Ana Mantecón

Unsaturated modified poly(vinyl alcohol). Crosslinking through double bonds

Poly(vinyl alcohol) (PVA) was esterified with 10-undecenoyl chloride to give polymers with different degrees of modification which were studied in order to find how the concentration of reactive sites can influence the crosslinking process. The polymers obtained were characterized by spectroscopic techniques, elemental analysis and thermal methods. Weight average molecular weights and viscosities were determined. Thermal crosslinking of the double bonds on the side chain took place in all cases, but was overlapped by the degradation process. Thus, dicumyl peroxide had to be used to obtain the cured material and avoid degradation. Activation energies for radical initiated crosslinking were determined by means of dynamic DSC studies. Isoconversional kinetic analysis was applied to DSC data and the dependences of activation energies on conversion degrees were obtained and compared with those obtained from polymers with the same pendant chain but a more flexible polyether main chain.

Synthesis and Crosslinking of a Series of Dimeric Liquid Crystalline Epoxy Resins Containing Imine Mesogens

Eight aromatic imine liquid crystalline (LC) diepoxides with dimeric architecture from readily available commercial reagents were synthesized and characterized by spectroscopic techniques. We characterized their liquid crystalline mesophases by differential scanning calorimetry (DSC), hot-stage polarized-light optical microscopy (POM) and wide-angle X-ray diffraction (WAXS). The mesomorphism of the products was related to their structure, which varies in the length of the central spacer. Odd-membered spacer mesogens lead to the formation of smectic C mesophases, whereas even-membered samples of this series lead to the formation of smectic A and/or nematic mesophases. By relating the calculated molecular parameters to the layer spacings obtained by WAXS, we deduced the organization of the mesogens in the smectic phases, since the dimeric compounds present a variety of possible arrangements. Liquid crystal thermosets (LCTs) were obtained from these monomers by isothermal curing with equimolar amounts of 2,4-diaminotoluene (DAT). The curing process was studied by calorimetry and their thermal stability was evaluated by thermogravimetry (TGA). Most monomers produced nematic-like networks, but in one case a smectic C mesophase was also locked.

Poly(vinyl alcohol) modified with carboxylic acid anhydrides: crosslinking through carboxylic groups

The reaction of carboxylic acid anhydride with poly(vinyl alcohol) (PVA) leads to vinyl alcohol—vinyl ester copolymers which contain carboxylic acid groups. Esterification enables degrees of modification to be reached which depend on the chemical structure of the anhydride introduced and the ratio of the reagents in the feed. The copolymers obtained were characterized by spectroscopic techniques, elemental analysis, and thermal methods. These half-esters reacted in a second step with aromatic diglycidyl ethers to obtain tridimensional networks. This crosslinking reaction through the carboxylic groups was studied by differential scanning calorimetry. The water absorption of the linear and crosslinked polymers was determined gravimetrically as a function of time at room temperature.

Curing of N,N′-diglycidylimides with polyfunctional compounds

Abstract This paper describes the curing reactions of new N , N ′-diglycidylimides containing trimellitimide units. Reactions were carried out using several polyfunctional curing agents, viz. aromatic primary diamines and phthalic anhydride. Spectroscopic techniques were used to study the curing process. The course of reaction was followed by i.r. spectroscopy. Some intermediate species were detected by recording 13 C-NMR spectra until the products became insoluble in the usual deuterated solvents.

Study of Lanthanide Triflates as New Curing Initiators for Cycloaliphatic Epoxy Resins

Lanthanide triflates, a new class of cationic initiators, have been tested as curing agents for cycloaliphatic epoxy resins. Several metal salts in various proportions have been used. The triflate salts were compared with the conventional BF 3 MEA system. the processes have been kinetically evaluated by isoconversional analysis, time and temperature predictions have been made. Their mechanical properties have been evaluated by dynamic mechanical thermal analysis (DMTA).

Studies on the microstructure of poly(phenyl glycidyl ether) using the 13C nuclear magnetic resonance technique

Abstract Microstructural details of poly(phenyl glycidyl ether) (PPGE) and its optically active form obtained by the aluminium isopropoxide (AIP)/ZnCl2 ionic-coordinative initiator were analysed by nuclear magnetic resonance techniques. In order to assign the soluble fraction signals unmistakably, PPGE samples had to be synthesized using various cationic initiator systems. Several modifications were studied in the AIP/ZnCl2 initiator system (such as the use of various zinc salts and the addition of water) and the tacticity and irregularity contents of the polymers were determined.

New glycidyl ester compounds containing a preformed imide ring. I

Abstract The synthesis of the new esterglycidyl compounds produced by condensation of bis-carboxyimides with a large excess of epichlorohydrin were reported. To define the optimal conditions of condensation the process with monofunctional compounds were studied at first. For all synthesis, yield and epoxide and chlorine contents were found. The structure of glycidyl esters was determined by elementary analysis, IR and 1H and 13C NMR spectra. The physical properties were also defined.

New dimeric LC-epoxyimine monomers with oxyethylene central spacers. Crosslinking study

Abstract We have studied how substituting alkylene by oxyethylene spacers influences the mesomorphic behavior of LC-dimeric epoxy resins with imine groups in the mesogens. This structural variation has been shown to diminish the mesomorphic characteristics of the dimeric epoxy resins containing oxyethylene spacers. These compounds only show mesomorphic behavior when the mesogens are polarized by the presence of an ester and an ether group at their ends. When the ester group is located in the inner position, smectic mesophases have been observed. Depending on the parity of the central spacer, these smectic mesophases are of type A or C. Moreover, when the ether group is in the inner position only monotropic nematic mesophases are formed. By curing these compounds with primary or tertiary amines, the monotropic character and the low isotropization temperatures of compounds with the ether group in the central position prevent an ordered network from becoming fixed. However, LC-epoxy resins with ester groups in the inner position lead to the fixation of homogeneous smectic-C like networks only when the spacer was diethylene oxide.

Curing reaction of diepoxyimides. A DSC study

Abstract The crosslinking of diepoxyimides has been studied for 1,6-bis(N-glycidyl-4-oxycarbonyl-phthalimido) hexane. Diepoxyimides can cure by heating and also by the action of curing agents. DSC was used to follow the reaction; both dynamic and isothermal methods were applied in order to obtain the kinetic parameters for the self-curing and the curing by means of bis(4-aminophenyl)methane and phthalic acid anhydride. The values obtained for the reaction orders and activation energies from the various methods correlate fairly well, and were comparable to those reported for the curing of epoxyde systems.

Polymerization of phenylglycidylether derivatives with functional ester groups

Abstract A series of methyl ω -[ p -(2,3-epoxypropoxy)phenyl] alkanoate esters of different lengths is prepared using a multistep synthetic method. These compounds which have 0, 1, 2, 5, 8 and 11 methylene groups are homopolymerized and copolymerized with non-functionalized phenylglycidylether (PGE) using the ionic coordinative initiator described by Teyssie. Other ionic-coordinative initiators were found to be less effective. All homo- and copolymers are characterized by NMR spectroscopy and their tacticity is determined. Their thermal characteristics were also studied by DSC.