Correlations between the sol fraction and concentration of elastically active network chains

Relations between the concentration of elastically active network chains in the gel, v_eg, and the weight fraction of the gel, w_g′ have been examined in crosslinked systems obtained by stepwise alternating polyaddition of a mixture of a tri- and bi-functional monomer bearing one kind of functional groups to a bifunctional monomer bearing another kind of groups. A reduction factor has been found bringing the dependence between log v_eg and w_g almost to a single curve independent of the parameters characterising the initial composition of the system and conversion of the functional groups.     

Formation of a soluble hyperbranched polymer via initiator–fragment incorporation radical copolymerization of divinyl adipate and isobutyl vinyl ether

The copolymerization of divinyl adipate (DVA) with isobutyl vinyl ether (IBVE) was conducted at 70 and 80 °C in benzene using azobisisobutyronitrile (AIBN), at a concentration as high as 0.50 mol l^?1 as the initiator, where the concentrations of DVA and IBVE were 0.40 and 0.60 mol l^?1, respectively. The copolymerization proceeded homogeneously, without any gelation, to yield soluble copolymers in spite of the high molar ratio of DVA as an excellent cross‐linker for IBVE. The copolymer yield increased with time, and the number‐average molecular weight (M_n = 0.9–2.4 × 10⁴ g mol^?1) from gel permeation chromatography (GPC) and molecular weight distribution (M_w/M_n = 1.5–7.6) of the resulting copolymer increased with copolymer yield. The cyanopropyl group, as a fragment of AIBN, was incorporated as a main constituent in the copolymer, the fraction of which increased from ca 10 to ca 20 % with copolymer yield, hence indicating that the copolymerization is an initiator–fragment incorporation radical polymerization. The copolymers also contained IBVE units (10–30 %) and DVA units with intact double bond (8–36 %) and without double bond (45 %). The intrinsic viscosity of the copolymer was very low (0.1 dl g^?1) at 30 °C in tetrahydrofuran. The results from GPC–multi‐angle laser light scattering (MALLS), transmission electron microscopy (TEM) and MALLS revealed that individual copolymer molecules were formed as hyperbranched nanoparticles. Copyright © 2004 Society of Chemical Industry     

Characterization of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) biosynthesized by mixed microbial consortia fed fermented dairy manure

The bioplastic poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), was isolated from a bioreactor using mixed microbial consortia fed volatile fatty acids (VFA), from fermented dairy manure, as the carbon source. The molar fraction of 3‐hydroxyvalerate (3HV) amounted to 0.33 mol mol^?1 for two isolated PHBV samples as determined by GC‐MS and ¹H‐NMR spectroscopy. The chemical, thermal, and mechanical properties were determined. The PHBVs had relatively high M_w (～790,000 g mol^?1). Only a single glass transition temperature (T_g) and melting point (T_m) were observed. Isolated PHBVs exhibited good flexibility and elongation to break as compared with commercial PHBVs with lower HV. The diad and triad sequence distributions of the monomeric units were determined by ¹³C‐NMR spectroscopy and followed Bernoullian statistics suggesting that the PHBVs were random. The PHBV sequence distribution was also characterized by electrospray ionization‐mass spectrometry (ESI‐MSⁿ) after partial alkaline hydrolysis to oligomers showing a random 3HV distribution. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40333.     

Electrochemical measurements for studying the polymerization process and critical point behaviors of hydrogels

We propose a new technique based on electrochemical measurements for studying the critical point behaviors of the sol–gel transition of acrylamide–N,N′‐methylene bisacrylamide hydrogels. In this technique, no chemical activator is used for accelerating the polymerization reaction. However, a potential difference is applied by means of silver and calomel electrodes placed in the reaction mixture. The silver electrode begins to be ionized and loses its electrons. The free radicals, ^?O₃S? O^?, H^?, and ^?OH, form on the silver electrode via persulfate dissociation. The polymerization is initiated by means of these free radicals. The current measured during the gelation processes passes through a maximum (a Gaussian‐like behavior) and varies linearly with the reaction time during linear polymerization. All the parameters (the monomer, initiator, and crosslinker concentrations, the applied voltage, and the stirring rate of the reacting mixture) affecting the current have been studied in detail. We show that the maxima appearing in the current–time plots correspond to the gelation thresholds, the so‐called sol–gel transition points. We also analytically prove that the current monitors the weight‐average degree of polymerization (DP_w) and the gel fraction (G) below and above the threshold, respectively. The scaling behaviors of DP_w and G have been tested near the gelation thresholds, and we have observed that the critical exponents γ and β, defined for DP_w and G, agree with the predictions by mean‐field theory. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Branching by copolymerization of monovinyl and divinyl monomers in continuous-flow stirred reactors

The effect on molecular weight distribution of copolymerization with divinyl monomers, which leads to branch points in an otherwise linear polymer, is calculated for a continuous-flow stirred reactor. It is found that steady state operation of the reactor becomes impossible at a degree of branching equal to only half that which causes gellation in a batch reactor. In steady state operation the ratio of weight to number average degree of polymerization cannot exceed 7, this ratio being 2 in the absence of branching. The classical result that the fraction of mers coupled at the gel point is 1/(D?P_w)_o, where (D?P_w)_o is the weight-average degree of polymerization without branching, does not apply in a CFSR at any steady state conversion. Such deviations appear in batch reactions only when gelation occurs at high conversions.     

Swelling Behaviour of Cured Urea–Formaldehyde Resin Adhesives with Different Formaldehyde to Urea Mole Ratios

As a part of understanding of the network structure of urea–formaldehyde (UF) resin adhesives, this study examined the swelling behaviour of cured UF resin adhesives with four different formaldehyde–urea (F/U) mole ratios, using Flory–Rehner thermodynamic theory and field emission-scanning electron microscopy (FE-SEM) to relate the swelling behaviour to consequently induce micromorphological changes. Cured UF resin films before and after acetone extraction were exposed to swelling in dimethyl sulphoxide at three different temperatures. For the first time, this study reported the experimentally determined swelling parameters, such as sol fraction (ω_sol), polymer volume fraction (φ_p), polymer–solvent interaction parameter (χ), and the number average molecular weight between cross-links (M_c), for cured UF resin adhesives. Both ω_sol and M_c decreased as the F/U mole ratio increased. But these values increased with an increase in the swelling temperature. The extraction resulted in negative ω_sol values, suggesting the removal of a scattered distribution of ω_sol in the cured UF resins. The micromorphology helped to explain the differences in the molecular integrity of the resins, indicating a close relationship between the swelling behaviour and the morphological changes after the swelling.     

The maximum extent of reaction in gelled systems

Just how far reactions can go after gelation during the cure of telechelic prepolymers has been a debatable point for some time. Utilizing a recently devised method,⁷ the curing reactions of some telechelic prepolymers were followed after the gel point. Extents of reaction above 90% occurred only in systems of average functionality close to two, functionality being the average number of reactive groups per molecule. Among systems of higher functionality, maximum extents of reaction of about 70% were most common. The final extent of reaction was only a few per cent above the extent of reaction at the gel point. The maximum extent of reaction varied with the concentration of reactive species and the relationship was a linear one at each functionality of the system. The data were consistent with P_A²/r = {0.88/[(h ? 1)(j ? 1)]} + 0.10 where P_A is the fraction of prepolymer reactive groups initially present which have reacted, r is the ratio of the initial number of crosslinking groups to prepolymer reactive groups, and h and j are weighted average functionalities of the two reactants. It is suggested that the limiting factor in defining the final extent of reaction in these systems is the accessibility of reactive groups as determined by solid geometry rather than thermodynamics or reaction kinetics. The final extent of cure is regularly dependent on functionality and one cannot regard functionality and maximum extent of reaction as independent variables.     

A new perspective and comparative study on demixing and gelation behavior of cellulose acetate,cellulose acetate propionate and cellulose acetate butyrate ternary solutions

Cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) were fabricated as membrane via nonsolvent induced phase separation process. N,N‐Dimethylformamide (DMF) and N,N‐Dimethylacetamide (DMAc) as solvents and water as nonsolvent were employed. Ternary phase diagrams for all six ternary systems were constructed using Flory‐Huggins theory. In this way, cloud points as well as Berghman's points were determined. Modulus of polymers steepened in various concentration of solvent/nonsolvent mixtures were measured to find the weight fraction of polymer (w_p) in which vitrification takes place. W_P values for CA, CAP, and CAB were obtained 0.59, 0.67, and 0.74 in presence of DMF while those were 0.69, 0.74, and 0.84 in presence of DMAc; whereas glass transition temperatures (T_g) for three polymers were determined 180°C, 142°C, and 101°C correspondingly. Pure water flux for CA, CAP, and CAB membrane increased from 75.7 to 83.4 and 290.3 and from 109.6 to 116.1 and 400.3 L/m² h bar when DMF and DMAc were used as solvents, respectively. Results revealed that as T_g of polymer decreases, the membrane structure vitrifies at higher polymer concentration with more porous structure, bigger pores, higher permeate flux followed by decrease in mechanical strength. POLYM. ENG. SCI., 58:1135–1145, 2018. © 2017 Society of Plastics Engineers     

The Lewis Acid-Catalyzed Synthesis of Hyperbranched Oligo(glycerol–diacid)s in Aprotic Polar Media

The Lewis acid, titanium (IV) butoxide [15% (w/w; catalyst/reactants)], was used to catalyze the condensation of 0.05 mol glycerol with 0.10 mol of succinic acid, glutaric acid, and azelaic acid to produce oligomers. The reactions were refluxed in dilute solutions of dimethylsulfoxide (DMSO) or dimethylformamide (DMF) for 24 h. The oligomers were obtained, on average, in 84% yield and were soluble in polar organic solvents. Analysis by gel permeation chromatography determined that the oligomers had a number of average molecular weights (M _n ) ranging from 2,118 to 3,245 g/mol, with degrees of polymerization (DOP) ranging from 12.2 to 13.4 repeat units. The oligomers had low polydispersities (M _w /M _n ) that averaged ≈1.33. Degrees of branching were determined by one-dimensional and two-dimensional ¹H NMR and ¹³C NMR and varied from 25 to 80%. Like M _n and the DOP values, the degrees of branching were dependent on the aliphatic chain length of the diacid. MALDI-TOF mass spectrometry was used to detect ionated species that were unique to branched molecules. It was also used to validate NMR studies that suggested that some diacids were terminated with dimethylamine, generated from the hydrolysis of DMF, by as much as 36%.     

Preparation and properties of silicone‐containing poly(methyl methacrylate) gels

Poly(methyl methacrylate) (PMMA) gels with varying amounts of silicone and solvent and constant amounts of crosslinker were prepared by solution free radical crosslinking copolymerization of methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) comonomer systems. They were then studied in benzene at a total monomer concentration of 3.5 mol L^?1 and 70 °C. The conversion of monomer, volume swelling ratio, weight fraction and gel point were measured as a function of the reaction time, silicone concentration and benzene content up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in benzene, gel fraction and Fourier‐transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by SEM. Based on the obtained results, it was concluded that the FTIR data did not have the capacity to show the presence of the VTES or TEOS moiety in these kinds of copolymers. On the other hand, the variation of weight fraction of gel, W_g, and its equilibrium volume swelling ratio in benzene, q_v, exhibited the same behaviour as that of MMA/EGDM copolymers. Also, the dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percent of conversion and gel fraction. Finally, TEOS is not an ideal silicone compound for reaction in the MMA/EGDM copolymerization system, whereas VTES is a suitable silicone comonomer for this system and it has been proved useful. Copyright © 2005 Society of Chemical Industry     

Fermentative production of fumaric acid from Eucalyptus globulus wood hydrolyzates

Fumaric acid (FA) was produced from Eucalyptus globulus wood by successive steps of hydrothermal processing (to solubilize hemicelluloses and to increase the susceptibility of solids to enzymatic hydrolysis), enzymatic hydrolysis and fermentation with Rhizopus arrhizus DSM 5772. For comparative purposes, additional fermentations were carried out using synthetic media. Single stage fermentation of synthetic media led to a medium containing 11.8 g FA L^?1 (Y_P/S = 0.60 g g^?1). Operating in fed batch mode, the fourth stage increased the FA concentration from 19.7 up to 43.6 g L^?1 (Y_P/S = 0.71 g g^?1). Hydrolyzate fermentation in a single stage resulted in lower fumaric acid concentration (9.65 g L^?1) and yield (0.35 g g^?1). Additional fermentations were carried out in media made with hydrolyzates subjected to membrane processing, adsorption or ion exchange. The highest yield (Y_P/S = 0.44 g g^?1) was reached in media made up of ion‐exchange treated hydrolyzates and a commercial glucose solution in proportion 85/15 w/w. Copyright © 2011 Society of Chemical Industry     

Calculation of molecular parameters for stepwise polyfunctional polymerization

Our recursive method is extended to calculate several new parameters for stepwise polyfunctional polymerization. In the pregel region we calculate weight average molecular weight, M_w, for polydisperse reactants and effective average functionality, f_e, of a reacting mixture. These quantities are useful for systems employing reactive oligomers. We also calculate weight average number of branches per molecule, B_w, and the weight average of a longest chain. These should be useful for viscosity relations. In the postgel region we give relations for the extent of reaction in the soluble fraction. This result can be used to calculate sol properties directly from existing pregel relations. We also calculate the weight fraction of pendant chains on the gel, w_p, and the average molecular weight of the elastically effective network chains, M_c,w.     

The thermal,mechanical and viscoelastic properties of poly(butylene succinate-<Emphasis Type="Italic">co</Emphasis>-terephthalate) (PBST) copolyesters with high content of BT units

Poly(butylene succinate-co-terephthalate) (PBST) copolyesters, with rigid butylene terephthalate (BT) units varying from 50 to 70 mol%, were synthesized via direct esterification route. The chemical structure and comonomer composition were characterized by ¹H NMR. The weight-average molecular weights (M _w ) of the prepared products measured by GPC spanned a range of 1.39 × 10⁵–1.93 × 10⁵ with corresponding M _w /M _n value of 2.23–2.42. Based on the WAXD analysis, PBST copolyesters were identified to have the same crystal structure as that of poly(butylene terephthalate) (PBT). The researches on the thermal properties showed that the melting temperature and decomposed temperature of PBST copolyesters increased with the increasing content of rigid BT units through DSC and TGA measurement. Furthermore, the tensile test results presented that the copolyester with higher content of BT units had higher initial modulus, higher breaking strength but lower elongation at break. Additionally, the viscoelastic properties of the prepared PBST films were analyzed by DMA measurement. It was found that both storage modulus (E′) and loss modulus (E″) corresponding to the peak tended to heighten with the increase of BT units, indicating the copolyester with higher BT units content had the more prominent viscoelasticity. The peak of loss factor (tan δ) curve shifted to higher temperature as the content of rigid BT units increased due to the increasing of the glass transition temperature (T _g).     

Effects of functionality and temperature on gel points in random polymerisation

First, the relationship between gel point and average functionality for an RA₂+R′B_f type polymerisation has been investigated by measuring the product of extents of reaction at gelation (α_c) for sebacoyl chloride (SC)/polyoxyproplyene (POP)diol/POP triol mixtures reacting at various initial dilutions in diglyme as solvent at 60°C. Intramolecular reaction always delays gelation and a generalisation of the Ahmad-Stepto gel point expression has been used to interpret the gelation data in terms of the ring-forming parameter λ′_ab. From the variation of λ′_ab with initial dilution, values of b, the effective bond length of the chain forming the smallest ring structure, have been derived. It is found that b decreases with average polyol functionality (f_w). This decrease apparently compensates for the increase in λ′_ab with f_w, so that ring formation is less sensitive to functionality than may have been expected. It is found that the Ahmad-Stepto expression does not predict a consistent relationship between λ′_ab, f_w and the gel dilution of reactive groups. Second, the effect of temperature on the gel point has been studied by measuring α_c for SC/POP triol mixtures reacting at various initial dilutions in diglyme as solvent at 27° C, 40° C and 60° C. At a given temperature, b decreases as triol molar mass increases, indicating that the POP residue of the chain forming the smallest ring structure is more flexible than the SC residue. This result is in keeping with those from previous investigations,^1,2 For a given triol, α_c decreases as temperature increases, indicating an increase in chain stiffness with temperature. Values of d In <r²>/dT are derived and found to be larger than those for linear chains.     

Long-chain branching in low-density polyethylene

A sample of a commercial low-density polyethylene was fractionated and values of number ? M_n and weight-average M_w, molecular weights obtained together with intrinsic viscosities [η], measured in decalin at 135° and in a theta-solvent, diphenyl at 118°. Results are compared with those obtained using samples of high-density polyethylene, of narrow molecular weight distribution, in decalin at 135° and in diphenyl at 125°. Values of the z-average mean square radius of gyration (S^?2)_z, are converted to the weight-average unperturbed state. The branching parameters g and g¹ thus obtained, indicate that long-chain branching increases with increasing molecular weight. Intrinsic ivscosities under theta-conditions for the low-density polyethylene fractions lead to a relationship [η]_θ = K _w^0·20, agreeing with the treatment of Zimm and Kilb. Some of the approximations involved in the estimation of long-chain branching are discussed.     

Hydrophobic surface properties of fluoropolyetherimide blends for pervaporation membranes

The well‐known polyetherimide (ULTEM 1000) is obtained by step‐reaction of bisphenol. A diphthalic anhydride (BAPA) with m‐phenylene diamine and newly related fluorinated poly etherimides synthesized from BAPA and 2,3‐bis(2,2,3,3,4,4,5,5,5‐nonafluoropentyl)butan‐1,4 diamine (NFD) led to compatible blends over the entire range of composition. Miscible one‐phase blends have been suggested by a good correlation of T_g versus NFD monomer unit weight fraction (w) (Fox and Couchman equations) and a regular morphology by scanning electron microscopy. Surface energy of blend films fell from 45.3 to 27.4 mJ m^?2 for w ≥ 0.1 corresponding to a NFD molar fraction y ≥ 0.06. Cast‐evaporated films from fluorinated copolyetherimides and blends with y < 0.15 were ductile and gave conveniently hydrophobic non‐porous membranes that withstood the experimental conditions of pervaporation tests. Copyright © 2003 Society of Chemical Industry     

Effect of intramolecular cycles on the polycyclotrimerization of aromatic dicyanates

The gel conversions (α_gel) for the polycyclotrimerization of aromatic dicyanates are significantly higher than the classical mean-field value of 0.5. The reasons for the higher gel conversion, which is consistent with all experimental results of different structures of monomers, were inductively attributed to the accessibility effect of the functional group and the substitution effect, as well as the effect of the intramolecular cyclization. Nevertheless, the former two effects on the gel conversion can be quantitatively represented in terms of the extent of the intramolecular cyclization. Some theoretical expressions (including gel conversion and crosslink density with respect to the conversion) were derived by use of the recursive method with due consideration of the intramolecular cyclization. These expressions (with only one experimental parameter, α_gel) were found to be effective in describing gel fraction–conversion data for various polycyanurates. A dramatic change in the product value of ΔC_p · T_g was also found in the vicinity of the gel point for all different structures of aromatic dicyanate systems. The dramatic change in ΔC_p · T_g occurs at the gel point rather than the expected mean-field gel conversion of 0.5, presumably due to the intramolecular cyclization. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1927–1938, 1999     

Synthesis of poly(D,L‐lactic acid) modified by triethanolamine by direct melt copolycondensation and its characterization

Using D ,L ‐lactic acid (LA) and multifunctional group compound triethanolamine (TEA) as starting materials, a novel biodegradable material poly(D ,L ‐lactic acid‐triethanolamine) [P(LA‐TEA)] was directly synthesized by simpler and practical melt polycondensation. The appropriate synthetic condition was discussed in detail. When the molar feed ratio LA/TEA was 30/1, the optimal synthesis conditions were as follows: a prepolymerization time of 12 h; 0.5 weight percent (wt %) SnO catalyst; and melt copolycondensation for 8 h at 160°C, which gave a novel star‐shaped poly(D,L ‐lactic acid) (PDLLA) modified by TEA with the maximum intrinsic viscosity [η] 0.93 dL g⁻¹. The copolymer P(LA‐TEA) as a different molar feed ratio was characterized by [η], Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H‐NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). Increasing the molar feed ratio of LA/TEA, T_g and M_w increased. However, all copolymers were amorphous, and their T_g (12.2°C–32.5°C) were lower than that of homopolymer PDLLA. The biggest M_w was 9400 Da, which made the biodegradable polymer be potentially used as drug delivery carrier, tissue engineering material, and green finishing agent in textile industry. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Anaerobic co‐digestion of food waste leachate and piggery wastewater for methane production: statistical optimization of key process parameters

BACKGROUND: Anaerobic co‐digestion of refractory liquid organic wastes is an alternative environmental management strategy with economic benefits arising out of biogas production. Laboratory‐scale experimental investigations were carried out on the anaerobic co‐digestion of two liquid organic wastes, food waste leachate (FWL) and piggery wastewater (PWW). Three important parameters affecting methane yield were chosen for this study, namely, mixing ratio, alkalinity and salinity, which were optimized using response surface methodology. RESULTS: The results were analyzed statistically and the optimum conditions identified as: mixing ratio (FWL: PWW) 33 (in terms of volatile solid, w/w) (2 on v/v), alkalinity 2850 mg CaCO₃ L^?1, and salinity 3.4 g NaCl L^?1. Under the optimum conditions, a cumulative methane yield (CMY) of 310 mL CH₄ g^?1 VS_added and VS reduction (VSR) of 54% were predicted. Mixing ratio and alkalinity showed the greatest individual and interactive effects on CMY and VSR (P < 0.05). A confirmation experiment under optimum conditions showed a CMY and VSR of 323 mL CH₄ g^?1 VS_added and 50%, respectively. This was only 1.04% and 1.1%, respectively, different from the predicted values. CONCLUSION: Anaerobic co‐digestion of FWL and PWW carried out under the optimum condition may be a feasible and efficient treatment option for methane production. Copyright © 2012 Society of Chemical Industry