Introduction, polymer modification

Introduction Polymer Modification—Some Problems and Possibilities—Areas in Need of Research... 

Polymer Modification. The introduction of functional groups on polysdanes using the alkah metal coupling of dichlorosilanes is extremely difficult to achieve. Some polymers and copolymers with 2-(3-cyclohexenyl)ethyl substituents on siUcon have been made, and these undergo hydrogen hahde addition to the carbon—carbon double bond (94,98). 

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

Most observations of rate retardation in polymer modifications have been attributed to steric hindrance. In order to estimate the steric influence of the relatively bulky triethyIbenzylammonium substituent on unreacted site during quaternization, quinuclidine was chosen as nucleophile. It is well known that nucleophilicity of quinuclidine in displacement reactions is greater than that of triethylamine, since bicyclic amines are less sterically hindered. Preliminary experiments on the quaternization of chloromethylated polysulfone with quinuclidine in DMSO showed that the reaction velocity was too rapid to investigate using our experimental techniques, i.e., 85% conversion was obtained with three minutes. Therefore, we were forced to add a less polar solvent to DMSO in order to reduce the reaction rate. It was found that a 50 50 (v/v) mixture of dioxane and DMSO dissolved both chloromethylated and quaternized polysulfone so the rate could be measured in a homogeneous system. The introduction of a nonpolar solvent reduced the initial rate of triethylamine substitution fourfold (Table III, run 17). 

Polyisobutylene has the chemical properties of a saturated hydrocarbon. The unsaturated end groups undergo reactions typical of a hindered olefin and are used, particularly in the case of low mol wt materials, as a route to modification eg, the introduction of amine groups to produce dispersants for lubricating oils. The in-chain unsaturation in butyl mbber is attacked by atmospheric ozone, and unless protected can lead to cracking of strained vulcanizates. Oxidative degradation, which leads to chain cleavage, is slow, and the polymers are protected by antioxidants (75). 

However, the chief purpose of introduction of fillers into PCM is to make possible the modification of polymers and thereby create materials with a prescribed set of physico-mechanical properties, and, obviously, the properties of filled materials may be controlled by, for example, varying the type of the base polymer (the matrix ) and filler, its particle size distribution and shape. It may not require a large quantity of filler [7]. Thanks to considerable advances in PCM research, their use in a broad range of industries — machine building, construction, aerospace technology, etc. — has become extensive [8 — 11]. 

The chemical modification of unsaturated polymers via homogeneous catalytic means offers a potentially useful method for introduction of desirable functional groups on the polymer chains. 

Further, N-methyl dithiocarbamate (MDTC) (.9) and N-metylglycine (sarcosine) (10) were similarly incorporated into PVC matrices resulting in the derivatives usable to chelate forming and introduction of thiol-function as shown in following scheme. Of the two main purpose of modification of commercial polymers 1) improvement of original property of each polymer and 2) incorporation of new function into the polymeric materials, our studies would be served from the viewpoint of the latter as the fundamental design for PVC and PECH with specific functions. 

These novel carbon nanostructures can also be modified by (a) doping, that is the addition of foreign atoms into the carbon nanostructure, (b) by the introduction of structural defects that modify the arrangement of the carbon atoms and (c) by functionalization involving covalent or noncovalent bonding with other molecules. These modifications opened up new perspectives in developing novel composite materials with different matrices (ceramic, polymer and metals). For example, polymer composites containing carbon nanostructures have attracted considerable attention due to... 

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