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 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.     

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.     

Synthesis and self-assembly of miktoarm star copolymers of (polyethylene)2−(polystyrene)2

We report on the synthesis and self-assembly of a novel well-defined miktoarm star copolymer of (polyethylene)₂−(polystyrene)₂, (PE)₂−(PS)₂, with two linear crystalline PE segments and two PS segments as the building blocks based on chain shuttling ethylene polymerization (CSEP), click reaction and atom transfer radical polymerization (ATRP). Initially, alkynyl-terminated PE (PE-) was synthesized via the esterification of pentynoic acid with hydroxyl-terminated PE (PE−OH), which was prepared using CSEP with 2,6-bis[1-(2,6-dimethylphenyl) imino ethyl] pyridine iron (II) dichloride/methylaluminoxane/diethyl zinc and subsequent in situ oxidation with oxygen. (PE)₂−(OH)₂ was then obtained by the click reaction of PE- with diazido and dihydroxyl containing coupling agent. The two hydroxyl groups in (PE)₂−(OH)₂ were then converted into bromisobutyrate by esterification. At last, the (PE)₂−(PS)₂ miktoarm star copolymers were synthesized by ATRP of styrene initiated from (PE)₂−Br₂ macroinitiator. All the intermediates and final products were characterized by ¹H NMR and gel permeation chromatography (GPC). The self-assembly behavior was studied by dynamic light scattering (DLS) and atomic force microscopy (AFM). The crystallization of the (PE)₂−(PS)₂ miktoarm star copolymers was studied by differential scanning calorimetry (DSC).     

Synthesis of star-shaped polymers by coupling reaction between multifunctional core and terminal functionalized polymers

Star-shaped polymers that consist of well-defined polystyrene (PS) arms were successfully synthesized in high yield by coupling reaction between multifunctional core molecules and hydroxyl-terminated PS in the presence of 1, 3-dicyclohexylcarbodiimide and 4-(dimethylamino) pyridine at room temperature. Several systems were investigated: (1) Pyromellitic dianhydride (PMDA) and hydroxyl-terminated PS (PS-OH) with narrow molecular weight distribution, which was prepared by atom transfer radical polymerization (ATRP) of St with 2-hydroxyethyl bromoisobutylate (HEBiB) as initiator. (2) PMDA and PS-OH prepared by conventional free radical polymerization, with 2-mercaptoethanol as chain transfer agent. (3) Narrow molecular weight distributed alternating copolymer of maleic anhydride (MA) and styrene (St), which was obtained via reversible addition fragmentation chain transfer polymerization (RAFT) process, and PS-OH obtained by ATRP. The formation of star-shaped PSs was confirmed by proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC).     

Microwave synthesis: An alternative approach to synthesize conducting end-capped polymers

Within this study microwave assisted syntheses of functionalized polystyrene (PS), via ATRP, and tetra-aniline (TANI) end-capped polymers are demonstrated. Compared to conventional heating, microwave irradiation process in pulsed mode shows the feasibility of conducting end-capped polymers synthesis with no degradation, strong acceleration of polymerization rate and coupling reaction, controlled size and chemical formulation. Conducting polymers with controlled architectures in terms of molecular size of both the insulating (PS) and the conducting (TANI) moieties show a conductivity above 10⁻¹ S cm⁻¹ when containing 2 wt% TANI while composites of PS and TANI exhibited a conductivity of ca 10⁻⁵ S cm⁻¹ when containing more than 7 wt% TANI.     

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 AB2-type star polymers via combination of ATRP and click chemistry

Homo/miktoarm star polymers were successfully synthesized via combination of the “arm-first” and “coupling-onto” strategies. Firstly, the multifunctional coupling agent (core), 2, 4, 6-tris(3-ethynylphenyl)-1,3,5-triazine-2,4,6-triamine (TPTTA), was synthesized. Secondly, the linear polystyrene-Cl (PS-Cl) and poly(2-(dimethylamino)ethyl methacrylate)-Br (PDMAEMA-Br) were prepared by atom transfer radical polymerization (ATRP) method. Then, the linear PS-Cl and PDMAEMA-Br chains were modified by a nucleophilic substitution reaction with sodium azide. Finally, homo/miktoarm star polymers PS₃ and PS(PDMAEMA)₂ were designed by click reaction between the core (TPTTA) and the arm precursor (PS-N₃ or PDMAEMA-N₃). The structures of the PS₃, PS(PDMAEMA)₂ and the precursors were all characterized by NMR, FT-IR, UV and GPC analysis. Moreover, the self-assembly behaviors of the miktoarm amphiphilic copolymer PS(PDMAEMA)₂ was also investigated by transmission electron microscopy (TEM).     

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     

Synthesis of star polymers by “core-first” one–pot method via ATRP: Monte Carlo simulations

Results of the simulation of star polymers synthesis by one–pot, core–first method are presented. The simulated ideal living polymerization process consists of two steps. In the first one (core growth) an atom transfer radical polymerization (ATRP) of a crosslinker is performed. When the crosslinker conversion is close to completion, a bifunctional monomer is added and the ATRP polymerization of the monomer takes place from the obtained cores to form linear arms of the stars. The simulation method is based on dynamic lattice liquid (DLL) algorithm, which takes into account changes of local dynamics resulting from polymerization and formation of complex polymer molecules. In the first stage of the synthesis (core formation), in addition to the effect of concentrations of initiator and crosslinker, the rate of intramolecular crosslinking is also very important. This process “consumes” the reactive crosslinker in the cores, limiting the core size and preventing further star–star coupling. The effect of various parameters on star size and internal structure was studied. These parameters involve the rate of intramolecular crosslinking, initial concentrations of the components and the moment of monomer addition. The results can be used as guidelines for the experimental work on star synthesis.     

Synthesis of linear tetrablock quaterpolymers via atom transfer radical polymerization and a click coupling approach

We report the synthesis of a well-defined linear tetrablock quaterpolymer of poly(butyl acrylate)-b-polystyrene-b-poly(methyl acrylate)-b-poly(methyl methacrylate) by combining atom transfer radical polymerization (ATRP) and a click coupling approach. For this purpose, polystyrene-b-poly(butyl acrylate) (AB) was prepared by ATRP using macroinitiator as α-trimethylsilyl(TMS)-alkyne ω-bromo polystyrene. The α-(TMS) end of the AB diblock copolymer was deprotected using tetrabutylammonium fluoride (TBAF) in THF. The ω-azide end of the CD diblock copolymer was made from poly(methyl methacrylate)-b-poly(methyl acrylate) (CD) via transformation of the bromine chain end by a simple nucleophilic substitution reaction with NaN₃ in DMF. Click coupling between the ω-azide end in CD diblock copolymer with the α-alkyne end in the AB diblock copolymer was then performed by Cu¹-catalyzed (3+2) cycloaddition. Gel permeation chromatography (GPC), FT-IR and ¹H NMR spectroscopy confirmed the successful formation of a linear ABCD tetrablock copolymer via ATRP and click coupling.     

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.     

Star polymers via atom transfer radical polymerization from adamantane-based cores

A series of novel multifunctional initiators derived from adamantane-based derivatives have been used in the syntheses of various styrenic and (meth)acrylic star polymers by atom transfer radical polymerization (ATRP). Conditions were identified in each system to produce star polymers with nearly monomodal molecular distributions. These synthesized star polymers have glass transition temperatures similar to those known for high-molecular-weight linear polymers. We obtained a series of adamantane-contained star polymers covering a wide range of molecular weights by adjusting the monomer-to-initiator ratio and the solvent polarity. Because of reaction heterogeneity and inevitable termination processes, the occurrence of star-star coupling led to a lower than predicted molecular weight polydispersity. When hydrolyzed from their cores by NaOH, the values of M_w of the arms of the PMMA star polymer did not change with reaction time, at least for the first 48 h of the reaction, which implies that no significant PMMA hydrolysis occurs within this interval of time.     

Synthesis and characterization of ABC ternary segregated H-shaped copolymers

The synthesis of a novel ABC ternary segregated H-shaped copolymer is described, of which a central poly(ethylene glycol) (PEG) chain is terminated on both sides by polystyrene (PS) and poly(tert-butylacrylate) (PtBA) chains. The synthetic procedure involves functionalization of PEG by 2-bromosuccinic anhydride followed by esterification of 1,6-hexanediol, which gives its ends the bifunctional nature that allows sequential growth of two PS, then two PtBA arms via atom transfer radical polymerization (ATRP). The resulting segregated H-shaped copolymers were characterization by NMR spectroscopy and gel permeation chromatography (GPC). All these copolymers were affirmed to have well-defined structures and narrow molecular weight distributions.     

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.     

Synthesis and characterization of well-defined comb-like branched polymers

Well-defined comb-like branched polymers having one branch in each repeating unit have been successfully synthesized by the coupling reaction of living polystyrene (PS) and polyisoprene (PI) anions with 1, 1-diphenylethenyl (DPE) groups along PS backbone prepared via atom transfer radical polymerization (ATRP) of 4-vinylbenzyloxy benzophenone (Sc) followed by Wittig reaction. The resulting comb-like branched polymers were characterized by IR, ¹H-NMR, gel permeation chromatography (GPC) and static light scattering (SLS) in detail. The effect of living chains and DPE group molar ratio on grafting efficiency was discussed. The results show the coupling reaction of living chains and DPE groups was highly effective, and the coupling efficiency can be controlled via the feed molar ratios of living chains and DPE groups. Moreover, the effect of molecular weights of backbone (PSe) and PSLi or PILi on grafting efficiency was also discussed. The results show that when excess living polymers were used, the almost quantitative grafting efficiency could be achieved. __________ Translated from Acta Polymerica Sinica (China), 2007, (3): 203–208 [译自: 高分子学报]     

A one-pot approach to dendritic star polymers via double click reactions

A class of well-defined dendritic star polymers with poly (ε-caprolactone) (PCLs) on the periphery has been prepared via one-pot double click reactions (Cu-catalyzed azide/alkyne click chemistry, i.e., CuAAC and Diels–Alder [4+2] cycloaddition reactions). The predecessors for Diels–Alder reaction, maleimide end-functionalized PCLs were produced by ring-opening polymerization (ROP). Obtained dendritic star polymers were characterized by ¹H NMR, size exclusion chromatography (SEC), UV/vis, and fluorescence spectroscopy.     

Synthesis and properties of amphiphilic star block copolymers with star macroinitiators based on a one‐pot approach

Previously, star polystyrenes (PSs) have been prepared by atom transfer radical polymerization (ATRP) of N‐[2‐(2‐bromoisobutyryloxy)ethyl]maleimide (BiBEMI) with a large excess of styrene (St) in one pot. But linear PSs were also present during the formation of the star polymers. In the work reported here, we found that control of the formation of star polymers using a one‐pot approach can be improved by using a two‐step process. The polymerization was conducted first at a low temperature to form multifunctional cores by copolymerization of BiBEMI and St. Second, on increasing the temperature, homopolymerization of St occurred to grow PS arms. Then a series of amphiphilic star polystyrene‐block‐poly(acrylic acid)s, (S₁₄A_x)₁₆, were prepared by ATRP of tert‐butyl acrylate with the star PSs as macroinitiators, followed by selective acidolysis of the poly(tert‐butyl acrylate) blocks. Their micellization was studied using dynamic light scattering, which suggested that (S₁₄A₁₁₂)₁₆ amphiphilic star block copolymers could form unimolecular micelles in a basic aqueous solution. Then pyrene molecules were encapsulated using the (S₁₄A₁₁₂)₁₆ amphiphilic star copolymers and the loading capacity was investigated with UV and fluorescence spectroscopy. © 2013 Society of Chemical Industry     

A new approach to 3-miktoarm star polymers using a combination of reversible addition-fragmentation chain transfer (RAFT) and ring opening polymerization (ROP) via “Click” chemistry

The synthesis of AB₂-type miktoarm star polymers using a combination of reversible addition-fragmentation chain transfer (RAFT), ring opening polymerization (ROP) and “Click” chemistry was demonstrated in this work. An azide functional RAFT agent was used to polymerize butyl acrylate, polyethylene glycol acrylate and N-isopropylacrylamide monomers. Propargylamine was reacted with glycerine carbonate to obtain a dihydroxy functional alkyne compound which was used for the ring opening polymerization of ?-caprolactone (?-CL) and lactide. The resulting alkyne functional polycaprolactone (PCL) and polylactide (PLA) polymers were reacted with azide functional polymers in the presence of copper bromide (CuBr) catalyst to obtain miktoarm star polymers. The polymers were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The star polymers had low polydispersity (∼1.3) with well-defined structures. These polymers have a number of potential applications including crosslinking agents for polyurethane (PU) coatings for biodegradable and fouling release applications.     

Synthesis and characterisation of hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) backbones via atom transfer radical polymerisation

Hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) (PMMA-b-PBA) backbones have been prepared via atom transfer radical polymerisation (ATRP) together with a nucleophilic substitution reaction. A hydroxyl-functionalised PMMA macroinitiator (HO-PMMA-Br) was prepared via ATRP at the optimised reaction temperature (60 °C) using 2-hydroxyethyl 2-bromoisobutyrate as the initiator. The high functionality of the bromo end group in the macroinitiator was confirmed by both ¹H NMR technique and a chain-extension reaction. Electrospray ionisation mass spectrometer proved to be a valuable tool for characterising PMMAs with a bromo end group (PMMA-Br), which provided signals corresponding to the intact polymers although multiply charged polymer chains were observed. The well-defined block copolymers HO-PMMA-b-PBA-Br were obtained by the ATRP of n-butyl acrylate using HO-PMMA-Br as a macroinitiator in a one-pot reaction at 100 °C. The kinetics as well as the dependence of the M_n,SEC and PDIs of the obtained block copolymers on the conversions of n-butyl acrylate in the chain-extension reaction suggested negligible radical termination during the reaction, demonstrating that the well-defined HO-PMMA-b-PBA-Br with a high functionality of bromo end group were obtained. The nucleophilic substitution reaction of a monohydroxyl-functionalised block copolymer HO-PMMA-b-PBA-Br with 5-amino-1-pentanol in dimethyl sulfoxide at room temperature was verified with ¹H and ¹³C NMR techniques, which resulted in a series of telechelic polymers HO-PMMA-b-PBA-OH with a functionality of hydroxyl groups up to 1.7 according to the gradient polymer elution chromatography.