Highly branched poly(N-isopropyl acrylamide) was prepared with either carboxylic acid (HB-PNIPAM-COOH) or trihistidine (HB-PNIPAM-3His) end groups. The triHis peptide was linked to the polymer by the N-terminus leaving the C-terminus as the ultimate chain end functionality. The presence of the triHis end groups altered the pH responsive behaviour of the polymers so that the HB-PNIPAM-3His polymer had elevated cloud points at both low and high pH, compared to pH 5.5, whereas the cloud points of HB-PNIPAM-COOH aqueous solutions increased as pH increased. Above the cloud point HB-PNIPAM-COOH formed colloidally stable dispersions but the HB-PNIPAM-3His flocculated. However, both polymers formed gels above the cloud point at concentrations of 2.5 weight percent. The addition of triHis end groups had the effect of decreasing the gel temperature and both systems provided gels with storage moduli of 103 to 104 Pa.
使用
羧酸 (HB-
PNIP
AM-COOH) 或三组
氨酸 (HB-
PNIP
AM-3His) 端基制备高度支化的聚(N-异丙基
丙烯酰胺)。三组
氨酸肽通过 N 末端与聚合物连接,留下 C 末端作为最终的链端功能。三组
氨酸端基的存在改变了聚合物的 pH 响应行为,因此与 pH 5.5 相比,HB-
PNIP
AM-3His 聚合物在低 pH 和高 pH 下的浊点均升高,而 HB-
PNIP
AM-COOH 的浊点
水溶液随着pH值的增加而增加。高于浊点,HB-
PNIP
AM-COOH 形成胶体稳定的分散体,但 HB-
PNIP
AM-3Hi 发生絮凝。然而,两种聚合物在浓度为 2.5 重量%时均在浊点以上形成凝胶。添加三组
氨酸端基具有降低凝胶温度的作用,并且两个系统都提供储能模量为 103 至 104 Pa 的凝胶。