MADIX Polymerization of Captodative Ethyl α‐Acetoxyacrylate with Acrylate Monomers

Summary: MADIX homopolymerization of a captodative monomer, ethyl‐α‐acetoxyacrylate (EAA) was investigated using AIBN as an initiator and O‐ethyl‐S‐(1‐methoxycarbonyl)ethyl dithiocarbonate as a transfer agent at 70 °C in a mixture of iPrOH and H₂O. The experimental results revealed that this transfer agent had no effect on the polymerization reaction when compared with a free radical polymerization. Copolymerization of ethyl‐α‐acetoxyacrylate, with different acrylic monomers, such as butyl acrylate (BuA), acrylic acid, N,N‐(dimethylamino)ethyl acrylate and N,N‐dimethyl acrylamide, was then studied by MADIX polymerization using the same transfer agent. All the prepared copolymers were characterized by ¹H NMR and size exclusion chromatography, and the obtained results were in accordance with theoretical predictions regarding molecular weight and copolymer composition. Futhermore, the living character of the polymerization has been checked by the chain extension of poly(EAA‐stat‐BuA) with vinyl acetate (Vac) which led to poly(EAA‐stat‐BuA)‐block‐poly(VAc).

     

Synthesis and Characterization of New Acrylate and Methacrylate Monomers with Pendant Pyridine Groups

To overcome some drawbacks of polyvinylpyridines, new monomers of acrylate and methacrylate type with pendant pyridine groups i.e., 4‐(3‐methacryloylpropyl)pyridine 1a and 4‐(3‐acryloylpropyl)pyridine 1b were successfully prepared, although it turned out to be challenging work to synthesize the acrylate monomer 1b . First polymerization studies showed that the new monomers could be polymerized easily by atom transfer radical polymerization (ATRP). The new polymers show excellent characteristics, such as very good solubility, low glass‐transition temperature, and easy quaternization.

Design and structure of new monomers 1a and 1b .     

Modification of Natural Rubber by Grafting with Hydrophilic Vinyl Monomers

Summary: The grafting of two hydrophilic vinyl monomers, dimethylaminoethyl acrylate (DMAEA) and dimethylaminoethyl methacrylate (DMAEMA), onto natural rubber latex was carried out by emulsion polymerization using redox initiation. The effects of the redox initiator concentration and type (cumene hydroperoxide/tetraethylenepentamine, CHP/TEPA; tert‐butyl hydroperoxide/tetraethylenepentamine, t‐BHP/TEPA; potassium persulfate/potassium metabisulfite, K₂S₂O₈/K₂S₂O₅), the monomer concentration and the reaction temperature on the conversion, the grafting efficiency, the water absorption and the contact angles of the grafted copolymers films, and the colloidal stability of the latexes at low pH, were investigated. Infrared spectroscopic analysis confirmed that DMAEA and DMAEMA were grafted onto the natural rubber particles. The hairy layer structure of NR‐g‐poly(DMAEMA) latex particles was investigated by transmission electron microscopy using positive and negative stainings with OsO₄ and phosphotungstic acid, respectively.

TEM micrograph of NR‐g‐poly(DMAEMA) latex particles stained with 2% OsO₄.     

Online monitoring of Silicone Network Formation by Means of In‐Situ Mid‐Infrared Spectroscopy

The ReactIR™ reaction analysis system was used to monitor the crosslinking copolymerization of trimethylsilyl methacrylate with α,ω‐methacryloyl‐terminated oligo(dimethylsiloxane). Characteristic infrared bands proved useful to determine the total methacrylate concentration. After less than 12 h at 60 °C using 0.14% 2,2′‐azoisobutyronitrile (AIBN), the methacrylate conversion during the crosslinking reaction exceeded 98%. The comparison of the crosslinking reaction with a methacrylate homopolymerization showed that significant autoacceleration occurred during network formation.

Time‐dependent monomer conversion [M]/[M]₀ for TMSMA homopolymerization (run H in Table 1) and the corresponding crosslinking polymerization (run N) as revealed by the peak at 1 326 cm⁻¹.     

Monomers for Adhesive Polymers, 7a

Homopolymerization and copolymerization of N‐(2‐hydroxyethylmethyl)acrylamide ( 1 ) with N,N′‐diethyl‐1,3‐bis(acrylamido)propane ( 2 ) have been studied in ethanol/water solvents or in bulk. The polymerization rate exponent depends on the polymerization temperature and increased from 0.99 at 50 °C to 1.21 at 75 °C. The initial polymerization rate dependence on temperature between 50 and 75 °C in Arrhenius coordinates was linear. However, the slope increased with an increase in monomer concentration. The overall activation energy E_a varied from 64 kJ · mol^?1 at 0.5 mol · L^?1 to 76 kJ · mol^?1 at 2.0 mol · L^?1 monomer concentration. In addition, the reaction order with respect to the initiator AIBN deviated from the standard free radical polymerization kinetics. The exponent 0.42 indicated a significant participation of primary radicals in termination reactions. The polymerization reaction order declined from ideality as well, and the E_a and polymerization enthalpy changed with the batch composition variation, which could be explained through monomer/monomer, monomer/solvent, or monomer/polymer complexation. The chain transfer to polymer was considered as an origin for the polymer network formation in monomer 1 homopolymerization if its concentration in the batch was 1 mol · L^?1 or higher. The more intensive polymerization acceleration with the monomer dilution and the greater heat released reduction with decrease in the monomer 1 to 2 ratios were evidenced in copolymerization. Nevertheless, the deviations from conventional reaction kinetics were not as pronounced as with acrylic or methacrylic acid polymerizations.

     

Supplemental Activator and Reducing Agent Atom Transfer Radical Polymerization of 2‐Hydroxyethyl Acrylate from High Molar Mass Poly(ethylene oxide) Macroinitiator in Dilute Solution

Triple hydrophilic asymmetric poly(2‐hydroxyethyl acrylate)‐b‐poly(ethylene oxide)‐b‐poly(2‐hydroxyethyl acrylate) (PHEA‐b‐PEO‐b‐PHEA) triblock copolymers are obtained by copper(0) catalyzed reversible deactivation radical polymerization (RDRP). Copper wire catalyzed polymerization of HEA from large PEO (M_n = 35 000 g mol^?1) macroinitiator in dimethylsulfoxide or in water fails to reach high monomer conversion in a controlled manner contrary to what is previously published with a shorter PEO macroinitiator. Catalysis by nascent Cu(0) particles generated by disproportionating CuBr in water allows rapid polymerization and high monomer conversion with a rather good control of both dispersity and HEA block length. Model disproportionation experiment shows that HEA influences the disproportionation/comproportionation equilibrium. Larger quantities of HEA lead to higher apparent rate constants and less disproportionation of CuBr which is in agreement with the supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) mechanism and not with the single electron transfer–living radical polymerization (SET‐LRP) mechanism.

     

Gas‐Phase Assisted Surface Polymerization of Vinyl Monomers with Fe‐Based Initiating Systems

Summary: Gas‐phase assisted surface polymerization (GASP) of methyl methacrylate (MMA) and styrene (St) was investigated with Fe‐based radical initiating systems, FeCl₂/2,2′‐bipyridine (Bpy)/methyl α‐bromophenylacetate (MBPA), etc. GASP with these initiating systems proceeded to produce corresponding polymers on substrate surfaces. The resulting PMMA had very high PDI values, suggesting an uncontrolled reaction. In an attempt to control the GASP, polymerization with a simple initiating system, Fe(0)/MBPA, was examined on Fe(0)‐metal surfaces, resulting in significant polymerization activity to produce high‐molecular‐weight PMMA. The results of time‐course tests on GASP of MMA and St suggested that a change had taken place to produce physically controlled propagation sites on the Fe(0) powder surfaces.

GASP schemes with a simple initiating system Fe(0)/MBPA.     

Measurement of Transfer Coefficients to Monomer for n‐Butyl Methacrylate by Molecular Weight Distributions from Emulsion Polymerization

The average kinetic coefficient for chain transfer to monomer 〈k_tr,M〉 in the free‐radical polymerization of n‐butyl methacrylate (BMA) has been determined by the analysis of molecular weight distributions obtained by seeded emulsion polymerization under conditions such that chain transfer to monomer is the dominant chain‐stopping event. Measurements between 40 and 70 °C gave data fitting an Arrhenius‐type relationship with exponential factor E_A = 30 900 ± 4 500 J · mol^?1 and pre‐exponential factor log A = 3.45 ± 0.15. The value for E_A is comparable with published data for chain transfer to monomer from methyl methacrylate (MMA) and n‐butyl acrylate (BA). The A value, however, is 1–3 orders of magnitude smaller, suggesting that there is more hindrance for chain transfer to monomer for BMA than for either MMA or BA.

     

Synthesis of Poly(lauryl acrylate) by Single-Electron Transfer/Degenerative Chain Transfer Living Radical Polymerization Catalyzed by Na2S2O4 in Water

Living radical polymerization of lauryl acrylate was achieved by SET/DTLRP in water catalyzed by sodium dithionite. The work describes the synthesis of a highly hydrophobic and polar monomer in aqueous medium. The plots of versus conversion and ln[M]₀/[M] versus time are linear, indicating a controlled polymerization. This method leads to α,ω-diiodopoly(lauryl acrylate)s that can be further functionalized. The MWDs were determined using a combination of three detectors: RALLS, DV, and RI. The method studied in this work represents a possible route to prepare well-tailored macromolecules made of LA in environment friendly reaction medium. The syndiotactic content is 75%.

     

Relationship Between Architecture and Adhesion in Polyurethane‐Based Copolymers, 2

Summary: This study describes the chain extension, with polycaprolactone diols, of polyurethane‐graft‐poly(butyl acrylate)s which were first prepared by the step growth polymerization of a mixture of diphenylmethane‐4,4′‐diisocyanate (MDI) and α,α′‐dihydroxyl‐poly(butyl acrylate)s. The success of the chain extension reaction was studied and confirmed by ¹H NMR, SEC and DSC analysis. The incorporation of polycaprolactone sequences in the polyurethane chains modified their specific adhesive properties, bringing cohesion to the material, as demonstrated by tack measurements.

PUR‐graft‐PBA extended with PCL.     

Tunable Shell Thickness in Silica Nanospheres Functionalized by a Hydrophobic PMMA‐PSt Diblock Copolymer Brush via Activators Generated by Electron Transfer for Atom Transfer Radical Polymerization

An improved strategy to synthesize SiO₂‐PMMA nanoparticles with tunable shell thickness is demonstrated, via iron (III) catalyst‐mediated activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP). To investigate the effect of the content monomer and ligand on the PMMA shell thickness, hydrophobic PMMA‐PSt diblock copolymer brushes on the surface of the silica nanospheres are designed and synthesized by AGET ATRP. Transmission electron microscopy (TEM) and field‐emission scanning electron microscopy (FESEM) show that the product has a core‐shell‐like structure and that the average shell thickness of the PMMA can easily be tuned by simply adjusting the amount of monomer or ligand. In addition, the M _n of the PMMA can be tuned from 37 800 to 62 400 g mol^?1 by changing the shell thickness, and the PDI is 1.213–1.473. These results confirm the living nature of the polymerization.

     

Control of the radical polymerization by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl and its sodium salt

The control of the radical polymerization of styrene by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl is reported here in bulk at 90 °C, 120 °C and in miniemulsion. Similarly, the control by its sodium complex is reported in bulk at 90 °C.

M _n vs. conversion for 3 , 3Na , and TEMPO.     

Blue Light Emission from a Fluorene‐Carbazole‐Fluorene Trimer Incorporated as the Side Chain into a Polynorbornene

Summary: A well defined blue electroluminescent fluorene‐carbazol‐fluorene trimer 3,6‐bis‐(9,9‐dihexyl‐9H‐fluoren‐3‐yl)‐9‐alkyl‐9H‐carbazole was synthesized using a Suzuki type cross coupling reaction as the key step. A way to attach this chromophore to a norbornene was developed and the resulting electroactive monomer was polymerised using the “3^rd generation Grubbs catalyst” (N,N‐bis(mesityl) 4,5‐dihydroimidazol‐2‐ylidene)(3‐bromo‐pyridine)₂(Cl)₂Ru?CHPh), yielding an amorphous polymer with a narrow molecular weight distribution, which was used to build a light‐emitting diode exhibiting electroluminescence peaking at 410 nm.

Incorporation of the fluorene‐carbazol‐fluorene trimer as the emissive layer in an ITO/PEDOT:PSS/emitter/Ca/Al light emitting device.     

Counterintuitive Photomodulation of the Thermal Phase Transition of Poly(methoxy diethylene glycol acrylate) in Aqueous Solution by trans–cis Isomerization of Copolymerized Azobenzenes

The non‐ionic monomer (methoxy diethylene glycol) acrylate is copolymerized with its azo‐dye‐functionalized acrylate analogue using reversible addition–fragmentation chain transfer (RAFT) polymerization. Copolymerization is increasingly difficult with increasing amounts of the azo‐dye‐bearing monomer. The resulting water‐soluble polymers are thermosensitive, exhibiting lower critical solution temperature (LCST) behavior, which can be modulated by the photoinduced trans–cis isomerization of the dye. While already small contents of the hydrophobic azobenzene group reduce the phase‐transition temperatures of the copolymers strongly, photoisomerization of the apolar trans‐state to the more‐polar cis‐state has only a small effect, and decreases rather than increases the cloud points.

     

Relationship between Architecture and Adhesive Properties of Macromolecular Materials, 1

This study deals with the preparation of polyurethane‐graft‐poly(n‐butyl acrylate)s copolymers by polymerization of diphenyl‐methane‐4,4‐di‐isocyanate (MDI) with α,α′‐di‐hydroxyl‐poly(n‐butyl acrylate)s of different sizes as macromonomers. The polyaddition has been studied on the basis of kinetic measurements, and the comb‐like structure of the resulting polymer has been well‐established. Such grafted copolymers display specific adhesive properties in connection with their comb‐like architecture.

     

Novel Brush Copolymers via Controlled Radical Polymerization

Summary: A combination of reversible addition‐fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) techniques were applied for the synthesis of novel polymer brushes by using the “grafting from” approach or a combination of “grafting through” and “grafting from” methods. The procedure included the following steps: (1) Synthesis of 2‐(2‐bromoisobutyryloxy)ethyl methacrylate (BIEM), (2a) RAFT homopolymerization of BIEM to obtain PBIEM as the polymer backbone. (2b) RAFT copolymerization of BIEM and PEO macromonomer (PEOMA, = 450 g · mol^?1, = 9) to obtain a more hydrophilic polymer backbone. Well‐controlled copolymers containing almost 25 mol‐% of PEOMA were obtained, and (3) ATRP homopolymerization of methyl acrylate (MA) and copolymerization of MA with 1‐octene using both PBIEM homopolymer and poly(BIEM‐co‐PEOMA) as polyinitiators resulted in brushes with densely grafted homopolymer and copolymer side chains, respectively. Well‐controlled copolymer side chains containing 15 mol‐% of 1‐octene were obtained. Relatively narrow molar mass distributions (MMD) were obtained for the ATRP experiments. The formation of the side chains was monitored using size exclusion chromatography (SEC) and NMR spectroscopy. The copolymer composition in the side chain was confirmed using ¹H NMR spectroscopy. Contact angle measurements indicated that for the brush polymers, containing 1‐octene in the side chain, there was a decrease in the surface energy, as compared with the brush polymers containing only the homopolymer of MA in the side chain.

Tapping‐mode SFM images for the poly(BIEM)‐graft‐poly(MA‐co‐octene) brush polymer, dip coated from dilute THF solution on mica.     

Critically Evaluated Rate Coefficients for Free‐Radical Polymerization, 5,

Summary: Propagation rate coefficients, k_p, for free‐radical polymerization of butyl acrylate (BA) previously reported by several groups are critically evaluated. All data were determined by the combination of pulsed‐laser polymerization (PLP) and subsequent polymer analysis by size exclusion (SEC) chromatography. The PLP‐SEC technique has been recommended as the method of choice for the determination of k_p by the IUPAC Working Party on Modeling of Polymerization Kinetics and Processes. Application of the technique to acrylates has proven to be very difficult and, along with other experimental evidence, has led to the conclusion that acrylate chain‐growth kinetics are complicated by intramolecular transfer (backbiting) events to form a mid‐chain radical structure of lower reactivity. These mechanisms have a significant effect on acrylate polymerization rate even at low temperatures, and have limited the PLP‐SEC determination of k_p of chain‐end radicals to low temperatures (<20 °C) using high pulse repetition rates. Nonetheless, the values for BA from six different laboratories, determined at ambient pressure in the temperature range of ?65 to 20 °C mostly for bulk monomer with few data in solution, fulfill consistency criteria and show excellent agreement, and are therefore combined together into a benchmark data set. The data are fitted well by an Arrhenius relation resulting in a pre‐exponential factor of 2.21 × 10⁷ L · mol^?1 · s^?1 and an activation energy of 17.9 kJ · mol^?1. It must be emphasized that these PLP‐determined k_p values are for monomer addition to a chain‐end radical and that, even at low temperatures, it is necessary to consider the presence of two radical structures that have very different reactivity. Studies for other alkyl acrylates do not provide sufficient results to construct benchmark data sets, but indicate that the family behavior previously documented for alkyl methacrylates also holds true within the alkyl acrylate family of monomers.

Arrhenius plot of propagation rate coefficients, k_p, for BA as measured by PLP‐SEC.     

Controlled Radical Polymerization of Vaporized Vinyl Monomers on Solid Surfaces under UV Irradiation

Summary: In order to prepare well‐defined polymers on solid surfaces in the gas phase, a gas phase‐assisted surface polymerization (GASP) of vinyl monomers was carried out on solid surfaces pre‐coated with a photoiniferter, 2‐cyanoprop‐2‐yl N,N′‐dimethyldithiocarbamate, under UV irradiation. The GASP of methyl methacrylate (MMA) resulted in the formation of polymer on the surfaces and showed a proportional relationship between and polymer yield. Consecutive copolymerization of MMA and styrene led to the formation of a block copolymer, which was confirmed by a selective solvent fractionation method. These results demonstrate that controlled radical polymerization of vaporized monomer occurred on the solid surfaces.

Expected mechanism of GASP under UV irradiation.     

Photopolymerization of Reactive Mesogens

Summary: The photopolymerization of two reactive mesogens with photopolymerizable acrylate endgroups, the methyl substituted 1,4‐phenylene‐bis{4‐[6‐(acryloyloxy)hexyloxy]benzoate} 1 and acrylic acid 6‐{4‐[6‐(6‐acryloyloxyhexyloxy)naphthalen‐2‐yl]‐phenoxy}hexyl ester 2 has been investigated using Photo‐DSC measurements. Photocrosslinking of 1 in the nematic phase at 100 °C leads to a final conversion of 87% of the acrylate groups. It is possible to perform photopolymerization with very small amounts of photoinitiator. Even with 0.001% (10 ppm) of photoinitiator, 47% of the acrylate groups polymerize within 15 min. The polymerization of the reactive mesogen 2 proceeds faster in the smectic A phase at 100 °C compared to the isotropic phase at 120 °C and leads to a higher conversion of 75%. This can be explained by an increased local concentration of the acrylate groups between the layers of the smectic cores.

Photopolymerization of reactive mesogens.     

Surface Properties of Mesophase‐Forming Fluorinated Bicycloacrylate/Polysiloxane Methacrylate Copolymers

Novel random copolymers were synthesized by free‐radical polymerization of a bicycloacrylate monomer carrying a fluorocarbon chain side group (BAF10) with a methacrylate monomer having a polysiloxane side graft (SiMA). The copolymers with higher contents of BAF10 gave rise to a well‐ordered smectic bilayer mesophase. The surface structure of the derived polymer films was investigated by measurements of the contact angle with several interrogating liquids and X‐ray photoelectron spectroscopy (XPS) at different photoemission angles. The values of the contact angles were used to evaluate the film surface tension, following different additive‐component and equation‐of‐state methods. The low surface energies found were attributed to the pronounced hydrophobicity and oleophobicity of the outermost surface caused by the preferential segregation of the fluorocarbon chains to the polymer–air interface.