Poly degradation properties

Poly(esters) (Table 11.2) are the first class of polymers discussed, as they are the most widely investigated of all of the polymer families for oral protein delivery. Poly(esters) used for oral drug delivery have primarily been biodegradable polymers (Figure 11.1). Biodegradation is the primary delivery mechanism for poly(ester) polymers used for protein and peptide delivery. The degradation properties of poly(esters) are dependent on the monomers used to produce the poly(ester). Several poly(esters) are discussed in detail in the following sections. 

The tacticity of PLA influences the physical properties of the polymer, including the degree of crystallinity which impacts both thermo-mechanical performance and degradation properties. Heterotactic PLA is amorphous, whereas isotactic PLA (poly(AA-lactide) or poly (55-lac tide)) is crystalline with a melting point of 170-180°C [26]. The co-crystallization of poly (RR-lactide) and poly(55-lactide) results in the formation of a stereocomplex of PLA, which actually shows an elevated, and highly desirable, melting point at 220-230°C. Another interesting possibility is the formation of stereoblock PLA, by polymerization of rac-lactide, which can show enhanced properties compared to isotactic PLA and is more easily prepared than stereocomplex PLA [21]. 

Much better differentiation of plastic waste from general refuse and segregation of the recovered plastic materials according to resin type is obtained by presorting of the waste at the householder level. As already discussed in connection with the properties of mixtures of PVC and poly(vinyl acetate), or polystyrene with rubber, crude mixtures of two or more polymers usually result in degraded properties relative to those achievable from any of the more rigorously segregated component materials. For this reason, for... 

Kinnane CR, Such GK, Antequera-Garcia G, et al. (2009) Low-fouling poly(lV-vinyl pyrolli-done) capsules with engineered degradable properties. Biomacromolecules 10 2839-2846... 

C. G. Jeong, S.J. HoUister, Mechanical, permeability and degradation properties of 3D designed poly(l,8-octanedioTco-citrate) scaffolds for soft tissue engineering, J. Biomed. Mater. Res. B Appl. Biomater. (2010) 142-149. 

Shi, Q., Chen, C., Gao, L., Jiao, L., Xu, H., Guo, W. Physical and degradation properties of binary or ternary blends composed of poly (lactic acid), thermoplastic starch and GMA grafted POE. Polym. Degrad. Stab. 96, 175-182 (2011)... 

Although the potential number of poly(alkylene terephthalate) copolymers is vast, only a few appear to have merited interest due to their thermal degradation properties. These include ... 

Tuncel, A., et al., Monosize poly(ethylcyanoaciylate) microspheres Preparation and degradation properties, Journal of Biomedical Materials Research, 29 721-728 (1995). 

In an attempt to gain an element of control over the mechanical, physical and degradation properties of PLA, large-scale efforts are currently underway to chemically and physically modify PLA throng copolymerization and physical blending with prudently chosen secondary constituents. Without immediate consideration for the issue of financial accessibility of PLA-based products, a logical, con lementary conqx)nent to PLA is poly(8-caprolactone)[PCL]. PCL is a flexible, semi-crystalline(Tg -60°C, Tm 60°C) aliphatic polyester with unique biodegradation characteristics and superior thermal and hydrolytic stabihty. ... 

Copolymerization of different poly(a-hydroxy acids) is a way to tune the properties of the resulting polyester. By varying the ratio of laetide to glycolide in poly(lactide-co-glycolide) (PLGA) (Fig. 6.3) it is possible to achieve the desired physieal, chemical, surface and degradation properties. 

Poly(D,L-lactic acid), PDLLA (in short name) is an amorphous polymer due to the random positions of its two isomeric monomers within the polymer chain. It has a similar but slightly lower expected Tg than PLLA in the range of 50—60°C. It is also expected to have weaker mechanical properties mainly due to the fact that PDLLA is an amorphous polymer while PLLA is a semi-crystalline polymer. The degradation properties of PDLLA should be between that of PGA and PLLAPD. In vivo completion of degradation of PDLLA takes over a year, in most cases between 12 and 16 months, as shown in Table 7.3. 

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