PAN Homopolymer Research Articles

Preparation of superhydrophilic poly(acrylonitrile/acrylic acid) electrospun membrane and its application in oil/water separation

Copolymer consisting of acrylonitrile (AN) and acrylic acid (AA) segments with different molar ratios were synthesized via a mixed-solvent precipitation polymerization method. The prepared polymer was then applied to fabricate nanofiber membrane via electrospinning technique. It was found that when the molar ratio of AN/AA was 80/20, the resultant membrane presented outstanding hydrophilicity with a water contact angle of 0° and water adsorption ratio of 17.10. In addition, the breaking force of optimized membrane was increased by more than 60% when comparing with those of pure PAN homopolymer counterpart due to the hydrogen bonding interaction resulting from the carboxyl groups in AA chain segments. The developed membrane possessed fascinating underwater oleophobicity with oil contact angle over 150° and could effectively separate oil/water mixture and oil-in-water emulsion with excellent separation efficiency beyond 95%, ascribing to the hydration layer on the membrane surface and size-sieving effect arising from the multi-scale pore size in the material. The current study provides a novel insight into the fabrication of hydrophilic membrane for oily wastewater treatment for practical applications.

Property and Structure Characterization of High Molecular Weight Polyacrylonitrile Polymers Initiated by 2,2'-Azobis (2-methyl propionamide) Dihydrochloride Using Aqueous Deposited Polymerization Technique

Powdery high molecular weight polyacrylonitrile (HMW-PAN) polymers were successfully synthesized by aqueous deposited polymerization (ADP) method with 2,2'-azobis (2-methyl propionamide) dihydrochloride (AIBA) as the initiator and itaconic acid (IA) as comonomer. The utilization of IA into the ADP system was conducive to relax the proceeding of thermo-oxidation process. Differential scanning calorimeter (DSC) curves of obtained PAN copolymers showed the doublet peaks character under air atmosphere, attributing to the exothermic cyclization and oxidative reactions during heat-treatment process. With the utilization of IA in the reaction system, crystallinity and grain sizes of the PAN polymers decreased. The stretching vibration of nitrile group (C≡N) at 2240cm-1 was the strongest peak in both Fourier transform infrared spectra (FTIR). And the stretching vibration and bending of CH2 were the stronger peaks in FTIR. Amido group (NH2), carbonyl group (C=O) and C-O single bond existed in FTIR of PAN homopolymer and copolymers, indicating occurrence of C≡N hydrolysis during polymerization process except carboxyl group (COOH) introduced by IA.

Preparation and Stabilization of High Molecular Weight Poly (acrylonitrile-co-2-methylenesuccinamic acid) for Carbon Fiber Precursor.

Bifunctional comonomer 2-methylenesuccinamic acid (MLA) was designed and synthesized to prepare acrylonitrile copolymer P (AN-co-MLA) using mixed solvent polymerization as a carbon fiber precursor. The effect of monomer feed ratios on the structure and stabilization were characterized by elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), X-ray diffraction (XRD), proton nuclear magnetic (1H NMR), and differential scanning calorimetry (DSC) for the P (AN-co-MLA) copolymers. The results indicated that both the conversion and molecular weight of polymerization reduce gradually when the MLA content is increased in the feed and that bifunctional comonomer MLA possesses a larger reactivity ratio than acrylonitrile (AN). P (AN-co-MLA) shows improved stabilization compared to the PAN homopolymer and poly (acrylonitrile-acrylic acid-methacrylic acid) [P (AN-AA-MA)], showing features such as lower initiation temperature, smaller cyclic activation energy, wider exothermic peak, and a larger stabilization degree, which are due to the ionic cyclization reaction initiated by MLA, confirming that the as-prepared P (AN-co-MLA) is the potential precursor for high-performance carbon fiber.

High molecular weight of poly(acrylonitrile-co-3-aminocarbonyl-3-butenoic acid methyl ester) used as carbon fiber precursor: preparation and stabilization

A bifunctional 3-aminocarbonyl-3-butenoic acid methyl ester (ABM) was used to prepare high molecular weight poly(acrylonitrile-co-3-aminocarbonyl-3-butenoic acid methyl ester) [P(AN-co-ABM)] by suspension polymerization in aqueous medium. The influence of ABM monomer feed ratios on the structure and stabilization of P(AN-co-ABM) was characterized by element analysis, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Based on reactivity ratio calculation, the comonomer ABM possesses greater reactivity than acrylonitrile. The molecular weight of P(AN-co-ABM) in this work is 10 times larger, as compared to the one prepared by solution polymerization; it is the key to producing high-performance carbon fiber. The FTIR, XRD and DSC results illustrate that the stabilization of P(AN-co-ABM) is significantly improved as compared with PAN homopolymer and P(AN-AA-MA), for instance, lower initiation temperature, smaller cyclization activation energy (Ea), broadened exothermic peak and larger stabilization extent, due to the ionic cyclization initiated by ABM, which makes the resultant P(AN-co-ABM) a potential precursor for carbon fiber.

Chitosan-g-poly (acrylonitrile-co-acrylic acid) for wastewater treatment application

Chitosan is a biodegradable natural based polymer obtained from chitin (N-deacetylated derivative), the second most abundant polysaccharide after cellulose and soluble in most organic acids. Graft copolymerization of poly (acrylonitrile-co-acrylic acid) onto chitosan has been successfully carried out using potassium persulfate as an initiator in an aqueous medium. The PAN and PAA homopolymer formed during the reaction were removed from the Chitosan grafted copolymer by Soxhlet extraction using ethanol as the solvent. The prepared graft copolymerization was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) to confirm the formation of the copolymer. The prepared chitosan-g-copolymer at ratio 25:75% of AN-co-AA was treated with metal solutions containing cadmium ions, times and pH at room temperature. It[Am1] was found that the optimum condition was pH=5, Time 120min and dose of adsorbent 3 mg /L. The results revealed that the chitosan-g-copolymer prepared was excellent in removing the heavy metals than the copolymer alone. Hence, chitosan-g- poly- AN-co-AA could open the way for wastewater treatment. The thermal stability and the electrical conductivity for all prepared samples before and after grafing were measured. By studying the thermal stability at the different ratio of AN and AA in samples co1, co2, co3, it was found that the most thermal stability sample ratio is co3 due to increasing the ratio of AN. While in sample co1 with a high ratio of AA, the thermal stability decrease according to the fast decomposition of –COOH of acrylic acid. The conductivity was 3.85x10-7 which is more than the copolymer without chitosan, which increases the electron density of the copolymer through the end group effect. As the result of σ has a range 10-8 S/cm-1 10-6 S/cm-1so, all the prepared sample can be used as an electrostatic dissipation application.

The mechanism of thermal stabilization of polyacrylonitrile

The two-step stabilization of a thoroughly characterized PAN homopolymer was studied by various methods including thermogravimetric analysis (TGA), evolved gas analysis (EGA), differential scanning calorimetry (DSC), Fourier transformed infrared spectroscopy (FTIR), oxygen microanalysis and theoretical energy calculations. Stabilization was carried out with pre-treatment in inert atmosphere, and the reactions taking place as well as the structure of the polymer formed were compared to those occurring in one-step (direct) oxidation. Five separate exothermic regions were detected in DSC measurements and they were assigned to seven reaction steps, for which appropriate mechanisms were proposed together with the relationship among individual reactions. The effect of stereoregularity on ring formation is discussed and a new scheme is suggested, which includes the cyclization of alternating nitrile groups in the gauche conformation. The number of successive rings formed during cyclization is determined with three independent methods and compared to previous concepts reported in the literature. The positive effect of pre-treatment in inert atmosphere on the structural stability of PAN during the subsequent pre-carbonization treatment is also demonstrated and explained by considering the mechanism of the reactions taking place during the process.

Spectroscopic Analyses on Chain Structure and Thermal Stabilization Behavior of Acrylonitrile/Methyl Acrylate/Itaconic Acid-based Copolymers Synthesized by Aqueous Suspension Polymerization

We have synthesized a series of copolymers with different compositions of acrylonitrile (AN, 80–100 wt%), methyl acrylate (MA, 4–20 wt%) and itaconic acid (IA, 0–3 wt%) by using an efficient aqueous suspension polymerization, and have investigated the molecular structure and thermal stabilization behavior of PAN homopolymer, AN/MA-based bipolymers, and AN/MA/IA-based terpolymers by adopting 1H/13C-NMR and thermal FT-IR analyses. The viscosity-average molecular weight of the synthesized polymers were measured to be ~263,000 g/mol. The reactivity ratios of AN and MA for all the copolymers were evaluated to be 0.99 and 1.05, respectively. Accordingly, the output compositions of the synthesized copolymers were quite consistent with the input monomer compositions. The 13C NMR analysis revealed that all the synthesized polymers have an atactic chain configuration, regardless of the feed composition. The structural evolutions during the thermal stabilization process of the copolymers in air environment were characterized by monitoring the temperature-dependent changes of characteristic absorbance bands at 2240 cm-1 (C≡N), 1595 cm-1 (C=N) and 1660 cm-1 (C=O) with aid of thermal FT-IR spectroscopy. It was found that the IA unit in the terpolymers accelerated the oxidation and cyclization reactions, unlike the retarding effect of MA unit, and that the onset temperatures of the oxidation reaction of the copolymers with IA unit was lower than that of the cyclization reaction.

A high molecular weight acrylonitrile copolymer prepared by mixed solvents polymerization: II. effect of DMSO/water ratios on polymerization and stabilization

A bifunctional comonomer β-methylhydrogen itaconate was synthesized to prepare high molecular weight poly [acrylonitrile-co-(β-methylhydrogen itaconate)] [P (AN-co-MHI)] by mixed solvents polymerization, which was used as carbon fiber precursor instead of acrylonitrile terpolymers. The effect of dimethyl sulfoxide (DMSO)/deionized water ratios on the polymerization, structure and stabilization of P (AN-co-MHI) was studied by elemental analysis, UV-Visible Spectroscopy, fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The highest viscosity-average molecular weight (76.72 × 104 g/mol) of P(AN-co-MHI) was obtained in the mixed solvents of DMSO/deionized water = 10/90 (wt/wt) due to the zero chain transfer constant of deionized water for radical ~ ~ ~AN·, which is 10 times larger than that of P(AN-co-MHI) copolymers prepared in DMSO solution polymerization under the same conditions and is beneficial to improving the tensile strength of resulting carbon fiber. The composition of P(AN-co-MHI) was controlled by the ratio of DMSO/deionized water in the mixed solvents, it is attributed to the changes of AN/MHI ratio taking part in the polymerization reactions, which is caused by the different solubility of AN in the mixed solvents. From elemental analysis and FTIR studies, it can be found out that the content of MHI in P(AN-co-MHI) copolymer becomes larger with the increase of DMSO content in the mixed solvents. The FTIR, XRD and DSC results show that the stabilization of P(AN-co-MHI) copolymer was significantly improved by MHI compared with PAN homopolymer and poly (acrlonitrile-methyl acrylate-acrylic acid) terpolymer, such as larger extent of stabilization, lower initiation temperature and smaller Ea of cyclization, which is beneficial to preparing high performance carbon fiber.

Effect of comonomer on the viscoelastic behavior of co-poly (acrylonitrile) solutions

Three copolymers of acrylonitrile-methacrylic acid [P(AN-co-MAA)], acrylonitrile-ammonium salt of methacrylic acid [P(AN-co-AMA)], acrylonitrile-methacrylamide-itaconic acid [P(AN-MAM-IA)] and PAN homopolymer were synthesized by aqueous dispersion polymerization technique. The polymerization conditions were adjusted in such a way to produce polymers with similar composition and molecular weight. The influence of comonomer nature on the viscoelastic behavior and spinnability of copolymer/dimethylsulfoxide (DMSO) solutions were investigated. It was found that incorporation of these comonomers into PAN chains led to intense decrease in zero-shear viscosity to lower value as well as appearance of distinct plateau in comparison with PAN homopolymer. However, comparing the results of complex viscosity and shear viscosity of each PAN polymer showed different shear-thinning behavior, typical deviation from Cox-Merz rule at high deformation rates. Amongst these copolymer solutions, P(AN-co-AMA) exhibited the longest relaxation time (λ) at low and medium frequencies. The lower values of frequency dependence of G′ (n′) and cross over frequency (ωc) of storage modulus (G′) and loss modulus (G″) indicated that P(AN-co-AMA) was more elastic than other PAN copolymer solutions. The log-log plots of tan δ versus ω demonstrated that the comonomer nature affects the sol-gel transition behavior and elastic character of copolymer solutions. On average, based upon the slope of logGʹ versus logGʺ data, the incorporation of comonomers inside PAN chains led to ~50 % increase in the homogeneity of solutions compared to PAN homopolymer.

Poly (acrylonitrile-co-methyl methacrylate) nanoparticles: I. Preparation and characterization

This work concerns the preparation and characterization of poly (acrylonitrile-co-methyl methacrylate) Copolymer, P(AN-co-MMA), nano-particles using precipitation polymerization technique. Potassium per-sulfate redox initiation system was used to perform polymerization process in an alcoholic aqueous system. The impact of different polymerization conditions such as comonomer concentration and ratio, polymerization time, polymerization temperatures, initiator concentration and co-solvent composition on the polymerization yield and particle size was studied. Maximum polymerization yield, 70%, was obtained with MMA:AN (90%:10%) comonomer composition. Particle sizes ranging from 16nm to 1483nm were obtained and controlled by variation of polymerization conditions. The co-polymerization process was approved by FT-IR and TGA analysis. The copolymer composition was investigated by nitrogen content analysis. Copolymers with a progressive percentage of PAN show thermal stabilities close to PAN Homopolymer. SEM photographs prove spherical structure of the produced copolymers. The investigated system shows promising future in the preparation of nanoparticles from comonomers without using emulsifiers or dispersive agents.

A high molecular weight acrylonitrile copolymer prepared by mixed solvent polymerization: I. effect of monomer feed ratios on polymerization and stabilization

A bifunctional comonomer β-methylhydrogen itaconate (MHI) was employed to prepare high molecular weight poly[acrylonitrile-co-(β-methylhydrogen itaconate)] [P(AN-co-MHI)] copolymers by radical polymerization in a mixed solvent of dimethyl sulfoxide/deionized water = 60/40 (wt/wt), which was used as a carbon fiber precursor instead of acrylonitrile terpolymers for improving the stabilization and spinnability simultaneously. The structure and stabilization of P(AN-co-MHI) copolymers with different monomer feed ratios were characterized by elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results show that both the polymerization conversion and molecular weight reduce with the increase of MHI content in the feed due to the larger molecular volume of MHI. The monomer reactivity ratios were calculated by Fineman–Ross and Kelen–Tüdõs methods and the reactivity of MHI is higher than that of AN. Two parameters Es = A1618 cm−1/A2244 cm−1 and SI = (I0 − Is)/I0 were defined to evaluate the extent of stabilization and the activation energy (Ea) of the cyclization. The FTIR, XRD and DSC results show that P(AN-co-MHI) copolymers exhibit significantly improved stabilization characteristics than the PAN homopolymer and poly(acrlonitrile–methyl acrylate–acrylic acid) terpolymer, such as a larger extent of stabilization, lower initiation temperature and smaller Ea of cyclization, which is attributed to the ionic initiation of the MHI comonomer and is beneficial for preparing high performance carbon fiber.

Structure evolution and mechanism of polyacrylonitrile and related copolymers during the stabilization

The structure evolution and thermal behaviors of polyacrylonitrile homopolymer (PAN) and terpolymer [P(AN–MMA–IA)] containing about 4.19 wt% methyl methacrylate (MMA), 0.98 wt% itaconic acid (IA) and 94.83 wt% acrylonitrile (AN) during heat treatments were studied by Fourier transform infrared (FTIR), differential scanning calorimetry and thermogravimetry. It was found that the presence of IA comonomer in PAN promoted the cyclization reactions significantly though initiating the cyclization reactions at lower temperature and proceeding at a faster rate than these of PAN homopolymer. Moreover, it was found that the dehydrogenation was based on the formation of cyclized structures. From the results of FTIR analysis, we found the MMA comonomer blocked the cyclization reactions to some extent. Extent of cyclization reactions at different temperatures was calculated through the data of FTIR. The sequence of reactions happened during the stabilization was oxidation > cyclization > dehydrogenation. The higher rate constant k implied that the ionic mechanism actually showed a kinetic advantage at low temperature over the free radical mechanism, even though the MMA comonomer inhibited cyclization reactions to some extent.

Preparation and thermal properties of poly[acrylonitrile-co-(β-methylhydrogen itaconate)] used as carbon fiber precursor

In order to replace terpolymer with bipolymer, a bifunctional comonomer β-methylhydrogen itaconate (MHI) containing carboxyl group and ester group was synthesized to prepare poly[acrylonitrile-co-(β-methylhydrogen itaconate)] [P(AN-co-MHI)] bipolymers used as carbon fiber precursor for improving the stabilization and spinnability at the same time. The P(AN-co-MHI) bipolymers with different monomer feed ratios were characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The results show that both the polymerization conversion and molecular mass of P(AN-co-MHI) reduce with the increasing MHI amounts in the feed due to the larger molecular volume of MHI than acrylonitrile (AN). The monomer reactivity ratios were calculated by Fineman–Ross and Kelen–Tudos methods, the results show good agreement and MHI possesses higher reactivity than AN. Two parameters \( E_{\text{s}} = A_{{1,629\,{\text{cm}}^{ - 1} }} /A_{{2,244\,{\text{cm}}^{ - 1} }} \) and \( SI = (I_{0} - I_{\text{S}} )/I_{0} \) were defined to evaluate the extent of stabilization, and the activation energy (Ea) of the cyclization was calculated by Kissinger method and Ozawa method. The FTIR, XRD, and DSC results show that P(AN-co-MHI) bipolymers exhibit significantly improved stabilization characteristics than PAN homopolymer, such as larger extent of stabilization, lower initiation temperature, and smaller Ea of cyclization, which is attributed to the ionic initiation by MHI comonomer and it is beneficial to preparing high-performance carbon fiber.

Preparation and Characterization of Poly (Acrylonitrile-co-1-Acryloylpyrrolidine- 2-Carboxylic Acid) with High Molecular Weight

1-acryloylpyrrolidine-2-carboxylic acid (APCA) monomer was copolymerized with acrylonitrile (AN) by aqueous suspension polymerization. High molecular weight (HMW) copolymers of AN and APCA [poly(AN-co-APCA)] with different copolymer composition were successfully prepared by employing azobisisobutyronitrile (AIBN) as initiator and polyvinyl alcohol (PVA) as dispersant in a H2O/N,N-dimethylformamide (DMF) mixture at 60°C. The PAN homopolymer and copolymers were characterized by elemental analysis (EA), nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The EA results indicated that the content of oxygen increased significantly in PAN copolymers with increasing APCA content. The APCA copolymer composition calculated from the EA was higher than that from 1H NMR spectra. The FTIR spectra of PAN and poly(AN-co-APCA) with different monomer ratios confirmed that the contents of APCA units in the copolymer chains increased with increasing APCA content in the feed. The DSC exotherms revealed that copolymerization with APCA could slow the rate of the exothermic reactions during the heat-treatment processes. The XRD results indicated that the PAN homopolymer and copolymers poorly crystallized and the crystallinity decreased with increasing APCA contents.

Preparation and evaluation of polyaniline and polypyrrole modified water‐dispersible conducting nanocomposites of polyacrylonitrile with silica

AbstractWater‐dispersible conducting nanocomposites were prepared by precipitating polyaniline (PANI)/polypyrrole (PPY) in an aqueous suspension of polyacrylonitrile–SiO2 (PAN–SiO2) via K2CrO4–NaAsO2 redox polymerization. Incorporation of PANI and PPY in the composites was confirmed by the FTIR spectrum. Scanning electron microscopic analyses for the PANI–(PAN–SiO2) and PPY–(PAN–SiO2) composites indicated formation of lumpy aggregates with irregular sizes. TEM analyses revealed formation of spherical particles with size ranging between 80 and 150 nm for PANI–(PAN–SiO2) nanocomposite and 75–150 nm for PPY‐(PAN‐SiO2) nanocomposites, respectively. Thermal stabilities of the PANI–(PAN–SiO2) and PPY–(PAN–SiO2) nanocomposites were higher than those of the individual base polymers. Conductivity values of PANI–(PAN–SiO2) nanocomposite (10−3 S cm−1) and PPY–(PAN–SiO2) nanocomposite (10−4 S cm−1) were remarkably improved relative to that for PAN homopolymer (>10−11 S cm−1). Both of these composites produced a permanently stable aqueous suspension when the polymerization was conducted in presence of nanodimensional SiO2 as a particulate dispersant. Copyright © 2004 Society of Chemical Industry

Thermal behavior of acrylonitrile carboxylic acid copolymers

AbstractPolyacrylonitrile (PAN) and copolymer of acrylonitrile–vinyl acids prepared by solution polymerization technique have been characterized by Differential Scanning Calorimetry (DSC) (under dynamic as well as isothermal conditions), themograviemetric analysis (TGA), and on‐line DSC‐FTIR spectroscopy. The DSC of copolymers was carried out at 5°C/min in nitrogen and air. In nitrogen atmosphere the DSC exotherm show a very sharp peak, whereas, in air atmosphere DSC exotherm is broad, and starts at a much lower temperature compared to what is observed in nitrogen atmosphere. The initiation temperature of PAN homopolymer is higher than that for the copolymers. For instance, the initiation temperature of PAN in air is 244°C, whereas, the onset of exothermic reaction is in the range of 172 to 218°C for acrylonitrile–vinyl acid copolymers. As the vinyl acid content increases the ΔH value reduces. The ΔH value of PAN in air was 7025 J/g, whereas, for P(AN‐AA) with 5.51 mol % of acid it was 3798 J/g. As the content of acrylic acid comonomer is increased to 17.51 mol % the value of ΔH decreases further to 1636 J/g. The same trend was observed with MAA and IA as well. DSC‐FTIR studies depict various chemical changes taking place during heat treatment of these copolymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 685–698, 2003

Evolution of structure and properties of PAN precursors during their conversion to carbon fibers

The formation and evolution of structure, and the changes of properties during the preoxidation, precarbonization, and carbonization of different PAN precursors were studied by the combination of DSC, FT-IR, SEM and some traditional measurements, such as density and mechanical properties of various fibers. The exothermic regime of polyacrylonitrile-based precursors made of acrylonitrile/itaconic acid (AN/IA) copolymers or acrylonitrile/acrylamide (AN/AM) copolymers is much broader and the cyclization reaction starts at lower temperature, compared to that of PAN homopolymer precursors, but AM appears to be more effective in separating the exothermic reactions corresponding to preoxidation stages in DSC curves as compared to IA. If AN/IA (97.5/2.5 w/w) precursors and AN/AM (97.5/2.5 w/w) precursors are designated as P1 and P2, respectively, the AM-containing commercial precursors (P3) are thermally more stable than the P2 ones, and the density of P3 is higher than that of P1 or P2. This may result from the difference of aggregation morphology among the original precursors, since it is dense for P3 precursors, whereas P2 and P1 precursors have some voids. The tensile strength of resultant carbon fibers from P3 precursors was better than that of carbon fibers from P2 or P1 after identical conditions of preoxidation are employed.

Effect of the Drawing Process on the Thermal Stability of Gelatine-polyacrylonitrile Graft Copolymer Fibres

The thermal stability of gelatine-polyacrylonitrile graft copolymers fibres obtained under various conditions of deformation has been studied. The thermal properties of examined fibres depend on the synthetic component of the fibre forming material – polyacrylonitrile which appears in the form of grafted PAN chains and PAN homopolymer. It was stated that the highest thermal stability have those fibres which formation process included two stages of drawing with the use of deformation close to the maximal values, with the value of the total draw ratio amounting to 691%. It should be supposed that with such a drawing process, already in its first stage, are created advantageous conditions for the formation of paracrystalline regions to a larger extent and their orientation along the fibre axis.

Thermal behaviour of acrylonitrile copolymers having methacrylic and itaconic acid comonomers

The effect of comonomers, methacrylic (MAA 3–6mol%) and itaconic acid (IA 2–3mol%) on the glass transition temperature, Tg, hydration melting and thermo-oxidative stabilization of acrylonitrile copolymers has been studied by differential scanning calorimetry (DSC). While, two Tg‘s were observed, near 70 and 140°C, for PAN homopolymer, copolymers showed another baseline shift below 70°C. The melting point, Tm, of PAN and copolymer, P(AN/IA) containing 3.2mol% of IA, has been reduced to 186 and 158°C, respectively, in high-pressure DSC. The copolymers showed two distinct melting peaks in the first heating cycle, but the melt on subsequent cooling exhibited a single exotherm due to crystallization. The melting point of IA copolymer (158°C) was found to be lower than that of MAA copolymer (164°C) and PAN homopolymer (186°C). Tm further decreases with increase in the comonomer content. In the second heating cycle, observed Tm is higher than that noted in the first heating run, indicating some amount of physical transformations. The enthalpy of fusion, ΔHf decreases with the incorporation of comonomers, e.g. it is maximum for PAN homopolymer (57.8Jg−1) and minimum for P(AN/IA) copolymer (26Jg−1) having 3.2mol% of IA content. The lower entropy of fusion (ΔSf) of copolymers indicates that they are less mobile in the molten state. DSC of copolymers run in air atmosphere, at a heating rate of 10°Cmin−1, shows a broader exotherm compared to homopolymer. But, the broadening of exotherm seems to be more in P(AN/IA) polymers than P(AN/MAA) and the onset of cyclization shifts to a lower temperature as compared to PAN. The activation energy of nitrile cyclization, Ea, for PAN is found to be 30kcalmol−1. For copolymer P(AN/IA), IA=3.2mol%, Ea is 18kcalmol−1.

Effect of reaction medium on radical copolymerization of acrylonitrile with vinyl acids

Radical polymerization of acrylonitrile (AN) with methacrylic acid (MAA) and itaconic acid (IA) was carried out in a mixture of dimethylformamide (DMF) and water at 70°C using α, α′-azobisisobutyronitrile (AIBN) as an initiator. Monomer feed in the polymerization vessel was 98:2 (AN:MAA/IA) in the molar ratio, and the DMF:H2O ratio was varied between 20:80 and 80:20 (w/w). Copolymers were characterized by FTIR, carbon, hydrogen, nitrogen elemental CHN analysis, 1H- and 13C-NMR, and viscometry. The rate of polymerization (Rp) was found to decrease with an increase in DMF concentration in the reaction medium, that is, in 20% DMF for AN–MAA system, the Rp is 1.23% min−1 in 1 h of polymerization, while in 80% DMF, Rp is reduced to 0.37% min−1. The nature of the vinyl acid also affects the Rp. It has been shown that the rate of polymerization is higher for an AN–MAA system as compared to an AN–IA system (Rp = 1.0% min−1) and the methacrylic or itaconic acid content in the copolymer increases with an increase in the DMF concentration. The MAA content in the poly(AN–MAA) polymer produced in 20% DMF is 3.2 mol %, which increases to 6.1 mol % (calculated through FTIR spectra) when DMF is increased to 80% in the reaction medium. The intrinsic viscosity [η] of the poly(AN–IA) and poly(AN–MAA) copolymers in DMF was found to be in the range of 0.67–2.90 dLg−1 depending on the reaction medium. In determining the intrinsic viscosity, a definite deviation from rectilinearity of the concentration dependence in the high-dilution region is observed, thereby demonstrating the polyelectrolyte behavior of these polymers. Through FTIR and NMR spectral studies, PAN homopolymer and other copolymers have shown the formation of a small quantity of acrylamide units. In addition copolymer P10, which contains 10.1 mol % IA, has shown anhydride formation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1640–1652, 2001