Synthesis and characterization of four‐arm star‐shaped polymers and copolymers

Four‐arm star‐shaped polymers and copolymers were obtained by transition metal‐catalyzed atom‐transfer radical polymerization (ATRP). The polymers were characterized by FTIR and ¹H‐NMR spectroscopy. Gel permeation chromatography results indicated the formation of polystyrene and polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) arms with controlled molecular weights. In dilute solution, the linear polymers had higher inherent viscosities than star‐shaped ones. Thermogravimetric analysis showed a similar degradation mechanism for linear and star‐shaped polymers. Differential scanning calorimetry indicated the successful formation of diblock star‐shaped copolymers. Copyright © 2006 Society of Chemical Industry     

Synthesis and characterization of a novel liquid crystalline star‐shaped polymer based on α‐CD core via ATRP

Well‐defined side‐chain liquid crystalline star‐shaped polymers were synthesized with a combination of the “core‐first” method and atom transfer radical polymerization (ATRP). Firstly, the functionalized macroinitiator based on the α‐Cyclodextrins (α‐CD) bearing functional bromide groups was synthesized, confirmed by ¹H‐NMR, MALDI‐TOF, and FTIR analysis. Secondly, the side‐chain liquid crystalline arms poly[6‐(4‐methoxy‐4‐oxy‐azobenzene) hexyl methacrylate] (PMMAzo) were prepared by ATRP. The characterization of the star polymers were performed with ¹H‐NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and thermal polarized optical microscopy (POM). It was found that the liquid crystalline behavior of the star polymer α‐CD‐PMMAzo_n was similar to that of the linear homopolymer. The phase‐transition temperatures from the smectic to nematic phase and from the nematic to isotropic phase increased as the molecular weight increased for most of these samples. All star‐shaped polymers show photoresponsive isomerization under the irradiation with Ultraviolet light. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fe‐mediated ARGET atom transfer radical polymerization of methyl methacrylate in ionic liquid‐based microemulsion

Poly(methyl methacrylate) (PMMA) was synthesized by activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) of MMA in ionic liquid‐based microemulsion with polyoxyethylene sorbitan monooleate (Tween 80) as surfactant. The polymerization was carried out at 25°C with CCl₄ as initiator, FeCl₃·6H₂O/N,N,N′,N′‐tetramethyl‐1,2‐ethanediamine (TMEDA) as catalyst complex in the presence of reducing agent ascorbic acid (VC). The polymerization kinetics showed the feature of controlled/″living″ process as evidenced by a linear first‐order plot. The well‐controlled polymers were obtained with narrow polydispersity indices and the ionic liquid‐based microemulsions were transparent with a particle size less than 30 nm. The obtained polymer was characterized by ¹H NMR and gel permeation chromatography. The chain extension was successfully achieved by the obtained PMMA macroinitiator/FeCl₃·6H₂O/TMEDA/VC initiator system based on ARGET ATRP method. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis of star–comb‐shaped polymer with porphyrin‐core and its self‐assembly behavior study

5,10,15,20‐tetra(4‐hydroxyphenyl)porphyrin (THPP) was synthesized by the condensation of pyrrole with 4‐hydroxybenzaldehyde in the presence of solvent (propionic acid). Subsequently, the resulting THPP was converted to a tetrafunctional star‐shaped macroinitiator (porphyrin‐Br₄) by esterification of it with 2‐bromopropanoyl bromide, and then atom transfer radical polymerization (ATRP) of styrene was conducted at 110°C with CuCl/2,2′‐bipyridine as the catalyst system. The resulting product was reacted with NBS to obtain star‐shaped initiator porphyrin‐(PSt‐Br)₄, which was used the following ATRP of the GMA to synthesize star–comb‐shaped grafted polymer porphyrin‐(PSt‐g‐PGMA)₄. The number molecular weight was 2.3 × 10⁴ g/mol, and the dispersity was narrow (M_w/M_n = 1.32). The structure of the polymers was investigated by NMR, UV–vis, IR, and GPC measurement. The self‐assembly behavior of the polymer porphyrin‐(PSt‐g‐PGMA)₄ was studied by DLS and AFM. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of PMMA‐PTHF‐PMMA and PMMA‐PTHF‐PST linear and star block copolymers

Combination of cationic, redox free radical, and thermal free radical polymerizations was performed to obtain linear and star polytetramethylene oxide (poly‐THF)‐polymethyl methacrylate (PMMA)/polystyrene (PSt) multiblock copolymers. Cationic polymerization of THF was initiated by the mixture of AgSbF₆ and bis(4,4′ bromo‐methyl benzoyl) peroxide (BBP) or bis (3,5,3′,5′ dibromomethyl benzoyl) peroxide (BDBP) at 20°C to obtain linear and star poly‐THF initiators with M_w varying from 7,500 to 59,000 Da. Poly‐THF samples with hydroxyl ends were used in the methyl methacrylate (MMA) polymerization in the presence of Ce(IV) salt at 40°C to obtain poly(THF‐b‐MMA) block copolymers containing the peroxide group in the middle. Poly(MMA‐b‐THF) linear and star block copolymers having the peroxide group in the chain were used in the polymerization of methyl methacrylate (MMA) and styrene (St) at 80°C to obtain PMMA‐b‐PTHF‐b‐PMMA and PMMA‐b‐PTHF‐b‐PSt linear and star multiblock copolymers. Polymers obtained were characterizated by GPC, FT‐IR, DSC, TGA, ¹H‐NMR, and ¹³C‐NMR techniques and the fractional precipitation method. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 219–226, 2004     

Facile synthesis and characterization of star‐shaped polystyrene: self‐condensing atom transfer radical copolymerization of N‐[4‐(α‐bromoisobutyryloxy)phenyl]maleimide and styrene

BACKGROUND: Generation of stars around in situ formed cores provides a facile approach to star‐shaped polymers. Therefore the self‐condensing atom transfer radical copolymerization (SCATRCP) of N‐[4‐(α‐bromoisobutyryloxy)phenyl]maleimide (BiBPM) and a large excess of styrene (St) was investigated. RESULTS: BiBPM and St formed a charge transfer complex (CTC), which underwent the SCATRCP, leading to the branched core initiating the atom transfer radical polymerization of St, finally giving star‐shaped polystyrene (PS). Kinetic and structural study showed that a higher dosage of BiBPM resulted in an enhanced polymerization rate, a higher degree of branching and a larger number of short PS arms. Differential scanning calorimetry suggested that the glass transition temperature of the star‐shaped PS decreased with molecular weight. Melt rheometry showed that even a slightly branched architecture of the PS led to a significantly lower viscosity; both the melt flow index and the activation energy increased with the degree of branching. CONCLUSION: Due to the preferential consumption of BiBPM and formation of a CTC, even a very low dosage of BiBPM could lead to star‐shaped PS, which, in comparison with linear analogues, could possess much better melt fluidity. Copyright © 2008 Society of Chemical Industry     

自由基聚合制备甲基丙烯酸甲酯-苯乙烯嵌段共聚物

以偶氮二异丁腈为引发剂,乙二硫醇（EDT）为链转移剂进行甲基丙烯酸甲酯（MMA）的自由基聚合,得到了含有残余巯基的聚甲基丙烯酸甲酯大分子链转移剂（HS-PMMA）,继而以HS-PMMA作为大分子链转移剂进行苯乙烯的自由基聚合,采用普通自由基聚合方法合成了结构可以设计的嵌段共聚物。     

Preparation of nano‐sized poly(ethylene oxide) star microgels via reversible addition‐fragmentation transfer polymerization in selective solvents

Poly(ethylene oxide) (PEO) star microgels with a cross‐linked polystyrene core were successfully prepared by reversible addition‐fragmentation transfer polymerization of styrene (St) and divinylbenzene (DVB) with dithiobenzoate‐terminated PEO monomethyl ether (DTB‐MPEO) as macro chain transfer agent in mixtures of ethanol and tetrahydrofuran (THF). The formation of star polymers was affected by polymerization time, solvents and St:DVB:DTB‐MPEO molar ratios. Narrow polydispersed star microgels with high molecular weight were obtained under appropriate polymerization conditions. Transmission electron micrographs suggest that PEO star polymers could form nano‐size spherical micelles in mixtures of water and THF, which further demonstrates the amphiphilic nature of the star polymers. Copyright © 2006 Society of Chemical Industry     

2‐Mercapto thioxanthone as a chain transfer agent in free‐radical polymerization: A versatile route to incorporate thioxanthone moieties into polymer chain‐ends

2‐Mercapto thioxanthone (TX‐SH) was used as a chain transfer agent in free‐radical polymerization of methyl methacrylate (MMA) and styrene (St), by using 2,2′‐azobisisobutyronitrile (AIBN) as an initiator at 70°C. Chain transfer constants were found to be 1.41 and 0.12 for St and MMA, respectively. The use of TX‐SH as a chain transfer agent leads to the formation of polymers with thioxanthone (TX) end groups. The incorporation TX moiety was confirmed by spectral measurements. Polymers obtained this way were used as triplet photosensitizer in free‐radical polymerization of MMA in the presence of a hydrogen donor such as N‐methyldiethanolamine (MDEA). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3766–3770, 2007     

Synthesis and characterization of PMMA/SiO2 organic–inorganic hybrid materials via RAFT‐mediated miniemulsion polymerization

In this article, we first carried out the surface modification of SiO₂ using silane coupling agent KH570, and then prepared PMMA/SiO₂ organic–inorganic hybrid materials by conventional free radical polymerization and RAFT polymerization in miniemulsion, respectively. The kinetics comparisons of these two polymerizations were studied. PMMA/SiO₂ hybrid materials were characterized by gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis. Experimental results indicated that the polymerization behavior of MMA in miniemulsion showed controlled/living radical polymerization characteristics under the control of RAFT agent. Incorporation of RAFT agent and SiO₂ nanoparticles improved the thermal properties of polymers, the thermal stability of polymers increased with increasing content of SiO₂ nanoparticles. The structures and morphologies of SiO₂, modified SiO₂, and PMMA/SiO₂ hybrid materials were characterized by FT‐IR and TEM. TEM results showed that the addition of modified SiO₂ nanoparticles to miniemulsion polymerization system obtained different morphology latex particles. Most of modified SiO₂ nanoparticles were wrapped by polymer matrix after polymerization. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

A Synthetic Approach to Star‐Like Polymers of Styrene and Butyl Acrylate by Linking Reactions using Functionalized Methacrylates

Summary: Coupling reactions between terminal functionalized polymer chains were chosen for the synthesis of star‐like polymers consisting of polystyrene and polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] arms. For the preparation of terminal functionalized polymer chains a side reaction of the 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) mediated free radical polymerization of methacrylates could be used successfully to convert TEMPO terminated polymers into end functionalized polymers. The number of functionalized monomer units attached to the polymer chain is directly related to the TEMPO concentration during this reaction. Different polystyrenes and polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] block copolymers were functionalized with a variable number of epoxide and alcohol groups at the chain end. For the determination of the optimal reaction parameters for the coupling reactions between these polymer chains, epoxy functionalized polystyrenes were converted with hydroxy functionalized polystyrenes under basic and acidic conditions. By activation with sodium hydride or boron trifluoride star‐like polymers were synthesized under mild conditions. The transfer of the reaction conditions to coupling reactions between end functionalized polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] copolymers showed that star‐like polymers with more than 12 arms were formed using boron trifluoride as activating agent.

     

Non‐covalent interactions of pyrene end‐labeled star poly(ɛ‐caprolactone)s with fullerene

Pyrene end‐labeled star poly(?‐caprolactone)s (PCLs) with polyhedral oligomeric silsesquioxane (POSS) core were prepared by combination of copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) click chemistry and ring‐opening polymerization techniques. First, ?‐caprolactone (?‐CL) is polymerized by using 1‐pyrene methanol as initiator and stannous octoate as catalyst to obtain α‐pyrene‐ω‐hydroxyl telechelic PCL with different chain lengths. Then, its hydroxyl group is converted to acetylene functionality by esterification reaction with propargyl chloroformate. Finally, the CuAAC click reaction of α‐pyrene‐ω‐acetylene telechelic PCL with POSS‐(N₃)₈ leads to corresponding pyrene end‐labeled star‐shaped PCLs. The successful synthesis of pyrene end‐labeled star polymers is clearly confirmed by ¹H‐nuclear magnetic resonance, Fourier transform infrared, gel permeation chromatograph, differential scanning calorimeter, and thermogravimetric analysis. Furthermore, non‐covalent interactions of obtained star polymers with fullerene are investigated in liquid media. Based on Raman spectroscopy and visual investigations, the star polymer having shorter chain length exhibited better and more stable dispersion with fullerene. The amount of pyrene units present per polymer chains can directly influence the dispersion stability of fullerene. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46520.     

Synthesis of alkyne‐terminated xanthate RAFT agents and their uses for the controlled radical polymerization of N‐vinylpyrrolidone and the synthesis of its block copolymer using click chemistry

Two new alkyne‐terminated xanthate reversible addition‐fragmentation chain‐transfer (RAFT) agents: (S)‐2‐(Propynyl propionate)‐(O‐ethyl xanthate) (X₃) and (S)‐2‐(Propynyl isobutyrate)‐(O‐ethyl xanthate) (X₄) were synthesized and characterized and used for the controlled radical polymerization of N‐vinylpyrrolidone (NVP). X₃ showed better chain transfer ability in the polymerization at 60°C. Molecular weight of the resulted polymer increased linearly with the increase in monomer loading. Kinetics study with X₃ showed the pseudo‐first order kinetics up to 67% monomer conversion. Molecular weight (M_n) of the resulting polymer increased linearly with the increase in the monomer conversion up to around 67%. With the increase in the monomer conversion, polydispersity of the corresponding poly(NVP)s initially decreased from 1.34 to 1.32 and then increased gradually to 1.58. Chain‐end analysis of the resulting polymer by ¹H‐NMR and FTIR showed clearly that polymerization started with radical forming out of xanthate RAFT agent. Living nature of the polymerization was also confirmed from the successful homo‐chain extension experiment and the hetero‐chain extension experiment involving synthesis of poly(NVP)‐b‐polystyrene amphiphilic diblock copolymer. Formed alkyne‐terminated poly(NVP) also allowed easy conjugation to azide‐terminated polystyrene by click chemistry to prepare well‐defined poly(NVP)‐b‐polystyrene block copolymers. Resulting polymers were characterized by GPC, ¹H‐NMR, FTIR, and thermal study. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Design and synthesis of star polymers with hetero-arms by the combination of controlled radical polymerizations and click chemistry

An alternative approach to the synthesis of well-defined star polymers with hetero-arms was described. An azide-functionalized dithioester chain transfer agent (CTA-N₃) was designed and synthesized. Using CTA-N₃ as the reversible addition-fragmentation chain transfer (RAFT) agent, styrene was polymerized in a controlled manner. The so-obtained polystyrene showed a high proportion of azide-functionalized chains (PS-N₃, about 92%). The azide end-capped PS-N₃ could be assembled, via click reaction with a bromide-containing trialkyne coupling agent, to form a 3-arm star polystyrene (PS₃-Br) with a narrow molecular weight distribution. PS₃-Br could further serve as a macro-initiator for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). Accordingly, well-defined star polymers containing three polystyrene and one poly(methyl methacrylate) (PMMA) arms, and with a narrow molecular weight distribution, were successfully prepared.     

Well‐defined polymers containing 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane moiety: Synthesis,mechanism, and applications in catalysis

A series of well‐defined different chain lengths polymers, which contain the organometallic 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane core in the main chain, was obtained in one‐pot via a novel 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane (complex A )/azobisisobutyronitrile (AIBN) initiating system used in reverse atom transfer radical polymerization of styrene in different concentrations. The introduction of organotin complex A was supported by ¹H‐NMR, ¹³C–NMR, and the Inductive Coupled Plasma Emission Spectrometer analysis of the organotin‐containing polymer. Moreover, the mechanism of polymerization was investigated by changing the ratio of complex A to AIBN. It was concluded that the complex A not only acted as an important part of the initiator system but also introduced the functional organometallic group into the polymer chain. Additionally, the organotin‐containing polymer could be used as catalyst for esterification, and the reaction products' conversion could reach high up to 99% and does not decrease after four successive cycles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

An investigation into the degree and rate of polymerization of poly(methyl methacrylate) in the ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate

Room‐temperature ionic liquids (ILs), including 1‐butyl‐3‐methylimidazolium hexafluorophosphate, [bmim⁺][PF₆^?], were investigated as replacements for volatile organic compounds in the free‐radical solution polymerization of poly(methyl methacrylate) (PMMA). The latter was synthesized in benzene and [bmim⁺][PF₆^?] at 70 °C via a free‐radical process and the degree and rate of polymerization were compared based on the solvent used. The degree of polymerization was found to be five times higher in [bmim⁺][PF₆^?] than in benzene, while the rate of reaction was approximately four times faster in [bmim⁺][PF₆^?]. The results indicate the potential for using ILs to produce high‐molecular‐weight polymers and block structures based on the increased free‐radical stability in ILs. Copyright © 2004 Society of Chemical Industry     

Tuning the Mechanical Properties of Multiblock Copolymers Generated by Polyfunctional RAFT Agents

When employing polyfunctional reversible addition–fragmentation chain transfer (RAFT) agents (e.g., polytrithiocarbonates) in a reversible‐deactivation radical polymerization, a redistribution of the RAFT groups being connected to polymer segments occurs, which leads to a characteristic distribution of blocks in the polymer. The authors show that by adding bifunctional RAFT agents to such a system, the average number of blocks and their distribution may be tailored, proving that in principle any RAFT agent may be combined with a polyfunctional RAFT agent to tailor its topology. The authors thus add star‐shaped RAFT agents and develop multiblock copolymers of styrene and n‐butyl acrylate having incorporated star‐shaped topological features and investigate the materials via tensile testing. Using this novel mixing approach, the material toughness is substantially increased compared to multiblock copolymers obtained from pure polyfunctional RAFT agent, and stress whitening is prevented. Importantly, the approach yields copolymers with a significantly higher toughness compared to conventional blends of star and multiblock copolymers.

     

Polymerization of methyl methacrylate with a thermal iniferter: Diethyl 2,3‐dicyano‐2,3‐di(p‐tolyl)succinate

A hexa‐substituted ethane type compound, diethyl‐2,3‐dicyano‐2,3‐di(p‐tolyl)succinate (DCDTS), was successfully synthesized and used for initiation of methyl methacrylate (MMA) polymerization. The reaction demonstrated the characteristics of a “living” polymerization; i.e., both the yield and the molecular weight of the resulting polymers increased linearly with increasing reaction time, the molecular‐weight distribution of PMMA obtained was ～1.60 and almost unaffected by the conversion, and the resultant polymer can be chain extended by adding fresh MMA. End group analysis of the resultant PMMA confirmed that DCDTS behaves as a thermal iniferter for MMA polymerization. A block copolymer was prepared from the resultant PMMA, which contains a hexa‐substituted C? C bond functional end group. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2566–2572, 2001     

Modeling of “living” free‐radical polymerization processes. I. Batch,semibatch, and continuous tank reactors

A comprehensive mathematical model is developed for “living” free‐radical polymerization carried out in tank reactors and provides a tool for the study of process development and design issues. The model is validated using experimental data for nitroxide‐mediated styrene polymerization and atom transfer radical copolymerization of styrene and n‐butyl acrylate. Simulations show that the presence of reversible capping reactions between growing and dormant polymer chains should boost initiation efficiency when using free nitroxide in conjunction with conventional initiator and also increase the effectiveness of thermal initiation. A study shows the effects of the value of the capping equilibrium constant and capping reaction rate constants for both nitroxide‐mediated styrene polymerization (using alkoxyamine as polymer chain seeds) and atom transfer radical polymerization of n‐butyl acrylate (using methyl 2‐bromopropionate as chain extension seeds). Also the effect of introducing additional conventional initiator into atom transfer radical polymerization of n‐butyl acrylate is studied. It is found that the characteristics of long chain growth are determined by the fast exchange of radicals between growing and dormant polymer chains. Polymerization results in batch, semibatch, and a series of continuous tank reactors are analyzed. The simulations also show that a semibatch reactor is most flexible for the preparation of polymers with controlled architecture. For continuous tank reactors, the residence time distribution has a significant effect on the development of chain architecture. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1630–1662, 2002     

Synthesis and properties of liquid‐ crystalline triblock copolymers by ATRP,having electron‐transporting thiadiazole unit

ABA‐type block copolymers composed of 2,5‐diphenyl‐1,3,4‐thiadiazole (DPTD) oligoester and poly(methyl methacrylate) (PMMA) segments (M_n = 16 200 and 23 000) were synthesized by atom‐transfer radical polymerization and their liquid‐crystalline (LC) and photoluminescence (PL) properties were examined. The structures of block copolymers were identified by Fourier transform infrared and ¹H NMR spectroscopies. Differential scanning calorimetry measurement, polarizing microscopy observation and wide‐angle X‐ray analysis revealed that the block copolymers form thermotropic LC phase (smectic C) independent of molecular weights of PMMA segments, but a model polymer (PMMA segments having the DPTD unit in the central part) has no LC melt. Solution and solid‐state PL spectra indicated that all the block copolymers display blue emission arising from the DPTD unit. Their quantum yields are 17–21%, which increase with the PMMA chain lengths. The block copolymers have good aligned structures in the LC states, but their order parameter (S) values in sheared LC states were lower than those in the sheared LC compounds. The PL properties in the LC states were independent of the LC aligned structures. Cyclic voltammetry measurements showed that these block copolymers have deep HOMO levels compared with polymers composed of oxadiazole rings. Copyright © 2007 Society of Chemical Industry