Abstract

Hyperbranched poly(ester amide) polymer (Hybrane™ S1200, M_n 1200 g mol⁻¹) was functionalized with maleic anhydride (MA) and propylene sulfide, to obtain multifunctional cross-linkers with fumaric and thiol end groups, S1200MA and S1200SH, respectively. The degree of substitution (DS) of maleic acid groups was controlled by varying the molar ratio of MA to S1200 in the reaction mixture. Hydrogels were obtained by UV cross-linking of functionalized S1200 and poly(ethylene glycol) diacrylate in aqueous solutions. Compressive modulus increased with decreasing S1200/PEG ratio and also depended on the DS of the multifunctional cross-linker (S1200). Also, heparin-based macromonomers together with functionalized hyperbranched polymers were used to construct novel functional hydrogels. The multivalent hyperbranched polymers allowed high cross-linking densities in heparin modified gels while introducing biodegradation sites. Both heparin presence and acrylate/thiol ratio had an impact on degradation profiles and morphologies. Hyperbranched cross-linked hydrogels showed no evidence of cell toxicity. Overall, the multifunctional cross-linkers afford hydrogels with promising properties that suggest that these may be suitable for tissue engineering applications.

Abstract

Abstract

Hydrophobically modified water-soluble polymers have been prepared by copolymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and isodecyl methacrylate (iDMA) in N,N-dimethylformamide under nitrogen atmosphere, varying the composition feed. Fluorescence spectroscopy was used to further confirm the copolymers self-aggregate in water. Critical concentration of the self-aggregate formation (CAC) decreased by increasing the molar fraction of iDMA in the AMPS_co copolymers and varied between 1.20 and 0.04 g/L depending on the degree of hydrophobic modification. Hence, copolymer composition and charge density allowed tuning the pseudomicellar characteristics of these new amphiphilic copolymers. The addition of a salt or a low-molecular-weight surfactant was studied. Binding of CTAB to the AMPS_co copolymers leads to a high decrease of CAC, i.e., 0.006 g/L. Effect of the composition in the viscosimetric behavior of the hydrophobically modified copolymers AMPS_co was investigated. The removal of single metal ions, Cu²⁺, and m-cresol from aqueous solutions by ultrafiltration with the help of the copolymers was investigated. Equilibrium dialysis experiments demonstrate that the formation of hydrophobic microdomains can be used to control the sequestration of foulants, and thus these novel copolymers have potential application as polymeric surfactants in micellar-enhanced ultrafiltration processes for water purification. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

The photopolymerization of bicontinuous microemulsions was simultaneously monitored with differential scanning calorimetry and fluorescence. The kinetics and mechanism of the reaction were studied throughout the entire photopolymerization reaction. The role played by the surfactant in the kinetics and morphology was studied. The nature of the surfactant changed the autoacceleration process and final conversion. The behavior was explained as a result of the differences in the interfacial properties. Anionic cetyltrimethylammonium bromide (CTAB) gave rise to a more flexible interfacial film than anionic sodium dodecyl sulfate (SDS), resulting in competition between the intramolecular and intermolecular reactions in the former systems. As cyclization did not contribute to the increase in the degree of crosslinking, SDS photopolymerization gave solids with a more rigid microstructure. Fluorescence methodology was applied to monitor bicontinuous microemulsion polymerization and to reveal the microstructure and morphology development during photopolymerization. The microemulsion composition was designed to prepare nanoporous, crosslinked materials. Even though the nanostructure of the precursor microemulsions was not retained because of phase separation during polymerization, mesoporous solids were obtained. Their morphologies depended on the nature of the surfactant, and membranes with open cells were successfully prepared with CTAB, whereas more complex morphologies resulted with SDS. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5291–5303, 2006

The results of following the fluorescence of selected probes during the entire range of curing of acrylic-based adhesives are presented in this work. The change of fluorescence parameters has been continuously measured during the photocrosslinking reactions of acrylic adhesive systems under UV-irradiation. Real-time FT-IR (RT-FT-IR) has been used to measure the conversion reached at different irradiation times. Intensity ratio, maximum emission wavelength and the first moment of fluorescence have been used as parameters to correlate with the double bond conversion degree. Two-slope plots have been obtained during UV-curing, which correspond to the different stages of the crosslinking reaction. Also, the size of fluorescent probe appears to be a parameter that influences the sensing time in which the probe can detect the changes in viscosity/polarity occurring along the UV-curing process. The results are compared with those of commercial probes such as dansylamide and prodan. The use of the fluorescence technique allowed us to understand the mechanism taking place and the role of the binder matrix, depending on the photoinitiator used. This information is not obtained when the reaction is followed by the conventional RT-FT-IR technique.

The photopolymerization of acrylic-based adhesives has been studied by Fourier transform infrared and fluorescence analysis in real time. Real-time infrared spectroscopy reveals the influence of the nature of the photoinitiator on the kinetics of the reaction. Furthermore, the incident light intensity dependence of the polymerization rate shows that primary radical termination is the predominant mechanism during the initial stages of the curing of the acrylic system with bis(2,4,6-trimethylbenzoyl) phenyl phosphine oxide (TMBAPO) as a photoinitiator. The fluorescence intensity of selected probes increases during the ultraviolet curing of the adhesive, sensing microenvironmental viscosity changes. Depending on the nature of the photoinitiator, different fluorescence–conversion curves are observed. For TMBAPO, the fluorescence increases more slowly during the initial stage because of the delay in the gel effect induced by primary radical termination. Mechanical tests have been carried out to determine the shear modulus over the course of the acrylic adhesive ultraviolet curing. In an attempt to extend the applications of the fluorescence probe method, we have undertaken comparisons between the fluorescence changes and shear modulus. Similar features in both curves confirm the feasibility of the fluorescence method for providing information about microstructural changes during network formation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4236–4244, 2002

A series of different copolymers of 2-acrylamido-2-methylpropanesulfonic acid, AMPS, and butyl methacrylate, BuMA, were prepared by free radical polymerization at 70°C in N,N ′-dimethylformamide under nitrogen atmosphere varying the composition feed. The polyamphiphiles isolation was carried out by passing the polymeric solutions through a sodium cation exchange resin. The stabilities of the obtained homopolymers and copolymers were characterized by thermal analysis (TGA, DSC). Fluorescent probes were used to study the hydrophobic microdomain formation due to the association phenomena observed in water solution when the amphiphilic copolymer concentration was increased. The fluorescence emission of amino derivatives of 7-nitrobenz-2-oxa-1,3-diazole (NBD) showed sensitivity to detect polarity and microviscosity changes in the microenvironment of the copolymers. The minimum concentration for the hydrophobic microdomains formation, C_m , decreased by increasing the molar fraction of BuMA in the AMPS_Co copolymers. Hence, copolymer composition and charge density allowed tuning the pseudo-micellar characteristics of these new polyamphiphilic copolymers.

The use of the fluorescence technique for monitoring the UV-curing of two polyurethane-based adhesives containing acrylic monomers is described in this paper. The increase of the fluorescence intensity as well as the maximum wavelength shift on emission was measured in real time during the photopolymerisation process. The established relationship between fluorescence and conversion allowed monitoring of the course of the process beyond vitrification. In that sense, all the fluorescent probes studied were sensitive to the formulation curing and in some cases, the range of conversions in which they were useful was limited by their size and probably, by the free volume fraction in the polymeric matrix. Moreover, polymerisation rates were obtained from fluorescent kinetic profiles and used to carry out a comparative study of the different photosensitive formulations. The real time FTIR (RTIR) results show the highest photoinitiation efficiency of the photoinitiator 2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone (Irgacure 369) compared to that of 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651). The limitation of RTIR method for monitoring slow post-reactions was overcome by the use of the fluorescence-based method. Thus, a fluorescence intensity increase and a blue-shift of the emission band were measured after the limiting conversion was attained. Dynamic mechanical analysis showed that the glass transition temperature of the polymer increases during prolonged exposure to irradiation confirming the increase of the system rigidity.