Abstract: Provided are a carbon fiber bundle having a high strand elastic modulus and high strand strength, and having balanced physical properties even when the average diameter of carbon fiber single-fibers is large, and a method for producing the same. The carbon fiber bundle of the present invention has an average diameter of carbon fiber single-fibers of 5.7 ?m or more and 6.5 ?m or less, substantially no twist, a strand strength of 4.7 GPa or more, and a strand elastic modulus of 320 GPa or more.

Abstract: Provided a carbon fiber bundle in which the average diameter of carbon fiber single-fibers is increased without reducing the strand strength and strand elastic modulus of the carbon fibers, and a method for producing the same. Also provided is a carbon fiber suitable for a carbon fiber composite material having excellent compressive strength in the fiber axial direction. The carbon fiber bundle of the present invention has a strand strength of 4.5 GPa or more, a strand elastic modulus of 320 GPa or more, substantially no twist, and an average diameter of carbon fiber single-fibers of 6.5 ?m or more and 8.5 ?m or less.

Abstract: A polymer composition, in which a differential distribution value in a differential molecular weight distribution curve of the polymer composition, as measured by gel permeation chromatography, satisfies Equation 1 and a maximum value of a normalized back-scattering intensity of a 35 wt % base oil solution of the polymer composition, where a size q of a scattering vector of small-angle X-ray scattering at 25° C. is in a range of 0.07 nm?1 or more and 2 nm?1 or less, is 40 cm?1 or more.

Abstract: The present invention provides: a carbon fiber that gives a carbon fiber bundle having a high strand strength and a high strand elastic modulus and has reduced defects; a carbon fiber bundle including the carbon fiber; and a production method for a carbon fiber bundle having a high strand strength and a high strand elastic modulus and having reduced defects in single fibers. The carbon fiber of the present invention is such that the number of voids in a cross-section of a single fiber is 8 or less; the carbon fiber bundle of the present invention includes the carbon fiber of the present invention; and in the production method for a carbon fiber bundle of the present invention, a temperature increase rate in a case of raising a heating temperature from 1,800° C. to 2,200° C. is 300° C./min to 600° C./min.

Abstract: A polymer composition, in which a differential distribution value in a differential molecular weight distribution curve of the polymer composition, as measured by gel permeation chromatography, satisfies Equation 1 and a maximum value of a normalized back-scattering intensity of a 35 wt % base oil solution of the polymer composition, where a size q of a scattering vector of small-angle X-ray scattering at 25° C. is in a range of 0.07 nm?1 or more and 2 nm?1 or less, is 40 cm?1 or more.