as coating material of the inner capillary surface in CE‐UV and CE‐MS, providing EOF reversing together with fast and efficient baseline separation of peptides and basic proteins. Finally, the feasibility of the polymer‐coated capillary was shown through the analysis of lysozyme in a cheese sample.

Correction of diffraction effects in confocal raman microspectroscopy

A mathematical approach developed to correct depth profiles of wet-chemically modified polymer films obtained by confocal Raman microscopy is presented which takes into account scattered contributions originated from a diffraction-limited laser focal volume. It is demonstrated that the problem can be described using a linear Fredholm integral equation of the first kind which correlates apparent and true Raman intensities with the depth resolution curve of the instrument. The calculations of the corrected depth profiles show that considerable differences between apparent and corrected depth profiles exist at the surface, especially when profiles with strong concentration gradients are dealt with or an instrument with poor depth resolution is used. Degrees of modification at the surface obtained by calculation of the corrected depth profiles are compared with those measured by FTIR-ATR and show an excellent concordance.

Synthesis of randomly aminated polyvinylpyrrolidone and its use in the preparation of hydrolyzable conjugates

In this work, a versatile synthetic route to functionalize vinylpyrrolidone (VP) with protected or unprotected aliphatic primary amine groups is described for the first time. Using these monomeric precursors polyvinylpyrrolidones (PVPs) with controlled load of side amine groups randomly distributed along the chains have been prepared. These functionalized VP and PVP systems are active molecules highly desirable for further couplings, i.e. they can easily afford the simple preparation of water soluble covalent side chain conjugates onto the PVP backbone. To show the potential of this functionalization, we have prepared functionalized polymers as a controlled release delivering vehicle, employing the bactericide and preservative 2-phenoxyethanol as a hydroxyl-containing model drug.

Chlorosulfonation of polystyrene substrates for bioanalytical assays: distribution of activated groups at the surface

In this work the activation of transparent PS substrates by chlorosulfonation is described and their distribution in the subsurface region is analyzed. For this purpose XPS, FTIR-ATR and colorimetry have been used. It is shown that the electrophilic aromatic substitution of polystyrene in pure chlorosulfonic acid is extremely quick with complete surface coverage by chlorosulfonic groups achieved after only a 10 minute reaction time at -10 °C. It is further demonstrated that the reaction is very surface selective and that even after reaction times as long as 3 hours, the modification is limited to a layer with a thickness of less than one micron. The activated PS substrates can be further functionalized in a second step with carboxylic groups. Due to the excellent optical transparency that the samples maintain upon modification, the modified systems were successfully probed for use in ELISA assays.

PVC bearing primary aliphatic or aromatic amine groups

The preparation of PVC compounds bearing primary aliphatic and/or aromatic amine groups exhibit several challenges which have been faced in this work. On the one hand, this polymer has never before been modified with aliphatic amine groups in a controlled manner or with a tailored degree of substitution. In this work we present a way to obtain, for the first time in a very selective way and with high degrees of substitution, PVC bearing aliphatic primary amine groups by chemical modification of the polymer. The modifier used for this purpose is 4-aminomethylthiophenol that has been synthesized starting from inexpensive benzyl chloride that is reacted with potassium phthalimide yielding a protected amine functionality. The aromatic thiol functionality, required for the introduction of the modifier molecule by nucleophilic substitution of PVC chlorine atoms is achieved by chlorosulfonation in para-position of the aromatic ring and reduction of the chlorosulfonyl group using sodium borhydride. This compound is used to modify PVC bearing a protected primary amine. The free amine is obtained after deprotection of the phthalimide moiety using hydrazine. On the other hand, the synthesis of primary aromatic amines has been described in the past using expensive precursors. In this work, 2-aminothiophenol or 3-aminothiophenol are used in order to modify the polymer with primary aromatic amine groups using inexpensive starting material.

Nonmigrating Equivalent Substitutes for PVC/DOP Formulations as Shown by a TG Study of PVC with Covalently Bound PEO–PPO Oligomers

Monoamino functionalized ethylenoxide (EO)/propylenoxide oligomers (Jeffamine) are linked chemically to poly(vinyl chloride) (PVC) using trichlorotriazine chemistry in order to prepare nonmigrating internally plasticized materials. The dependence of the plasticizer efficiency on both the number of anchoring points to the chains and the PVC/plasticizer compatibility is investigated using oligomers of different molecular weight and hydrophilic-hydrophobic balance. Hydrophilic oligomers (containing predominantly EO) of molecular weights between 2000 and 5000 g mol-1 exhibit excellent plasticizer efficiency, nearly identical to di-2-ethylhexylphthalate (DOP) in conventional PVC/DOP mixtures and may therefore be used as nonmigrating equivalents for DOP.

Effect of Ionizing Radiation on the Chemical Structure and the Physical Properties of Polycaprolactones of Different Molecular Weight

Polymers used in the biomedical sector can be exposed to ionizing radiation (X-ray, gamma) in vivo as implants or ex vivo for sterilization purposes (gamma, electron beam). This ionizing radiation can, at certain levels, cause degradation of the polymer. Polycaprolactones (PCL) of different molecular weights were irradiated with electron beam and the changes in their chemical structure and physical properties with the dose were evaluated. Electron beam irradiation produced crosslinking and chain scission in the PCL chain without significant predominance of one mechanism over the other. Minimum dose for gelation decreased with the increase in PCL molecular weight whereas crosslinking efficiency was almost independent of PCL molecular weight. Carboxylic groups, hydroxyl groups and new saturated hydrocarbon species were detected by proton nuclear magnetic resonance (NMR). These species were consistent with a mechanism where chain scission could take place at any bond in the PCL chain with preference in the –COO–CH2– bond. Crosslinking decreased significantly the crystallization temperature of PCL. Tensile properties decreased continuously with the increase in dose. Irradiation with gamma rays produced a faster decay in mechanical properties than electron beam.

Readily Available Highly Active [Ti]-Adamantyl-BINOL Catalysts for the Enantioselective Alkylation of Aldehydes

A series of enantiopure (R)-adamantyl 1,1′-binaphthalene-2,2′-diols were successfully synthesized in a straightforward one-step reaction from commercial products with excellent overall yields. The activity of chiral titanium catalyst derived from (R)-3,6,6′-tri(adamantan-1-yl)-[1,1′-binaphthalene]-2,2′-diol ligand, (R)-(2)-Ti, in the enantioselective asymmetric alkylation of aldehydes is significantly enhanced (up to 98% yield and 99% ee).