Surface energy. With the grafted brush monolayers of PP1-5, the surface energy of Si substrates can be modified accordingly as evidenced by the static water contact angle ranging from (38.9 ± 0.7)° to (69.2 ± 0.1)° (Figure ). With the amide backbone, polypeptoids are polar in nature, yet by introducing side chains of different polarity, the overall polarity of the polymer can be tuned.