Prepolymers synthesis and chain extension

Segmented polyurethanes were synthesized from the a, to diol polyethers listed in Table I and the diisocyanates IV, V, and VI by the two-step process shown in Figure 1 or the three-step process in Figure 2. In all cases, chain extension of isocyanate-terminated prepolymers was accomplished with ethylenediamine. The synthesis took place in a 2 1 (v/v) mixture of dimethyl sulfoxide and 4-methyl-2-pentanone at 60°C. 

Figure 6.3 Two-step polyurethane synthesis. First step prepolymer synthesis from a diisocyanate and a macrodiol. Second step chain extension.

The purified POC prepolymer was then lyophilized for the next step of chain extension. In the second step, chain extension was achieved by dissolving pie-POC in 1,4-dioxane (3 wt%) and allowing it to react with HDI using stannous octoate as a catalyst (0.1 wt%). The reaction was terminated on the disappearance of the isocyanate peak located at 2267 cm", which was determined by Fourier transform infiaied (FT-IR) analysis. HDI was chosen here as a chain extender as it has previously been used in the synthesis of various biodegradable PUs [36-41]. To obtain aoss-linked CUPE, the material was postpolymerized in an oven at 80 °C for predetermined durations (0.5, 1, 2, 3 days). Free carboxylic acids and hydroxyl groups available on CUPEs allow for further biofunctionalization. 

B. Copolyurethane elastomers from two diisocyanates randomly distributed (PUci), were synthesized starting from PEA. In the prepolymer synthesis a melt mixture was used 26.4g (0.1 mol) of DBDI with 25g (0.1 mol) of MDl which was introduced in the anhydrous polyol at once [3]. The remaining synthesis steps - the chain extension, curing and postcuring - were performed as in the case of general proceditre (A). 

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