1. Field of the Invention
The present invention relates to a composition of polybutene-1 and a process for preparing the same and, more particularly, to a composition and a process for the preparation of polybutene-1 which has less gel content and less fish eyes and which can preferably be used in the field of film.
2. Description of Related Art
A homopolymer of polybutene-1 or a copolymer of butene-1 with another olefin, as generally called polybutene-1, has been used for pipes for warm water due to its excellent creep resistance at high temperatures or in the film field due to its high orientation at a low degree of stretching. Such conventional polybutene-1, however, has the drawback that it is remarkably poor in moldability or forming performance because of its low speed of crystallization. Hence, various attempts have so far been made to solve the drawback of conventional polybutene-1.
In order to accelerate the cystallization speed, for example, U.S. Pat. No. 4,321,334 proposes using a nucleating agent in preparing polybutene-1. In this process, however, it is so difficult to disperse the nucleating agent in polybutene-1, that it cannot be said to produce the effect to a sufficient degree. Particularly, when polybutene-1 obtained by this process is formed to film, the film suffers from the disadvantage that fish eyes are caused to thereby give a poor appearance.
Further, Japanese Patent Unexamined Publication (kokai) No. 123,607/1980 discloses a process for preparing crystalline polybutene-1 having a high bulk density by subjecting a small amount of .alpha.-olefin other than butene-1 to preliminary polymerization in the process for preparing polybutene-1. As this process is developed with the object to provide polybutene-1 with high bulk density by using a small amount of the other .alpha.-olefin for preliminary polymerization, the above-identified patent publication is silent about the problems of gel content and fish eye. Turning now to specific examples of the description of the patent publication, it can be noted that they do not use a molecular weight modifier, such as hydrogen or the like, during preliminary polymerization. Hence, it can be presumed that a polymer obtainable by this preliminary polymerization may have a too high molecular weight, thereby causing gel and fish eye in large numbers.