Synthesis of hydroxy- and dihydroxy-end-capped poly(<Emphasis Type="Italic">n</Emphasis>-butyl acrylate)s and their use as reactive stabilizers for the preparation of polyurethane latexes

Well-defined hydroxy end-functionalized poly(n-butyl acrylate)s (PBA-OH and PBA-(OH)₂), were prepared by atom transfer radical polymerization (ATRP) and used as reactive stabilizers for the preparation of polyurethane in dispersed medium. PBA-OH was obtained by end-capping the growing poly(n-butyl acrylate) chains with allyl alcohol added in excess at the end of the polymerization. The two hydroxyl functions of PBA-(OH)₂ were fixed at one end of the poly(n-butyl acrylate) chains either by initiation or by chain-end functionalization reactions. The latter were protected under the form of cyclic acetal and attached either to the initiator bearing a secondary bromine or to the terminating agent carrying a poorly reactive vinylic unsaturation. PBA-OH and PBA-(OH)₂ have been successfully used as reactive stabilizers (surfmers) to prepare core-shell polyurethane particles in dispersed medium. The final particle size was found to be very much dependent to parameters such as the molar mass, concentration and valence of the reactive stabilizer as well as the manner of addition of the reactants during the procedure.     

Polyaddition reaction in a dispersed medium: elaboration of new core-shell polyurethane particles

The elaboration in a dispersed organic medium of calibrated polyurethane particles with a core-shell structure is presented in this paper. The objective could be achieved by using a series of reactive steric stabilizers of the type ω-(OH)_x-poly(n-butyl acrylate), -polystyrene, -polysiloxane or -polybutadiene (x=1 or 2) that play the role of surfmers during the polyaddition reaction between ethylene glycol and tolylene-2,4-diisocyanate, in cyclohexane as a dispersant medium. The final size of the polyurethane particles (0,5-10 μm) was found to be a function of the steric stabilizer characteristics (nature, molar mass and concentration) and of the addition procedure of the different reactants. These novel particles constituted of a polyurethane core and various shells depending on the stabilizer used exhibit specific and original properties.     

Fourier transform IR spectroscopic study on phase transitions of copolymers of <Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide and alkyl acrylates in water

Copolymers of N-isopropylacrylamide (IPA) and alkyl acrylates [methyl acrylate (MA), ethyl acrylate, and butyl acrylate] or vinyl acetate have been prepared and their phase transitions in water have been observed by means of IR spectroscopy. The incorporation of these alkyl acrylates into a poly(IPA) (PIPA) chain induces a decrease in the phase-transition temperatures, T_p, and the magnitude increases with increasing size of the alkyl chains. The profiles of the C=O stretching absorption bands of the ester groups [9(C=O)_ester] and the IR bands due to IPA units exhibit critical changes at the T_p of these copolymers. The 9(C=O)_ester bands shift slightly toward higher wavenumbers (blueshift) upon phase transition, while the amide I and amide II bands of the IPA units undergo a blueshift and a redshift, respectively. Analysis of the 9(C=O)_ester band of PIPA-MA by using a curve-fitting method shows that it consists of three components, at 1,703, 1,720, and 1,738 cm^-1. The relative peak area of the largest component (1,720 cm^-1) is almost constant, and those of the 1,703-cm^-1 and 1,738-cm^-1 components increase and decrease with increasing temperature during the phase transition, respectively. However, the changes are rather small, suggesting that changes in hydrogen bonding of the C=O groups of MA units upon phase transition are not significant. The 9(C=O)_ester bands of other comonomers examined here also exhibit similar changes. The situation is consistent with the change in the hydration states of the amide groups of IPA units, most of which associate with water molecules through hydrogen bonds even after the phase separation.     

Dispersion polymerization of MMA in supercritical CO2 stabilized by random copolymers of 1H,1H–perfluorooctyl methacrylate and 2‐(dimethylaminoethyl methacrylate)

A series of random copolymers, composed of 1H,1H‐perfluorooctyl methacrylate (FOMA) and 2‐dimethylaminoethyl methacrylate (DMAEMA) were prepared as stabilizers for the dispersion polymerization of methyl methacrylate in supercritical CO₂ (scCO₂). Free‐flowing, spherical poly(methyl methacrylate) (PMMA) particles were produced in high yield by the effective stabilization of poly(FOMA‐co‐DMAEMA) containing 34–67 w/w % (15–41 m/m %) FOMA structural units. Less stabilized but micron‐sized discrete particles could be obtained even with 25 w/w % (10 m/m %) FOMA stabilizer. The result showed that the composition of copolymeric stabilizers had a dramatic effect on the size and morphology of PMMA. The particle size was controllable with the surfactant concentration. The effect of the monomer concentration and the initial pressure on the polymerization was also investigated. The dry polymer powder obtained from dispersion polymerization could be redispersed to form stable aqueous latexes in an acidic buffered solution (pH = 2.1) by an electrostatic stabilization mechanism due to the ionization of DMAEMA units in the stabilizer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1365–1375, 2008     

Production of micron-sized polystyrene particles containing PEG near the particles surface

Polystyrene (PS) particles in the size range of 1-7 µm, containing poly(ethylene glycol) or PEG on the particles surface, were prepared by multi-step seeded polymerizations. Micron-sized PS particles were first prepared by dispersion polymerization using 2,2'-azobisisobutyronitrile as initiator and polyvinyl pyrrolidone as stabilizer. Conventional swelling method was then used to increase the size of the PS particles with a large amount of styrene in presence of oil soluble initiator, benzoyl peroxide. In the final step, the PS particles have been used to carry out seeded polymerization with small amount of styrene in presence of poly(ethylene glycol)-azo or PEGA initiator with average molecular weights of the PEG chains of 200 and 3000 g mol^-1 , respectively. The average size, size distribution, and surface morphology indicate that seeded polymerization in the final step with small amount of styrene in presence of PEGA is the best way to produce monodisperse polystyrene particles containing PEG near the particles surface.     

Hydroxy and Di-Hydroxy End-Capped Polybutadiene as Reactive Steric Stabilizers for the Synthesis of Polyurethane Particles in Organic Dispersant Media

Summary: The synthesis of polyurethane particles by polyaddition of ethylene glycol (EG) and tolylene-2,4-diisocyanate (TDI) in cyclohexane at 60 °C was investigated in the presence of ω-hydroxy and ω,ω′-dihydroxy polybutadiene, used as reactive steric stabilizers. The effect of the functionality and concentration of the reactive polybutadiene, as well as the monomer addition procedure, onto the polyurethane particle formation was studied. Calibrated PUR particles with an average diameter in the range 1–2 µm could be readily obtained.     

Comparison between properties of polyether polytriazole elastomers and polyether polyurethane elastomers

In order to explore the application of click chemistry in the field of elastomer materials, the comparison between the properties of polyurethane and polytriazole elastomers has been carried out. Propargyl‐terminated ethylene oxide‐tetrahydrofuran copolymer (PTPET) has been prepared from the ethylene oxide‐tetrahydrofuran copolymer (PET) by end modification. Using polyisocyanate N100 and polyazide compounds as cross‐linkers, PET polyurethane and PTPET polytriazole elastomers have been prepared through urethane and copper‐catalyzed azide‐alkyne huisgen [3 + 2] dipolar cycloaddition reactions, respectively. Mechanical properties indicate that, to be different from those of polyurethane elastomers, the modulus E and stress σ_b of polytriazole elastomers increase at first, and then decrease with the increase in R. At around the stoichiometric ratio, the modulus E and stress σ_b reach a maximum, and the strain ε_b reaches a minimum. Swelling tests demonstrate that the M_c of polytriazole elastomers has a minimum value at the stoichiometric ratio. The dynamic mechanical analysis indicates that both polyurethane and polytriazole elastomers have the same glass transition temperature of ?64°C, although polytriazole elastomers exhibit lower dissipation factor tan δ. Thermal analysis shows that polytriazole elastomers have better thermal stability than polyurethane elastomers. Copyright © 2014 John Wiley & Sons, Ltd.     

Ion-selective electrodes based on metalloporphyrins for gibberellic acid determination in agricultural products

This work describes the construction, evaluation and analytical application of electrodes selective to the gibberellate anion for the determination of gibberellic acid in agricultural products. Several types of PVC membrane electrodes without internal reference solution were prepared using the manganese(III) complex of meso -tetraphenylporphyrin (TPP) as ionophore and dibutyl phthalate (DBP), as plasticizer. The incorporation of lipophilic chemical species as additives, was also carried out aiming the evaluation of the response characteristics of the electrodes. To accomplish the analysis of commercial agricultural products a selective membrane composed of 28.0% (w/w) of PVC, 66.0% (w/w) of plasticizer and 6% (w/w) of ionophore was used, with no additive. This potentiometric unit presented a linear response between 10^-4 and 10^-1 mol L^-1 in gibberellate, a slope of about ⫙ mV dec^-1 and a reproducibility of about ǃ mV day^-1. The potentiometric analysis of gibberellic acid in commercial products was carried out by direct potentiometry and the results obtained were compared with those provided by HPLC.     

Influence of flocculant charge on the dewaterability of flocculated clay suspensions

The influence of charged components of cationic polyelectrolytes on the dewatering of clay-containing suspensions was investigated with a view to better predicting the efficiency of flocculating agents. In flocculation and dewatering experiments on suspensions of harbour sediment and gravel washings, flocculating agents of the polyacrylamide-co-(trimethylammoniumpropyl chloride) (PTCA) type exhibited different dewatering efficiencies depending on the degree of cationicity, F. For harbour sediment, a dewatering index, I_D, of 80 was achieved with the highly charged PTCA 3 (F=40%) at 30% lower flocculant dose than with the weakly cationic PTCA 1 (F=3%). However, for gravel washings PTCA 1 proved to be more effective: for comparable degrees of dewatering (I_D=80) approximately 40% less flocculant was required than for PTCA 3. In shear experiments on gravel washings and model suspensions with particles of differing size (d₅₀=0.5 und 5.7 µm) weakly cationic PTCA 1 exhibited an increased floc stability at lower concentrations than is necessary to achieve maximum I_D values. For harbour sediments and model suspensions with unimodal particle size distributions this stability did not occur until the doses used were higher than the concentrations needed to achieve maximum I_D values.     

Graft copolymers having hydrophobic backbone and hydrophilic branches. XXIII. Particle size control of poly(ethylene glycol)-coated polystyrene nanoparticles prepared by macromonomer method

Monodisperse polymeric nanospheres, which consist of polystyrene cores and poly(ethylene glycol) (PEG) branches on their surfaces, were prepared by the dispersion copolymerization of styrene (St) with PEG macromonomers that had a methacryloyl (MMA-PEG) or p-vinylbenzyl (St-PEG) end group in various organic solvent/water media. Electron spectroscopy for chemical analysis (ESCA) of the nanosphere surfaces indicated that PEG macromonomer chains were favorably located on their surfaces. The morphologies of the nanospheres were observed via a scanning electron micrograph (SEM), and particle sizes were estimated by a submicron particle analyzer. When both the concentration of macromonomers and molecular weight were higher, small nanospheres in diameter were obtained. Larger nanospheres in diameter were obtained using macromonomers with low molecular weight at lower concentration. The functions that correlate the diameter (D_n) on different concentration units were D_n = K[St]^0.64[MMA-PEG]^{−0.53±0.01}[I]^−0.49 and D_n = K[St]^0.80[St-PEG]^{−0.69±0.01}[I]^−0.22, where [I], [St], [MMA-PEG], and [St-PEG] are initiator, styrene, MMA-PEG, and St-PEG macromonomer concentration in feed, respectively. When the reaction parameters such as the molecular weight of the macromonomers were properly chosen, the particle size could be controlled in a range from ca. 80 to 3100 nm. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2155–2166, 1999     

Dispersion polymerization accompanied by CO2 fixation: Synthesis of particles of polymers bearing cyclic carbonate and epoxide moieties

Radical dispersion polymerization of glycidyl methacrylate accompanied by CO₂ fixation yielded particles of polymers bearing cyclic carbonate and epoxide moieties in the presence of polymeric dispersion stabilizers. Cellulose acetate successfully stabilized the dispersion, whereas poly(N‐vinylpyrrolidone) did not. Spherical particles with diameters of 1–10 μm could be prepared under the optimized conditions. The epoxide moieties in the particle were hydrolyzed selectively keeping the shapes of the particles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and solution properties of comblike polymers from octadecyl methacrylate and acrylic acid

Amphiphilic polymers consisting of a statistical distribution of octadecyl methacrylate (ODMA) and acrylic acid in respective molar ratios of 83-22 and 17-78 mol% and in a molecular-weight range of 2.35-4.70᎒⁴ gmol^-1 have been synthesized. The series of polymers consisting of various mole fractions of ODMA and acrylic acid are expected to exhibit unique characteristics resembling ionomer to hydrophobically modified polyelectrolytes. The changes in the I₃/I₁ emission intensity ratios of pyrene, occurring in the presence of tetrahydrofuran (THF) solutions of the polymers have been taken as the main basis for inferring solution structures. The polymers are found to form random-coil to collapsed-coil/aggregated structures in THF solvent depending on the copolymer compositions. The polymer consisting of 83 mol% ODMA and 17 mol% acrylic acid behaves as an ionomer, capable of forming collapsed-coil structures at concentrations of 0.02 gml^-1 and above as shown by a very high I₃/I₁ of 1.20 (I₃/I₁ of pyrene in THF is 0.85). In contrast, the poly(octadecyl methacrylate) homopolymer and the sets of copolymers consisting of a very high proportion of acrylic acid to an extent of 73 mol% and above contribute to almost negligible or very small changes in I₃/I₁ similar to the homopolymer, poly(octadecyl methacrylate), suggesting the formation of random-coil structures.     

Photo fragmentation of metal clusters stored in a penning trap

Photo fragmentation studies of stored mass selected metal cluster ions of a large size range are reported. The experimental method and the data evaluation are described in detail. Gold cluster ions were produced by laser vaporization and stored in a Penning trap. After size selection they were electronically excited by irradiation with a pulsed laser beam. Relaxation by evaporation of neutral atoms and dimers was observed as a function of photon energy. From these data upper and lower limits for dissociation energies are determined for Au⁺_n (n=3 to 23).     

A study of starch addition on burst effect and diameter of polyurethane microspheres containing theophylline

Theophylline was encapsulated in polyurethane prepared with hexamethylene diisocyanate (HMDI), polycaprolactone (PCL) (M_W = 530 and 2000 g/mol) diols, and starch as polyols and butanediol as chain extender. Polyurethane microspheres were prepared in two reactors; after polyurethane preparation by mixing PCL/starch, HMDI and theophylline in the first reactor, microspheres formation was achieved by transferring the reaction mixture to an aqueous medium (moving at 5000 rpm) of the second reactor. Fourier transform infrared (FTIR) was employed to confirm polyurethane formation during the course of reactions. FTIR spectrum revealed bands at 1729–1733 cm^?1 and 3340–3347 cm^?1 which indicates carbonyl and NH of amine groups, respectively. Scanning electron microscopy (SEM) was used to study the morphology of the samples. SEM confirmed the formation of microspheres with spherical morphology. Particle size investigation with optical microscopy revealed a size distribution of 8–70 µm. Controlled release of theophylline from the microspheres was performed in phosphate buffered saline (PBS) at pH = 7.4 and monitored with a ultraviolet (UV) spectrometer at 274 nm. Drug release profiles showed that starch addition reduced the release rate around 24% for microspheres prepared from PCL with a molecular weight of 2000 g/mol and it had negligible effect on a molecular weight of 530 g/mol. Copyright © 2007 John Wiley & Sons, Ltd.     

Interfacial crosslinking of self‐assembled triblock copolymer nanoparticles via alkoxysilane hydrolysis and condensation

The use of amphiphilic triblock copolymers bearing a reactive alkoxysilane middle block as polymeric stabilizers is reported in this work. A series of poly(ethylene glycol) methyl ether methacrylate‐b‐(3‐trimethoxysilyl)propyl methacrylate‐b‐benzyl methacrylate (PEGMA‐b‐MPS‐b‐BzMA) triblock copolymers were prepared by RAFT solution polymerization and polymerization‐induced self‐assembly (PISA), respectively, where the various block lengths and overall composition were varied. The copolymers prepared by solution polymerization were employed as oil‐in‐water stabilizers where upon application of a catalyst, the 3‐(trimethoxysilyl)propyl methacrylate (MPS) block at the droplet interface was crosslinked to yield capsule‐like structures. The effectiveness of interfacial crosslinking was validated by dynamic light scattering and electron microscopy. In situ self‐assembly by the PISA method resulted in spherical nanoparticles of controllable size that were readily crosslinked by addition of base, with significant enhancement of colloidal stability. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1897–1907     

Reactive surfactants in heterophase polymerization

The mechanism for the formation of polymer particles in the dispersion polymerization of methyl methacrylate and styrene in alcohol-water mixtures has been investigated. Methacrylic based poly(ethylene oxide) macromonomers and poly(vinyl-pyrrolidone) have been used as steric stabilizers. Dynamic light scattering as well as transmission electron microscopy have been applied to determine the evolution of the average particle size at the beginning of the polymerization. Stable nuclei from 80 to 400 nm in diameter size were detected. The nucleation process was quite rapid and completed within less thanca. 0.1% monomer conversion. The experimental results are compared with those predicted by the multibin kinetics model for coalescence developed by Paine [(1990) Macromolecules 23: 3109].A series of publication from the EU program Human Capital and Mobility (CHRX CT 93-0159)     

Effects of polystyrene-b-poly(aminomethyl styrene)s as stabilizers on dispersion polymerization of styrene in alcoholic media

The effects of polystyrene-b-poly(aminomethyl styrene) (PS_n-b-PAMS_m) stabilizers on the particle size (D_n) and size distribution (PSD) in dispersion polymerization of styrene were investigated. The block copolymers, PS_n-b-PAMS_m, were prepared as follows: (i) atom transfer radical polymerization (ATRP) of styrene (PS-Br), (ii) ATRP of vinylbenzylphthalimide with the PS-Br (PS-b-PVBP), and (iii) treatment of the PS-b-PVBP with hydrazine. When the dispersion polymerization of styrene proceeded at 60 °C in ethanol with PS₁₉-b-PAMS₁₃₀ stabilizer, spherical polystyrene particles with D_n=0.91 μm (PSD = 1.01) were obtained. The particle size was strongly affected by the copolymer composition. With an increase in PAMS block length from m=54 to 100 in PS₁₇-b-PAMS_m, particle diameter became smaller from 1.55 to 0.91 μm. On the other hand, an increase in the length from m=20 to 82 in PS₃₄-b-PAMS_ms caused an increase in particle size from 0.35 to 0.70 μm. Titration of the particles suggests that 14–81% of stabilizers used in the polymerization system were attached on the polystyrene particle surfaces, depending on the composition of the block copolymers. Thus, for the dispersion polymerization of styrene, PS_n-b-PAMS_m block copolymers have both functions as a stabilizer during polymerization and surface-modification sites of polystyrene particles.     

One‐shot synthesis of high molar mass polyurethane in supercritical carbon dioxide

Well‐defined polyurethane–polydimethylsiloxane particles of tunable diameter in the range of 0.5–20 μm were synthesized in “one‐shot” by step‐growth polymerization using supercritical carbon dioxide (scCO₂) as a dispersant medium. Polymerizations were carried out at 60 °C and above 25 MPa, after the solubility of each reactant in scCO₂ has been determined in its typical reaction concentration. The synthesis of such copolymers was achieved by polyaddition between short aliphatic diols, that is, ethylene glycol, 1,4‐butanediol (BD) or polyethylene oxide (M_n = 200 g mol^?1), and tolylene‐1,4‐di‐isocyanate (TDI) in the presence of mono or di‐isocyanate‐terminated polydimethylsiloxane (PDMS) as reactive stabilizers and dibutyltin dilaurate as a catalyst. The nature of the diol used as well as the functionality of the reactive stabilizer incorporated was found to have a dramatic effect on the molar mass and the morphology of the resulting product. Thus, copolymers obtained from the polyaddition of BD and TDI in the presence of di‐isocyanate‐terminated PDMS exhibit molar mass up to 90,000 g mol^?1. Thermal behaviors of copolymers were also examined by differential scanning calorimetry. All samples exhibited only one glass transition temperature (T_g) and were found to be totally amorphous. A logical decrease of the T_g was observed as the length of the diol incorporated increased, that is, as the density of urethane linkages within the polymer decreased. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5649–5661, 2007     

Cationic polymerization of isobutylene coinitiated by AlCl3 in the presence of ethyl benzoate

<正>The cationic polymerizations of isobutylene(IB) coinitiated by AlCl_3 were carried out in solvent mixture of n-hexane /methylene dichloride(n-hex/CH_2Cl_2) of 60/40 V/V in the presence of ethyl benzoate(EB) at various temperatures range from-80℃to-30℃.The effects of EB concentration([EB]) and polymerization temperature on monomer conversion,weight-average molecular weight(M_w) and molecular weight distribution(MWD,M_w/M_n) of polyisobutylene (PIB) products were investigated.The rate of polymerization decreased while M_w of PIB products increased with increasing [EB].The polymers with high molecular weight could be prepared in the presence of a suitable amount of EB.Significantly, the polymers with high M_w of 80.2×10~4 and 65.4×10~4 could be produced at-80℃and-70℃at[EB]=0.24×10~(-3) mol/L respectively,which were much higher than that(M_w=57.9×10~4) of PIB prepared at-100℃in the absence of EB.A simple but effective method for preparing the high molecular weight polyisobutylenes was developed in this work.It has been also found that the activation energy for propagation(E_p) depended on the polymerization temperature range in the presence of EB.An obvious inflection of the linear plots of lnX_n versus 1/T_p occurred at the temperature range from-60℃to-50℃at four different concentrations of EB from 0.19×10~(-3) mol/L to 0.33×10~(-3) mol/L,and thus the inflection temperature(T_(inf)) was in the range of-60℃to-50℃.When[EB]was in the range of 0.24×10~(-3) mol/L to 0.33×10~(-3) mol/L,E_p was determined to be around-12 kJ/mol when the polymerization was carried out at temperatures from-80℃to T_(inf) and to be around-28 kJ/mol at temperatures from T_(inf) to-15℃respectively.     

Effect of reaction parameters on the dispersion polymerization of 1‐vinyl‐2‐pyrrolidone

Nonporous hydrogel microspheres 0.1–1.3 μm in diameter were prepared by the dispersion copolymerization of 1‐vinyl‐2‐pyrrolidone and ethylene dimethacrylate as a crosslinking agent. The crosslinking was evidenced by solid state ¹³C NMR and elemental analysis. The effect of various parameters including selection of solvent (cyclohexane, butyl acetate), initiator (4,4′‐azobis(4‐cyanopentanoic acid), 2,2′‐azobisisobutyronitrile, dibenzoyl peroxide) and stabilizer on the properties of resulting microspheres has been studied. Dynamic light scattering and photographic examination were used for determination of the diameter and polydispersity of microspheres. Increasing concentration of steric stabilizer in the initial polymerization mixture decreased the particle size. The particle size depended on the molecular weight of polystyrene‐block‐hydrogenated polyisoprene stabilizer, but not on the number of PS and polybutadiene blocks in the styrene–butadiene block copolymer stabilizers. Dibenzoyl peroxide used as an initiator resulted in agglomeration of particles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 653–663, 2000