Showing papers in "Journal of Polymer Science Part A in 1983"

Morphology and grafting in polybutylacrylate‐polystyrene core‐shell emulsion polymerization

Abstract: The morphology of polybutylacrylate–polystyrene (PBA–PS) core-shell latex particles prepared by seeded emulsion polymerization was investigated as a function of the addition method of styrene (St). The thin layer chromatography/flame ionization detector (TLC–FID) technique was used to characterize the morphology of the core-shell latexes. It was found that grafting PS to the PBA core occurs during seeded emulsion polymerization. The percentage of grafting depended on the method of addition of St, being greatest for the batch reaction, less for the preswollen batch reaction, and least for the semibatch reaction. Upon aging the PBA core-polymer migrated out of the latex particles with a low degree of grafting to form dumbellshaped particles, whereas the PBA–PS core-shell particles with a high degree of grafting remained spherical because of the emulsifying ability of graft copolymer.

Curing epoxy resins with anhydrides. Model reactions and reaction mechanism

Abstract: The mechanism of acid curing of epoxy resins catalyzed with tertiary amines was investigated by using model systems composed of phenylglycidyl ether and benzoic acid or acetic acid anhydrides in the presence of benzyldimethylamine. The reaction was studied by NMR spectrometry, liquid chromatography, and ozone absorption. The main findings are that (1) the tert-amine is bound chemically and irreversibly during the reaction under the formation of a quaternary ammonium salt and (2) 1-phenyloxypropanediol-2,3-dibenzoate or diacetate is the main reaction product. The suggested reaction mechanism involves initiation in which the tertiary amine reacts with the epoxy group, giving rise to a zwitterion that contains a quaternary nitrogen atom and an alkoxide anion; the latter immediately reacts with the anhydride and quaternary salt is formed. In a later stage the carboxy anion of the quaternary salt reacts first with the epoxy group, then with the anhydride. By this reaction diester is formed and the carboxy anion is regenerated.

The mechanisms of latex particle formation and growth in the emulsion polymerization of styrene using the surfactant sodium dodecyl sulfate

Abstract: A new method is presented that provides experimental information which is qualitatively and quantitatively sensitive to assumptions made as to the mechanisms of free radical entry and of latex particle formation in emulsion polymerization systems. The technique is applied to a styrene nucleation system employing sodium dodecyl sulfate as surfactant at well above the critical micelle concentration. The data cannot be fitted even qualitatively by a simple one-step nucleation mechanism, whether it involves micellar entry or homogeneous nucleation. It is found, on the other hand, that the results can be accurately fitted by assuming that coagulation events between primary colloidal particles, perhaps formed by homogeneous nucleation, dominate both the nucleation process and the entry of free radicals into mature latex particles. In addition, the data indicate that the rate of free radical entry into the latex particles decreases with increasing particle size, at least for particles of unswollen radius less than ca. 40 nm.

Quantitative DSC evaluation of phase segregation rate in linear segmented polyurethanes and polyurethaneureas

Abstract: Linearly segmented polyurethanes and polyurethaneureas are known to be phase separated; one phase is the soft phase, the other, the hard domain. Quantitative evaluation of the degree of phase separation was obtained by DSC. An estimation of the dispersed soft segments outside the soft phase can be made by ΔCp measurements and the increase in glass transition (Tg) can be attributed to the presence of hard blocks in the soft phase. The segregation rate depends on the nature of the soft segments which decrease from hydrogenated polybutadiene to polybutadiene to polyether. It also depends on the nature of the chain extender from aliphatic to aromatic diol and from aliphatic to aromatic diamine. The presence of soft segments in hard domains can be related to the thermoplastic behavior of the polyurethanes and polyurethaneureas.

The formation of “inverted” core‐shell latexes

Abstract: It has been found that when hydrophobic monomers are polymerized in the presence of highly hydrophilic polymer seed particles, the second-stage hydrophobic polymers form cores surrounded by the first-stage hydrophilic polymers, resulting in “inverted” core-shell latexes. The formation of core-shell morphology by this inversion process has been found to be dependent on the hydrophilicity and molecular weight of the first-stage hydrophilic polymers and the extent of phase separation between the two polymers involved. Particle morphology has been examined by electron microscopy, surface acid titration, alkali swelling of particles, and surface reactivity.

Phase transfer catalysis in dehydrofluorination of poly(vinylidene fluoride) by aqueous sodium hydroxide solutions

Abstract: The reaction of poly(vinylidene fluoride) (PVDF) powder with aqueous sodium hydroxide solutions in the presence of quaternary ammonium or phosphonium halides as phase transfer catalysts afforded dehydrofluorinated polymers. The structure of the products was investigated by infrared spetroscopy, and a fluorine-substituted conjugated polyene structure was suggested which was found to be stable against air oxidation. Tetrabutylammonium bromide and tetrabutylphosphonium bromide were the most active among the catalysts used. The effects of the reaction conditions on the conversion are described. The treatment of PVDF films under phase transfer conditions increased the wettability of the surface and electric conductivity. The reaction of PVDF with potassium hydroxide in 2-propanol proceeded not only by elimination but also by substitution of hydroxide ions.

Polyimides containing oxyethylene units

Abstract: Four aromatic dinitro compounds containing oxyethylene units 1,2-bis(4-nitrophenoxy)ethane, bis(2)-(4-nitrophenoxy)ethyl ether, 1,2-bis(2)-(4-nitrophenoxy)ethoxy)ethane, and bis(2-(2-(4-nitrophenoxy)ethoxy)ethyl) ether were prepared by an aromatic nucleophilic substitution reaction that involved 1-fluoro-4-nitrobenzene and the appropriate oxyethylene glycol. Each of the dinitro compounds could be reduced chemically or catalytically to produce the diamines 1,2-bis(4-aminophenoxy)ethane, bis(2-(4-amino-phenoxy)ethyl ether, 1,2-bis(2-(4-aminophenoxy)ethoxy)ethane, and bis(2-(2-(4-aminophenoxy)ethoxy)ethyl) ether. Polymerization of the diamines was carried out in m-cresol with toluene as an azeotroping agent. Polymides derived from 5,5′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis-1,3-isobenzofuradione exhibited good solubility in chlorinated solvents, glass transition temperatures as low as 140°C, as evidenced by viscous flow, and good thermal stability; a 5% weight loss generally occured at greater than 450°C. Isothermal aging studies conducted at 600°F(315°C) for 200 h indicated that weight loss is directly related to oxyalkylene chain length–10% for the shortest and 50% for the longest chain.

Mechanism of imidazole catalysis in the curing of epoxy resins

Abstract: The mechanism of imidazole catalysis in the curing of epoxy resins was studied using the PGE/1-methylimidazole, 2-methylimidazole, and 1,2-dimethylimidazole model systems and another model system based on trichloromethylethylene oxide. It was demonstrated that imidazolium systems, generated in the curing reaction, show an inherent instability leading to cleavage of an NC bond or the 2-CH bond (2-unsubstituted imidazoles). Fourier-transform infrared spectroscopy was used to follow specific changes in the IR spectrum of the curing mixture during polymerization. The identification of carbonyl absorptions occurring during the polymerization led to the conclusion that ketone formation is a general occurrence in the cure of epoxides with nitrogen compounds. We have also shown that imidazoles are regenerated during the curing process by at least two routes. One pathway for the regeneration of the catalyst involves N-dealkylation of the imidazole via a substitution process. Another route, β-elimination, afforded carbonyl compounds, which account for the previously unexplained appearence of infrared bands in the 1650–1770 cm−1 region during the curing process. These investigations demonstrated the true catalytic function of the imidazole. Possible mechanisms for the regeneration of the catalyst are also suggested.

Characterization of poly(D,L-lactic acid) by gel permeation chromatography

Abstract: A number of samples of poly(D,L-lactic acid) (PLA) with weight-average molecular weights Ṁw in the range 15,000-350,000 were prepared by a ring-opening polymerization. The molecular weight distributions (MWDs) of these samples were determined by gel permeation chromatography (GPC). The method involves a universal calibration of the columns on the basis of polystyrene standards and a rapid iteration algorithm leading to the establishment of the Mark-Houwink relationship. In addition, osmometry and viscometry data are presented. The effect of hydrolytic degradation on the MWD of two PLA samples was studied by GPC.

Batch and semicontinuous emulsion copolymerization of vinyl acetat–butyl acrylate. I. Bulk, surface, and colloidal properties of copolymer latexes

Abstract: Vinyl acetate (VAc)–butyl acrylate (BuA) comonomer mixtures with various composition were polymerized by batch and semicontinuous emulsion polymerization processes. PVAc and PBuA homopolymer latexes as well as the (VAc-BuA) copolymer latexes were characterized with respect to particle size, molecular weight, acid end groups on particle surfaces, and colloidal stability against electrolytes. The surface and colloidal properties of these latexes were also compared before and after aging and acid hydrolysis. The average particle size of batch latexes was independent of copolymer composition, whereas for semicontinuous latexes it decreased with increasing BuA content and was always lower than that of the corresponding batch latex. The molecular weight distribution (MWD) for batch latexes was narrower and much less dependent on composition than that of the semicontinuous latexes; bimodal MWD was found in most semicontinuous latexes with a substantial amount of low MW fraction. The total weak and strong acid end groups on particle surfaces for semicontinuous latexes is higher, and more dependent on composition, than the batch latexes. Acid-induced hydrolysis results in a drastic change in the type and concentration of the surface groups of the semicontinuous latex particles. Colloidal stability against electrolytes showed that both electrostatic (due to surface acid groups) and steric [due to surface poly(vinyl alcohol)] mechanisms are contributing. However, for semicontinuous latexes, increasing PVAc content above 50 mol % resulted in a proportional increase and ultimately dominant role of steric stabilization. The results were interpreted in terms of differences in reactivity ratios and water solubilities of the two monomers and their effects on the locus of initiation and growth in the two polymerization processes, as well as the monomer sequence within the polymer chain and degree of homogeniety of the copolymer composition within the particle.

Diaryliodonium salts as thermal initiators of cationic polymerization

Abstract: Diaryliodonium salts (I) undergo efficient thermal decomposition in the presence of copper (II) compounds. Such systems can be employed as a novel class of latent thermal initiators for cationic polymerization. An investigation of the mechanism of the reaction demonstrated that the copper (II) compound is first reduced to the corresponding copper (I) compound, which subsequently reduces the diaryliodonium salt. The cationic polymerization of some typical monomers using these new initiators was carried out to demonstrate the scope of their utility.

Liquid crystal polymers. 15. Synthesis and liquid crystalline properties of alkyl‐substituted polyesters

Abstract: La substitution par un alkyle dans une serie de polyesters cristaux liquides diminue fortement leurs temperatures de transition vitreuse, points de fusion, points d'eclaircissement et les stabilites thermiques des mesophases. Les polymeres avec des substituants n-alkyle lateraux a 8 atomes de carbone ou plus longs ne forment pas de phase liquide cristalline

Macromers by carbocationic polymerization. IV. Synthesis and characterization of polyisobutenyl methacrylate macromer and its homopolymerization and copolymerization with methyl methacrylate

Abstract: This article describes the synthesis and characterization of a new macromer, polyisobutenyl methacrylate (PIB-MA), its free-radical homopolymerization and copolymerization with methyl methacrylate (MMA) to afford the graft copolymer poly(methyl methacrylate-g-isobutylene) (PMMA-g-PIB), the characterization of these polymers, and some physical-mechanical (stress-strain) measurements of the graft copolymer. The key intermediate toward the synthesis of the target macromer was the preparation of polyisobutenyl chloride PIB-Clt by the minifer technique. As shown by 1 H-NMR spectroscopy, and independently by IR spectroscopy coupled with Mn determination, the PIB-MA macromer carries one terminal methacrylate function per polyisobutylene chain. The free-radical homopolymerization of PIB-MA to very high-molecular-weight product was achieved in bulk at 60°C. The free-radical copolymerization of PIB-MA with MMA also occurs readily and is a convenient route to PMMA-g-PIB. The reactivity of PIB-MA is almost identical to that of MMA; however, in highly viscous systems its rate of diffusion to the reaction site is reduced.

Aromatic bisvinyl ethers: A new class of highly reactive thermosetting monomers

Abstract: Aromatic bisvinyl ethers, prepared by the condensation of bisphenols with 2-chloroethyl vinyl ether in the presence of sodium hydroxide, are a new class of thermosetting monomers. These new materials can be polymerized cationically by using diaryliodonium salts as photo and thermal initiators to produce crosslinked resins whose physical and thermal characteristics resemble those of epoxy resins.

Selective surface modification of polymers by means of hydrogen and oxygen plasmas

Abstract: An ESCA investigation has been made of the changes in surface functionalization for a series of polymers effected by means of low-powered inductively coupled rf plasmas excited in hydrogen and oxygen. Reactions in each case are confined to the outermost surfaces of the polymer films and the use of oxygen plasmas leads to extensive oxidative functionalization. Bisphenol-A polycarbonate and polyethylene terephthalate exhibit similar overall reactivities to both oxygen and hydrogen plasmas, while polystyrene is shown to be substantially more reactive than high-density polyethylene to the plasma treatments of interest in this work. Comparison has been made of the effects of straight hydrogen and oxygen plasmas and of sequential hydrogen/oxygen and oxygen/hydrogen plasma treatments.

Investigation of the structure of silk film regenerated with lithium thiocyanate solution

Abstract: The Silk fibers of the mulberry (Bombyx Mori) were dissolved in a 70% lithium thiocyanate solution. Dissolved silk was regenerated by casting the films from the solution after dialyzing. The films were investigated by infrared (IR) spectroscopy and x-ray diffraction analysis. It was found that the freshly prepared film was amorphous. The transformation to the β-form could be brought about by heating, solvent induced crystallization, ultraviolet (UV) radiation, and prolonged storage. The mechanism of this transformation is discussed.

Batch and semicontinuous emulsion copolymerization of vinyl acetate–butyl acrylate. II. Morphological and mechanical properties of copolymer latex films

Abstract: Vinyl acetate/(VAc)-butyl acrylate/(BuA) copolymer latex films of various copolymer compositions were investigated for their morphological properties by electron microscopy techniques, and for their mechanical properties by dynamic mechanical spectroscopy (DMS), differential scanning calorimetry (DSC), and tensile strength measurements. Batch copolymer latex films showed domains of PBuA dispersed in PVAc matrix; the domain sizes were increased with increased BuA content. Semicontinuous latex films were homogeneous in composition. Glass transition temperatures Tg determined from DMS and DSC indicated the presence of two, low and high, transition temperatures for batch latex films. The two temperatures approached the individual homopolymers, with increased PBuA content up to 51 mol %. Semicontinuous latex films showed only one single Tg. Tensile properties of the batch copolymer films showed a higher ultimate tensile strength, higher Young's modulus, and lower percent elongation to break compared to semicontinuous latex films. These differences were found to reflect the effect of mode of monomer addition during the emulsion copolymerization process on the particle morphology, and confirmed earlier data on bulk, colloidal, and surface properties of the same copolymer latexes.

Syndiotactic 1,2‐polybutadiene with Co‐CS2 catalyst system. IV. Mechanism of syndiotactic polymerization of butadiene with cobalt compounds–organoaluminum–CS2

Abstract: A mechanism is proposed for the polymerization of syndiotactic 1,2-polybutadiene (s-PB) with soluble cobalt-organoaluminum-CS2. The proposed active species have structures which consist of side-on coordination of CS2 to cobalt, anti-π-allyl growing end, cisoid bidentate coordination of butadiene, and activation by complex formation with organoaluminum at the nonbonded sulfur of the coordinated CS2. This proposal is based on findings for the aluminum-free catalyst Co(C4H6)(C8H13)-CS2. It is tentatively interpreted that syndiotactic 1,2 polymerization proceeds under the influence of the side-on coordinated CS2, by which the reactivity between the terminal carbons of butadiene and the C3 of the π-allyl end is enhanced.

Photoconductivity and hole transport in polymers of aromatic amine‐containing methacrylates

Abstract: Substantial hole transport can be achieved in organic polymers simply by incorporating aromatic amine groups into the monomer. Hole mobilities similar to or greater than those in poly(N-vinyl-carbazole) (PVK) were measured in a series of high molecular weight arylamine-substituted polymethacrylates. The hole transport in these polymers is electric-field-dependent as in PVK, varying between E and E2 within a range of 4 × 104 − ∼9 × 105 V/cm. The polymers also exhibit carrier generation in ultraviolet (UV) light in the range of absorption. Synthesis of the monomers, their polymerization, and the general properties of these polymers are discussed.

New polymer synthesis. IX. Synthesis of poly(ether sulfone)s from silylated diphenols or hydroxybenzoic acids

Abstract: The condensation polymerizations of bis(4-flurophenyl) sulfone with the bistrimethylsilyl derivates of bisphenol-A, 4,4′-dihydroxydiphenyl sulfone, 1,5′-dihydroxynaphthalene, 3-hydroxybenzoic acid, and 4-hydroxybenzoic acid were investigated. These polycondensations were only successful when potassium or cesium fluoride was used as catalyst. The yields were in the range of 91–98% and the number molecular weights in the range of 2,500–17,500 depending on the reaction conditions. Viscosity and GPC measurements were conducted and glass transitions were determined. Crystallization was never observed.

Mechanism of thermal depolymerization of trimethylsiloxy‐terminated polydimethylsiloxane

Abstract: “Catalyst-free” trimethylsilyl end-blocked polydimethylsiloxanes of Mn = 68,300 and 111,000 were isothermally depolymerized above 400°C. The volatilized products were a mixture of cyclic oligomers and trace quantities of Me3Si(OSiMe2)nOSiMe3 (n = 0,1). The relative degree of polymerization was followed as a function of fractional conversion. The data were consistent with the oretical curves for a mechanism involving initiation by random siloxane bond cleavage followed by a rapid and complete unzipping of the kinetically active fragments. It is suggested that catalysis may be responsible for the initiation process, thus accounting for the low activation energy (43 Kcal/mol) relative to the siloxane bond energy (108 kcal/mol).

Preparation of monodisperse reactive styrene‐glycidyl methacrylate latexes by the emulsifier‐free dispersion copolymerization technique

Abstract: Latexes based on styrene-glycidyl methacrylate copolymers were prepared by the emulsifier-free dispersion copolymerization technique. The main factors affecting the size and morphology of the latex particles and their distribution are the initiator concentration (K2S2O8), the total ionic strength of the aqueous phase, and the total monomer concentration. The existence of critical values for these variables was demonstrated. In the range in which these factors had values below the critical, the synthesized latex particles were spherical, homogeneous, and in varied sizes, depending on the abovementioned parameters in the range of 220–500 nm. Above the critical values of these variables the latex particles consisted of spherical aggregates of smaller particles. The reactive oxirane groups of the latex particles were modified later by hydrolysis, ammonolysis, reaction with Na2S, or periodic acid oxidation of the hydrolyzed or ammonolyzed forms of the latex particles.

Intumescent flame retardants for polymers. II. The polypropylene‐ammonium polyphosphate‐polyurea system

Abstract: The mechanism of action of ammonium polyphosphate (APP) and polyurea (PU) as flame retardant (FR) agents for polypropylene (PP) was examined. The APP–PU system behaves as an intumescent flame-retardant (IFR) formulation. Comparison of the oxygen index (OI) measured on molded pellets and rods, values of the polymer temperature measured just below the burning surface, and visual considerations describe the IFR action of this system. A strong synergism between APP and two of the four polyureas investigated here was ascertained with a maximum 3:1 ratio. Thermogravimetric (TG), OI, nitrous oxide index (NOI), and char-residue measurements were made. On the basis of our data, it can be concluded that polyurea acts as a catalyst for the charring reactions of the APP on PP.

Ultra‐fast polymerization of epoxy‐acrylate resins by pulsed laser irradiation

Abstract: The 337.1-nm emission of a pulsed nitrogen laser was shown to initiate the crosslinking polymerization of epoxy-acrylate photoresists effectively. We evaluated the extent of curing from the amount of insoluble polymer formed and by the decrease in infrared (IR) absorption of the reactive double bond at 810 cm−1. With the large power density available in the laser pulse (0.5 MW cm−2) rates of polymerization as high as 108 mol L−1 s−1 were observed in the presence of air. Quantum yield measurements indicated that each photon absorbed can create as many as 450 crosslinks; the kinetic chain length was calculated as ca. 4000 double bonds polymerized per initiating radical. During the induction period due to oxygen inhibition each photoinitiator radical consumed 1 O2 molecule. The influence of the monomer and photoinitiator used on the sensitivity of the resin was examined; the best performing formulation contained the epoxy-acrylate oligomer, pentaerythritol triacrylate, as monomer and 2,2 dimethoxy-2-phenyl-acetophenone as photoiniatior. All the formulations studied can be cured by a single 500-kW laser pulse of 8 ns duration, provided that the irradiation is carried out in an inert atmosphere or with a focused laser beam.

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. III.†1H- and 13C-NMR study of highly syndiotactic 1,2-polybutadiene

Abstract: The 1H and 13C-NMR spectra of highly crystalline syndiotactic 1,2-polybutadiene (s-PB) are discussed in order to clarify the mechanism of butadiene polymerization with cobalt compound–organoaluminum–CS2 catalysts. Cis opening of the double bonds in the syndiotactic polymerization is affirmed by the study of the copolymer from perdeuteriobutadiene and cis,cis-1,4-dideuteriobutadiene. S-PB (mp 210°C) has 99.7% 1,2 units, 0.3% isolated cis-1,4 units, and 99.6% syndiotacticity. Polymer ends (2-methyl-3-butenyl group and conjugated diene structure) are also determined. The differences in free energy of activation between 1,2 and cis-1,4 propagation and between syndiotactic and isotactic propagation are 14.0 and 9.6 kcal/mol, respectively, for Co(acac)3-AlEt3-AlEt2Cl-CS2, and 6.7 and 5.7 kcal/mol, respectively, for the aluminum-free Co(C4H6)(C8H13)CS2 system. The conformation of s-PB in o-dichlorobenzene at 150°C is described by the sequence (tt)1.6(gg)(tt).

Graft polymerization of acrylic monomers onto starch fractions. I. Effect of reaction time on grafting methyl methacrylate onto amylose

Abstract: A study was made of the ceric-ammonium-nitrate-initiated graft polymerization of methyl methacrylate (MMA) onto a lineal fraction of starch (amylose). Grafting yields were determined by extraction with appropriate solvents: 1,2-dichloroethane for homo-PMM, and 0.5N NaOH for ungrafted amylose. Percent grafting was calculated by acid hydrolysis with 1N HCl. Molecular weights of PMMA side chains were determined by gel permeation-chromatography. Grafting efficiencies ranged from 72 to 83%, grafting, from 190 to 271%, and frequency of attachment of side chains, from 900–1250 glucose units per chain. The results observed are discussed.