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, Tg ∼ −62 °C) to significantly low branching
(<10/1000 C, Tm ∼ 125 °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.