Synthesis, molecular characterization, evaluation of polymorphic behavior and indentation response in isotactic poly(propylene-co-1-heptene) copolymers

• Propylene-co-1-heptene copolymers are synthesized in a wide composition range.
• The trigonal δ form is not achieved in these copolymers at any 1-heptene content.
• The mesomorphic phase is easily obtained at high comonomer contents.
• Crystallinity seems to be the key structural feature in the hardness values obtained.
• Viscous contribution reaches a constant value if only mesomorphic form is developed.

Different polymorphs are developed in isotactic poly(propylene-co-1-heptene) copolymers depending on 1-heptene molar content and thermal history: monoclinic and orthorhombic crystallites as well as mesomorphic entities. Indentation hardness values and deformability are found to be related to those variables as well as to crystallinity degree. Consequently, mechanical behavior can be tailored mainly by varying all of these parameters and a range from rigid to soft and more easily deformable materials is attained by synthesis of copolymers based on isotactic propylene with 1-heptene as comonomeric unit. Evaluation of the influence of molecular weight, intrinsic viscosity and microstructural details is also performed.

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