R. Velichkova

Modification of styrene-isoprene block copolymers—3. Addition of maleic anhydride—mechanism

Abstract The mechanism and site of addition of maleic anhydride to styrene-isoprene block copolymers have been investigated. Conditions have been found for modification of the olefinic unsaturation up to 15–20% without crosslinking. 1 H-NMR and 13 C-NMR and i.r. spectra showed that the modification conducted at 70°C with α,α′-azoisobutyronitrile as initiator proceeds only as substitution at allylic positions.

Separation and characterization of ɛ-caprolactone oligomers by gel permeation chromatography

SummaryIt is shown that the combined use of gel permeation chromatography and the isocyanate method of determination of hydroxyl end groups extends the possibilities for studying complex oligomer mixtures of ɛ-caprolactone. Oligomer mixtures of ɛ-caprolactone obtained by (C6H5)3CSbCl6 and by (C6H5)3CK are investigated. At initiation by both the initiators — the cationic and the anionic one — a covalent bond between the initiator and the polymer chain is formed. In the case of the initiation by (C6H5)3CK intramolecular transesterification proceeds which results in cyclic oligomers. At initiation by (C6H5)3CSbCl6 linear oligomers are formed. It is assumed that the ɛ-caprolactone polymerization by (C6H5)3CSbCl6 proceeds by alkyl-oxygen bond scission.

Modified poly(vinyl acetals)

Abstract New amphiphilic copolymers based on poly(vinyl alcohol) have been synthesized. By reaction with aliphatic and aromatic aldehydes, poly(vinyl acetals) (PVAc) having various degrees of acetalization have been obtained. The products with 40–50% acetalization possess appropriate hydrophilic-hydrophobic character. Modification of PVAc by various methods of grafting leads to poly(vinyl acetal)-g-poly(ethylene oxide). Their structural characteristics and swelling behaviour have been investigated.

Modification of styrene-isoprene copolymers—2. Chain extension with ethylene oxide

Abstract Chain extension of styrene-isoprene hydroxyl-terminated prepolymers was used to obtain polymers having different sequences and lengths of styrene, isoprene, ethylene oxide and 1,3,6-trioxacyclo-octane blocks. The structures and the chemical and composition homogeneities of the copolymers were determined by 1H-NMR and i.r. spectra, GPC analyses (with u.v. and RI detectors), DSC and by data on swelling and surface tension behaviour.

Modification of styrene-isoprene copolymers—1. End-terminated products

Abstract Functionalization of various types of mono- and α, ω-bifunctional copolymers was achieved by termination with carbon dioxide, the potassium salt of chloracetic acid, maleic anhydride, carbon disulphide or ethylene oxide. The functionality was determined on the basis of M n (GPC and VPO) and the concentration of the end-groups obtained from 1H-NMR and i.r. spectra. The experimental conditions for quantitative carbonation and hydroxylation without side reactions were established.

Modification of styrene-isoprene block copolymers—4. Addition of maleic anhydride-kinetic investigations

Abstract A kinetic study of the addition of maleic anhydride to styrene-isoprene block copolymers at 60, 70 and 80° in the presence of α,α′-azoisobutyronitrile has been made using i.r. spectroscopy. The reaction is first order with respect to maleic anhydride. The order with respect to α,α′-azoisobutyronitrile varies from 0.7 at 80° to 1.1 at 60°. The apparent rate constants have been determined by the Guggenheim method.

Polymerization of ε-caprolactone initiated by stable salts. Initiation mechanism

Abstract The mechanism of initiation of e -caprolactone polymerization by stable salts has been investigated. Gel permeation chromatography and 1 H-NMR spectroscopy were used for determining the compositions of the reaction mixtures and of the polymers. It was established that the initiation proceeds by addition of the initiator to the monomer.

Modification of styrene-isoprene block copolymers—5. Grafting

Abstract Various graft copolymers were obtained by ring-opening of succinic groups in styrene-isoprene block copolymers, modified with maleic anhydride, using reagents containing nucleophilic groups. Comblike hydrophilic graft copolymers were prepared using polyethylene glycol-550-monomethyl ether or polyethylene glycol-2000-monomethyl ether. By interaction with hydroxypropyl methacrylate, ethanolamine or ethylene diamine, films with various extents of crosslinking were obtained. Copolymers were characterized by 1 H-, 13 C-NMR and i.r. spectra, GPC and LS analyses. The thermal behaviour of polyethylene glycol grafted copolymers was studied by DSC. Amphiphilic properties of the products were examined by investigation of their water uptake, contact angle, interfacial tension and Cu 2+ transfer.

Hydride transfer to stable carbenium salts

SummaryThe interaction between (C6H5)3CSbCl6, (C6H5)2CHSbCl6, (ClC6H4)3CSbCl6 and poly(ɛ-caprolactone), dimers of α-methyl-styrene and of 1,1-diphenylethylene is investigated. By the use of 1H-NMR spectroscopy it is found that hydride transfer proceeds to the stable salts.

Polymerization of δ-valerolactone and β-propiolactone initiated by stable salts. Initiation mechanism

Abstract The initiation of δ-valerolactone and β-propiolactone polymerization by stable organic cation salts has been investigated. GPC and 1H-NMR spectroscopy were used. The results are compared with previous results on e-caprolactone polymerization. It is concluded that initiation of polymerization for lactones with stable salts is mainly by addition of the initiator to the monomer and that the steric hindrance of the initiator cation is of importance. Initiation by hydride transfer takes place in some cases and is discussed.