Synthesis and properties of poly α-esters containing fluorine: I. introduction and precursor preparation

Present knowledge relating to the effect of fluoroaromatic residues on the properties of polymers and the limited literature on the synthesis and properties of fluorine-containing polyesters are briefly discussed. The use of α-hydroxy carboxylic acid anhydrosulphites in the preparation of poly α-esters is described, together with the potential use of this route in the evaluation of the effect of fluoroaromatic substituents on the properties of these polymers. Details of a series of new Grignard syntheses of α-pentafluorophenyl-α-hydroxy carboxylic acids from the commercially available bromopentafluorobenzene and of the conversion of these acids to the anhydrosulphites via the reaction of thionyl chloride on the anhydrous cupric salts of the acids are presented. In this way a series of intermediates has been synthesised from which new fluorine-containing polymers may be prepared.     

Studies of the reactions of anhydrosulphites of α-hydroxy acids,part IX. thermal polymerisation of anhydrosulphites of α-hydroxy α-methyl carboxylic acids

The anhydrosulphites of a series of unsymmetrically substituted α-hydroxy acids have been prepared and their susceptibility to polymerisation by thermal decomposition studied. The first order rate determining ring scission process, leading to the formation of a reactive α-lactone intermediate which then undergoes spontaneous polymerisation, is the predominant mechanism even with substituents up to C₈. As the length of the n-alkyl substituent is increased the rate of decomposition and thus polymerisation increases until a plateau value is reached at around C₃. Further increase in substituent length decreases the rate of decomposition, an effect which is attributed to steric hindrance of the leaving group by long (C₆—C₈) substituents.     

Anhydrocarboxylate and anhydrosulphite derivatives of α-thiocarboxylic acids: Synthesis,purification and characterisation

The syntheses of anhydrosulphite and anhydrocarboxylate derivatives of α-thioglycollic and α-thiolactic acids by reaction of thionyl chloride and phosgene with both the parent acids and their copper salts have been examined. The preferred method, involving direct reaction with the acid, produced reasonable (30–65% depending on acid structure) yields of the required compounds. Successful synthesis of the anhydrocarboxylate of α-thioisobutyric acid involved the simultaneous addition of phosgene and pyridine to the acid solution in order to promote formation and cyclisation of the intermediate. Characterisation of the purified products was carried out by infrared and mass spectrometry together with gas evolution techniques.     

Photochemistry of α,α′-Disubstituted Azoalkanes. I. Photosolvolytic Inversion and Substitution of α,α′-Dichloro- and α,α′-Dialkoyloxyazoalkanes

A series of α,α′-dichloro (α DClA), α,α′-dialkoyloxy- (αDAlA) and α,α′-dibenzoxy-azoalkanes (αDBeA) without α-aryl substituents was found to undergo meso ? dl photointerconversion upon direct irradiation through Pyrex in the presence of oxygen in a number of solvents. Furthermore, irradiation of α,α′-dipropionoxy-azoalkanes in benzene in the presence of excess acetic acid leads to substitution of the propionoxy groups by acetoxy groups in addition to meso ? dl photointerconversion. Similar irradiation in the presence of CH₃CO₂D does not lead to deuterium substitution of the β-hydrogens. The presence of benzenethiol radical scavenger does not affect the course of these photoreactions. Photosolvolysis schemes involving heterolysis (in the case of αDAlA and αDBeA) or an unstable intermediate (in the case of αDClA) are proposed.     

Untersuchungen zur proteasekatalysierten und chemischen Peptidbindungsknüpfung mit α-trifluormethylsubstituierten α-Aminosäuren

Protease Catalyzed and Chemical Peptide Bond Formation with α-Trifluoromethyl Substituted α-Amino Acids Subtilisin, α-chymotrypsin and papain catalyzed hydrolyses of α-trifluoromethyl substituted N-benzyloxycarbonyl amino acid methylesters (Z-TFM-Xaa-OMe) 1 can be achieved only in the case of 3,3,3-trifluoroalanine. Enzymatic incorporation of Z-TFM amino acids 2 into N-terminal position of dipeptides also fails. In contrary, dipeptides with a TFM amino acid moiety in N-terminal position, e.g. TFM-Phg-L-Phe-OMe 5 , react with H-Leu-NH₂ to give the corresponding tripeptides 6 in high yield. Z protected dipeptide derivatives 8 with N-terminal TFM amino acids can be obtained via 4-trifluoromethyl-5-(4H)-oxazolones 7 .     

Radiation degradation of α-substituted acrylate polymers and copolymers

Radiation degradation is observed in poly(methyl α-chloroacrylate), poly(methyl α-cyanoacrylate), and poly(α-chloroacrylonitrile) homopolymers and their respective MMA copolymers when γ-irradiated in vacuo. Polymer degradation susceptibilities are quantified in terms of G(scission radicals) and G(scission) ? G(crosslinks), measured by EPR and membrane osmometry, respectively, values by these two methods are compared. Higher G(rads) values ranging from 2 to 6 and [G(s) ? G(x)] values ranging from 2 to 11 are obtained for the substituted polymers and copolymers relative to the values for PMMA (1.6; 1.9), a standard e-beam positive resist, which suggests that these modified polymers are more sensitive e-beam resists than PMMA.     

Untersuchungen zur Knüpfung der Peptidbindung mit α-trifluormethylsubstituierten α-Aminosäuren

Chemical Peptide Bond Formation with α-Trifluoromethyl Substituted α-Amino Acids The reaction of α-trifluoromethyl substituted N-^tbutoxycarbonyl amino acids (Boc-TFM-Xaa-OH) 1 with dicyclohexylcarbodiimide results in formation of 2-^tbutoxy-4-trifluoromethyl-5(4H)-oxazolones 2 within minutes. Compounds 2 react with amino acid esters to give Boc protected dipeptide esters 4. However, at room temperature compounds 2 decompose to give Leuchs anhydrides 3 , via retro ene reaction. Therefore, α-trifluoromethyl substituted N-^tbutoxycarbonyl amino acids (Boc-TFM-Xaa-OH) are of limited value for peptide synthesis.     

Spektroskopische Untersuchungen an 4-Nitrophenylhydrazonen sekundärer und tertiärer α-Ketocarbonsäureamide

Spectroscopic Studies on 4-Nitrophenylhydrazones of Secondary and Tertiary α-Ketoamides 4-Nitrophenylhydrazones of secondary and tertiary α-ketoamides both exist in two stable isomeric forms (E/Z) with respect to the position of the substituents at the CN-Bond. But whereas the Z-form of the secondary amides can be easily assigned by means of intramolecular hydrogen bond, this criterion in case of most the derivatives of tertiary amides fails. As shown by derivatives of glyoxylic acid this deviation is evidently caused by steric facts due to the double substituted amide group and the alkyl residue on the α-C-atom.     

Organocatalytic Enantioselective Aziridination of α‐Substituted α,β‐Unsaturated Aldehydes: Asymmetric Synthesis of Terminal Aziridines

The first example of a highly enantioselective organocatalytic aziridination of α‐substituted α,β‐unsaturated aldehydes is presented. The reaction is catalyzed by simple chiral amines and gives access to highly functional terminal azirdines containing an α‐tertiary amine stereocenter in high yields and enantiomeric ratios (95.5:4.5–98:2).     

Preparation and Application of Iron‐substituted (Z)‐Enals: Synthesis of 5‐Substituted α,β‐Butenolides

A reaction sequence furnishing cyclic β‐[η⁵‐C₅H₅(CO)₂Fe]‐substituted enals 5 starting from β‐keto esters 1 is described. Organolithiums were found to react smoothly with the iron‐substituted enals yielding α,β‐butenolides 6 by an intramolecular cyclocarbonylation of the lithiumalkoxide initially formed. The influence of e.g. the reaction temperature and the solvent on the reaction cascade is discussed. A reaction mechanism is proposed.     

Cationic copolymers of α,β‐poly‐(N‐2‐hydroxyethyl)‐DL‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy): synthesis and characterization

In the present study the derivatization of two water‐soluble synthetic polymers, α,β‐poly(N‐2‐hydroxyethyl)‐DL ‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy), with glycidyltrimethylammonium chloride (GTA) is described. This reaction permits the introduction of positive charges in the macromolecular chains of PHEA and PAHy in order to make easier the electrostatic interaction with DNA. Different parameters affect the reaction of derivatization, such as GTA concentration and reaction time. PHEA reacts partially and slowly with GTA; on the contrary the reaction of PAHy with GTA is more rapid and extensive. The derivatization of PHEA and PAHy with GTA is a convenient method to introduce positive groups in their chains and it permits the preparation of interpolyelectrolyte complexes with DNA. © 2000 Society of Chemical Industry     

A Ring‐Closing Metathesis Approach to Cyclic α,β‐Dehydroamino Acids

A comprehensive study on the synthesis and ring‐closing metathesis (RCM) of α,β‐dehydroamino acids is described. This sequence has led to the formation of a range of biologically relevant functionalized nitrogen heterocycles. The incorporation of chiral building blocks in the RCM precursors eventually resulted in the formation of optically active 4‐substituted cyclic dehydroamino acids. In addition, olefin isomerization under metathesis conditions was observed for a number of compounds, which could be successfully inhibited either by the introduction of allylic substituents or by the addition of a ruthenium hydride scavenger.     

Highly Efficient Suzuki Coupling Reaction of α‐Chloroalkylidene‐β‐lactones and β‐Lactams with Organoboronic Acids

The activation of C Cl bond of (Z)‐α‐chloroalkylidene‐β‐lactones and (E)‐α‐chloroalkylidene‐β‐lactams via the Suzuki cross‐coupling reaction is reported in this paper. Alkyl, heteroaromatic, substituted phenyl‐ and alkenylboronic acids can be coupled with a wide variety of α‐chloroalkylidene‐β‐lactones and β‐lactams in excellent yields within a short period of time. The cross‐coupling reaction of optically active substrates leads to the optically active compounds without racemization of the corresponding chiral center.     

Photosensitive polymers: Synthesis,characterization, and photocrosslinking properties of polymers with pendant α,β-unsaturated ketone moiety

Acrylate and methacrylate monomers with the photodimerizable α,β-unsaturated ketone moiety, such as 4-cinnamoylphenyl, 4-(4-methoxycinnamoyl)phenyl, 4-(4-nitrocinnamoyl)phenyl, or 4-(4-chlorocinnamoyl)phenyl, were prepared and homopolymerized using benzoyl peroxide as the initiator at 70°C in methyl ethyl ketone. The poly(meth)acrylates were characterized by ultraviolet, infrared, ¹H-nuclear magnetic resonance (NMR), and ¹³C-NMR spectra, and gel permeation chromatography. Their thermal properties were studied by thermogravimetric analyses in air and nitrogen, and differential scanning calorimetry. The photocrosslinking properties of the polymers were investigated as thin films and in solution in the presence and absence of sensitizer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2111–2120, 1998     

Cationic polymerization of α-methyl styrene from polydienes. II. Tensile properties of poly(butadiene-g-α-methyl styrene) and poly(styrene-b-butadiene-g-α-methyl styrene) copolymers

Tensile properties of poly(butadiene-g-α-methyl styrene) copolymers have been investigated on molded samples. These graft copolymers show thermoplastic elastomer behavior because of their graft copolymer structure. Both modulus and strength increase with increasing α-methyl styrene content and tensile strength is highest at the 45–50% by weight α-methyl styrene level. Tensile strength at elevated test temperatures is considerably higher for these poly(butadiene-g-α-methyl styrene) copolymers than for styrene-butadiene-styrene triblock polymers. This is attributed to the higher glass transition temperature for poly(α-methyl styrene) segments compared to polystyrene segments. The oil acceptance of these graft copolymers appears to depend on the number of loose polybutadiene chain ends. Thus, the tensile strength of oil-extended poly(butadiene-g-α-methyl styrene) copolymers was considerably lower than oil-extended poly(styrene-b-butadiene-g-α-methyl styrene) copolymers even though both copolymers contained equal hard segment contents.     

Reaktion von γ-Halogen-α-cyancrotonsäurenitrilen mit Aminen

Reaction of α-Cyano-γ-halo-crotonitriles with Amines α-Cyano-γ-halo-crotonitriles 1 react with primary amines and ammonia, respectively to form substituted 2-amino-3-cyanopyrroles. From arylamines, 1-arylpyrroles are obtained; with alkylamines, however, 2-alkylaminopyrroles result. Starting from γ-bromonitrile 1b and ammonia, the formation of pyrrole is connected with a rearrangement. The reaction of α-chlorocyclohexylidenemalonitrile 1c with hydrazine yields the dihydropyridazine 11 which can be converted by thermal dehydrocyanogenation to the 3-aminopyridazine 12 .     

Photosensitivities and rates of photocrosslinking of poly(vinyl α-cyanocinnamate) and poly(vinyl α-cyanocinnamoxy acetate)

The photosensitivities and the rates of photocrosslinking of poly(vinyl α-cyanocinamate) and poly(vinyl α-cyanocinnamoxyacetate) were investigated. The photocrosslinkings of these polymers proceeded mainly through radical addition, and these polymers showed higher photosensitivities than poly(vinyl cinnamate) and poly(vinyl cinnamoxyacetate), in spite of lower rates of photocrosslinking of the former polymers.     

Interface formation of Ca with poly(p-phenylene α,α′-diphenyl vinylene) and poly(p-phenylene α-phenyl vinylene)

We have investigated the interface formation of Ca with poly(p-phenylene α,α′-diphenyl vinylene) (PPV-DP) and poly(p-phenylene α-phenyl vinylene) (PPV-P) using X-ray photoemission spectroscopy (XPS). Similarly to our earlier findings in metal/PPV interface formation, the O 1s peak shifted toward a lower binding energy as soon as Ca was deposited on to the polymers. This was accompanied by the formation of Ca? O, suggesting a chemical origin for the O 1s shift. By contrast, the C 1s peak shift toward a lower binding energy was observed relatively later, after about 4 Å of Ca deposition. At the same time, a new C 1s component became noticable at about ?1.5 eV relative to the initial C 1s peak. This component signifies the possibility of polymer disruption by the Ca atoms to form Ca? C species. The C 1s peak shift is attributed to Ca induced surface band bending and barrier formation as in the case of metal/PPV interface formation. The disruption of the polymer may also induce changes in the interface electronic states and contribute to the C 1s peak shift. From the intensity attenuation analysis, we conclude that the initial 15 Å of Ca overlayer is contaminated by the Ca? O and Ca? C species and the overlayer is pure beyond 15 Å of Ca coverage.     

Synthesis of α, α′, β-trideuterovinyl acetate

Reaction conditions for the synthesis of α, α′, β-trideuterovinyl acetate by the continuous vapour phase catalytic reaction of deuteroacetylene and acetic acid-d (CH₃COOD) are described.     

Grafting of ethyl α-cyanacrylate on poly(vinyl alcohol)

Because hydrophilic copolymers containing cyanacrylate elements should be useful as components of adhesives in surgery, the conditions of grafting of ethyl α-cyanacrylate on poly(vinyl alcohol) were studied. Two anthraquinone derivatives were applied as sensitizers in UV-initiated grafting; 2,6-disulfoanthraquinone sodium salt proved to be especially efficient. IR spectra and derivatograms of poly(vinyl alcohol-g-ethyl α-cyanacrylate) are described.