温敏性SA/P(NIPAM-co-AM)水凝胶分子运动的固体核磁共振研究
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摘要
将不同比例的N-异丙基丙烯酰胺(NIPAM)和丙烯酰胺(AM)引入到聚阴离子海藻酸钠(SA)网络中,采用原位自由基聚合法制备了具有温敏特性的互穿网络SA/P(NIPAM-co-AM)水凝胶。采用固体NMR研究了P(NIPAM-co-AM)分子链在不同温度,尤其是在临界温度附近不同基团的运动状态变化。结果表明:当温度低于低临界溶解温度(LCST)时,体系中分子链运动较快;当温度高于LCST时,由于疏水作用增强,水凝胶结构收缩,分子链运动减慢。实验还观察到,不同的基团在不同频段的运动对于温度的响应并不同步,而是有着一定的顺序。利用低场核磁共振(LF-NMR)原位研究了复合水凝胶的溶胀过程,结果表明水分子的扩散和大分子链段的松弛同步进行,符合non-Fickian模型的溶胀特征。
The SA/P(NIPAM-co-AM)hydrogel was prepared by in situ free radical copolymerization with different contents of N-isopropyl acrylamide(NIPAM)and acrylamide(AM)in sodium alginate(SA)network.By changing the composition ratio,a series of thermalsensitive hydrogels with different lower critical solution temperatures(LCST)were prepared.And under the condition of a low AM/NIPAM mass ratio,the LCST of the gel is linearly correlated with the increase of the ratio.Meanwhile,the presence of carboxyl group and amino group also makes the gel responsive to pH value,which can expand the application of the hydrogels.Solid-state NMR was used to study the molecular dynamics at different temperatures,especially near the LCST.When the temperature is lower than the LCST,the mobility of molecular chain is quick;when temperature is higher than LCST,the molecular mobility decreases due to the collapse of the network.The mobility of different groups in different frequencies do not change synchronizedly,but in certain sequence.The high-frequency motion of the main chain is first affected by temperature(298K),followed by high-frequency motion of the side chain(301K),and finally the lowfrequency motion of the side chain(304 K).The low-frequency motion of the main chain is not significantly affected by temperature.The macroscopic changes occur after the reduction of the mobility of all the groups(305 K).In addition,using the low field nuclear magnetic resonance(LF-NMR)the swelling process of composite gel is studied in situ.The diffusion of water molecules and the relaxation of macromolecular chains are synchronized,which conform to the swelling model of non-Fickian diffusion.
The SA/P(NIPAM-co-AM)hydrogel was prepared by in situ free radical copolymerization with different contents of N-isopropyl acrylamide(NIPAM)and acrylamide(AM)in sodium alginate(SA)network.By changing the composition ratio,a series of thermalsensitive hydrogels with different lower critical solution temperatures(LCST)were prepared.And under the condition of a low AM/NIPAM mass ratio,the LCST of the gel is linearly correlated with the increase of the ratio.Meanwhile,the presence of carboxyl group and amino group also makes the gel responsive to pH value,which can expand the application of the hydrogels.Solid-state NMR was used to study the molecular dynamics at different temperatures,especially near the LCST.When the temperature is lower than the LCST,the mobility of molecular chain is quick;when temperature is higher than LCST,the molecular mobility decreases due to the collapse of the network.The mobility of different groups in different frequencies do not change synchronizedly,but in certain sequence.The high-frequency motion of the main chain is first affected by temperature(298K),followed by high-frequency motion of the side chain(301K),and finally the lowfrequency motion of the side chain(304 K).The low-frequency motion of the main chain is not significantly affected by temperature.The macroscopic changes occur after the reduction of the mobility of all the groups(305 K).In addition,using the low field nuclear magnetic resonance(LF-NMR)the swelling process of composite gel is studied in situ.The diffusion of water molecules and the relaxation of macromolecular chains are synchronized,which conform to the swelling model of non-Fickian diffusion.
引文
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[16]侯立峰,黄海龙,杨仲丽,等.固体核磁共振研究纤维素凝胶/聚ε-己内酯复合材料的结构与分子运动[J].功能高分子学报,2018,31(6):585-594.
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[20]张念一,黄秀晶,陈莉,等.化学/离子交联水凝胶的透光度溶胀行为和力学性能[J].高分子材料科学与工程,2014,30(4):64-69.
[21]梁伯润,查刘生,张高奇.SA分子量及用量对SA/PNIPAAm semi-IPN水凝胶溶胀性能的影响[J].高分子材料科学与工程,2009,25(9):97-104.
[22]李海燕,曹建.N-异丙基丙烯酰胺pH敏感型水凝胶的制备及对甲基紫吸附性能研究[J].化学工程师,2015,29(3):61-64.
[2]PARK T G.Temperature modulated protein release from pH/temperature-sensitive hydrogels[J].Biomaterials,1999,20(6):517-521.
[3]LIM D,LEE E,KIM H,et al.Multi stimuli-responsive hydrogel microfibers containing magnetite nanoparticles prepared using microcapillary devices[J].Soft Matter,2015,11(8):1606-1613.
[4]MIYATA T,ASAMI N,URAGAMI T.A reversibly antigen-responsive hydrogel[J].Nature,1999,399(24):766-768.
[5]KUCKLING D,HARMON M E,FRANK C W.Photo-cross-linkable PNIPAAm copolymers:Synthesis and characterization of constrained temperature responsive hydrogel layers[J].Macromolecules,2002,35(16):6377-6383.
[6]LIU Y Y,FAN X D.Synthesis and characterization of pH and temperature-sensitive hydrogel of N-isopropylacrylamide/cyclodextrin based copolymer[J].Polymer,2002,43(8):4997-5003.
[7]于跃芹,李延顺,祝纯静,等.PNIPAAm/CMC半互穿网络水凝胶的合成及性质研究[J].高分子材料科学与工程,2011,27(2):13-15.
[8]陈韩婷,樊晔,方云.全亲水无规共聚物P(NIPAM-co-AA)的pH和温度双重刺激响应性水相自组装[J].物理化学学报,2014,30(7):1290-1296.
[9]邓字巍,易昌凤,徐祖顺.聚(N-异丙基丙烯酰胺)类材料的应用[J].功能高分子学报,2004,17(2):317-324.
[10]卓仁禧,张先正.温度及pH敏感聚(丙烯酸)/聚(N-异丙基丙烯酰胺)互穿聚合物网络水凝胶的合成及性能研究[J].高分子学报,1998(1):39-42.
[11]MARCELO G,AREIAS L R P,VICIOSA M T,et al.PNIPAm-based microgels with a UCST response[J].Polymer,2017,116:261-267.
[12]CAYKARA T,KIPER S,DEMIREL G.Thermosensitive poly(N-nisopropylacrylamide-co-acrylamide)hydrogels:Synthesis,swelling and interaction with ionic surfactants[J].European Polymer Journal,2006,42(2):348-355.
[13]FRANK H,ZIENER U,LANDFESTER K.Synthesis of different mesoporous SiO2structures by using PNIPAM-co-PSparticles as templates[J].Macromolecular Symposia,2014,337(1):18-24.
[14]张高奇,查刘生,周美华,等.海藻酸钠和聚N-异丙基丙烯酰胺半互穿网络水凝胶的溶胀动力学研究[J].高分子学报,2005(1):35-39.
[15]张高奇,梁伯润,周美华,等.海藻酸钠和聚(N-异丙基丙烯酰胺)半互穿网络水凝胶的制备及性能研究[J].功能高分子学报,2004,17(1):41-45.
[16]侯立峰,黄海龙,杨仲丽,等.固体核磁共振研究纤维素凝胶/聚ε-己内酯复合材料的结构与分子运动[J].功能高分子学报,2018,31(6):585-594.
[17]ANDERSSON M,MAUNU S L.Volume phase transition and structure of poly(N-isopropylacrylamide)microgels studied with 1 H-NMR spectroscopy in D2O[J].Colloid Polymer Science,2006,285(3):293-303.
[18]ZENG F,TONG Z.NMR investigation of phase separation in poly(N-isopropyl acrylamide)/water solutions[J].Polymer,1997,38(22):5539-5544.
[19]郭肖青,朱平,张怡,等.海藻纤维吸附性能的测试与研究[J].印染助剂,2007,24(11):10-13.
[20]张念一,黄秀晶,陈莉,等.化学/离子交联水凝胶的透光度溶胀行为和力学性能[J].高分子材料科学与工程,2014,30(4):64-69.
[21]梁伯润,查刘生,张高奇.SA分子量及用量对SA/PNIPAAm semi-IPN水凝胶溶胀性能的影响[J].高分子材料科学与工程,2009,25(9):97-104.
[22]李海燕,曹建.N-异丙基丙烯酰胺pH敏感型水凝胶的制备及对甲基紫吸附性能研究[J].化学工程师,2015,29(3):61-64.