Synthesis and Characterization of Poly(trimethylene oxide)‐block‐Polystyrene and Poly(trimethylene oxide)‐block‐Polystyrene‐block‐Poly(methyl methacrylate) by Combination of Atom Transfer Radical Polymerization (ATRP) and Cationic Ring‐Opening Polymerization (CROP)

Summary: Diblock copolymers, poly(trimethylene oxide)‐block‐poly(styrene)s abbreviated as poly(TMO)‐block‐poly(St), and triblock copolymers, poly(TMO)‐block‐poly(St)‐block‐poly(MMA)s (MMA = methyl methacrylate), with controlled molecular weight and narrow polydispersity have been successively synthesized by a combination of atom transfer radical polymerization (ATRP) and cationic ring‐opening polymerization using the bifunctional initiator, 2‐hydroxylethyl α‐bromoisobutyrate, without intermediate function transformation. The gel permeation chromatography (GPC) and NMR analyses confirmed the structures of di‐ and triblock copolymers obtained.

GPC curves of (a) poly(St); (b) diblock copolymer, poly(St)‐block‐poly(MMA) before precipitation; (c) poly(St)‐block‐poly(MMA) after precipitation in cyclohexane/ethanol (2:1); (d) triblock copolymer, poly(TMO)‐block‐poly(St)‐block‐poly(MMA).     

Salt‐Induced Micelle Behavior of Poly(sodium acrylate)‐block‐Poly(N‐isopropylacrylamide) by ATRP

Temperature‐ and pH‐sensitive diblock copolymers PAANa₇₅‐b‐PNIPAM_m are prepared by a combination of reverse and normal ATRP in aqueous solution at room temperature. The block copolymer is also stimuli‐sensitive with respect to salt in the aqueous solution, and forms spherical star‐like micelles with a PNIPAM core and an expanded PAANa shell for PAANa₇₅‐b‐PNIPAM₇₆ as well as spherical crew‐out micelles with a PNIPAM core for PAANa₇₅‐b‐PNIPAM₅₁₁₀, as indicated by a fluorescence probe technique and TEM. A three‐stage model mechanism of phase transition driven by small molecule salt is proposed.

     

Synthesis of Novel Linear PEO‐b‐PS‐b‐PCL Triblock Copolymers by the Combination of ATRP,ROP, and a Click Reaction

A new strategy to synthesize a series of well‐defined amphiphilic PEO‐b‐PS‐b‐PCL block copolymers is presented. First, bromine‐terminated diblock copolymers PEO‐b‐PS‐Br are prepared by ATRP of styrene, and converted into azido‐terminated PEO‐b‐PS‐N₃ diblock copolymers. Then propargyl‐terminated PCL is prepared by ROP of ε‐caprolactone. The PEO‐b‐PS‐b‐PCL triblock copolymers with from 1.62 × 10⁴ to 1.96 × 10⁴ and a narrow PDI from 1.09 to 1.19 are finally synthesized from these precursors. The structures of these triblock copolymers and their precursors have been characterized by NMR, IR, and GPC analysis.

     

Polystyrene‐block‐poly(methyl methacrylate): Initiation Issues with Block Copolymer Formation Using ARGET ATRP

The synthesis, kinetics, and characterization of polystyrene and poly(methyl methacrylate) block copolymers produced by ARGET ATRP are discussed. Halogen exchange is used and the polymerization appears to be living in the generation of the second block. On further investigation, the GPC traces exhibit a shoulder, which suggests poor initiation of the macroinitiator. Previous reports suggest that to increase the initiation efficiency of the second block, 10% styrene monomer should be added to the mixture. Upon adding the 10% styrene for the second block ARGET ATRP polymerization, the appearance of a well‐initiated polymer is observed. However, at greater conversions the results clearly demonstrate the production of a homopolymer/block copolymer mixture.     

Preparation of Polyisobutene‐graft‐Poly(methyl methacrylate) and Polyisobutene‐graft‐Polystyrene with Different Compositions and Side Chain Architectures through Atom Transfer Radical Polymerization (ATRP)

Polyisobutene‐graft‐poly(methyl methacrylate) and polyisobutene‐graft‐polystyrene with controlled compositions and side chain architectures were prepared through atom transfer radical polymerization (ATRP). Poly[isobutene‐co‐(p‐methylstyrene)‐co‐(p‐bromomethylstyrene)] (PIB) was used as a macroinitiator in the presence of CuCl or CuBr as a catalyst and dNbpy as a ligand. The compositions were controlled by the conversion of the monomer with polymerization time. The molecular weight distributions of the side chains were controlled through ATRP in the presence/absence of a halogen exchange reaction. DSC and DMA measurements showed that graft copolymers have two glass transition temperatures suggesting microphase separated behavior, which was also confirmed by SAXS measurements. The phase and dynamic mechanical behaviors were strongly affected by the compositions and/or the side chain architectures. The properties of the graft copolymers were controlled in a wide range leading to toughened glassy polymers or elastomers.     

Physical Properties of PBMA‐b‐PBA‐b‐PBMA Triblock Copolymers Synthesized by Atom Transfer Radical Polymerization

The physical properties of well‐defined poly(butyl methacrylate)‐block‐poly(butyl acrylate)‐block‐poly(butyl methacrylate) (PBMA‐b‐PBA‐b‐PBMA) triblock copolymers synthesized by atom transfer radical polymerization (ATRP) are reported. The glass transition and the degradation temperature of copolymers were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC measurements showed phase separation for all of the copolymers with the exception of the one with the shortest length of either inner or outer blocks. TGA demonstrated that the thermal stability of triblock copolymers increased with decreasing BMA content. Dynamic mechanical analysis was used for a preceding evaluation of adhesive properties. In these block copolymers, the deformation process under tension can take place either homogeneously or by a neck formation depending on the molecular weight of the outer BMA blocks and on the length of the inner soft BA segments. Microindentation measurements were also performed for determining the superficial mechanical response and its correlation with the bulk behavior.

Stress‐strain curves for the different PBMA‐b‐PBA‐b‐PBMA specimens at room temperature and at 10 mm/min.     

A Novel Macroinitiator for the Synthesis of Triblock Copolymers via Atom Transfer Radical Polymerization: Polystyrene‐block‐poly(bisphenol A carbonate)‐block‐polystyrene and Poly(methyl methacrylate)‐block‐poly(bisphenol A carbonate)‐block‐poly(methyl methacrylate)

Summary: Bis(hydroxy)telechelic bisphenol A polycarbonate (PC) was prepared via melt polycondensation of bisphenol A (BPA) and diphenyl carbonate (DPC) using lanthanum(III ) acetylacetonate as a catalyst for transesterification. Subsequently, the polycarbonate was converted to a bifunctional macroinitiator for atom transfer radical polymerization (ATRP) with the reagent, α‐chlorophenylacetyl chloride. The macroinitiator was used for the polymerization of styrene (S) and methyl methacrylate (MMA) to give PS‐block‐PC‐block‐PS and PMMA‐block‐PC‐block‐PMMA triblock copolymers. These block copolymers were characterized by NMR and GPC. When styrene and methyl methacrylate were used in large excess, significant shifts toward high molecular weights were observed with quantitative consumption of the macroinitiator. Several ligands were studied in combination with CuCl as the ATRP catalyst. Kinetic studies reveal the controlled nature of the polymerization reaction for all the ligands used.

Formation of a bifunctional ATRP macroinitiator by esterification of bis(hydroxy)telechelic PC with α‐chlorophenylacetyl chloride.     

Double Hydrophilic Poly(ethylene oxide)‐block‐Poly(dehydroalanine) Block Copolymers: Comparison of Two Different Synthetic Routes

Two different synthetic pathways give access to the amphiphilic block copolymer poly(ethylene oxide)‐block‐poly(tert‐butoxycarbonylaminomethylacrylate). In the first approach, two end‐functionalized segments are linked via click chemistry; and in the second approach, a poly(ethylene oxide) (PEO) based macroinitiator is chain extended via atom transfer radical polymerization (ATRP). In both cases the linking unit consists of an amide group, which is necessary to effectively deprotect the corresponding polymer precursor without cleavage of both segments. For this, amide‐containing ATRP initiators are employed and successful synthesis by nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC) analyses before comparing both pathways is demonstrated. After deprotection, a novel double hydrophilic block copolymer, poly(ethylene oxide)‐block‐poly(dehydroalanine), is obtained, which is investigated using SEC (aqueous and DMSO) and ¹H‐NMR spectroscopy. Containing a potentially zwitterionic PDha segment and a high density of both amino and carboxylic groups, pH‐dependent aggregation of the block copolymer is expected and is studied using dynamic light scattering, revealing interesting solution properties. The corresponding polymers are applied in various areas including drug delivery systems or in biomineralization.     

Polyester/Poly(meth)acrylate Block Copolymers by Combined Polycondensation/ATRP: Characterization and Properties

Polyester/poly(meth)acrylate block copolymers are synthesized using a combination of polycondensation and ATRP. All block copolymers are characterized by means of NMR and GPC. Agreement between theoretical molecular weights of the polymers with observed GPC values suggests controlled polymerization. In the case of unsaturated‐polyester‐based block copolymers the main chain double bond in the polyester backbone remains almost unaffected during ATRP. The unsaturated block copolymers are crosslinkable and can form networks upon photoirradiation in the presence of a suitable photoinitiator. These copolymers might be interesting candidates for coatings with better overall properties than those based on neat polyesters.

     

Synthesis of Polyacrylonitrile‐block‐Polystyrene Copolymers by Atom Transfer Radical Polymerization

Summary: The synthesis of polyacrylonitrile‐block‐polystyrene (PAN‐b‐PS) copolymers by atom transfer radical polymerization (ATRP) is reported. Chain extension of bromine terminated PAN macroinitiators with styrene was performed using a CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalyst system and 2‐cyanopyridine as a solvent. The first‐order kinetic plots of styrene consumption showed a significant curvature, indicating a progressive decrease in the concentration of active species during copolymerization. The loss of the bromide end group was mainly ascribed to the elimination of HBr, as shown by ¹H NMR spectroscopy. By varying the molar ratio of either the catalyst or the monomer to the initiator, a series of PAN‐b‐PS copolymers were prepared, with polydispersities as low as 1.3, and molar compositions ranging from 8.6/91.4 to 35.5/64.5.

¹H NMR spectra of PAN‐b‐PS in DMF‐d₇ at 80 °C.     

Synthesis and Characterization of Semicrystalline Polyethylene‐graft‐Poly(acrylic acid) Copolymers

Hydrophilic polyolefin materials were prepared by grafting tBA from PE macroinitiators bearing functionalized norbornene units capable of initiating an ATRP. This method produced semicrystalline graft copolymers (PE‐graft‐PtBA) with narrow molecular weight distributions (1.2–1.4) and tunable tBA content (2–21 mol‐%). Incorporation of tBA resulted in a decrease in crystallinity, but little change in the melting point of the products. Subsequently, the tBA moieties were converted into acrylic acid units through chemical and thermal means to generate PE‐graft‐PAA copolymers. The increased hydrophilicity of the resulting materials was verified by ATR‐IR, solid‐state ¹³C NMR spectroscopy, contact angle measurements, and TGA.

     

New Star‐Branched Poly(acrylonitrile) Architectures: ATRP Synthesis and Solution Properties

Summary: Atom transfer radical polymerization (ATRP) has been chosen as “living”/controlled free radical polymerization system to synthesize a number of novel poly(acrylonitrile) (PAN) architectures. The reaction conditions for the synthesis of linear samples with control over molar mass and molar mass distribution have been investigated together with the possibility of obtaining copolymers of acrylonitrile with small quantities of methyl acrylate (max. 5 mol‐%). Well‐defined star polymers with 3, 4 and 6 arms have been successfully synthesized together with linear chains initiated by a bifunctional initiator and star‐branched polymers with a hyperbranched poly(ester amide) as core. Molar masses were determined by NMR and GPC with the latter leading to a significant over estimation. Solution viscosity studies indicated that the stiff structure of the PAN chains is still maintained in the homopolymer star architectures and that the incorporation of small quantities of methyl acrylate as comonomer has a stronger effect on chain flexibility than the incorporation of star‐branch points.

     

A Tandem Controlled Radical Polymerization Technique for the Synthesis of Poly(4‐vinylpyridine) Block Copolymers: Successive ATRP,SET‐NRC,and NMP

Poly(methyl methacrylate)‐block‐poly(4‐vinylpyridine), polystyrene‐block‐poly(4‐vinyl pyridine), and poly(ethylene glycol)‐block‐poly(4‐vinylpyridine) block copolymers are synthesized by successive atom transfer radical polymerization (ATRP), single‐electron‐transfer nitroxide‐radical‐coupling (SET‐NRC) and nitroxide‐mediated polymerization (NMP). This paper demonstrates that this new approach offers an efficient method for the preparation of 4‐vinylpyridine‐containing copolymers.

     

1H,1H,2H,2H‐Perfluorodecyl‐Acrylate‐Containing Block Copolymers from ARGET ATRP

Block copolymers of 1H,1H,2H,2H‐perfluorodecyl acrylate (AC8) were obtained from ARGET ATRP. To obtain block copolymers of low dispersity the PAC8 block was synthesized in anisole with a CuBr₂/PMDETA catalyst in the presence of tin(II) 2‐ethylhexanoate as a reducing agent. The PAC8 block was subsequently used as macroinitiator for copolymerization with butyl and tert‐butyl acrylate carried out in scCO₂. To achieve catalyst solubility in CO₂ two fluorinated ligands were employed. The formation of block copolymers was confirmed by size exclusion chromatography and DSC.

     

A Convenient Method for the Synthesis of the Amphiphilic Triblock Copolymer Poly(L‐lactic acid)‐block‐Poly(L‐lysine)‐block‐Poly(ethylene glycol) Monomethyl Ether

The amphiphilic triblock copolymer PLA‐b‐PLL‐b‐MPEG is prepared in three steps through acylation coupling between the terminal amino groups of PLA‐b‐PZLL‐NH₂ and carboxyl‐terminal MPEG, followed by the deprotection of amines. The block copolymers are characterized via FT‐IR, ¹H NMR, DSC, GPC, and TEM. TEM analysis shows that the triblock polymers can form polymeric micelles in aqueous solution with a homogeneous spherical morphology. The cytotoxicity assay indicates that the final triblock polymer micelles after deprotection show low cytotoxicity against Bel7402 human hepatoma cells. MPEG and PLL were introduced into the main chain of PLA affording a kind of ideal bioabsorbable polymer materials, which is expected to be useful in drug and gene delivery.

     

Synthesis of Hydroxyl‐Terminated Poly(vinylcarbazole‐ran‐styrene) Copolymers by Nitroxide‐Mediated Polymerization

A series of poly(vinylcarbazole‐ran‐styrene) copolymers with terminal hydroxyl groups were synthesized using nitroxide mediated polymerization (NMP) with the hydroxyl‐functional initiator VA‐086 and TEMPO as the mediator at 130 °C. Polymerizations were studied as a function of vinylcarbazole feed content, target molecular weight, and VA‐086/TEMPO ratio. The characterization of the copolymers was done by GPC and NMR. For feed concentrations of 40 mol‐% vinylcarbazole, copolymers with vinylcarbazole concentration up to 33 mol‐% could be obtained with narrow molecular weight distributions (PDI = 1.35) and exhibit pseudo‐“living” character up to conversions of about 20% if the target molecular weight was >100 kg · mol^?1. ¹H NMR indicated that the hydroxyl group was retained sufficiently with a functionality typically of about 0.7 hydroxyl groups per chain. Copolymers synthesized with higher vinylcarbazole feed content exhibited slower kinetics and were less controlled, resulting in much broader molecular weight distributions. The absence of control could be attributed to the absence of thermal initiation by vinylcarbazole which is advantageous toward controlling the radical concentration during the polymerization.

     

Novel polymeric surfactants: Synthesis of semi‐branched,non‐ionic triblock copolymers using ATRP

This article reports the synthesis of novel amphiphilic triblock copolymers with a semi‐branched PLURONIC^®7R structure by atom transfer radical polymerization (ATRP) in aqueous media. Poly(ethylene oxide)s (PEOs) with molecular weights 10 000 and 16 000 were end‐functionalized and used as bifunctional macroinitiators for the polymerization of oligo(propylene oxide) monomethacrylate by ATRP in a 1/3 v/v water/methanol mixture and in a 1/1 v/v water/1‐propanol mixture. Deviations from first‐order kinetics with respect to the monomer concentration were observed indicating that termination reactions were taking place. However, linear plots were obtained, when ln[M]₀/[M] was plotted against time^2/3 as suggested by Fischer. The effect on the control of the polymerization by adding Cu(II)Br₂ to the polymerization medium has been investigated. When 10 mol‐% of Cu(II)Br₂ was substituted for Cu(I)Br, normal first‐order kinetics were observed. A large reduction in the rate of polymerization was observed for the polymerization initiated by bifunctional PEO10 000 initiator, but almost no reduction in the rate of polymerization was observed, when the bifunctional PEO16 000 initiator was used. When the polymerizations were conducted in 1/1 v/v water/1‐propanol, unexpectedly high rates of polymerization were observed.

Synthesis of amphiphilic block copolymers with a semi‐branched PLURONIC^®R architecture using ATRP.     

Synthesis and Surface Attachment of ABC Triblock Copolymers Containing Glassy and Rubbery Segments

Summary: The synthesis of an ABC triblock copolymer containing glassy and rubbery segments was conducted using a combination of living anionic and atom transfer radical polymerizations (ATRP). A poly(dimethylsiloxane) (pDMS) macroinitiator ( = 6 200; = 1.19) was prepared by living anionic ring‐opening polymerization, followed by hydrosilation reactions to incorporate 2‐bromoisobutyrate end groups for initiation of ATRP. The ATRP of styrene (S) using the pDMS macroinitiator yielded a diblock copolymer ( = 66 730; = 1.38). Chain extension of the pDMS‐b‐pS macroinitiator with 3‐(dimethoxymethylsilyl)propyl acrylate (DMSA) by ATRP yielded an ABC triblock copolymer. The latter reactive segment was covalently attached to silanol groups on a silicon wafer. The presentation of either glassy pS or flexible pDMS segments of the brushes attached to the surface was reversibly controlled by treatment with selective solvents for each segment.

Surface immobilization of pDMS‐b‐pS‐b‐pDMSA triblock copolymer to Si wafer. Treatment of brush with toluene, methanol, or annealing yields brush with hard pS surface. Treatment with hexane selectively solvates pDMS, and the soft layer is presented to the brush surface.     

Self‐Assembly and Photoresponsivity Property of Amphiphilic ABA Triblock Copolymers Containing Azobenzene Moieties in Dilute Solution

The self‐assembly and photoresponsivity of amphiphilic azobenzene‐containing ABA triblock copolymers PA6C_m‐b‐PEG_n‐b‐PA6C_m synthesized by atom transfer radical polymerization (ATRP) were reported. Different self‐assembly morphologies formed by the gradual addition of water to the copolymer solutions in THF. The formation process and aggregate morphology were characterized by UV–Visible spectroscopy and transmission electron microscope (TEM). The triblock copolymers start to form aggregates at the critical water content (CWC). With the addition of water, the aggregates show different morphologies, such as spherical micelles, vesicles, network‐like aggregates, and colloidal spheres, which involves the transformation between primary and secondary aggregates and the association/disassociation of aggregates. Photoresponsive property and aggregation behavior of these copolymers in solution under UV–Visible light irradiation were also investigated.

     

Syntheses and Specific Interactions of Poly(ε‐caprolactone)‐block‐poly(vinyl phenol) Copolymers Obtained via a Combination of Ring‐Opening and Atom‐Transfer Radical Polymerizations

Summary: A series of PCL‐b‐PVPh diblock copolymers were prepared through combinations of ring‐opening and atom‐transfer radical polymerizations of ε‐caprolactone and 4‐acetoxystyrene, and subsequent selective hydrolysis of the acetyl protective group. This PCL‐b‐PVPh diblock copolymer shows a single glass transition temperature over the entire composition range, indicating that this copolymer is able to form a miscible amorphous phase due to the formation of intermolecular hydrogen bonding between the hydroxyl of PVPh and the carbonyl of PCL. In addition, DSC analyses also indicated that the PCL‐b‐PVPh diblock copolymers have higher glass transition temperatures than their corresponding PCL/PVPh blends. FT‐IR was used to study the hydrogen‐bonding interaction between the PVPh hydroxyl group and the PCL carbonyl group at various compositions.

FT‐IR spectra in the 1 680–1 780 cm^?1 for PCL‐b‐PVPh copolymers with various PVPh contents.