Higher Polymerization Rate Research Articles

Naphthalimide‐Based Dyes as Photoinitiators under Visible Light Irradiation and their Applications: Photocomposite Synthesis, 3D printing and Polymerization in Water

AbstractIn this work, six new fluorescent dyes derived from the naphthalimide scaffold (Napht1–Napht6) were synthesized and used as high‐performance photoinitiating systems (PISs) in two and three‐component systems (combined with iodonium salt (Iod) and/or an electron donor amine (such as N‐phenylglycine[NPG])) for the radical photopolymerization of acrylate and methacrylate monomers under visible light using a light‐emitting diode at 405 nm. Markedly, these dyes were never synthesized before. In fact, these PISs showed high initiation efficiency with both demonstrating high final reactive function conversions and high polymerization rates. A further interest of our study is to determine the effect of the different substituents (chromophoric group) on the naphthalimide function, concerning the efficiency of initiation of the free radical polymerization. In order to improve the mechanical properties of the obtained polymers, these derivatives were also tested for the photopolymerization of a blend of acrylate/epoxy monomers (TA/EPOX); these latter properties were characterized by traction tests. To demonstrate the initiation efficiency of these dyes, several methods and characterization techniques were used, including steady state photolysis, real‐time Fourier transform infrared spectroscopy, emission spectroscopy as well as cyclic voltammetry. In our study, these naphthalimides were used for the synthesis of photocomposites (one and multiple layers of glass fibres) using a UV@395 nm (4 W/cm2) conveyor, as well as in the preparation of 3D printed polymers. Markedly, one of the naphthalimide derivatives (Napht‐4) can be used as a new high‐performance water soluble photoinitiator for photopolymerization in water and hydrogel synthesis.

Preparation of Iron Filler‐Based Photocomposites and Application in 3D Printing

AbstractThe introduction of metallic fillers to polymers via the photopolymerization approach can endow the composite materials with some unique properties, but the relevant research is still scarce due to the issue of light penetration and inner filter effect. Herein, for the first time the fabrication of photocomposites based on fine iron powder (i.e., a typical kind of metallic filler) is reported in this work. The free radical polymerization of two different acrylate monomers, poly(ethylene glycol) diacrylate and trimethylolpropane triacrylate, is performed in the presence of iron filler under mild conditions (i.e., light emitting diode (LED)@405 nm irradiation at room temperature under air). And the real‐time Fourier transform infrared spectroscopy reveals remarkable photopolymerization kinetics of acrylates with high final conversions and fast polymerization rates despite the increasing contents of iron filler in the composites. Interestingly, the 3D printing technique is applied to the iron filler‐based composites to produce tridimensional patterns with excellent spatial resolution. This work not only paves the way for the investigation of photocomposites based on metallic fillers through photochemical methods, but also broadens the potential application prospects.

Polymerization ability of new 4,4'-substituted 1,3-diphenoxypropan-2-yl methacrylates

Set of new 4,4'-substituted 1,3-diphenoxypropan-2-ol-based methacrylate monomers were designed. Their free radical polymerization provided three homopolymers. These novel polymers were characterized with NMR, IR spectroscopies, as well as DSC and SEC. The effect of substituents in the 4,4-position on the rate of homopolymerization of monomers was investigated and analyzed. It was found, that the highest polymerization rate is observed for monomer with acceptor substituents. For monomer with a donor substituent, the lowest polymerization rate was observed. Glass transition temperature decreased in a row: unsubstituted > acceptor substituent > donor substituent.

Quasiliving cationic ring-opening polymerization of 2-ethyl-2-oxazoline in benzotrifluoride, as an alternative reaction medium

Cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazoline (EtOx) was systematically investigated in benzotrifluoride (BTF), which is considered as an environmentally less harmful solvent than many conventional reaction media. Simultaneously, polymerizations in conventional solvents, such as acetonitrile, N,N-dimethylacetamide and toluene, were also carried out for comparison in the 80–100 °C temperature range. Kinetic experiments revealed that the monomer consumption occurs by first order kinetics and the number average molecular weights linearly increase in line with the theoretical molecular weight as a function of monomer conversion. These findings indicate that the polymerization takes place by quasiliving CROP in all the investigated solvents, including BTF as well, resulting in PEtOx with prederminded molecular weights and polydispersities of 1.3–15. The highest polymerization rates were obtained in BTF, resulting in high conversions in short reaction times at 100 °C reaction temperature. The Arrhenius parameters of the polymerization of EtOx in BTF indicates relatively high activation energy in comparison with other applied solvents, however, a compensation effect between the activation energies and frequency factor is observed for such polymerization in a variety of solvents. Our findings are expected to enable the convenient synthesis of polyoxazolines and polyoxazoline-based well-defined polymer architectures in BTF, an environmentally advantageous alternative solvent to harmful polymerization media, with high polymerization rates in short reaction times without the need for any special conditions or equipment.

Mono vs. Difunctional Coumarin as Photoinitiators in Photocomposite Synthesis and 3D Printing

This work is devoted to investigate three coumarin derivatives (Coum1, Coum2, and Coum3), proposed as new photoinitiators of polymerization when combined with an additive, i.e., an iodonium salt, and used for the free radical polymerization (FRP) of acrylate monomers under mild irradiation conditions. The different coumarin derivatives can also be employed in three component photoinitiating systems with a Iod/amine (ethyl 4-dimethylaminobenzoate (EDB) or N-phenylglycine (NPG)) couple for FRP upon irradiation with an LED @ 405 nm. These compounds showed excellent photoinitiating abilities, and high polymerization rates and final conversions (FC) were obtained. The originality of this work relies on the comparison of the photoinitiating abilities of monofunctional (Coum1 and Coum2) vs. difunctional (Coum3) compounds. Coum3 is a combined structure of Coum1 and Coum2, leading to a sterically hindered chemical structure with a relatively high molecular weight. As a general rule, a high molecular weight should reduce the migration of initiating molecules and favor photochemical properties such as photobleaching of the final polymer. As attempted, from the efficiency point of view, Coum3 can initiate the FRP, but a low reactivity was observed compared to the monofunctional compound (Coum1 and Coum2). Indeed, to study the photochemical and photophysical properties of these compounds, different parameters were taken into account, e.g., the light absorption and emission properties, steady state photolysis, and fluorescence quenching. To examine these different points, several techniques were used including UV-visible spectroscopy, real-time Fourier Transform Infrared Spectroscopy (RT-FTIR), fluorescence spectroscopy, and cyclic voltammetry. The photochemical mechanism involved in the polymerization process is also detailed. The best coumarins investigated in this work were used for laser writing (3D printing) experiments and also for photocomposite synthesis containing glass fibers.

Novel Photoinitiators Based on Benzophenone-Triphenylamine Hybrid Structure for LED Photopolymerization.

In this study, a new generation of photoinitiator (PI) based on hybrid structures combining benzophenone and triphenylamine is proposed. Remarkably, these photoinitiators (noted monofunctional benzophenone-triphenylamine (MBP-TPA) and trifunctional benzophenone-triphenylamine (TBP-TPA)) are designed and developed for the photopolymerization under light-emitting diodes (LEDs). Benzoyl substituents connected with triphenylamine moiety contribute to the excellent absorption properties which results in both high final conversions and polymerization rates in free radical photopolymerization (FRP). Remarkably, TBP-TPA owning trifunctional benzophenone group exhibits a better Type II PI behavior than well-known 2-isopropylthioxanthone for photopolymerization under LED@365 and 405nm irradiation. FRP and cationic photopolymerization of TBP-TPA-based systems are applied on 3D printing experiments, and good profiles of the 3D patterns are observed. The high molecular weight of TBP-TPA associated with it trifunctional character can also be very interesting for a better migration stability of PIs that is a huge challenge. The development of this new generation of photoinitiators based on benzophenone hybrid structures is a real breakthrough. It reveals that the novel versatile photoinitiators based on benzophenone-triphenylamine hybrid structures have great potentials for future industrial applications (e.g., 3D printing, composites, etc.).

Novel Norrish type I flavonoid photoinitiator for safe LED light with high activity and low toxicity by inhibiting the ESIPT process

In this study, flavonoid with N,N-diphenylamino group, 2-(4-(diphenylamino)phenyl)-3-hydroxy-4H-chromen-4-one (3HF–OH) was designed and synthesized as low-toxicity photoinitiator for photopolymerization under safe visible LED sources, however, low photoinitiation activity of 3HF–OH was found due to the excited state proton transfer (ESIPT) process. Hence, by replacing the 3-position hydroxyl group of 3HF–OH with benzoyl chloride and benzenesulfonyl chloride, flavonol carboxylate (3HF–C) and flavonol sulfonate (3HF–S) were synthesized, respectively. 3HF–C and 3HF–S showed not only one-component photoinitiating activity but also two-component photoinitiating activity when they were used with triethanolamine (TEOA) and iodonium salt (ONI) under safe, long-wavelength LED soft light sources. Photopolymerization kinetics reveals that photoinitiator 3HFs at low concentration exhibits the high polymerization rate and conversion. Results also showed that 3HF–S has much higher photoinitiation activity during photopolymerization compared with 3HF–OH and 3HF–C. The high extinction coefficient and aggregation-induced emission (AIE) characteristics of 3HF–S were observed, which proved that reducing the photoinitiator usage can effectively progress the photopolymerization activity. At the same time, the low usage of 3HF–S further reduces the toxicity of the cured material. Through electron spin resonance (ESR) experiment, the photoinitiation and sensitization mechanisms of these photoinitiators were observed. The school badge structure of hydrogels could be successfully 3D printed with 3HF–S and the stiffness of the structure was sufficient for further processing without breaking the structure. Moreover, the use of the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) method confirmed the lower toxicity for the final photopolymer provided.

Synthesis of di- and triacrylamides with tertiary amine cores and their evaluation as monomers in dental adhesive interfaces

Purpose/aimIn an attempt to increase the service life of dental adhesive interfaces, more hydrolytically and enzymatically-stable methacrylate alternatives, such as methacrylamides, have been proposed. The aim of this study was to investigate polymerization behavior, as well as mechanical and biological properties of experimental adhesives containing multi-functional acrylamides. Materials and methodsMulti-functional acrylamides (N,N-Bis[(3-methylaminoacryl)propyl]methylamine - BMAAPMA, Tris[(2-methylaminoacryl)ethyl]amine - TMAAEA, N,N’-bis(acrylamido) 1,4-diazepane - BAADA, N,N-Diethyl-1,3-bis(acrylamido)propane - DEBAAP) or HEMA (2-Hydroxyethyl methacrylate - control) were added at 40 wt% to UDMA. 0.2 wt% DMPA and 0.4 wt% DPI-PF6 were used as initiators. Polymerization kinetics was followed in real-time in near-IR during photoactivation (320–500 nm, at 630 mW/cm2). Water sorption/solubility and flexural strength/modulus were measured according to ISO 4049. 1H NMR was used to assess monomer degradation kinetics. MTT assay was used to assess cytotoxicity against OD-21 and DPSC cells. Biofilm formation and adhesion were assessed by Luciferase Assay and Impingement technique, respectively. Solvated adhesives (40 vol% ethanol) were used to test interfacial adhesion strength. The results were analyzed by ANOVA/Tukey's test (α = 0.05). ResultsIn general, the pure methacrylate mixture had higher rate of polymerization (Rpmax), degree of conversion (DC) at Rpmax, and final DC than the acrylamides. Flexural properties after water storage decreased between 11 and 65%, more markedly for acrylamides. Interfacial bond strength was greater and more stable long-term for the newly synthesized acrylamide formulations (less than 4% reduction at 6 months) compared to the methacrylate experimental control (42% reduction at 6 months). HEMA degraded by almost 90%, while the acrylamides showed no degradation in acidic conditions. Cytotoxicity and biofilm formation, in general, were similar for all groups. ConclusionsDespite demonstrating high water sorption, the acrylamide-containing materials had similar mechanical and biological properties and enhanced interfacial bond strength stability compared to the methacrylate control.

High performance dyes based on triphenylamine, cinnamaldehyde and indane-1,3-dione derivatives for blue light induced polymerization for 3D printing and photocomposites

In this research, high performance dyes based on triphenylamine, cinnamaldehyde and indane-1,3-dione derivatives have been designed/synthesized and evaluated as photoinitiators for visible light photopolymerization. The introduction of light-emitting diodes (LEDs) as low-cost and secured sources of irradiation is one of the major purposes in this study, where a LED at 405 nm was used for both the cationic polymerization (CP) of thin epoxide samples and the free radical polymerization (FRP) of thin TMPTA films. The proposed dyes showed very high efficiencies in the presence of the two-component photoinitiating systems based on Dye/Iodonium salt (Iod) couples or Dye/Amine (such as N-Phenylglycine (NPG) or ethyl 4-(dimethylamino)benzoate (EDB)) couples for the FRP and/or CP, highlighting their importance through a photo-oxidation (with Iod) process but also through a photo-reduction (with amine) process. The examined dyes are also able to initiate the FRP of thin acrylate films in the presence of the three-component (Dye/Iod/NPG) systems where very high rates of polymerization (Rp) and great final reactive function conversions (FCs) were achieved. A new dye (Dye 4) is proposed here for the first time (never synthesized before) and a new synthetic pathway for Dye 3 is also established. Objectives of this work concern the study of the photoinitiating abilities of the different photoinitiating systems using FTIR technique but also the study of the chemical mechanisms which was mainly examined in solution. The use of the investigated systems for 3D printing experiments (using LED projector or laser diode @405 nm) is particularly outlined. Finally, the production of thick glass fiber photocomposites presenting excellent depth of cure is also accomplished in the presence of these dyes (using near-UV conveyor: LED@395 nm).

A water soluble and highly reactive bisphosphonate functionalized thioxanthone-based photoinitiator

A new water soluble bisphosphonate functionalized thioxanthone (TXBP2) is synthesized from aza-Michael addition reaction of 2-(2-aminoethoxy)-9H-thioxanthen-9-one and tetraethyl vinylidene bisphosphonate. This photoinitiator shows excellent water-solubility of 86 g L−1 compared to Irgacure 2959 (5 g L−1). It has a λmax in the near UV–visible region, ~400 nm. The photoinitiation effectiveness of TXBP2 is studied by photo-DSC for photopolymerization of trimethylolpropane triacrylate and poly(ethylene glycol) diacrylate (PEGDA, Mn = 575 D). It shows very high polymerization rates and conversions with bis-(4-tert-butylphenyl)-iodonium hexafluorophosphate or ethyl 4-(dimethylamino)benzoate, compared to thioxanthone. The photochemical mechanisms investigated by laser flash photolysis and fluorescence indicate that the reaction involves both singlet and triplet pathway. Water solubility, biocompatibility and high reactivity make this photoinitiator a promising candidate for biomedical applications.

In-silico based development of photoinitiators for 3D printing and composites: Search on the coumarin scaffold

In this work, the in-silico rational design of new photoinitiators by molecular modeling for specific wavelength (here 405 nm) and specific applications (3D printing, composites) is reported. A large number of (keto)coumarin derivatives were investigated by molecular modeling and their synthesis and more detailed photochemical investigations are based on obtaining structures having both excellent predicted light absorption properties @405 nm and high excited state energy levels (to ensure high photochemical reactivity). More particularly, four new families of coumarins were designed (4 of the 19 proposed coumarins were never synthesized (N2,M6,T1,T6)): the first family is based on Nitrocoumarins (N1-N6), the second one on Methoxybenzene-based coumarins and Ethoxycoumarins (M1-M6), the third one on Thiophene-based coumarins (T1-T6) and the last family studied concerns Alkyne-based coumarin (A1). The purpose of this work concerns the study of the photoinitiating ability of these compounds in different monomers for different polymerization processes (free radical, cationic) using FTIR technique. The different compounds reported in this work are very efficient to initiate the free radical polymerization of (meth)acrylates but also the cationic polymerization of epoxides upon mild irradiation conditions using a Light Emitting Diode (LED) at 405 nm as visible light source. Nitrocoumarins were identified as the best candidates for photoinitiation among the different families of coumarins investigated in this work. More precisely, nitrocoumarins are characterized by very good polymerization profiles, great final reactive function conversions (FC) and also high rates of polymerization (Rp). The electrochemical and photochemical properties of the different compounds were also studied to get a deeper insight into the photochemical mechanisms supporting the initiation process. A full picture of the involved photochemical mechanisms is provided. Thanks to the astounding polymerization initiating ability of these coumarins, their use in 3D printing applications can be worthwhile. Remarkably, using these compounds, the preparation of photocomposites was possible even in difficult light penetration conditions resulting from the presence of fibers inside the resins.

Synthesis of Di- and Triacrylamides with Tertiary Amine Cores and Their Evaluation as Monomers in Dental Adhesive Interfaces

Abstract Purpose/aim In an attempt to increase the service life of dental adhesive interfaces, more hydrolytically and enzymatically-stable methacrylate alternatives, such as methacrylamides, have been proposed. The aim of this study was to investigate polymerization behavior, as well as mechanical and biological properties of experimental adhesives containing multi-functional acrylamides. Materials and methods Multi-functional acrylamides (N,N-Bis[(3-methylaminoacryl)propyl]methylamine - BMAAPMA, Tris[(2-methylaminoacryl)ethyl]amine - TMAAEA, N,N’-bis(acrylamido) 1,4-diazepane - BAADA, N,N-Diethyl-1,3-bis(acrylamido)propane - DEBAAP) or HEMA (2-Hydroxyethyl methacrylate - control) were added at 40 wt% to UDMA. 0.2 wt% DMPA and 0.4 wt% DPI-PF6 were used as initiators. Polymerization kinetics was followed in real-time in near-IR during photoactivation (320–500 nm, at 630 mW/cm2). Water sorption/solubility and flexural strength/modulus were measured according to ISO 4049. 1H NMR was used to assess monomer degradation kinetics. MTT assay was used to assess cytotoxicity against OD-21 and DPSC cells. Biofilm formation and adhesion were assessed by Luciferase Assay and Impingement technique, respectively. Solvated adhesives (40 vol% ethanol) were used to test interfacial adhesion strength. The results were analyzed by ANOVA/Tukey's test (α = 0.05). Results In general, the pure methacrylate mixture had higher rate of polymerization (Rpmax), degree of conversion (DC) at Rpmax, and final DC than the acrylamides. Flexural properties after water storage decreased between 11 and 65%, more markedly for acrylamides. Interfacial bond strength was greater and more stable long-term for the newly synthesized acrylamide formulations (less than 4% reduction at 6 months) compared to the methacrylate experimental control (42% reduction at 6 months). HEMA degraded by almost 90%, while the acrylamides showed no degradation in acidic conditions. Cytotoxicity and biofilm formation, in general, were similar for all groups. Conclusions Despite demonstrating high water sorption, the acrylamide-containing materials had similar mechanical and biological properties and enhanced interfacial bond strength stability compared to the methacrylate control.

Coumarins as Powerful Photosensitizers for the Cationic Polymerization of Epoxy-Silicones under Near-UV and Visible Light and Applications for 3D Printing Technology.

In this study, eight coumarins (coumarins 1–8) are proposed as near-UV and blue light sensitive photoinitiators/photosensitizers for the cationic polymerization (CP) of epoxysilicones when combined with 4-isopropyl-4’-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate (IOD). Among these coumarins, four of them (coumarins 1, 2, 6 and 8) have never been reported in the literature, i.e., these structures have been specifically designed to act as photoinitiators for silicones upon near UV and visible irradiation. Good final reactive epoxy function conversions (FCs) and also high rates of polymerization (Rp) were achieved in the presence of the newly proposed coumarin-based systems. The polymers generated from the photopolymerization of epoxysilicones can be considered as attractive candidates for several applications such as: elastomers, coatings, adhesives, and so on. The goal of this study focuses also on the comparison of the new proposed coumarins with well-established photosensitizers i.e., 1-chloro-4-propoxythioxanthone (CPTX), 9,10-dibutoxyanthracene (DBA) or some commercial coumarins (Com. Coum). As example of their high performance, the new proposed coumarins were also used for laser write experiments upon irradiation with a laser diode at 405 nm in order to develop new cationic 3D printing systems.

Advanced Aging study on Triple-GEM Detectors

We present here a new study of the aging of Triple-GEM detectors in contaminated environment. The goal of this experiment is to evaluate the influence of the ionization power of particles on the longevity of the gaseous detectors and therefore determine the best configurations required to reliably reproduce the classical aging phenomena in laboratory. A 100 cm2 triple-GEM detector operating in Ar/CO 2 (70/30%) was irradiated simultaneously with low energy X-rays and 5.5 MeV alpha particles. Hydrocarbons and Si-based molecules were added to the gas mixture in order to accelerate the aging and simulating many years of slow gas pollution. We measured the evolution of the detector performance in two irradiated zones and we performed a systematic chemical analysis of the GEM foils to measure the polymer concentration and thus the potential aging effects. The detector collected a total charge of 165 mC/cm2 in the two irradiated sectors with no performance loss. Chemical analysis revealed a greater Si-based polymers concentration in the region irradiated with alpha particles. This is due to their higher ionization power, with respect to low energy X-rays, which generate denser electron avalanches and, thus, a higher polymerization rate. Further studies have to be performed in order to validate this result, at different experimental conditions and with different detector technologies.

Size effect of semiconductor quantum dots as photocatalysts for PET-RAFT polymerization

Larger QDs result in a higher polymerization rate and a better fit ofMn,GPCwithMn,theoreticalfor PET-RAFT polymerization using CdSe QDs photocatalysts.

Emulsifier-free emulsion polymerization of acrylonitrile-butadiene-carboxylic acid monomers: a kinetic study based on polymerization pressure profile

Emulsion polymerization of acrylonitrile-butadiene-carboxylic acid monomers (XNBR latexes) in the absence of emulsifier is associated with thermodynamic and kinetic complexities and is very sensitive to colloidal stability. In this paper, polymerization pressure profiles were utilized for kinetic studies of emulsifier-free emulsion terpolymerization of acrylonitrile, butadiene and two carboxylic acid monomers (i.e., acrylic acid and methacrylic acid). It was found that the type and amount of acidic monomer have a great impact on the nucleation rate as well as particle size distribution and carboxyl group distribution of XNBR latexes. Also, the type of the acidic monomer affects the rates of entry and exit of radicals to and from particles and consequently the average number of radicals per particle, where a higher rate of polymerization was observed for methacrylic acid latexes. The reaction temperature has profound effects on polymerization rate, particle size distribution and colloidal stability of the latex. Partitioning of pressure profiles into four distinct regions in accordance with well-established intervals of Harkins model and analyzing particle size distribution and carboxyl group distribution, established a conceptual framework for kinetic studies in emulsion polymerization of XNBR latexes.

Improvement in zinc complexes bearing Schiff base in ring-opening polymerization of ε-caprolactone: A five-membered ring system

The ring-opening polymerizations of ε-caprolactone (CL) using 5- and 6-membered ring Zn complexes bearing Schiff base as catalysts were comparatively studied. The 5-membered ring Zn complexes exhibited a considerably higher polymerization rate than the 6-membered ring Zn complexes (2–12 fold for CL polymerization) did. X-ray data revealed that 5-membered ring L5-Ph2Zn creates larger empty space around the Zn center than 6-membered ring L6-Bn2Zn. This allows higher interaction between the initiator and Zn complex and easy CL coordination.

Preparation of PMMA nanolatex via microemulsion polymerization initiated by UV direct radiation at low temperature

By combining the microemulsion polymerization with UV direct initiation, an efficient polymerization method was developed due to its advantages in terms of high polymerization rate and conversion, lower polymerization temperature, high purity polymer. To be more specific, in the absence of initiator and under UV direct radiation, the polymerizations of MMA/Water/emulsifier microemulsion system were successfully accomplished at low temperature (26 ∼ 35°C) and PMMA nanolatex with the average diameter of 9.5 nm and narrow diameter distribution was obtained. The effects of UV intensity, monomer concentration, emulsifier concentration and temperature on polymerization rate and intrinsic viscosity of polymer were researched. The apparent activation energy of the reaction and polymerization kinetics of Rp are obtained as the following: Rp∝[IUV] 1.25[M]1.04[E]−2.57, Ea=14.45KJ/mol.

Exploitation of the Nanoreactor Concept for Efficient Synthesis of Multiblock Copolymers via MacroRAFT-Mediated Emulsion Polymerization.

Multiblock copolymers are a class of polymeric materials with a range of potential applications. We report here a strategy for the synthesis of multiblock copolymers based on methacrylates. Reversible addition-fragmentation chain transfer (RAFT) polymerization is implemented as an emulsion polymerization to generate seed particles as nanoreactors, which can subsequently be employed in sequential RAFT emulsion polymerizations. The segregation effect allowed the synthesis of a high molar mass (>100,000 g·mol-1) decablock homopolymer at a high polymerization rate to an extent not previously achieved. A heptablock copolymer containing seven different 100 unit blocks was also successfully prepared, demonstrating how the strategy can be employed to precisely control the polymer composition at a level hitherto not accessible in environmentally friendly aqueous emulsion polymerization. Importantly, the methodology is a batch process without any intermediate purification steps, thus, rendering industrial scale up more feasible.

Low temperature effect on ATRP of styrene and substituted styrenes enabled by SaBOX ligand

A series of side-armed bisoxazoline (SaBOX) ligands have been designed and prepared, which exhibited high activity under (SARA) ATRP conditions even at low temperatures. Notably, both polymerization rate and controllability on molecular weight (MW) were significantly improved by using 4-MeOSt as monomer instead of styrene under the conditions in this work, which is significantly different from the previous reports that only oligomers were produced in the conventional ATRP of 4-MeOSt due to the presence of cationic species. Systematic studies indicated that SaBOX ligand enabled the low polymerization temperature, which is necessary to suppress the cationic polymerization process and produce high MW polymers rather than oligomers during the ATRP of 4-MeOSt. Meanwhile, the highly active SaBOX ligand guaranteed the high polymerization rate and good controllability. Moreover, by employing these SaBOX ligands, the controlled ATRP of styrene and substituted styrenes could be successfully achieved at low temperatures (−30 °C–25 °C), producing polymers with molecular weights close to theoretical values and relatively narrow molecular weight distributions (Đs = 1.2–1.5). More notably, the triad syndiotacticity (rr) of polystyrene was gradually enhanced from 48% to 62% by lowering the polymerization temperature, which demonstrated that the stereospecificity could be tuned in ATRP of styrene for the first time. The improved syndiotacticity and the subdued side reactions indicated the superiority and necessity of the polymerization at low temperature for ATRP in some aspects.