Bulk and Structure Modification of Polymers

The in situ bulk polymerization of vinyl monomers in PET and the graft polymerization of vinyl monomers to PET are potential useful tools for the chemical modification of this polymer. The distinction between in situ polymerization and graft polymerization is a relatively minor one, and from a practical point of view may be of no significance. In graft polymerization, the newly formed polymer is covalently bonded to a site on the host polymer (PET), while the in situ bulk polymerization of a vinyl monomer results in a polymer that is physically entraped in the PET. The vinyl polymerization in the PET is usually carried out in the presence of the swelling solvent, thereby maintaining the swollen PET structure during polymerization. The swollen structure allows the monomer to diffuse in sufficient quantities to react at the active centers that have been produced by chemical initiation (with AIBM) before termination takes place. 

As one tries to write down an analysis of the developments in the block polymers area, one realizes very soon that it is going to consist of a series of variations on a theme a theme which is the increasing ly stronger reality, in our everyday scientific life, of what can be now really called "the molecular engineering of polymers properties", i.e. the possibility to control, through precise (although sometimes small) modifications of molecular structures, the final bulk properties and macroscopic behaviour of polymeric materials. In other words, one deals there with a very acti ve version of the studies on structure-properties inter relationships, a question which by the way has always been a focal point among the many diversified interests of Professor Mark. 

Hydrogels that are based on natural products are more acceptable from the standpoint of toxicity-related issues and are therefore preferable to azo-based polymers. However, chemical derivatization, if performed without proper understanding, can lead to modifications of the hydrogels to products that will not degrade readily in the colon because it is possible that the new structures will not be recognized by the colonic bacterial enzymes for degradation. Also, bulk degradation is preferred to surface erosion because it... 

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