Graft copolymers obtained by radiation grafting of methacrylic acid onto polypropylene films

Direct radiation grafting of methacrylic acid (MAA) onto polypropylene films (PP) was studied. The effect of different solvents such as benzene, distilled water, dimethyl formamide, isopropanol, isopropanol/water-mixture, on the swelling and the grafting process of MAA onto (PP) films was investigated. It was found that the grafting process was enhanced under vacuum irradiation in benzene as a diluent for MAA as compared with other solvents examined. The dependence of the grafting rate on such monomer concentrations was found to be 1.2 order. The relationship between the grafting rate and film thickness gave a negative first order dependence. This grafting system proceeded by a diffusion controlled process. Some selected properties of the grafted films such as mechanical and electrical properties, swelling behaviour, and gel determination, were also investigated.     

A general method of analysis for high volume air samples. I

Summary Sulphuric acid, found as such in air, may be measured accurately by separation of the sulphuric acid from the sample matrix by microdiffusion at 200° C, which effectively separates volatile from nonvolatile sulphate. The muasurement of the separated volatile sulphate (sulphuric acid) may then by carried out by a microtitration specific for sulphate or by square wave polarography, the latter method being much more rapid.The method proposed is free from the inaccuracies and ambiguities associated with procedures which depend upon p_h measurement or non-specific acid-base titration.

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Zusammenfassung In Luftproben als solche auftretende Schwefelsäure läßt sich genau bestimmen, indem man sie vorher durch Mikrodiffusion bei 200° von nichtflüchtigem Sulfat abtrennt. Die Messung erfolgt dann entweder durch eine spezifische Mikrosulfattitration oder durch Rechteck-Wellen-Polarographie. Letztere Methode ist rascher. Das vorgeschlagene Verfahren ist frei von Unsicherheiten und Ungenauigkeiten, wie sie anderen Verfahren anhaften, die auf der p_h-Messung oder auf unspezifischer Säure-Base-Titration beruhen.

     

Block copolymers of polystyrene and poly(dimethyl siloxane). I. Synthesis and characterization

The block copolymers of the ABA type, poly(dimethyl siloxane-b-styrene-b-dimethyl siloxane), were synthesized by the anionic polymerization of styrene and cyclic siloxane monomer, hexamethyl cyclotrisiloxane (D₃) or octamethylcyclotetrasiloxane (D₄), with lithium or sodium biphenyl as initiator. The effect of initiator concentration, gegenion, and the polymerization temperature for styrene on molecular weight distribution (MWD) was investigated. Gel permeation chromatography (GPC) data show broader MWD of polystyrene prepared by sodium biphenyl in comparison to that produced by lithium biphenyl. The block copolymers have been characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectra. The influence of dimethylsiloxy units on thermal stability of the copolymers has also been discussed.     

Anionic copolymers of caprolactam with laurolactam (nylon 6/12 copolymers)—I. Preparation and general properties

Copolyamides of high mol.wt were obtained by the anionic copolymerisation of ?-caprolactam with ω-laurolactam at 180°C, using a sodium caprolactamate-N-phenylcarbamoylcaprolactam initiator activator system. The proportions of co-units in the copolymers were close to those in the comonomer feeds. The copolymers were crystalline and substantially fully hydrogen-bonded over the whole range of compositions, except at 50/50 mole% ratio, each displayed only one crystalline phase corresponding to that of the major component. T_m and density measurements indicated a crystallinity minimum at 50 60 mole% NH(CH₂)₅CO unit content. The properties of the copolyamides were consistent with random copolymeric structures.     

Radical grafting on lignin. Part I. Radiation-induced grafting of styrene onto hydrochloric acid lignin

By irradiation with gamma rays styrene was grafted onto hydrochloric acid lignin. When the graft polymers were subjected to nitrobenzene oxidation, the vanillin yields indicated two kinds of reaction occurring in the grafting. Polystyrene branches were separated from the graft polymers, and their M?_n were determined osmometrically. At grafting ratios of up to 100 the vanillin yields diminished proportionately with increasing grafting, and the M?_n of the branches, 5000, was unchanged. At grafting ratios of more than 100 the vanillin yields were constant, independent of the ratios, but the M?_n values of the branches increased with grafting. Paper chromatography of the aromatic acids obtained by oxidation of methylated lignin and the graft polymer indicated that isohemipic and metahemipic acids were more abundant in the acid fraction of the graft polymer than in the lignin itself. A qualitative mass analysis of the gaseous products evolving from the irradiated lignin showed the presence of hydrogen molecules only. Gamma-ray radiation brought about no change in the yields of vanillin. It was therefore concluded that radiation grafting on lignin at grafting ratios of less than 100 proceeded through the addition of the styrene polymer radicals to the aromatic nuclei of the lignin and that then branches propagated from the aliphatic part of the lignin, where C? H bond scission had been caused by the irradiation. The grafting sites of lignin would be C-5 and C-6 of the guaiacyl nucleus and, probably the β and γ carbon atoms of the aliphatic side chain of the lignin.     

A general method for the formation of diaryl selenides using copper(I) catalysts

We report a mild, palladium-free synthetic protocol for the cross coupling reaction of aryl iodides and phenyl selenol using 10 mol% CuI/neocuproine, NaOt-Bu or K₂CO₃ as base, in toluene, at 110°C. Using this protocol, we show that a variety of diaryl selenides can be synthesized in good yields from commercially available aryl iodides.     

A general method for the formation of aryl-sulfur bonds using copper(I) catalysts

[reaction: see text] We report a mild, palladium-free synthetic protocol for the cross-coupling reaction of aryl iodides and thiols using 10 mol % CuI and 10 mol % neocuproine, with NaOt-Bu as the base, in toluene at 110 degrees C. Using this protocol, we have shown that a variety of aryl sulfides can be synthesized in excellent yields from readily available iodides and thiols.     

Arm-first method as a simple and general method for synthesis of miktoarm star copolymers

Miktoarm star copolymers containing two or more arm species were synthesized by atom transfer radical polymerization using a simple and general "arm-first" method, that is, one-pot cross-linking a mixture of different linear macroinitiator (MI) species by a divinyl cross-linker, such as divinylbenzene. Using linear MIs with a high degree of bromine chain-end functionality, including polyacrylate, polystyrene, polymethacrylate and poly(ethylene oxide), resulted in high-yield star polymers (>90%). Characterized by liquid adsorption chromatography techniques, which separated star polymers on the basis of the chemical composition of arms, the obtained star product was proved to be miktoarm star copolymers containing two or more arm species in one molecule, instead of mixture of different homoarm star polymers. Within our investigation, the molar ratios of the arms in the miktoarm star copolymers were always in agreement with the composition of the initial MI mixture, indicating the powerful capacity of this arm-first method for synthesis of miktoarm star copolymers with potentially any molar ratios and species of the arms. By using a mixture containing five types of linear MIs with different chemical compositions, miktoarm star copolymers containing five kinds of arms were synthesized for the first time, which significantly expanded the methodologies for synthesis of miktoarm star copolymers by living polymerization techniques.     

Block copolymers of poly(ethylene terephthalate–polybutylene terephthalate). I. Preparation and crystallization behavior

Block copolymers of two crystallizable compounds, poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), were developed with PET as the major component and the amount of PBT varying from 1.0 to 20.0 wt %. These block copolymers were prepared by end-group coupling of preformed oligomers. All polymers prepared were of equivalent molecular weight as determined by the intrinsic viscosity method. Thermal properties were determined by differential thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). With increasing PBT content, the block copolymers showed a general decrease in the values of glass transition temperature, melting temperature, initial decomposition temperature, and maximum decomposition temperature. The heat of fusion and heat of crystallization first increased and then decreased slightly. Rates of crystallization were determined by measuring density as a function of time of isothermal crystallization carried out at 95°C. It was found that small amounts of PBT increased the crystallization rate considerably over that of PET. Random copolymers did not show this phenomenon and behaved more like pure PET. The crystallization behavior of block copolymers was analyzed by the Avrami equation and Avrami exponents were determined. Results were explained on the basis that the faster-crystallizing PBT blocks crystallized first and provided built-in nucleation sites for the subsequent crystallization of PET, thus resulting in a relatively fast-crystallizing copolyester.     

Polymeric catalysis: Imidazoles grafted onto poly(vinylamine). I. Synthesis and grafting of imidazolylalkanoic acids

Some ω-(1-imidazolyl) and ω-[4(5)-imidazolyl]alkanoic acids were synthesized and grafted onto poly(vinylamine) with an amide bond. These water-soluble grafts were used to study the kinetics of the esterolysis of activated phenyl esters. The 1-substituted imidazoles were prepared by the reaction of the sodium salt of imidazole with the ethyl ω-bromoalkanoates. The 4(5)-substituted imidazoles were prepared from urocanic acid or 4(5)-hydroxymethylimidazole. The ω-(1-imidazolyl)alkanoic acids were grafted onto poly(vinylamine) via their acyl–guanidine derivatives; the 3-[4(5)-imidazolyl]propanoic acid was grafted with a water-soluble carbodiimide.     

Electron microscopic studies of SBS block copolymers I. A method to study the temperature dependence of phase separation

The potential applicability of a Film Formation Method of Crystal Growth to the study of morphological aspects of amorphous polymers was investigated using transmission electron microscopic techniques. A wide variety of morphologies of styrene-butadiene-styrene triblock copolymer can be achieved by varying the solvent power and film preparation temperatures. The effect of film preparation temperature indicates that below 100 °C (the glass transition temperature of polystyrene), there is very little change in the size of domains; above 100 °C a drastic change in morphology is observed. Not only is there rapid coarsening of both the constituent phases of the polymer above 100 °C, but also an intermixing of both phase components of the block copolymer. It was demonstrated that some monomeric materials are effective in maintaining the original morphology of the film; i. e. phase mixing is prevented.     

Graft copolymers of polyurethane with various vinyl monomers via radiation-induced miniemulsion polymerization: Influential factors to grafting efficiency and particle morphology

Graft copolymers of polyurethane (PU) with various vinyl monomers were synthesized through a one-pot but two-step miniemulsion polymerization process. Firstly, the polycondensation of isophorone diisocyanate (IPDI) with hydroxyl-terminated polybutadiene (HTPB) had been performed in aqueous miniemulsion at 40 °C in order to obtain PU dispersions. Consecutively, an in-situ graft copolymerization of the vinyl monomers with the synthesized PU was initiated by γ-ray radiation at room temperature. The grafting efficiency of PU with vinyl monomer (G_PU/monomer) was calculated from ¹H NMR spectra and the particle morphology of the final hybrid latex was observed by transmission electron microscopy (TEM). As there was no monomer transferring in miniemulsion system, homogenous hybrid particles would be synthesized provided that the monomer was miscible with PU, such as styrene. With the increase of the polarity of the monomer, the compatibility of PU with monomer decreased. G_PU/monomer varied as G_PU/styrene(37%)>G_{PU/butyl acrylate (BA)}(21%)>G_{PU/methyl methacrylate (MMA)}(12%). The proportion of homogeneous nucleation would increase as the hydrophilicity of the monomer increased. High temperature would destabilize the miniemulsion so as to result in a less grafting efficiency. Compared to the phase separation during the seeded emulsion polymerization, the miniemulsion polymerization method facilitated the preparation of homogeneous materials owing to its monomer droplet nucleation mechanism.     

Photoexcited behavior of nitrogen heteroaromatics (I). photoesterification of phenanthridine in carboxylic acid.

Photoirradiation of phenanthridine (I) derivatives in carboxylic acid caused esterification of (I). Different reactivity from those of other heteroaromatics is discussed.     

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

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

A general method for the n-alkylation of thioamides.

Thioamides are N-alkylated in a two-step procedure: (i) Reaction with an aldehyde and benzotriazole yields an adduct which is (ii) reduced to the N-alkylthiomide by NaBH₄.     

A general method for synthesis of folic acid, its conjugates and analogues (author's transl)]

A general method for synthesis of folic acid, its conjugates and analogues . A new and general method for the synthesis of folic acid, folic acid conjugates and folic acid analogues is described. The key step, i.e. the condensation of N(2′)-acetyl-6-formyl-pterine (I: R¹ ? COCH₃) with aminoaryl derivatives II, is achieved by refluxing in absolute ethanol to afford the azomethines III. NaBH₄-reduction followed by basic hydrolysis gives pure V products in high yield, free from 7-isomers.     

Free-radical grafting of monomers to polydienes. I. Effect of reaction conditions on grafting of styrene to polybutadiene

The radical-induced grafting of styrene onto polybutadiene (PBD) in benzene solution at 60°C has been studied. Provided the PBD concentration is kept below about 1.0 monomermole/l. the polymerization of styrene shows normal kinetic behavior. The proportion of polystyrene incorporated as graft is independent of the initiator (benzoyl peroxide) concentration but increases as the ratio of PBD to styrene in the reaction medium increases. Azobisisobutyronitrile produces no graft copolymer in this system. It appears that the reaction leading to graft formation is direct attack of initiator radicals on the rubber, probably by a hydrogen-abstraction reaction.