Page 558 - Carrahers_Polymer_Chemistry,_Eighth_Edition

16 Reactions on Polymers

Reactions occurring on polymers in nature and industry is widespread. In nature, reactions on poly-
mers serve as the basis for information transfer, synthesis of needed biomaterials, degradation of
biomaterials, and in fact reactions of polymers are at the core of life itself. Nature also reacts with
synthetic polymers as they age, degrade, cross-link, and so on. Synthetic polymers also serve as the
basic material for the production of many important fibers, elastomers, and plastics. The nature of

these reactions is govern similarly whether the source and site of polymer is nature or made-made.
There are some differences especially with respect to the precision of the interaction and predicted
outcome. Some polymer interactions, such as those that transfer information, must occur with a very
high degree of precision for each and every incident. By comparison, naturally induced degrada-
tion of natural and synthetic polymers through weathering occurs through general steps that can be
described in some statistical manner.
Reactions on synthetic polymers often mimic similar reactions involving small molecules where
size is the main difference. There are some exceptions such as where near groups may hinder or assist
in the reaction where differences occur. Here, the main differences are often kinetic, though some

geometrical differences are found for specific cases. Reactions where the rate of reaction in polymers
is enhanced by the presence of neighboring groups are called anchimeric assistance reactions.
While there are many possible routes, most degradations can be described as occurring through
two general routes—unzipping and random scission. Polymers such as polysiloxanes and polysul-
fur undergo unzipping reactions forming preferred internal cyclic products unless the end group is
capped in such a manner as to discourage unzipping. In unzipping, one end begins to “unzip” and
this process continues down the chain until it is completed. Random scission is the normal deg-
radation pathway for most natural (such as polycarbonates [PC]) and synthetic polymers. Here, a
long chain is attacked at some site, normally one that is exposed and of the exposed sites, one that
is stressed. Thus, while random scission implies a random statistical manner of chain breakage,
superimposed on this are more complex considerations of exposure and stress and the likelihood
that a particular site is susceptible to that particular type of bond breakage.
This chapter describes many of the important reactions of polymers. Synthesis and curing (cross-
linking) of polymers and telomerization are chemical reactions of polymers that have been dis-
cussed in previous chapters.

16.1 REACTIONS WITH POLYOLEFINES AND POLYENES

As with other carbon, hydrogen, and oxygen-containing materials, the main products of combustion
in the presence of oxygen are water and carbon dioxide. Such polymers can be reacted with vari-
ous reactants giving products analogous to those obtained from small alkanes and alkane-intense
compounds. The moderating conditions between reactions of small molecules and polymers involve
contact between the polymer segments and the reactants.
Polyolefines, like simple alkanes, can be chlorinated by chlorine giving hydrogen chloride and

chlorinated products such as Tyrin, used as plasticizers and flame retardants, and poly(vinyl dichlo-

ride), that has better heat resistance than PVC and is used for hot water piping.
Reactions with polyenes are similar to the reactions of alkenes. Thus, Hermann Staudinger
found that polyenes such as Hevea brasiliensis could be hydrogenated, halogenated, hydrohalo-
genated, and cyclized. This classic work was done in the early 1900s. In fact, Berthelot hydro-
genated H. brasiliensis in 1869. Chlorinated rubber (Tornesit and Parlon) is produced by the

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