聚异丙基丙烯酰胺高分子在甲醇水溶液中溶解性的拉曼光谱研究

通过测量-13℃(低于低临界溶解温度(LCST))时聚异丙基丙烯酰胺(PNIPAM)高分子在甲醇水溶液中的拉曼光谱非一致效应(NCE),试图从PNIPAM与溶剂分子间的相互作用角度理解PNIPAM的溶解性.通过比较甲醇水溶液中加入PNIPAM前后甲醇分子C-O伸缩所对应的NCE变化,我们认为:甲醇摩尔分数(x)在1.0-0.90范围内,PNIPAM优先吸附甲醇分子;x=0.80-0.50时,PNIPAM优先吸附水分子;而x=0.50-0.20时,PNIPAM破坏了甲醇与水所形成的三元环稳定结构.进一步比较加入PNIPAM或其单元结构--异丙基丙酰胺(NIPPA)对甲醇水溶液NCE的影响,发现PNIPAM通过链段间的疏水协同作用吸附了甲醇分子.我们认为在甲醇水溶液的低浓度区间,这种协同作用破坏了甲醇与水形成的三元环团簇结构,而当温度升高时这种结构又重新形成,导致了PNIPAM在甲醇水溶液中的混致不溶现象.

Solubility of Poly(N-isopropylacrylamide)in Aqueous Methanol from Raman Spectroscopy

We measured the non-coincidence effect (NCE) in the Raman spectrum of poly(N-isopropylacrylamide) (PNIPAM) in aqueous methanol at -13 ℃ (below the lower critical solution temperature, LCST). This was done to investigate the solubility of PINPAM in aqueous methanol by considering molecular interactions. Changes of NCE when adding PNIPAM to an aqueous methanol solution show that at the molar fraction of methanol x=1.0-0.90, PNIPAMpreferentially adsorbs methanol and at x=0.80-0.50, PNIPAMpreferentially adsorbs water. At x=0.50-0.20, PNIPAM breaks down the ring structure composed of two methanol molecules and one water molecule. Further comparison between the changes of NCE when adding PNIPAM and its monomer NIPPA indicates that PNIPAM adsorbs methanol cooperatively through hydrophobic interactions. This cooperative interaction breaks down the methanol-water ring structure at low methanol concentrations. The cononsolvency phenomenon of PNIPAM in a methanol solution when heating above the LCST temperature is attributed to a reformation of the methanol-water ring structure.