Synthesis of novel chitin derivatives having poly(2-alkyl-2-oxazoline) side chains

Novel chitin derivatives having poly(2-alkyl-2-oxazoline) side chains, i.e., chitin-graft-poly(2-methyl-2-oxazoline) ( 4a ) and chitin-graft-poly(2-ethyl-2-oxazoline) ( 4b ), were synthesized by means of the reaction of ca. 50% deacetylated chitin ( 3 ) with living poly(2-methyl-2-oxazoline) ( 2a ) and poly(2-ethyl-2-oxazoline) ( 2b ), respectively. The reaction between amino groups of 3 and the oxazolinium active species of 2 was examined by changing molar ratios of the feed ([ 2 ]₀/[D -glucosamine units of 3] ₀, ranging from 1,0 to 9,9) under mild conditions (at 27°C in dimethyl sulfoxide (DMSO)). 4a having monodisperse poly(2-methyl-2-oxazoline) side chains on almost every D -glucosamine unit of the main chain was obtained in 35% yield. The number of poly(2-alkyl-2-oxazoline) side chains was roughly controlled by the molar feed ratio of 2 and 3 . 4 is soluble in water, N,N-dimethylformamide, and DMSO, and partially soluble in methanol, acetonitrile, and chloroform. 4 shows improved solubilities in organic solvents, compared with 3 or chitin. The molecular motion of 4b in aqueous solution was discussed by employing ¹H NMR analytical data measured with changing temperature and solvent. In D₂O and, especially, in DMSO, it is suggested that motion of the chitin backbone is restricted, compared with that of the poly(2-ethyl-2-oxazoline) side chain. The content of the side chain in 4 was calculated from the ¹H NMR spectra recorded in D₂O/CD₃CO₂D (vol. ratio 95:5) above 60°C.     

Kinetics and mechanism of the isomerization polymerization of 2-methyl-2-oxazoline by benzyl chloride and bromide initiators. Effect of halogen counteranions

Kinetic studies of the isomerization polymerization of 2-methyl-2-oxazoline ( 2 ) initiated with benzyl chloride ( 1a ) or bromide ( 1b ) were carried out by NMR spectroscopy. The polymerization initiated with 1a proceeded exclusively via a covalently bonded alkyl chloride species 5 , whereas the polymerization of the system initiated with 1b proceeded via a oxazolinium bromide 10 as the propagating end. The propagation rate constant k_p with 1a was about 1/40 of that found with 1b at 40°C in CD₃CN. The mechanistic difference is explained by the different nucleophilicities of the counteranions, Cl^— and Br^—. A model compound for the propagation with 1b as initiator was also examined changing the temperature and the solvent.     

Synthesis and copolymerization of macromonomers based on 2-nonyl- and 2-phenyl-2-oxazoline

Several macromonomers were prepared by cationic ring-opening polymerization of 2-nonyl- and 2-phenyl-2-oxazoline using different techniques of functionalization. Introduction of the unsaturated functional group directly via a suitable termination agent proved to be superior to the use of a phenol-functionalized initiator and to the introduction of hydroxyl end groups via hydrolysis of the reactive cationic chain end and subsequent esterification with methacryloyl chloride. The macromonomers were characterized by spectroscopic techniques as well as GPC. One of the 4-vinylbenzyl-terminated macromonomers was copolymerized with MMA in different ratios. The copolymerization parameter r₁ was determined to be 0.75. The resulting graft copolymers were characterized regarding number of grafts per chain, molar mass, and glass transition temperature.     

1,3-Oxazoline intermediates in reactive processing applications, 2.multiphase polymer blends via in-situ cationic melt phase polymerization of 2-phenyl-1,3-oxazoline

2-Phenyl-1,3-oxazoline was injected into poly(ethene-co-methacrylic acid), containing 4,25 mol-% methacrylic acid units, at 225°C. In the first stage, 2-phenyl-1,3-oxazoline reacted with carboxylic acid groups to form esteramide side chains via grafting reaction. In the second stage, 2-phenyl-1,3-oxazoline containing methyl 4-nitrobenzensulfonate initiator was added to initiate in-situ cationic polymerization, yielding poly(N-benzoylethylenimine) as dispersed phase with 0,2–3,5 μm average diameter. Morphological, mechanical and thermal properties of poly-(ethene-co-methacrylic acid) blends, prepared by grafting combined with in-situ polymerization of 2-phenyl-1,3-oxazoline, were investigated.     

Copolymerization via zwitterion, 8. β-butyrolactone and 2-ethyl-2-oxazoline

2-Ethyl-2-oxazoline (ETOX) as nucleophilic monomer and β-butyrolactone (BUL) as electrophilic monomer were copolymerized in bulk in the absence of initiator at 45°C. Copolymers were characterized by elemental analysis, IR, ¹H NMR, and ¹³C NMR spectroscopy. The copolymer composition was determined by elemental analysis and by ¹H NMR spectroscopy. All copolymers contain a BUL:ETOX mole ratio greater than one.     

Ring-opening-closing alternating copolymerization of 2-methyl-2-oxazoline with N-methyldiacrylamide

This paper describes a new ring-opening-closing alternating copolymerization (ROCAC) of 2-methyl-2-oxazoline (five-membered cyclic imino ether, 1 ) with N-methyldiacrylamide ( 2 ). The reaction of a 1 : 1 monomer feed ratio proceeded without any added catalyst to give an alternating copolymer 3 having two structural units formed by ring-opening and ring-closing (cyclization). The structure of copolymer 3 was determined by ¹H, ¹³C NMR, and IR spectroscopies. The extent of cyclization was at most 65%. The copolymerization was reasonably explained by a mechanism of propagation via zwitterion intermediates.     

New chitin-based polymer hybrids, 3. Miscibility of chitin-graft-poly(2-ethyl-2-oxazoline) with poly(vinyl alcohol)

The miscibility of blends of poly(vinyl alcohol) (PVA) with chitin-graft-poly(2-ethyl-2-oxazoline) ( 1 ) and poly(2-ethyl-2-oxazoline) homopolymer (PEtOZO) was investigated. Calorimetric results showed a single glass transition temperature (T_g) in the entire range of compositions for both blend systems, which indicated that PVA is miscible with both the graft copolymer 1 and PEtOZO. The T_g of PVA is also shifted to lower temperature upon blending with the graft copolymer 1 . IR analysis revealed the existence of specific interactions via hydrogen bonding between the hydroxyl groups in PVA and the carbonyl groups in the poly(2-ethyl-2-oxazoline) side chain of graft copolymer 1 . The results show that the interaction of graft copolymer 1 with PVA is increased by introduction of longer poly(2-ethyl-2-oxazoline) side chains. Thermal decomposition (TG) measurements supported the compatibility of PVA with graft copolymer 1 and with PEtOZO, and showed that the thermal stability of PVA is improved upon blending with 1 or PEtOZO.     

Star polymers and block copolymers of 2-oxazolines using chloroformates as initiators

Polyfunctional chloroformates were applied to the polymerization of 2-phenyl-2-oxazoline and 2-methyl-2-oxazoline. The use of a trifunctional initiator, viz. the chloroformate of 2,2-bis(hydroxymethyl)-1-butanol, led to three-arm star polymers of 2-oxazolines. Two macromolecular initiators, viz. poly(ethylene oxide) with two chloroformate end groups (α-chloroformyl-ω-chloroformyloxypoly(oxyethylene)) with number-average molar masses 350 g/mol ≤ M?_n ≤ 6000 g/mol and α-chloroformyl-ω-methoxypoly(oxyethylene) with M?_n = 350 and 750 g/mol were applied for the synthesis of poly(2-oxazoline)-block-poly(ethylene oxide)-block-poly(2-oxazoline) and poly(2-oxazoline)-block-poly(ethylene oxide) copolymers, respectively.     

Copolymerization via zwitterion, 5. β-butyrolactone and 2-methyl-2-oxazoline

The zwitterionic copolymerization of 2-methyl-2-oxazoline (MOX) as nucleophilic monomer with β-butyrolactone (BUL) as electrophilic monomer was investigated in bulk and in solution (CH₃CN) at 45°C. The copolymer composition was around 1,5/1,0 (BUL/MOX) as was established by ¹H NMR. ¹H and ¹³C NMR spectroscopy were used to identify the copolymers. The IR spectroscopy supported the NMR results. On the other hand, the copolymers behave as polyelectrolytes, according to viscosity determinations. A copolymerization mechanism through a zwitterion species is suggested.     

Cationic polymerization involving covalent propagating species

Cationic polymerizations of some cyclic imino ethers using methyl iodide as initiator were found to propagate via covalent growing species of alkyl iodide nature. The propagation mechanism of the polymerization was examined by direct observation of the reaction system by means of NMR spectroscopy and by indirect kinetic analysis. Among six monomers, 2-oxazoline ( 1 ), 2-phenyl-2-oxazoline ( 2 ), and 2-phenyl-5,6-dihydro-4H-1,3-oxazine ( 3 ) were found to be polymerized with CH₃I via covalent growing species. On the other hand, 2-methyl-2-oxazoline ( 4 ) and 5,6-dihydro-4H-1,3-oxazine ( 5 ) were polymerized with CH₃I via ionic growing species. For the polymerization of 5-methyl-2-oxazoline ( 6 ) initiated by CH₃I, a mechanism of propagation via an equilibrium mixture of ionic and covalent propagating species ( 22 and 21 , respectively) was presented. In all cases of the polymerizations of these six monomers by methyl p-toluenesulfonate as initiator, the growing species were ionic ones having structures of the corresponding cyclic onium p-toluenesulfonates.     

Free radical polymerisation studies of 4-substituted styrenes, 2. Termination and chain transfer in the polymerisation of styrene, 4-methoxystyrene and 4-methylstyrene

The bulk polymerisation of styrene, 4-methoxystyrene and 4-methylstyrene was investigated at 60°C using 2,2′-azoisobutyronitrile (AIBN) as the initiator. Initial rates (R_i⁰) and efficiencies (f) of initiation were calculated from the radioactive content of the polymer obtained by labelling the initiator as either [methyl-¹⁴C₄]AIBN or [cyano-¹⁴C₂]AIBN. Rates of polymerisation determined gravimetrically are in good agreement with rates determined by the dilatometer technique. An empirical linear relationship between the number of initiator fragments and the degree of monomer conversion was noted. Factors affecting the termination of polymer radicals are discussed and compared with other published work. The polymerisation reaction is terminated predominantly by combination in the case of all three monomers, and chain transfer constants to initiator and to monomer are of the order of 10^?3 and 10^?5, respectively.     

Vinyl polymerization, 311. Synthesis and polymerization of 2-bromoethoxyphenoxyphosphoryl methacrylate

2-Bromoethoxyphenoxyphosphoryl methacrylate ( 5 ) was synthesized by the reaction of 2-bromoethyl phenylchlorophosphonate ( 3 ) with silver methacrylate and then polymerized by a radical initiator. The resulting polymer was soluble in DMF, but insoluble in other organic solvents. The hydrolysis of the polymer with sulfuric acid led to the corresponding poly(methacrylic acid) with a molecular weight of M_n=4,4·10⁵ (P_n=5,1·10³). 5 was copolymerized with acrylonitrile and the monomer reactivity ratio was determined: r₁ = 2,20, r₂=0,27.     

New hyperbranched poly(ether amide)s via nucleophilic ring opening of 2-oxazoline-containing monomers

An AB₂ monomer containing one oxazoline and two phenolic units was synthesized. The polymerization of the monomer 2-(3,5-dihydroxyphenyl)-1,3-oxazoline in N-methylcaprolactam resulted in a well-defined and fully soluble, high molar mass, hyperbranched polymer with etheramide structure. The hydrolysis of some oxazoline groups as side reaction limits the achieved molar mass when the polymerization is carried out in tetramethylene sulfone or in bulk. The polymers were characterized by one (1D) and two (2D) dimensional ¹H and ¹³C NMR spectroscopy which allowed to determine the degree of branching to be 50% as expected from statistics. DSC and TGA measurements revealed a glass transition temperature of 176°C and a decomposition onset of 330°C. The thermal ring-opening reaction was studied in situ by DSC measurements.     

Synthesis of new amphiphilic star polymers derived from a hyperbranched macroinitiator by the cationic ‘grafting from’ method

New amphiphilic star polymers possessing a hyperbranched core and hydrophilic graft arms have been prepared. The synthetic strategy involved esterification of the 4,4-bis(4′-hydroxyphenyl)valeric acid based hyperbranched polymer with 3-(chloromethyl)benzoyl chloride to obtain the hyperbranched macroinitiator followed by cationic ring-opening polymerization of 2-methyl-2-oxazoline to give amphiphilic polymers. Exchange of the chloride counter ion with trifluoromethanesulfonate (KCF₃SO₃ or AgCF₃SO₃) or iodide (KI) anions leads to higher polymerization rates. Phenyl 2-(chloromethyl)benzoate was used as a model initiator to study the effect of different coinitiators on the initiator efficiency. KI as a coinitiator yielded 56–86% initiator conversion whereas only 30–37% initiator conversion was achieved with KCF₃SO₃ or AgCF₃SO₃ as coinitiator after quantitative monomer consumption. Photon correlation spectroscopy (PCS) in methanol and chloroform for selected graft copolymers revealed the formation of single star molecules ranging from 22 to 50 nm in diameter.     

13C NMR spectroscopy of 2-formamido-2-methylpropyl acrylate and poly(2-formamido-2-methylpropyl acrylate)

The synthesis and characterization of 2-formamido-2-methylpropyl acrylate (FMPA) is reported. ¹³C NMR spectra of FMPA in CDCl₃, CD₃OD, DMSO-d₆, DMF-d₇, and D₂O exhibit two pairs of lines for all seven carbon atoms at room temperature; the ratio of the two conformers varies moderately with solvent (21 : 79 to 41 : 59). The conformers are believed to involve strong internal hydrogen bonding which is not completely broken even by the addition of trifluoroacetic acid to CDCl₃ (1/1, v/v). However, the pairs of lines coalesce in turn as the temperature is raised to 120°C in DMSO-d₆. FMPA was polymerized at 35°C in DMF and CHCl₃, using a free radical initiator and the polymer was characterized by ¹³C NMR spectroscopy.     

1,3-Oxazoline intermediates in reactive processing applications, 1. Melt grafting of poly(ethene-co-methacrylic acid) with 2-substituted 1,3-oxazolines

A novel family of functional ethene copolymers with various side chains were prepared by melt grafting of poly(ethene-co-methacrylic acid), containing 3,00 and 4,25 mol-% of methacrylic acid, with 2-substituted 1,3-oxazolines such as 2-phenyl-1,3-oxazoline, 2-undecyl-1,3-oxazoline, 2-heptadecyl-1,3-oxazoline, and 4-(1,3-oxazolin-2-yl)phenyl 4-methoxybenzoate. ¹H NMR and FTIR studies of the polymer microstructures revealed that carboxylic acid groups reacted with 1,3-oxazolines within few minutes to form esteramide-coupled side chains in very high yields. Torque of the reaction mixture, mechanical and thermal properties of the graft copolymers were measured. In the case of 2-heptadecyl-esteramide-substituted polyethenes, the side-chain cocrystallization accounted for higher crystallinity of the resulting graft copolymers.     

Efficient Synthesis of Macromolecular DO3A@Gn Derivatives for Potential Application in MRI Diagnostics: From Polymer Conjugates to Polymer Nanoparticles

Herein, the synthesis of three different macromolecular DO3A@Gn conjugates based on poly(2-oxazoline)s is presented. Therefore, poly(2-methyl-2-oxazoline) is synthesized by a ring-opening, cationic polymerization and the polymerization is terminated with DO3A(tBu)₃ . The best results are obtained after 48 h at 120 °C with degree of termination of 86%. After deprotection of the DO3A ligand and complexation with Gn³⁺, relaxivity as measured with a magnetic field strength of 9.4 T (400 MHz) reveals values for r₁ of up to 2.32 mm ⁻¹ s⁻¹. The concept is extended to a block copolymer based on 2-heptyl-2-oxazoline and 2-methyl-2-oxazoline that is again terminated with DO3A(tBu)₃ to form micelles with a size of 12.6 ± 0.7 nm after DO3A(tBu)₃ termination and deprotection of the 1,4,7,10-tetraazacyclododecane-N,N,N,N-tetraacetic acid ligand. After complexation with Gn³⁺, relaxivity r₁ is 10.1 mm ⁻¹ s⁻¹ as determined from the slope of the plot of 1/T₁ against the gadolinium(III) concentration at 9.4 T. Finally, crosslinked nanoparticles are prepared from amphiphilic macro-monomers that form micelles in water and are crosslinked throughout the core in the presence of azoisobutyronitrile (AIBN). The nanoparticle is 32.9 ± 7.8 nm in size after Gn³⁺ complexation and reveals a relaxivity r₁ of 6.77 mm ⁻¹ s⁻¹.     

Synthese und charakterisierung von linearem poly(iminoethylen)

Linear poly(iminoethylene) was synthetised by cationic polymerization of 2-methyl-2-oxazoline using BF₃? O(C₂H₅)₂, SnCl₄, and CH₃COBF₄ as initiators and in the presence or absence of CH₃CN. The resulting product, poly(N-acetyliminoethylene), was then hydrolysed in basic medium. The resulting poly(iminoethylene) was identified and characterized by ¹H NMR, ¹³C NMR, X-ray diffraction, and differential scanning calorimetry (DSC). The synthetised polymer will be used as a polymeric support in ionic-exchange resins as well as in macromolecular pesticides.     

Synthesis and ring-opening polymerization of 2-acetoxymethyl-2-alkyltrimethylene carbonates and of 2-methoxycarbonyl-2-methyltrimethylene carbonate; a comparison with the polymerization of 2,2-dimethyltrimethylene carbonate

The polymerization of 2-acetoxymethyl-2-alkyltrimethylene carbonates (alkyl = methyl: AMTC, alkyl = ethyl: AETC) and of 2-methoxycarbonyl-2-methyltrimethylene carbonate (MMTC) in toluene with sec-butyllithium as initiator results in the respective polymer with yields between 78% and 88%. The analysis of the polymer microstructure by means of NMR spectroscopy reveals linear chains without branching due to an attack of the active chain end at the ester moiety of the repeating units. Poly(MMTC) and poly(-AETC) afford crystalline materials upon precipitation from solution while poly-(AMTC) is amorphous; after quenching from the melt all materials are amorphous. Copolymerization of AMTC, AETC and MMTC with 2,2-dimethyltrimethylene carbonate (DTC) results in random copolymers. The kinetics of the polymerization of AETC and MMTC revealed that the ester side chain enhances the rate of propagation compared to the polymerization of DTC. The apparent rate constants of propagation in toluene with lithium alcoholate as active sites at 23°C were determined to be k_app^DTC = 4 ċ 10⁻³ s⁻¹, k_app^AETC = 4,28 ċ 10⁻² s⁻¹, and k_app^MMTC = 2,57 ċ 10⁻² s⁻¹. Studies of ring-chain equilibria in solution of tetrahydrofuran revealed that on the basis of the theory of Jacobson-Stockmayer the characteristic ratios of the polymers are C_∞^PDTC = 7,1, C_∞^PMMTC = 8,6, C_∞^PAETC = 9,9, and C_∞^PAMTC = 13,4.     

Vinyl polymerization initiated with the lanthanum versatate/p-chlorobenzenediazonium tetrafluoroborate system

The system of lanthanum versatate ( 1 ) and p-chlorobenzenediazonium tetrafluoroborate ( 2 ) was found to induce effectively polymerizations of electron-accepting monomers such as methyl methacrylate ( 3 ) and di-2-ethylhexyl itaconate (DEHI). The polymerization rate (R_p) was expressed by R_p = k[ 1 / 2 ]^0,44 [ 3 ]^0,65 at 50°C fixing the mole ratio of 1 and 2 at unity. The overall activation energy of the polymerization was calculated to be 37, 1 kJ · mol^?1. The spin trapping result revealed that the initiator system produces p-chloropheneyl radicals. The polymerization system of DEHI was observed to involve ESR-observable propagating polymer radicals, indicating that the polymerization initiated with the 1/2 system proceeds through radical mechanism. During the polymerization, the ESR spectrum was changed in shape, suggesting that the propagating polymer radicals interact with some species formed by the initiation reaction. Interacting polymer radicals were also observed in the polymerizations of diethyl itaconate and N-dodecylmaleimide with the 1/2 system. The polymerization systems of MMA, styrene and butyl acrylate were also found to involve ESR-observable radicals, although it is vague whether they are propagating polymer radicals or not.