High-pressure free-radical copolymerization of ethene and 2-ethylhexyl acrylate

The free-radical copolymerization of ethene (E) and 2-ethylhexyl acrylate (EHA) is studied between 150 and 250°C and at pressures from 1500 to 2500 bar. The reactions which were induced either thermally or laser-photochemically are carried out in two types of continuously operated devices and also within a batch reactor. The precision in the determination of reactivity ratios is considered in detail for the continuous experiments taking the error structure of the copolymer composition measurement into account. The reactivity ratios r_E and r_EHA at 220°C and 2000 bar are found to be 0,050 ± 0,002 and 3,9 ± 0,9, respectively. From the ethene rich reaction mixtures r_E is available with higher precision than is r_EHA. The E/EHA reactivity ratios are found to be very close to literature data for the E/butyl acrylate (BA) copolymerization. Fitting of the combined data set, for E/EHA and E/BA, yields for the activation energy and activation volume of the ethene reactivity ratio E_A(r_E) = (11,9) kJ · mol⁻¹ and ΔV^≠(r_E) = -(8,2 ± 3,5) cm³ · mol⁻¹, respectively.     

Effect of pressure on the termination rate constant in free radical polymerization. Correlation between rate constant and monomer viscosity

Viscosities of six kinds of monomers—styrene, methyl methacrylate, butyl methacrylate, butyl acrylate, vinyl acetate, and octyl methacrylate—were measured under high pressures up to 1000 bar at 30°C. The pressure dependences of the viscosities could be well expressed by an exponential function and correlated with the effect of the termination rate constant determined previously. Therefore, the termination constants at various pressures can be predicted by the evaluation of the pressure dependence of the viscosity of the corresponding monomer. The applicability of O'Driscoll's termination theory under high pressure is also discussed.     

High-pressure free-radical copolymerization of ethene and butyl methacrylate

The free-radical copolymerization of ethene (E) and butyl methacrylate (BMA) is studied between 160 and 250°C at 2000 bar. The reactions which were induced thermally are carried out in a continuously operated device at total monomer conversions mostly below 1%. Monomer feed concentrations are obtained from measured mass fluxes. Copolymer composition is determined via elemental analysis. Reactivity ratio data, r_E and r_BMA, are derived from non-linear least squares fitting of the monomer mixture and copolymer compositions. r_E and r_BMA, e. g. at 190°C and 2 000 bar, are found to be 0,044 ± 0,003 and 10,9 ± 1,1, respectively. Simulation studies suggest that depropagation of BMA units has no major influence on the copolymerization kinetics at the reaction conditions of the present study. The r_BMA data are clearly different from r_A, the acrylate reactivity ratio for E-methyl acrylate, E-butyl acrylate, and E-2-ethylhexyl acrylate copolymerizations. By adopting the simplifying terminal model, from reactivity ratios and from extrapolated homo-propagation rate coefficients, cross-propagation rate coefficients are derived. The activation energy of such coefficients primarily reflects the type of monomer molecule whereas the free-radical chain-end influences the pre-exponential factor. A few experiments were carried out to estimate the pressure dependence of r_E. It turns out that the arithmetic mean of homo-propagation activation volumes provides a reasonable estimate of the pressure dependence of cross-propagation. The available data for r_E and r_BMA allow to model monomer concentration vs. polymer composition behavior of free-radical E-BMA copolymerization at technically relevant temperatures and pressures.     

Emulsion copolymerization of vinyl chloride with butyl acrylate

The emulsion copolymerization of vinyl chloride and butyl acrylate initiated by ammonium peroxodisulfate at 60°C in the presence of an anionic emulsifier was investigated. Random copolymers of butyl acrylate and vinyl chloride covering several sets of monomer compositions were synthesized by emulsion copolymerization conducted to both low and high conversions. The rate of butyl acrylate polymerization at medium conversion was found to be proportional to the 0,5 and 1,0 power of the butyl acrylate concentration for the system with and without vinyl chloride. The overall rate of poymerization was found to decrease with increasing vinyl chloride concentration in the monomer feed. The particle size increases with increasing vinyl chloride monomer concentration in the monomer feed and conversion. The decrease in molecular weight of butyl acrylate/vinyl chloride copolymer is accompanied with the incease of vinyl chloride concentration in the monomer feed and of conversion. The results are discussed in terms of radical desorption, particle nucleation and the dependence of the equilibrium monomer concentration on the reactor pressure.     

Functionalized initiators for group transfer and metal-free anionic polymerization for the synthesis of macromonomers: overview and new results

Vinylphenyloxy- and allyloxy-substituted silyl ketene acetals are presented as new functionalized initiators for group transfer polymerization (GTP). All initiators initiated GTP of butyl acrylate in tetrahydrofuran with tetrabutylammonium cyanide as catalyst to yield butyl acrylate macromonomers with number-average molecular weights somewhat lower than those calculated for an ideal living polymerization and with polydispersities of about 1,8–2,6. For the metal-free anionic polymerization, functionalized initiators were obtained introducing allyloxy and vinylbenzyl groups into tetrabutylammonium diethyl malonate. Both compounds initiated a very rapid polymerization of butyl acrylate in tetrahydrofuran with high monomer conversion. The number-average molecular weights of the macromonomers, produced in a semi-batch procedure, reached nearly theoretical values, the polydispersities were about 1,2. In all macromonomers the functionality with respect to terminal vinyl and allyl groups was near one, so that they can be used with other monomers to form graft copolymers, e. g., in a free-radical polymerization.     

Aqueous polymerization of vinyl monomers in the presence of surfactants, 3. System: Acrylamide/poly(butyl acrylate) latex

The kinetics of the polymerization of acrylamide initiated by potassium peroxodisulfate in aqueous medium is studied in the presence of poly(butyl acrylate) latex. The rate of acrylamide polymerization increases with the concentration of the latex in the reaction system. The increase is especially pronounced at concentrations of solid latex higher than 100 g per dm³ of polymerization mixture. The activation energy of the acrylamide polymerization in the presence of poly(butyl acrylate) latex is 85,8 kJ · mol^?1. This value is substantially higher than the value of 70,7 kJ · mol^?1 found for the activation energy of the polymerization of acrylamide in the absence of poly(butyl acrylate) latex. A set of reactions is proposed and the equation describing the simultaneous homopolymerization of acrylamide and grafting of poly(butyl acrylate) latex with acrylamide is derived.     

Studies on the Copolymerisation of N‐Arylmaleimides with Alkyl(meth)acrylate

The paper describes the synthesis, characterisation and polymerisation of N‐phenylmaleimide (NPM) and N‐tolylmaleimide (NTM) with butyl acrylate. Eight copolymer samples were obtained by varying the mole fraction of N‐arylmaleimide in the initial feed from 0.2 to 0.7. Structural and molecular characterisation of the samples was done using ¹H NMR spectroscopy and intrinsic viscosity measurement. Copolymer composition was determined by taking the ratio of intensities of signals due to —OCH₂ (butyl acrylate) at δ = 4.0 ± 0.1 ppm and aromatic proton at δ = 7.1–7.4 ppm of NPM/NTM. The reactivity ratio of NPM: butyl acrylate and NTM: butyl acrylate were found to be r₁ = 2.49 ± 0.01 : r₂ = 2.83 ± 0.03 and r₁ = 0.48 ± 0.04 : r₂ = 1.75 ± 0.04, respectively. NTM showed much less reactivity as compared to NPM. Thermal stability of the copolymers was evaluated by recording TG/DTG traces in nitrogen atmosphere. Tercopolymers were also prepared by taking 0.3/0.5 and 0.4/0.4 mole fraction of MMA/NPM or NTM. The mole fraction of butyl acrylate in all these tercopolymers was kept constant at 0.2. Structural, molecular and thermal characterisation was also carried out.     

Hydrogels for buccal drug delivery: properties relevant for muco-adhesion

In order to develop a muco-adhesive hydrogel for buccal drug delivery it is necessary to understand fully the properties determining adhesiveness as well as mechanisms involved. In this study we measured glass transition temperatures, water contact angles and the peel- and shear detachment forces from porcine oral mucosa, of acrylic acid and butyl acrylate copolymers. The contact angle maximizes at 50% butyl acrylate content. The glass transition temperature decreases from 0% to 100% butyl acrylate. There seems to exist a certain combination of contact angle and glass transition temperature which is related to adhesiveness. This strongly suggests that, in order to obtain a muco-adhesive hydrogel, at least two properties have to be optimized: (1) the polarity of the polymer surface and (2) the molecular mobility of the polymer groups.     

Copolymerization of ethene with methyl acrylate and ethyl 10-undecenoate using a cationic palladium diimine catalyst

The cationic palladium catalyst [(ArN=C(Me)C(Me)N=Ar)Pd(CH₃)(NC—CH₃)]⁺BAr'₄^- (Ar = 2,6-C₆H₃(CH(CH₃)₂); Ar' = 3,5-C₆H₃(CF₃)₂) (DMPN/borate) was applied in ethene homopolymerization as well as ethene copolymerization with polar monomers such as methyl acrylate and ethyl 10-undecenoate. Both ethene homo- and copolymerization afforded amorphous, branched polyethenes with glass temperatures around –65°C and very similar high degree of branching (105 branched C/1000C), which was independent of temperature and ethene pressure. Copolymerization with polar comonomers gave polyethylene containing both alkyl and ester-functional alkyl side chains. The ratio of both types of short chain branches was influenced by the feed concentration of polar monomer. In the presence of sterically hindered phenols (e. g., 2,6-di-tert-butyl-4-methylphenol (BHT)) and tetramethylpiperidine-N-oxyl radical (TEMPO) acrylate homopolymerization was prevented. BHT addition promoted both catalyst activity and methyl acrylate incorporation significantly. Polymerization reaction, polymer microstructures and polymer properties of polar and non-polar branched polyethenes were investigated.     

Emulsion copolymerization of styrene and butyl acrylate with itaconic acid

The emulsion copolymerization of styrene with itaconic acid and butyl acrylate with itaconic acid (methylenesuccinic acid), initiated by a redox system in the presence of a nonionic emulsifier, was studied at 40°C. Examination of the influence of itaconic acid on the copolymerization with both monomers showed that the presence of itaconic acid had a negative influence on copolymerization conversion and on the rate of copolymerization. the reaction order with respect to itaconic acid is ?0,34 for the copolymerization of itaconic acid with styrene and ?1,40 for its copolymerization with butyl acrylate. In the case of the copolymerization with styrene, itaconic acid has no effect on particle number concentration and particle size. Itaconic acid participates in particle nucleation during its copolymerization with butyl acrylate. Formation of oligomeric radicals in the water phase led to a decreasing number of particles and to increasing particle size.     

High solids-content nanosize polymer latexes made by microemulsion polymerization

Polymer nanoparticles were prepared from monomers such as styrene (St), butyl methacrylate (BMA), butyl acrylate (BA), methyl methacrylate (MMA), and methyl acrylate (MA) using a modified microemulsion polymerization process. With this process high polymer: surfactant weight ratios (7 : 1 or greater), relatively concentrated (10–30 wt.-%) latexes and small (10–20 nm) particle diameters were attained. Nucleation mechanisms were investigated through observations of the particle size change during the polymerization.     

Nitroxide‐Mediated Radical Polymerization with Bisaminooxy Compounds as Initiators – Controlled Biradical Polymerization

Summary: The bisaminooxy compounds Bis‐TEMPO and Bis‐TIPNO derived from 2,2,6,6‐tetramethyl‐piperidine‐1‐oxyl (TEMPO) and 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐oxyl (TIPNO) were applied as “biradical initiators” for the nitroxide‐mediated radical polymerization (NMRP) of styrene and n‐butyl acrylate. It was shown by comparison with analogous alkoxyamines as unimolecular initiators and mixing experiments of mono‐ and biradical species, that in the case of the biradical initiators chain growth occurs at both sides under NMRP conditions. This enables a two‐step synthesis of A‐B‐A‐triblock copolymers. Kinetics and molecular mass development were investigated for the controlled biradical polymerization of styrene at different initiator concentrations, temperatures, and with addition of acetic anhydride as accelerator. For the controlled biradical polymerization of n‐butyl acrylate with Bis‐TIPNO, the effect of added free nitroxide relative to the initiator concentration was studied. The poly(styrene‐block‐n‐butyl acrylate‐block‐styrene) copolymers with higher block length prepared by this method show two glass transition temperatures, which indicates microphase separation of the polymer blocks.

Structure of poly(styrene‐block‐n‐butyl acrylate‐block‐styrene), synthesized by nitroxide‐mediated radical polymerization with Bis‐TIPNO as initiator.     

Photosensitized polymerization of butyl acrylate under high pressure

The propagation and termination rate constants for butyl acrylate polymerization under high pressure at 30°C were measured by the rotating sector method. The effect of pressure on the individual rate constant was determined and the activation volumes for the propagation and the termination were obtained as ?22,5 cm³/mol and 20,8 cm³/mol, respectively, and the overall activation volume was ?26,3 cm³/mol. The rate constant and its dependence on pressure were compared with data previously obtained on methyl methacrylate and butyl methacrylate polymerizations, and the problem concerning the differences of the pressure effect between these reactions were discussed.     

Assignment of finely resolved 13C NMR spectra of polyacrylates

¹³C NMR spectra of poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA), poly(isopropyl acrylate) (PIPA), poly(butyl acrylate) (PBA), and poly(isobutyl acrylate) (PIBA) with various tacticities were determined. It was found that methine carbon resonances of PIPA split into triad sequences and those of PEA, PBA and PIBA show a mm triad at high field. Methylene carbon spectra of polyacrylates were assigned in terms of hexad sequences using HECTOR (¹³C-¹H COSY) spectra.     

Temporally Controlled Ultrasonication‐Mediated Atom Transfer Radical Polymerization in Miniemulsion

Due to the increasing requirement for more environmentally and industrially relevant approaches in macromolecules synthesis, ultrasonication‐mediated atom transfer radical polymerization (sono‐ATRP) in miniemulsion media is applied for the first time to obtain precisely defined poly(n‐butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) homopolymers, and poly(n‐butyl acrylate)‐block‐poly(tert‐butyl acrylate) (PBA‐b‐PtBA) and poly(n‐butyl acrylate)‐block‐poly(butyl acrylate) (PBA‐b‐PBA) copolymers. It is demonstrated in the reaction setup with strongly hydrophilic catalyst copper(II) bromide/tris(2‐pyridylmethyl)amine (Cu^IIBr₂/TPMA) responsible for two principal mechanisms – interfacial and ion‐pair catalysis reflecting single‐catalyst approach. This solution turns out to be an excellent tool in controlled preparation of well‐defined polymers with narrow molecular weight distribution (up to Ð = 1.28) and preserves chain‐end functionality (DCF = 0.02% to 0.32%). Temporal control over the polymer chain growth is successfully conducted by turning the ultrasonication on/off. Taking into consideration long OFF stage (92.5 h) during ultrasonication‐induced polymerization in miniemulsion, synthesis is efficiently reinitiated without any influence on controlled characteristics maintaining the precise structure of received PBA homopolymers, confirmed by narrow molecular weight distribution (Ð = 1.26) and high retention of chain‐end functionality (DCF = 0.01%). This procedure constitutes an excellent simple and eco‐friendly approach in preparation of functional polymeric materials.     

High-pressure free-radical copolymerization of ethene and methyl acrylate

The free-radical copolymerization of ethene (E) and methyl acrylate (MA) is studied between 220 and 290°C at 2000 bar. The reactions which have been induced thermally are carried out in a continuously operated device at total monomer conversions mostly below 1%. Monomer concentrations are obtained from measured mass fluxes. Copolymer composition is determined via elemental analysis. Reactivity ratio data, r_E and r_MA, are derived from non-linear least squares fitting of the monomer mixture and copolymer compositions. r_E and r_MA, e.g., at 220°C and 2000 bar, are found to be 0,045 ± 0,002 and 5,3 ± 0,2, respectively. The r_E and r_MA values slightly, but significantly, differ from corresponding data for ethene-butyl acrylate (BA) and ethene-2-ethylhexyl acrylate (EHA) copolymerizations. Toward higher temperature r_E increases and the acrylate (MA, BA, EHA) reactivity ratio r_A decreases. The temperature dependences of r_E and r_A can not be distinguished for the three ethene-acrylate systems. From an experiment at two levels of polymerization pressure, 1500 and 2000 bar, the pressure dependence of r_E has been estimated. The available data for r_E and r_A allow to model monomer concentration vs. polymer composition behavior of free-radical ethene-acrylate copolymerizations at technically relevant temperatures and pressures.     

Rate coefficients for free-radical polymerization of butyl acrylate to high conversion

The free-radical polymerization of butyl acrylate is studied between 25°C and 80°C at pressures up to 2500 bar. The reaction is measured by applying excimer laser techniques in conjunction with time-resolved high-pressure near infrared spectroscopy. Rate coefficients of propagation, k_p, and termination, k_t, are obtained for an extended temperature, pressure, and conversion range. The dependence of k_t on conversion is analyzed by means of a kinetic model which considers segmental diffusion, translational diffusion, and reaction diffusion. It turns out that free-radical termination is essentially determined by reaction diffusion.     

A kinetic study of free radical copolymerization of styrene/butyl acrylate

The free radical copolymerization at 50°C of styrene with butyl acrylate was carried out in bulk. Although the copolymer composition is well described by the Mayo-Lewis terminal model, the copolymerization rate is not. As many other systems recently examined, the data are well represented by the "implicit penultimate effect" model. Values of monomer and radical reactivity ratios are qualitatively rationalized in terms of the enthalpic and entropic models.     

Preparation of Soft Shape Memory Polymer and Its Application as a Compliant Thermal‐Triggered Gripper

A shape memory polymer always experiences a large modulus change above and below its transition temperature. Cooling down below its transition temperature leads to a sharp modulus increase. That helps the temporary shape fixing, however, it also gives the material noncompliant character, which may be a harmful factor in some applications. In this work, an approach is proposed to prepare a soft shape memory polymer with low modulus even at low temperature. The realization of this polymer depends on the mixing of two raw materials through nano‐latex blending technique. By using styrene, meth acrylate, and n‐butyl acrylate as model monomer, two kinds of core–shell latexes are synthesized, which have a triblock structure as polystyrene‐b‐poly (styrene‐co‐meth acrylate)‐b‐polystyrene and polystyrene‐b‐poly (n‐butyl acrylate)‐b‐polystyrene, respectively. Blending in the unit of nano‐latex particle helps them mixing very homogenously and forms co‐continuous morphology. The blending ratio is tuned to prepare materials with modulus lower than 50 MPa at 20 °C, meanwhile with excellent shape memory performance. Such a soft shape memory polymer shows unique advantage as a compliant thermal‐triggered gripper to stick and place objects.