Increasing Monomer Conversion Research Articles

Enhancing the Kinetics of Vapor-based Polymerization by Pulsed Filament Approach.

Initiated chemical vapor deposition is a versatile technique for synthesizing conformal polymer films on both planar and porous surfaces. It can retain functional groups and avoid undesired cross-linking. However, there is still room for enhancing its performance without altering the feed parameters. Here, we investigate a pulsed iCVD approach to improve the deposition process, achieved by switching on and off the resistively heated filament periodically. By strategically switching off the filament, a shortage of thermally activated primary radicals was created, which allowed uninterrupted chain propagation with fewer termination reactions and potentially increased monomer conversion rates. This has caused significantly faster deposition kinetics with a higher molecular weight and longer chain length for poly(glycidyl methacrylate) compared to continuous deposition. Spectra analyses confirmed that the functionality and stoichiometry ratios remained intact throughout the pulsed deposition process. The pulsed iCVD method is therefore a competitive and sustainable tool, demonstrating fast deposition kinetics and a well-preserved functionality.

Photo Fenton RAFT Polymerization of (Meth)Acrylates in DMSO Sensitized by Methylene Blue.

A novel open-to-air photo RAFT polymerization of a series of acrylate and methacrylate monomers mediated by matching chain transfer agent irradiated by far-red light in DMSO is reported. Hydroxyl radical (•OH) generated from methylene blue (MB) sensitized decomposition of H2 O2 via photo-Fenton like-reaction is used for polymerization initiation. The "living/control" characteristic is evidenced by kinetic study, in which a pseudo first order curve and linearly increases of molecular weight with the increase of monomer conversion are observed. The living end-group fidelity is characterized by MALDI-TOF-MS and 1 H NMR results, and confirmed by successful chain extension. The temporary controllability is proved by light on/off switch experiment. This article is protected by copyright. All rights reserved.

Control of the composition of matrix resin for the design of MABS resin with good transparency and toughness

Transparent methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) resin was prepared by blending the matrix resin with rubber toughened particles. The refractive index of matrix resin was characterized, which proved the transmittance of MABS resin improved with decreasing differences in the two-phase refractive index. Controlling the refractive index of the matrix resin was comparable to that of rubber, increasing acrylonitrile (AN) content in the matrix resin to improve toughening efficiency of the rubber particles to the matrix. When the proportion of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) (PMMA/SAN) was 71.6/28.4 or the initial weight ratio of MMA/St/AN was 78/16.5/5.5, the MABS resin had an optimal transmittance of 90 %. The AN content of the former was 6.5 %, and the impact strength was 155 J/m. The actual AN content of the latter was 12.5 %, and the impact strength was 172 J/m. Additionally, the refractive index of methacrylate-styrene-acrylonitrile (MSAN) decreased with increasing monomer conversion. When the monomer conversion reached 76.5 %, the change in the composition of MSAN was insignificant as the monomer conversion continued to increase. Moreover, MABS resin had a broad processing temperature window with MSAN copolymer as the matrix resin compared to the blends of PMMA and SAN, which were 170–240 °C and 190–200 °C, respectively.

ICAR ATRP-induced surface self-assembly in the fabrication of the surface nanostructures

Polymerization induced surface self-assembly (PISSA) technology is a state-of-the-art method in the fabrication of the hierarchical surface nanostructures. Previously, we demonstrated that reversible addition−fragmentation chain transfer (RAFT) polymerization-based PISSA could be used to construct hierarchical surface nanostructures on the silica particles. Atom transfer radical polymerization (ATRP) has many advantages, especially in the synthesis of the macroinitiator. In this research initiators for continuous activator regeneration (ICAR) ATRP-induced PISSA approach is used to fabricate surface nanostructures. Poly(ethylene glycol) (PEG) macroinitiator and poly(oligo(ethylene glycol) monomethyl ether methacrylate-co-2-(2-bromoisobutyrnyloxy) ethyl methacrylate) (P(OEGMA-co-BIEM)) polymer brush macroinitiator on silica particles are used to initiate ATRP of styrene in methanol/water mixture. With the chain extensions, POEGMA-g-PS graft copolymer brushes and “free” PEG-b-PS block copolymer chains make surface coassembly into surface nanostructures. With an increase in monomer feeding ratio, the surface morphology gradually changes from small-sized spherical surface micelles (s-micelles), to big-sized s-micelles, and to asymmetric layered structures. Kinetics studies indicate that with an increase in monomer conversion there is a transition from homogeneous to heterogeneous polymerization.

Multi-stimuli responsive amphiphilic diblock copolymers by a combination of ionic liquid-mediated cationic polymerization and recyclable alloy nanoparticle-mediated photoRDRP

Poly(alkyl vinyl ether)-containing multifunctional block copolymers (BCPs) are challenging to synthesize and still limited in numbers despite their possible applications in high-tech areas. This article presents the synthesis of unprecedented amphiphilic poly(2-thioethyl vinyl ether)-block-poly(poly(ethylene glycol) methacrylate) (PTEVE-b-PPEGMA) BCPs via sequential ionic liquid-mediated cationic polymerization of CEVE and recyclable alloy-mediated photoRDRP of PEGMA, followed by post-polymerization modification of the pendant -CH2CH2Cl functionality to -CH2CH2SH. Controlled nature of both the cationic polymerization and photoRDRP was demonstrated by the first-order kinetic and linear increase of molecular weight with increase of monomer conversion, keeping low dispersity values. The synthesized PTEVE-b-PPEGMA BCP exhibited a dual (redox and temperature) stimuli-response. The cloud point of PTEVE-b-PPEGMA BCP can be tuned by changing the PEGMA mol% in the BCP. Amphiphilic PTEVE-b-PPEGMA diblock copolymer undergoes self-aggregation forming spherical nano-objects. These promising PTEVE-b-PPEGMA diblock copolymers could be used for many applications, including dual stimuli-responsive materials, materials with tunable hydrophobicity, and contaminant removal.

Enhancing the mechanical properties of photosensitive binder jetting PLA via dual curing and thermal treatment

AbstractThis study aims to enhance the mechanical properties of the 3D‐printed poly(lactic acid) (PLA) specimen fabricated by a photosensitive binder jetting via the method of dual curing and thermal treatment. The layer solidification was activated by light in light‐curing mode, and the combination of light and chemical in dual‐curing mode. The 3D‐printed specimens were then immediately subjected to thermal treatment at 120°C for 30 min. The effects on mechanical properties of 3D‐printed PLA specimens in terms of layer thickness, curing system, and thermal treatment were investigated using three‐point bending test. The results demonstrated that the dual curing improved monomer conversion and mechanical properties of the specimens in comparison with the light‐curing mode. The thermal treatment also increased monomer conversion and physically interfacial binding between PLA powder and binder matrix. The flexural modulus and strength of dual‐cured 3D‐printed PLA specimens after thermal treatment were increased by 79% and 81%, respectively, compared to those of light‐cured specimens before thermal treatment. Furthermore, their cytotoxicity test with the printing layer thicknesses of 0.2 and 0.25 by MTT assay revealed non‐toxic to MC3T3‐E1 cells. Therefore, the 3D‐printed PLA part in this study has a potential for biomedical applications.

백금계 촉매와 Hydrosilane 개시제를 이용한 아세트산 비닐 합성

In this work, a series of hydrosilanes including phenylsilane, diphenylsilane, triethylsilane (TES), and tris(trimethylsilyl)silane combined with catalytical amount of platinum complex such as dichloro(1,5-cyclooctadiene) platinum (COD) and dichloro(dicyclopentadienyl)platinum have been used to initiate the polymerization of vinyl acetate (VAc) at 70-95 ℃. An ultrahigh molecular weight PVAc with number-average molecular weight (M<SUB>n</SUB>) up to 1.17×10<SUP>6</SUP> Da and polydispersity index (PDI) of 2.59 has been synthesized using TES as an initiator in the presence of 9.7 ppm of COD. A kinetic study indicates that the polymerization at VAc/TES/COD molar ratio = 3.0×10<SUP>5</SUP> : 60 : 1 smoothly reached 81.0% conversion in 28.0 h at 85 ℃, producing PVAc with M<SUB>n</SUB> increasing linearly from 1.41×105 to 6.01×10<SUP>5</SUP> Da with the increase of monomer conversion. A mechanistic investigation revealed that COD was firstly reduced by reductive TES, producing Pt nanoparticles and corresponding silane radicals to initiate the polymerization of VAc.

Molecular Weight Distribution in Ring‐Opening Polymerization of Propylene Oxide Catalyzed by Double Metal Complex: A Model Simulation

AbstractIn the present work, method of moments is used to model the molecular weight distribution (MWD) of polypropylene glycol (PPG) produced with ring‐opening polymerization of propylene oxide catalyzed by double metal complex (DMC), and an explicit expression about the polydispersity index (PDI) of PPG is obtained. The simulated results indicate that decreasing the initial concentration ratio of monomer to total chains (K1) or increasing the rate constant ratio of chain transfer to propagation (K2) leads to smaller PDI. Reducing the concentration of DMC can induce larger PDI. When the PPG's initial PDI (i.e., PDI of initiator) increases, PDI of the final PPG grows up linearly. However, with the increase of monomer conversion, PDI increases first and then decreases, that is, there is a critical conversion. The possible lack of chain transfer at the beginning of polymerization and the insufficient chain transfer caused by increased K1, decreased concentration of catalyst, and decreased K2 will cause larger PDI, namely, broad MWD.

Unique self-catalyzed bio-benzoxazine derived from novel renewable acid-containing diamines based on levulinic acid and furfurylamine: Synthesis, curing behaviors and properties

4,4-bis[5-(aminomethyl)furan-2-yl]pentanoic acid (BAFP), brand new renewable acid-containing diamines, was first utilized as feedstock for preparing fully biomass-based benzoxazine with self-catalytic characteristic. The resulting acid-containing bio-benzoxazine was prepared through Schiff base strategy. The onset ring-opening polymerization temperature of resulting benzoxazine is 173 °C determined by DSC, much lower than that of analogous bisfurfurylamine-based biobenzoxazine free of carboxylic group. The curing kinetics of as-prepared benzoxazine was probed by non-isothermal DSC method. The curing reaction consisted of three stages with overlapped regions with each other. The first stage was ascribed to initiation reaction triggered by protons of acid, with a activation energy of 116.9 KJ/mol calculated by Flynn-Wall-Ozawa method; the second stage was named combination-catalyzed stage for the fact that acid proton and phenolic proton was co-catalyzed the chain propagation, with a activation energy of 118.0 KJ/mol; The third stage was diffusion-controlled curing reaction with a activation energy of 137.3 KJ/mol. More interesting, the calculated apparent activation energy of three reactions decreased with the increase of monomer conversion.

Systems and methods for processing heavy oils by oil upgrading followed by distillation

Monodisperse poly(styrene-co-acrylonitrile) (poly(St-co-AN)) microspheres are synthesized by precipitation polymerization in ethanol/water using redox initiator under mild conditions. The microspheres have a core-shell structure with the PSt-rich core and the PAN-rich shell. The formation process shows many differences in a typical precipitation polymerization. The particles form in a short time of less than 15 min. The increase in initiator concentration leads to the increase in monomer conversion and the microsphere size. The increased water content in the ethanol/water mixed solvent controls the surface morphology of the microspheres from smooth to rambutan-like surface, due to the enhanced polarity and hydrogen bond interactions of the mixed solvent. Mechanism is analyzed by the detailed investigation on the influences of preparation parameters on the microspheres. It is confirmed that there exists two phases, say monomer droplets and continuous phase, in the reaction system. The initiation took place in the continuous phase, while the formation and growth of the microspheres occurred in the droplets. PAN segments can serve as the stabilizer in the system.

Theory of chain growth in chemical oxidative polymerization of aniline derivatives

A theoretical approach has been proposed for the establishment of quantitative relationship between the number-average molecular weight of products of the oxidative polymerization of aromatic amines and both reagent concentrations and temperature. The derived equation to estimate the number-average degree of polymerization was evaluated using the corresponding experimental data reported in the literature. It was demonstrated that the developed theory can adequately describe an increase in the molecular weight of aromatic amine polymers upon an increasing monomer conversion and decreasing temperature and oxidizer/monomer molar ratio. Proposed assumptions about the mechanism of chain growth in the oxidative polymerization of aromatic amines reflect the key features of influence of the ratio of reactants and acidity of the medium, as well as the structure of oxidizing agent on the number-average degree of polymerization of the resulting polymers. Predictions about the influence of various factors on the molecular weight of products of the oxidative polymerization of aromatic amines have been made.

Facile synthesis of monodisperse poly(styrene-co-acrylonitrile) microspheres using redox initiator in ethanol/water: Special formation mechanism

Monodisperse poly(styrene-co-acrylonitrile) (poly(St-co-AN)) microspheres are synthesized by precipitation polymerization in ethanol/water using redox initiator under mild conditions. The microspheres have a core-shell structure with the PSt-rich core and the PAN-rich shell. The formation process shows many differences in a typical precipitation polymerization. The particles form in a short time of less than 15 min. The increase in initiator concentration leads to the increase in monomer conversion and the microsphere size. The increased water content in the ethanol/water mixed solvent controls the surface morphology of the microspheres from smooth to rambutan-like surface, due to the enhanced polarity and hydrogen bond interactions of the mixed solvent. Mechanism is analyzed by the detailed investigation on the influences of preparation parameters on the microspheres. It is confirmed that there exists two phases, say monomer droplets and continuous phase, in the reaction system. The initiation took place in the continuous phase, while the formation and growth of the microspheres occurred in the droplets. PAN segments can serve as the stabilizer in the system.

Controlled Radical Polymerization of Vinyl Chloride Mediated by Xanthene-9-Thione

The controlled radical polymerization (CRP) of vinyl chloride monomer (VCM), a low activity monomer with high radical reactivity, is still a true challenge. In this study, a novel CRP of VCM with high monomer conversion at 45 °C with xanthene-9-thione (XT) as mediator and bis(4-tert-butylcyclohexyl)peroxydicarbonate (TBCP) as initiator is achieved. The Mn of the produced poly(vinyl chloride) (PVC) increases slightly with increasing monomer conversion and could be mediated in the range from 6k to 12k by simply changing the molar ratio of TBCP/XT while the dispersity maintains around 2.0. The fidelity of XT dormant groups of PVC-XT is about 60–80% and depends on the ratio of TBCP/XT. With the as-prepared PVC-XT as macroinitiator, block copolymerizations of methyl methacrylate (MMA), n-butyl acrylate (BA), and styrene (St) are carried out and the PVC-b-PMMA, PVC-b-PBA, and PVC-b-PSt block copolymers have been synthesized successfully.

Surface Nanostructures Fabricated by Polymerization-Induced Surface Self-Assembly

Surface properties of materials are strongly dependent on surface chemistry and surface structures. The fabrication of hierarchical surface nanostructures will endow solid surfaces with new functionalities and properties. In this research, we propose the polymerization-induced surface self-assembly (PISSA) approach for surface reconstruction. In this approach, two macro-CTAs, one grafted on silica particles and the other molecularly dissolved in solution, were used in reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization, and surface micelles (s-micelles) with different morphologies and sizes on silica particles were fabricated. Kinetics studies demonstrate that there are two critical points on a plot of ln([M]0/[M]t) vs polymerization time, corresponding to the onsets of surface assembly and the self-assembly of block copolymers. The morphology of s-micelles is dependent on the monomer conversion and the length of macro-CTA. For macro-CTA with short chain length, with an increase in monomer conversion the s-micelles experience a morphology change from spherical s-micelles to layered structures. For macro-CTA with long chain length, the average size of s-micelles increases with monomer conversion. In this research, we demonstrate PISSA can be used as a versatile method for surface modification.

ZnO as photocatalyst for photoinduced electron transfer–reversible addition–fragmentation chain transfer of methyl methacrylate

AbstractIn this article, photoinduced electron transfer–reversible addition–fragmentation chain transfer (PET‐RAFT) polymerization of methyl methacrylate (MMA) was investigated at moderate temperature in N,N‐dimethylformamide with ZnO as photocatalyst. The polymerization has a living characteristic: a linear increase in molecular weight (Mn,GPC), good agreement between experimental (Mn,GPC) and theoretical molecular weights (Mn,th), a decrease in molecular weight distribution (Mw/Mn) with increasing monomer conversion, and chain extension. The PET‐RAFT polymerization of MMA can be regulated by switching “ON” and “OFF” the light.

The influence of using sodium dithionite as SARA agent in miniemulsion ATRP

ABSTRACTThe supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) of butyl acrylate (nBA) and styrene (Sty) using miniemulsion is reported for the first time. The polymerization was carried out in the presence of Cu(II)Br2‐based catalytic systems using EHA6TREN or BPMODA* and sodium dithionite (Na2S2O4) as SARA agent. Kinetic data revealed a controlled polymerization for both monomers, with a very stringent control over the molecular weight distribution (Ð ≤ 1.2) but low monomer conversion. Reaction conditions were optimized in an attempt to understand the kinetics of polymerization, aiming to increase the final monomer conversion while maintaining the control over the polymerization. Self‐chain extension reactions revealed low chain end fidelity, which corroborate the impossibility of increasing monomer conversion even after the judicious variation of the main polymerization parameters (monomers, surfactant, deactivator, and Na2S2O4 concentrations, and its method of addition). The data presented suggest a particular feature of Na2S2O4 in these polymerization systems involving the significant formation of dead chains ends, which has never been observed for any other reported system using this SARA agent. In contrast, control ARGET miniemulsion experiments under the same reaction conditions and using ascorbic acid as reducing agent allowed to achieve high monomer conversions. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 879–888

The Feasibility and Functional Performance of Ternary Borate-Filled Hydrophilic Bone Cements: Targeting Therapeutic Release Thresholds for Strontium.

We examine the feasibility and functionality of hydrophilic modifications to a borate glass reinforced resin composite; with the objective of meeting and maintaining therapeutic thresholds for Sr release over time, as a potential method of incorporating antiosteoporotic therapy into a vertebroplasty material. Fifteen composites were formulated with the hydrophilic agent hydroxyl ethyl methacrylate (HEMA, 15, 22.5, 30, 37.5 or 45 wt% of resin phase) and filled with a borate glass (55, 60 or 65 wt% of total cement) with known Sr release characteristics. Cements were examined with respect to degree of cure, water sorption, Sr release, and biaxial flexural strength over 60 days of incubation in phosphate buffered saline. While water sorption and glass degradation increased with increasing HEMA content, Sr release peaked with the 30% HEMA compositions, scanning electron microscope (SEM) imaging confirmed the surface precipitation of a Sr phosphate compound. Biaxial flexural strengths ranged between 16 and 44 MPa, decreasing with increased HEMA content. Degree of cure increased with HEMA content (42 to 81%), while no significant effect was seen on setting times (209 to 263 s). High HEMA content may provide a method of increasing monomer conversion without effect on setting reaction, providing sustained mechanical strength over 60 days.

Preparation and kinetic characterization of attapulgite grafted with poly(methyl methacrylate) via R-supported RAFT polymerization

Poly(methyl methacrylate) brushes grafted from attapulgite nanoparticles (ATP@PMMA) were prepared by R-Supported reversible addition-fragmentation chain transfer polymerization (RAFT). ATP was firstly activated, and allowed to react with γ-aminopropyltriethoxysilane (APTES), 4,4′-azobis(4-cyanovaleric acid) (ACVA) and bis(thiobenzoyl) disulfide stepwise to afford 4-cyanopentanoic acid dithiobenzoate functionalized ATP (ATP-CPADB). Then, RAFT polymerizations of MMA mediated by the different systems were conducted and compared systemically. The grafting process was verified by FTIR, XRD, XPS, TGA and TEM data. Kinetic behavior indicated that the anchored CPADB is more effective before diffusing into the bulk phase. The grafting ratio (Gr), while Mn of grafted and free polymer increased linearly with increasing monomer conversion in presence of free CPADB, giving the hybrid particles with more homogeneous distribution of grafted polymer layer.

Research of Atom Transfer Radical Polymerization of Methyl Polypropylene

The methyl polypropylene was prepared bsaed on toluene as solvent, cuprous bromide (CuBr) / copper bromide (CuBr2)/tris (2-dimethylaminoethyl) amine (Me6TREN) as catalyst, azo dimethoxyisoquinolin heptanenitrile (V-70) as radical additive, 2-bromoisobutyrate (EtBiB) as initiator. The polymerization reaction was initiated by using the ultimate atomic radical polymerization (UATRPSM), whose chain reaction was manifested in linear first-order kinetics. In this study, the conversion of monomers, polymer dispersion coefficient and the relative molecular weight with monomer conversion rate changes were studied by gas chromatography (GC) and gel permeation chromatography (GPC). The results show that the final monomer conversion was 87%; with increasing monomer conversion, polymer dispersion coefficient (PDI) decreases and reaches the optimum value 1.19, while the relative molecular weight of the linear growth, and prove the reaction was precise control.

Mechanistic investigation of nonisothermal suspension polymerization of vinyl chloride

Vinyl chloride suspension polymerization using different temperature trajectories was carried out in a pilot scale batch reactor. Detailed understanding of the conversion at which the primary particles become motionless (Xm) and the key effects of Xm on morphology development of PVC grains were provided. Motionless conversion is estimated for poly(vinyl chloride) (PVC) grains prepared with different temperature trajectories by cold plasticizer absorption measurements. The porosity of PVC grains (prepared isothermally and nonisothermally) shows a maximum at a certain conversion that is considered motionless conversion. With increasing monomer conversion, the cold plasticizer uptake decreases dramatically with conversions greater than motionless conversion until the monomer phase is completely exhausted (Xf) and continues to slightly decrease after Xf. The decrease in cold plasticizer absorption is more pronounced for PVC grains produced nonisothermally by lower initial temperature. The results obtained by scanning electron microscopy and Brabender® plastography showed that the changes in internal structure and fusion behavior of PVC grains after Xm would be much lower when early aggregates of primary particles are formed. Scanning electron microscopy photographs indicate that applying the variable temperature with negative slope accelerates networking between the primary particles inside the polymerizing monomer droplets. The Brabender® plastograph measurements indicate a lower time and temperature of fusion and a higher degree of gelation for nonisothermally produced resin in which the temperature trajectory follows a greater negative slope. J. VINYL ADDIT. TECHNOL., 24:84–92, 2018. © 2015 Society of Plastics Engineers