Cyclodextrins in polymer synthesis: free radical polymerization of cyclodextrin complexes with oxazoline‐functionalized vinyl monomers as guest molecules in aqueous medium

The synthesis of five new oxazoline functionalized vinyl monomers N‐[4‐(4′,5′‐dihydrooxazol‐2‐yl)phenyl]acrylamide ( 3 a ), N‐[4‐(4′,5′‐dihydrooxazol‐2‐yl)phenyl]‐2‐methylacrylamide ( 3 b ), N‐{10‐[4‐(4′,5′‐dihydrooxazol‐2‐yl)phenylcarbamoyl]decyl}‐2‐acrylamide ( 5 a ), N‐{10‐[4‐(4′,5′‐dihydrooxazol‐2‐yl)phenylcarbamoyl]decyl}‐2‐methylacrylamide ( 5 b ) and N‐[4‐(4′,5′‐dihydrooxazol‐2‐yl)‐phenyl]‐4‐vinylbenzamide ( 7 ) is described. With an equimolar amount of 2,6‐dimethyl‐β‐cyclodextrin (DMCD) these monomers formed hydrophilic inclusion complexes 3 a,b‐DMCD , 5 a,b‐DMCD and 7‐DMCD . These complexes were polymerized radically in an aqueous medium. Resulting polymers P‐(3 a, b) , P‐(5 a, b) and P‐(7) precipitated during the polymerization due to unthreading of the cyclodextrin from the growing polymer chain. The remaining oxazoline moiety offers possibilities of further modification of the polymers, e. g. grafting in a cationic ring opening polymerization with commercially available alkyloxazolines.     

Association thickener by host guest interaction of a β-cyclodextrin polymer and a polymer with hydrophobic side-groups

A host polymer with pending β-cyclodextrin side-groups and a guest polymer with pending hydrophobic 4-tert-butylanilide side groups were synthesized by polymeranalogous reactions starting from poly[(maleic anhydride)-alt-(isobutene)] (M̄_w = 60000). The inclusions of both polymers with complementary monomeric guests and hosts are proven by microcalorimetry. The interaction of the host polymer and the guest polymer in aqueous solution is accompanied by a tremendous increase in viscosity.     

Octadecyl maleamic acid salt as a microreactor for its copolymerization reaction with butyl acrylate in aqueous medium

The hydrogelator, octadecyl maleamic acid salt (ODMAS), has been shown to perform as a microreactor in copolymerization reaction with butyl acrylate in aqueous medium thereby providing functionalized latex. The evidence for occurrence of controlled polymerization reaction inside the microreactor is drawn from the composition and the polydispersity index of the copolymers. The copolymers generated under microreactor conditions or in other words, from emulsion phase provided by the hydrogelator exhibit significant incorporation of ODMAS with narrow polydispersity index. For example, a copolymer with ODMAS as high as 0.62 m and polydispersity index at 1.39 could be achieved. On the contrary, the solution copolymerization reactions in THF resulted in low yield of polymers with molecular weight at 10(3) order and polydispersity index in range of 2.53-2.91. The particle size distribution of the latexes remains almost invariant at 74 +/- 4 nm, over the concentration range of 0.12-0.62m with standard deviation (sigma) of 0.12-0.22. The surface area/molecule of ODMAS on the latex particle has been estimated to be 0.21 nm(2)/molecule. The polymerized latexes exhibit zeta potential at 64 +/- 3 mV and surface tension in range of 42.8-47.9 mN m(-)(1) respectively. This is indicative of coverage of latex with ODMAS.     

Cyclodextrins in polymer synthesis: free radical polymerisation of cyclodextrin complexes of cyclohexyl and phenyl methacrylate in aqueous medium

The polymerisation mechanism of 2,6-dimethyl-β-cyclodextrin (Me₂-β-CD) complexes of phenyl methacrylate ( 1 ) and cyclohexyl methacrylate ( 2 ) is described. The polymerisation of the complexes 1 a and 2a was carried out in water with potassium peroxodisulfate/potassium hydrogensulfite as initiator. The unthreading of the Me₂-β-CD during the polymerisation led to water-insoluble poly(phenyl methacrylate) ( 1b ) and poly(cyclohexyl methacrylate) ( 2b ). By comparison, analogously prepared polymers from uncomplexed monomers 1 and 2 in homogeneous organic solvent (THF) with AIBN as radical initiator showed significantly lower viscosities and were obtained in lower yields in both cases.     

Cyclodextrins in polymer synthesis: free radical polymerization of cyclodextrin host‐guest complexes of methyl methacrylate or styrene from homogenous aqueous solution

The polymerization of methylated β‐cyclodextrin (m‐β‐CD) 1 : 1 host‐guest compounds of methyl methacrylate (MMA) ( 1 ) or styrene ( 2 ) is described. The polymerization of complexes 1 a and 2 a was carried out in water with potassium peroxodisulfate (K₂S₂O₈)/sodium hydrogensulfite (NaHSO₃) as radical redox initiator at 60°C. Unthreading of m‐β‐CD during the polymerization led to water‐insoluble poly(methyl methacrylate) (PMMA) ( 3 ) and polystyrene ( 4 ). By comparison, analogously prepared polymers from uncomplexed monomers 1 and 2 in ethanol as organic solvent with 2,2′‐azoisobutyronitrile (AIBN) as radical initiator showed significantly lower molecular weights and were obtained in lower yields in all cases. Polymerization of m‐β‐CD complexed MMA in water, initiated with 2,2′‐azobis(N,N ′‐dimethyleneisobutyroamidine) dihydrochloride, occurred much faster than the polymerization of uncomplexed MMA in methanol under similar conditions. Furthermore, it was shown, that the precipitation polymerization of complexed MMA from homogeneous aqueous solution can be described by equations (P_n^–1 ∝ lsqb;Irsqb;^0.5) similar to those for classical polymerization in solution.     

Application of poly(N-isopropylacrylamide) with pendent β-cyclodextrin to separation of a guest substance in an aqueous solution

Poly(N-isopropylacrylamide) with pendent β-cyclodextrin (PNI-PAAm-CD) was prepared by copolymerization of acryloyl-β-CD and NIPAAm. During the temperature-induced phase separation of an aqueous solution of PNIPAAm-CD, Toluidine Blue dye in the solution was separated into the precipitate of PNIPAAm-CD by way of inclusion complex formation.     

Radical polymerization and copolymerization of methyl α-(2-carbomethoxyethyl)acrylate,a dimer of methyl acrylate,as a polymerizable α-substituted acrylate

Polymerization and copolymerization of methyl α-(2-carbomethoxyethyl)acrylate (MMEA), which is known as a dimer of methyl acrylate, were studied in relation to steric hindrance-assisted polymerization. The propagating polymer radical from MMEA was detected as a five-line spectrum and quantified by ESR spectroscopy during the bulk polymerization at 40–80°C. The absolute rate constants of propagation and termination (κ_p and κ_t) for MMEA at 60°C (κ_p = 19 L/mol s and κ_t = 5.1 × 10⁵ L/mol s) were evaluated using the concentration of the propagating radical at the steady state. The balance of the propagation and termination rates allows polymer formation from MMEA. The polymerization rate of MMEA at 60°C was less than that of MMA by a factor of about 4 at a constant monomer concentration. Although no influence of ceiling temperature was observed at a temperature ranging from 40 to 70°C, addition-fragmentation in competition with propagation reduced the molecular weight of the polymer. The content of the unsaturated end group was estimated to be 0.1% at 60°C to the total amount of the monomer units consisting of the main chain. MMEA exhibited reactivities almost similar to those of MMA toward polymer radicals. It is concluded that MMEA is one of the polymerizable acrylates bearing a substituted alkyl group as an α-substituent. Characterization of poly(MMEA) was also carried out. © 1996 John Wiley & Sons, Inc.     

A computational study on the reactivity enhancement in the free radical polymerization of alkyl α‐hydroxymethacrylate and acrylate derivatives

The free radical polimerizability behavior of alkyl α‐hydroxymethacrylate (RHMA) derivatives ( M1–M3 ) has been modeled by considering the propagation of the dimeric units of the compounds of interest. All the transition structures in this class of monomers are stabilized by long‐range C?O…H? C interactions. The RHMA monomer bearing the ester functionality ( M2 ) polymerizes slightly faster than the one with the ether functionality ( M1 ) because of stronger electrostatic interactions between the C?O and H? C groups. 2‐(Methoxycarbonyl)allyl benzoate ( M3 ) shows higher reactivity as compared to M1 and M2 due to stronger electrostatic interactions. The same type of study has been carried out for hexyl ( M4 ), benzyl ( M5 ), and phenyl ( M6 ) acrylate derivatives whose increasing reactivity has been attributed to the presence of C?O…H? C, C?O…H‐? as well as π–π stabilizing interactions, respectively. While B3LYP/6‐31+G(d) has been used to locate the stationary points along the free radical polymerization of nonaromatic species, long‐range stabilizing interactions have only been detected with M06‐2X/6‐31+G(d). The kinetics that we obtain with this latter methodology for the free radical polymerization reactions of M1 – M6 agree well qualitatively with experiment. An implicit solvent model has reproduced the kinetics of M1–M3 in benzene the best. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Backbiting and β‐scission reactions in free‐radical polymerization of methyl acrylate

Multiple mechanisms of backbiting and β‐scission reactions in free‐radical polymerization of methyl acrylate are modeled using different levels of theory, and the rigid‐rotor harmonic‐oscillator (RRHO) and hindered‐rotor (HR) approximations. We identify the most cost‐effective computational method(s) for studying the reactions and assess the effects of different factors (e.g., functional type and chain length) on thermodynamic quantities, and then identify the most likely mechanisms with first‐principles thermodynamic calculations and simulations of nuclear magnetic resonance (NMR) spectra. To this end, the composite method G4(MP2)‐6X is used to calculate the energy barrier of a representative backbiting reaction. This calculated barrier is then compared with values obtained using density functional theory (DFT) (B3LYP, M06‐2X, and PBE0) and a wavefunction‐based quantum chemistry method (MP2) to establish the benchmark method. Our study reveals that the barriers predicted using B3LYP, M06‐2X, and G4(MP2)‐6X are comparable. The entropies calculated using the RRHO and HR approximations are also comparable. DFT calculations indicate that the 1:5 backbiting mechanism with a six‐membered ring transition state and 1:7 backbiting with an eight‐membered ring transition state are energetically more favored than 1:3 backbiting and 1:9 backbiting mechanisms. The thermodynamic favorability of 1:5 versus 1:7 backbiting depends on the live polymer chain length. The activation energies and rate constants of the left and right β‐scission reactions are nearly equal. The calculated and experimental ¹³C and ¹H NMR chemical shifts of polymer chains affected by backbiting and β‐scission reactions agree with each other, which provides further evidence in favor of the proposed mechanisms. © 2013 Wiley Periodicals, Inc.     

Determination of reactivity ratios for ethylene/α-olefin copolymerization catalysed by the C2H4[Ind]2ZrCl2/methylaluminoxane system

The present study reports values of reactivity ratios for ethylene/1-hexene, ethylene/1-octene and ethylene/1-decene copolymerizations promoted by C₂H₄[Ind]₂ZrCl₂/MAO. The comonomer reactivities are markedly influenced by the number of carbon atoms of the α-olefin. The ethylene/1-decene copolymerization depends on the concentration of α-olefin in the feed.     

Host/guest complex of β-cyclodextrin/5-thia pentacene-14-one for photoinitiated polymerization of acrylamide in water

β-Cyclodextrin (β-CD) was used to complex the photoinitiator, 5-thia pentacene-14-one (TX-A), yielding a water-soluble host/guest complex. IR, UV–Vis and fluorescence spectroscopy were employed to characterize complexed β-CD/TX-A. Photoinitiated polymerization of acrylamide in water was achieved with β-CD/TX-A in the presence of N-methyldiethanolamine (MDEA). Excellent polymerization yields were observed in air saturated solutions when MDEA was added.     

Cyclodextrins as chiral stationary phases in capillary gas chromatography. Part IV: Heptakis(2,3,6-tri-O-pentyl)-β-cyclodextrin

O-Perpentylated β-cyclodextrin has been evaluated as chiral stationary phase in capillary gas chromatography. Enantioselectivity is observed towards many chiral hydroxy compounds, including cyanohydrins and carbohydrates. Most importantly, the enantiomers of many olefins and alkyl halides can be resolved on this chiral phase. The thermal stability of the cyclodextrin derivative exceeds 200°C.