Reactions on Polymers Polymer Modification

The title of this chapter has also been slightly amended, Reactions on Polymers being preferred to Reactions of Polymers because the former is more specific. Nevertheless, a great diversity of material could still be included under the new title and as before a measure of selectivity has been imposed. Again, photochemistry, crosslinking reactions, and direct radiation or radical-induced grafting reactions have been omitted. 

During the period covered by this article a number of books and review articles have been published. Some of these are fairly general. Others deal with one polymer, for example polyisoprene, or one aspect of the subject such as the effects of tacticity in polymer reactions or pKjlymer modifications with polymerizable monomers.  

Two useful review articles on the theory of the kinetics and statistics of reactions of functional groups on polymers have appeared. Both polymer-analogous and intramolecular transformation reactions are influenced by a number of specifically macromolecular effects. These include neighbouring-group effects, configurational and conformational effects, electrostatic and supermolecular effects. The incorporation of all these factors into a general theory of macromolecular reactions is extremely difficult. These reviews provide introductions to the mathematical models as well as state-of-the-art overviews. 

A recent paper describes a mathematical model for the chlorination of polyethylene in a bubble column reactor, the model was used to optimize product quality in the continuous chlorination of polyethylene. Another theoretical treatment deals with the change in polymer reactivity during the course of a macromolecular reactions in solution or in the melt. The reactivity of a transforming unit in the polymer depends on its microenvironment, including nearest neighbours on the same chain and on other chains, as well as small molecules in the reacting system. The equations derived describe the kinetic curve, the distribution of units, and the compositional heterogeneity of the products. 

Calculations have shown that proximity and orientation constraints are not serious in intramolecular reactions of pairs of terminal groups connected by a poly methylene chain. Hence, calculations based on a core-probability model show good agreement with experimental data.  

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The same fluoroalkoxy substituents, however, are able to enhance substitutional reactivity of fluorinated polyphosphazenes by originating methatetical exchange reactions on polymers in the presence of new nucleophiles and under appropriate experimental conditions. Thus, a series of exchange reactions at phosphorus atoms bearing the trifluoroethoxy substituents in PTFEP have been describedbyH.R. Allcock [508] (Fig. 13),Cowie [482,483] (Fig. 14), and Ferrar [509] (Fig. 15), while surface modification of PTFEP films were reported by Allcock [514,515] (Fig. 16 or 17) and by Lora [516] (Fig. 18). 

The first section, Chemical Reactions on Polymers, deals with aspects of chemical reactions occurring on polymers—aspects relating to polymer size, shape, and composition are described in detail. One of the timely fields of applications comprises the use of modified polymers as catalysts (such as the immobilization of centers for homogeneous catalysis). This topic is considered in detail in Chapters 2, 3, 8, 9, and 11 and dealt with to a lesser extent in other chapters. The use of models and neighboring group effect(s) is described in detail. The modification of polymers for chemical and physical change is also described in detail in Chapters 2 (polystyrene) 4 (polyvinyl chloride) 5 (polyacrylic acid, polyvinyl alcohol, polyethyleneimine, and polyacrylamide) 6 (polyimides) 7 (polyvinyl alcohol) 8 (polystyrene sulfonate and polyvinylphosphonate) 10 (polyacrylamide) and 12 (organotin carboxylates). 

This book contains papers presented at the symposium on Polymer Modification held at the National American Chemical Society Meeting in Orlando, Florida, August, 1996. The chemistry presented is broad ranging, and includes grafting and chemical oxidation reactions, and many other chemical modifications. 

This paper illustrates its application to problems encountered in studies on polymer modification reactions, polymer epimerization reactions, p-cresol-formaldehyde condensation reactions, and monomer-promoted polyaddition reactions. A 23-statement CSMP program was written, for example, to duplicate the predictor-corrector program of Bauer for simulating irreversible polymer modification reactions. 

In spite of the relatively low performance/cost ratio of the respective products, application of reactions on polymers are of continuous interest for synthesis of amine functionalized polymers. The technique of modification of solid polymers by exploitation of their reactive moieties under heterogeneous conditions allows properties to be tailored and optimized according to specific needs and requirements. Telechelic polymers are used for the synthesis of materials with predictable and controlled properties. Application of carefully designed macromolecules provides systems with functional groups dispersed along the polymer chain or bond at the end of macromolecules. 

Frechet wrote a very relevant and well-documented review on this subject. Many of the findings relating to the use of phase transfer catalysis in organic synthesis can be applied to the chemical modification of polymers as far as the features specific to polymer chemistry (Section 1.3 to 1.5) are taken into account. Moreover it is worth underlining that in a number of cases phase transfer catalyzed reactions on polymers involve three distinct phases instead of the two that are in most classical organic reactions. 

Benham, J. L. and J. F. Kinstle (eds.), Chemical Reactions on Polymers , ACS, Washington, DC, 1988. A presentation of the recent and emerging technology on polymer modification and specialty polymers by chemical reactions. 

UV irradiation on a polymer surface produces chemical modification as well as wettability and bondability improvement. It causes chain scission and oxidation on polymer surfaces. -iven in the presence of an inert gas [45]. Carbonyls are found to be introduced onto polyethylenes on UV irradiation. Sivram et al. [46] have used photochemical treatments for surface modification of polymers. They have generated surfaces of vaying surface energies by simple organic reactions. 

Today modifications can be roughly grouped into two categories - a. physical modifications including entanglement and entrapment and radiation induced changes and b. chemical modifications where chemical reactions on the polymer are emphasized. This distinction is often unclear at best. 

PVA Formation Reaction. Poly(vinyl alcohol) is itself a modified polymer being made by the alcoholysis of poly(vinyl acetate) under acid or base catalysis as shown in Equation 1 (6.7). This polymer cannot be made by a direct polymerization because the vinyl alcohol monomer only exists in the tautomeric form of acetaldehyde. This saponification reaction can also be run on vinyl acetate copolymers and this affords a means of making vinyl alcohol copolymers. The homopolymer is water soluble and softens with decomposition at about 200°C while the properties of the copolymers would vary widely. Poly(vinyl alcohol) has been widely utilized in polymer modification because ... 

The third possibility for synthesizing polymeric substances is the modification of existant natural or synthetic macromolecules (see Chap. 5). These processes can either be chemical or physical. Chemical modifications are reactions on macromolecules without degradation of the main chain (macromolecular substitution routes, polymer-analogous reactions ) like, for example, hydrolysis. 

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