Molecular Weight Of Polyacrylonitrile Research Articles

Rapid and Nondestructive Determination of Polyacrylonitrile Molecular Weight by Fourier Transform near-Infrared (NIR) Spectroscopy

The molecular weight of polyacrylonitrile (PAN) precursors plays an important role in specifying the properties of prepared carbon fibers. However, it is challenging to rapidly and conveniently determine the accurate molecular weight of PAN. Herein, a practical and facile molecular weight determination model of PAN based on near-infrared spectroscopy (NIR) combined with partial least squares (PLSs) is reported. Using the spectral modeling range from 4000 to 6000 cm−1 with standard normal variate (SNV) or multiplicative scatter correction (MSC) combined with smoothing and first-order differential, the optimized models with main factors number of nine are achieved. The models were systematically evaluated by root mean square error of calibration (RMSEC), root mean square error of prediction (RMSEP), and root mean squares error of cross-validation (RMSECV). In the determination of the molecular weight of the samples based on these optimized models, the value of the relative standard deviation is only 0.9%, and the value of deviation from the established gel permeation chromatography (GPC) method is between −0.037 × 105 and 0.051 × 105. The results show that the reported NIR method has promising potential for the rapid and nondestructive determination of the molecular weight of PAN in production processes.

High molecular weight poly(acrylonitrile-co-3-aminocarbonyl-3-butenoic acid methyl ester) prepared by mixed solvent polymerization I. effect of monomer feed ratios on polymerization and stabilization

In order to improve the pre-oxidation performance and molecular weight of polyacrylonitrile (PAN). In this work, 3-aminocarbonyl-3-butenoic acid methyl ester) (ABM) was used as comonomers to formulate high molecular weight poly(acrylonitrile-co-3-amino-carbonyl-3-butenoic acid methyl ester) [P(AN-co-ABM)] copolymer by radical polymerization in the mixed solvent of dimethyl sulfoxide/deionized water =60/40 (wt/wt). The highest molecular weight of resultant P(AN-co-ABM) is 4.87 × 105 g/mol, 5 times larger than that prepared by solution polymerization under the same reaction conditions. The monomer reactivity ratios are calculated by Fineman-Ross and Kelen-Tudos methods based on the elemental analysis results. Thermal properties of P(AN-co-ABM) copolymer with different monomer feed ratios were studied by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry in detail. The results show that the stabilization of P(AN-co-ABM) has been significantly improved by ABM, confirmed by the lower initiation temperature and broader exothermic peak in DSC curves, larger extent of stabilization from FTIR and XRD studies, and smaller Ea of cyclization, which is due to the initiation of ABM through ionic mechanism. This study clearly shows that high molecular weight P(AN-co-ABM) copolymer is a better material for carbon fiber precursor.

Synthesis of high molecular weight and narrow molecular weight distribution poly(acrylonitrile) via RAFT polymerization

AbstractWell‐defined polyacrylonitrile (PAN) of high viscosity‐average molecular weight (Mη = 405,100 g/mol) was successfully synthesized using reversible addition‐fragmentation chain transfer polymerization. The polymerization exhibits controlled characters: molecular weights of the resultant PANs increasing approximately linearly with monomer conversion and keeping narrow molecular weight distributions. The addition of 0.01 equiv (relative to monomer acrylonitrile) of Lewis acid AlCl3 in the polymerization system afforded the obtained PAN with an improved isotacticity (by 8%). In addition, the influence of molecular weights and molecular weight distributions of PANs on the morphology of the electrospun fibers was investigated. The results showed that, under the same conditions of electrospinning, average diameter (247–1094 nm) of fibers increased with molecular weights of PANs, and it was much easier to get “uniform” diameter fibers while using PANs with narrow molecular weight distributions as the precursor of electrospinning. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

SET-LRP of acrylonitrile catalyzed by tin powder

Sn(0)-mediated single electron transfer-living radical polymerization (SET-LRP) of acrylonitrile (AN) with carbon tetrachloride (CCl4) as initiator and hexamethylenetetramine (HMTA) as ligand in N, N-dimethylformamide (DMF) was studied. The polymerization obeyed first order kinetic. The molecular weight of polyacrylonitrile (PAN) increased linearly with monomer conversion and PAN exhibited narrow molecular weight distributions. Increasing the content of Sn(0) resulted in an increase in the molecular weight and the molecular weight distribution. Effects of ligand and initiator were also investigated. The block copolymer PAN-b-polymethyl methacrylate with molecular weight at 126,130 and polydispersity at 1.36 was successfully obtained. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Preparation and Electromagnetic Properties of Carbon Nanofiber/Epoxy Composites

Carbon nanofibers (CNFs) with diameters ranging from 50 nm to 150 nm were prepared from polymer blends of polyacrylonitrile (PAN)/polymethyl methacrylate (PMMA) via a wet-spinning method and subsequent thermal treatment. The main factors that influence the diameter of the CNFs, including molecular weight of PAN, mass ratio of PAN/PMMA, and spinning draw ratio, are discussed. The formation of graphitization structures of the blend fibers during the carbonization process was investigated by Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray diffraction spectroscopy. The complex permittivity ϵ (ϵ′ − jϵ″), complex permeability μ (μ′ − jμ″), and microwave absorption properties of CNF/epoxy composites were studied in the X-band frequency range (8.2–12.4 GHz). ϵ′, ϵ″, μ′, and μ″’ were found to increase with increased CNF content. Measured values of these parameters were used to determine the reflection loss at various sample thicknesses, based on a model of a single-layered plane wave absorber backed by a perfect conductor. The calculated results showed that the composite with a CNF content of 8 wt% and a thickness of 2.1 mm would give a maximum reflection loss of −34 dB at 10.5 GHz with the −10 dB bandwidth over the extended frequency range of 8.8–12.4 GHz.

2‐Cyanoprop‐2‐yl dithiobenzoate mediated reversible addition–fragmentation chain transfer polymerization of acrylonitrile targeting a polymer with a higher molecular weight

AbstractThe reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylonitrile (AN) mediated by 2‐cyanoprop‐2‐yl dithiobenzoate was first applied to synthesize polyacrylonitrile (PAN) with a high molecular weight up to 32,800 and a polydispersity index as low as 1.29. The key to success was ascribed to the optimization of the experimental conditions to increase the fragmentation reaction efficiency of the intermediate radical. In accordance with the atom transfer radical polymerization of AN, ethylene carbonate was also a better solvent candidate for providing higher controlled/living RAFT polymerization behaviors than dimethylformamide and dimethyl sulfoxide. The various experimental parameters, including the temperature, the molar ratio of dithiobenzoate to the initiator, the molar ratio of the monomer to dithiobenzoate, the monomer concentration, and the addition of the comonomer, were varied to improve the control of the molecular weight and polydispersity index. The molecular weights of PANs were validated by gel permeation chromatography along with a universal calibration procedure and intrinsic viscosity measurements. 1H NMR analysis confirmed the high chain‐end functionality of the resultant polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1272–1281, 2007

Anionic Polymerization of Acrylonitrile with Trivalent Phosphorus Compounds

In order to see if the anionic polymerization of acrylonitrile initiated by trivalent phosphorous compounds is a living polymerization, and to see how high the molecular weight of polyacrylonitrile can be reached, the polymerization of acrylonitrile using triethylphosphite (TEP), phenyldiethoxyphosphine (PEP) and diphenylethoxyphosphine (DPP) was investigated. TEP was found to be a better initiator than the others, producing polymers with extremely high molecular weights. The polymerization system is a living type as the molecular weight increases until the system is exposed to air. However, the molecular weight polydispersity was in the range of 2.2–2.6 due to the complexity of initiation. The average molecular weight (Mw) reached 375,000, while that of a commercial polyacrilonitrile obtained by emulsion polymerization was 113,000. The polymer solutions obtained by the anionic polymerization became gel on standing, but they became sol when more solvent (DFM) was added and heated. The majority of polymers were slightly yellow due to the formation of imide linkages. The copolymerization with methylacrylate resulted in low molecular weight copolymers, with a ratio of acrylonitrile to methylacrylate units of 10.

Graft polymerization of acrylonitrile onto spherocrystals formed from jet cooked cornstarch

Ceric ammonium nitrate-initiated graft polymerizations of acrylonitrile (AN) onto spherocrystals formed in slowly-cooled solutions of jet-cooked cornstarch yielded graft copolymers containing higher percentages of grafted polyacrylonitrile (PAN) than comparable polymers prepared from granular cornstarch. Weight percentages of PAN in grafted spherocrystals, prior to extraction with dimethylformamide to remove ungrafted PAN, were over 60% when 2.0 g of AN per gram of polysaccharide was used, and were about 55% with 1.5 g of AN. Copolymers prepared from the small (toroidal) and large (spherical) spherocrystals contained similar amounts of grafted PAN. Molecular weights of PAN in grafted spherocrystals were higher by about a factor of six than the PAN molecular weight in grafted granular cornstarch. The calculated number of anhydroglucose units separating each PAN graft was also higher for the spherocrystal graft copolymers, indicating that the higher percentage of grafted PAN in the spherocrystal polymers (relative to grafted granular cornstarch) was due to the higher molecular weight of grafted PAN and not to a greater number of grafts on the starch backbone. Gross morphologies of the cornstarch granules and spherocrystals used as starting materials were maintained after graft polymerization. Moreover, the PAN particles remaining after starch was removed by acid hydrolysis were similar in appearance to their respective graft copolymers. PAN-grafted cornstarch granules and PAN-grafted spherocrystals both exhibited birefringence patterns similar to those of the un-grafted starting materials, although the patterns were less clear. Birefringence patterns of PAN particles remaining after removal of the starch moiety were also similar. X-ray diffraction patterns of PAN-grafted spherocrystals were similar to those of the un-grafted starting materials; however, the major amylose reflections of the 6 1 V-helical pattern occurred at slightly higher angles, and the amylose peak intensities were smaller. When ethanol was used to wash the PAN-grafted large (spherical) particles, the 7 1 V-helical pattern was converted to the 6 1 V-helical pattern exhibited by the PAN-grafted small (toroidal) particles.

Effect of Low-Temperature Solution Polymerization Conditions of Acrylonitrile on the Molecular Characteristics of Polyacrylonitrile

Acrylonitrile (AN) was solution-polymerized in dimethyl sulfoxide (DMSO) and tertiary butyl alcohol (TBA) at 30,40 and 50°C using a low temperature initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN), and effects of polymerization conditions were investigated in terms of molecular structures of polyacrylonitrile (PAN). Low polymerization temperature by adopting ADMVN proved to be successful in obtaining PAN of high molecular weight with smaller temperature rise during polymerization. Through a polymerization of AN in DMSO at 30°C, PAN having weight-average molecular weight (M w ) of 931,000 was obtained, whose polydispersity index of 1.89. For the same polymerization conditions, DMSO was slightly superior to TBA in increasing molecular weight of PAN. In addition, DMSO was superior to TBA in diminishing molecular structural defects such as enaminonitrile structure in PAN polymerized, indicating that differences in polymerization and termination rates due to a different polymerization mechanisms using two polymerization solvents. The M w , linearity, molecular structural regularity, and whiteness were higher with PAN polymerized at lower temperatures.

“Living” radical polymerizations of vinyl monomers initiated by aged “Cr2++ BPO” in homogeneous solution

Monomer is added to chromium(II) acetate (Cr2+) and benzoyl peroxide (BPO) previously treated at 10°C in dimethylformamide (DMF)(the ageing process), and polymerizations are performed. It is found that the degree of polymerization of poly(methyl methacrylate)(PMMA) obtained at 30°C or below increases with an increase in monomer conversion and the single peak of a molecular weight distribution curve shifts with monomer conversion. These results suggest that a “living” polymerization occurs in the homogeneous polymerization of MMA initiated by the aged “Cr2++ BPO” system.The polymerizations of various vinyl monomers with this initiator system are carried out at 25°C. The polymerization activity is relatively high for MMA, acrylonitrile, methyl acrylate and acrylamide but low for styrene, vinyl acetate and vinyl chloride. The molecular weights of polyacrylonitrile and poly(methyl acrylate) also increase with the monomer conversion.By copolymerizing MMA with acrylonitrile, it is found that polymerizations with aged “Cr2++ BPO” proceed via a free radical intermediate. The polymerization rates (Rp) of MMA at 25 and 30°C are expressed by the following relation, Rp= const.[aged “Cr2++BPO”]0.7–1.0[MMA].The mechanism of a “living” radical polymerization is discussed in terms of a transition metal complex with free radicals.

Anionic homogeneous polymerization of acrylonitrile and methacrylonitrile by quaternary ammonium hydroxides

AbstractAqueous solutions of quaternary ammonium hydroxides were used, for the first time, as initiators for the anionic homogenous polymerization of acrylonitrile and methacrylonitrile in dimethylformamide. The molecular weight of polyacrylonitrile was independent of catalyst and monomer concentrations, while that of polymethacrylonitrile increased linearly with monomer concentration. Infrared spectra showed the presence of primary alcohol groups in both polyacrylonitrile and polymethacrylonitrile. Polyacrylonitrile contained terminal double bonds which were absent in the methacrylonitrile polymers. On the basis of these and additional evidence, initiation by hydroxyl anion and termination by chain transfer to monomer is suggested for acrylonitrile polymerization; while termination of methacrylonitrile polymerization is by water. Molecular weight decreased with increase in size and electropositivity of the quaternary ammonium positive counterion in the following order: (CH3)4NOH > (C2H5)4NOH > (CH3)3C6H5CH2NOH.

The molecular weight of polyacrylonitrile

AbstractThere is a surprising lack of agreement between the values which have been reported for both the number‐average and weight‐average molecular weights of polyacrylonitrile. We have undertaken an investigation of both whole polymers and polymer fractions to discover and eliminate the sources of systematic error which would lead to these differences, and thereby to develop procedures yielding reliable molecular weight values for this polymer. Our experience indicates that the procedure which must be followed to obtain reliable osmotic data depends upon the conditions under which the polymer was prepared, whether the sample is a whole polymer or a fraction, and the purity of the solvent. Designating solution polymers by S and those prepared in an aqueous system with a persulfate‐bisulfite initiator by A, we conclude that reliable M̄n values can be obtained for S polymers by using dimethylformaide (DMF) which has been purified by deionization or distillation, for fractions of A polymers by using deionized DMF, and for whole A polymers by performing the measurements upon DMF solutions which have been deionized by passage through a column of Amberlite MB‐3 resin. Fictitiously low M̄n values are observed for A polymers dissolved in distilled DMF. The value of the secon virial coefficient is very ensitive to the presence of traces of water. Turning to weight‐average molecular weights, a 60% discrepancy exists between the values obtained from light scattering by Stockmayer and Casassa and by Bisschops from sedimentationdiffusion. We believe the correct M̄w values lie midway between these. A part of the 60% difference is due to the omission of a correction to the sedimentation data for the effect of hydrostatic pressure. This correction was evaluated from sedimentation data by the procedure of Oth and Desreux and increases the molecular weight values deduced from sedimentation by 30%. The remainder of the difference appears to be due to the effects of depolarization and fluorescence upon the light scattering data. Thus, our data for two fractions which exhibited a limiting depolarization ρu = 0.09 yielded high M̄w values standing in agreement with the relation of Stockmayer and Casassa, while the result obtained for a whole polymer having a negligible limiting depolarization agrees with those obtained from the corrected sedimentation data. The latter polymer also exhibited a more normal scattering behavior. A comparison of the weight and number‐average values indicates that the M̄w/M̄n ratio is 2.1 ± 0.1 for the whole S polymers and 2.8 ± 0.3 for the whole A polymers. The broader distribution in the latter case suggests that termination occurs by both coupling and disproportionation in the aqueous polymerization.

Polymerization of Olefins with Trialkylboron Catalysts. I. Polymerization of Vinylchloride and Acrylonitrile

Abstract It was found that trialkylboron is an excellent catalyst for the polymerization to some olefins which have comparatively large polarities. Vinylchloride and acrylonitrile were polymerized with this catalyst at a comparatively low temperature, and white polymers were usually obtained. Vinylchloride was polymerized in bulksolution- and emulsion-system, and the rate of polymerization or the relation between the yield and the concentration of catalyst was investigated. Generally, the molecular weight of the polyvinylchloride was small (less than 50,000). The polymerization of acrylonitrile was studied chiefly in a solution system. Usually, the molecular weight of polyacrylonitrile was fairly large.