Polymers advantages/drawbacks

Foaming of PAI will result in heat resistant foams. There are such foams made from other types of polymers. Advantages and drawbacks of t5 ical... 

Foaming of PAI will result in heat-resistant foams. There are such foams made from other types of polymers. Advantages and drawbacks of typical high heat-resistant foams are compared in Table 14.2. PI resin foams are regarded as one of the most applicable materials by virtue of their excellent heat stability and flame retardancy. Research has been targeted to improve the physical properties and to simplify the process of preparation. On the other hand, PAI resins exhibit a better heat resistance than poly(ether imide) resins. In addition, they can be more easily processed in the melt. 

Several pathways have been explored for their synthesis sequential addition of monomers to an initiator solution, reaction between co-functional polymers and more recently site transformation techniques. Each of these methods has advantages and drawbacks. 

This strategy appears to be very attractive because of the possibility of completely solubilizing the support in most of the common solvents. From a chemical perspective, that property allows one to benefit from all the solvent conditions used in classical solution chemistry. This could prove to be very advantageous, especially to obtain stereoselective glycosylation without neighboring-group assistance. Moreover, isolation and purification of the polymer is easily achieved by precipitation usually in diethyl ether or methyl-tert-butyl ether (MTBE) and recrystallisation from ethanol. One major drawback of this type of support is its tendency to solidify at low temperature, thus limiting the variety of temperature conditions. 

One of the extensively used synthetic polymers used as a support for immobilization of biocatalysts is polyacrylamide (PAAm) [287,288], The major advantage is that it can be polymerized either chemically or by using radiation. Advantages of y-ray polymerization against chemical polymerization is that the polymerization can be carried out even under frozen conditions thus allowing the matrix to be molded to any form such as beads or membranes [289-291], However one of the major drawbacks of this polymer especially in a membranous form is its brittleness. 

It is well recognized that in vitro angiogenesis assays can have clear advantages. However, the major drawback of all of these assays is that they require the endothelial cells to be removed from their natural microenvironment, which alters their physiological properties. To study angiogenesis in vivo, the most frequently used assay systems exploit chicken chorio-allanto-ic membrane (CAM) [28,60], the corneal pocket [61], transparent chamber preparations such as the dorsal skin fold chamber [62,63], the cheek pouch window [64] and polymer matrix implants [65,66]. 

In this regard, PHB is a very interesting polymer since its mechanical properties vary over a range comparable to that of i-PP or PET. A change in PHB microstructure would allow synthesis of tailor-made products for certain applications. This advantage, however, has some drawbacks in the commercial market. This... 

---