Unexpected Cononsolvency Behavior of Poly (N‐isopropylacrylamide)‐Based Microgels

Poly (N‐isopropylacrylamide) (pNIPAm)‐based microgels undergo a transition from fully water swollen (solvated) to deswollen (desolvated) as the temperature of the water they are dissolved in is increased >32 °C. In this submission, we examine how the temperature of this transition, i.e., the volume phase transition temperature (VPTT), depends on the concentration of methanol (MeOH) in water the microgels are dissolved in. To accomplish this, pNIPAm‐based etalons are utilized, and it is shown that the VPTT for the microgels is much less than that previously observed for linear pNIPAm and pNIPAm‐based microgels. Furthermore, and most interestingly, it is determined that the microgels can collapse in solutions containing high MeOH (>∼65% MeOH) concentration. This is in contrast to previous studies, which show that no VPTT is observed for pNIPAm in aqueous solutions containing >∼65% MeOH.

     

Assembly of Preformed Gold Nanoparticles onto Thermoresponsive Poly(N‐isopropylacrylamide)‐Based Microgels on the Basis of Au‐thiol Chemistry

The assembly of preformed gold nanoparticles (AuNPs ) onto the thermoresponsive poly(N ‐isopropylacrylamide) (PNIPAM )‐based microgels was achieved on the basis of the driving force of Au‐thiol chemistry. The loading amount of AuNPs can be controlled by varying the ratio of AuNPs relative to PNIPAM ‐based microgels. The as‐prepared PNIPAM /Au hybrid microgels showed well‐defined reversible swelling/deswelling transition in response to temperature, which can be employed to tune the plasmonic property of hybrid microgels. As the temperature was increased, the position of localized surface plasmon resonance (LSPR ) band red‐shifted to some extent mainly due to the increase in the local refractive index around AuNPs .     

Temperature‐Modulated Water Filtration Using Microgel‐Functionalized Hollow‐Fiber Membranes

In the present work, we investigate the potential of aqueous polymer microgels in membrane technology, especially for filtration applications. The poly(N‐vinylcaprolactam)‐based microgels exhibit thermoresponsive behavior and were employed to coat hollow‐fiber membranes used for micro‐ and ultrafiltration. We discuss the preparation of microgel‐modified membranes (by “inside‐out” as well as “outside‐in” filtration in dead‐end mode). The clean‐water permeability and stability of these membranes was studied not only as a function of time, but also of temperature. The microgel‐modified membranes exhibit a reversible thermoresponsive behavior whereby both the resistance and the retention increased with decreasing temperature.     

Thermoresponsive Poly(2‐oxazine)s

The monomers 2‐methyl‐2‐oxazine (MeOZI), 2‐ethyl‐2‐oxazine (EtOZI), and 2‐n‐propyl‐2‐oxazine (nPropOZI) were synthesized and polymerized via the living cationic ring‐opening polymerization (CROP) under microwave‐assisted conditions. pEtOZI and pnPropOZI were found to be thermoresponsive, exhibiting LCST behavior in water and their cloud point temperatures (T_CP) are lower than for poly(2‐oxazoline)s with similar side chains. However, comparison of poly(2‐oxazine) and poly(2‐oxazoline)s isomers reveals that poly(2‐oxazine)s are more water soluble, indicating that the side chain has a stronger impact on polymer solubility than the main chain. In conclusion, variations of both the side chains and the main chains of the poly(cyclic imino ether)s resulted in a series of distinct homopolymers with tunable T_CP.     

Thermoresponsive hydrophobic copolymer grafted on agar microspheres for all‐aqueous bioseparations

Agar microspheres were prepared by water–oil emulsification and cross‐linked under alkaline condition. The thermoresponsive hydrophobic copolymer, poly(N‐isopropylacrylamide‐co‐lauryl methacrylate‐co‐acrylamide), was grafted on the agar microspheres via atom transfer radical polymerization. The agar microspheres grafted with copolymers were characterized by light microphotography, elemental analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and X‐ray photoelectron spectroscopy. The chain lengths and hydrophobic monomer ratio of the grafting linear polymer had significant effects on the hydrophobicity and adsorption capacity of agar microspheres at different temperatures. The thermoresponsive microspheres were used for separation of proteins and showed binding and release behavior by change of temperatures without change in mobile phase composition. Thus, we suggest thermoresponsive agar microspheres as an alternative separation media for all‐aqueous bioseparations.     

Low‐Temperature Synthesis of Thermoresponsive Diblock Copolymer Nano‐Objects via Aqueous Photoinitiated Polymerization‐Induced Self‐Assembly (Photo‐PISA) using Thermoresponsive Macro‐RAFT Agents

Photoinitiated reversible addition‐fragmentation chain transfer (RAFT) dispersion polymerization of 2‐hydroxypropyl methacrylate is conducted in water at low temperature using thermoresponsive copolymers of 2‐(2‐methoxyethoxy) ethyl methacrylate and oligo(ethylene glycol) methacrylate (M_n = 475 g mol⁻¹) as the macro‐RAFT agent. Kinetic studies confirm that quantitative monomer conversion is achieved within 15 min of visible‐light irradiation (405 nm, 0.5 mW cm⁻²), and good control is maintained during the polymerization. The polymerization can be temporally controlled by a simple “ON/OFF” switch of the light source. Finally, thermoresponsive diblock copolymer nano‐objects with a diverse set of complex morphologies (spheres, worms, and vesicles) are prepared using this particular formulation.

     

Thermoresponsive drug controlled release from chitosan‐based hydrogel embedded with poly(N‐isopropylacrylamide) nanogels

A facile synthetic strategy was developed for the preparation of thermoresponsive nanocomposite hydrogels comprising crosslinked chitosan (CS) networks and poly(N‐isopropylacrylamide) [p(NIPAAm)] nanogels. First, thermoresponsive p(NIPAAm) nanogels were synthesized via emulsion polymerization. The p(NIPAAm) nanogels were introduced into methacrylamide CS (MC) solution and the free‐radical initiated crosslinking reaction of MC produced nanogel‐embedded hydrogels. The last step involves the loading of the antibacterial model drug levofloxacin (LFX) into the prepared nanocomposite hydrogels by allowing the preformed hydrogels to swell to equilibrium in the drug's aqueous solution. The integration of p(NIPAAm) nanogel into CS networks facilitates thermoresponsive release of LFX with an enhancement of the drug‐loading capacity within the hydrogel. Notably, thermoresponsive drug‐release was achieved without unwarranted modification of the hydrogel's dimension and shape, although an increase in temperature caused the collapse of the p(NIPAAm) nanogels. The thermoresponsive property of the investigated nanocomposite hydrogel is beneficial and may offer broad opportunities for drug temperature‐triggered release for clinical applications. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1907–1914     

Thermoresponsive diblock copolymer micellar macro‐RAFT agent‐mediated dispersion RAFT polymerization and synthesis of temperature‐sensitive ABC triblock copolymer nanoparticles

The micellar macro‐RAFT agent‐mediated dispersion polymerization of styrene in the methanol/water mixture is performed and synthesis of temperature‐sensitive ABC triblock copolymer nanoparticles is investigated. The thermoresponsive diblock copolymer of poly(N,N‐dimethylacrylamide)‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] trithiocarbonate forms micelles in the polymerization solvent at the polymerization temperature and, therefore, the dispersion RAFT polymerization undergoes as similarly as seeded dispersion polymerization with accelerated polymerization rate. With the progress of the RAFT polymerization, the molecular weight of the synthesized triblock copolymer of poly(N,N‐dimethylacrylamide)‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine]‐b‐polystyrene linearly increases with the monomer conversion, and the PDI values of the triblock copolymers are below 1.2. The dispersion RAFT polymerization affords the in situ synthesis of the triblock copolymer nanoparticles, and the mean diameter of the triblock copolymer nanoparticles increases with the polymerization degree of the polystyrene block. The triblock copolymer nanoparticles contain a central thermoresponsive poly [N‐(4‐vinylbenzyl)‐N,N‐diethylamine] block, and the soluble‐to‐insoluble ‐‐transition temperature is dependent on the methanol content in the methanol/water mixture. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2155–2165     

Argon‐Plasma‐Induced Ultrathin Thermal Grafting of Thermoresponsive pNIPAm Coating for Contractile Patterned Human SMC Sheet Engineering

A new method for ultrathin grafting of pNIPAm on PDMS surfaces is introduced that employs plasma activation of the surface followed by thermal polymerization. This method is optimized for human primary SMC attachment and subsequent intact cell sheet detachment by lowering the temperature. The contractile gene expression of the cells showed that the contractile phenotype of the SMCs which is induced by aligning the cells through micropatterning is more preserved after thermoresponsive cell sheet detachment in contrast with enzymatic detachment. Given its simplicity and low cost, this thermoresponsive grafting method can be utilized for engineering patterned cell sheets for future bottom‐up tissue engineering techniques.

     

Linear and comb‐like acrylonitrile/N‐isopropylacrylamide copolymers synthesized by the combination of RAFT polymerization and ATRP

We describe the synthesis of three novel thermoresponsive copolymers of acrylonitrile (AN) with N‐isopropylacrylamide (NIPAM) by a combination of reversible addition‐fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP). Linear copolymer polyacrylonitrile (PAN)‐b‐PNIPAM was directly prepared by RAFT polymerization. Comb‐like copolymers were synthesized by ATRP using brominated AN/2‐hydroxyethyl methacrylate copolymers as macroinitiators, which were prepared by RAFT polymerization. FT‐IR, NMR, and GPC were employed to characterize the synthesized copolymers. Results indicate that the polymerization processes can be well controlled and the resultant copolymers have well‐defined structures as well as narrow polydispersity. Then dense films were fabricated from these thermoresponsive copolymers and the surface wettability was evaluated by water contact angle measurements at different temperatures. It is found that the surface wettability is temperature‐dependant and both the transition temperature and decrement of water contact angle are affected by the copolymer shapes as well as the length of PNIPAM blocks. Considering the excellent fiber‐ and membrane‐forming properties of PAN‐based copolymers, the obtained thermoresponsive copolymers are latent materials for functional fibers and membranes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 92–102, 2009     

Thermosensitive and control release behavior of poly (N‐isopropylacrylamide‐co‐acrylic acid) latex particles

In this work, poly(N‐isopropylacrylamide‐co‐acrylic acid) (poly(NIPAAm‐AA)) copolymer latex particles (microgels) were synthesized by the method of soapless emulsion polymerization. Poly(NIPAAm‐AA) copolymer microgels have the property of being thermosensitive. The concentration of acrylic acid (AA) and crosslinking agent N,N′‐methylenebisacrylamide were important factors to influence the lower critical solution temperature (LCST) of poly(NIPAAm‐AA) microgels. The effects of AA and crosslinking agent on the swelling behavior of poly(NIPAAm‐AA) microgels were also studied. The poly(NIPAAm‐AA) copolymer microgels were then used as a thermosensitive drug carrier to load caffeine. The effects of concentration of AA and crosslinking agent on the control release of caffeine were investigated. How the AA content and crosslinking agent influenced the morphology and LCST of the microgels was discussed in detail. The relationship of morphology, swelling, and control release behavior of these thermosensitive microgels was established. A new scheme was proposed to interpret the control release of the microgels with different morphological structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5734–5741, 2008     

AuNPs/PNIPAM复合颗粒的制备及其温敏性质

将金纳米颗粒(AuNPs)组装到聚N-异丙基丙烯酰胺(PNIPAM)水凝胶微球表面制备出AuNPs/PNIPAM复合颗粒. 将PNIPAM 凝胶的温敏特性与AuNPs的光学性质结合, 通过改变温度调节AuNPs的局部表面等离子共振(LSPR)吸收峰位置. 研究结果表明, 温度升高使AuNPs的LSPR吸收峰发生红移, 并且这种效应是可逆的. 同时发现, AuNPs的光学性质还可以作为表征PNIPAM水凝胶微球温敏行为的一种手段. 利用透射电镜、紫外-可见光谱仪及动态光散射仪对AuNPs/PNIPAM复合颗粒的形貌、光学性质、粒径变化等进行了分析.     

Thermoresponsive hydrogel of poly(glycidyl methacrylate‐co‐N‐isopropylacrylamide) as a nanoreactor of gold nanoparticles

The synthesis of a thermoresponsive hydrogel of poly(glycidyl methacrylate‐co‐N‐isopropylacrylamide) (PGMA‐co‐PNIPAM) and its application as a nanoreactor of gold nanoparticles are studied. The thermoresponsive copolymer of PGMA‐co‐PNIPAM is first synthesized by the copolymerization of glycidyl methacrylate and N‐isopropylacrylamide using 2,2′‐azobis(isobutyronitrile) as an initiator in tetrahydrofuran at 70 °C and then crosslinked with diethylenetriamine to form a thermoresponsive hydrogel. The lower critical solution temperature (LCST) of the thermoresponsive hydrogel is about 50 °C. The hydrogel exists as 280‐nm spheres below the LCST. The diameter of the spherical hydrogel gradually decreases to a minimum constant of 113 nm when the temperature increases to 75 °C. The hydrogel can act as a nanoreactor of gold nanoparticles because of the coordination of nitrogen atoms of the crosslinker with gold ions, on which a hydrogel/gold nanocomposite is synthesized. The LCST of the resultant hydrogel/gold nanocomposite is similar to that of the hydrogel. The size of the resultant gold nanoparticles is about 15 nm. The hydrogel/gold nanocomposite can act as a smart and recyclable catalyst. At a temperature below the LCST, the thermoresponsive nanocomposite is a homogeneous and efficient catalyst, whereas at a temperature above the LCST, it becomes a heterogeneous one, and its catalytic activity greatly decreases. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2812–2819, 2007     

Thermoresponsive Organic–Inorganic Hybrid Large‐Compound Vesicles

Herein, gelated thermoresponsive large‐compound vesicles (LCVs) are reported for the first time. The LCVs are prepared by self‐assembly of poly(ethylene oxide)‐block‐poly[N‐isopropylacrylamide‐random‐3‐(trimethoxysilyl)propyl methacrylate] [PEO‐b‐P(NIPAM‐r‐TMPM)] in DMF‐water mixture. Then, sol‐gel reaction of the reactive PTMPM block is performed to stabilize the LCVs. LCVs with higher cross‐linking density keep almost the same size under different temperatures while LCVs with lower cross‐linking density display obviously thermoresponsive size transition between 22 and 36 °C. The gelated LCVs exhibit enhanced permeability with temperature elevation and their permeabilities at different temperatures all elevate with increasing the cross‐linking density.

     

One‐Pot Synthesis of Microcapsules with Nanoscale Inclusions

Temperature responsive poly(N‐isopropylmethacrylamide) (pNIPMAm) microgel capsules around 1 µm containing multiple poly(N‐isopropylacrylamide) (pNIPAm) nanoinclusions were prepared. This structure was achieved through the addition of a cross‐linked pNIPMAm shell to stable, monodispersed aggregates of pNIPAm chains. This one‐pot synthetic approach resulted in core/shell microgels at high temperature wherein only the shell (pNIPMAm) component contained stable, covalent cross‐links between chains. Thus, upon decreasing the temperature following synthesis, the majority of the encapsulated pNIPAm chains escaped from the shell, resulting in nearly hollow microcapsules. Remnant pNIPAm segments in the microcapsule then form nanoparticulate inclusions upon raising the temperature.

     

Application of photopolymer to core‐hair type microgels with various hair length

The new microgels, called “core‐hair” type microgels, were synthesized. They have a hair moiety consisting of the oxyhexano‐1,7‐diyl (? O? (CH₂)₅? C(O)? ) group as a spacer and the acryloyl group for polymerization. The hair length depends on the number of spacer units, and affects the viscosity and the thixotropy index of the microgel. These core‐hair microgels show the pseudo‐plastic flow of a non‐Newtonian fluid with moderate to high dispersibility in water or alcoholic solvents. Due ­to their viscosities and dispersibilities, these core‐hair microgels are useful for photopolymer, e.g. for screen printing. Therefore, these microgels were actually applied to screen printing and confirmed pattern forming on a screen printing plate through water development. We now discuss the relation between the viscosity, the dispersibility, the photosensitivity, and the rate of photopolymerization to the hair length of the microgel. Copyright © 2001 John Wiley & Sons, Ltd.     

N‐vinylcaprolactam‐based microgels: Synthesis and characterization

Poly(N‐vinylcaprolactam) (PVCL) is well known for its thermoresponsive behavior in aqueous solutions. PVCL combines useful and important properties; it is biocompatible polymer with the phase transition in the region of physiological temperature (32–38 °C). This combination of properties allows consideration of PVCL as a material for design biomedical devices and use in drug delivery systems. In this work, PVCL based temperature‐sensitive crosslinked particles (microgels) were synthesized in a batch reactor to analyze the effect of the crosslinker, initiator, surfactant, temperature, and VCL concentration on polymerization process and final microgels characteristics. The mean particle diameters at different temperatures and the volume phase‐transition temperature of the final product were analyzed. To obtain information about the inner structure of microgel particles, semicontinuous polymerizations were carried out and the evolution of the hydrodynamic average particle diameters at different temperatures of the microgel synthesized was investigated. In the case of microgel particles obtained in a batch reactor the size and the swelling‐de‐swelling behavior as a function of the temperature of the medium can be tuned by modulating the reaction variables. When the microgel particles were synthesized in a semibatch reactor different swelling‐de‐swelling behaviors were observed depending on particles inner structure. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2510–2524, 2008     

Thermoresponsive conductivity of poly(N‐isopropylacrylamide)/potassium chloride gel electrolytes

A series of thermoresponsive polymer gel electrolytes (PGEs) based on poly(N‐isopropylacrylamide) in aqueous potassium chloride was synthesized by radiation‐induced polymerization and gelation using γ rays from a ⁶⁰Co source. The electric conductivity and swelling properties of the PGE were determined as a function of temperature. It was found that the electric conductivity of the PGE depended strongly on the swelling ratio; most notably, it changed drastically near the volume phase‐transition temperature of the PGE. The temperature/conductivity profile of the PGE exhibits a maximum peak at a certain temperature that is defined as the maximum conductivity temperature (T_max). The T_max of all of the PGEs prepared by low‐dose irradiation agreed with the temperature, near the end of the volume phase transition, where the PGE was completely shrunken. Consequently, the conductivity of gels should provide a good method with which the totally shrunken temperature of the thermoresponsive gels can be monitored with good temperature precision. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 134–141, 2002     

Dual Temperature and Thiol‐Responsive POEOMA‐Multisegmented Polydisulfides: Synthesis and Thermoresponsive Properties

New thermoresponsive polydisulfides of POEOMA multiblocks linked with disulfide bonds having redox‐responsive properties are reported. These POEOMA‐multisegmented polydisulfides were synthesized by a new method employing a combined RAFT/aminolysis and reversible thiol‐disulfide redox reaction that centers on the synthesis of new disulfide‐labeled difunctional RAFT agent. RAFT polymerization proceeded in living fashion, yielding well‐defined POEOMA copolymers with middle disulfides and terminal RAFT species. They were then used as precursors for thiol‐disulfide polyexchange induced by aminolysis and reductive reaction followed by oxidation: these polydisulfides with different molecular weights and end groups ex hibited tunable thermoresponsive properties and thiol‐responsive degradation.     

Resolving Optical and Catalytic Activities in Thermoresponsive Nanoparticles by Permanent Ligation with Temperature‐Sensitive Polymers

Thermoresponsive nanoparticles (NPs) represent an important hybrid material comprising functional NPs with temperature‐sensitive polymer ligands. Strikingly, significant discrepancies in optical and catalytic properties of thermoresponsive noble‐metal NPs have been reported, and have yet to be unraveled. Reported herein is the crafting of Au NPs, intimately and permanently ligated by thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM), in situ using a starlike block copolymer nanoreactor as model system to resolve the paradox noted above. As temperature rises, plasmonic absorption of PNIPAM‐capped Au NPs red‐shifts with increased intensity in the absence of free linear PNIPAM, whereas a greater red‐shift with decreased intensity occurs in the presence of deliberately introduced linear PNIPAM. Remarkably, the absence or addition of free linear PNIPAM also accounts for non‐monotonic or switchable on/off catalytic performance, respectively, of PNIPAM‐capped Au NPs.