A variety of coupling agents to couple polymer-alkali metal to produce a variety of higher molecular weight species have been employed in the past, such as silicon-containing materials as described in U.S. Pat. No. 3,244,664; polyfunctional agents such as described in U.S. Pat. No. 3,281,383; and lactones such as described in U.S. Pat. No. 3,627,745. Combinations of certain coupling agents have been described, such as divinylbenzene and a haloalkane in U.S. Pat. No.3,661,873; or combinations of silicic compounds and dialkenyl compounds in U.S. Pat. No. 3,725,369; or divinylbenzene and active halogen compounds in U.S. Pat. No. 3,725,370.
Nevertheless, improvements in coupling procedures and methods still are required, since in some instances problems continue to exist.
These problems have been particularly apparent in trying to make haze-free, clear, impact-resistant resinous polymers. Resinous copolymers are described in such as U.S. Pat. Nos. 3,639,517, and 4,091,053, both of these describing particular methods of initiator addition, as well as subsequent coupling procedures. Other patents also describe resinous impact-resistant copolymers such as U.S. Pat. Nos. 4,180,530, 4,221,884, 4,284,980, 4,248,981, 4,248,982, 4,248,983, all being star-shaped copolymers, and requiring a random diene/arene mid-block for radial arm, five of them employing a multiple initiator addition to produce a polymodal product, one being monomodal.
A problem arising in many coupling procedures has been the haze which develops in resinous coupled copolymers, since high clarity is exceedingly desirable, yet while maintaining impact-resistant characteristics of the resinous polymer. To produce a haze-free product, yet maintain the other physical properties, has indeed been a problem.