The initial
impetus for design and synthesis of biodegradable polymers
was derived from their ecological value. In the past,
design of polymeric materials was focused on optimization
of strength and longevity. Currently, almost all synthetic
polymers available commercially are unable to be assimilated
into the biosphere. This fact presents an environmental
problem, as about 6% of our solid waste is composed
of synthetic polymeric materials. Disposal of biodegradable
polymers would be much easier. More importantly, biodegradable
polymers have found uses in agriculture, medicine, and
pharmaceutics. Absorbable sutures, surgical implants,
controlled release agricultural chemicals and drugs,
and mulching materials for crops are a few valuable
applications of biodegradable polymers. Since 1973,
we have prepared and studied the biodegradabilities
of new substituted and unsubstituted linear polymers
containing one or more types of hydrolyzable linkages
such as amide, enamine, ester, urea, and urethane. The
biodegradabilities were found to vary with the nature
of the linkage, the nature of the substituent, the configuration
of the polymer chains, the conformation of the polymer
chains, and the morphology of the polymers. Hydrogen-bonding
rings are semi-rigid structural units when incorporated
into polymer chains and can provide rigidity to the
polymer materials. Monomeric and polymeric liquid crystals
containing hydrogen-bonded rings have been prepared
and their transition temperatures found to be much lower
than their hydrocarbon analogs. Polymeric 1,3-diketone
and their enol-keto forms are being studied as possible
intermediates in the biodegradation of polymeric glycols
and hydrocarbons. New high temperature stable polymers
are being developed for applications as adhesives and
composites.
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