Poly glycol

In order to become useful dmg delivery devices, biodegradable polymers must be formable into desired shapes of appropriate size, have adequate dimensional stability and appropriate strength-loss characteristics, be completely biodegradable, and be sterilizahle (70). The polymers most often studied for biodegradable dmg delivery applications are carboxylic acid derivatives such as polyamides poly(a-hydroxy acids) such as poly(lactic acid) [26100-51-6] and poly(glycolic acid) [26124-68-5], cross-linked polyesters poly(orthoesters) poly anhydrides and poly(alkyl 2-cyanoacrylates). The relative stabiUty of hydrolytically labile linkages ia these polymers (70) is as follows ... 

Polymeric, prepared as thin smooth films (with the exception of poly(glycolic acid))... 

The various POPs and POEs are all PAGs, and various derivatives are available. They are also called polyoxyalkylenes poly glycols or polyether glycols. 

Other common poly glycol-based antifoams include certain derivatives of polyethylene glycol (PEG), which are condensation polymers of ethylene glycol. An example is polyethylene glycol-8 dioleate. Apart from its antifoam properties, PEG-8 dioleate is also used in cooling water inhibitor formulations as a surface cleaner, in the formation of a corrosion-inhibiting surface film. Additionally, it is employed as an oil-soluble emulsifier for other defoamer chemistries. 

Poly(glycolic acid) Dexon Davis Geek Biomedical b... 

Poly (glycolic acid) (PGA), 41, 42, 85 preparation of, 99 Polyheterocyclization concept, 265 Poly(hexafluorobisphenol-A), 361 Poly(hexamethylene adipamide), 5 Poly(hexamethylene adipate), 5 Poly(hexamethylene fumarate) synthesis, 100-101... 

Gilding, D. K., and Reed, A. M., Biodegradable polymers for use in surgery poly(glycolic)/poly(lactic acid) homo- and copolymers 1, Polymer. 20. 1459, 1979. 

Miller, R. A., Brady, J. M., and Cutright, D. E., Degradation rates of oral resorbable implants (polylactates and poly-glycolates) Rate modification with changes in PLA/PGA copolymer ratios, J. Biomed. Mater. Res., 11, 711, 1977. 

W. J., Degradation rates of polymei and copolymers of poly-lactic and poly glycolic acids. Oral Surg. Oral Med. Oral Pathol.,... 

FIGURE 22 Semilog plot of the in vitro rate of hydrolytic chain scission of PCL, poly glycolic acid-co-lactic acid, and a 1 1 blend of the two polymers, demonstrating the use of blends to modify degradation rates. (From Refs. 64 and 65.)... 

The rate of hydrolysis of the partially ethoxylated polymer was retarded, although not to the extent calculated from theory (Fig. 25), suggesting some contribution to the rate of chain scission by an uncatalyzed process. End-capping poly (glycolic acid-co-lactic acid) has a similar effect on the rate of hydrolysis of this polyester (100). 

Blending of PCL and poly(glycolic acid-co-lactic acid) has been also used to control the rate of chain scission of the composite. 

Thus, while these two polymers differ greatly in their rate of hydrolytic chain cleavage, gel permeation chromatography (GPC) analysis of a 1 1 blend of PCL and poly(glycolic acid-co-lactic acid) in pH 7.4 buffer showed that both components of the blend were subject to the same rate of chain cleavage (65). 

Based on these studies, it is obvious that poly(N-acylhydroxy-proline esters) are very slowly degrading polymers. These materials may therefore be useful for long-term applications, such as implantable, multiyear contraceptive formulations. For such applications the degradation rates of poly (lactic acid)/poly (glycolic acid) devices would probably be too rapid. 

In summary, preliminary results from two animal models (rabbit and mouse) indicate that poly(N-palmitoylhydroxyproline ester) elicits a very mild, local tissue response that compares favorably with the responses observed for established biomaterials such as medical grade stainless steel or poly(lactic acid)/poly(glycolic acid) implants. At this point, additional assays need to be performed to evaluate possible allergic responses, as well as systemic toxic effects, carcinogenic, teratogenic, or mutagenic activity, and adaptive responses. 

Phase transfer catalysis (PTC) refers to the transfer of ions or organic molecules between two liquid phases (usually water/organic) or a liquid and a solid phase using a catalyst as a transport shuttle. The most common system encountered is water/organic, hence the catalyst must have an appropriate hydrophilic/lipophilic balance to enable it to have compatibility with both phases. The most useful catalysts for these systems are quaternary ammonium salts. Commonly used catalysts for solid-liquid systems are crown ethers and poly glycol ethers. Starks (Figure 4.5) developed the mode of action of PTC in the 1970s. In its most simple... 

Anionic emulsifiers, such as alkali salts of fatty acids, can be applied in anionic latices. Are particularly important as wetting and foaming agents in latex technology. Poly(glycol) ethers act as nonionogenic emulsifiers. 

Common biodegradable polymers for medical devices are constructed from synthetic linear aliphatic polyesters. One material commonly used for internal sutures is poly(glycolic acid) (PGA). PGA is synthesized from the dimer of glycolic acid (Fig. 13.1.l). 1... 

Figure 13.1.1 The synthesis of poly(glycolic acid) (PGA) from the dimer of glycolic acid.

These fibres contain long chains of poly glycols or polyesters between polyurethane blocks. Urethane gets copolymerised with suitable polyol or polyester and then melt spun as monofilament or polyfilament yarn. The urethane blocks are in a randomly disordered fashion in the yarn. When stretched they uncoil and straighten out. 

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