Introduction of unsaturated pendant groups to polyethylene by gamma-ray irradiation under a 1,3-butadiene atmosphere

Ultra-high-molecular-weight polyethylene ((M) over bar(v): 5 x 10(6), 100-t imes elongated film) was irradiated with gamma-rays under a 1,3-butadiene a tmosphere at room temperature. Electron paramagnetic resonance (EPR) measur ements indicated that the radicals formed on the polyethylene substrate dur ing the irradiation were short-lived. EPR, Fourier transform IR spectroscop y, solid-state NMR, and differential scanning calorimetry of the as-irradia ted materials indicated that butadiene molecules were covalently bound to t he polyethylene chains as pendant groups bearing trans-vinylene and vinyl f unctions in a ratio of 3:1. Some crosslinks among the pendants, or between pendants and the main chains were produced. The number of unsaturated penda nts introduced (including bridges) per carbon atom of the polyethylene main chain was dependent on the irradiation dose and the butadiene pressure, an d was 0.096 butadiene units for 10 kGy irradiation under a 304 kPa butadien e atmosphere. The unsaturated pendants or bridges on the polyethylene chain thus introduced may be good targets to functionalize polyethylene by coval ent modification.