Copolymerization of acrylic acid to nylon-6 by trapped radicals—I. Vapour phase grafting

Film of nylon-6 has been γ-irradiated in vacuo to various doses D. Grafting has been effected by subsequent exposure in vacuo to vapour at 50° of composition 9.1 wt% acrylic acid and 90.9 wt% water. Determinations have been made of total vapour uptake as well as the individual swellings due to monomer and water. For D ? ca. 2 Mrad, the initial rate of grafting R_g increased with D in accord with R_g ∝ D^β with β = 0.45 ± 0.05, thus suggesting bimolecular chain termination. However, for D ? ca. 2 Mrad, there is no further increase in R_g. This is attributed in part to the fact that the radical yield is proportional to dose only for D ? ca. 2.5 Mrad. Diffusion controlled grafting has been predicted elsewhere to be characterized by β = 0.67. Grafting proceeds from the surface and the initial stages are concluded to be essentially free from diffusion control, since (a) β ≠ 0.67, (b) the rate of uptake of monomer vapour >R_g and (c) a large change in film thickness yields only a very small change in R_g.     

Copolymerization of acrylic acid to nylon-6 by trapped radicals—II: Liquid phase grafting and properties of copolymers

Initial rates of grafting, R_g, have been determined for film of nylon-6, which had been -,,-irradiated in vacuo and subsequently immersed in outgassed, aqueous, acrylic acid at 50'. Equilibrium swellings due to water and to monomer are attained rapidly by nylon-6 and give rise to a high R_g. During grafting a constant swelling due to water occurs immediately but the rate of uptake of monomer is less than R_g, These effects are discussed on the basis of compatibility. At a fixed equilibrium monomer concentration, [AA], in the film, R_g ∝ D^β where D is the dose and β = 0.94. At a fixed dose, R_g ∝ [AA]^α where α = 1.04. The value of β indicates mainly monomolecular termination by radical burial. This is postulated to occur by trapping of growing grafts in crystalline regions and/or transfer from them to such regions. By selectively dyeing and sectioning films of different degrees of grafting (DG), the progress of the grafting front inwards has been shown to follow closely the corresponding grafting curve of DG vs time. Grafting does not alter the moisture regain of nylon. Surface resistance and swelling in water change with DG, the effect being enhanced markedly by converting the grafts to their sodium salts.     

Molecular weights of backbones in graft copolymers

Copolymerization of a monomer X with an existing polymer yields a copolymer contaminated by poly-X homopolymer and ungrafted polymer. Measurements on the pure copolymer can yield only the molecular weights of the cumulative backbone portion and of the cumulative graft portion. However, if the grafts can be isolated, then the molecular weights of their individual chains may be determined also. Since it is not isolatable, the backbone is not amenable to similar treatment. Equations are derived for the molecular weights (of any average) of individual backbone chains; they are expressed in terms of the following experimentally accessible quantities: (i) molecular weight of original polymer; (ii) molecular weight of ungrafted portion: and (iii) fraction by weight of the original polymer which remains ungrafted. The procedure is thus the analogue, applied to the backbone, of chemical isolation applied to the grafts. The treatment has been examined for copolymers prepared by grafting acrylic acid to nylon-6 by mutual irradiation.     

Kinetic aspects of the Diels-Alder reaction between poly(styrene-co-furfuryl methacrylate) and bismaleimide

The crosslinking Diels-Alder reaction between styrene-furfuryl methacrylate copolymer samples (poly(ST-co-FM)) and bismaleimide (BM) at 25 °C in chloroform was studied by following the decay in UV absorbance of the maleimide (MI) group at 320 nm. Reaction conditions were changed by using copolymers with different mole fraction of FM, F_FM, and by employing different initial molar ratios of reactants (furan group within FM and MI group within BM). Second order kinetics were obeyed. ¹³C NMR spectra showed that, even when all reactants had been converted to an insoluble crosslinked network, unreacted MI groups remained, presumably in the form of singly reacted pendant BM molecules. The fractions of MI groups remaining unreacted were found to be 0.49, 0.34 and 0.22 for FM:MI mole ratios in the initial mixture of 2, 1 and 0.5 respectively, when using a copolymer of F_FM=0.1354. An attempt was also made to follow the kinetics of network formation by ¹³C NMR spectroscopy, using the peak areas for reacted and unreacted MI and FM groups, but many of the findings were subject to some uncertainty for reasons, which are discussed. However, because the peak areas were considered reliable for unreacted MI groups, the rate constant, k, was evaluated, thereby. Overall using UV and NMR the values of k lay within the interval (0.8-3.6) × 10⁻⁵ dm³ mol⁻¹ s⁻¹.     

Observations on the swelling characteristics of the zwitterionic hydrogel of poly(1-3-sulfopropyl)-2-vinyl-pyridinium-betaine hydrogel

Samples of poly[1-(3-sulfopropyl)-2-vinyl-pyridinium-betaine] (PSPV) have been synthesized to high conversion by free radical polymerization in aqueous solution of the zwitterionic monomer SPV with several concentrations of the crosslinker N,N′-methylene-bis-acrylamide (MBA). The densities of the resultant xerogels increased regularly with the content of MBA. Hydrogels obtained by swelling them in water and aqueous KSCN solution were examined by gravimetric and dimensional analysis. The water contents increased with decreasing content of MBA, the value of 92.7 wt% at the lowest MBA content being higher than that for other zwitterionic hydrogels. Enhanced swelling occurred in 1 M aq. KSCN at each MBA content, the total swelling being 98.1 wt% at the lowest crosslinker content. Swelling increased with increasing temperature. An approximate procedure to formulating swelling equilibrium in term of the volume fraction of water in hydrogel, in conjunction with the van’t Hoff equation, yields a small positive value for the enthalpy of swelling. This is compared with values derived similarly for other hydrogels.     

CONTROLLING THE 3D NANOSCALE ORGANIZATION OF BULK HETEROJUNCTION POLYMER SOLAR CELLS

In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology acco...     

Selective adsorption to cellulose in cadoxen solution

Refractive index and density increments at constant composition and also at constant chemical potential have been measured on solutions of cellulose in alkaline aqueous cadoxen. Apparent and true molecular weights of cellulose in this solvent have been determined by light scattering. The findings indicate that [Cd(en)₃]²⁺ ions are preferentially adsorbed to the polymer to the average extent of two ions per three anhydroglucose subunits. Molecular models have shown that this effect is feasible sterically. In cadoxen alone the specific conductance increased with increasing concentration of cadmium and, for a fixed cadmium concentration, the specific conductance was observed to decrease with increasing concentration of dissolved cellulose. This was attributed to reduced overall ionic mobility resulting from selective adsorption of complex cadmium ions to the polymer chain. An analysis has been proposed to quantify this interaction.     

Some properties of polyethylene terephthalate-acrylic acid copolymers and ionomers

Acrylic acid has been grafted to polyethylene terephthalate (PET) by mutual irradiation, and the resulting copolymers converted to their sodium, calcium and lead salts. The electrical surface resistance of PET was reduced by grafting, the effect being most pronounced for the copolymer in the form of its sodium salt. The thermal stability of PET was studied by thermogravimetric analysis and differential thermal analysis, and activation energies were derived for the thermal decompositions; similar studies were made for the acidic and ionomeric copolymers. The stability of acidic copolymer was found to be lower than that of ungrafted PET; enhanced thermal stability was obtained only in the metallated copolymers.     

Network and thermodynamic properties of hydrogels of poly[1-(3-sulfopropyl)-2-vinyl-pyridinium-betaine]

Samples of poly[1-(3-sulfopropyl)-2-vinyl-pyridinium-betaine] (PSPV) have been synthesized to high conversion by free radical polymerization in aqueous solution of the zwitterionic monomer SPV with several concentrations of the crosslinker N,N′-methylene-bis-acrylamide (MBA). Hydrogels obtained by swelling them in water and aqueous KSCN solution were examined by gravimetric and dimensional analysis, and by compression-strain measurements. The derived effective crosslinking density ν_e was only ca. 11% of the theoretical value, indicating low efficiency of chemical crosslinking by MBA. At 298 K increasing content of MBA produces increases in the values of ν_e, elastic moduli and polymer-water interaction parameter χ. At a fixed MBA content, increasing temperature led to decreases in the values of ν_e, elastic moduli and χ, but an increase in water content of hydrogel. For swelling in aq. KSCN solution the mechanical properties are insensitive to content of salt. Experimental and theoretical analysis afforded values of the water/polymer, salt/water and salt/polymer interaction parameters. Where appropriate the findings are compared with those reported for a different zwitterionic hydrogel and a neutral non-zwitterionic hydrogel.