Radical Polymerization Of N-isopropylacrylamide Research Articles

Combining photocontrolled-cationic and anionic-group-transfer polymerizations using a universal mediator: enabling access to two- and three-mechanism block copolymers.

An ongoing challenge in polymer chemistry is accessing diverse block copolymers from multiple polymerization mechanisms and monomer classes. One strategy to accomplish this goal without intermediate compatibilization steps is the use of universal mediators. Thiocarbonyl thio (TCT) functional groups are well-known mediators to combine radical with either cationic or anionic polymerization, but a sequential cationic-anionic universal mediator system has never been reported. Herein, we report a TCT universal mediator that can sequentially perform photocontrolled cationic polymerization and thioacyl anionic group transfer polymerization to access poly(ethyl vinyl ether)-block-poly(thiirane) polymers for the first time. Thermal analyses of these block copolymers provide evidence of microphase separation. The success of this system, along with the established compatibility of radical polymerization, enabled us to further chain extend the cationic-anionic diblock using radical polymerization of N-isopropylacrylamide. The resulting terpolymer represents the first example of a triblock made from three different monomer classes incorporated via three different mechanisms without any end-group modification steps. The development of this simple, sequential synthesis using a universal mediator approach opens up new possibilities by providing facile access to diverse block copolymers of vinyl ethers, thiiranes, and acrylamides.

Synthesis and characterization of functional thermoresponsive photoactive copolymers and study of their thermal and photoluminescence properties

ABSTRACT Poly(N-isopropyl acrylamide-co-disperse yellow 7 methacrylate) (PNIPAM) copolymers were synthesized by radical polymerization of N-isopropyl acrylamide with disperse yellow 7 methacrylate using 2,2/-Azo-bis-isobutyronitrile (AIBN) as an initiator. N-isopropyl acrylamide is a thermoresponsive monomer, and disperse yellow 7 methacrylate is a photoactive monomer. The synthesized photoactive and thermoresponsive copolymers were characterized by FTIR, NMR, and UV-Vis spectrophotometer with a temperature variation. A proton NMR signal at 8.16 ppm is observed for aromatic protons surrounded by an azo (-N=N-) group. The peak that appeared at 4.0 ppm is due to the CH-CONH group. The amide group proton of CONH appeared at 8.16 ppm. The molecular weights of homopolymers (like PNIPAM and PDY7MA) and their copolymers (PNIPDY) were observed to be 104 and 103 Da, respectively. The optical band gaps for synthesized copolymers, PNIPDY-1B, PNIPDY-2B, and PNIPDY-3B, are 2.98 eV, 2.95 eV, and 2.91 eV, respectively. The multiple emission spectra were observed at 407 nm, 428 nm, and 460 nm for the excitation energy of 365 nm due to the n-π* and π-π* transitions of the azobenzene chromophore. Thermal properties were also studied using TGA analysis. Stimuli-responsive polymers are widely used in optoelectronics and photonics, such as optical switching, optical information storage devices, liquid crystal display technology, and diffractive optical elements.

Thermoresponsive and antibacterial two-dimensional polyglycerol-interlocked-polynipam for targeted drug delivery.

Two-dimensional polymeric networks are a new class of polymers with interesting physicochemical and biological properties. They promise a wide range of future biomedical applications including pathogen interactions, drug delivery, bioimaging, photothermal, and photodynamic therapy, owing to their unique features, such as high surface area and multivalent interactions at nano-biointerfaces. In this work, a thermosensitive two-dimensional polymeric network consisting poly(N-isopropylacrylamide) (pNIPAM) chains that are mechanically interlocked by a polyglycerol platform was synthesized and used for bacteria incapacitation. Two-dimensional hyperbranched polyglycerol (2D-hPG) was synthesized by a graphene-assisted strategy and used for encapsulation of azobisisobutyronitrile (AIBN). Radical polymerization of N-isopropylacrylamide by encapsulated AIBN resulted in thermoresponsive platforms with ~ 500 nm lateral size and 20–50 nm thickness. Due to its porous structure, 2D-PNPG was able to efficiently load antibiotics, such as tetracycline (TC) and amoxicillin (AMX). The rate of release of antibiotics from 2D-PNPG and the antibacterial activity of the system correlated with the variation of temperature as a result of the thermosensitivity of 2D-PNPG. This study shows that two-dimensional polymers are efficient platforms for future biomedical applications including drug delivery and bacteria incapacitation.Graphical abstract Thermoresponsive two-dimensional nanomaterials with the ability of loading therapeutic agents and antibacterial activity are synthesized and characterized.

Smart Hydrogels: Preparation, Characterization, and Determination of Transition Points of Crosslinked N-Isopropyl Acrylamide/Acrylamide/Carboxylic Acids Polymers.

Smart hydrogels (SH) were prepared by thermal free radical polymerization of N-isopropyl acrylamide (NIPAAm), acrylamide (AAm) with acrylic acid (A) or maleic acid (M), and N,N′-methylene bisacrylamide. Spectroscopic and thermal characterizations of SHs were performed using FTIR, TGA, and DSC. To determine the effects of SHs on swelling characteristics, swelling studies were performed in different solvents, solutions, temperatures, pHs, and ionic strengths. In addition, cycle equilibrium swelling studies were carried out at different temperatures and pHs. The temperature and pH transition points of SHs are calculated using a sigmoidal equation. The pH transition points were calculated as 5.2 and 4.2 for SH-M and SH-A, respectively. The NIPAAm/AAm hydrogel exhibits a critical solution temperature (LCST) of 28.35 °C, while the SH-A and SH-M hydrogels exhibit the LCST of 34.215 °C and 28.798 °C, respectively, and the LCST of SH-A is close to the body. temperature. Commercial (CHSA) and blood human serum albumin (BHSA) were used to find the adsorption properties of biopolymers on SHs. SH-M was the most efficient SH, adsorbing 49% of CHSA while absorbing 16% of BHSA. In conclusion, the sigmoidal equation or Gaussian approach can be a useful tool for chemists, chemical engineers, polymer and plastics scientists to find the transition points of smart hydrogels.

Novel Thermosensitive Polymer-Modified Liposomes as Nano-Carrier of Hydrophobic Antitumor Drugs

Thermo-sensitive polymer-modified liposomes are able to achieve site-specific delivery of drugs. In this work, thermo-sensitive polymers were synthesized by atomic transfer radical polymerization of N-isopropyl acrylamide (NIPAAm) and N,N-dimethyl acrylamide (DMAAm) using bromoisobutyryl distearoyl phosphoethanolamine (DSPE-Br) as initiator. The resulting PNIPAAm-DSPE and P(NIPAAm-DMAAm)-DSPE polymers were characterized using proton nuclear magnetic resonance, Fourier transform infrared, and ultraviolet–visible spectroscopy. PNIPAAm-DSPE and P(NIPAAm-DMAAm)-DSPE exhibit a lower critical solution temperature of 34.0 and 46.9°C in water, and 29.8 and 38.8°C in phosphate buffered saline, respectively. Paclitaxel-loaded thermo-sensitive liposomes were prepared using film hydration method, followed by post-insertion of P(NIPAAm-DMAAm)-DSPE into the liposome bilayer. Drug release of traditional and thermosensitive liposomes was comparatively studied at 37 and 40°C. The total release and release rate of thermosensitive liposomes at 40°C were much higher than those at 37°C. And drug release is higher for thermosensitive liposomes than for traditional liposomes because insertion of thermo-sensitive polymer chains affects the system's stability. MTT assay showed that thermo-sensitive liposomes present no cytotoxicity to L929 cells at the tested concentrations, and paclitaxel-loaded liposomes have significant cytotoxicity against A549 cancer cells. Therefore, it is concluded that P(NIPAAm-DMAAm)-DSPE modified thermo-sensitive liposomes could be promising as nano-carrier of antitumor drugs.

On the relationship between the fullerene reactivity and degree of substitution

The kinetics of radical polymerization of N-isopropylacrylamide (NIPA, initiator of AIBN) in the presence of some C60 derivatives was studied. It was established experimentally and by quantum chemical calculations that the ability of fullerene to add radicals decreased sharply after the destruction of six double bonds in the C60 molecule due to the addition of six free radicals or other particles. The calculations show that the energy of bond formation between the seventh initiator radical and C60 is by 20 times lower than that in the case of previous six radicals, and the further addition of radicals is impossible. It was experimentally found that the maximally possible number of added initiator radicals can be much higher. Moreover, during radical polymerization of NIPA a polymer layer grows around the C60 molecules with maximally possible number of already added initiator radicals. The layer consists of polymer NIPA chains chemically bound with C60. A possible mechanism explaining this fact is discussed.

Formation of star-like water-soluble polymeric structures in the process of radical polymerization of N-isopropylacrylamide in the presence of C60

The formation of star-like N-isopropylacrylamide (NIPA) polymeric structures in the presence of C60 occurs in two steps. In the polymerization induction period, water-insoluble cores of future star-like polymers (SP) are formed. The cores are composed of one or more C60 molecules linked by a C—C bond, five or six initiator radicals, and several short NIPA polymeric chains. The formation of SP begins after the induction period and continues until the end of polymerization through gradual growth of the polymeric layer at the cores. The solubility of SP in water is determined by a certain initial concentration of NIPA. It is suggested that the mechanism of these processes is determined by a dependence of C60 reactivity on the degree of its “substitution”.

Preparation and characterization of the pH and thermosensitive magnetic molecular imprinted nanoparticle polymer for the cancer drug delivery

A novel pH and thermosensitive magnetic nanoparticle polymer composite [poly(NIPAAM@Fe3O4 MNPs/TMSPMC/DOX)] was synthesized by radical polymerization of N-isopropylacrylamide (NIPAAM) and the methacrylate functionalized Fe3O4 nanoparticles/DOX complex using AIBN and EGDMA, and used as a drug carrier for the DOX drug delivery. Formation of poly(NIPAAM@Fe3O4 MNPs/TMSPMC/DOX) was confirmed by FTIR, XRD, UV–Vis, VSM, TGA–DTA and SEM. The results showed the high DOX loading controls release. Moreover, it showed the lower critical solution temperature of 40°C which can be beneficial in cancer drug delivery, since the temperature of cancer cells is higher than normal ones, and DOX can be released selectively in cancer cells.

Design, preparation and characterization of ulvan based thermosensitive hydrogels

The present study is focused on the exploitation and conversion of sulphated polysaccharides obtained from waste algal biomass into high value added material for biomedical applications. ulvan, a sulphated polysaccharide extracted from green seaweeds belonging to Ulva sp. was selected as a suitable material due to its chemical versatility and widely ascertained bioactivity. To date the present work represents the first successful attempt of preparation of ulvan-based hydrogels displaying thermogelling behaviour. ulvan was provided with thermogelling properties by grafting poly(N-isopropylacrylamide) chains onto its backbone as thermosensitive component. To this aim ulvan was properly modified with acryloyl groups to act as macroinitiator in the radical polymerization of N-isopropylacrylamide, induced by UV irradiation through a “grafting from” method. The thermogelling properties of the copolymer were investigated by thermal and rheological analyses. Sol–gel transition of the copolymer was found to occur at 30–31°C thus indicating the feasibility of ulvan for being used as in-situ hydrogel forming systems for biomedical applications.

Seeded precipitation polymerization for the synthesis of gold-hydrogel core-shell particles: the role of surface functionalization and seed concentration

Polymer encapsulation is an important pathway to stabilize inorganic nanoparticles, allow their phase transfer to different media, and access inter-particle distance control in particle assembly. In the past, hydrogels were shown to be a versatile encapsulation material offering rather thick polymeric shells through free radical precipitation polymerization. In this work, we systematically investigate the influence of nanoparticle surface functionalization and concentration on the formation of core-shell microgels. Spherical gold nanoparticles are used as seeds in the radical polymerization of N-isopropylacrylamide and N,N′-methylenebisacrylamide. We find that the encapsulation occurs via precipitation of oligomers/polymers onto the seed particle surface, independent of the presence of polymerizable groups. Furthermore, we identify the seed concentration regime where almost exclusively core-shell particles are formed. In this concentration range, the hydrogel thickness is precisely controllable by the amount of seeds. Monitoring the polymerizations in situ by dynamic light scattering and absorbance spectroscopy provides first insights into the encapsulation mechanism and its time dependence.

Synthesis of water-soluble starlike poly(N-isopropylacrylamides) with fullerene C60 as a multifunctional core

New water-soluble starlike polymers with a fullerene core are synthesized via the radical polymerization of N-isopropylacrylamide in the presence of fullerene C60. The starlike structures of the polymers are studied by the methods of gel-permeation chromatography and scanning-electron microscopy.

Preparation and chiral recognition of thermosensitive poly(N-isopropylacrylamide) microgels containing modified L-phenylalanine groups

Thermosensitive poly[N-isopropylacrylamide(NIPAM)-co-N-acryloyl-L-phenylalanine ethyl ester (NALPE)] microgels were prepared by the free radical polymerization of NIPAM and chiral monomer, NALPE. Such microgels exhibited spherical shape and favorable monodispersity. Increasing the content of NALPE units would enhance the average diameter, but decrease the thermosensitivity and volume-phase transition temperatures of the microgels. Compared with PNIPAM microgels, the microgels containing NALPE units performed chiral recognozable capacities for D-phenylalanine and D-tartaric acid, and the enantioselectivity and adsorption capacity of the microgels improved with increasing the temperature and/or the content of NALPE units.

말단 아민기를 갖는 폴리(N-이소프로필아크릴아미드) 및 알긴산 나트륨-g-폴리(N-이소프로필아크릴아미드)의 합성과 열응답 특성

열응답성 고분자인 폴리(N-이소프로필아크릴아미드) (PNIPAAm) 말단에 아민기를 갖는 PNIPAAm-<TEX>$NH_2$</TEX> 및 이들 알긴산 나트륨에 그래프팅시킨 공중합체를 합성하고 이들의 여러 가지 특성들을 분석하였다. PNIPAAm-<TEX>$NH_2$</TEX>를 합성하기 위하여 N-이소프로필아크릴아미드를 라디칼 중합할 때 2-aminoethanethiol hydrochloride (AESH)를 연쇄이동제로 사용하였다. AESH 농도를 높이면 PNIPAAm-NH2의 분자량이 작아지며 PNIPAAm-<TEX>$NH_2$</TEX> 수용액의 하한임계용액온도(LCST)가 낮아졌다. N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide 및 N-hydroxysuccinimide를 사용하여 PNIPAAm-<TEX>$NH_2$</TEX>를 graft-onto 방법으로 알긴산 나트륨에 그래프팅시킨 alginate-g-PNIPAAm 공중합체 역시 온도에 따라 팽윤-수축 거동을 하였으며, PNIPAAm-<TEX>$NH_2$</TEX>보다 약간 높은 온도에서 LCST를 나타내었고, 그래프트된 PNIPAAm의 양이 많아질수록 팽윤비가 커졌다. Amino group-terminated poly(N-isopropylacrylamide) (PNIPAAm-<TEX>$NH_2$</TEX>) was synthesized via a radical polymerization of N-isopropylacrylamide (NIPAAm) using 2-aminoethanethiol hydrochloride (AESH) as a chain transfer agent. The molecular weight of the PNIPAAm-<TEX>$NH_2$</TEX> was controlled by changing the concentration of AESH. The LCST of the aqueous solution of PNIPAAm-<TEX>$NH_2$</TEX> increased slightly with increasing the AESH concentration. Alginate-g-PNIPAAm copolymer was synthesized by grafting PNIPAAm-<TEX>$NH_2$</TEX> onto sodium alginate using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide and N-hydroxysuccinimide. The formation of the grafted copolymers was confirmed by FTIR spectroscopy, solubility in water, and SEM-EDS. Alginate-g-PNIPAAm also exhibited swelling-deswelling behavior. However, it showed a LCST at a slightly increased temperature compared to PNIPAAm. The swelling ratio of the alginate-g-PNIPAAm hydrogel increased with the increase of the grafted PNIPAAm content.

Terminally Functionalized Thermoresponsive Polymer Brushes for Simultaneously Promoting Cell Adhesion and Cell Sheet Harvest

For preparing cell sheets effectively for cell sheet-based regenerative medicine, cell-adhesion strength to thermoresponsive cell culture surfaces need to be controlled precisely. To design new thermoresponsive surfaces via a terminal modification method, thermoresponsive polymer brush surfaces were fabricated through the surface-initiated reversible addition-fragmentation chain transfer (RAFT) radical polymerization of N-isopropylacrylamide (IPAAm) on glass substrates. The RAFT-mediated grafting method gave dithiobenzoate (DTB) groups to grafted PIPAAm termini, which can be converted to various functional groups. In this study, the terminal carboxylation of PIPAAm chains provided high cell adhesive property to thermoresponsive surfaces. Although cell adhesion is generally promoted by a decrease in the grafted PIPAAm amount, the decrease also decelerated thermally-induced cell detachment, whereas the influence of terminal modification was negligible on the cell detachment. Consequently, the terminally modified PIPAAm brush surfaces allowed smooth muscle cells (SMCs) to simultaneously adhere strongly and detach themselves rapidly. In this study, SMCs were unable to reach a confluent monolayer on as-prepared PIPAAm brush surfaces (grafted amount: 0.41 μg/cm(2)) without terminal carboxylation due to their insufficient cell-adhesion strength. On the other hand, though a decrease in the PIPAAm amount allowed SMCs to form a confluent cell monolayer on the PIPAAm brush surface, the SMCs were unable to be harvested as a monolithic cell sheet by low-temperature culture at 20 °C. Because of their unique property, only terminal-carboxylated PIPAAm brush surfaces achieved rapid harvesting of complete cell sheets by low-temperature culturing.

Preparation and swelling behaviors of rapid responsive semi-IPN NaCMC/PNIPAm hydrogels

Semi-interpenetrating network(semi-IPN) hydrogels composed of sodium carboxylmethyl cellulose(NaCMC) and poly N-isopropylacrylamide(PNIPAm) were prepared by free radical polymerization of N-isopropyl acrylamide(NIPAm) in dimethylsulfoxide(DMSO) in the presence of NaCMC. The structures of hydrogels were characterized by Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM) and differential scanning calorimetry(DSC). SEM images show that the hydrogels present porous network structures. Most water in the hydrogels were free water and freezing water. The equilibrium swelling ratio(ESR) and swelling rate(SR) were quite different at various swelling temperature. ESR of the hydrogels ranged abruptly from 15.2 g/g to 1.56 g/g and the hydrogels changed from transparent into opaque with swelling temperature changing from 33 °C to 34 °C, that is to say, the hydrogels exhibited the good temperature sensitivity at about 33 °C similar to low critical solution temperature(LCST) of pure PNIPAm, swelling rate were very different at below and above LCST due to hydrogel swelling with different swelling mechanism. Moreover, the semi-IPN hydrogels swelled much rapidly than pure PNIPAm hydrogels did at room temperature, the equillibrium swelling ratio(ESR) and swelling rate of the hydrogels increased with increasing of NaCMC content, i e. It is suggested that NaCMC could be potential for preparation of porous and rapid swelling hydrogels

Synthesis and thermo-responsive properties of chitosan-g-poly (N-isopropylacrylamide) and HTCC-g-poly(N-isopropylacrylamide) copolymers

Carboxyl group-terminated poly(N-isopropylacrylamide) (PNIA-COOH) was synthesized via radical polymerization of N-isopropylacrylamide (NIA) using mercaptoacetic acid (MAA) as a chain transfer agent. The molecular weight of the PNIA-COOH was controlled by changing the molar ratio of MAA to NIA. A water-soluble chitosan derivative, N-(2-hydroxy)propyl-3-trimethylammonium chitosan chloride (HTCC), was also synthesized by reacting chitosan with glycidyltrimethylammonium chloride. Then, chitosan-g-PNIA and HTCC-g-PNIA copolymers were synthesized using the “graft-onto” method by reacting PNIA-COOH with chitosan and HTCC, respectively. The formation of the grafted copolymers was confirmed by Fourier transform infrared spectroscopy, solubility test in water, and scanning electron microscopy — energy dispersive spectroscopy. The thermo-responsive behaviors of the grafted copolymers and the change in lower critical solution temperature (LCST) were also studied. Chitosan-g-PNIA was insoluble in water and behaved like a thermo-responsive hydrogel due to the crosslinking-point action of the chitosan backbone. The swelling ratio of chitosan-g-PNIA increased with increasing PNIA content. HTCC-g-PNIA behaved as a water-soluble thermo-responsive polymer. Compared to the homo PNIA, the LCST of HTCC-g-PNIA was slightly increased.

Soap-Free Emulsion Polymerization of Poly(ethylene glycol)-block-poly(N-isopropylacrylamide): Elucidation of Specific Reaction Fields for Quasi-Living Polymerization by Time-Resolved SANS

Poly(ethylene glycol)-block-poly(N-isopropylacrylamide) (PEG-b-PNIPAAm) was synthesized by radical polymerization of N-isopropylacrylamide (NIPAAm) from the radically activated chain ends generated...

Swelling Behavior of Stimuli-Sensitive Hydrogels Based on N-Isopropylacrylamide and Sodium Acrylate Copolymer

Stimuli-sensitive poly (N-isopropylacrylamide-co-sodium acrylate) [poly (NiPAAm-co-SA)] hydrogels are prepared by free radical polymerization of N-isopropylacrylamide (NiPAAm) and sodium acrylate (SA) using N, N'-methylene bisacrylamide (BIS) as a crosslinking agent. The effects of SA content, crosslinking agent concentration and the pre-gel solution concentration on the swelling behavior of poly (NiPAAm-co-SA) hydrogel are investigated systematically. The results indicate that the swelling capacities increase with an increase in the amount of hydrophilic poly (sodium acrylate) anionic units, and thermo-sensitivity is weakened simultaneously. The effect of the pre-gel solution concentration on the swellabilities of poly (NiPAAm-co-SA) is more than that of the crosslinking agent concentration. Furthermore, the pH-sensitivity of the networks is also investigated, and it is found that the swelling behavior of poly (NiPAAm-co-SA) hydrogels obviously improves when the pH value is 5.

One-pot fabrication of magnetic nanocomposite microcapsules

Fe 2O 3 nanoparticles can self-assembly at liquid–liquid interfaces to form stable water-in-oil Pickering emulsions. Novel magnetic and thermo-sensitive microcapsules were one-pot fabricated by radical polymerization of N-isopropylacrylamide (NIPAm) at the aqueous phases of Pickering emulsions at 60 °C. The obtained PNIPAm was deposited from the water phases onto the interfaces of water-in-oil Pickering emulsions to form Fe 2O 3/PNIPAm nanocomposite shells because of its hydrophobicity at this reaction temperature. Pickering emulsion polymerization opens up a new route to fabricate a variety of hollow and hybrid microcapsules.

Heterotactic poly(N-isopropylacrylamide) prepared via radical polymerization in the presence of fluorinated alcohols

Radical polymerization of N-isopropylacrylamide in toluene at −40°C in the presence of fourfold amounts of fluorinated alcohols was investigated. The 13C NMR analysis of the obtained polymers suggested that the addition of fluorinated alcohols induced heterotactic specificity in radical polymerization of NIPAAm, although syndiotactic poly(NIPAAm)s were obtained by adding alkyl alcohols as we have previously reported. To the best of our knowledge, this is the first synthesis of heterotactic poly(NIPAAm).