Macro Initiator Research Articles

Functionalization of Starch for Macro-Initiator of Atomic Transfer Radical Polymerization (ATRP)

Using of petro-polymers such as polymethylmethacrylate, polypropylene and polyethylene in the world has been undergoing a critical problem due to significantly decreasing of petroleoum stock as monomer sources. Therefore reducing of the petro-polymer usage should be performed by using natural resources such as modified starches.This study reported addition of an acyl bromide compound to substitute hydroxyl groups on the starch obtains a macro initiator for graft-copolymerizing polymethylmethacrylate (PMMA) onto the functionalized starch as starch-g-PMMA through atomic transfer radical polymerization (ATRP) method. The starch activation through the substitution of the hydroxyl functional group creates ability of the starch to transfer a radical atom onto a petro-monomer such an alkylmethacrylate which furthermore polymerize into starch-g-PMMA at mild condition. This paper reported study of the starch activation describing about screening catalysts and acyl bromide compounds, optimizing process variables such as amount ratio of a selected acyl bromide compound to starch and temperature. The functionalized starchs were analysed by 13-CNMR, FTIR, titration and their morphology was observed by FE-SEM.

Self-assembly of a biodegradable branched PE-PCL-b-PEC amphiphilic polymer: synthesis, characterization and targeted delivery of doxorubicin to cancer cells

A novel biodegradable branched block copolymer was synthesized by the ring-opening polymerization of ethylene carbonate using pre-synthesized four-armed pentaerythretol poly(ε-caprolactone) (PE-PCL) as a macro initiator. Folic acid was conjugated with the end-group of the block copolymer and self-assembled in water to form polymer micelles (PMs). The very low critical micelle concentration of the block copolymer suggests its potential application in advanced drug delivery systems. The PMs are spherical in shape and have an average size of 80 nm, which is suitable for the delivery of drugs. The hydrophobicity of pentaerythretol poly(ε-caprolactone) and its branched structure can accommodate high amounts of doxorubicin. Compared with a blank sample, PMs containing encapsulated doxorubicin show a much higher cytotoxicity towards HeLa cells. A high rate of release of doxorubicin in vitro at pH 5.0 shows that the system is responsive to pH. Confocal laser scanning microscopy showed that the doxorubicin-loaded PMs were internalized into the HeLa cells.

Synthesis of ABA Type Block Copolymers of Poly(Ethylene Glycol) and Poly(Dodecyl Vinyl Ether) and Its Using as Surfactant in Emulsion Polymerization

A poly(ethylene glycol) (PEG) based macroinitiator (MI) with terminal chloride atom at both ends was prepared by the reaction of PEG-400 with chloroacetyl chloride and used for the cationic polymerization of dodecyl vinyl ether (DVE) yielding ABA type block copolymer. The block copolymer was then used as the surfactant for the emulsion polymerization of vinyl acetate and styrene in the presence of potassium persulfate as an initiator. The effects of new polymeric emulsifier on the physicochemical properties of obtained latexes were investigated depending on surfactant percentage in homopolymerizations.

Star Synthesis Using Macroinitiators via Electrochemically Mediated Atom Transfer Radical Polymerization

Electrochemically mediated atom transfer radical polymerization (eATRP) was investigated for synthesis of star polymers using macroinitiators (MIs), achieving high star yield with low Cu catalyst loading (∼100 ppm, w/w). The arm first method, using MIs, is one of the most robust procedures for star polymer synthesis. During the polymerization, MIs can react with cross-linkers (divinyl or multivinyl compounds) for initial chain extension followed by the cross-linking reaction. The MIs can be transformed to arms of the star, and the cross-linker can form the star core. In this study, poly(ethylene oxide) (PEO, Mn = 2000) based MIs (PEO MIs) were prepared, and the chain-end functionalities were confirmed by 1H NMR analysis. The ATRP functionalized PEO MIs were then used for the star synthesis by reacting with ethylene glycol diacrylate cross-linkers. Various experimental conditions were conducted for optimizing star formation, including MI concentration, MI to cross-linker molar ratio, and applied potential (Eapp).

Hydroxyalkylation and Polyether Polyol Grafting of Graphene Tailored for Graphene/Polyurethane Nanocomposites

Graphene functionalization by hydroxyalkylation and grafting with polyether polyols enables polyurethane (PU) nanocomposites formation by in situ polymerization with isocyanates combined with effective covalent interfacial coupling. Functionalized graphene (FG) hydroxylation is achieved either by alkylation, transesterification, or grafting of thermally reduced graphite oxide. In the presence of K2 CO3 as catalyst the reaction of FG-OH with ethylene carbonate at 180 °C affords hydroxyethylated FG, whereas transesterification with castor oil produces riconoleiate-modified FG polyols. In the "grafting-from" process, FG-alkoholate macro initiators initiate the graft polymerization of propylene oxide to produce hybrid FG polyols containing 38 and 59 wt% oligopropylene oxide. In the "grafting-to" process 3-ethyl-3-hydroxymethyl-oxetane is cationically polymerized onto FG-OH, producing novel hyperbranched FG-based polyether polyols. Whereas hydroxylation and grafting of FG greatly improve FG dispersion in organic solvents, polyols and even PU, as confirmed by transmission electron microscopy, matrix reinforcement of FG/PU is impaired by increasing alkyl chain length and polyol graft copolymer content.

大分子引发剂的主链柔性对PDLC电光性能的影响

Polymer dispersed liquid crystal(PDLC) films were prepared with living graft macro-initiator(MI) with different main-chain flexibility,synthesized by reversible addition-fragmentation chain transfer(RAFT) and iniferter polymerization with four kinds of monomers with different glass transition temperature.The effect of main-chain flexibility of MIs on morphologies,transmittance,switching voltage and hysteresis of PDLC films based on graft polymer had been investigated.It was observed that the OFF-state transmittance(TOFF) and the size of LC droplet decreased at first and then increased with the increase in main-chain flexibility of MIs,and both showed the lowest value when MI was RAFT-P(BMA-co-CMSI).However,Vth and Vsat showed an opposite trend.It was found that the Vth value first increased from 8.0 V to 17.7 V and then decreased to 7.3 V,while the Vsat value first increased from 25.6 V to 32.9 V and then decreased to 20.2 V.In addition,the hyste-resis showed complex changes,due to a variety of factors.Therefore,the change of main-chain flexibility of MIs successfully improved the electro-optical properties of PDLC films based on graft polymer.

Organic Catalyst-Mediated Ring-Opening Polymerization for the Highly Efficient Synthesis of Polyester-Based Star Polymers

A facile, highly efficient, and metal-free synthesis of well-defined polyester-based core cross-linked star (CCS) polymers with yields of up to 96 % was achieved via an organic catalyst (i.e., methanesulfonic acid) mediated ring-opening polymerization (ROP) at room temperature, through either a two-pot or a one-pot, two-step strategy. CCS polymers with narrow molecular weight distributions (PDI ≤ 1.3) and macroinitiator (MI) conversions of 90-96% were prepared using poly(ε-caprolactone) (PCL) MIs with molecular weights ranging from 9.9 to 36.2 kDa and [4,4'-bioxepane]-7,7'-dione (BOD) as the cross-linker. Furthermore, transesterification was identified as being responsible for the small percentage of unincorporated low molecular weight polymer remaining and star-star couplings in the star formation. Compared to CCS polymers synthesized via the methanesulfonic acid-mediated ROP, CCS polymers prepared via ROP mediated by high transesterification rate catalysts (i.e., stannous octoate (Sn(Oct)2)) suffer from much lower star purity (ca. 70%) and star-star coupled products due to more prominent transesterification side-reactions.

Direct preparation of various morphologies of polymeric aggregates by controlled polymerization

This article reviews the preparation of various morphologies of the polymeric aggregates in the dispersion or emulsion polymerization with macro-initiator (or transfer agent) as stabilizer. The polymerization-induced self-assembling and reorganization are responsible for the formation of various morphologies. Generally, the controlled/living polymerizations including living anionic polymerizations and controlled radical polymerizations are applied in the preparations. During the polymerization, the block copolymers are formed. With gradual increase of the second block in the copolymers, the phase is seperated, then forms spherical micelles with the second blocks as core and macro initiator as shell. Further increase of the polymer chains will result in the transform of the morphologiesfrom the spherical micelles to other morphologies. The various morphologies formed in several polymerization systems are described, the possible mechanism of morphologies formation are proposed and the questions and further developments orientation in this areas are presented in this paper.

Facile synthesis of thermoresponsive block copolymers of N-isopropylacrylamide using heterogeneous controlled/living nitroxide-mediated polymerizations in supercritical carbon dioxide

A new protocol for preparation of thermoresponsive poly(N-isopropylacrylamide, NIPAM) containing block copolymers is described. It involves two successive heterogeneous controlled/living nitroxide-mediated polymerizations (NMPs) in supercritical carbon dioxide (scCO2) using N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)]nitroxide (SG1), as the nitroxide. Precipitation NMPs give narrow dispersity macroinitiators (MIs), and a first report of the controlled/living polymerization of N,N-dimethylacrylamide (DMA) in scCO2 is described. The MI is then used in an inverse suspension NMP of NIPAM in scCO2 resulting in the efficient preparation of block copolymers containing DMA, tert-butyl acrylate and styrene. Aqueous cloud point temperature analysis for poly(DMA)-b-poly(NIPAM) and poly(acrylic acid)-b-poly(NIPAM) shows a significant dependence on poly(NIPAM) chain length for a given AB block copolymer.

Polymerization-Induced Color Changes of Polydiacetylene-Containing Liposomes and Peptide Amphiphile Fibers

Polydiacetylenes have received much attention due to their intrinsic optical properties. Their inclination to change color in response to environmental factors has been extensively exploited in the sensing of analytes. In this study we functionalized diacetylene-containing peptide amphiphiles and phospholipids with α-bromo esters so that they could be used as initiators in atom transfer radical polymerization (ATRP) reactions. Subsequently, the supramolecular assemblies formed by these molecules upon their addition to water, namely peptide amphiphile fibers and liposomes, were stabilized by polymerizing the diacetylene moieties present in the molecules. As a result, highly colored, disassembly resistant, macro initiators were created. To investigate whether steric crowding on the surface of these assemblies could influence the color of the polydiacetylenes, we utilized the initiator functionality that had been introduced prior to assembly in ATRP. We found that the chromatic properties of the polydiacetylenes were directly related to the formation of polymer on the surface of peptide amphiphile fibers as well as liposomes. Furthermore, we were able to demonstrate that the progress of this color change could be monitored with UV-visible spectroscopy.

Styrenated sunflower oil polymers from raft process for coating application

AbstractOil‐based macroinitiator (MI) obtained from sunflower oil was styrenated using reversible addition–fragmentation chain transfer polymerization (RAFT) in the presence of phenacyl morpholine dithiocarbamate (PMDC) as chain transfer agent. The solvent effect and effect of the molar ratio of the transfer agent, PMDC, on polydispersity and molecular weight of the polymers were investigated. The obtained results showed that, 1,4‐dioxane is a better solvent and 1/4 molar ratio of [MI]/[PMDC] provides relatively low polydispersities. No homopolystyrene was detected under these conditions, indicating the efficiency of PMDC in the chain transfer process. Livingness of the polymerization process was confirmed by chain extension with styrene using the preformed polymer as macrotransfer agent. The film properties of styrenated oil samples were determined according to the related standards. To improve film properties, the polymer obtained by RAFT technique was modified by reaction with MI. The resulting material gave transparent films with good film properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Hyperbranched homo and thermoresponsive graft copolymers by using ATRP‐macromonomer initiators

AbstractMacromonomer initiators behave as macro cross‐linkers, macro initiators, and macromonomers to obtain branched and cross‐linked block/graft copolymers. A series of new macromonomer initiators for atom transfer radical polymerization (MIM‐ATRP) based on polyethylene glycol (Mn = 495D, 2203D, and 4203D) (PEG) were synthesized by the reaction of the hydroxyl end of mono‐methacryloyl polyethylene glycol with 2‐bromo propanoyl chloride, leading to methacryloyl polyethylene glycol 2‐bromo propanoyl ester. Poly (ethylene glycol) functionalized with methacrylate at one end was reacted with 2‐bromopropionyl chloride to form a macromonomeric initiator for ATRP. ATRP was found to be a more controllable polymerization method than conventional free radical polymerization in view of fewer cross‐linked polymers and highly branched polymers produced from macromonomer initiators as well. In another scenario, ATRP of N‐isopropylacrylamide (NIPAM) was initiated by MIM‐ATRP to obtain PEG‐b‐PNIPAM branched block/graft copolymers. Thermal analysis, FTIR, 1H NMR, TEM, and SEM techniques were used in the characterization of the products. They had a thermo‐responsive character and exhibited volume phase transition at ∼ 36°C. A plasticizer effect of PEG in graft copolymers was also observed, indicating a lower glass transition temperature than that of pure PNIPAM. Homo and copolymerization kinetics were also evaluated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Dealing with the legacy of gross human rights violations in Guatemala: grasping the mismatch between macro level policies and micro level processes

This article addresses the important nexus between macro level responses and micro level processes when dealing with the aftermath of gross human rights violations. It focuses on the case of Guatemala and the issue of financial compensation for people affected by the internal armed conflict. One of the key mechanisms of the horror of the counter-insurgency war was the forced mass involvement of the civilian population through the imposition of the Civil Defence Patrols in rural indigenous communities. This raises the thorny question of who is victim in a micro reality of blurred lines between victims and perpetrators. Several socio-political parameters ensured that two distinct compensation programmes were created: one aimed at compensating the ex-civil patrollers; and a National Reparations Programme for the victims. Ethnographic accounts from Maya Q'eqchi' victims and ex-civil patrollers reveal that these two state initiatives expose frustration and incomprehensiveness among the beneficiaries towards both programmes and reveal a mismatch between macro initiatives and micro reality, which undermines the fragile process of rebuilding community trust.

“Arm-First” Synthesis of Core-Cross-Linked Multiarm Star Polyethylenes by Coupling Palladium-Catalyzed Ethylene “Living” Polymerization with Atom-Transfer Radical Polymerization

We report in this article the “arm-first” synthesis of core–shell-structured multiarm polyethylene (PE) star polymers having multiple linear-but-branched PE arms joined at a cross-linked polydivinylbenzene (polyDVB) core. This synthesis is achieved in two steps by coupling two mechanistically incompatible polymerization techniques, Pd-catalyzed coordinative ethylene “living” polymerization and atom-transfer radical polymerization (ATRP). Ethylene “living” polymerization was first carried out using a functionalized Pd–diimine catalyst, [(ArN═C(Me)–(Me)C═NAr)Pd(CH2)3C(O)O(CH2)2OC(O)C(CH3)2Br]+SbF6– (Ar = 2,6-(iPr)2C6H3) (1), to directly synthesize narrow-distributed PE macroinitiators (MIs) containing an end-capping 2-bromoisobutyryl group active for initiating ATRP. Featured with controllable molecular weights at low polydispersity, the PE MIs are employed subsequently in the second step to initiate cross-linking polymerization of divinylbenzene (DVB) via ATRP to obtain the core-cross-linked star polymers. As a demonstration, three PE MIs at different lengths (number-average molecular weight of 7.3, 10.3, and 13.7 kg/mol, respectively) were specifically synthesized and employed for star construction. In the ATRP step, the effects of the various polymerization parameters, including MI concentration, the molar ratio of DVB to MI, and MI length, on the polymerization kinetics, star yield, average arm number, and average molecular weights of the star polymers were investigated systematically. By controlling the polymerization parameters, a range of PE star polymers having narrow-distributed arm lengths (7.3–13.7 kg/mol) and controllable average arm numbers (ca. 5–43 per star) have thus been successfully synthesized. A study on dilution solution properties of these star polymers having various structural parameters reveals their spherical chain conformation and resemblance of rigid spheres and high-generation dendrimers, with their intrinsic viscosity depending primarily on arm length while not on arm number or polymer molecular weight.

Trans-disciplinary Care: A New Approach to Improving the Effectiveness of Tobacco Use Interventions

T use disorders devastate lives and financial well-being, and constitute one of the largest public health problems the world faces today. A main cause of avoidable illness and death, tobacco-related mortality rates lead to more than 435,000 deaths per year, in the United States alone1–3 with millions more affected by tobacco-related illnesses. Annually, nearly 96 billion dollars are lost to medical costs directly related to smoking.4 While smoking is the most prevalent form of tobacco use, all forms of tobacco use pose dangers to health. The well-being of entire communities, particularly underserved communities, is affected, making tobacco use one of the largest public challenges facing the health care system today. Tobacco use, like any addiction, is complex, affecting individuals, families, and communities in many ways. It is critical that tobacco use disorders be addressed in both micro (individual) interventions and macro (community-wide) initiatives with the challenges of working with underserved populations considered. Evidence suggests interventions which have been proven effective with the general population will work with underserved populations, if those interventions are made available. The key components of evidence-based tobacco use interventions center on dynamic system changes incorporating policy support and performance feedback mechanisms. Incorporating current developments in national standards surrounding the creation of medical homes and meaningful use of electronic health records, and reinforced with a trans-disciplinary approach, evidence-based smoking cessation practices can have an effect on tobacco use in underserved communities. One of the new ways to increase the effectiveness of tobacco interventions being explored is the utilization of trans-disciplinary teams, now being developed in health care organizations around the country. An evolution from inter-disciplinary care, transdisciplinary care is a multi-disciplinary team in which all members have expanded knowledge and training in the disciplines of other team members. In a transdisciplinary team model, all members of the team address tobacco use and reinforce goals, regardless of the main purpose of the visit. This shared reinforcement, along with the transmission

Synthesis and Characterization of Poly(methyl methacrylate-block-ethylene glycol-block-methyl methacrylate) Block Copolymers by Reversible Addition-Fragmentation Chain Transfer Polymerization

Synthesis of poly(methyl methacrylate-block-ethylene glycol-block-methyl methacrylate) triblock copolymers by reversible addition–fragmentation chain transfer (RAFT) by using a novel dual macro initiator (RAFT-agent) is reported. RAFT-agent is obtained from potassium salt of the ethyl xanthegonate and the terminally brominated poly(ethylene glycol) (Br-PEG-Br) which is synthesized by the reaction of poly(ethylene glycol) [PEG] with Mn= 3000 Dalton and 3-bromopropionyl chloride. The principal parameters such as monomer concentration, initiator concentration, and polymerization time that affect the polymerization reaction are evaluated. The characterization of the products is achieved using Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H-NMR), gel-permeation chromatography (GPC), thermogravimetric analysis (TGA), and fractional precipitation (γ) techniques. Molecular weights of the polymers obtained from GPC agreed with the theoretical values. RAFT polymerization is used to control the polymerization of MMA over a broad range of molecular weights.

Uniform PEO Star Polymers Synthesized in Water via Free Radical Polymerization or Atom Transfer Radical Polymerization

Amphiphilic star shaped polymers with poly(ethylene oxide) (PEO) arms and cross-linked hydrophobic core were synthesized in water via either conventional free radical polymerization (FRP) or atom transfer radical polymerization (ATRP) techniques using a simple "arm-first" method. In FRP, PEO based macromonomers (MM) were used as arm precursors, which were then cross-linked by divinylbenzene (DVB) using 2,2'-azoisobutyronitrile (AIBN). Uniform star polymers (Mw/Mn < 1.2) were achieved through adjustment of the ratio of PEO MM, DVB, and AIBN. While in case of ATRP, both PEO MM, and PEO based macroinitiator (MI) were used as arm precursors with ethylene glycol diacrylate as cross-linker. Even more uniform star polymers with less contamination by low MW polymers were obtained, as compared to the products synthesized by FRP.

Synthesis of Polystyrenes−Poly(alkyl methacrylates) Block Copolymers via Anionic Polymerization Using an Integrated Flow Microreactor System

The polystyrene living polymer end, which was produced by butyllithium initiated anionic polymerization of styrene in a flow microreactor system was found to be effectively trapped with 1,1-diphenylethylene. The resulting organolithium species could be used as a macro initiator for anionic polymerization of alkyl methacrylates to obtain styrene−alkyl methacrylate diblock copolymers using an integrated flow microreactor system. A high level of control of molecular weight was achieved at easily accessible temperatures such as +24 to −28 °C by virtue of the fast mixing, fast heat transfer, and residence time control. Triblock copolymers were also synthesized by sequential introduction of styrene and two different alkyl methacrylates in a similar manner.

Synthesis and characterization of cellulose-b-polystyrene

A block copolymer of cellulose and polystyrene (PS) was synthesized through atom transfer radical polymerization. Macroinitiators (MIs) were prepared by introducing 2-chloroacetamide to the reducing end of cellulose (degree of polymerization=20, 50, 250). Subsequently, MIs were copolymerized with styrene monomer in a system of N,N,N′,N″,N″-pentamethyldiethylenetriamine/CuCl or CuBr/ascorbic acid at 130 °C. The resulting copolymers were characterized by 1H nuclear magnetic resonance and size-exclusion chromatography. The kinetic study indicated that the polymerization was controllable. The efficacy of copolymers in compatibilizing an immiscible cellulose/PS blend was confirmed by microscopic observation. The mechanism of thermal and thermo-oxidative decomposition of the blend was investigated by thermogravimetry. Block copolymerization of cellulose and styrene was carried out by ATRP. Macroinitiators were prepared from three types of cellulose (DP=20, 50, 250). The resulting copolymers were characterized by 1H NMR and SEC. The miscibility of the immiscible cellulose/PS blend was improved by the addition of block copolymer.

The nuances of knowledge creation and development in Indian pharmaceutical industry

PurposeBased on strategic management approaches, this paper aims to develop a systemic and dynamic model of knowledge creation. The boundaries of the environment are changing in terms of contract research, in‐licensing, out‐licensing where strategic intent also changes and gets redefined.Design/methodology/approachThis is an exploratory study using available theories and evidences of companies fanning in different directions in the form of novel types of alliances. Suitable propositions are developed for further study.FindingsThe study concludes that organisations will have to reach for tacit knowledge and enhance the knowledge stock by constantly absorbing and assimilating new ideas and research findings.Research limitations/implicationsMore study in depth and across a variety of companies is required to validate the findings particularly comparing the research and development (R&amp;D) paths of organisations located in multiple countries. Not merely big firms, even small to medium‐sized enterprises (SMEs) can be the subject of further study.Originality/valuePrevious studies concentrated on conservation, accumulation and recycling of knowledge without considering the absorption capacity of firms. This study takes for its heart the absorptive capacity as the ingredient of dynamic learning opportunities. Both for micro and macro initiatives, a joint interaction is necessary for knowledge to germinate and grow. Organisational learning is also a part of this process. Intellectual property in specialised research fields therefore must be created and defended.