Rheological and Spectroscopic Characterizations of the Properties of a Prepolymer for High-Temperature Applications: The IP960 System

Of the thermostable polymers on the market the American PMR-15 resin is a reference compound. Nevertheless, its defects have necessitated the development of new polymers such as IP960. The object of this work is to characterize IP960 which is soluble in the diglyme until the imide oligomer stage. HPLC and 1H NMR analyses of the prepolymer demonstrate its polymolecularity. Several isomer forms, due to possible conformations of the nadimide endcaps, are present in equal amounts in the medium. The combined use of differential scanning calorimetry and rheological techniques have allowed us to study and to explain the evolution of properties of the prepolymer with temperature (glass transition, crosslinking etc). Using FTIR spectroscopy, we have studied the structure of the polymer network. Our results seem to confirm the validity of the crosslinking diagram of nadic structures proposed by Wong and co-workers. Thermomechanical analysis of the crosslinked compound shows that the Tg of the polymer is close to 292 °C. It also reveals on the curb of the modulus G″, namely the presence of two peaks γ and β associated with secondary mechanical relaxations within macromolecular chains ( Tγ = −102 °C; Tβ =68 °C).

Study of Thermal Aging of Nadimide Polymer: Physicochemical Characterization of the Properties of the Crosslinked IP960 System

In order to evaluate the thermostability of the IP960 polymer, we have characterized the physicochemical properties of samples exposed at 295 °C for periods up to 3000 h. According to the time of thermal treatment, various phenomena occur such as an increase in glass transition temperature and crosslink density. After a minimal period of 200 h at 295 °C, the weight loss of samples is representative of the degradation of crosslinked IP950. Using FTIR, we have analysed the changes in the chemical structure of the polymer. We propose a mechanism which could explain the degradation of the crosslinked compound.

Rheological Study of a High-Performance Polyimide. Interpretation of the Secondary Mechanical Relaxations of a Nadimide Crosslinked System

Thanks to the study of model compounds, we have been able to determine the origin of three rheological transitions observed in the thermomechanical analysis of a crosslinked nadimide resin, in the thermal range (-150 °C–-400 °C). The first one, localized at about 300 °C, is attributable to the glass transition of the crosslinked compound. The two others (called γ and β) are respectively situated at -100 °C and 70 °C. They are due to localized motions of rigid segments comprising aromatic structures and imide rings.

Rheological and small-angle neutron scattering studies of aqueous solutions of branched PEO-PPO-PEO copolymers

Tetronic 908 is a four-branched copolymer comprised of polyethylene oxide (PEO) and polypropylene oxide (PPO) blocks fixed on an aliphatic diamine. In aqueous solution, this polymer has an amphiphilic character due to the difference in PEO and PPO solubilities with increase in temperature. This system presents interesting rheological properties depending on the polymer concentration in solution and temperature. At low temperatures and/or concentrations, the solution behaves as a Newtonian fluid. For a weight percentage p comprised between 2% and 22%, the viscosity of the solution goes through a maximum. Small-angle neutron scattering experiments show that the increase in viscosity is due to progressive aggregation of chains. For weight percentages higher than p=22%, the viscosity of the system diverges and the mixture becomes gel-like. In fact, spectromechanical measurements show that the solution behaves as an entangled polymer with a high relaxation time in the flow zone. Small-angle neutron scattering (SANS) studies of the same solution reveal the presence of several peaks indicating that the micelles are organized in a cubic structure. We have developed a model that suitably describes the SANS curves of this system in the region where micelles are formed. Our model considers that micelles are trilayered spherical entities that coexist with unimers by obeying an equilibrium reaction. Moreover, it allows the calculation of several parameters such as the volume fraction of micelles, their size, and composition. The evolution of these parameters with temperature and polymer concentration is detailed. Comparisons with literature models are presented and discussed. This compilation of results has permitted the establishment of precise relations between the structure of this polymer in solution and its rheological properties.

[The rheumatism of acne conglobata (author's transl)]

The authors report a case of painful joint, para-articular and muscular involvement accompanying acne conglobata. Fifteen other cases of rheumatism associated with this very special type of acne have been reported. The patients affected are young men suffering from acne conglobata (severe form of acne characterised by its ulcerating course and the possibility of its being accompanied by systemic manifestations), who suddenly develop fever, an altered general state and assymetrical arthralgia involving mainly the large joints, accompanied by signs of muscular involvement. The course is one of spontaneous recovery, relapses being possible. This falls within the context of the group of rheumatic disorders associated with the signs of an inflammatory skin disease.