Polymer networks degradation

Other transitions such as degradation and phase separation may be also observed during the formation of the polymer network. Degradation is usually present when high temperatures are needed to get the maximum possible conversion. Phase separation may take place when the monomers are blended with a rubber or a thermoplastic, to generate rubber-modified or thermoplastic-modified polymer networks. In these cases, formulations are initially homogeneous but phase-separate during the polymerization reaction. This process is discussed in Chapter 8. 

Coagents ate often used with peroxides to increase the state of cure. Some coagents, such as polybutadiene or multifimctional methacrylates, are used at high levels to form polymer grafts or interpenetrating networks. Other coagents such as triaHyl cyanurate, triaHyl trimelHtate, and y /i -phenjiene bismaleimide are used at low levels to reduce the tendency of the polymer to degrade by chain scission. 

Polymers dynamics of polymer chains microviscosity free volume orientation of chains in stretched samples miscibility phase separation diffusion of species through polymer networks end-to-end macrocyclization dynamics monitoring of polymerization degradation... 

The sol-gel procedure enables encapsulation of enzymes in optically transparent, porous silicate matrices, under mild room-temperature conditions. The small pores prevent microbial degradation and, due to the biomolecule size, they will not diffuse out of the polymer network. The physical encapsulation avoids self-aggregation effects as well as protein unfolding and denaturalization. At the same time, the catalytic activity is maintained as the enzymes are able to react with small substrates that can transfer across or within the support, assuring continuous transformations [75]. 

One of the first examples is a polymer network that consists of polyvinylalco-hol crosslinked by a thrombin-degradable peptide-linker [108] and the encapsulated antibiotic Gentamycin. In the case of a wound infection, the thrombin content increases dramatically. This enzyme degrades the co-network, and releases the Gentamycin, which then fights a possible bacterial infection (see Fig. 7). Suzuki and Tanihara have shown that the antibiotic is only released in the presence of thrombin and only then effectively kills S. aureus and P. aeruginosa cells [109, 110],... 

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