新型钴酞菁接枝温敏聚合物的制备及性能

采用2,4,6-三氯-1,3,5-三嗪对四氨基钴酞菁进行改性,并以共价键接枝到聚N-异丙基丙烯酰胺上制得一种新型温敏性高分子催化剂——钴酞菁接枝温敏聚合物,并采用UV-Vis、TG等对其进行表征.对钴酞菁接枝温敏聚合物、温敏聚合物和小分子金属酞菁进行溶解性测试,结果表明与四氨基钴酞菁相比,所合成的钴酞菁接枝温敏聚合物能溶解于水和大多数有机溶剂,且该聚合物水溶液具有良好的温敏性,其最低临界溶解温度(LCST)为34.5℃.采用浊度法考察了不同比例的混合溶剂(乙醇/水、DMF/水)对LCST的影响,结果表明随着有机溶剂含量的增加,LCST先下降后升高,而当有机溶剂增加到一定程度时温敏性消失.本文还考察了钴酞菁接枝温敏聚合物对2-巯基乙醇的催化活性,结果表明随着温度升高,催化活性也不断提高,而当温度超过LCST时催化活性急剧下降,聚合物从溶液中析出.基于这些特性,该温敏聚合物负载酞菁作为一种新型的催化剂可实现均相催化、异相分离.     

聚氨酯微球的接枝改性及温敏特性

以N-异丙基丙烯酰胺(NIPAAm)为单体, 二苯甲酮(BP)为光敏剂, 过硫酸胺(APS)为自由基引发剂, 采用溶液中光接枝方法制备了具有温度敏感特性的聚氨酯微球(PUS). 傅里叶变换红外光谱(FTIR)和扫描电子显微镜(SEM)结果表明, 在聚氨酯微球表面形成了聚异丙基丙烯酰胺(PNIPAAm)接枝聚合物层. 在接枝过程中, 延长反应时间与增加引发剂浓度均有利于提高接枝率. 常温下, 接枝率随反应时间延长呈线性增长, 当反应时间超过40 min后, 接枝率基本保持稳定; 而引发剂浓度对接枝率的影响存在最佳优化值, 即其浓度为单体质量分数的3%. 采用差示扫描量热法(DSC)对接枝改性前后聚氨酯微球的温敏特性进行分析表征, 证实改性后的微球在35 ℃左右出现低临界互溶温度(LCST), 在此温度附近表现出对温度敏感特性. 接触角测试与溶胀测试结果表明, 在低临界互熔温度以下, 接枝改性的聚氨酯微球具有良好的亲水性.     

棉纤维的N-异丙基丙烯酰胺接枝共聚及产物的温敏性研究

以硝酸铈铵(CAN)、过硫酸钾(KPS)及H2O2/H2A(双氧水/抗坏血酸)为引发体系,采用溶液自由基接枝法制备了具有温敏性的棉纤维N-异丙基丙烯酰胺接枝共聚物(cotton-g-PNIPAAm);在上述3种引发剂作用下的接枝反应可以达到的接枝率(G)排序为G(H2O2/H2A)>G(KPS)>G(CAN);研究了其他因素如引发剂浓度、反应时间、反应温度和单体浓度等对接枝率的影响,得出了优化的接枝反应条件;接枝样品的FTIR分析图谱和SEM观察均表明样品表面已接枝了聚N-异丙基丙烯酰胺;DSC分析显示,棉纤维N-异丙基丙烯酰胺接枝共聚物的低临界溶解温度(LCST)与纯的聚N-异丙基丙烯酰胺凝胶(LCST=32.48℃)相似,约为32~33℃;接枝率的变化对试样LCST的影响很小,但其可逆焓变(ΔH)会随接枝率的提高而增加;采用滴水试验法(AATCC 79)和毛效试验法(FZ/T 01071)检测棉纤维的N-异丙基丙烯酰胺接枝共聚物在不同温度时的吸水性变化,显示试样具有温敏特性,其中接枝率介于25%~45%的试样温敏性较高,过低或过高的接枝率均不利于获得高的温敏性;棉纤维的N-异丙基丙烯酰胺接枝共聚物试样的可逆焓变(ΔH)随试样膨胀/收缩时间变化的研究和分析结果表明,棉纤维的N-异丙基丙烯酰胺接枝共聚物对温度变化的响应比纯聚N-异丙基丙烯酰胺凝胶快.     

丙烯腈-N-异丙基丙烯酰胺接枝共聚物的合成及其对聚丙烯腈分离膜的改性

以巯基乙胺盐酸盐(AESH)为链转移剂、2,2'-偶氮二异丁腈为引发剂,合成了具有端氨基的聚(N-异丙基丙烯酰胺)(PNIPAAm);与甲基丙烯酰氯反应,得到可聚合的PNIPAAm大分子单体;进而与丙烯腈共聚,合成了丙烯腈-N-异丙基丙烯酰胺接枝共聚物(P(AN-g-NIPAAm)).基于浸没沉淀相转化法制备了聚丙烯腈/P(AN-g-NIPAAm)共混膜.红外及核磁分析表明,通过调控AESH的浓度可制备得到不同链长的PNIPAAm大分子单体;用激光光散射进一步测定了共聚物的重均分子量;采用鼓泡接触角及浊度测定考察了共聚物的温敏特性;XPS结果证实PNIPAAm链在膜表面发生富集;纯水压滤实验发现所制备的分离膜40℃(高于PNIPAAm的LCST)时的水通量是25℃(低于PNIPAAm的LCST)时的近2倍,具有较明显的温敏性.     

温度敏感性P(MEO2MA-co-OEGMA)共聚物的合成与性质

利用原子转移自由基聚合(ATRP)方法合成了组成递变的2-甲基-2-丙烯酸-2-(2-甲氧基乙氧基)乙酯(MEO₂MA)与寡聚乙二醇甲醚甲基丙烯酸酯(OEGMA)共聚物P(MEO₂MA-co-OEGMA). 核磁共振氢谱(¹HNMR)和凝胶渗透色谱(GPC)表征了聚合物的结构、分子量及其分布. 通过测定透光率、粘度、激光粒度分析了共聚物组成对共聚物低临界溶解温度(LCST)的影响, 考察了共聚物组成、浓度、盐浓度、盐种类、温度对其溶液相行为的影响. 结果表明: 所合成的共聚物具有温度敏感性, 其LCST 可以通过合成时共聚单体MEO₂MA与OEGMA投料比的改变来调控, 随着OEGMA量的增加共聚物的LCST升高, 共聚物溶液浓度升高其LCST减小, 随盐溶液浓度的增大共聚物的LCST降低, 共聚物的LCST降低主要受盐溶液中阴离子价数的影响; HCl的引入使共聚物水溶液的LCST降低; NaOH的引入使共聚物水溶液的LCST升高.     

正离子PVA基温敏性聚合物的合成与表征及其温敏性研究

通过对聚乙烯醇(PVA)进行正离子化和缩醛化改性,制备了一种新型PVA基温敏性聚合物(CAPVA),其盐水溶液表现出最低临界溶解温度(LCST).在LCST温度以下,CAPVA能溶解于水中,其水溶液清澈透明;温度高于LCST后,CAPVA聚集并从水中分离析出.利用元素、表面电荷分析和核磁共振谱对CAPVA的结构进行了表征,并用浊度法研究了正离子接枝率、缩醛度和溶液中NaCl浓度对CAPVA温敏性的影响.     

无规共聚物P(MEO2MA-co-OEGMA)的合成及其在水溶液中温度诱导相转变行为

利用原子转移自由基聚合(ATRP)方法,由单体2-(2-甲氧基乙氧基)甲基丙烯酸乙酯(MEO₂MA)和寡聚(乙二醇)甲基醚甲基丙烯酸酯(OEGMA, M_n = 500 g·mol^-1)合成了无规共聚物P(MEO₂MA-co-OEGMA).并采用动态光散射(DLS)、紫外光谱及透射电子显微镜(TEM)等技术考察聚合物在水溶液中的温度响应性聚集行为,获得其在水溶液中的最低临界溶解温度(LCST)及其随组成的变化规律.结果表明,该聚合物具有良好且可逆的温度响应行为,这主要归因于聚合物与水分子之间氢键作用,及其分子本身疏水作用之间为了保持一种微妙的动态平衡而自发对聚集形态进行的“自我调整”,从而达到新的热力学平衡状态的结果.该聚合物的LCST与聚合物中单体OEGMA所占的摩尔比例呈线性关系,可以通过改变单体的摩尔配比实现对聚合物LCST的调控.     

单电子转移活性自由基聚合制备温敏型荧光纤维素纳米晶

在混合反应溶剂体系DMF/H2O中,利用表面引发的单电子活性自由基聚合法(SET-LRP)制备了接枝有荧光和温敏性聚(N-异丙基丙烯酰胺)(PNIPAAM)刷的纤维素纳米晶.红外光谱和固体核磁共振13C谱中PNIPAAM特征峰的出现证明了接枝的成功.接枝前后的重量变化和核磁共振1H谱分析表明,随着混合溶剂中水的比例增加,单体转化率和接枝聚合物刷的分子量逐渐增加.热重和示差扫描量热分析显示,随着纤维素纳米晶表面接枝聚合物刷长度的增加,其分解温度和玻璃化转变温度均由低温向高温方向移动,并逐渐接近纯PNIPAAM的相应温度.由于PNIPAAM的温敏性,表面接枝的纤维素纳米晶表现出与染料溶液相反的温致荧光增强性能.     

芴酮引发光接枝改性LDPE膜的研究

采用紫外光引发接枝表面改性的方法,以芴酮(FL)为引发剂,在低密度聚乙烯(LDPE)薄膜表面上接枝丙烯酸(AA)、甲基丙烯酸(MAA)、丙烯酸甲酯(MA)、甲基丙烯酸甲酯(MMA)、丙烯酰胺(AM)等单体,以赋予薄膜表面新的化学性质.考察了引发剂浓度、紫外光的辐照时间、辐照强度、单体种类对LDPE薄膜接枝程度的影响.结果表明,在一定范围内,增加芴酮浓度,可以提高单体的接枝率,但当芴酮浓度达到5%时,接枝率反而下降.延长辐照时间至4 min和提高紫外光的辐照强度达100 W/m2,均有利于接枝反应的进行.不同单体在LDPE膜上的接枝能力与单体的活性、单体与基材的相容性等因素有关.接枝后,LDPE与水的接触角下降程度不仅与单体在膜上的接枝量有关,还与接枝单体的亲水性能密切相关.     

手性温敏凝胶Poly(NIPAM-co-AAc-L-Trp)的制备及性能

利用L-色氨酸(L-Trp)为手性源,经酯化、缩合等反应制备手性单体AAc-L-Trp,进而在交联剂N,N’-亚甲基双丙烯酰胺(MBAA)和引发剂偶氮二异丁腈(AIBN)的作用下,与N-异丙基丙烯酰胺(NIPAM)发生自由基共聚制备了一种可用于手性拆分的新型手性温敏水凝胶Poly(NIPAM-co-AAc-L-Trp),其结构经IR确证.通过对其温敏性研究发现,相比于PNIPAM凝胶,疏水性手性单体的引入使Poly(NIPAM-co-AAc-L-Trp)凝胶的温敏性下降,LCST随着手性单体含量的增加而降低.以DL-苯丙氨酸为模型药物对其手性识别和拆分性能进行研究,结果表明,手性温敏凝胶可选择性地吸附D-型对映体,且吸附量随着手性单体含量增加而增加;提高温度(45°C)有利于手性温敏凝胶对DL-苯丙氨酸的拆分.     

Monodisperse thermoresponsive microgels of poly(ethylene glycol) analogue-based biopolymers

Monodisperse microgels of P(MEO2MA-co-OEGMA) have been synthesized by using free radical polymerization. Microgels with a variety of particle radii ranging from 82 to 412 nm have been obtained with different surfactant concentrations. The particle size distribution is extremely narrow and even better than that for PNIPAM microgels. Pure MEO2MA microgels have an LCST of about 22 degrees C. The LCSTs corresponding to the molar ratio of OEGMA to MEO2MA at 10 and 20% are 31 and 37 degrees C, respectively. Microgels in water self-assemble into various phases, including a crystalline phase with iridescent colors, which are the result of Bragg diffraction from differently oriented crystalline planes. Considering that PEG is nontoxic and anti-immunogenic as proven by the FDA, thermoresponsive P(MEO2MA-co-OEGMA) microgels may have many exciting biomedical applications.     

Point by point comparison of two thermosensitive polymers exhibiting a similar LCST: is the age of poly(NIPAM) over?

The present Communication compares the thermosensitivity in dilute aqueous solutions of well-defined copolymers composed of 95% of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and 5% of oligo(ethylene glycol) methacrylate (OEGMA, Mn = 475 g.mol-1) and poly(N-isopropylacrylamide) (PNIPAM) samples having similar degrees of polymerization and chain-ends. The thermoresponsive behavior of P(MEO2MA-co-OEGMA) was found to be overall comparable, and in some cases, superior to PNIPAM. Hence, P(MEO2MA-co-OEGMA) copolymers can be considered as ideal structures, which combine both the properties of poly(ethylene glycol) and PNIPAM in a single macromolecule.     

Synthesis and self-assembly behavior of thermoresponsive poly(oligo(ethylene glycol) methyl ether methacrylate)-POSS with tunable lower critical solution temperature

This article reports on the synthesis of a novel amphiphilic polyhedral oligomeric silsesquioxane (POSS) end-capped poly(2-(2-methoxyethoxy)ethyl methacrylate)-co-oligo(ethylene glycol) methacrylate) (POSS-P(MEO₂MA-co-OEGMA)). These thermoresponsive organic–inorganic hybrid polymers exhibit critical phase transition temperature in water, which can be finely tuned by changing the feed ratio of OEGMA and MEO₂MA. The lower critical solution temperature (LCST) of POSS-P(MEO₂MA-co-OEGMA) increases from 31 to 59 °C with the increasing of OEGMA content. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies show that these polymers can self-assemble into spherical micelles with the thermosensitive block into the corona and the POSS forming the core, and larger aggregates are formed when the temperature values are above their LCSTs. These thermoresponsive polymers POSS-P(MEO₂MA-co-OEGMA) with self-assembly behavior and tunable tempetature-responsive property have the potential applications in material science and biotechnology.     

Tuning the low critical solution temperature of polymer brushes grafted on single‐walled carbon nanotubes and temperature dependent loading and release properties

A nondestructive method was developed for grafting and retrieving polymer brushes from single‐walled carbon nanotubes (SWCNT)s based on mussel‐inspired chemistry. Thermo‐responsive polymer brushes were grafted on SWCNTs by coating the tubes with polydopamine as a reactive underlayer and sequential surface‐initiated atom transfer radical polymerization of oligo(ethylene glycol) methacrylate (OEGMA, M_n = 475) and 2‐(2'‐methoxyethoxy)ethyl methacrylate (MEO2MA). Copolymer brushes were retrieved from the SWCNTs using 1 M NaOH to destroy the crosslinked polydopamine coating, and after that, the pristine properties of the SWCNTs were preserved. The low critical solution temperature (LCST) and molecular weight of the copolymer were measured using a nephelometer and gel permeation chromatograph, respectively. The loading and release behavior of Rhodamine 6G on responsive polymer‐grafted SWCNTs demonstrates that the copolymer brushes confer the SWCNTs an LCST dependence. This method can accurately confirm the molecular weights and polydispersity of stimuli‐responsive polymers grafted on any other nanoparticles and predict their controlled release behavior. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1807–1814     

Synthesis and micellization of thermoresponsive galactose‐based diblock copolymers

Thermoresponsive double hydrophilic diblock copolymers poly(2‐(2′‐methoxyethoxy)ethyl methacrylate‐co‐oligo(ethylene glycol) methacrylate)‐b‐poly(6‐O‐methacryloyl‐D ‐galactopyranose) (P(MEO₂MA‐co‐OEGMA)‐b‐PMAGP) with various compositions and molecular weights were obtained by deprotection of amphiphilic diblock copolymers P(MEO₂MA‐co‐OEGMA)‐b‐poly(6‐O‐methacryloyl‐1,2:3,4‐di‐O‐isopropylidene‐D ‐galactopyranose) (P(MEO₂MA‐co‐OEGMA)‐b‐PMAlpGP), which were prepared via reversible addition‐fragmentation chain transfer (RAFT) polymerization using P(MEO₂MA‐co‐OEGMA) as macro‐RAFT agent. Dynamic light scattering and UV–vis studies showed that the micelles self‐assembled from P(MEO₂MA‐co‐OEGMA)‐b‐PMAlpGP were thermoresponsive. A hydrophobic dye Nile Red could be encapsulated by block copolymers P(MEO₂MA‐co‐OEGMA)‐b‐PMAGP upon micellization and released upon dissociation of the formed micelles under different temperatures. The galactose functional groups in the PMAGP block have specific interaction with HepG2 cells, and P(MEO₂MA‐co‐OEGMA)‐b‐PMAGP has potential applications in hepatoma‐targeting drug delivery and biodetection. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Thermoresponsive poly(N-isopropyl acrylamide)-grafted polycaprolactone films with surface immobilization of collagen

Thermoresponsive poly(N-isopropylacrylamide) (P(NIPAAm))-grafted polycaprolactone (PCL) films with a suitable amount of immobilized cell-adhesive collagen were prepared to improve cell adhesion and proliferation above the lower critical solution temperature (LCST, 32°C) of P(NIPAAm) without destroying cell detachment properties at lower temperatures. Covalently tethered P(NIPAAm) brushes on PCL film surfaces were first prepared via surface-initiated atom transfer radical polymerization (ATRP). The alkyl bromide end groups of the grafted P(NIPAAm) brushes were used in nucleophilic substitution reactions for the direct coupling of collagen to produce the collagen-immobilized thermoresponsive PCL surface. At 37°C, the cell attachments on the collagen-immobilized thermoresponsive PCL surface were enhanced substantially. The attached cells could be recovered simply by lowering culture temperature. The P(NIPAAm)-grafted PCL films with immobilized collagen are potentially useful as adhesion modifiers for advanced cell culture and tissue engineering applications.     

Thermogelation of amphiphilic poly(asparagine) derivatives

Thermoresponsive sol–gel transition polymers based on biodegradable poly(amino acid) were synthesized by the reaction of poly(succinimide) with dodecylamine and amino alcohols. The introduction of the hydrophobic amine into the thermoresponsive poly(amino acid)s induced the sol–gel transition in phosphate buffer saline. The effects of the side chain structure, molecular weight, concentration of the polymer, and the additives (inorganic salts and urea) in the solution on the thermoresponsive behaviors were systematically investigated. A relationship between the lowest critical solution temperature (LCST) in the dilute solution and the viscosity reduction of the concentrated solution upon heating was observed. The present poly(amino acid)s showing a thermoresponsive sol–gel transition in aqueous solutions possess immense potential as an injectable biodegradable hydrogel system for various biomedical applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation and characterization of a thermoresponsive gigaporous medium for high-speed protein chromatography

A high-speed thermoresponsive medium was developed by grafting poly(N-isopropylacrylamide-co-butyl methacrylate) (P(NIPAM-co-BMA)) brushes onto gigaporous polystyrene (PS) microspheres via surface-initiated atom transfer radical polymerization (ATRP) technique, which has strong mechanical strength, good chemical stability and high mass transfer rate for biomacromolecules. The gigaporous structure, surface chemical composition, static protein adsorption, and thermoresponsive chromatographic properties of prepared medium (PS–P(NIPAM-co-BMA)) were characterized in detail. Results showed that the PS microspheres were successfully grafted with P(NIPAM-co-BMA) brushes and that the gigaporous structure was robustly maintained. After grafting, the nonspecific adsorption of proteins on PS microspheres was greatly reduced. A column packed with PS–P(NIPAM-co-BMA) exhibited low backpressure and significant thermo-responsibility. By simply changing the column temperature, it was able to separate three model proteins at the mobile phase velocity up to 2167 cm h⁻¹. In conclusion, the thermoresponsive polymer brushes grafted gigaporous PS microspheres prepared by ATRP are very promising in ‘green’ high-speed preparative protein chromatography.     

Investigation of the swelling behavior of hydrogels derived from high-molecular-weight poly(2-ethyl-2-oxazoline)

Thermoresponsive hydrogels are of great importance as smart materials. They are usually composed of cross-linked polymers with a lower critical solution temperature (LCST). Although much is known about networks of poly(N-isopropylacrylamide), all other polymers are somewhat neglected. In this work, the temperature-dependent swelling behavior of differently cross-linked thermoresponsive poly(2-ethyl-2-oxazoline) (PEtOx) hydrogels were investigated with regard to varying parameters of the network composition. It was found that the degrees of swelling of the hydrogels converge for a certain polymer/solvent system at a distinct temperature independent of its degree of cross-linking. Furthermore, this temperature correlates with the LCST of the respective starting PEtOx. Its net chain molecular weight M_c only affects the maximum degree of swelling and thus, the swelling–deswelling rate of the hydrogel. The fundamental structure/property relations found in this study could be useful to predict the behavior of other thermoresponsive hydrogels.