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Chain extension with diisocyanates is undoubtedly the most commonly applied chain‐extension approach for aliphatic polyesters (Figure 3.4). A large number of different diisocyanates have been used as linking molecules in the preparation of aliphatic poly(ester‐urethane)s. Various isocyanates are listed in Table 3.1 together with the type of prepolymer used.

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 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].

FIGURE 3.4 Chain‐extension reactions of LA‐based prepolymers using diisocyanates.

TABLE 3.1 Diisocyanates Used in the Preparation of Aliphatic Poly(ester‐urethane)s

Name	Prepolymer Composition	Reference
1,6‐Hexamethylene diisocyanate	l‐LA, 1,4‐butanediol	[43]
1,4‐Butanediisocyanate	ɛ‐caprolactone (CL), 1,4‐butanediol	[44]
1,6‐Hexamethylene diisocyanate	1,3‐propanediol, succinic acid	[45]
1,4‐Butanediisocyanate	PLA, 1,4‐butanediol	[46]
Methylenediphenyl diisocyanate	LA	[47]
4,4′‐Dicyclohexylmethane diisocyanate	l‐LA, 1,4‐butanediol	[48]
Isophorone diisocyanate	l‐LA, 1,4‐butanediol	[48]
Ethyl 2,6‐diisocyanohexanoate	CL, glycolide, inositol	[49]
1,6‐Hexamethylene diisocyanate	l‐LA, mandelic acid	[50]
1,6‐Hexamethylene diisocyanate	l‐LA, malic acid	[50]
Methylene diphenyl isocyanate	l‐LA, butyl glycidyl ether	[51]