Molecular Weight Distribution Of Poly Research Articles

Encapsulation of organic ultraviolet photoprotective actives into poly(methyl methacrylate) nanoparticles for sunscreen formulations

AbstractSkin cancer is the most common of all cancers worldwide. This way, it is mandatory to adopt an adequate sun protection routine, including sunscreen lotions. However, despite the proven effectiveness of numerous chemical filters, many of them are also known for their allergenic and carcinogenic potential effects, which can be mitigated by exploring some encapsulation routes. Thus, the present work evaluates the influence of seven distinct ultraviolet (UV) organic filters on the final particle size and molecular weight distributions of poly(methyl methacrylate) (PMMA) beads. Moreover, the sun protection factors (SPF) of the loaded nanoparticles are also evaluated when used for preparation of sunscreen formulations. The UV filters did not affect the course of MMA miniemulsion polymerizations significantly, enabling the synthesis of loaded nanoparticles. Nevertheless, adding the filters shifted the particle size distributions toward larger diameters, which are appropriate for cosmetic formulations. Based on the SPF analyses, it was also possible to observe a 12‐fold increase in the SPF values of the prepared formulations and an increase in the critical wavelength. Therefore, the in situ incorporation of distinct UV filters during miniemulsion MMA polymerizations constitutes a robust and versatile technology to produce PMMA nanoparticles loaded with UV filters for preparation of sunscreen formulations.

Modeling of Poly(Ethylene Terephthalate) Homogeneous Glycolysis Kinetics.

Polymer composites with various recycled poly(ethylene terephthalate)-based (PET-based) polyester matrices (poly(ethylene terephthalate), copolyesters, and unsaturated polyester resins), similar in properties to the primary ones, can be obtained based on PET glycolysis products after purification. PET glycolysis allows one to obtain bis(2-hydroxyethyl) terephthalate and oligo(ethylene terephthalates) with various molecular weights. A kinetic model of poly(ethylene terephthalate) homogeneous glycolysis under the combined or separate action of oligo(ethylene terephthalates), bis(2-hydroxyethyl) terephthalate, and ethylene glycol is proposed. The model takes into account the interaction of bound, terminal, and free ethylene glycol molecules in the PET feedstock and the glycolysis agent. Experimental data were obtained on the molecular weight distribution of poly(ethylene terephthalate) glycolysis products and the content of bis(2-hydroxyethyl) terephthalate monomer in them to verify the model. Homogeneous glycolysis of PET was carried out at atmospheric pressure in dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP) solvents with catalyst based on antimony trioxide (Sb2O3) under the action of different agents: ethylene glycol at temperatures of 165 and 180 °C; bis(2-hydroxyethyl) terephthalate at 250 °C; and oligoethylene terephthalate with polycondensation degree 3 at 250 °C. Homogeneous step-by-step glycolysis under the successive action of the oligo(ethylene terephthalate) trimer, bis(2-hydroxyethyl) terephthalate, and ethylene glycol at temperatures of 250, 220, and 190 °C, respectively, was also studied. The composition of products was confirmed using FTIR spectroscopy. Molecular weight characteristics were determined using gel permeation chromatography (GPC), the content of bis(2-hydroxyethyl) terephthalate was determined via extraction with water at 60 °C. The developed kinetic model was found to be in agreement with the experimental data and it could be used further to predict the optimal conditions for homogeneous PET glycolysis and to obtain polymer-based composite materials with desired properties.

Synthesis, Characterization, and Optical, Electrical and Thermal Stabilities of Poly(phenoxy-imine)s Containing Methyl and Hydroxyl Groups

The four different Schiff base compounds were synthesized from condensation reaction of benzaldehyde, 2-hydroxybenzaldehyde, 3-hydroxybenzaldehyde and 2-hydroxy-1-napthaldehyde with 4-amino-3-methylphenol. Then, the Schiff bases were converted into poly(phenoxy-imine)s by oxidative polycondensation in aqueous alkaline medium using NaOCl as oxidant. The structures of synthesized monomers and polymers were determined by Fourier transform infrared, proton-carbon-13 nuclear magnetic resonance (1H-13C-NMR) and ultraviolet–visible (UV–Vis) spectroscopies. The surface morphology of poly(phenoxy-imine)s was determined by scanning electron microscopy images. The molecular weight distributions of poly(phenoxy-imine)s were studied with gel permeation chromatography measurements. The optical properties of compounds were determined from UV–Vis spectroscopy and fluorescence spectroscopy measurements. Electrochemical properties of the compounds were determined by cyclic voltammetry analysis. The solubility tests of the synthesized compounds were performed in various organic solvents. Thermal properties of the compounds were determined by thermogravimetric and differential thermal analysis and differential scanning calorimetry. The electrical conductivity of undoped and iodine-doped poly(phenoxy-imine)s was measured by four-point probe technique at room temperature. The synthesized poly(phenoxy-imine)s show good electrical conductivity with iodine doping and the conductivity increases with the increase in iodine vapor contact time.

Anionic Polymerization of 2‐Hexyl[3]dendralene

AbstractIn this study, the polymerization behavior of 2‐hexyl[3]dendralene (H3D), which is an alkyl‐group‐derived [3]dendralene, is examined. The polymerization of H3D in tetrahydrofuran (THF) at −78 °C with potassium naphthalenide as the initiator affords poly(H3D) with a narrow molecular weight distribution, although a small shoulder peak is observed at a high molecular weight even before the monomer is completely consumed. The molecular weight distribution of poly(H3D) prepared in heptane is broader than that prepared in THF, indicating that the nucleophilic addition of a propagating carbanion to the carbon–carbon double bond in the polymer chain occurs in addition to polymerization. Furthermore, the microstructure of poly(H3D) is investigated by NMR. Signals corresponding to the conjugate addition structure, that is, 1,4‐ and 4,6‐structures, are exclusively observed. Poly(H3D) prepared in heptane contains a higher content of the 4,6‐structures compared with those prepared in THF.

Poly(ethylene-co-BMA) via dual concurrent ATRP–RAFT and its thermokinetic study

Well-defined copolymers of ethylene and butyl methacrylate (BMA) (poly(ethylene-co-BMA)) with narrow molecular weight distribution were synthesized via dual concurrent atom transfer radical polymerization (ATRP) and reversible addition–fragmentation chain transfer (RAFT) polymerization using 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid as an alkyl pseudo-halide initiator, ascorbic acid/FeCl3/2,2′ bipyridine as the ATRP catalyst system and ethyl-2-bromo-isobutyrate as co-initiator in N, N′-dimethyl formamide at 100 °C. From size exclusion chromatography result, controlled molecular weight with narrow molecular weight distributions of poly(ethylene-co-BMA) was obtained in every case. The experimental results indicated that dual concurrent ATRP–RAFT polymerization is more successful over free radical or RAFT polymerization in terms of controlling molecular weight and polydispersity. X-ray diffraction analysis demonstrated the amorphous behaviour of poly(ethylene-co-BMA) while thermogravimetric analysis reveals that the main decomposition of poly(ethylene-co-BMA) occurs in the range 300–420 °C. The multivariate nonlinear regression analysis was performed to establish the mechanism and kinetic model and found that n-dimensional Avrami–Erofeev (An) mechanism was responsible for the decomposition of the synthesized poly(ethylene-co-BMA). The apparent activation energy (E a) of decomposition of the synthesized copolymer was found to be 211.88 kJ mol−1.

Living anionic polymerization of (E)-1,3-pentadiene and (Z)-1,3-pentadiene isomers

The anionic polymerization of (E)-1,3-pentadiene (EP) and (Z)-1,3-pentadiene (ZP) together with mixture of the E/Z isomers are investigated, respectively. The kinetic analysis shows that the activation energy for EP (86.17 kJ/mol) is much higher than that for ZP (59.03 kJ/mol). GPC shows that it is the EP rather than the ZP isomer that undergoes anionic living polymerization affording quantitative products of the polymers with well-controlled molecular weights and narrow molecular weight distributions (1.05 ≤Đ ≤ 1.09). In addition, THF as polar additive has proved its validity to reduce the molecular weight distribution of poly(ZP) from 1.38 to as low as 1.19. The microstructure and sequence distributions of polypentadiene are characterized by 1H NMR and quantitative 13C NMR. Finally, the distinctive reaction activity of two isomers can be elucidated by two different mechanisms which involve the presence of four forms of zwitterions for EP and the typical [1,5]-sigmatropic hydrogen-shift phenomenon for ZP. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2291–2301

The use of ionic liquids as an organocatalyst for controlled ring-opening polymerization of ϵ-caprolactone

The controlled ring-opening polymerization of ϵ‑caprolactone in bulk catalyzed by ionic liquids, thus, avoiding the use of metal catalyst, solvent and base, is reported. These mild conditions led to living polymerization with good conversions and molecular weight distributions of poly(ϵ‑caprolactone). Finally, an activation mechanism is suggested based on the results of an in-situ FTIR polymerization analysis using various ionic liquid catalysts.

Modeling of Molecular Weight Distribution in Ring-Opening Polymerization of l,l-Lactide

The molecular weight distributions of poly(lactic acid) produced by ring-opening polymerization of l,l-lactide in bulk melt are measured and compared with the ones predicted using a kinetic model accounting for reversible catalyst activation, reversible propagation, reversible chain transfer to cocatalyst, and intermolecular transesterification. The same values of the model parameters as evaluated in previous works are used without any adjustment; i.e. the model is used in a fully predictive way. In order to calculate the complete molecular weight distribution, the model equations are solved through two different numerical methods, “direct integration” of the population balances at all values of chain length, and “fractionated moments”, where the chains are artificially classified into two different categories, depending upon the experienced reaction steps. The accuracy of the molecular weight distributions calculated in the latter case is evaluated by comparison with those computed by solving the model e...

Semifluorinated multiple pendant group bearing poly(arylene ether) copolymers prepared at room temperature

Novel semifluorinated poly(arylene ether) copolymers are prepared by aromatic nucleophilic substitution reactions between 4-phenoxy-2,3,5,6-tetrafluorobenzonitrile and various bisphenols in the presence of potassium carbonate as a base at room temperature. The molecular weights and molecular weight distribution of poly(arylene ether) copolymers are determined by the substitution groups in 4-phenoxy moiety and the reactivity of bisphenols. The highest molecular weights of copolymers are achieved with base to phenol ratio of 1.5 at room temperature, but the molecular weights of copolymers decreases with increasing reaction temperature and decreasing the base concentration. The copolymers synthesized from 4-phenoxy-3-(trifluoromethyl)-2,3,5,6-tetrafluorobenzonitrile/4-phenoxy-3,5-bis(trifluoromethyl)-2,3,5,6-tetrafluorobenzonitrile and 4,4′-(hexafluoroisopropylidene)diphenol shows high molecular weights (M n = 2.0–2.7 × 104) and low molecular weight distributions (M w/M n = 1.25–1.4) compared to other substituted groups in 4-phenoxy moieties of PFBN and other bisphenols combinations. The poly(arylene ether) copolymers synthesized from bisphenol-A exhibit high thermal stability compared to 4,4′-(hexafluoroisopropylidene)diphenol copolymers and the char yield of copolymers are >40 %.

Emulsion polymerization of vinyl acetate using iodine-transfer and RAFT radical polymerizations

This study deals with control of the molecular weight and molecular weight distribution of poly(vinyl acetate) by iodine-transfer radical polymerization and reversible addition-fragmentation transfer (RAFT) emulsion polymerizations as the first example. Emulsion polymerization using ethyl iodoacetate as the chain transfer agent more closely approximated the theoretical molecular weights than did the free radical polymerization. Although 1H NMR spectra indicated that the peaks of α- and ω-terminal groups were observed, the molecular weight distributions show a relatively broad range (Mw/Mn = 2.2–4.0). On the other hand, RAFT polymerizations revealed that the dithiocarbamate 7 is an excellent candidate to control the polymer molecular weight (Mn = 9.1 × 103, Mw/Mn = 1.48), more so than xanthate 1 (Mn = 10.0 × 103, Mw/Mn = 1.89) under same condition, with accompanied stable emulsions produced. In the Mn versus conversion plot, Mn increased linearly as a function of conversion. We also performed seed-emulsion polymerization using poly(nonamethylene L-tartrate) as the chiral polyester seed to fabricate emulsions with core-shell structures. The control of polymer molecular weight and emulsion stability, as well as stereoregularity, is also discussed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Effect of different ligands on the controlled polymerization of monodisperse polystyrene nanospheres by atom transfer radical polymerization in an aqueous emulsion

Polystyrene nanospheres have been synthesized by atom transfer radical polymerization (ATRP) to control the molecular weight distribution in the aqueous system. The crucial factor in such a system is the ligand that adjusts the solu- bility of the catalyst in different phases to control the concentration of both the activator and the deactivator in reaction phase. The effect of different ligands including ethylenediamine, 1,10-phenanthroline (phen) and 4,4-dinonyl-2, 2-bipyridyl (dNbpy) on the catalytic solubility in the organic and aqueous phase has been investigated. The molecular weight distribu- tion of polymer obtained in this way was analyzed by gel permeation chromatography (GPC). It showed that the obtained polymer particles presented a broad molecular weight distribution (polydispersity index 1.78) with ethylenediamine as the ligand, but the polymerization rate was high and conversion reached 96.8%. The molecular weight distribution of poly- styrene was narrowest with dNbpy as ligand, but the conversion was lowest and only achieved to 69%. Possible reasons were the influence of the structure of three different ligands on the control of ATRP reaction. SEM and GPC indicated that the polystyrene nanospheres presented regular sphere with a diameter of about 120 nm and uniform molecular weight dis- tribution, which possessed a significant potentials in drug carrier field.

Step-Growth Polymerization of Poly(phenylcarbosilane) and Its Structural and Physical Properties

The polymerization and molecular weight distribution of poly(phenylcarbosilane) (PPCS) depend on the temperature and pressure conditions under which it is synthesized using the Kumada rearrangement reaction. Its degree of polymerization is related not only to its physical properties such as solubility and boiling point but also to its chemical structure. In this study, soluble PPCS having a weight-average molecular weight (Mw) in the range of 2,500–3,000 was selectively isolated through distillation or fractional precipitation, and its chemical structure and physical properties were studied via FT-IR, NMR, GPC, and thermal analysis. The analytical data indicate that the Si–CH2–Si backbone and Si–Si bond are formed through step-growth polymerization and are clearly detected after purification. The differences in the thermal behavior of PPCS in air and in nitrogen were also investigated.

Kinetics and Molecular Weight Characterization of Poly (2-Ethylhexyl Acrylate) and Liquid Crystal (5CB) Composites

The effect of initiator and liquid crystal 4-cyano-4′-n-pentylbiphenyl (5CB) concentrations on the monomer conversion and molecular weight distributions of the polymer in the free-radical polymerization of 2-ethylhexylacrylate (2-EHA) has been studied and characterized using Fourier transform infrared spectroscopy, differential scanning calorimetry, and gel permeation chromatography. A slight effect of the concentration of the photoinitiator has been observed both on the monomer conversion and the molecular weight distribution of poly (2-EHA). Increasing the amount of 5CB in the initial mixture leads to a decrease of conversion, glass transition temperature of the polymer, molar mass of polymer and of the polydispersity.

Stimuli Responsive Poly(1-[11-acryloylundecyl]-3-methyl-imidazolium bromide): Dewetting and Nanoparticle Condensation Phenomena

A stimuli-responsive homopolymer poly(ILBr) is fabricated via a "two-phase" atom transfer radical polymerization (ATRP) process, where ILBr stands for the reactive ionic liquid surfactant, 1-[11-acryloylundecyl]-3-methyl-imidazolium bromide. An extraordinarily wide molecular weight distribution (PDI = 6.0) was obtained by introducing the initiator (4-bromomethyl methyl benzoate) in a heterogeneous two-phase process. The molecular weight distribution of poly(ILBr) was characterized by size-exclusion chromatography (SEC). The resulting homopolymer was found to be surface active and stimuli responsive. Poly(ILBr) films coated on quartz exhibit stimuli-responsive dewetting after ion exchange of Br(-) by PF(6)(-). This dewetting phenomenon can be understood in chain segmental terms as a stimuli-induced structural relaxation and appears to be the first such reported stimuli-responsive polymeric dewetting. Titrating aqueous poly(ILBr) with aqueous bis(2-ethylhexyl)sulfosuccinate induces nanophase separation and results in the condensation of nanoparticles 30-60 nm in diameter.

A combined metabolic/polymerization kinetic model on the microbial production of poly(3-hydroxybutyrate)

In the present work, an integrated dynamic metabolic/polymerization kinetic model is developed for the prediction of the intracellular accumulation profile and the molecular weight distribution of poly(3-hydroxybutyrate) (P(3HB) or PHB) produced in microbial cultures. The model integrates two different length/time scales by combining a polymerization kinetic model with a metabolic one. The bridging point between the two models is the concentration of the monomer unit (i.e. 3-hydroxybutyryl-CoA) produced during the central aerobic carbon metabolism. The predictive capabilities of the proposed model are assessed by the comparison of the calculated biopolymer concentration and number average molecular weight with available experimental data obtained from batch and fed-batch cultures of Alcaligenes eutrophus and Alcaligenes latus. The accuracy of the proposed model was found to be satisfactory, setting this model a valuable tool for the design of the process operating profile for the production of different polymer grades with desired molecular properties.

Modified frontal polymerization of poly(methyl methacrylate)

AbstractIn this work, we propose a modified frontal polymerization method to build a uniform reaction front by gradually immersing the reacting mixture in a thermal bath. This scheme allows uniform materials to be obtained with nearly constant molecular weights and polydispersities and a low residual monomer concentration. A comparative study of the molecular weight distributions of poly(methyl methacrylate)s obtained by bulk polymerization, frontal polymerization, and frontal polymerization with the proposed gradual immersion is presented. Samples obtained by these methods show that materials obtained by bulk polymerization and by frontal polymerization are less uniform than those obtained by frontal polymerization with gradual immersion in a thermal bath. The obtained uniformity is directly related to a stabilizing effect of the reaction front by the gradual immersion of the reactor in a constant‐temperature bath and to a reduction in the reaction rate promoted by a moderate transfer agent concentration. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preparation of monodisperse nanoparticles containing poly(propylene imine)(NH2)32‐polystyrene

AbstractPolypropylenimine dendrimer (DAB‐Am‐32, generation 4.0) was converted into a macroinitiator DAB‐Am‐32‐Cl via reaction with 2‐chloropropionyl chloride. Monodisperse nanoparticles containing poly(propylene imine)(NH2)32‐polystyrene were prepared by emulsion atom transfer radical polymerization (ATRP) of styrene (St), using the DAB‐Am‐32‐Cl/CuCl/bpy as initiating system. The structure of macroinitiator was characterized by FTIR spectrum, 1H NMR, and 13C NMR. The structure of poly(propylene imine)(NH2)32‐polystyrene was characterized by FT‐IR spectrum and 1H NMR; the molecular weight and molecular weight distribution of poly(propylene imine)(NH2)32‐polystyrene were characterized by gel permeation chromatograph (GPC). The morphology, size and size distribution of the nanoparticles were characterized by photon correlation spectroscopy (PCS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The effects of monomer/macroinitiator ratio and surfactant concentration on the size and size distribution of the nanoparticles were investigated. It was found that the diameters of the nanoparticles were smaller than 100 nm (30–80 nm) and monodisperse; moreover, the particle size could be controlled by monomer/macroinitiator ratios and surfactant concentration. With the increasing of the ratio of St/DAB‐Am‐32‐Cl, the number‐average diameter (Dn), weight‐average diameter (Dw) were both increased gradually. With enhancing the surfactant concentration, the measured Dh of the nanoparticles decreased, while the polydispersity increased. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2892–2904, 2009

Determination of Chemical Composition Distribution and Molecular Weight Distribution of Poly(2-(perfluoroalkyl)ethyl acrylate-co-alkyl acrylate) by High Performance Liquid Chromatography and Size Exclusion Chromatography

The molecular weight distribution (MWD) of poly(2-(perfluoroalkyl)ethyl acrylate-co-alkyl acrylate) can be determined by size exclusion chromatography (SEC) using an appropriate mobile phase such as a mixture of HCFC225 and THF; however, the chemical composition distribution (CCD) of the copolymer has not been elucidated. We developed an HPLC method for determining the CCD by using a silica-based column modified by polyfluorinated groups, a devised mobile phase gradient system, and an evaporative light scattering detector. In this system, polymers having perfluoroalkyl units are retained on the column through interaction between fluorinated groups and elute at longer retention times. It has become apparent that the copolymer has a broad and characteristic CCD of three components, consisting of fluorinated and non-fluorinated forms and their copolymer. Two-dimensional development of MWD and CCD of the copolymer, called cross-fractionation, is also examined and discussed.

Bimodal molecular weight distribution of poly(styrene‐co‐acrylonitrile) formed by conventional free‐radical copolymerization of acrylonitrile and styrene in room temperature ionic liquids

AbstractConventional free‐radical copolymerization of acrylonitrile (AN) and styrene (St) was realized in room temperature ionic liquids (RTILs), 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([Bmim][BF4]) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([Bmim][PF6]), under mild conditions. The copolymerization in RTILs was more rapid than that in traditional solvent DMF. Poly(styrene‐co‐acrylonitrile) (SAN) prepared in RTILs had higher molecular weight than that prepared in DMF or by bulk copolymerization. SAN with bimodal molecular weight distribution (MWD) were obtained in most of the reaction conditions in [Bmim][BF4] and some conditions in [Bmim][PF6]. By the analysis of reaction phenomena and fluorescence behavior, the reason of the difference in MWD could be attributed to the difference of reaction system compatibility mainly caused by the immiscibility of macromolecule with RTIL. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4420–4427, 2006

Cholesterol Tethered Poly(DL-Lactic Acid) for Promoting Osteoblast Attachment and Growth

In poly(DL-lactic acid)-cholesterol oligomers (LC), a novel cholesterol modified poly(DL-lactic acid) (PLA), was synthesized via bulk polymerization of DL-lactide using cholesterol initiator. Gel permeation chromatography (GPC) and 1H nuclear magnetic resonance spectroscopy (1H-NMR) results indicated a narrow molecular weight distribution of poly (DL-lactic acid)-cholesterol oligomers (LC). Mouse MC3T3 osteoblast-like cells were selected as a model system to test the cell behavior of cholesterol modified PLA substrates. The osteoblast attachment, proliferation, and viability revealed that the cholesterol modified PLA was significantly osteoblast compatible and may have potential as a bone tissue engineering material.