AbstractBy using oriented polypropylene prepared by forced quenching in a zone‐drawing‐type apparatus, the effect of taut tie molecules on the modulus is studied by measuring the changes of superstructure with an increasing draw ratio and the temperature at which the oriented polypropylene was annealed. Superstructure is analyzed by means of an x‐ray method, differential scanning calorimetry, thermal shrinkage, birefringence, and infrared spectrum. Modulus increases with an increasing orientation function of amorphous chains, ƒa, and is decided only by the value of ƒa, so long as the higher value of orientation function of the crystalcaxis does not change with the draw ratio or annealing. The taut tie molecules in ultrahigh‐modulus polypropylene are loosened by annealing at temperatures below 420 K, but would be incorporated into folded lamellar crystals above the annealing temperature of 420 K. The taut tie molecules does not always have a 31helix con
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