Yin Xiangchun, Hoffman Allan S, Stayton Patrick S
Department of Bioengineering, University of Washington, Seattle, Washington 98195, USA.
Biomacromolecules. 2006 May;7(5):1381-5. doi: 10.1021/bm0507812.
Temperature- and pH-sensitive random copolymers of N-isopropylacrylamide (NIPAAm) and propylacrylic acid (PAA) were prepared using the reversible addition fragmentation chain transfer (RAFT) polymerization method. The lower critical solution temperatures (LCSTs) (or phase separation temperatures) of the NIPAAm-co-PAA copolymer solutions were measured by the cloud-point method. At slightly acidic conditions, the LCST decreased with increase in PAA content, which suggests that the hydrophobic propyl group of PAA has a greater influence on the LCST than the polar carboxylic acid group at those conditions. An increase of pH led to a significant increase in LCST of the copolymers due to the ionization of the -COOH group. The LCSTs were studied as a function of copolymer composition over the pH range from 5.0 to 7.0. Because the pK(a) of the polymers can be tuned to fall close to neutral pH, these polymer compositions can be designed to have phase transitions triggered near physiological pH or at slightly acidic pH values that fall within acidic gradients found in biology. The NIPAAm-co-PAA copolymers thus display tunable properties that could make them useful in a variety of molecular switching and drug delivery applications where responses to small pH changes are relevant.
采用可逆加成-断裂链转移（RAFT）聚合法制备了N-异丙基丙烯酰胺（NIPAAm）和丙基丙烯酸（PAA）的温度和pH敏感型无规共聚物。通过浊点法测定了NIPAAm-co-PAA共聚物溶液的低临界溶液温度（LCSTs）（或相分离温度）。在弱酸性条件下，LCST随PAA含量的增加而降低，这表明在这些条件下，PAA的疏水丙基对LCST的影响比极性羧酸基团更大。由于-COOH基团的电离，pH值的升高导致共聚物的LCST显著增加。在pH值为5.0至7.0的范围内，研究了LCSTs与共聚物组成的关系。由于聚合物的pK(a)可以调节至接近中性pH值，因此可以设计这些聚合物组合物，使其在生理pH值附近或在生物学中发现的酸性梯度内的弱酸性pH值下触发相变。因此，NIPAAm-co-PAA共聚物具有可调谐的特性，这可能使其在各种与对小pH变化的响应相关的分子开关和药物递送应用中有用。
