Rubén V. Figini

Dynamics properties of polymer solutions (I). Dilute-semidilute transition

Measurements of viscosity and dielectric relaxation were carried out using several solutions of cellulose trinitrate polymer in isophorone in the dilute and the semidilute regime. In each case, the renormalization group theory was applied to the data using the De Genness blobs model for connecting dynamic and conformational quantities. There was adequate agreement between the experimental results and the theoretical predictions to show universal behavior. The values of β were independent of both molecular weight and polymer concentration and could be used to describe a variety of dynamic properties. These findings suggest that only one scaling variable is necessary for such purposes.

Emulsion-precipitation polymerization of diisopropyl fumarate

The emulsion polymerization of diisopropyl fumarate initiated with a redox initiator and an anionic emulsifier was investigated. The study includes conversion and particle number determinations as a function of time, temperature and the concentrations of initiator, emulsifier and monomer. The reaction is characterized by a limiting conversion following a linear increase of the conversion with time from the beginning on. The reaction rate is very much higher than those obtained in bulk or in solution polymerization. Taking into account the results and the response of the system to an addition of styrene and toluene, a mechanism of radical occlusion together with a diffusion-controlled propagation in the polymer matrix is proposed. The very high apparent activation energies for the propagation and limiting conversion suggest a complex behavior. Die mit einem Redoxsystem initiierte Emulsionspolymerisation von Diisopropylfumarat in Gegenwart eines anionischen Emulgators wurde untersucht. Umsatz und Teilchenzahl wurden als Funktion von Zeit und Temperatur sowie von Initiator-, Emulgator- und Monomer-Konzentration gemessen. Die Reaktion ist charakterisiert durch einen begrenzten Umsatz, der von Beginn an einer zeitlichen linearen Zunahme der Polymerausbeute folgt. Die Reaktionsgeschwindigkeit ist viel hoher als jene, die bei Polymerisation in Substanz oder Losung beobachtet wird. Unter Berucksichtigung der kinetischen Ergebnisse und des Verhaltens des Systems bei Zugabe von Styrol und Toluol kann ein Mechanismus von “radical occlusion” zusammen mit einem diffusionskontrollierten Kettenwachstum in den Polymerpartikel vorgeschlagen werden. Die sehr hohe scheinbare Aktivierungsenergie fur das Kettenwachstum und den Grenzumsatz deuten auf ein komplexes kinetisches Verhalten der Polymerisation hin.

On the crystalline nature of poly(di-isopropyl fumarate)

SummaryMolecular order of poly(di-isopropylfumarate) (PDIPF), obtain ed by free-radical initiation, is investigated by calorimetric measurements and X-ray diffraction analysis. It is found that the polymer decomposes without melting at temperatures above 200°C while displaying two endothermic transitions, probably of the solid-solid type, at 65 and 126°C respectively. Further evidence of crystalline order and orientability is provided by the X-ray experiments which show one equatorial (11.16 Å) and two meridional (4.81 and 2.40 Å) reflections respectively. The corresponding stereoselective nature of the polymerization reaction is interpreted as resulting from the steric influence of the bulky isopropyl substituents of the monomer.

Thermodynamic and hydrodynamic properties of aliphatic polyesters, 3. Analysis of osmotic and light scattering data of poly(β‐propiolactone) in 2,2,2‐trifuloroethanol in terms of a universal scaling law for the osmotic pressure in the excluded volume limit

Osmotic and light scattering data of poly(β-propiolactone) in 2,2,2-trifluoroethanol, a thermodynamically very good solvent, are analyzed in terms of a universal scaling law for the osmotic pressure in the excluded volume limit. The polymolecularity correction function to calculate osmotic pressures from light scattering data is deduced and a numerical method to treat simultaneously all the measured osmotic pressures at different concentrations is developed. It is shown that, for a given concentration, provided the molecular weight of the polymer species together with its radius of gyration is known, the osmotic pressure of its dilute and semidilute solutions can be calculated.