Triol-based polyester

Figure 11 shows plots according to equation(lO) of stress-strain data for triol-based polyester networks formed from the same reactants at three initial dilutions (0% solvent(bulk), 30% solvent and 65% solvent). Only the network from the most dilute reactions system has a strictly Gaussian stress-strain plot (C2 = 0), and the deviations from Gaussian behaviour shown by the other networks are not of the Mooney-Rivlin type. As indicated previously, they are more sensibly interpreted in terms of departures of the distribution of end-to-end vectors from Gaussian form. 

Figure 11. Mooney-Rivlin plot of stress-strain data (32) for three triol-based polyester networks prepared from sebacoyl chloride and LHT240 at various initial dilutions in diglyme as solvent. Conditions P100 is 0% solvent P130 is 30% solvent PI 65 is 65% solvent.

Bioresorbable poly(ester urethanes) have been developed by reacting lysine diisocyanate (LDI) with polyester diols or triols based on D,L-lactide, caprolac-tone, and other copolymers [45]. In these systems, aliphatic polyesters such as PLGA or PCL form the soft segments and the polypeptides form the hard segments [46]. A resorbable elastomeric poly(ester urethane) called Degrapol is available commercially. It is currently being used to develop porous scaffolds for tissue engineering applications. 

Similar systems can be developed with polyester prepolymers with the addition of an ester-based plasticizer. Polyesters are very much tougher than polyether so they make better, softer materials. One commercial system uses a blend of a short-chain triol with either MOCA or Ethacure 300, with the addition of some plasticizer for the very softest material. The most-used triol is Isonol 93, which is now known as Conap AH50. 

By using, together with a diol, a triol such as TMP or glycerol it is possible to obtain polyesters with a functionality (f) higher than 2 OH groups/mol, situated in the range of 2-3 OH groups/mol. These polyester polyols are used for flexible PU foam fabrication. Flexible PU foams based on polyester polyols have a unique property their clickability (capacity to be easily cut) and are used in laminates for textile industry. 

Polyesters derived from e-caprolactone and ethylene glycol and triols, such as trimethylolpropane, have been employed for the preparation of different types of urethane coatings, including nonyellowing systems (88. 89). These types of polyesters exhibit improved hydrolytic stability and low-temperature properties as compared to adipate polyester based urethanes. 

As stated, tertiary amines catalyze both the hydroxyl/isocyanate and the water/isocyanate reactions. One-shot foams utilizing primary hydroxyl-terminated polyesters as well as all types of prepolymer foams require tertiary amine catalysis only. Polypropylene ether one-shot foam formulations based on triols, in part, because of their low viscosity (about 300 cP versus 10000-30000 cP for polyesters or prepolymers) require the use of tertiary amine-metal catalyst combinations, even if the percentage of primary hydroxyl groups in the polyether is increased by capping with ethylene oxide. This is because of the relatively low polypropylene glycol activity. 

Polyols are selected on the basis of cost, rate of esterification, stability during high temperature processing, functionality, and hydrolytic stability of their esters. The most widely used diol is NPG, and the most widely used triol is TMP. A comparison of results of testing films of coatings made with a series of polyesters from several polyols is given in Reference 167. Coatings based on CHDM polyesters cross-linked with MF resins showed the best hydrolytic stability. 

The chemistry involved in curable poly(ester imide) formulations is well established, and it is still based on trimellitic anhydride, methylene dianiline, and low molecular weight polyesters of aromatic dicarboxylic acids and glycols, along with a classical heterocyclic triol, 2,4,6-trishydroxyethyl isocyanurate (THEIC), as it is shown in Scheme (29). The composition is formulated in a way that the final polymers, although linear, contain free —OH groups, both as chain ends and as side reactive groups. At the moment of... 

Many polyurethane systems commonly are based on reacting either a polyester or polyether polyol with a diisocyanate. Then this isocyanate-terminated prepolymer is later crosslinked with a curative or chain extender, which is typically a diol, triol, or diamine. 

The polyhydroxy components of urethane sealants are mostly hydroxyl-terminated saturated polyesters or poly ethers. Most polyesters used in urethane sealants have been standard condensation products of dibasic acids (such as adipic acid or phthalic anhydride) with glycols and triols (such as propylene glycol, glycerin, or trimethylol propane). Polyester-based urethane sealants are hard and tough, have relatively good adhesion in joints, but are deficient in hydrolytic stability and exterior durability. 

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