Poly -nitroacetanilide

Figure 3 shows the results of sin investigation of the pH-sensitivity of a crosslinked poly(ortho ester) prepared from 3,9-bis(ethylidene 2,4,8,10-tetraoxaspiro [5,5] undecane), triethylene glycol, and 1,2,6-hexanetriol. In these studies, a marker molecule, p-nitroacetanilide was incorporated into the polymer, and the rate of release of p-nitroacetanilide was assumed to correspond to the rate of erosion of the polymer. This assumption is not entirely accurate because some diffusional release occurs. However, the method is a good measure for determining the changes in erosion rates with changes in external pH. 

Figure 3 Effect of external pH on erosion rate of crosslinked poly(ortho ester) prepared from 3,9-bis(ethylidene 2,4,8,10-tetraoxaspiro [5,5] undecane), triethylene glycol, and 1,2,6-hexanetriol. Disks 5.5 x 0.75 mm p-nitroacetanilide loading 2 wt. ...

The hydrolysis rate of poly (ortho esters) can be further manipulated by a combination of hydrophilicity and the use of diols that contain a pendant carboxylic acid, such as 9,10-dihydroxystearic acid [36]. Figure 16 shows the release of a marker compound p-nitroacetanilide from a hydrophobic matrix prepared from a 60/40 mole ratio of frans-cyclohexanedimethanol and 1,6-hexanediol containing varying amounts of 9,10-dihydroxystearic acid. While there is a noticeable effect, it is relatively minor. However, when the hydrophilicity of the matrix is increased by using a 60/10/30 mole ratio of trans-cyclohexanedimethanol, 1,6-hexanediol and triethylene glycol, the effect of 9,10-dihydroxystearic acid is greatly magnified, as shown in Fig. 17. 

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