Ligia Gargallo

Unperturbed dimensions of polyvinylpyrrolidone in pure solvents and in binary mixtures

Abstract The properties of dilute solutions of polyvinylpyrrolidone in various solvents are studied by measurements of viscosity and osmotic pressure. The unperturbed dimensions are determined in two theta solvents, in good solvents and in solvent mixtures. The existence of unperturbed states which are different in pure solvents, salty/aqueous media and organic/aqueous media is discussed on the basis of the nature of the side-group interactions in the chain itself and with the solvent. The results show, in general, a variation of the unperturbed dimensions with the solvent nature.

Effect of the side chain structure on the glass transition temperatures of some poly(thiocarbonate)S

Abstract A series of poly(thiocarbonate)s with aliphatic, aromatic and cycloaliphatic side groups has been prepared and the glass transition temperatures ( T g )s of these polymers were measured by differential scanning calorimetry (DSC). The magnitude of the T g was related to the bulkiness, flexibility, and polarity of the pendant groups attached to the polymer main chain. A general decrease in T g values is observed when these polymers are compared with the corresponding poly(carbonate)s analogues. Theoretical calculation of T g for some of the polymers were carried out using the method described by Van Krevelen et al. These values are in fair agreement with the experimental values. The critical value of the chain length at which T g becomes constant ( T g −8 was calculated for all the polymers using the relation proposed by Cowie. It was found that the molecular weights of the polymers are too low for T g to become independent of the chain length.

Synthesis and solution properties of comb-like poly(mono-n-alkyl-itaconates): 2. Poly(monododecyl itaconate)

Abstract The monoester of itaconic acid with n-dodecyl alcohol was synthesized and polymerized. Polymer fractions were characterized by viscometry, size exclusion chromatography (s.e.c.) and light scattering. Thermodynamic and dimensional parameters were determined and calculated. The results found are 67 A for the statistical segment length l and 8 A for the chain diameter d . These results are compared with those reported previously for a similar compound.

Polymer conformation and viscometric behaviour—II. Conformational transition in (benzyl methacrylate-cyclohexylmethyl methacrylate) copolymers in dilute solution

Abstract Copolymers of benzyl methacrylate with cyclohexylmethyl methacrylate were synthesized. The reactivity ratios of the monomers were established. Osmotic and viscometric measurement were made in isobutyl methyl ketone (IMK) and toluene at 25° for a copolymer of equimolar composition. The viscometric relations in both solvents were established. Viscometric studies of fractions of the 1:1 copolymer show discontinuities in the intrinsic viscosity [η] as a function of temperature and sharp changes in the unperturbed dimensions of the chain in IMK. Variations of the refractive index increment in the same temperature range were observed. This behaviour is interpreted as a conformational transition of the copolymer chain. The results are discussed in relation to the behaviour of the homopolymers in the same solvent.

2-Vinylpyridine-co-N-vinyl-2-pyrrolidone and 4-vinylpyridine-co-N-vinyl-2-pyrrolidone copolymers : Synthesis and reactivity ratios

Copolymers containing 2-vinylpyridine (2VPy) and 4-vinylpyridine (4VPy) with N-vinyl-2-pyrrolidone (VP) (2VPy-co-VP and 4VPy-co-VP, respectively) were synthesized and characterized. Copolymers with different compositions were obtained. The reactivity ratios were estimated by using the classical Finemann–Ross and Kelen Tudos linear procedures. These parameters were also estimated by using a computer program based on a non-linear minimization algorithm (NLMA), starting from the values of r1 and r2 obtained by the above linear procedures. Random copolymers with zones containing vinylpyridine blocks were obtained.

Bio-foam enhances larval retention in a free-spawning marine tunicate

Here we report a mechanism that reduces dispersal of early developing stages and larvae in a free-spawning intertidal and shallow subtidal tunicate, Pyura praeputialis (Heller 1878), in the Bay of Antofagasta, Chile. The spawning of gametes by the tunicate into the naturally turbulent aerated seawater decreases their surface tension and induces the formation of a bio-foam. Water collected from foamy intertidal pools and tide channels showed a high concentration of P. praeputialis early developing stages and tadpole larvae in the foam. Because gametes are synchronically spawned for external fertilization and larvae settle near adults, our results suggest that this bio-foam increases fertilization success and effective settlement of their short-lived larvae in the vicinity of the adults spawning the gametes. This mechanism reinforces published evidence suggesting that local retention of intertidal and inshore marine invertebrate larvae may be more common than previously thought, offering, for instance, new perspectives for the design and networking of marine protected and management areas.

Synthesis, solution properties and chain flexibility of poly(2,6-dimethylphenyl methacrylate)

Abstract The dilute solution properties of poly(2,6-dimethylphenyl methacrylate) (PDMP) in various solvents were studied by viscosity, size exclusion chromatography (s.e.c.) and osmotic pressure measurements. The Kuhn-Mark-Houwink-Sakurada (KMHS) relationships were established. The unperturbed dimensions 2 > 1 2 0 , the rigidity factor σ, the characteristic ratio C ∞ , and the thermodynamic parameters were determined by using the Stockmayer-Fixman equation, from viscometric data in good and theta conditions in pure and mixed solvents. The results show that preferential adsorption of water in the mixture THF/water, should not play an important role in the determination of the conformational parameters in this system. In addition, the measured rigidity of PDMP can be explained assuming that this polymer behaves as a kinked-chain molecule. The conformational behaviour of this polymer is analysed in terms of the effect of the side chain structure in relation to poly(phenyl methacrylate) (PPh).

Interaction of polyvinylpyrrolidone with small cosolutes in aqueous and non aqueous media

Abstract The properties of dilute solutions of polyvinylpyrrolidone (PVP) in aqueous and non-aqueous solvents in the presence of small molecules are studied by measurements of intrinsic viscosity, [η]. The unperturbed dimensions are determined in pure solvents and in solvent mixtures. There are different unperturbed states, depending on the solvent and the solvent/cosolute mixture. These results are discussed on the basis of the nature of the side group interaction with the solvent and the cosolute. The role of the preferential adsorption of one of the cosolute on the polymer was considered. It would seem that the solvent plays an important role in the type of interaction.

Polymer conformation and viscometric behaviour

SummaryThe viscometric and refractometric behaviour of poly (benzyl methacrylate) (PBM) in isobutyl methyl ketone (IMK) as a function of the temperature was studied. The viscometric relations in IMK and toluene by membrane osmometry and GPC at 25°C were established. The viscometric results show discontinuities in the intrinsic viscosity [η] in IMK and sharp changes in the conformational and thermodynamic parameters Kθ and B. The variation on the unperturbed dimensions of the polymer chain was attributed to a conformational transition. The influence of the side groups was analyzed. The conformational behaviour of this polymer was compared with the saturated corresponding poly (cyclohexyl methyl methacrylate).

Synthesis and monomer reactivity ratios of (vinylcyclohexane-co-N-vinyl-2-pyrrolidone) copolymer

A copolymer containing vinylcyclohexane (VCH) and N-vinyl-2-pyrrolidone (VP) at different compositions was synthesized and characterized. The monomer reactivity ratios (MRR) were estimated by using the classical Fineman–Ross and Kelen–Tudos linear fitting methods. These parameters were also estimated using a nonlinear computational fitting procedure, known as reactivity ratios error in variable model (RREVM). In this case, the values of MRR are rVP=2.2 and rVCH=0.0. Composition shifts and MRR values for (vinylcyclohexane-co-N-vinyl-2-pyrrolidone) copolymer (VCH-co-VP) are interpreted in terms of the relative comonomeric structures. A copolymer with zones containing VP blocks with isolated units of VCH between them is obtained. The presence or absence of the resonance stabilization effect is taken into account. The results are compared with those of similar related copolymeric systems.