Hexamethylene diisocyanate extension

Recently, Cohn and Salomon synthesized and characterized a series of PLCL thermoplastic bioelastomers by two-step synthesis procedure. First, ring-opening polymerization of L-lactide initiated by the hydroxyl terminal groups of the PCL chain. Second, chain extension polymerization of these PLA-PCL-PLA triblocks initiated by the hexamethylene diisocyanate (HDl). 

Curing of the acetylenic polyacetals to rubbery polyurethanes could be achieved with any of a number of commercially available diisocyanates, including 2,4-toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), dianisidine diisocyanate (DADI), and 4,4 -diisocyanatodiphenyl-methane (MDI). The first two diisocyanates were studied most extensively. The reactions were carried out in solution in benzene, toluene, and ethylene bromide, and in bulk. The bulk reaction, which is the only... 

Microencapsulation by interfacial polycondensation is a usefiil method to microencapsulate a liquid core material. Especially, polyurea and polyurethane microcapsules have been extensively investigated in various industries [209]. For example, aliphatic hexamethylene diisocyanate (HMDI) and aliphatic ethylene diamine (EDA) have been used to prepare polyurea microcapsules containing insecticide called diazinon [210]. A urea linkage is formed immediately by the reaction between an amine and an isocyanate group (see Figure 4.31), and a polyurea is synthesized by the reaction between an amine with two or more amine groups and an isocyanate with two or more isocyanate groups. 

Gu et al. reported that a high-molecular-weight biodegradable lactic acid polymer was successfully synthesized in two steps. First, the lactic acid monomer was oligomerized to low-molecular-weight hydroxyl-terminated prepolymer the molecular weight was then increased by chain extension using 1,6-hexamethylene diisocyanate as the chain extender. The results showed that the obtained polymer had an M of 27,500 g-mol" and an Af of 116,900 g mol after 40 min of chain extension at 180°C [13]. 

Third the chain extension through reacting with chain extenders such as 1,6-hexamethylene diisocyanate (HDl) was also developed. Such strategy has resulted in cross-linked urethane-doped polyester elastomers (CUPEs) based on POC [19], cross-linked urethane-doped BPLP (CUBPLP)... 

When hexamethylene diisocyanate is used as a chain extender, high molecular weight polyesters can be obtained. The chain extension reaction results in a significant increase of polyester the molecular weight and also in an increased tensile strength. The rate of biodegradation is rather affected by the crystallinity, rather than by the molar mass. 

The most frequently used diisocyanate in the preparation of aliphatic poly(ester-urethane)s is 1,6-hexamethylene diisocyanate because of its low toxicity, and the use of this isocyanate will accordingly be discussed in more detail. Numerous examples of the use of diisocyanate chain extension of aliphatic polyesters can be found in the scientific publications and in the patent literature [52-54]. 

TEG, or PEG-2000. These spirocycles were used as initiators for the ring-expansion polymerization of Z-lactide in chlorobenzene at 120 °C. The resulting cyclic block co-polymers were reacted in situ with aliphatic dicarboxylic acid dichlorides (ADADs) or with hexamethylene diisocyanate (HMDI) to achieve chain extension. 

While the reduced enzymatic susceptibility of the aromatic ester bonds is caused by the interaction of the long chains in the polymer, the chain length itself has no direct influence on the biodegradability above a minimum molar mass. Tests with copolyesters from terephthalic acid, adipic acid and 1,4-butanediol, which were chain extended with hexamethylene-diisocyanate, did not result in a decrease in the biological degradation rate (in a compost simulation test), although the molar mass of the prepolyesters of about 48,000 D was increased to 232,000 D by the chain extension [85]. 

The synthesis of multiblock cyclic carbonate copolymers was presented by Kricheldorf and Rost. First, telechelic random copolymers were prepared by copolymerization of CL and TMC in bulk using bismuth(III) hexanoate [Bi(OHex)3] as an initiator. A-B-A triblock copolymers were synthesized by chain extension of these random copolymers with l-LA. Finally, the triblock copolymers were transformed into multiblock copolymers by chain extension with 1,6-hexamethylene diisocyanate. It is worth mentioning that all three synthetic steps were performed in a one-pot procedure. ... 

Highly flexible foams generally use aliphatic diisocyanates for chain extension, for instance, hexamethylene diisocyanate (HMDI),... 

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