Polar Additive Triggered Branching Switch and Block Polyolefin Topology in Living Ethylene Polymerization

Branching is paramount in polyolefins and their copolymers because it renders state-of-the-art topologies and thus directly determines polymer properties. A polar additive, commonly acting as a coordinating ancillary ligand in olefin polymerization, is usually a poisonous reagent to shut down the reaction. Also, it is generally assumed to have very little or even no impact on polyethylene (PE) architecture in terms of branching. We now demonstrate the finding that the degree of branching in palladium promoted ethylene polymerization can drastically be switched from ultrahigh branching (>200/1000 C, T-g similar to -62 degrees C) to significantly low branching (<10/1000 C, T-m similar to 125 degrees C) by acrylonitrile as a polar additive (up to 4000 equiv). Key features that a polar additive does not shut down the reaction and significantly switches the degree of branching and importantly does not induce chain transfer (living mode, PDI < 1.10) readily enable the preparation of diblock topologies of amorphous ultrahighly branched PE and semicrystalline lightly branched PE. A further new concept that acrylate serves as a polar comonomer and acrylonitrile acts as a regulator of branching gives access to functionalized PE with tunable branching degrees.