Viorica Gaina

Re-Mendable Polyurethanes

Novel re-mendable polyurethanes were prepared by the Diels-Alder cycloaddition reaction of urethane bismaleimides to bisfuryl monomers. The urethane bismaleimides were synthesized by an addition reaction of 4-maleimidophenylisocyanate to macrodiols, such as polycaprolactone diol (Mn − 1250 and 2000), PEA-2000 and PBA-2000. The bisfuryl monomers were obtained by the reaction of 2-furfuryl alcohol with hexamethylene diisocyanate or by open-ring reaction of the oxirane ring from diglycidyl bisphenol A with furfuryl amine.

Optical properties of some new azo photoisomerizable bismaleimide derivatives.

Novel polythioetherimides bearing azobenzene moieties were synthesized from azobismaleimides and bis-2-mercaptoethylether. Kinetics of trans-cis photoisomerization and of thermal conversion of cis to trans isomeric forms were investigated in both polymer solution and poly(methyl methacrylate) doped films using electronic absorption spectroscopy. Thermal recovery kinetics is well described by a two-exponential relation both in solution and polymer matrix, while that of low molecular weight azobismaleimide fit a first-order equation. The photoinduced cis-trans isomerization by visible light of azobenzene chromophores was examined in solution and in polymer films. The rate of photoinduced recovery was very high for azobismaleimides.

Novel Thermally-Reversible Epoxy-Urethane Networks

Thermally-reversible epoxy-urethane networks are prepared by the reaction of diamines and diepoxy monomers containing two Diels–Alder adducts. The diepoxy compounds are formed via a Diels–Alder reaction between two epoxy-containing furans and bismaleimides having urethane moieties. The urethanebismaleimides were obtained by the reaction of 4-maleimidophenylisocyanate with poly(tetrahydrofuran) diols with M n = 650, 1000 and 1450. The epoxy-urethane networks display two glass transition temperatures in the range of –70 and –50°C for the soft segment and 81–84°C for the hard segment. At temperatures exceeding 116°C the retro Diels–Alder reaction occurs, which leads to a significant loss in modulus.

Studies on new hybrid materials prepared by both Diels–Alder and Michael addition reactions

New polyurethane chemically crosslinked networks containing silica were synthesized by both Diels–Alder polymerization and Michael addition reaction. Structural characterization of the products was evidenced by proton nuclear magnetic resonance and attenuated total reflectance in conjunction with Fourier transform infrared spectroscopy techniques. Differential scanning calorimetry was used to demonstrate the thermally remendable character of the materials obtained through Diels–Alder polymerization. The influence of increasing silica content on the glass transition temperatures was studied. It was observed that the glass transition temperatures increased with increasing silica content. Absolute heat capacities and crosslinking densities were determined for the thermoreversible materials. A comparison between materials obtained through Diels–Alder process and Michael addition method was studied. A kinetic study was conducted via an isoconversional method. Morphological studies were conducted by atomic force microscopy technique.

Study on the Chemical Modification of Poly(Vinyl Alcohol) with 4-Maleimidophenyl Isocyanate

Poly(vinyl alcohol) (PVA) was structurally modified by the reaction of hydroxyl groups with 4-maleimidophenyl isocyanate (MPI). The substitution degree of the modified PVA was determined by 1H-NMR spectra and varied in the range 7.7 and 34.4%. Structures of polymers were confirmed by ATR-FTIR and 1H-NMR spectroscopy and properties were studied by thermal and mechanical analysis (dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis and stress-strain). By heating of modified PVA at 200°C, the glass transition temperature and modulus were improved.

Polyimides Containing 1, 4-Dithiine Units and their Corresponding Thiophene 2, 3, 4, 5 Tetracarboxylimide Units

Polyimides containing 1, 4-dithiine units and corresponding thiophene units were synthesized by the nucleophilic substitution reaction of bis(dichloro-maleimide) arylene derivatives with sodium sulfide. Their structures were confirmed by IR and UV spectroscopy and elemental analysis. The polymers were characterized by viscosimetric measurements, softening points and thermogravimetric data.

Bismaleimides and Biscitraconimides with Bisallyl Groups

Bismaleimides and biscitraconimides with bisallyl groups were synthesized by the condensation reaction of 3(4)-maleimidobenzoic chloride or 3(4)-citraconimidobenzoic chloride with diallylbisphenol A. Diallylbisphenol A was prepared by the reaction of bisphenol A with allyl bromide followed by Claisen thermal rearrangement by heating at 180° C. The structures were confirmed by IR, 1 H NMR, 13 C NMR spectroscopy. The compounds were characterized by differential scanning calorimetry and thermal analysis.

THERMAL CHARACTERIZATION OF POLYAMINOBISMALEIMIDE PREPOLYMERS

Polyaminobismaleimide prepolymers were obtained by a Michael addition reaction of a 4,4′-diaminodiphenylmethane (DDM) to 4,4′-bismaleimidodiphenylmethane (BMI) by melt polymerization, in various molar ratios of DDM:BMI. The thermal parameters of the polyaddition reaction and the thermal polymerization were evaluated by differential scanning calorimetry (DSC). The DDM:BMI molar ratio and the reaction time influence the residual amine groups and number-average molecular weight (Mn).

New Bismaleimide-Epoxy Resin System

New functional epoxy resins were prepared by the reaction of dialyldiglycicylbisphenol A (DADGBPA) with diaminodiphenylmethane. DADGBPA was prepared by reaction of o,o′-diallylbisphenol A with epichlorhydrine. By reaction of functional epoxy resins with bismaleimides, new epoxy-bismaleimide resins with good thermostability were obtained. The thermal properties of epoxy resins and epoxy-bismaleimide resins were determined by DSC and TGA measurements.

Studies on Diels–Alder thermoresponsive networks based on ether–urethane bismaleimide functionalized poly(vinyl alcohol)

Thermoreversible networks obtained by the Diels–Alder cycloaddition reaction of poly(vinyl furfural) with urethane bismaleimides containing polyether chain were synthesized. The formation of the networks was confirmed by attenuated total reflectance in conjunction with Fourier transform infrared spectroscopy (ATR–FTIR). The materials thermal properties were investigated using differential scanning calorimetry (DSC) and a coupling of dynamic thermogravimetry with Fourier transform infrared spectroscopy and mass spectrometry (TG–FTIR–MS) for pyrolysis behaviour under nitrogen atmosphere. A thermal decomposition mechanism of the networks and poly(vinyl furfural) was discussed via evolved gas analysis. The thermoreversibility of the networks was demonstrated by the presence of the endothermic peak characteristic to the retrodienic process on the DSC heating curves and also the appearance of the exothermic peak, due to the dienic process, on the DSC cooling curve. The dynamic contact angle and free surface energy values of the networks were determined. Measures of the heterogeneity and roughness of the surfaces suggested that the surfaces of the networks’ films are more homogenous than the initial poly(vinyl furfural) surface. Dynamic water vapour sorption studies were conducted.