High functionalized polymer systems

A variety of polymer compositions that use this type of polymerization chemistry can be envisioned. In addition to the polyarylate homopolymers that have been described in this chapter, random or block copolymers can be prepared with reasonable ease by the combination of different monomers or oligomers. These compositions can be designed to optimize thermal, mechanical, dielectric, or optical properties of a polymer system. Also, the trifluorovinyl ether functionality can be incorporated into other high-performance polymer systems with relative ease.34,35 The perfluorocyclobutane polyarylate chemistry is a versatile approach to the preparation of high-performance polymers, which is just beginning to demonstrate its utility. 

One strategy for making highly functionalized polymers is first to cany out polymerization of a system bearing functionalizable appendages, and then after polymerization to react those appendages to introduce new functionality into the polymer. Such an approach can be advantageous in instances where the monomer that would in principle lead directly to the functionalized polymer fails itself to be useful as a polymerization substrate. 

The incorporation of carbohydrates into non-polysaccharide structures is an important strategy to attain i) highly functional polymers U) specific biological functions, and Hi) complex systems that act as smart materials. Polyesters with carbohydrate or polyol repeat units in the chain can be produced by chemical methods. However, elalH)rate protection-deprotection steps are needed to avoid crosslinking between polyol units. Multi-step routes to non-crosslinked polyol polyesters limit the potential of their practical use. 

As well as functional monomer polymerization and PPM, one-pot polymerization has also been used to obtain a highly functionalized polymer. One-pot polymerization combines polymerization with other compatible reactions to achieve the target new polymer in the same reactor. In contrast to functional monomer polymerization, one-pot polymerization can form the functional monomer in situ and thus avoid the purification step necessary with functional monomer synthesis. This approach also avoids hindrance from the polymer backbone, leading to a higher modification yield compared with the normal PPM approach. With less time and cost, the desired polymer can be achieved and functionalized with a high yield in one pot. Some reactions such as the CuAAC click reaction and enzymatic transesterification have been used for construction of a one-pot polymerization system with controlled/living radical polymerization approaches to achieve new functional polymers [119-125]. 

Boronic acids (69 and 70) (Fig. 45) with more than one boronic acid functionality are known to form a polymer system on thermolysis through the elimination of water.93 Specifically, they form a boroxine (a boron ring system) glass that could lead to high char formation on burning. Tour and co-workers have reported the synthesis of several aromatic boronic acids and the preparation of their blends with acrylonitrile-butadiene-styrene (ABS) and polycarbonate (PC) resins. When the materials were tested for bum resistance using the UL-94 flame test, the bum times for the ABS samples were found to exceed 5 minutes, thereby showing unusual resistance to consumption by fire.94... 

The balance of this chapter deals with the specific chemistry associated with producing hydrocarbon and functionalized polymers in addition to providing the most recent studies available on appropriate catalyst systems for ADMET condensation chemistry. Current work on the use of the ADMET reaction for modeling commercial high volume polymers such as polyethylene is also presented. 

The requirements for solid-phase synthesis are diverse. The support must be insoluble, in the form of beads of sufficient size to allow quick removal of solvent by filtration, and stable to agitation and inert to all the chemistry and solvents employed. For continuous-flow systems, the beads also must be noncompressible. Reactions with functional groups on beads imply reaction on the inside of the beads as well as on the surface. Thus, it is imperative that there be easy diffusion of reagents inside the swollen beads and that the reaction sites be accessible. Accessibility is facilitated by a polymer matrix that is not dense and not highly functionalized. A matrix of defined constitution allows for better control of the chemistry. Easier reaction is favored by a spacer that separates the matrix from the reaction sites. Coupling requires an environment of intermediate polarity such as that provided by dichloromethane or dimethylformamide benzene is unsuitable as solvent. 

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