Boric acid was added (2.0 g, 32.3 mmol) and the suspension was stirred vigorously for 10 minutes at room temperature to ensure the boric acid was fully dispersed. Then the reaction mixture was heated to reflux, and the temperature was monitored and kept between 110-115 °C for 3 days. After cooling to room temperature, the toluene was removed under reduced pressure and the resulting viscous liquid further dried in a vacuum oven at 40 °C overnight to give the crude PBS polymer as a cloudy viscous oil. The crude PBS was redissolved in hexane (~350 mL) using a combination of stirring, heating, and ultrasound sonication. The resulting solution was filtered through a 0.45 μm PTFE syringe filter to remove any excess and unreacted boric acid. The hexane was removed under reduced pressure and the purified polymer dried in the vacuum oven at 120 °C overnight to give PBS as a clear solid. The PBS was stored under vacuum between measurements and then heated to 120 °C under vacuum prior to any measurements to remove any residual moisture.