Deepa, Puthanparambil; Dr. Jayakannan, M(National Institute for Interdisciplinary Science and Technology(CSIR), February , 2008)
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Abstract:
In this introduction part, importance has been given to the elastomeric
properties of polyurethanes. Emphasis has been laid to this property based on
microphase separation and how this could be modified by modifying the segment
lengths, as well as the structure of the segments. Implication was also made on the
mechanical and thermal properties of these copolymers based on various analytical
methods usually used for characterization of polymers. A brief overview of the
challenges faced by the polyurethane chemistry was also done, pointing to the fact
that though polyurethane industry is more than 75 years old, still a lot of questions
remain unanswered, that too mostly in the synthesis of polyurethanes. A major
challenge in this industry is the utilization of more environmental friendly “Green
Chemistry Routes” for the synthesis of polyurethanes which are devoid of any
isocyanates or harsh solvents.The research work in this thesis was focused to develop non-isocyanate green
chemical process for polyurethanes and also self-organize the resultant novel
polymers into nano-materials. The thesis was focused on the following three major
aspects:(i) Design and development of novel melt transurethane process for
polyurethanes under non-isocyanate and solvent free melt condition.
(ii) Solvent induced self-organization of the novel cycloaliphatic
polyurethanes prepared by the melt transurethane process into microporous
templates and nano-sized polymeric hexagons and spheres.
(iii) Novel polyurethane-oligophenylenevinylene random block copolymer
nano-materials and their photoluminescence properties.
The second chapter of the thesis gives an elaborate discussion on the “Novel
Melt Transurethane Process ” for the synthesis of polyurethanes under non-isocyanate
and solvent free melt condition. The polycondensation reaction was carried out
between equimolar amounts of a di-urethane monomer and a diol in the presence of a
catalyst under melt condition to produce polyurethanes followed by the removal of
low boiling alcohol from equilibrium. The polymers synthesized through this green
chemical route were found to be soluble (devoid of any cross links), thermally stable and free from any isocyanate entities. The polymerization reaction was confirmed by various analytical techniques with specific references to the extent of reaction which is the main watchful point for any successful polymerization reaction.
The mechanistic aspects of the reaction were another point of consideration for the
novel polymerization route which was successfully dealt with by performing various
model reactions. Since this route was successful enough in synthesizing polyurethanes
with novel structures, they were employed for the solvent induced self-organization
which is an important area of research in the polymer world in the present scenario.
Chapter three mesmerizes the reader with multitudes of morphologies depending upon
the chemical backbone structure of the polyurethane as well as on the nature and
amount of various solvents employed for the self-organization tactics. The rationale
towards these morphologies-“Hydrogen Bonding ” have been systematically probed
by various techniques. These polyurethanes were then tagged with luminescent
0ligo(phenylene vinylene) units and the effects of these OPV blocks on the
morphology of the polyurethanes were analyzed in chapter four. These blocks have
resulted in the formation of novel “Blue Luminescent Balls” which could find various
applications in optoelectronic devices as well as delivery vehicles.