Ethylenic copolymer, composition containing said copolymer, and ethylenic copolymer film

A film formed from an ethylenic copolymer obtained through copolymerization of (a) ethylene and (b) at least one member selected from α-olefins having from 3 to 20 carbon atoms, diene compounds and cyclic olefins, wherein:

• (1) the ratio of the weight average molecular weight (Mw) of the copolymer to the number average molecular weight (Mn) thereof, Mw/Mn, falls between 1.5 and 4, said molecular weights being measured through gel permeation chromatography in terms of polyethylene, and the weight average molecular weight (Mw) falls between 3,000 and 1,000,000,
• (2) a compositional distribution curve of the copolymer obtained through temperature rising elution fractionation analysis contains an essential peak consisting of the following areas, all shown in FIG. 1, an area A, an area B, an area C, and a peak defining an area D that is attributable to a high branch component, wherein the area A indicates the range that is surrounded by a curve as obtained through Gaussian distribution approximation relative to the essential peak and a base line of the compositional distribution curve;
• the area B indicates the range that is surrounded by the compositional distribution curve, the Gaussian distribution approximation curve, and the base line and that is in the lower elution temperature side and is at an elution temperature higher than 32° C.;
• the area C indicates the range that is surrounded by the essential peak, the Gaussian distribution approximation curve, and the base line and that is in the higher elution temperature side;
• and the area D indicates the range that is surrounded by the compositional distribution curve and the base line and that is at an elution temperature between 25 and 32° C.;
• (3) the relationship between the half width at the half maximum (W/2) (°C.) of the Gaussian distribution approximation curve, and the average, n, of short-chain branches existing in the copolymer (per 1000 carbon atoms of the copolymer) satisfies the following equation:
• 0.704+0.147n≦W/2≦−0.055+0.577n,
• and
• (4) the resin density of the copolymer falls between 0.85 and 0.95 g/cm3 and the tear strength (TS, kgf/cm) of the copolymer satisfies the following equations:
• TS≧131.5−155×log [{B+C+D)/A}+0.1],
• and
• 0.1≦(B+C+D)/A≦1
• wherein A, B, C, and D are as defined above.