Tunable Lower Critical Solution Temperature of Poly(butyl acrylate) in Ionic Liquid Blends

We describe the lower critical solution temperature(LCST)-type phase behavior of poly(butyl acrylate)(PBA) dissolved in hydrophobic 1-alkyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl}amide ionic liquids(ILs). The temperature-composition phase diagrams of these PBA/ILs systems are strongly asymmetric with the critical composition shifted to low concentrations of PBA. As the molecular weight increases from 5.0×10~3 to 2.0×10~4, the critical temperature decreases by about 67 °C, and the critical composition shifts to a lower concentration.Furthermore, the LCST of PBA/ILs system increases as increasing the alkyl side chain length in the imidazolium cation. Using IL blends as solvents,the LCST of PBA can be tuned almost linearly over a wide range by varying the mixing ratio of two ionic liquids without modifying the chemical structure of the polymers.     

荧光探针法对N-异丙基丙烯酰胺-丙烯酰胺共聚物水溶液相变的研究

合成了多种不同配比的N 异丙基丙烯酰胺 (NIPAM )与丙烯酰胺 (AM )的共聚物 .用荧光探针法研究了共聚物溶液荧光光谱随温度升高而引起的变化 .研究表明 :共聚物的最低临界溶液温度 (LCST)取决于AM与NIPAM的组成比 .AM的比例越大 .LCST就越高 ,且有较好的正比关系 .通过以共价键连接于共聚物的荧光探针法 (标记法 )和以小分子探针混入共聚物水溶液的方法 (混入法 )测定上述体系LCST的结果比较 ,发现标记探针法具有较高的灵敏度 ,更适宜用来研究共聚物水相体系的相变问题 .     

Water-soluble silicon containing polymer resist

Poly(divinylsiloxyethylene glycol), which consists of alternating oligo(ethylene glycol)s (MW = 300) and divinylsiloxanes were prepared by a polycondensation reaction (M_n = 6500–9300, M_w/M_n = 2.01–2.27). The obtained polymer (PVSE300) showed a lower critical solution temperature (LCST) at 10.5°C, meaning that the polymer was soluble in water below the LCST. The glass transition temperature (T_g) and onset temperature of degradation (T_d) of the PVSE300 were −72.5 and +317.5°C, respectively. The hydrolytic stability of the PVSE300 in aqueous media was also examined and it was found that PVSE300 was fairly stable in cold water. The lithographic characteristics of PVSE300 were examined against UV and electron-beam (EB) exposure and it was found that the PVSE300 film showed a negative character when developed by cold water. The photosensitivity parameter, Dg⁵⁰, which denotes the dose at half remaining film thickness after development, against EB exposure was extremely high (1.0 μC/cm²) when a probe current and an accelerating voltage was 100 pA and 20 kV, respectively. A high durability for O₂ reactive ion etching (O₂ RIE) was also observed. The characteristics of PVSE300 against photoirradiation were also examined. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2827–2833, 1997     

Using 2-isopropyl-2-oxazine to explore the effect of monomer distribution and polymer architecture on the thermoresponsive behavior of copolymers

Poly(cyclic imino ether)s (PCIE) have emerged as a highly promising class of polymer for use in biomedical applications with their value being derived from their excellent biocompatibility, diverse chemistry, and tunable hydrophilicity. Here, we investigate the properties of poly(2-isopropyl-2-oxazine) (PiPrOz), a relatively unexplored PCIE, determining it to have a cloud point temperature (T_cp) below physiological temperature, not to crystallize from bulk or in solution, and to be highly biocompatible. Furthermore, a series of copolymers consisting of iPrOz and 2-methyl-2-oxazine (MeOz) was investigated with regard to the effect of monomer distribution and polymer architecture on thermoresponsive properties. To this end, linear block and statistical co-poly(2-oxazine)s (co-POz), along with three comb-shaped POz with block or statistical POz side chains were prepared. Each of the five polymers showed distinct thermoresponsive behavior, with the linear block co-POz undergoing micelle formation and the other polymers macroscopic phase-separation at different T_cps. The variety observed in response to heating clearly highlights the importance of monomer sequence and polymer architecture when designing thermoresponsive polymers. We anticipate that our findings will prove useful to polymer chemists seeking to prepare novel thermoresponsive biomaterials.     

Temperature-dependent interfacial properties of hydrophobically end-modified poly(2-isopropyl-2-oxazoline)s assemblies at the air/water interface and on solid substrates

We describe herein the properties at the air/water (A/W) interface of hydrophobically end-modified (HM) poly(2-isopropyl-2-oxazoline)s (PiPrOx) bearing an n-octadecyl chain on both termini (telechelic HM-PiPrOx) or on one chain end (semitelechelic HM-PiPrOx) for different subphase temperatures and spreading solvents using the Langmuir film balance technique. The polymer interfacial properties revealed by the π–A isotherms depend markedly on the architecture and molecular weight of the polymer. On cold water subphases (14 °C), diffusion of PiPrOx chains onto water takes place for all polymers in the intermediate compressibility region (5 mN m⁻¹). At higher subphase temperatures (36 and 48 °C), the HM-PiPrOx film exhibited remarkable stability with time. Brewster angle microscopy (BAM) imaging of the A/W interface showed that the polymer assembly was not uniform and that large domains formed, either isolated grains or pearl necklaces, depending on the polymer structure, the concentration of the spreading solution and the subphase temperature. The Langmuir films were transferred onto hydrophilic substrates (silica) by the Langmuir–Blodgett (LB) technique and onto hydrophobic substrates (gold) by Langmuir–Schaefer (LS) film deposition, resulting in the formation of adsorbed particles ranging in size from 200 to 500 nm, depending on the polymer architecture and the substrate temperature. The particles presented “Janus”-like hydrophilic/hydrophobic characteristics.     

Physicochemical characterization of the thermo‐induced self‐assembly of thermo‐responsive PDMAEMA‐b‐PDEGMA copolymers

Diblock copolymers of poly[2‐(dimethylamino)ethyl methacrylate]‐block‐poly[di(ethylene glycol) methyl ether methacrylate], PDMAEMA‐b‐PDEGMA, were synthesized by reversible addition–fragmentation chain transfer polymerization. The block ratio was varied to study the influence on the lower critical solution temperature and the corresponding phase transition in water. Therefore, turbidimetry, differential scanning calorimetry (DSC), dynamic light scattering (DLS), and laser Doppler velocimetry were applied. Additionally, asymmetric flow field‐flow fractionation (AF4) coupled to DLS and multiangle laser light scattering (MALLS) was established as an alternative route to characterize these systems in terms of molar mass of the polymer chain and size of the colloids after the phase transition. It was found that AF4–MALLS allowed accurate determination of molar masses in the studied range. Nevertheless, some limitations were observed, which were critically discussed. The cloud point and phase transition of all materials, as revealed by turbidimetry, could be confirmed by DSC. For block copolymers with block ratios in the range of 50:50, a thermo‐induced self‐assembly into micellar and vesicular structures with hydrodynamic radii (R_h) of around 25 nm was observed upon heating. At higher temperatures, a reordering of the self‐assembled structures could be detected. The thermo‐responsive behavior was further investigated in dependence of pH value and ionic strength. Variation of the pH value mainly influences the solubility of the PDMAEMA segment, where a decrease of the pH value increases the transition temperature. An increase of ionic strength leads to a reduction of the cloud point due to the screening of electrostatic interactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 924–935     

Design and synthesis of fluorescent core–shell nanoparticles with tunable lower critical solution temperature behavior and metal‐enhanced fluorescence

In this article, the preparation of fluorescent nanohybrids with core–shell structure and metal‐enhanced fluorescence (MEF) effect was presented. The fluorescent core–shell nanohybrids were prepared using silver nanoparticles (AgNPs) as cores and fluorophore tethered thermoresponsive copolymers with tunable lower critical solution temperature (LCST) from 15 to 90 °C as shells. These thermoresponsive copolymers were synthesized by the random copolymerization of oligo(ethylene oxide) acrylate and di(ethylene oxide) ethyl ether acrylate using reversible addition–fragmentation chain transfer polymerization and grafted on to AgNPs surface via Ag–S coordination interaction. By thermal manipulation of polymer spacer between AgNPs and fluorophores, the tunable MEF was achieved. It was also revealed that the fluorescent nanohybrids would exhibit maximal MEF when the polymerization degree was tuned to 350. The manipulation of the solution temperatures below and above LCST resulted in switchable MEF behavior. In addition, the phase transition process of the thermoresponsive copolymer was also studied by MEF effect using this fluorescent core–shell nanohybrid design. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 87–95     

Thermoresponsive Random Poly(ether urethanes) with Tailorable LCSTs for Anticancer Drug Delivery

A new class of thermoresponsive random polyurethanes is successfully synthesized and characterized. Poly(ethylene glycol) diol (M_n = 1500 Da) and 2,2‐dimethylolpropionic acid are reacted with isophorone diisocyanate in the presence of methane sulfonic acid catalyst. It is found that these polyurethanes are thermoresponsive in aqueous media and manifest a lower critical solution temperature (LCST) that can be easily tuned from 30 °C to 70 °C by increasing the poly(ethylene glycol) content. Their sharp LCST transitions make these random polyurethanes ideal candidates for stimuli‐responsive drug delivery applications. To that end, the ability of these systems to efficiently sequester doxorubicin (up to 36 wt%) by means of a sonication/dialysis method is successfully demonstrated. Additionally, it is also demonstrated that accelerated doxorubicin release kinetics from the nanoparticles can be attained above the LCST.

     

温度、pH双响应嵌段共聚物的合成与表征及其对蚕丝的改性

以2-溴代异丁酸乙酯为引发剂,Cu Br/PMDETA为催化体系,通过原子转移自由基聚合(ATRP)方法,合成了寡聚乙二醇甲基丙烯酸酯与丙烯酸叔丁酯的嵌段共聚物(PMEO2MA-b-Pt BA);通过水解脱去共聚物中丙烯酸叔丁酯嵌段上的叔丁基,使丙烯酸叔丁酯嵌段转化为丙烯酸嵌段,得到寡聚乙二醇甲基丙烯酸酯与丙烯酸的嵌段共聚物(PMEO2MA-b-PAA).通过溶液透光率和动态光散射(DLS)等方法,表征了合成得到的嵌段共聚物的温敏性能和p H响应性,发现嵌段共聚物在24~30℃,p H=4~8的范围内发生亲水性性质转变.以二环己基碳二亚胺(DCC)为缩合剂,在4-二甲氨基吡啶(DMAP)的催化下使PMEO2MA-b-PAA上的羧基与蚕丝上的氨基发生缩合反应,从而令共聚物接枝到蚕丝上,通过接触角和回潮率的测试发现改性后的蚕丝在28~42℃具温敏性,较共聚物的转变温度有所升高,其转变温度随p H的增大而上升.