Core-shell polyacrylate and polystyrene-block-polyacrylate stars

The polymerization of p-(iodomethyl)styrene (PIMS) yields well-defined branched polymers with reactive iodomethyl groups. The branched poly[p-(iodomethyl)styrene] was used as the transfer agent in the iodine mediated radical polymerization of vinyl monomers. The polymerization proceeds in a controlled way and yields polystyrene and poly(t-butyl acrylate) star polymers with reactive groups at the end of their arms. Polymers so obtained were also used to prepare stars with block copolymer arms: polystyrene-block-poly(t-butyl acrylate). The characterization of star structures was performed by NMR and gel permeation chromatography with absolute molar mass detection (MALLS). Preliminary characterization of the thermal properties of these novel materials is reported.     

Synthesis and characterization of branched polymers by a free radical approach using a novel ‘macroiniferter’

Free radical bulk polymerization of styrene and methyl methacrylate (MMA) was carried out using a novel ‘macroiniferter’ which resulted in branched polymers with relatively narrow molecular weight distribution. This approach involving the novel macroiniferter; poly[3-(t-butylperoxy)propyl disulfide] (PBPPDS) that has side chain peroxide groups and main chain disulfide linkages was developed to prepare soluble branched polymers as well as to control the extent of branching in vinyl polymers synthesized via a free radical route. The synthesis, characterization and thermal degradation studies of PBPPDS are reported here for the first time. The resulting polystyrene (PS) and poly(methyl methacrylate) (PMMA) polymers were characterized using gel permeation chromatography (GPC), intrinsic viscosity [η] measurements and the degree of branching was studied by the determination of g′ factor.     

Synthesis and characterization of polystyrene-b-tetraaniline stars from polystyrene stars with surface reactive groups prepared via ATRP

Functionalized star polymers with tetraaniline on their surface have been successfully prepared by substitution reaction of N-succinimidyl-terminated star polymers with tetraaniline. A novel functional initiator bearing N-succinimidyl group was used in atom transfer radical polymerization (ATRP) of styrene, and polystyrenes (PSts) having N-succinimidyl groups with narrow molecular weight distribution were obtained. The star polymers with reactive N-succinimidyl groups on their surface were synthesized by ATRP of divinylbenzene (DVB). The N-succinimidyl-terminated PSt, polymer stars with surface N-succinimidyl groups and the PSt-b-tetraaniline stars were characterized by ¹H NMR spectroscopy, FT-IR and gel permeation chromatography.     

Strain-promoted azide-alkyne cycloaddition “click” as a conjugation tool for building topological polymers

Strain-promoted azide-alkyne cycloaddition “click” reaction (SPAAC) was successfully used as a tool in synthesis of star polymers by grafting onto approach. The application of SPAAC method in star polymer synthesis was investigated for coupling reaction of the dibenzocyclooctyne (DIBO) end group of polystyrene (PS) and poly(ethylene glycol) (PEG) with coupling agents bearing 2, 3, or 4 azido groups. Firstly, well-defined linear DIBO-terminated PS was obtained by atom transfer radical polymerization (ATRP) of styrene using a DIBO containing ATRP initiator and linear DIBO-terminated PEG was obtained by terminal functionalization of PEG monomethyl ether (PEG-OH). Then a series of star PS and PEG bearing two, three and four arms were prepared respectively by subjecting SPAAC coupling reaction between the linear polymer-DIBO and the azido tethered core molecules at 30 °C without catalyst. The obtained star PS showed a well-defined structure after fractional precipitation to remove slightly excess linear polymers, and all the star polymers were characterized via Fourier transform infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance spectroscopy (¹H NMR), size exclusion chromatography (SEC) and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS).     

Intermolecular radical addition of alkoxyamines onto olefins: An easy access to advanced macromolecular architectures precursors

Novel “second generation” alkoxyamines, derived from N-(2-methylpropyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (so-called SG1) as initiators for nitroxide-mediated polymerization (NMP) were synthesized by intermolecular radical 1,2-addition (IRA) of a high dissociation rate constant alkoxyamine (BlocBuilder^®, also called MAMA-SG1) onto various activated olefins, such as n-butyl acrylate, acrylic acid, dimethylacrylamide, 2-hydroxyethylacrylate and styrene. The potential of this radical addition was further applied to the synthesis of multifunctional alkoxyamines as precursors for complex macromolecular architectures, namely 3- and 4-arm star polymers. For this, tri- and tetra-acrylates were synthesized by reaction of acryloyl chloride with the 1,1,1-tris(hydroxymethyl)ethane and pentaerythritol, respectively, in the presence of triethylamine. The addition of MAMA-SG1 onto these olefins led to the tri- and tetra-functional SG1-based alkoxyamines which were further used to prepare polystyrene stars of controlled molecular weights and polydispersity values not exceeding 2. The individual arms were recovered by hydrolysis of the ester groups of the star core originating from the alkoxyamine initiator under basic conditions. The decreasing molecular weight determined by GPC during hydrolysis demonstrated the star architecture of the polymers.     

Allyl functionalized telechelic linear polymer and star polymer via RAFT polymerization

Reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene using bisallyl trithiocarbonate as a chain transfer agent (CTA) was studied. The polymerization exhibited first-order kinetics and the molecular weight increased linearly with increase of monomer conversion. Well defined allyl-functionalized telechelic polystyrene (PS), poly(tert-butyl acrylate) (PtBA) and corresponding triblock copolymers, polystyrene-b-poly(n-butyl acrylate)-b-polystyrene (PS-b-PnBA-b-PS) and poly(tert-butyl acrylate)-b-polystyrene-b-poly(tert-butyl acrylate) (PtBA-b-PS-b-PtBA) were prepared as characterized with GPC and NMR analysis. The allyl-end groups of the telechelic PS have been switched to 1,2-dibromopropyl groups quantitatively by bromine addition reaction, further substitution of the bromide with azide was also made. Furthermore, star PS with allyl-end-functionalized arms was synthesized by RAFT polymerization of divinyl benzene using allyl-functionalized PS as a macro-CTA via arm-first approach. Star polymer with a thiol-functionalized core was generated by aminolysis reaction of the star polymer and ethylenediamine. As a result, difunctionalized star polymer with allyl and thiol groups was obtained and was used as a stabilizer for the formation of gold nanoparticles.     

Well-defined dibenzocyclooctyne end functionalized polymers from atom transfer radical polymerization

The dibenzocyclooctyne end functionalized agent 1 was designed as atom transfer radical polymerization (ATRP) initiator. The ATRP was then explored on three types of monomers widely used in free radical polymerization: methyl methacrylate, styrene, and acrylates (n-butyl acrylate and tert-butyl acrylate). The living polymerization behaviors were obtained for the methyl methacrylate and styrene monomers. The SPAAC click reactivity of dibenzocyclooctyne end group were demonstrated by successfully reacting with azide functionalized small chemical agents and polymers. Various topological polymers such as block and brush polymers were produced from strain-promoted azide-alkyne cycloaddition reaction (SPAAC) using the resultant dibenzocyclooctyne end functionalized poly(methyl methacrylate)/polystyrene as building blocks. For the acrylates, however, the polymerization did not hold the living characteristics with the dibenzocyclooctyne end functionalized ATRP initiator 1.     

Preparation of star polymers based on polystyrene or poly(styrene-b-N-isopropyl acrylamide) and divinylbenzene via reversible addition-fragmentation chain transfer polymerization

Star polymers based on styrene/divinyl benzene (St/DVB) and PSt-b-poly(N-isopropyl acrylamide) (NIPAAM)/DVB have been successively prepared by ‘arm-first’ method via reversible addition-fragmentation chain transfer (RAFT) polymerization. The linear macro RAFT agent PSt-SC(S)Ph was prepared by RAFT polymerization of St using benzyl dithiobenzoate and AIBN as RAFT agent and initiator. Successive RAFT polymerization of NIPAAM with PSt-SC(S)Ph as macro RAFT agent to afford diblock copolymer, PSt-b-PNIPAAM-SC(S)Ph. The coupling reactions of PSt-SC(S)Ph or PSt-b-PNIPAAM-SC(S)Ph in the presence of DVB produced the star copolymers, C(PSt)_n or C(PSt-b-PNIPAAM)_n. The molar ratio of DVB/PSt-SC(S)Ph and polymerization time influenced the yields, molecular weight and distribution of the star-shaped polymers, which was characterized by ¹H NMR and IR spectra, GPC measurements as well as DLS.     

Biobased miktoarm star copolymer from soybean oil,isosorbide, and caprolactone

Soybean oil-based macroinitiator was prepared from epoxidized soybean oil. A ¹H NMR quantitative method was utilized for the characterization of this macroinitiator. A kind of renewable carbohydrate derivate, 1,4: 3,6-Dianhydro-D-glucitol 2-acrylate 5-acetate (AAI) was prepared as the substitute monomer of styrene. Series of renewable miktoarm star copolymers initiated by soybean oil macroinitiator were obtained by atom transfer radical polymerization (ATRP) of AAI and ring-opening polymerization (ROP) of ε-caprolactone sequentially. The obtained miktoarm star block copolymers were characterized by ¹H NMR, FTIR, and DSC. The DSC results show well dependence of the thermal behaviors of these miktoarm star block copolymers on the component of the two kinds of segments. A new strategy of renewable resource utilization has been provided on polymeric materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48281.     

Synthesis of amphiphilic star block copolymers of polystyrene with PEG core via ATRP—control of chain architecture and the formation of core-shell type globular structure

Amphiphilic star block copolymers made of poly(ethylene glycol) (PEG) core and branched PS arms having controlled chain lengths and numbers were synthesized by atom transfer radical copolymerization (ATRP) of styrene and chloromethylstyrene (CMS) in the presence of tetrafunctional PEG macroinitiator. The chain lengths and number of PS chains were controlled by adjusting the initial feed ratio of CMS to styrene and CMS to hydrophilic tetrafunctional macroinitiator, respectively, for a given polymerization time. The obtained polymers have well defined and controlled architectures. Use of excess amount of CMS and longer reaction time leads to the synthesis of dendrimer like amphiphilic block copolymer having four hyperbranched polymer arms, whose shape is closer to globular core-shell structure compared to general star shape polymers.     

Effect of molecular architecture on the self-diffusion of polymers in aqueous systems: A comparison of linear, star, and dendritic poly(ethylene glycol)s

Star polymers with a hydrophobic cholane core and four poly(ethylene glycol) (PEG) arms, CA(EG_n)₄, have been synthesized by anionic polymerization. Pulsed-gradient spin-echo NMR spectroscopy was used to study the diffusion behavior of the star polymers, ranging from 1000 to 10,000 g/mol, in aqueous solutions and gels of poly(vinyl alcohol) (PVA) at 23 °C. The star polymers have a lower self-diffusion coefficient than linear PEGs at equivalent hydrodynamic radius. In water alone, the star polymers and their linear homologues have a similar diffusion behavior in the dilute regime, as demonstrated by the similar concentration dependence of the self-diffusion coefficients. In the semidilute regime, the star polymers tend to aggregate due to their amphiphilic properties, resulting in lower self-diffusion coefficients than those of linear PEGs. ¹H NMR T₁ measurements at 10-70 °C revealed that the PEG arms of the star polymers are more mobile than the core, suggesting the star polymers in solution have a conformation similar to that of poly(propylene imine) dendrimers.     

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     

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.

     

Structure-property relationship of a series of novel mesogen-jacketed liquid-crystalline polymers containing semirigid side chain with different numbers of alkoxy terminal groups

A series of vinyl monomers, 2, 5-bis [(4-methoxy benzyl) oxycarbonyl] styrene (MBCS); 2, 5-bis [(3, 5-dimethoxy benzyl) oxycarbonyl] styrene (DMBCS) and 2, 5-bis [(3, 4, 5-trimethoxy benzyl) oxycarbonyl] styrene (TMBCS) were synthesized and polymerized via free radical polymerization. The terminal groups of the semirigid side chain were systematically varied to investigate the effects of their numbers on the ability of mesophase formation of the resultant polymers. The chemical structures of the monomers were confirmed by elemental analysis, ¹H NMR and ¹³C NMR. The characterization of the polymers was performed with ¹H NMR, gel permeation chromatography (GPC). The phase structures and transition behaviors were studied using differential scanning calorimetry (DSC), polarized light microscopy (PLM) and one- and two-dimensional wide-angle X-ray diffraction (WAXD). The experimental results suggested that the ability of mesophase formation of the polymers decreased as the rigidity of side-chain group decreased and increased as the number of the alkoxy terminal group increased, and that all the polymers with high molecular weight showed stable columnar nematic phase (Φ_N).     

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     

Studies on the preparation of branched polymers from styrene and divinylbenzene

The self‐condensing vinyl polymerization of styrene and an inimer formed in situ by atom transfer radical addition from divinylbenzene and 2‐bromoisobutyl‐tert‐butyrate using atom transfer radical polymerization technique was studied. To study the polymerization mechanism and achieve high molecular weight polymer in a high polymer yield, the polymerization was carried out in bulk at 80°C. Proton nuclear magnetic resonance (¹H‐NMR) spectroscopy and gel permeation chromatography (GPC) coupled with multiangle laser light scattering (MALLS) were used to monitor the polymerization process and characterize the solid polymers. It is proved that the polymerization shows a “living” polymerization behavior and the crosslinking reaction has been restrained effectively due to the introduction of styrene. Polymers with high molecular weight (M_w.MALLS > 10⁵) can be prepared in high yield (near 80%). Comparison of the apparent molecular weights measured by GPC with the absolute values measured by MALLS indicates the existence of branched structures in the prepared polymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis of amphiphilic heteroarm star‐shaped polymer via free radical polymerization using polyfunctional chain transfer agent and its self‐assembly behavior

Amphiphilic heteroarm star‐shaped polymers have important theoretical and practical significance. In this work, amphiphilic heteroarm star‐shaped polymer was synthesized by the use of polyfunctional chain transfer agent via sequential free radical polymerization in two steps. First, conventional free radical polymerization of methyl methacrylate (MMA) initiated by 2,2′‐azobis (isobutyronitrile) (AIBN) was carried out in the presence of polyfunctional chain transfer agent, pentaerythritol‐tertrakis (3‐mercaptopropinate) (PETMP). At appropriate monomer conversion, about two‐arm s‐PMMA having two residual thiol groups at the chain center was obtained. Second, the s‐PMMA obtained above was used as macro‐chain‐transfer agent for free radical polymerization of acrylic acid (AA). The heteroarm star‐shaped polymer with the hydrophobic PMMA segment and the hydrophilic PAA segment was obtained. The successful synthesis of heteroarm star‐shaped polymers, (PMMA)₂(AA)₂, was confirmed by ¹H‐NMR and its self‐assembly behavior in different solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

星形聚合物的研究与应用进展

回顾了结构性能独特且应用颇为广泛的非线性星形聚合物研究现状;介绍了星形聚合物的特点、应用,以及通过活性聚合制备星形聚合物的不同合成方法,比较了各种合成方法的优缺点;综述了星形聚合物用作研究聚合物的支化模型、简化树形聚合物复杂的支化结构、获得聚合物支化信息的研究进展。     

Surface grafting of polymers onto glass plate: Polymerization of vinyl monomers initiated by initiating groups introduced onto the surface

The surface grafting of polymers onto a glass plate surface was achieved by the polymerization of vinyl monomers initiated by initiating groups introduced onto the surface. Azo groups were introduced onto the glass plate surface by the reaction of 4,4′-azobis(4-cyanopentanoic acid) with isocyanate groups, which were introduced by the treatment with tolylene-2,4-diisocyanate. The radical polymerization of various vinyl monomers was initiated by azo groups introduced onto the glass plate surface and the corresponding polymers were grafted from the surface: The surface grafting of polymers was confirmed by IR spectra, and the contact angle of surface, with water. The contact angle of the glass plate increased by the grafting of hydrophobic polymers, but decreased by the grafting of hydrophilic polymers. The radical postpolymerization was successfully initiated by the pendant peroxycarbonate groups of grafted polymer on the surface to give branched polymer-grafted glass plate. The cationic polymerization of vinyl monomers was also successfully initiated by benzylium perchlorate groups introduced onto the glass plate surface and the corresponding polymers were grafted onto the surface. The contact angle of the glass plate surface obtained from the cationic polymerization of styrene was larger than that obtained from the radical polymerization. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2165–2172, 1997     

Radical homopolymerization and copolymerizations of ring-methoxy substituted α-cyanostyrenes

Radical homopolymerization and copolymerizations of ring-methoxy substituted α-cyanostyrenes were studied using benzoyl peroxide and dimethyl 2,2′-azobisisobutylate at 60°C. It was found that the cyanostyrenes containing 2-methoxy cyanostyrene gave homopolymer in moderate yield and they were also copolymerized with vinyl monomers such as styrene and vinyl acetate. The relative reactivity of the cyanostyrenes towards a polystyryl radical (1/r₂) in the copolymerization of cyanostyrenes (M₁) and styrene (M₂) was correlated with the Hammett and Taft substituent constants of the methoxy groups and the ¹³C NMR chemical shift of the β-carbon of the cyanostyrenes. The enhancement of the radical polymerization reactivity by introducing a nitrile group in the captodative α-position of styrene was considered to be due to the suppression of the termination reaction and the activation of the propagation reaction. In addition, thermal properties such as glass transition and degradation temperatures of the cyanostyrene polymers obtained were also examined.