P. Bajaj

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.

Modification of Acrylic Fibers: An Overview

Abstract Among the vinyl monomers, acrylonitrile is the only monomer used for the production of synthetic fibers. Other vinyl monomers lack cohesive forces between the molecular chains of their polymers and, hence, can not compete with acrylonitrile [1]. Acrylic fiber has replaced wool in many major applications, particularly in hand knitting and hosiery garments. The majority of knitting yarns are usually bulky yarns which go into the manufacture of pullovers, sweaters, socks, etc. Acrylic fiber has been able to replace wool considerably in these applications. Blankets and carpets are other applications where acrylic fiber competes with wool [2] because of its high elasticity, color brilliancy, volumenosity, easy shampooing, resistance to pilling, good light and colorfastness values, etc.

Waterproof Breathable Polymeric Coatings Based on Polyurethanes

The performance of environmentally friendly water-based polyurethane dispersions (PUD) for waterproof breathable coating was studied. The effect of the nature of PUD, number of coatings, incorporation of additives, and processing conditions on the breathable properties of cotton fabric was evaluated. The relative proportions of hydrophilic and hydrophobic components had a direct influence on the breathable properties of the coated cotton samples. The increase in hydrophilic component resulted in an increased water vapor penetration and lower water resistance to water penetration in the coated samples. For all the compositions, the durability of the coatings was found to improve with the incorporation of polymeric binder in the coating formulation. The air permeability values of the coated samples were found to be orders of magnitude lower than the control (uncoated) fabric sample.

Structural investigations on hydrolyzed acrylonitrile terpolymers

Abstract Fibre forming terpolymers, containing acrylonitrile with vinyl acetate or methyl acrylate, and sodium methallyl sulphonate as a third comonomer, were hydrolyzed with H2SO4 (75% v/v) at 0° for 1–2 hr, and NaOH (5% w/v) at 40° for 1–4 hr, to study the influence of the comonomer on the extent of hydrolysis. Elemental analysis and i.r. spectroscopy were used to quantify the nitrile and amide-imide groups formed during hydrolysis. The induction period was longer in AN-vinyl acetate-sodium methallyl sulphonate terpolymer but the extent of hydrolysis approached the same value in the two terpolymers at the end of the reaction. 1H-NMR and 13C-NMR were employed to study the structural changes during the hydrolysis. The tacticity determinations through 13C-NMR revealed that there was a decrease in the ratio of isotactic to syndiotactic nitrile triads as the hydrolysis proceeded in the two terpolymers.

Saponification kinetics of acrylonitrile terpolymer and polyacrylonitrile

Abstract Saponification kinetics of acrylic terpolymer and polyacrylonitrile were studied. The influence of alkali concentration and the time of hydrolysis on the degree of saponification were determined by the residual nitrogen content. The order of reaction was graphically determined and the rate of saponification was found to be faster in the terpolymer than in the homopolymer. Chemical and infrared spectroscopy methods reveal that the reaction is initiated through cyclization of nitrile groups, followed by hydrolysis to amide and carboxylic groups of the [sbnd](C[dbnd]N)n[sbnd] segments produced. The saponification of nitrile groups in the terpolymer initially yields amide groups, then slows down to yield carboxylic groups.

Copolymerization of styrene and acrylonitrile with functional silanes

Styrene has been copolymerized to high conversions with vinylmethyl diacetoxysilane (VMDAS) and vinylmethyldiethoxysilane (VMDES) in bulk and in toluene at 60 using azobisisobutyronitrile (AIBN) as initiator. Acrylonitrile has also been copolymerized with VMDAS at 50 in bulk using AIBN. The compositions of the copolymers were determined from the silicon contents; reactivity ratios were calculated by the Kelen-Tudos method. The reactivity ratio r1 (styrene) is higher for styrene-VMDES than for styrene-VMDAS, indicating higher reactivity of VMDAS towards polystyryl radical. VMDAS was found to be more reactive towards the polyacrylonitrile than towards the polystyrene radical. The influences of the silicon comonomer on properties such as intrinsic viscosity, solubility, molecular weight distribution and thermal behaviour were also studied.

Configurational sequence lengths in polyacrylonitrile and poly(acrylonitrile-CO-haloalkyl acrylate/methacrylate)s determined by 13C n.m.r.

Abstract The tacticity and number average sequence length of like ( n o ), meso ( n m ) and racemic ( n r ) acrylonitrile (AN) triad units in polyacrylonitrile (PAN) prepared in both water and water—acetone (2:1 v/v) media and AN-3-chloro, 2-hydroxypropyl acrylate/methacrylate, AN-2-bromoethyl methacrylate and AN-2-chloroethyl acrylate copolymers have been calculated using 13C n.m.r. spectra of the polymer solutions concerned at a field strength of 24.99 MHz. The spectra reveal that PAN prepared in water medium has a greater percentage (33.4%) of isotactic units than PAN prepared in water-acetone (2:1 v/v) medium (28.3%). The tacticity distribution of AN sequences in PAN and the copolymers is found to be random ( n m ⋍ n r ⋍2.0 ) and the number average sequence length of AN sequences in a copolymer containing 14.8 mole% of 3-chloro, 2-hydroxypropyl methacrylate was 15.2.

Influence of Spinning Dope Additives and Spin Bath Temperature on the Structure and Physical Properties of Acrylic Fibers

We have studied the effect of spinning dope additives and spin bath temperatures on the structure and properties of wet spun acrylic fibers. The dope additives were secondary cellulose acetate, polyvinyl pyrrolidone, polyvinyl acetate, and glycerol. Amounts of 5% (w/w) of each of these were added to the spinning dope of acrylonitrile vinyl acetate sodium methallyl sulphonate (92.7:7.0:0.3 by wt) terpolymer, and wet spun using 45:50 (v/v) of dimethyl acetamide : water, varying the spin bath temper ature from 10 to 60°C. Fibers with 5% secondary cellulose acetate as an additive exhibited low density values, highest moisture regain (2.6% against 1.6% of the parent acrylic fiber), and a three- to four-fold increase in water retention values. The tenacity was greatest in fibers with 5% polyvinyl acetate, added and spun at a 45°C spin bath temperature. We also studied the microstructure of the protofibers and the final fibers using both optical and elecqon microscopy for a better understanding of the effect of spin bath temperature on physicomechanical properties.

Physicomechanical Properties of Fibers from Blends of Acrylonitrile Terpolymer and Its Hydrolyzed Products

Acrylonitrile terpolymer containing 92.7% acrylonitrile, 7% vinyl acetate, and 0.3% sodium methallyl sulphonate was hydrolyzed to degrees of hydrolysis of ∼0.104(T1B 1), ∼0.367 (T1B2), and ∼0.450 (T 1B3), respectively, at 40°C with 5% NaOH. Each of these polymers was blended with the parent terpolymer in a 10:90 ( w/w ) ratio and wet-spun using 45:50 (v/v) dimethyl acetamide : water, varying the spin bath tem perature from 10-60°C. The dope viscosity of the blends increased with the increase in the degree of hydrolysis of the product, which could be attributed to the bulky amide-imide groups. Spinnability was the best in a blend containing T1B3. After au toclaving, these fibers showed higher tenacity (174 kN·m/kg) and moisture regain (1.8%) compared to the parent fibers (124 kN·m/kg and 1.3%) and other blends. The influence of the bath temperature on the structure of the protofibers was also investigated.

Flame Retardant, Durable Press Finishes for Cotton and Polyester/Cellulosic Blends

Diammonium hydrogen phosphate (DAP) and N-methylol resins were applied to cotton and polyester/cellulosic blends using one step and two step sequential pad- dry-cure processes. Among the N-methylol resins studied, only urea formaldehyde treatment on phosphorylated cotton demonstrated the phenomenon of N-P synergism in terms of oxygen index, while no clear trend could be established in blends. The 45° angle burning rate at atmospheric oxygen concentration was accelerated by a trimethylol melamine treatment on phosphorylated cotton, while post-treatment with the same resin produced a slight retardation in the burning rate in 48/52 polyester/ viscose with respect to DAP treatment alone.