Prepolymer laboratory preparation

The partially aromatic PAs are exclusively made of die diamine-diacid type and not die amine-acid type. The aromatic diamines, similar to phenylene diamines, color easily and dieir polymers are conjugated, having a golden brown color. The aromatic diacids used in the formation of partially aromatic PAs are mainly terephthalic and isophthalic acids. Starting with the diacids, the PA salt is made first and with this the salt prepolymers are prepared. The prepolymerization is usually carried out in an autoclave to prevent die sublimation of the reactants. In a laboratory synthesis it would be preferable to avoid this autoclave step as one is not always available. It is possible to start with the more reactive esters, such as diphenyl isophtiialate, or with the acid chlorides starting with the reactive isocyanates is, in principle, also possible. The terephthalic and isophthalic acids are also used to modify PA-6,6 and PA-4,6 to more dimensionally stable copolymers.6,18... 

Polymers and copolymers were laboratory-prepared samples. Samples W4 and W7 of the diblock copolymer AB poly(styrene-fo-tetramethylene oxide) (PS—PT) were synthesized by producing a polystyrene prepolymer whose terminal group was transformed to a macroinitiator for the polymerization of THF. Samples B13 and B16 of the diblock copolymer AB poly[styrene-h-(dimethyl siloxane)] (PS-PDMS) were prepared by sequential anionic polymerization. Samples of statistical copolymers of styrene and n-butyl methacrylate (PSBMA) were produced by radical copolymerization. Details of synthetic and characterization methods have been reported elsewhere (15, 17-19). 

Isocyanate prepolymers were prepared in glass reaction vessels in a laboratory fume hood. The reaction vessel was equipped with a stirrer, temperature controller and nitrogen inlet. The reaction was carried out under a dry-nitrogen atmosphere to minimise exposnre to atmospheric moisture and polyol oxidation. 

Laboratory Preparation of Aqueous Polyurethane/Urea Dispersions using the Prepolymer Mixing Process... 

The molecular weight and its distribution of prepolymers were determined in THF by gel permeation chromatography (Waters Associates). Four different pore size columns (10, 10, 10 and 10 A i -Styrogels) and a refractive index detector were used. The instrument was calibrated with polyisoprene samples which were prepared similarly in this laboratory and whose number-average molecular weights were determined with a vapor phase osmometer (Wescan, Model 232 A) in toluene at 50 C. 

In contrast, the preparation of hydrogels from prepolymers via cross-linking condensation reaction offers a simple method for the preparation of films/mem-branes and coated surfaces. Here, in addition to the aforementioned laboratory equipment, a spin coater is necessary as well as a cabinet for drying and curing. The use of inert gas techniques is not required, since the underlying reaction is not affected by oxygen. 

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