Hydroboration and Oxidation of 1,2-PB

To obtain –OH functional end groups, the poly(butadiene) of exclusively (~100%) -1,2 microstructure is submitted to post-polymerization chemical modification reactions, namely hydroboration and oxidation. In this process, each vinyl bond (-CH=CH₂ per monomeric unit) is converted to -CH₂-CH₂-OH, leading to the desired -OH group in all monomeric units of the PB blocks. To perform the hydroboration reaction 0.15 g (3.3 mmol, 6.6 mL) of 9-BBN were introduced into 1 g of PS-b-PB_1,2-b-PDMS (sample 1, corresponding to 2.7 mmoles of the PB_1,2 segment) which was dissolved in tetrahydrofuran (0.2 w/v%) under nitrogen atmosphere at −15 °C. The solution was left to warm up to ambient conditions and was stirred for 24 h to ensure the completion of the hydroboration process. Notably, the 9-BBN is used in ~20% excess compared to the mol of the PB_1,2 block. Following this, the solution was placed at −25 °C, and 1 mL of properly degassed methanol was added to deactivate all the excess of the borane reagent. After 30 min, NaOH (3.1 mmoles 6 N, 10% excess compared to the borane moles) was introduced to prevent the development of crosslinked networks due to borane by-products. Following, the oxidizing agent H₂O₂ (6.2 mmoles 30% w/v solution, 50% excess compared to the NaOH moles) was added, and the solution was stirred at −25 °C for 2 h before being placed at 55 °C for 1 h, where the separation of the desired organic and aqueous phases occurred. The organic phase was poured into a 0.25 M NaOH solution, and subsequently, the polymer was dissolved in THF/MeOH and washed with 0.25 M NaOH twice using a Buhner funnel [28 (link),29 (link)]. Finally, the polymer was thoroughly washed with copious amounts of distilled water and placed in a vacuum oven to remove any volatile compounds. Coherent procedures were employed in all terpolymers. The chemical modification reactions for sample PB_1,2-b-PS-b-PDMS or sample 3 are provided in Scheme 1c. Similar reactions are followed for the other sequence of PS-b-PB_1,2-b-PDMS samples.