Showing papers in "Journal of Polymer Science Part A in 1979"

Photoinitiated cationic polymerization with triarylsulfonium salts

Abstract: Triarylsulfonium salts Ar3S+MXn− with complex metal halide anions such as BF4−, AsF6−, PF6−, and SbF6− are a new class of highly efficient photoinitiators for cationic polymerization. In this article we describe several synthetic routes to the preparation of these compounds along with their physical and spectroscopic properties. Mechanistic studies have shown that when these compounds are irradiated at wavelengths of 190–365 nm carbon-sulfur bond cleavage occurs to form radical fragments. At the same time the strong Brϕnsted acid HMXn, which is the active initiator of cationic polymerization that takes place in subsequent “dark” steps, is also produced. A study of the parameters that affect the photolysis of triarylsulfonium salts is reported with a measurement of the absolute quantum yields. The cationic polymerizations of four typical monomers—styrene oxide, cyclohexene oxide, tetrahydrofuran, and 2-chloroethyl vinyl ether—with triarylsulfonium salt photoinitiators are described.

Polylactide. II. Viscosity–molecular weight relationships and unperturbed chain dimensions

Abstract: Mark–Houwink equations for benzene and chloroform solutions of S-polylactide and racemic polylactide were established by end-group analysis of partly hydrolyzed polymers. Unperturbed chain dimensions calculated for both polymers reveal a considerable difference and suggest a helical conformation for S-polylactide in solution. This finding supports 1H-NMR observations that reveal chemical shift differences that appear when the same configurational sequence is present in two stable conformational states.

Polymerization of diacetylenes in multilayers

Abstract: The synthesis of extended and oriented very thin layers of polymers by solid-state polymerization of multilayers built up from monomolecular films of suitable monomers by means of the Langmuir-Blodgett (LB) technique has been felt to be a particular challenge for a long time. Attempts to make use of radiation-induced free radical polymerization of long-chain vinyl derivatives have been successful only in part (1–5).

Equilibrium study of polymer–polymer complexation of poly(methacrylic acid) and poly(acrylic acid) with complementary polymers through cooperative hydrogen bonding

Abstract: The degree of linkage, θ, defined as the ratio of the binding groups to the total of potentially interacting groups and the stability constant K of the polymer–polymer complexes in the systems poly(methacrylic acid)–poly(ethylene glycol), poly(acrylic acid)–poly(ethylene glycol), and poly-(methacrylic acid)–poly(vinyl pyrrolidone) in aqueous and aqueous alcohol media were determined as a function of temperature by potentiometric titration. It was found that θ and K are strongly dependent on chain length, temperature, and medium and that hydrophobic interaction is a significant factor in the stabilization of the complexes. The enthalpy and entropy changes and the cooperativeness parameter of the systems were calculated. A mechanism for the complexation in terms of cooperative interaction was proposed.

Dye‐sensitized photoinitiated cationic polymerization. The system: Perylene–triarylsulfonium salts

Abstract: Perylene has been found to photosensitize the photolysis of triarylsulfonium salts at wavelengths from 390 to 475 nm. Using perylene in combination with various triarylsulfonium salt photoinitiators, the photoinduced cationic polymerizations of cyclohexene oxide and 2-chloroethyl vinyl ether have been demonstrated using light of these wavelengths.

Thermotropic liquid crystalline polymers. I. Cholesterol‐containing polymers and copolymers

Abstract: An approach to the creation of thermotropic cholesterol-containing liquid crystalline polymers by the chemical binding of cholesterol molecules with side chains of comblike polymers is presented. This type of structure permits a decrease in the steric hindrances provided by the backbone chains for the purpose of realizing the liquid crystalline state. A number of new cholesteric esters of poly(N-methacryloyl-ω-aminocarbonic acid)s (PChMAA-n) with different side-chain lengths (n = 2–11) as well as a series of copolymers of ChMA-n with n-alkylacrylates and n-alkylmethacrylates have been synthesized. The experimental evidence of liquid crystalline structure formation in these polymers in glass, viscoelastic, and fluid states is discussed. Molecular and supermolecular structures of cholesterol-containing comblike polymers have been studied and the model of macromolecular packing in the liquid crystalline state is proposed. It is shown that the existence of a layered order of side methylene groups together with ordering of cholesterol groups is necessary to the production of the liquid crystalline state in these polymers.

Particle nucleation in emulsion polymerization. IV. Nucleation in monomer droplets

Abstract: Nucleation in finely dispersed monomer emulsions in competition with homogeneous and micellar mechanism was studied. The emulsions were prepared with a high-pressure homogenizer under varying homogenizing conditions and made stable by the addition of hexadecane to the monomer. Sodium dodecyl sulfate was used as emulsifer. The number of particles in latexes polymerized with potassium persulfate and benzoyl peroxide initiators was measured and plotted as a function of the free emulsifier concentrations. With persulfate initiator the particle number achieved a minimum in the transition region between droplet and water phase–micellar nucleation mechanisms. With very fine emulsions Smith–Ewart case II kinetics with n = 0.5 applied. The reaction rate, which differed from conventional emulsion polymerizations, decreased with time up to the point at which n began to increase. In these runs the particle size distribution became nearly monodisperse.

Epoxy resins. III. Application of fourier transform IR to degradation studies of epoxy systems

Abstract: Three cured epoxy resins were investigated under various degradation conditions by Fourier transform infrared (FTIR) spectroscopy for measurement. The epoxy resins were the diglyadyl ethers of bisphenol A (DGEBA), phenolphthalein (DGEPP), and 9,9-bis(4-hydroxyphenyl)fluorene (DGEBF). The thermal stability order of functional groups that incurred DGEBA was total methyl group ∼ total benzene ring > methylene > p-phenylene > ether linkage > isopropylidene. The oxidative thermal and photodegradation processes were found to be related to the classical autocatalytical oxidation of aliphatic hydrocarbon segments. The Wieland rearrangement, Norrish-type reaction, Claisen rearrangement, and other possible degradation mechanisms were suggested by the data.

Thermal decomposition of poly(butylene terephthalate)

Abstract: Detailed results of the overall thermal degradation of poly(butylene terephthalate) are reported. Laser microprobe analysis and dynamic mass spectrometric techniques were used to identify the primary volatile degradation products and initial pyrolysis reactions that control polymer degradation. A complex multistage decomposition mechanism was observed which involves two major reaction pathways. Initial degradation occurs by an ionic decomposition process that results in the evolution of tetrahydrofuran. This is followed by concerted ester pyrolysis reactions that involve an intermediate cyclic transition state and yield 1,3-butadiene. Simultaneous decarboxylation reactions occur in both decomposition regimes. Finally, the latter stages of polymer decomposition were characterized by evolution of CO and complex aromatic species such as toluene, benzoic acid, and terephthalic acid. Activation energies of formation for the main pyrolysis products were determined from the dynamic measurements of the major ion species and indicate values of E = 27.9 kcal/mole for the production of tetrahydrofuran and E = 49.7 kcal/mole for the production of butadiene.

Thermally reversible polymer systems by cyclopentadienylation. II. The synthesis of cyclopentadiene‐containing polymers

Abstract: The synthesis of polymers containing either terminal or pendant cyclopentadiene (CPD) groups has been studied. Using information obtained from model studies, the synthesis of polyisobutylenes containing a CPD terminus was accomplished by the use of the tert-butylchloride–dimethylcyclopentadienylaluminum initiator system. Isobutylene polymerization by this system under carefully chosen conditions is essentially transfer free, and termination occurs by cyciopentadienylation. The presence of CPD end group has been established by UV spectroscopy and reaction with maleic anhydride. Selectivity toward termination by cyclopentadienylation increases with decreasing temperatures; at −41°C and low conversion (<10%) ca. 72% of the polymer chains terminate in this manner. The synthesis of polymers containing randomly distributed pendant CPD groups along the chain has been accomplished by cyclopentadienylating with dimethylcyclopentadienylaluminum chlorobutyl rubber and chlorinated poly(ethylene-co-propylene) (Cl-EPM). Pendant CPD groups undergo Diels-Alder/retro-Diels-Alder condensations yielding thermally reversible networks; e.g., a cyclopentadienylated Cl-EPM was remolded three times to elastic sheets.

Particle nucleation in emulsion polymerization. II. Nucleation in emulsifier‐free systems investigated by seed polymerization

Abstract: Experiments with seeded polymerization in emulsifier-free systems were carried out with styrene in order to test the theory of particle nucleation presented in the first article in this series. The effect of amount, size, and surface charge density of the seed particles on the formation of new particles was investigated. An expression for the capture rate of oligomeric radicals from the water phase was evaluated in which the rate of capture was considered to be governed by the absorption of oligomers with chain length one less than the critical chain length for precipitation of the oligomer. Coagulation of primary particles was also included in the expression for the number of new particles obtained in the system. Limited coagulation of primary particles with already formed particles and with seed particles was found to play an important role in determining the final number of new particles found at the end of the runs.

Particle nucleation in emulsion polymerization. III. Nucleation in systems with anionic emulsifier investigated by seeded and unseeded polymerization

Abstract: Studies of seeded and unseeded polymerization of styrene using sodium dodecylsulfate as emulsifier have been carried out in order to investigate the mechanism of particle nucleation in such systems and to test the theory presented in Part I of this series. The rate of capture of water-soluble oligomeric radicals was considered to be governed by absorption of oligomers with chain length one less than the critical chain length. It was concluded that the micelles became the dominating loci for particle nucleation above CMC for the emulsifier. A complete nonsteady-state model for particle initiation above CMC which takes into account radical desorption and reabsorption has been developed. It was indicated that, even for styrene, desorption of radicals may play a role in controlling the radical and particle number of interval I under certain conditions. The model also showed that the efficiencies of particles in absorbing radicals could be calculated from physical parameters, such as diffusion constants and surface charge densities, which are available for the system.

Melamine–formaldehyde resins: Constitutional characterization by fourier transform 13C‐NMR spectroscopy

Abstract: The random chemical structures of melamine–formaldehyde resins, including methylated melamine–formaldehyde resins and urea–melamine formaldehyde resins, were investigated by 13C-NMR spectroscopy (Fourier transform). All the combined formaldehydes, methylol and methyl ether groups, methylene structures, and dimethylene ether structures were assigned. A 13C chemical shift of methylene carbon occurred by substitution of other constituents of the methylene group for a proton of the adjacent monosubstituted nitrogen atom, as shown in a 13C-NMR spectrum of urea–formaldehyde resins. It was found that the chemical shift of each corresponding carbon of both melamine resins and urea–melamine resins was almost superimposed with that of urea resins.

High‐conversion polymerization. IV. A definition of the onset of the gel effect

Abstract: The gel effect in free radical polymerization of vinyl monomers has been recognized as the result of the increased viscosity of the reaction solution of polymer in monomer, which causes a decrease in the rate of the termination reaction. This effect manifests itself as an increase in the rate of polymerization over that rate to be expected in its absence. Definition of the onset of the gel effect has become necessary for several purposes. Previously, it has been common to define the onset phenomenologically, i.e., in terms of the increase in the rate of polymerization. It is proposed here that the onset of the gel effect is best defined on a fundamental basis, i.e., as occurring at that conversion at which the rate of segmental diffusion of the polymeric radicals equals the rate of their translational diffusion. Experimental evidence is presented that shows that the small minima predicted by this definition do exist for both rates and degrees of polymerization. Measurements of the viscosities of solutions of polymers in their monomers suggest that the polymer concentrations at which the “chain-entanglement” phenomena are observed are the same as those for the onset of the gel effect for styrene, methyl methacrylate, and butyl methacrylate.

Metallo esters. VII. Stabilizing effect of sodium tert‐butoxide on the growth center in the anionic polymerization of methacrylic esters

Abstract: The growth center in the anionic polymerization of methacrylic esters is stabilized with alkaline alkoxides, sodium tert-butoxide in particular. The lifetime of the growth center was investigated in the polymerization of methyl methacrylate by evaluating yield and molecular weight distribution of the polymer formed when the monomer was added in two doses. The average lifetime of the original growth center stabilized by sodium tert-butoxide at 20°C under the given conditions was longer than several minutes. The stabilization of the growth center was also used in the stepwise copolymerization of n-butyl methacrylate and methyl methacrylate. The copolymer thus obtained in high yield was characterized as a block copolymer on the basis of its solubility, nuclear magnetic resonance (NMR) spectra, and measurements of the complex shear modulus.

Organosilane polymers. I. Poly(dimethylsilylene)

Abstract: Poly(dimethylsilylene) higher polymers prepared by alkali metal coupling of purified dimethyldichlorosilane were found to be high melting, largely crystalline polymers, soluble in solvents at temperatures above 200°C.

Graft copolymers containing nucleic acid bases and L‐α‐amino acids

Abstract: Graft copolymers of nucleic acid bases and L-α-amino acids on polyethyleneimine were synthesized, and carboxyl derivatives of adenine and thymine were grafted by the p-nitrophenyl ester method onto linear and branched polyethyleneimine. The carboxyl derivatives of nucleic acid bases were also grafted onto the monomeric graft copolymers of L-α-amino acids on polyethyleneimine; the carboxyl derivatives were obtained by the condensation of polyethyleneimine with L-α-amino acids with a coupling agent.

Anionic block copolymerization of ϵ‐caprolactam

Abstract: ϵ-Caprolactam anionic homopolymerization was studied in the presence of different model activators. On the basis of the results ester- and isocyanate-terminated polymers were used as macroactivators and nylon-6–polyvinyl or polydiene block copolymers were synthesized in high yields. The physical properties and morphology of a nylon–polybutadiene triblock copolymer were characterized.

Thermally reversible polymer systems by cyclopentadienylation. I. A model for termination by cyclopentadienylation of olefin polymerization

Abstract: The reaction between tert-butylchloride (t-BuCl) and dimethylcyclopentadienylaluminum (Me2AlCPD) was studied as a model for initiation by the tert-butyl cation (t-Bu⊕) and termination by cyclopentadienylation by the Me2Al(CPD)Cl⊖ counteranion of isobutylene polymerization. All reaction products formed in this model system have been identified and quantitatively determined. A comprehensive scheme that indicates pathways to these products was developed (scheme III). It is proposed that the predominant product, tert-butylcyclopentadiene (t-BuCPD), arises in the collapse of the t-Bu⊕-Me2Al(CPD)Cl⊖ ion pair, mainly by CPD⊖ transfer to the tert-butyl cation. The minor products are neopentane (t-BuMe) and isobutylene (i-C4H8), which are probably formed, respectively, by Me⊖ transfer to and proton loss from the t-butyl cation. Cyclopentadienylation selectivity increases by lowering the temperature and extrapolation of results suggests 100% cyclopentadienylation at −55°C. The t-BuCl/Me2AlCPD ratio strongly influences the overall reaction pathway. The reaction is first order in t-BuCl with ΔEa of ca. 7 kcal/mole (1,2-dichloroethane or chlorobenzene solvents, +24 to −29°C). Indirect evidence indicates that the kinetic product of cyclopentadienylation is 5-t-BuCPD and that this isomer cannot be tert-butylated; that is, the initiation of 5-t-BuCPD polymerization by t-Bu⊕ is sterically unfavorable. Detailed analysis of the chemistry and kinetics of the t-BuCl/Me2AlCPD model system holds important clues to the controlled polymerization of olefins leading to macromolecules with cyclopentadiene (CPD) termini.

Photooxidative degradation of cellulose: Reactions of the cellulosic free radicals with oxygen

Abstract: Photooxidative degradation of cellulose resulted in decreases of degree of polymerization (DP) and α-cellulose content, concurrently producing chromophoric groups; namely, carbonyl, carboxyl, and hydroperoxide groups within the polymer. Electron spin resonance (ESR) studies revealed that cellulosic carbon free radicals readily reacted with oxygen molecules at 143–160 K to produce peroxy radicals, whereas cellulosic oxygen free radicals were inert toward oxygen molecules throughout the photooxygenation reactions. At 77 K it is feasible that only photoexcited oxygen molecules reacted with cellulosic carbon free radicals to produce peroxide radicals. These radicals were themselves stabilized at 273 K by abstraction of hydrogen atoms from cellulose to produce polymer hydroperoxides. Simultaneously, new radical sites, which exhibited three-line ESR spectra, were generated in cellulose.

Influence of the conformational state of polymethacrylic acid on the photophysical properties of pyrene in aqueous solution: a fluorescent probe and laser photolysis study

Abstract: The excited state of pyrene observed in fluorescence and pulsed laser techniques is used to show that pyrene is solubilized in the polymer coil of aqueous solution of polymethacrylic acid (PMA) at pH 5, the pyrene is ejected into the aqueous phase of the system. In the presence of micellar solutions of surfactants increasing pH transports the pyrene from the polymer to the micellar aggregates. These fluorescence techniques are used to investigate the kinetics of expansion of the polymer coil. The system is suggested as a suitable model for the interaction of pyrene with biopolymers such as DNA.

1H‐NMR study of polyisoprenes

Abstract: 1H NMR spectra of polyisoprene were assigned using polymers of isoprene-1,1,4,4-d4, isoprene-1,1,5,5,5-d5, and isoprene-4,4-d2 polymerized with various catalysts. The methylene-proton signal at 2.1 ppm in cis-1,4- and trans-1,4-polyisoprenes was divided into H4- and H1-proton signals; H4 resonated at 2.21 ppm in both cis-1,4 and trans-1,4 units, whereas H1 resonated at 2.05, 2.21, and 2.15 ppm. Splitting due to the dyad sequences of 1,4 and 3,4 units was apparent. The methine-proton (H3) in a 3,4 unit showed a broad peak centered around 1.5 ppm in C6D6. The overlapping of this signal with the methyl-proton signals at 1.73 and 1.63 ppm resulted in some uncertainty in the determination of the microstructure of polyisoprene which contained a considerable amount of 3,4 unit.

Modification of properties of ion exchange membranes. VII. Relative transport number between various cations of cation exchange membrane having cationic polyelectrolyte layer and mechanism of selective permeation of particular cations

Abstract: Electrodialytic behavior of cation exchange membrane having cationic polyelectrolyte layer on its surface (relative transport number between two cations, P, current efficiency, and electric resistance of the membrane during the electrodialysis) was measured using various cations, and the mechanism of selective permeation of lower-valent cations than the higher and of larger hydrated cations than the smaller was investigated. The following conclusions were obtained: (1) the cationic polyelectrolyte layer narrowed the pathway for ions; (2) when the pathway was made narrower by other methods, the remarkable change of the permselectivity of the membrane did not occur; (3) the effectiveness of the cationic polyelectrolyte layer was depressed by the treatment with anionic polyelectrolytes to neutralize the cationic charge on the membrane surface; and (4) the cation with larger hydrated diameter (potassium ions) more easily permeated through the membrane having the polyelectrolyte layer than that with the smaller hydrated diameter (sodium ions). It is concluded that the change of P by the cationic charge layer on the membrane surface is based on the difference in the strength of the electrostatic repulsion between two cations against the cationic charge layer.

Photoinitiated cationic polymerization by triarylselenonium salts

Abstract: Triarylselenonium salts with complex metal halide anions such as BF, AsF, and SbF have been prepared and have been shown to be efficient photoinitiators of cationic polymerization. The photolysis rates of these compounds were studied and their quantum yields of photolysis were reported. Use of specific triarylselenonium salts in the polymerizations of cyclohexene oxide, epichlorohydrin, and 2-chloroethyl vinyl ether are described.