Grafting onto wool. IV. Interaction of polymer radicals in the viscous media of wool fibers

In order to study the termination reaction of polymer radicals in the viscous media of wool fibers, reduced, methylated, and S-carboxymethylated wool fibers were used for graft copolymerization of methyl methacrylate and styrene. With termination of poly(methyl methacrylate) radicals, two different termination reactions, recombination and disproportionation, were together involved in the grafting systems studied. The occurrences of two termination reactions in the system could be correlated with the mobility of the wool chain controlling the radical end mobility. With decreasing disulfide content in the fibers, disproportionation predominantly takes place among the mobilized chains. At a constant disulfide, the thiol content or the concentration of thiol anions becomes the determining factor for the termination reaction. A possible explanation for these phenomena in terms of the thiol and disulfide interchange reaction is presented. On the grafting of styrene, additional evidence was obtained that prevention and retardation of the interchange reactions followed mechanochemical bond scission of the disulfide and other covalent bonds and produced new free radicals which could initiate chain reactions.     

Grafting onto wool. V. Kinetics of graft copolymerization of methyl methacrylate in the viscous media of wool fibers

The graft copolymerization of methyl methacrylate in S-carboxymethylated wool fibers was investigated in the aqueous LiBr-K₂S₂O₈ system. The rate of grafting, the degree of polymerization of graft polymer, and the number of grafting sites were determined on varying the thiol content at a constant concentration of monomer. Kinetic considerations lead to the following expression in agreement with the experimental results: Z/DP = {(k_td + k_tc)/k_p²[M]²} R_p, where Z is the number of DNP endgroups of polymer; DP is the average degree of polymerization; k_p, k_td, and k_tc are the rate constants of propagation, termination by disproportionation, and termination by recombination, respectively; [M] is the concentration of monomer in fibers, and R_p is the overall rate of grafting. For wool fibers in media sufficiently high viscosity, the rate constants k_td and k_tc of diffusion-controlled termination are approximately equal and not affected by the change in cross-link density, provided that the thiol and disulfide interchange occurs. The possibility of occurrence of mechanical bond scission through a radical mechanism is involved in systems with extremely small amounts of thiol groups.     

Redox-initiated vinyl polymerization with thiourea as the reductant

A few redox systems containing thiourea as reductant have been found to be quite effective in initiating vinyl polymerization in aqueous media and polymers obtained in the process have all been found to contain amino endgroups to various extents by the application of dye techniques. Quite a few oxidants have so far been utilized for this purpose; among them are ferric chloride (Fe³⁺), ethylene dibiguanide complex salts of tripositive silver (Ag³⁺), hydrogen peroxide (H₂O₂), persulfate (S₂O₈^2?), bromate (BrO₃^?) + hydrochloric acid (HCl). In case of oxidants Fe³⁺ and Ag³⁺, amino endgroups are mainly incorporated in polymers; but in case of oxidants H₂O₂ and S₂O₈^2?, fragments of oxidants are also incorporated as hydroxyl and sulfate endgroups. BrO₃^?, however, forms a very efficient redox-initiating system with thiourea, as is evidenced by its capability of polymerizing even hydroquinone-stabilized water-soluble vinyl monomers at very low temperature (～0°C.) and at a quite rapid rate. Besides amino endgroups, sulfonate endgroups have also been detected in polymers in this case, and the relative extents of these two types of endgroups depend generally on the acid concentration of the system. Evidences so far collected indicate the generation of S? C(?NH)NH₂ radicals in the system by oxidation of isothiourea, HS? C(?NH)NH₂, and these are incorporated in polymers as endgroups. Sulfonate endgroups may be generated by oxidation of these amino-bearing endgroups. Suitable initiation mechanisms have been suggested in each case.     

Grafting of polymers with controlled molecular weight onto ultrafine silica surface

To graft polymers with controlled molecular weight and narrow molecular weight distribution, the grafting of polymers onto ultrafine silica surface by the termination of living polymer cation with amino groups introduced onto the surface was investigated. The introduction of amino or N-phenylamino groups onto the silica surface was achieved by the treatment of silica with γ-aminopropyltriethxysilane or N-phenyl-γ-aminopropyltrimethoxysilane. It was found that these amino groups on silica are readily reacted with living poly(isobutyl vinyl ether) (polyIBVE), which was generated with CF₃COOH/ZnCl₂ initiating system, and polyIBVE with controlled molecular weight and narrow molecular weight distribution is grafted onto the surface. By the termination of living poly(2-methyl-2-oxazoline), which was generated with methyl p-toluenesulfonate initiator, with amino groups on silica, polyMeOZO was also grafted onto the surface. The percentage of grafting of polymer onto the silica surface decreased with increasing molecular weight of the living polymer, because the steric hindrance of silica surface increases with increasing molecular weight of living polymer. Polymer-grafted silica gave a stable dispersion in a good solvent for grafted chains. © 1995 John Wiley & Sons, Inc.     

GRAFT COPOLYMERIZATION OF DENTAL COLLAGEN WITH METHYL METHACRYLATE

The graft copolymerization of MMA onto human dentin was studied with the redox system usingK_2S_2O_8+NaHSO_3 as initiator. The IR spectrum of the copolymer showed the presence of C=Oband at 1720 cm~(-1),C--O at 1260~(-1), CH_3, at 2850 cm~(-1). indicating the presence of polymerized me-thacrylate on the detin. The ppt. of the acid hydrolysis of the graft copolymer showed an -NH_3~+band of amino acid at 3200 cm~(-1). Most marked percent decreases in contents of amino acids inthe acid hydrolysate were observed in serine, tyrosine and methionine. The absolute amounts ofglycine, alanine and proline have also decreased markedly. This suggests that it was most proba-ble that the graft copolymerization occurred at these residues. The tubular stripes and cross sectioncavities of dentin tublets were covered with a high polymer graft which could be seen from the SEMpictures. The mol. wt. of this grafted high polymer, as determined by GPC, was higher than thatof the homopolymer and the former had a broader mol. wt. distribution. All these facts suggest-ed that a genuine graft copolymerization of MMA onto human dentin occurred.     

Characterization of the collagen–vinyl graft copolymers prepared by the ceric ion method. I. Solution properties

Graft copolymerization of vinyl monomers on to collagen was carried out by the ceric ion method. The grafted vinyl polymer chains were isolated by both acid and enzymatic hydrolysis of the collagen backbone in order to characterize the graft copolymers. Proof of grafting was obtained through the detection of amino acid endgroups in the grafts isolated by both the methods. The grafts isolated gave the characteristic blue color normally associated with the presence of amino acids. The presence of amino acid endgroups was further confirmed by dinitrophenylation of the isolated grafts. The absorption spectra of the dinitrophenylated(DNP) grafts showed absorption maximum in the ultraviolet region of 340–360 mμ, characteristic of DNP-amino acids. Soluble collagen grafted with polyacrylamide(PAA) formed fibrils on heating to 37°C at neutral pH but, unlike the native collagen, these fibrils did not redissolve on cooling at 2°C. These results show that the redispersion property of soluble collagen was impaired, probably by attachment of the PAA side chains to the collagen molecule. The turbidimetric titration behavior of the grafts, their general behavior of swelling in different solvents, and the intrinsic viscosity of the copolymers in mixed solvents also provided additional proof of grafting.     

Endgroup study of chlorate–sulfite-initiated acrylonitrile copolymer

Quantitative determination of endgroups in an acrylonitrile–methyl acrylate (90:10) copolymer polymerized with NaClO₃–Na₂SO₃ redox system in aqueous solution was carried out by conductometric and dyeing methods for SO₃H incorporated into polymer, x-ray analysis for S in polymer, and polarography for Cl in polymer. The number-average molecular weight was measured by osmometry. Determination of endgroups was done on both unfractionated polymer and fractionated polymer. On the average, 0.95 mole S and 0.71 mole SO₃H per molecule were found in unfractionated polymer. For fractionated polymer, 0.68 mole S and 0.69 mole SO₃H per molecule were found. A small amount of Cl was also found in both unfractionated polymer and fractionated polymer. The difference between results for the two polymers and polymerization kinetics are discussed.     

Stress-strain behaviour of graft copolymers of methyl methacrylate and natural wool fibres

The graft polymerization of methyl methacrylate onto wool, using LiBrK₂S₂O₈ and Na₂S₂O₃H₂O₂ redox systems as initiators, does not change dramatically the stress-strain behaviour of single fibres even for high graft yields. Variations in tensile properties are essentially due to an important radial swelling effect of the deposited polymer accompanied by a moderate increase of internal viscosity and, in the case of Na₂S₂O₃H₂O₂ initiation, to interference from oxidative processes.     

Preparation of a polymeric membrane crosslinked by the viologen structure from a cyanopyridinium salt polymer

The polymeric membrane crosslinked by a viologen structure was prepared by the reduction of the homopolymer with a pendant cyanopyridinium structure, poly(1-vinylbenzyl-4-cyanopyridinium perchlorate), chemically or electrochemically. The homopolymer in the state of membrane was reduced chemically by aqueous sodium dithionite (Na₂S₂O₄) to obtain the polymer containing viologen group (64 mol%) despite a heteogeneous reaction. When the membrane was reduced electrochemically, the resulting viologen moiety in the membrane showed reversible one- and two-electron redox behavior.     

Studies in some new initiator systems for vinyl polymerization. IV. Amino acids as the reducing component

Amino acids have been found to form good redox initiator systems with halogens (Cl₂ and Br₂), KBrO₃, KMnO₄, and Fe(NH₄)(SO₄)₂. The three systems, viz., glycine–Cl₂, taurine–Cl₂, and sulfamic acid–Cl₂ incorporate amine, carboxy (or sulfoxy), chlorine, and hydroxy endgroups in the resulting polymers, the monomer investigated being mainly methyl methacrylate. On the basis of endgroup results it is suggested that initiation through amino acid radical, chlorine radical and also through some hydroxyl radicals takes place. The probable termination mechanism is discussed.     

End‐group fidelity of copper(0)‐meditated radical polymerization at high monomer conversion: an ESI‐MS investigation

Copper(0)‐mediated radical polymerization (single electron transfer‐living radical polymerization) is an efficient polymerization technique that allows control over the polymerization of acrylates, vinyl chloride and other monomers, yielding bromide terminated polymer. In this contribution, we investigate the evolution of the end‐group fidelity at very high conversion both in the presence and in the absence of initially added copper (II) bromide (CuBr₂). High resolution electrospray‐ionization mass spectroscopy (ESI‐MS) allows determination of the precise chemical structure of the dead polymers formed during the polymerization to very high monomer conversion, including post polymerization conditions. Two different regimes can be identified via ESI‐MS analysis. During the polymerization, dead polymer results mainly from termination via disproportionation, whereas at very high conversion (or in the absence of monomer, that is, post‐polymerization), dead polymers are predominantly generated by chain transfer reactions (presumably to ligand). The addition of CuBr₂ significantly reduces the extent of termination by both chain transfer and disproportionation, at very high monomer conversion and under post‐polymerization conditions, offering a convenient approach to maintaining high end‐group fidelity in Cu(0)‐mediated radical polymerization. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Polymer Catalysts

Catalysts of reduced and unreduced PdCl₂ with hydrazine hydrate deposited on polyaminochloroquinones or polyaminochlorohydroquinones were obtained. Polyaminochloroquinones were prepared by solution polycondensation of chloranil with benzidine in the presence of an acceptor, sodium acetate, for the resulting hydrochloric acid. Polyaminochlorohydroquinones were obtained by a reduction reaction of polyaminochloroquinones with 2,2′ -diphenyl hydrazine. The polymer catalysts were tested in the styrene hydro-genation reaction. The polymers and polymer catalysts were studied by IR spectroscopy.     

Catalytic behavior of wool‐osmium tetroxide complex for asymmetric dihydroxylation of olefins

A new chiral polymer‐metal complex, wool‐osmium tetroxide (wool‐OsO₄) complex was prepared by a very simple method. This complex was found to be able to catalyze the asymmetric dihydroxylation of allylamine to (R)‐(+)‐3‐amino‐1, 2‐propanediol and allyl chloride to (S)‐(+)‐3‐chloro‐1,2‐propanediol. The optical yields amounted to 83.7 and 57.2%, and the product yields were 80.2 and 68.5% respectively. The experimental results showed that OsO₄ content in the complex, reaction time, allylamine/OsO₄ molar ratio and solvent all have an effect on the product and optical yields. Additionally, wool‐OsO₄ complex catalyst could be reused without any remarkable change in optical catalytic activity. Copyright © 2004 John Wiley & Sons, Ltd.     

Mode of termination in the copolymerization of vinyl acetate–isobutyl methacrylate and methyl methacrylate–methyl acrylate at 60°C

The mode of termination in the vinyl acetate–isobutyl methacrylate (VA–IBMA) and methyl methacrylate–methyl acrylate (MMA–MA) copolymerization systems has been investigated at 60°C. by using the dye-interaction technique for functional endgroup estimation. The results show that pairs of poly(vinyl acetate) radicals interact almost exclusively through a disproportionation mechanism. In the homopolymerization of methyl methacrylate and methyl acrylate, about 1.16 and 1.22 carboxyl-containing endgroups per polymer molecule have been estimated, which shows the predominance of disproportionation over combination in these termination reactions. In poly(isobutyl methacrylate) about 1.55 tagged initiator fragments per chain indicate that 29% of the total radicals terminate through the disproportionation mechanism. Cross termination in the (VA–IBMA) copolymerization system occurs almost entirely through combination for monomer feeds richer in isobutyl methacrylate content while for the MMA–MA system, combination is more important at intermediate monomer feed ratios. These results have been discussed in the light of different explanations for the reaction mechanism.     

Polymer effect in graft polymerizations of acrolein onto imidazole-containing polymer

The graft polymerizations of acrolein (AL) onto an imidazole (Im)-containing polymer, such as a homopolymer of 4(5)-vinylimidazole (VIm) and several copolymers of VIm-4-vinylpyridine (VPy), VIm-1-vinyl-2-pyrrolidone (VPr), and VIm-styrene (St), have been studied in ethanol at 0°C. The degree of polymerization (P?_n) of the resulting polyacrolein graft depended on the number of Im units in the Im-containing polymer which produced a decrease in P?_n of grafted polyacrolein. The P?_n of the graft polyacrolein was determined to be in the range of 5-23. The rate of polymerization (R_p) was expressed by R_p = k(PVIm) (AL)². The graft polymerizability of the AL was influenced by the comonomer in the parent polymer, and was found to be in the order of VIm homopolymer > VIm-VPr copolymer > VIm-VPy copolymer > VIm-St copolymer. R_p was affected by the functional group around the Im group in the Im-containing polymer. These results were discussed by assuming the conformation of the parent polymer in ethanol.     

Light scattering characterization of thermodynamic interaction of polymers in dilute solution. Effect of solvent and molecular weight

Interaction of nonidentical polymer molecules in a dilute solution of a mixture of two polymers is quantitatively characterized by A₂₄, the second virial coefficient for interaction of unlike species. This parameter is related to the compatibility of the two polymers in solution and is obtainable experimentally, e.g., by light scattering. With chemically markedly different polymers, A₂₄ depends neither on the molecular weight of the polymers nor on the solvent and becomes characteristic of the polymer pair. For a mixture of two copolymers or of a homopolymer and a copolymer with similar compositions, A₂₄ depends both on the solvent and on the molecular weight of polymers. Under such circumstances A₂₄ ceases to be a quantity given only by the chemical structure of the two polymers; however, under suitable conditions it remains a sensitive function of the difference between the chemical nature of polymer components.     

Tuning block copolymer phase behavior with a selectively associating homopolymer additive

We use polymer random phase approximation (RPA) theory to calculate the microphase separation transition (MST) spinodal for an AB + C diblock copolymer–homopolymer blend where the C homopolymers are strongly attracted to the A segment of the copolymers. Our calculations indicate that one can shift the MST spinodal value of the A ? B segmental interaction parameter (χ_ABN)_S to significantly lower values [i.e., (χ_ABN)_S < 10.5] upon the addition of a selectively attractive C homopolymer. For a sufficiently attractive C homopolymer, (χ_ABN)_S can be pushed to negative values, indicating microphase separation in what would appear to be a completely miscible diblock copolymer. Furthermore, we show that microphase separation can occur in diblock copolymer–homopolymer blends where the segmental interactions between all polymer constituents are attractive. By tuning the value of (χ_ABN)_S with a homopolymer additive, one is therefore able to tune the effective copolymer segregation strength and thus dramatically affect the blend phase behavior. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2083–2090, 2009     

Haloaldehyde Polymers. XIV. Endgroups in Polychloral

Chloral polymers prepared by anionic polymerization have alkoxide endgroups as terminal ends at the end of this polymerization. The initiating anion has, as expected, no influence on the type of terminal group formed. Polychloral with terminal alkoxide ends degrades easily thermally to monomeric chloral. Alkoxide endgroups in polychloral do not readily react with alkylating or acylating agents, although partial stabilization has been observed when alkoxide-terminated polymers were allowed to stand for periods of time; the endgroups seem to react either with impurities or with excess chloral in side reactions. With protic acids, alkoxide-terminated polychloral is transformed into hydroxyl-terminated polymer of higher thermal stability. Studies of the initiation step of the chloral polymerization revealed that above the ceiling temperature of polymerization, strong nucleophiles, such as soluble tertiary butoxide, initiate quantitatively, but polymerization does not proceed until the mixture is cooled. When chloral is initiated with weaker nucleophiles such as chloride or carboxylates, the initiation equilibrium is not on the side of the initiated species, although it shifts effectively as polymerization proceeds; with carboxylates as initiators the ester group has been found incorporated as the initial endgroup in polychloral. With sufficient amounts of lithium tertiary butoxide as anionic initiator, polychloral of low molecular weight was prepared. This polymer does not react with end-capping reagents (other than PCl₅) as does high molecular weight polychloral; in spite of considerable effort it was not possible to prepare low molecular weight soluble polychloral or oligomeric polychloral. Polychloral prepared with cationic initiators is thermally more stable than unstabilized anionically initiated polychloral but is generally crumbly and incoherent. The end-groups of such polymers are usually hydroxyl endgroups. Identification of endgroups of the polymers has been done where possible by IR spectroscopy, for the initiation reaction by NMR spectroscopy, but for high molecular weight insoluble polymers almost exclusively by comparative thermal polymer degradation.     

Controlled grafting of MMA onto cellulose and cellulose acetate

Homogeneous graft copolymerization of methyl methacrylate onto cellulose and cellulose acetate was carried out in various solvents and solvent systems taking ceric ammonium nitrate, tin (II) 2-ethyl hexanoate [Sn(Oct)₂] and benzoyl peroxide as initiators. The effect of solvents, initiators, initiator and monomer concentration, on graft yield, grafting efficiency and total conversion of monomer to polymer were studied. Formation of Ce³⁺ ion during grafting in presence of CAN enhances the grafting efficiency. Methylene blue was used as a homopolymer inhibitor and controlled the molecular weight of the grafted polymer and its effect on grafting was also studied. In presence of MB, amount of PMMA homopolymer formation reduced and consequently grafting efficiency increased. The number average molecular weights and polydispersity indices of the grafted PMMA were found out by gel permeation chromatography. The products were characterized by FTIR and ¹H-NMR analyses and possible reaction mechanisms were deduced. Finally, thermal degradation of the grafted products was also studied by thermo-gravimetric and differential thermo-gravimetric analyses.     

Prediction of molecular weight distributions in branched polymers

A theoretical treatment of long branching in radical polymerization in a continuous stirred tank reactor is presented. The treatment takes into account radical termination by disproportionation and/or combination, transfer to polymer and/or additive of low molecular weight, residence time, and injection of polymer. In the absence of added polymer, the molecular weight distribution depends upon four parameters which can be expressed as P?_n and ratios of the rate of polymerization to the rate at which radicals (a) leave the reactor, (b) combine, and (c) transfer to polymer. The kinetic equations were converted into a differential equation which was solved numerically to give polymer and radical moments. An analytical solution is presented for the case where combination is absent. P?_w/P?_n is predicted to increase smoothly in a markedly exponential manner with increasing polymer transfer, combination, P?_n, and mean residence time. At no stage do any of the moments become infinite unless the residence time is infinite. For polymers of wide distribution, the second and higher radical moments can exceed the corresponding polymer moments so that most of the large molecules leave the reactor as radicals. Beasley's and Nicolas's treatments are shown to be limiting cases at low polymer transfer.