M.J. Fernández-Berridi

Blends of amorphous and crystalline polylactides with poly(methyl methacrylate) and poly(methyl acrylate): a miscibility study

Abstract Blends of amorphous and crystalline polylactides (PDLA and PLLA) with poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) have been prepared. Thermal behaviour and miscibility of these blends along the entire composition interval were studied by differential scanning calorimetry (d.s.c.). The results were compared with those obtained by dynamic mechanical analysis (DMTA). Only one Tg was found in PDLA/PMA and PDLA/PMMA blends, indicating a high degree of miscibility in both systems. Nevertheless, the PDLA/PMMA blend presented enlargements of the Tg width at high PMMA contents. In this case, additional evidence of complete miscibility was obtained by studying the evolution of the enthalpic recovery peaks which appear after different thermal annealing treatments. When the polylactide used was semicrystalline (PLLA), once the thermal history of the blends had been destroyed, crystallization of PLLA was disturbed in both blends PLLA/PMMA and PLLA/PMA, but in a rather different fashion: in the first case crystallization was almost prevented while in the second one it was favoured. This behaviour was explained in terms of the effect of the higher stiffness as indicated by the value of Tg for PMMA compared to that for PMA.

Thermal and infra-red spectroscopic investigations of a miscible blend composed of poly(vinyl phenol) and poly(hydroxybutyrate)

Thermal properties of poly(vinyl phenol) (PVPh) and poly(hydroxybutyrate) (PHB) blends were investigated by differential scanning calorimetry over the entire range of composition. Mixtures with both bacterial (tactic) PHB and synthetic (amorphous) PHB were considered. In all cases, blends showed a unique glass transition temperature. The presence of 40% PVPh prevents bacterial PHB crystallization. Infra-red spectra showed the presence of hydrogen-bonded carbonyl signals which increased with PVPh fraction, showing the extent of specific interactions.

Graft copolymers for biomedical applications prepared by free radical polymerization of poly(L-lactide) macromonomers with vinyl and acrylic monomers

Abstract Poly( l -lactide) macromonomers have been copolymerized with methyl methacrylate, methyl acrylate N,N′-dimethyl acrylamide (DMA) and N-vinyl pyrrolidone (VP) in order to obtain biodegradable-biocompatible comb-like copolymers with different hydrophilic characteristics. Comonomer reactivity ratios have been determined and compared with those obtained when the same comonomers are copolymerized with a model compound of the macromonomer. All results are in the range of values reported in the literature for the same comonomers in similar copolymerization processes. However, macromonomer reactivity differs from that of the model compound, depending on the comonomer considered. Thus, striking deviations are found when VP or DMA are concerned. It seems that compatibility between the growing chain and the macromonomer plays the main role in the copolymerization behaviour of the macromonomer. Miscibility studies of blends of poly( dl -lactate) (PDLA) with poly(methyl methacrylate), poly(N,N′-dimethyl acrylamide) (PDMA) and poly(N-vinyl pyrrolidone) (PVP) confirmed the repulsive interactions between PDLA and PVP and PDMA chains, which account for the deviations in the reactivity of the macromonomer when compared with that of the model compound.

Survey on transport properties of liquids, vapors, and gases in biodegradable poly(3-hydroxybutyrate) (PHB)

The transport properties of carbon dioxide, water, and different organic solvents in bacterial poly(3-hydroxybutyrate) (PHB) at 30°C were investigated. CO2 sorption was measured by the gravimetric method using a recording microbalance at subatmospheric pressures. Results were adequately interpreted in terms of Henrys law. Organic solvent and water permeabilities for both vapors and liquid were measured using a gravimetric cell. The data were interpreted in different terms depending on the units in which permeability was measured. Most of the solvent-polymer systems showed the typical time-lag plot, but in liquid permeation experiments, some anomalous behaviors were observed, with a transient period of rapid permeation at the beginning of the experiment before reaching the steady state. The transport properties of PHB were compared with those of other polymers, either from synthetic or biodegradable origin.

Concerning the self‐association of N‐vinyl pyrrolidone and its effect on the determination of equilibrium constants and the thermodynamics of mixing

Hydroxylated (co)polymers form miscible blends with a wide variety of (co)polymers that contain proton acceptor groups, such as esters, ethers, pyridines, etc. The former strongly self-associate through the formation of OH/OH hydrogen bonded interactions, while the latter do not self-associate to any measurable exent. With appropiate self- and interassociation equilibrium constants and anthalpies of hydrogen bond formation, we have been able in the past to successfully predict the phase behavior of such hydrogen bonded polymer blends. At first glance, the vinyul pyrrolidone group appears to be just another proton acceptor and if the appropiate interassociation equilibrium constant value is determined we should be able to predict the phase behavior of hydroxylated (co)polymer blends with (co)polymers containing the vinyl pyrrolidone group. However, it is not that simple. Using infrared spectroscopy we demnstrate in this work that the pyrrlidone group strongly self-associates through transition dipole coupling. Ramifications to the determination of equilibrium constants, the free energy of mixing and the phase behavior of blends involving the vinyl pyrrolidone group are discussed.

Determination of the solubility parameter of poly(ethylene oxide) at 25°C by gas-liquid chromatography

Abstract The solubility parameter of poly(ethylene oxide) at 25°C has been determined using the method developed by DiPaola-Baranyi and Guillet, by the extrapolation of the values of the interaction parameter χ, at high temperatures, ranging from 70°–90°, 90°–110° and 110°–130°C down to 25°C. The values of the solubility parameter obtained, depending on the temperature ranges employed, are 9.8, 9.9 and 10.1, respectively.

Phenoxy blends: an approach to the miscibility by FTi.r. and chemical modification of the interacting sites

Abstract In this work, FTi.r. spectroscopy has been used in order to verify the proposed influence of the hydroxyl group, present in each monomeric unit of the phenoxy (PH) resin, in the observed miscibility of this polymer with a variety of other polymer families such as polyoxides or polyesters. Two different approaches have been used for this purpose. First, FTi.r. studies at different temperatures have been carried out on mixtures of PH with polyoxides, in order to demonstrate the higher strength of the hydrogen bonds in the mixture with respect to those existing between pure PH molecules. Second, chemical modification of the PH resin, with a controlled elimination of the repetitive hydroxyl, has been carried out intending to relate the percentage of hydroxyl substitution to the observed miscibility of PH. In the second approach, mixtures of PH and modified PH with poly(N-vinyl-2-pyrrolidone) have been studied.

Thermal and mechanical behaviour of self-curable waterborne hybrid polyurethanes functionalized with (3-aminopropyl)triethoxysilane (APTES)

Two series of self curable polyurethanes were synthesized using an aliphatic diisocyanate (isophorone diisocyanate), an anionic diol (2-bis(hydroxymethyl) propionic acid) and two different soft segments poly(1,4-butylene adipate) end capped diol (semicrystalline polyester) and poly (propylene glycol) end capped diol (amorphous polyether). In both cases the polyurethanes were end-capped with (3-aminopropyl)triethoxysilane to impart the films the ability to crosslink at room temperature. The thermal and mechanical properties of the cured films can be tailored with the alkoxysilane concentration. Thus, as the alkoxysilane content increases, the resulting systems present a higher degree of phase separation, according to both DSC and DMTA results. In addition, TGA results confirm that their thermal stability also increases and finally, the modulus increases and the strain decreases as a function of the crosslinking degree.

Determination of the interaction parameter χ of poly(ethylene oxide) by gas-liquid chromatography below the melting temperature

Abstract The interaction parameter χ of poly(ethylene oxide) in different solvents at temperatures below the melting point (Tm) of the polymer has been determined by means of the solubility parameters of the polymer and solvents at this temperature, chromatographically obtained from their values at higher temperatures (70°–140°C). The value of the interaction parameter so obtained is not only in good agreement with those calculated by other techniques but also independent of the temperature range employed in the chromatographic measurements. Moreover, using the equation-of-state theory formulation, we have determined values of the interaction parameter χ∗ for different poly(ethylene oxide)/probe systems and from it the contact interaction energy X12, in the temperature range between 70° and 140°C.

On the application of an association model to blends of phenoxy and ether-containing polymers

Abstract An association model is used to predict phase behaviour in mixtures of poly(hydroxy ether) of bisphenol A (phenoxy) (PH) with poly(alkylene oxide)s, poly(vinyl alkyl ether)s, aromatic polyethers and related copolymers. Equilibrium constants and enthalpies corresponding to self-association of PH and interassociation of PH with the second component were calculated from a Fourier transform infra-red spectroscopy study of low molecular weight analogues in dilute solutions. Transferability of the association constants between model compounds and polymer blends, as well as model predictions of blend miscibility and phase diagrams, are discussed.