5. Other conformationally restricted linear PU

The bicyclic structures of the dianhydrohexitols (1, 20, 21) provide conformational restriction and stiffness to the polymer chain, with a significant increase in the Tg. Galbis et al. [7] reported new conformationally restricted linear polyurethanes based on bicyclic carbohydrate-based monomers having D-gluco, galacto, and D-manno configurations (33, 43, 44) and their secondary hydroxyl groups protected as cyclic acetals (Figure 9). The T<sup>g</sup> values of these conformationally restricted polymers were similar to those observed for the polyurethanes [PU(Is-HDI) and PU(Is-MDI)] based on the isosorbide (1) [52] and higher than their acyclic analogs. They also proved that the diacetalization of the sugar unit of the polyurethane chain improved the thermal stability, which was comparable to those based on isosorbide.

The two orthoesters 86 and 87 having a rigid adamantane-like structure (Figure 10), obtained from naturally occurring myo-inositol (85), were used as new triol- and diol-type monomers to give the corresponding networked and linear polyurethanes by polyaddition reaction with diisocyanates [56].

Figure 9. Conformationally restricted hydroxy-polyurethanes based on hexitols.

Figure 10. myo-Inositol-based rigid adamantine-like monomers.

diaminoisoidide (83) as chain extender. The authors found that the PEU based on the isoidide

Thermoplastic and cross-linked bio-based PU with tailored properties and high renewable carbon content were synthesized from isosorbide (1), 1,3-propanodiol, and 1,1,1-tris-(hydroxymethyl) propane as the cross-linker reagent, in bulk by varying the molar ratio of the components and

The bicyclic structures of the dianhydrohexitols (1, 20, 21) provide conformational restriction and stiffness to the polymer chain, with a significant increase in the Tg. Galbis et al. [7] reported new conformationally restricted linear polyurethanes based on bicyclic carbohydrate-based monomers having D-gluco, galacto, and D-manno configurations (33, 43, 44) and their secondary hydroxyl groups protected as cyclic acetals (Figure 9). The T<sup>g</sup> values of these conformationally restricted polymers were similar to those observed for the polyurethanes [PU(Is-HDI) and PU(Is-MDI)] based on the isosorbide (1) [52] and higher than their acyclic analogs. They also proved that the diacetalization of the sugar unit of the polyurethane chain improved the thermal stability, which was comparable to those based on

The two orthoesters 86 and 87 having a rigid adamantane-like structure (Figure 10), obtained from naturally occurring myo-inositol (85), were used as new triol- and diol-type monomers to give the corresponding networked and linear polyurethanes by polyaddition reaction with

diisocyanate (11) exhibited satisfactory thermal and mechanical properties [54].

without using any chemical catalysts [55].

isosorbide.

176 Aspects of Polyurethanes

diisocyanates [56].

5. Other conformationally restricted linear PU

Figure 9. Conformationally restricted hydroxy-polyurethanes based on hexitols.

The linear polyurethanes obtained from 87 showed high values of Tg, ranging from 105 to 177C, due to the rigidity of the adamantane-like structure units introduced into the main chains. Tg's of the networked polyurethanes obtained from 86 were higher than those of the linear polyurethanes, and ranged from 155 to 248C.
