Urethane oligomer linkage

Hydrosilation reactions have been one of the earlier techniques utilized in the preparation of siloxane containing block copolymers 22,23). A major application of this method has been in the synthesis of polysiloxane-poly(alkylene oxide) block copolymers 23), which find extensive applications as emulsifiers and stabilizers, especially in the urethane foam formulations 23-43). These types of reactions are conducted between silane (Si H) terminated siloxane oligomers and olefinically terminated poly-(alkylene oxide) oligomers. Consequently the resulting system contains (Si—C) linkages between different segments. Earlier developments in the field have been reviewed 22, 23,43> Recently hydrosilation reactions have been used effectively by Ringsdorf 255) and Finkelmann 256) for the synthesis of various novel thermoplastic liquid crystalline copolymers where siloxanes have been utilized as flexible spacers. Introduction of flexible siloxanes also improved the processibility of these materials. 

Waste PETP was depolymerised by glycolysis to give hydroxyl-terminated oligomers(DPET), which were used in the synthesis of urethane oils. The effect of depolymerisation temps., the type of glycol and the amount of catalyst on the yield and composition of the depolymerisation products was studied. The physical properties of the urethane oils were compared with those of a commercially-available product. The reaction of DPET with isocyanates produced random linkage between different molecules with or without terephthaloyl groups. 15 refs. 

MDI is derived from the breakage reaction of the urethane linkage drawn in Scheme 12.1c, the polyester product are formed by intramolecular rearrangement of ether bonds, eliminating cyclic oligomers, and by radical breakage of the polyester chain to partly unsaturated linear oligoethers. 

The effect of varying the branching linkage of the oligomer from urea to urethane can be obtained by comparison of Formulations K,E,H, and F which constitute a simple 2x2 factorial design with the variables of urea vs urethane and diol molecular weight (520 vs 820). ... 

Table IV further Illustrates the effect of weight per urethane linkage, as well as that of oligomer molecular weight. If molecular weight and weight per urethane linkage are Increased by choice of polyol, without changing the stoichiometry, a decrease in viscosity is observed (compositions G, F, , K). In this case, the effect of urethane content dominates.

As molecular weight and weight per urethane linkage increase, the cure speed of those oligomers that do not contain a linear polyether decreases (Table IV, compositions G, E, I). This is primarily a dilution effect. The cure speed of those urethanes that contain a polyether correlates, once again, with the weight percent of polyether in the oligomer (Table IV, compositions J, K). 

The optical properties of these oligomers have been investigated [67]. Up to the penta-mer the dispersion in benzene obeys the one term Drude equation but the hexamer and mainly the heptamer show anomalous curves which are highly dependent on the solvent [68] and on temperature [69, 70]. These anomalous dispersion curves were only observed in aromatic hydrocarbons [68]. The authors attribute it to the formation of an ordered helical structure via intramolecular weak hydrogen bonding between urethane linkages. 

Diamines or diols can be used as chain extenders in copolymerization reactions, but urea linkages formed from diamines often lead to polymer insolubility.(28) Poor solubility is avoided by using diols, but this requires a two stage preparation (Scheme 1) because of the disparity in reactivity of alcohols and amines with isocyanates. To form urea and urethane linkages separately, the reaction between isophorone diisocyanate and benzene dimethanol was carried out first in bulk at 115 °C without catalyst (Equation 1). Secondly, reaction between aminopropyl endcapped dimethylsiloxane oligomers and diisocyanate intermediates was effected in THE at room temperature (Equation 2). Completion of the polymerization reaction was established by NMR and infrared spectroscopy.(8)... 

---