|dc.description.abstract||A detailed electron microscopic study of the morphology and
kinetics of crystallization of trans-1,4-polyisoprene with cis
isoprene units varying from Of to 19.8 has been carried out.
Two crystal structures of trans3., 4-polyisoprene (LIS and in p)
were generally observed.
In an unstrained film, lamellar single crystals which developed
into hedrites, sheaves and spherulites of both crystal modifications
were observed. The morphology attained was determined by the
growth rate and the nucleation density of the crystals. Electron
diffraction study suggests that the lamellar crystals have a
chain-folded configuration. In a strained film, a row nucleation
morphology was observed LIT and FIMP lamellar crystals were observed
to nucleate from the same central 'backbones'. The row nucleation
density of the lamellar crystals increases with strain. The growth
habits of the lamellar crystals in, both strained and unstrained
films were dependent on the film thinness, and on the proximity
and the orientation of the neighbouring crystals. Models for
the observed growth habits were discussed.
The lamellar thickness data agrees with the kinetic theory of
chain folding. The lamellar thickness of both crystal structures
increases with decreasing degree of supercooling. The fold surface
free energies estimated were 45.1 x 10-3 J/n2 and 60.1 x 10-3 J/m2
for the LIT and F ULF crystals of gotta percha respectively.
The growth kinetics data of the lamellar crystals determined
agrees with the existing theories of crystal growth. At the range
of temperature from 400 to 560, the HMF crystal has a faster growth
rate than the LMF crystallized at the same temperature. At the
same degree of supercooling, the LMF crystal has a faster
growth rate. The growth rates of both the LMF and HMF crystals
decrease as the cis content on a trans polymer chain increases.
With 66 cis units, the growth rate of the isomerized specimen
decreased to a value of 1/6 to 1/8 of that for gutta percha (0f
cis), whereas in cis-polyisoprene, the growth rate is retarded
by 100 times with the inclusion of trans isoprene unit.
This, difference in behaviour is discussed in terms of the possibility
of including non-crystallizable units in the crystal lattice.
The growth rate analysis showed the importance of determining
the equilibrium melting temperature and glass transition
temperature for each isomerized specimen to obtain meaningful