In the crystalline state, polymer chains are generally parallel to one another but
neighbouring chains of equivalent
conformation may differ in
chirality and/or orientation. Chains of identical
chirality and
conformation are isomorphous. Chains of opposite
chirality but equivalent
conformation are enantiomorphous. For example, two ...TG
+TG
+TG
+... helices of isotactic poly(propylene) are isomorphous. Isotactic poly(propylene)
chains of the ...TG
+TG
+TG
+... and ...G
−TG
−TG
−T... types are mutually enantiomorphous. With regard to orientation, consider a repeating
side group originating at atom
,
the first atom of the
side group being
.
For certain chain symmetries (helical, for instance) the bond vectors
have the same components (positive or negative)
along the
c axis for every
.
Two equivalent (isomorphous or enantiomorphous) chains in the crystal lattice, having
identical components of the bond vectors along
c, both positive or both negative, are designated isoclined; two equivalent chains
having bond vectors along
c of the same magnitude but opposite sign are designated anticlined.
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