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Temperature- and pH-Sensitive Nanohydrogels of Poly(N-Isopropylacrylamide) for Food Packaging Applications: Modelling the Swelling-Collapse Behaviour  [PDF]
Clara Fuci?os, Pablo Fuci?os, Martín Míguez, Issa Katime, Lorenzo M. Pastrana, María L. Rúa
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0087190
Abstract: Temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) nanohydrogels were synthesized by nanoemulsion polymerization in water-in-oil systems. Several cross-linking degrees and the incorporation of acrylic acid as comonomer at different concentrations were tested to produce nanohydrogels with a wide range of properties. The physicochemical properties of PNIPA nanohydrogels, and their relationship with the swelling-collapse behaviour, were studied to evaluate the suitability of PNIPA nanoparticles as smart delivery systems (for active packaging). The swelling-collapse transition was analyzed by the change in the optical properties of PNIPA nanohydrogels using ultraviolet-visible spectroscopy. The thermodynamic parameters associated with the nanohydrogels collapse were calculated using a mathematical approach based on the van't Hoff analysis, assuming a two-state equilibrium (swollen to collapsed). A mathematical model is proposed to predict both the thermally induced collapse, and the collapse induced by the simultaneous action of two factors (temperature and pH, or temperature and organic solvent concentration). Finally, van't Hoff analysis was compared with differential scanning calorimetry. The results obtained allow us to solve the problem of determining the molecular weight of the structural repeating unit in cross-linked NIPA polymers, which, as we show, can be estimated from the ratio of the molar heat capacity (obtained from the van't Hoff analysis) to the specific heat capacity (obtained from calorimetric measurements).
New Family of Functionalized Monomers Based on Amines: A Novel Synthesis that Exploits the Nucleophilic Substitution Reaction  [PDF]
Lissette Agüero, Luis G. Guerrero-Ramírez, Issa Katime
Materials Sciences and Applications (MSA) , 2010, DOI: 10.4236/msa.2010.13018
Abstract: Chemistry modifications are usually performed to introduce specific group that can increase properties and functionality of materials. In this study, we present the synthesis of six new functionalized monomers prepared by nucleophilic substitution reactions. Reaction of aliphatic and aromatic amines with acryloyl chloride at –20ºC, in presence of triethylamine allowed the synthesis of the corresponding amides. Proton nuclear magnetic resonance (1H NMR) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy and ultraviolet- visible (UV-Vis) measurements confirmed the success of the synthesis with a yield over 90%. These compounds emerged as potentially attractive monomers since they can be used to obtain stimuli-sensitive polymeric materials, due to the presence of amide and pyridine groups.
Novel thermosensitive poly (N-isopropylacrylamide-co-vinylpyrrolidone-co-methacrylic acid) nanosystems for delivery of natural products  [cached]
Omid Mashinchian,Roya Salehi,Gholamreza Dehghan,Ayoub Aganejad
International Journal of Drug Delivery , 2011,
Abstract: The purpose of this research was to synthesize polymer based smart nanosystems for delivery of important bioactive natural products such as sesquiterpene coumarin derivatives of ferula szowitsiana, farnesiferol C as a potent anticancer. To this aim, polymeric micelles were prepared using N-isopropylacrylamide (NIPAAM), vinyl pyrrolidone (VP) and methacrylate (MAA) as monomers which were cross-linked with N, N-methylene bis-acrylamide (MBA). The molar ratio of the PNIPAAm: VP: MAA group was 75.7:9.5:14.8. These micelles were further characterized upon their physicochemical properties using particle size analyzer, FT-IR, H-/C-NMR, HPLC. Particle size analyzer resulted in ~500 nm micelles with ~95% drug entrapments. Drug release from the polymeric micelles after 300 hours at 37°C and 40°C were 60 and 98 %, respectively. Upon these findings, it is proposed that the P (N-isopropylacrylamide-co-Methacrylic acid-co-Vinylpyrrolidone) micelles may be considered as thermosensitive delivery nanosystem. Keywords: N-isopropylacrylamide; Thermosensitive; Nanoparticles; Farnesiferol C; Amphiphilic polymers.
Influence of substitution on the optical properties of functionalized pentacene monomers and crystals: Experiment and theory  [PDF]
Y. Saeed,K. Zhao,N. Singh,R. Li,J. E. Anthony,A. Amassian,U. Schwingenschl?gl
Physics , 2013, DOI: 10.1016/j.cplett.2013.08.023
Abstract: The influence of solubilizing substitutional groups on the electronic and optical properties of functionalized pentacene molecules and crystals have been investigated. Density functional theory is used to calculate the electronic and optical properties of pentacene, TIBS-CF$_{3}$-pentacene, and TIPS-pentacene. The results are compared with experimental absorption spectra of solutions and the complex dielectric function of thin films in the 1 eV to 3 eV energy range. In all cases, the band gaps of the isolated molecules are found to be smaller than those of the crystals. The absorption spectra and dielectric function are interpreted in terms of the transitions between the highest occupied molecular orbitals and lowest unoccupied molecular orbitals. The bands associated to C and Si atoms connecting the functional side group to the pentacene in the (6,13) positions are found to be the main contributors to the optical transitions. The calculated dielectric functions of thin films agree with the experimental results. A redshift is observed in crystals as compared to molecules in experiment and theory both, where the amplitude depends on the packing structure.
Extension of the PNA world by functionalized PNA monomers eligible candidates for inverse Diels Alder Click Chemistry  [cached]
Manfred Wiessler, Waldemar Waldeck, Ruediger Pipkorn, Christian Kliem, Peter Lorenz, Heinz Fleischhacker, Manuel Hafner, Klaus Braun
International Journal of Medical Sciences , 2010,
Abstract: Progress in genome research led to new perspectives in diagnostic applications and to new promising therapies. On account of their specificity and sensitivity, nucleic acids (DNA/RNA) increasingly are in the focus of the scientific interest. While nucleic acids were a target of therapeutic interventions up to now, they could serve as excellent tools in the future, being highly sequence-specific in molecular diagnostics. Examples for imaging modalities are the representation of metabolic processes (Molecular Imaging) and customized therapeutic approaches (“Targeted Therapy”). In the individualized medicine nucleic acids could play a key role; this requires new properties of the nucleic acids, such as stability. Due to evolutionary reasons natural nucleic acids are substrates for nucleases and therefore suitable only to a limited extent as a drug. To use DNA as an excellent drug, modifications are required leading e.g. to a peptide nucleic acid (PNA). Here we show that an easy substitution of nucleobases by functional molecules with different reactivity like the Reppe anhydride and pentenoic acid derivatives is feasible. These derivatives allow an independent multi-ligation of functionalized compounds, e.g. pharmacologically active ones together with imaging components, leading to local concentrations sufficient for therapy and diagnostics at the same time. The high chemical stability and ease of synthesis could enhance nucleic chemistry applications and qualify PNA as a favourite for delivery. This system is not restricted to medicament material, but appropriate for the development of new and highly efficient drugs for a sustainable pharmacy.
Effect of the initiator on thermosensitive rate of poly(N-isopropylacrylamide) hydrogels
eXPRESS Polymer Letters , 2007, DOI: 10.3144/expresspolymlett.2007.35
Abstract: As the main of thermosensitive polymeric materials, poly(N-isopropylacrylamide) (PNIPAM) undergoes volume changes in response to external temperature changes. While in some potential applications, a fast response rate is needed. In this article, effect of the initiator on thermosensitivity of PNIPAM hydrogels was carried out. The characterization of the resulting hydrogels was gravimetrically measured, and the result displays that with increasing the initiator dosage, much faster deswelling rate and much faster shrinking/swelling dynamic response are obtained.
Thermosensitive Hydrogels and Microgels Based on N-isopropylacrylamide and Acrylamide with Incorporated Magnetite  [cached]
Korotych O.I.,Samchenko Yu.M.,Sukhodub L.F.,Ulberg Z.R.
Proceedings of the International Conference Nanomaterials : Applications and Properties , 2013,
Abstract: Hydrogels with magnetic properties (ferrogels) are very promising for medical application, first of all, for the design of targeted delivery systems with controlled release of drugs and for magnetic hyperthermia and could be obtained using different techniques (ex- and in-situ syntheses). The present work is devoted to the study of magnetite (Fe3O4) formation inside the nanoreactors of (co)polymeric gels (hydrogels and microgels) based on the derivatives of acrylic acid: N-isopropylacrylamide, acrylamide, and N,N¢-methylenbisacrylamide (crosslinking agent). Influence of hydrophilic–lipophilic balance of (co)polymeric templates, temperature, pH and concentration of iron cations on the magnetite formation inside polymeric matrixes were investigated along with the development of ferrogel preparation technique. Physical and chemical properties of obtained ferrogels have been studied with gravimetric analysis, thermogravimetric analysis, X-ray fluorescence spectroscopy, X-ray diffraction, optical and transmission microscopies, IR spectroscopy, etc.
Preparation and Characterization of Functionalized Polypropylene with Acrylamide and Itaconic Acid  [PDF]
A. R. Oromiehie, H. Ebadi-Dehaghani, K. Ansari, K. Karimi, Z. Rahmani, S. Mirbagheri
Journal of Materials Science and Chemical Engineering (MSCE) , 2014, DOI: 10.4236/msce.2014.210007
Abstract:

Functionalized polypropylene with acryl amide (AAm) and itaconic acid (IA) were prepared in the molten state in the presence of dicumyl peroxide. The effects of the concentration of both mono- mers on the degree of functionalization and properties of the products were investigated by FT-IR, contact angle measurement and DSC analysis. It was found that the degree of functionalization depends on the initial concentration of both monomers that used in the reaction. The influence of the AAm and IA content on the melting and crystallization temperature of PP was investigated by DSC. The contact angle of water on film surfaces of the functionalized PP (PP-g-AAm and PP-g-IA) decreased with increasing modified polymer content. From FT-IR spectra of functionalized PP a calculation was made of carbonyl index on the films surfaces. It was found that the higher intensity of the carbonyl index, the lower contact angle value and the lower crystallinity confirmed the ex- istence of functionalized AAm and/or IA in PP. It was concluded from the different characteriza- tion methods that the polarity and percentage of functionalized PP were increased up to 3 phr for both monomers, and then it was decreased by increasing the amount of monomers and had a threshold value, due to nucleating agents of monomers in PP.

Functionalization of Multi-Walled Carbon Nanotubes with Thermo-Responsive Azide-Terminated Poly(N-isopropylacrylamide) via Click Reactions  [PDF]
Xin Su,Ya Shuai,Zanru Guo,Yujun Feng
Molecules , 2013, DOI: 10.3390/molecules18044599
Abstract: Covalently functionalized multi-walled carbon nanotubes (MWNTs) were prepared by grafting well-defined thermo-responsive poly( N-isopropylacrylamide) (PNIPAM) via click reactions. First, azide-terminated poly( N-isopropylacrylamide) (N 3-PNIPAM) was synthesized by reversible addition fragmentation chain-transfer (RAFT) polymerization, and then the N 3-PNIPAM moiety was connected onto MWNTs by click chemistry. The products were characterized by means of FT-IR, TGA and TEM. The results show that the modification of MWNTs is very successful and MWNTs functionalized by N 3-PNIPAM (MWNTs-PNIPAM) have good solubility and stability in water. TEM images show the functionalized MWNTs are dispersed individually, indicating that the bundles of original MWNTs are separated into individual tubes by surface modification with polymer chains. These MWNTs modified with PNIPAM represent a potential nano-material for preparation of hydrophilic composite materials.
PNIPAM Poly (N-isopropylacrylamide): A Thermoresponsive “Smart” Polymer in Novel Drug Delivery Systems
Rashmi R Kokardekar, Vaibhav K Shah, Hardik R Mody
Internet Journal of Medical Update - EJOURNAL , 2012,
Abstract: Over the past years, extensive research has been carried out in designing and optimizing various drug delivery systems in order to maximize therapeutic effect and minimize unwanted effects of drugs. Many drug carrier systems have been developed on the basis of nanotechnology including systems based on polymeric nanoparticles. Polymeric drug delivery research has been extended to targeting of the drug at the specific site by utilizing various stimuli responsive systems which depend upon physiological conditions of the body such as pH of biological fluids and temperature of the human body. Thermoresponsive polymers with Lower Critical Solution Temperature (LCST) have been investigated for various biomedical and pharmaceutical formulations. One such polymer of considerable focus is PNIPAM Poly (N-isopropylacrylamide). PNIPAM is a thermosensitive polymer which has been utilized in many drug delivery systems including for cancer therapeutics. The present article deals with the properties of PNIPAM and their applications in different drug delivery systems.
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