Increase In Degree Of Polymerization Research Articles

Development of Poly−Cyclohexanone Resin Material for Coating Applications

In the present work, polymerization reactions of cyclohexanone were carried out in a high−pressure reactor. The effect of reaction parameters such as reaction time, temperature, and catalyst loading on hydroxyl value, iodine value, solubility, and average molecular weight of products was investigated. In the study, reaction time was varied from 10−17 hrs, reaction temperature was varied from 130−150 °C, catalyst concentration was varied from 20−40%. The result shows that the degree of polymerization and hydroxyl value of the products increases with the increase of reaction time, temperature and catalyst loading. As the degree of polymerization increases, the decrement in product solubility in a given solvent was observed. FTIR, GPC and TGA analysis was done for the developed products. Based on the present study, it is concluded that the in−house developed resin from cyclohexanone can be used for coating applications.

CSA-doped PANI semiconductor nanofilms: synthesis and characterization

Camphorsulfonic acid doped polyaniline (PANI-CSA) prepared by chemical oxidative polymerization is dip coated on glass plates with three different PANI:CSA weight ratios (1:0.5, 1:1 and 1:2). Films of thickness being <100 nm are termed as nanofilms. Fourier transform infrared spectroscopy indicated the presence of dopant and increase in degree of polymerization with increase in dopant level. X-ray diffraction studies revealed the amorphous nature of the films. Scanning electron microscopy showed very smooth morphology without any crack or pores. Hall-effect analysis showed that the increase in CSA weight ratio appreciably increases the conductivity of PANI-CSA films due to increase in carrier concentration and it also represents the semiconductivity (P-type) nature in all the films. UV–visible absorption spectra and photoluminescence spectra revealed that high intense absorption and emission peaks occur for the PANI-CSA film with PANI:CSA weight ratio (1:2). This appreciable increase is due to increase in charge carriers. Photoluminescence study of PANI-CSA films excited using 300 nm shows high intense peaks at 361 and 494 nm and a weak peak at 410 nm which confirmed the semiconducting nature of the film.

Disassembly of Block Copolymer Vesicles into Nanospheres through Vesicle Mediated RAFT Polymerization

Block copolymer vesicles have aroused great interest, whereas how vesicles being formed is not well clarified. In this contribution, the vesicle mediated RAFT polymerization was performed, and the disassembly of block copolymer vesicles during the RAFT polymerization was investigated. It was found that when a solvophilic block of poly(N,N-dimethylacrylamide) (PDMA) was introduced into the vesicles of the poly[N-(4-vinylbenzyl)-N,N-diethylamine]-block-polystyrene (PVEA-b-PS) diblock copolymer, the PVEA-b-PS vesicles were gradually disassembled. With the increasing polymerization degree of the PDMA block, vesicles were first flattened to form tubules, then tubules were broken to form the jellyfish-like morphology, and last jellyfish converted into worms and worms minced into nanospheres of poly[N-(4-vinylbenzyl)-N,N-diethylamine]-block-polystyrene-block-poly(dimethylacrylamide) (PVEA-b-PS-b-PDMA). It is believed that the present vesicle mediated RAFT polymerization affords a real-time observation of vesicle disassembly, which is helpful to clarify the assembly of block copolymer vesicles.

Development of Synthetic Ketonic Resin

In the present work, the self-polymerization reaction of cyclohexanone was studied to develop a synthetic resin. Synthetic resins are extensively used in paint industry to improve the adhesiveness of paints. Polymerization reactions were carried out in a high-pressure reactor. The results suggest that the self-polymerization of cyclohexanone mainly depends on alkali concentration, reaction temperature, and reaction time. As the ketone-to-alkali ratio decreases, the degree of polymerization increases, which leads to an increase in the hydroxyl value and softening point and a remarkable decrease in solubility. A good-quality solid resin could be obtained with a ketone-to-alkali ratio less than 5 in the temperature range between 130°C and 160°C and within the time duration of 12–22 h. These data may be useful to develop the desired quality of resin in the field of paint application.

Highly efficient photocatalytic H₂ evolution from water using visible light and structure-controlled graphitic carbon nitride.

The major challenge of photocatalytic water splitting, the prototypical reaction for the direct production of hydrogen by using solar energy, is to develop low-cost yet highly efficient and stable semiconductor photocatalysts. Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g-C3N4) from a low-cost precursor, urea, is reported. The g-C3N4 exhibits an extraordinary hydrogen-evolution rate (ca. 20 000 μmol h−1 g−1 under full arc), which leads to a high turnover number (TON) of over 641 after 6 h. The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5 % under visible light, which is nearly an order of magnitude higher than that observed for any other existing g-C3N4 photocatalysts. Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen-evolution rate is significantly enhanced.

Highly Efficient Photocatalytic H2 Evolution from Water using Visible Light and Structure‐Controlled Graphitic Carbon Nitride

AbstractThe major challenge of photocatalytic water splitting, the prototypical reaction for the direct production of hydrogen by using solar energy, is to develop low‐cost yet highly efficient and stable semiconductor photocatalysts. Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g‐C3N4) from a low‐cost precursor, urea, is reported. The g‐C3N4 exhibits an extraordinary hydrogen‐evolution rate (ca. 20 000 μmol h−1 g−1 under full arc), which leads to a high turnover number (TON) of over 641 after 6 h. The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5 % under visible light, which is nearly an order of magnitude higher than that observed for any other existing g‐C3N4 photocatalysts. Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen‐evolution rate is significantly enhanced.

Effect of dopant concentration on the properties of HCl-doped PANI thin films prepared at different temperatures

Polyaniline thin film doped with hydrochloric acid (PANI-HCl) has been prepared by chemical oxidative polymerization at three different temperatures (4°C, 13°C and 31°C) with two different dopant concentrations (1M, 2M). Fourier transform infrared spectroscopy indicated the presence of dopant and increase in degree of polymerization with decrease in temperature. X-ray diffraction revealed that all the films are of amorphous nature. Scanning electron microscopy showed fiber morphology with high dense inter-fiber fusion. Hall-effect analysis showed that appreciable increase in conductivity of the PANI-HCl films with 2M-dopant concentration prepared at low temperatures (4°C, 13°C) occurs due to increase in carrier concentration. It also indicates the films as P-type semiconductors. UV–vis absorption spectra and photoluminescence spectra revealed that the role of dopant concentration is highly effective in the films prepared at low temperatures. High intense absorption cum emission peaks observed for the films with 2M dopant concentration prepared at low temperatures is due to the decreased fiber diameter which increased the surface to volume ratio of the fibers and increased localized defect states. Photoluminescence spectra of the films excited using 300nm show high intense emission peaks at 360nm, 494nm and a weak peak at 409nm confirming the semiconductor nature.

Thermogelation Properties of ABA Triblock Copolymers of Poly(Ethylene Glycol) (B) and Copolyacrylates of Oligo(Ethylene Glycol)s (A) in Aqueous Solution

Novel triblock copolymers with poly(ethylene glycol) (PEG) middle chain and random copolymers of di(ethylene glycol) ethyl ether acrylate (DEGA) and oligo(ethylene glycol) methyl ether acrylate (OEGA) as side blocks were synthesized by ATRP. The thermal gelation behavior of their 20 wt% aqueous solutions was studied as a function of the molecular characteristics of the triblock copolymers. The results showed that both association and gelation temperatures decreased with increasing polymerization degree and decreasing OEGA monomer content of the polyacrylate block. Also, both temperatures increased with PEG length at smaller MW of the PEG chain, and decreased for higher MW PEG. Rheometrical measurements showed that the length of the PEG block is the most important factor influencing elastic modulus and even structure of the hydrogels formed at 37°C. [Supplementary materials are available for this article. Go to the publisher's online edition of Soft Materials for the following free supplemental resource(s): Supplementary material.doc]

Microstructure and friction properties of PVA/PVP hydrogels for articular cartilage repair as function of polymerization degree and polymer concentration

Low friction coefficients are required for biomaterials in order for them to be used in the repair of articular cartilage. In the present study, polyvinyl alcohol (PVA)/polyvinylpyrrolidone (PVP) hydrogels were synthesized with different degrees of polymerization in the PVA and different polymer concentrations. A repeated freezing-thawing method was used to prepare them. The microstructures of the synthesized compositions gave an insight into the effects of the preparation processes and properties of the hydrogel. The influences of PVA polymerization and polymer concentration on the swelling behavior of PVA/PVP hydrogels in phosphate-buffered saline (PBS) were examined. The friction coefficients of PVA/PVP hydrogels against stainless steel were measured using a rotating ball-on-plate tribometer. The testing variables were: (a) polymerization degree of PVA, (b) polymer concentration, (c) lubrication condition (dry, physiological saline, and bovine serum), (d) sliding speed and (e) load. With increasing polymer concentration and polymerization degree of PVA, the inner structures of the hydrogels tended to be denser. An effective drop in swelling ratio was observed for hydrogels in PBS. The friction coefficient increased with an increase in polymerization degree of PVA, while it decreased with an increase of polymer concentration in the low load region and under liquid lubrication. At long testing times, the friction coefficient of hydrogels under dry sliding conditions increased rapidly owing to a lack of the interstitial fluid, while the friction coefficient remained stable during the entire friction test when fluid lubricated. Biphasic lubrication is proposed to be the key reason for maintaining a low friction coefficient level for PVA/PVP hydrogel when sliding against stainless steel.

Surface Structure of Spin-Coated Fluorinated Polymers Films Dominated by Corresponding Film-Formation Solution/Air Interface Structure

In this paper, the relationship between the surface structures of spin-coated fluorinated polymer films and their corresponding film-formation solution/air interface structures was investigated. Film-forming poly(n-alkyl methacrylate) end-capped with 2-perfluorooctylethyl methacrylate (FMA; PFMAy-ec-PnAMAx-ec-PFMAy) was synthesized via a controlled/living atom-transfer radical polymerization (ATRP) technique. The structures both at solution interface and on the spin-coated film surface for these polymers were studied by X-ray photoelectron spectroscopy (XPS), sum frequency spectroscopy (SFG), and surface tension measurements. The results showed that, with increasing polymerization degree of PnAMA, the fluorinated moieties in PFMAy-ec-PnAMAx-ec-PFMAy adsorbed at the solution/air interface were gradually completely replaced by PnAMA segments, resulting in an increase in corresponding solution surface tension until it was equal to that of poly(n-alkyl methacrylate) solution. Additionally, it was observed for...

Ring‐opening polymerization of genipin and its long‐range crosslinking effect on collagen hydrogel

Polymeric genipin macromers, prepared by ring-opening polymerization at various pH values, are used as crosslinking agents to fix collagen hydrogels. The results indicate that as the dark color of polymeric genipin itself and the networks formed by long-range intermolecular crosslinking, the genipin-fixed collagen hydrogels displace darker color. The polymeric genipin prepared at higher pH value needs longer time to fully crosslink with collagen molecules. Moreover, polymerization of genipin reduces the yield of genipin-fixed collagen hydrogels due to low extent of crosslinking. Specially, the microscope photographs present the porous networks structures of genipin-fixed collagen hydrogels. The pore size increases with the increase in polymerization degree of genipin. The data of FTIR indicate the likely transition of -NH(2) groups in collagen chains into C=N. Owning to much more number of hydrophilic groups and more porous networks, collagen hydrogels fixed by genipin with higher polymerization degree have higher water absorption capacity. The equilibrium swelling of genipin-fixed collagen hydrogels is pH-responsive, which show "M" type changes with the pH values. The results obtained in the study suggest that the polymeric genipin prepared at various pH values lead to significant influence to the crosslinking characteristics and properties of collagen hydrogels.

The Use of Sodium Chlorite in Post-Oxidation of TEMPO-Oxidized Pulp: Effect on Pulp Characteristics and Nanocellulose Yield

Presence of aldehydes on cellulose nanofibers (alternatively called nanocellulose) produced from TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyle)-oxidized pulp could interfere with the grafting of selected compounds on the carboxyls group of the oxidized pulp or of the nanofibers produced from such pulps. A simple protocol, called post-oxidation, utilizing sodium chlorite under acidic conditions has been developed for TEMPO-oxidized native cellulose to oxidize the aldehydes to carboxyls. The chemical nature, degree of polymerization, nanocellulose yield, and brightness stability of the post-oxidized pulp was characterized and compared with those of pulps prepared by the post-oxidation methods published in the literature. A sodium chlorite charge of 10% was sufficient for the oxidation of the TEMPO-oxidized pulp, which had a residual aldehydes content of ∼100 mmol/kg. We had observed an increase in degree of polymerization, nanocellulose yield, and brightness stability due to post-oxidation. It was found that aldehyde groups contributed significantly to the brightness reversion and yellowing of the TEMPO-oxidized pulp.

Antidiabetic Potential and its Relationship with Polyphenol and Degree of Polymerization in Acalypha indica Linn Leaves

Acalypha indica commonly known as Kuppi belongs to family Euphorbiaceae. Traditionally the plant used as a laxative, anthelmintic, cathartic and the juice is used as a speedy emetic for children and expectorant. It is used by tribal areas of Maharashtra State as rheumatic arthritis and as antihyperglycemic. However, no scientific data is available to validate the ethnobotanical claim. Keeping the above information in view, the present study has been designed to evaluate its antidiabetic activity. In the present study, hydroalcoholic extract of leaves and its fractions were studied for its anti diabetic potential in alloxan induced diabetic rats. The poly phenolic, flavonoid and flavanone contents of hydroalcoholic extract and its fractions were also determined and correlated with its anti diabetic activity. The experimental data indicated that the hydroalcoholic extract and its chloroform soluble fraction has significantly lowered the elevated blood glucose levels by 36.82% and 61.52% respectively at dose level of 400 mg/kg per oral after 7 days as compared to diabetic control. The poly phenolic and flavonoid content of hydro alcoholic extract and its chloroform soluble fraction were found to be 7.9 ± 0.20 mg and 1.14 ± 0.21mg (gallic acid equivalent/ g extract) and flavonoid content 2.02 ± 0 .50 mg and 0.56 ± 0.003mg (rutin equivalent/g extract) respectively. The increased anti diabetic potential of chloroform fraction over hydro alcoholic extract is due to its partial purification achieved by fractionation which resulted in increase in degree of polymerization and segregation of secondary metabolites.

Antidiabetic potential of unripe Carissa carandas Linn. fruit extract

Carissa carandas commonly known as Karanda have a long history of use in traditional system of medicine. It is used by tribal healers of Western Ghat region of Karnataka as hepatoprotective and antihyperglycemic. However, no scientific data is available to validate the folklore claim. The present study has been designed to evaluate its unripe fruit for the antidiabetic activity. In the present study, methanol extract of unripe fruits and its fractions were studied for its antidiabetic potential. The methanol extract and its fractions were screened for antidiabetic activity in alloxan induced diabetic rats. The polyphenolic, flavonoid and flavanone contents of methanolic extract and its fractions were also determined and correlated with its antidiabetic activity. The experimental data indicated that the methanol extract and its ethyl acetate soluble fraction has significantly lowered the elevated blood glucose levels by 48% (p<0.001) and 64.5% (p<0.001) respectively at dose level of 400mg/kg per oral after 24h as compared to diabetic control. In order to assess the role of polyphenolic components in the relevant activity, polyphenolic and flavonoid contents were determined. The polyphenolic and flavonoid content of methanol extract and its ethyl acetate soluble fraction were found to be 15.8 ± 1.2mg and 18.55 ± 0.34 mg (gallic acid equivalent/g extract) and flavonoid content 2.92 ± 0.03 mg and 1.534 ± 0.30 mg (rutin equivalent/g extract) respectively. The increased antidiabetic potential of ethyl acetate fraction over methanol extract is due to its partial purification achieved by fractionation which resulted in increase in degree of polymerization and segregation of secondary metabolites.

Molecular Dynamics Simulation of Poly(ethylene terephthalate) Oligomers

Molecular dynamics simulations of poly(ethylene terephthalate) (PET) oligomers are performed in the isobaric-isothermal (NpT) ensemble at a state point typical of a finishing reactor. The oligomer size ranges from 1 to 10 repeat units. We report thermodynamic properties (density, potential energy, enthalpy, heat capacity, isothermal compressibility, and thermal expansivity), transport properties (self-diffusivity, zero-shear-rate viscosity, thermal conductivity), and structural properties (pair correlation functions, hydrogen bonding network, chain radius of gyration, chain end-to-end distance) as a function of oligomer size. We compare the results with existing molecular-level theories and experimental data. Scaling exponents as a function of degree of polymerization are extracted. The distribution of the end-to-end distance is bimodal for the dimer and gradually shifts to a single peak as the degree of polymerization increases. The scaling exponents for the average chain radius of gyration and end-to-end distance are 0.594 and 0.571, respectively. The values of the heat capacity, isothermal compressibility, and thermal expansivity agree well with the available experimental data, which are of much longer PET chains. The scaling exponents for the self-diffusivity and zero-shear-rate viscosity are, respectively, -2.01 and 0.96, with the latter one being close to the theoretical prediction 1.0 for short-chain polymers.

Time dependence of the electronic structure of an electron-beam-irradiated C60 film

Time dependence of the electronic structure of an electron-beam (EB) irradiated C60 film (20–30 nm thick) has been examined using in situ high-resolution ultraviolet photoelectron spectroscopy. It is found that the electronic states of the C60 film have been changed continuously from an insulator (pristine C60 films) to a semiconductor and finally to a metal as EB-irradiation time increased. This can be explained by the increase in polymerization degree of a C60 polymer with a given cross-linked structure derived from the general Stone–Wales rearrangement from [Beu et al.,Phys. Rev. B 72, 155416 (2005)]. In addition, this finding suggests that the electronic properties of the C60 film can be controlled only in the EB-irradiated region by varying the irradiation time, which is interesting when applied to electronic devices.

Preparation and characterization of carbon-coated ZnO and CaO powders by pyrolysis of PVA

Carbon-coated ZnO and CaO powders were prepared by Poly(vinyl alcohol) (PVA) pyrolysis at 700 °C in inert atmosphere and characterized for their potential utilization in the field of antibacterial ceramics. No peaks corresponding to carbon were detected after XRD measurements of as-coated powders; that is, carbon coating is amorphous. Certain increase in specific surface area was observed after coating in all powders. Based on additional characterizations supported by SEM observations and particle size distributions, it is concluded that the formation of nanoporous structure of coated carbon layer resulted in an increase in the surface area. Some agglomeration also observed after treating powders that decreased with increasing polymerization degree of PVA used as a carbon precursor.

DyNAs: Constitutional Dynamic Nucleic Acid Analogues

Dynamic cationic polymers were generated in aqueous media from functionally complementary monomers bearing nucleobase groups. (1)H NMR spectroscopy was used to follow the polycondensation reaction of the nucleobase-appended dihydrazides 1 and 2 with the dialdehydes B and C. The reversibility of these polymers was established by proton NMR spectroscopy through exchange of the dihydrazide 2 with polymer 1 B. The polymers 1 B, 2 B, 1 C, and 2 C represent dynamic biopolymers of nucleic acid type, DyNAs. Electrostatic interaction of these polymers with polyanionic entities, such as polyphosphates, polynucleotides, and polyaspartic acid, was shown to take place. It induces a change in size of the dynamic polymer, as it responds by an increase in degree of polymerization to an increase of the overall anionic charge introduced, that is, to the total electrostatic interaction.

Polymer holography II – The theory of hologram growth

The theory describing in molecular terms radical photopolymerization due to which the refractive index modulation distribution producing a hologram is formed. The theory extends the usual only-diffusion concept to early stages of polymerization, where the opposite diffusion of short polymers (oligomers) is possible which is reduced with increasing polymerization degree. The results of the theory are compared with our experimental results. The idea that, inversely, the experimentally detected curves describing the hologram growth may be used for the study of polymerization kinetics is put forward.

Molecular Weight Dependent Charge Carrier Mobility in Poly(3,3‘ ‘-dioctyl-2,2‘:5‘,2‘ ‘-terthiophene)

Poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene), a polymer recently used for the fabrication of organic field effect transistors, has been fractionated into five fractions distinctly differing in their molecular weights (Mn), with the goal of determining the influence of the degree of polymerization (DPn) on its principal physicochemical parameters. It has been demonstrated that within the Mn range studied (from 1.5 kDa to 10.5 kDa by SEC), corresponding to DPn from 10 to 38, the polymer band gap steadily decreases with growing molecular weight, which is clearly manifested by an increasing bathochromic shift of the band originating from the pi-pi* transition. The same trend is observed for the HOMO level, determined from the onset of the p-doping in cyclic voltammetry, which shifts from -5.10 eV to -4.90 eV for the lowest and the highest molecular weight fractions, respectively. The most pronounced influence of DPn has been found for the charge carriers' mobility-one of the most important parameters of field effect transistors (FETs) fabricated from this polymer. A fourfold increase in DPn results in an increase of the carriers' mobility by more than 3 orders of magnitude. Comparison of these results with those obtained for fractionated regioregular poly(3-hexylthiophene) shows a strikingly similar behavior of both polymers with respect to the molecular weight.