Synthesis of Well‐Defined Telechelic Macrophotoinitiator of Polystyrene by Combination of ATRP and Click Chemistry

A new well‐defined telechelic macrophotoinitiator of polystyrene was synthesized by combination of ATRP and click chemistry. The ATRP of styrene by means of 2‐oxo‐1,2‐diphenylethyl‐2‐bromopropanoate (PI‐Br) initiator with CuBr/2,2′‐bipyridine yields polystyrene with photoactive benzoin (PI) and bromine (Br) group (PI‐PSt‐Br). Subsequently, PI‐PSt‐Br was converted to PI‐PSt‐N₃ by simple nucleophilic substitution reaction. Alkyne functionalized benzoin (PI‐alkyne) was synthesized by using benzoin photoinitiator and propargyl bromide. Then the coupling reaction between PI‐PSt‐N₃ and PI‐alkyne was performed by Cu(I) catalysis. The spectroscopic studies revealed that low‐polydispersity polystyrene with desired photoinitiator functionality at both end of the chain, PI‐PSt‐PI, was obtained.

     

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.

     

Novel Glycopolymer Brushes via ATRP: 1. Synthesis and Characterization

The synthesis and characterization of a series of glycopolymer brushes with P(methyl 6‐O‐methacryloyl‐α‐D‐glucoside) (P(6‐O‐MMAGIc)) side chains (SCs) is reported. The formation of well‐defined glycopolymer brushes is confirmed by ¹H NMR spectroscopy and size exclusion chromatography (SEC) with a MALLS detector. Four multifunctional macroinitiators with different topologies and molar masses are prepared. The P(6‐O‐MMAGIc) SCs are cleaved from the backbone and analyzed by ¹H NMR and SEC–MALLS, which further confirmed the synthesis of well‐defined glycopolymer brushes. The grafting efficiency of P(6‐O‐MMAGIc) from the different macroinitiators are determined to be in the range 0.37 < f < 0.55.     

Synthesis and Characterization of PDMS‐, PVP‐, and PS‐Containing ABCBA Pentablock Copolymers

Amphiphilic ABCBA pentablock copolymers based on PVP, PS, and PDMS were synthesized using a combination of ATRP and RAFT polymerizations. The PVP‐block‐PS‐block‐PDMS‐block‐PS‐block‐PVP pentablock copolymer was characterized using a variety of chromatography and spectroscopic methods which showed that a high degree of end group and molecular weight control can be achieved. Preliminary analysis of the aqueous solution behavior of the pentablock copolymer showed that it self‐assembles in water in order to shield the PDMS and PS segments from the water.

     

Direct and Reverse ATRP of MMA in Aqueous Dispersed Medium in the Presence of a Bipyridine‐Functionalized Block Copolymer Support

Summary: In a recent communication (Macromol. Rapid Commun. 2002 , 23, 871), we reported the synthesis of a bipyridine containing amphiphilic polymer and its usage as macroligand in the atom transfer radical polymerization (ATRP) of MMA in aqueous dispersed medium. Investigations on the mechanism and locus of nucleation by transmission electron microscopy (TEM) studies herein of latex particles prepared by direct ATRP using oil‐soluble ethyl 2‐bromoisobutyrate as initiator revealed a broad particle size distribution between 250 nm and 1 μm, suggesting two nucleation sites, micelles and monomer droplets. By using the water‐soluble initiator 2,2′‐azoisobutyramidine‐dihydrochloride (V‐50) reverse ATRP experiments were conducted at 90 °C. Kinetic measurements showed a sigmoidal slope of monomer conversion versus time as a first indication for an emulsion‐like process. Controlled polymerization behavior was achieved at a ratio of radicals versus Cu(II ) deactivator of 1:8. TEM measurements of polymer latex particles obtained by reverse ATRP revealed particle sizes between 100 and 400 nm. Residual copper content of eight PMMA samples prepared by direct and reverse ATRP was determined to be 0.01–0.03 wt.‐% (theoretical 0.73 wt.‐%) and indicated that on average 96–99% of all copper used in a polymerization experiment can be removed from the polymer latex particles by a simple precipitation/washing step.

Direct and reverse ATRP experiments of MMA in aqueous media in the presence of an amphiphilic, water‐soluble block copolymer with pendent bipyridine units.     

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.     

Novel Brush Copolymers via Controlled Radical Polymerization

Summary: A combination of reversible addition‐fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) techniques were applied for the synthesis of novel polymer brushes by using the “grafting from” approach or a combination of “grafting through” and “grafting from” methods. The procedure included the following steps: (1) Synthesis of 2‐(2‐bromoisobutyryloxy)ethyl methacrylate (BIEM), (2a) RAFT homopolymerization of BIEM to obtain PBIEM as the polymer backbone. (2b) RAFT copolymerization of BIEM and PEO macromonomer (PEOMA, = 450 g · mol^?1, = 9) to obtain a more hydrophilic polymer backbone. Well‐controlled copolymers containing almost 25 mol‐% of PEOMA were obtained, and (3) ATRP homopolymerization of methyl acrylate (MA) and copolymerization of MA with 1‐octene using both PBIEM homopolymer and poly(BIEM‐co‐PEOMA) as polyinitiators resulted in brushes with densely grafted homopolymer and copolymer side chains, respectively. Well‐controlled copolymer side chains containing 15 mol‐% of 1‐octene were obtained. Relatively narrow molar mass distributions (MMD) were obtained for the ATRP experiments. The formation of the side chains was monitored using size exclusion chromatography (SEC) and NMR spectroscopy. The copolymer composition in the side chain was confirmed using ¹H NMR spectroscopy. Contact angle measurements indicated that for the brush polymers, containing 1‐octene in the side chain, there was a decrease in the surface energy, as compared with the brush polymers containing only the homopolymer of MA in the side chain.

Tapping‐mode SFM images for the poly(BIEM)‐graft‐poly(MA‐co‐octene) brush polymer, dip coated from dilute THF solution on mica.     

Parallel Synthesis of Polymer Libraries Using Atom Transfer Radical Polymerization (ATRP)

Parallel atom transfer radical polymerization (ATRP) of styrene and t‐butyl acrylate (t‐BA) was investigated. A series of ATRP polymerizations were carried out in parallel with varying targeted molecular weight ( ) and showed excellent reproducibility of , polydispersity, and conversion. In addition, polymerizations were done to determine the effect of inhibitor on styrene polymerization, yielding similar results. In synthesizing a library of polymers having varying using ATRP, polymers having lower reach their target values earlier and the others continue to react under heating, resulting in peak broadening for the low polymers. Reinitiation experiments indicated that termination reactions were taking place resulting in “dead” polymer chains which were unable to reinitiate polymerization.

     

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.

     

Towards Semiconducting Graft Copolymers: Switching from ATRP to “Click” Approach

The synthesis of two polyconjugated graft copolymers based on a poly(fluorene‐phenylene) backbone and polystyrene side chains is described here. The two different approaches followed, ATRP growth of side chains from a preformed conjugated backbone and “click” connection of well‐defined polymeric chains to the backbone, led to different results in terms of solubility and material properties. While the ATRP method seems to be responsible of a partially cross‐linked and nonsoluble copolymer, the “click” approach provides a graft copolymer, which is completely soluble, showing atypical spectroscopic properties that are here elucidated.

     

Synthesis of Symmetrical Triblock Copolymers of Styrene and N‐isopropylacrylamide Using Bifunctional Bis(trithiocarbonate)s as RAFT Agents

Six new bifunctional bis(trithiocarbonate)s were explored as RAFT agents for synthesizing amphiphilic triblock copolymers ABA and BAB, with hydrophilic “A” blocks made from N‐isopropylacrylamide and hydrophobic “B” blocks made from styrene. Whereas the extension of poly(N‐isopropylacrylamide) by styrene was not effective, polystyrene macroRAFT agents provided the block copolymers efficiently. End group analysis by ¹H NMR spectroscopy supported molar mass analysis and revealed an unexpected side reaction for certain bis(trithiocarbonate)s, namely a fragmentation to simple trithiocarbonates while extruding ethylenetrithiocarbonate. The amphiphilic block copolymers with short polystyrene blocks are directly soluble in water and self‐organize into thermoresponsive micellar aggregates.

     

Synthesis and Characterization of Styrene/Butyl Acrylate Linear and Star Block Copolymers via Atom Transfer Radical Polymerization

Summary: Well‐defined styrene (S) and butyl acrylate (BA) linear and star‐like block copolymers are synthesized via atom transfer radical polymerization (ATRP) using di‐ and trifunctional alkyl halide initiators employing the Cu/PMDETA (N,N,N′,N″,N″‐pentamethyldiethylenetriamine) catalyst system. Initial addition of Cu^II deactivator and utilization of halogen exchange techniques suppresses the coupling of radicals and improves cross‐propagation to a large extent, which results in better control over the polymerization. Two types of star‐like PBA/PS block copolymers are prepared by using core‐first techniques: a trifunctional PBA or PS macroinitiator extended with the other monomer. Block copolymers with a well‐defined structure and low polydispersity (PDI = ) are obtained in both cases. A trifunctional PBA₃ macroinitiator with = 136 000 g · mol^?1 and PDI = 1.15 is extended to (PBA‐PS)₃ star‐like block copolymer with = 171 100 g · mol^?1 and PDI = 1.15. A trifunctional PS₃ macroinitiator with = 27 000 g · mol^?1 and PDI = 1.16 g · mol^?1 is extended to (PS‐PBA)₃ with = 91 500 g · mol^?1 and PDI = 1.40. The individual star‐like macromolecules as well as their aggregates are visualized by atomic force microscopy (AFM) where the PS and PBA adopt the globular and extended conformation, respectively. For the PBA core star block copolymers, PS segments tend to aggregate either intramolecularly or intermolecularly. PS core star block copolymers form aggregates with a PS core and emanating PBA chains. Most aggregates have ‘n × 3’ arms but minor amounts of ‘defective’ stars with 4, 5, 8, or 11 arms are also observed. The AFM analysis shows that PS core star block copolymers contain about 92% three‐arm block copolymers, and the efficiency of cross‐propagation is 97.3%.

Schematic representation of the synthesis of BA/S star‐like block copolymers by ATRP, and their resultant AFM images.     

Atom‐Transfer Radical Copolymerization of Furfuryl Methacrylate (FMA) and Methyl Methacrylate (MMA): A Thermally‐Amendable Copolymer

Polymers of furfuryl methacrylate (FMA) are interesting materials because of the presence of the furfuryl group as the reactive diene functionality in the pendent group. Copolymers of FMA and MMA were prepared using atom‐transfer radical polymerization (ATRP) catalyzed by CuCl, in combination with HMTETA as a ligand at 90 °C. It was very difficult to prepare by conventional radical polymerization because of several side reactions involving the reactive diene group. The copolymer composition was calculated using ¹H NMR studies. The reactivity ratios of FMA and MMA (r₁ and r₂) were determined using the Finemann‐Ross and Kelen‐Tudos linearization methods. The reactivity ratios obtained were r₁ = 1.56 and r₂ = 0.56. Diels‐Alder chemistry was carried out using the reactive diene of the copolymers and a maleimide as the dienophile. Interestingly, the resultant material was observed to be thermo‐reversible as evidenced by FT‐IR spectroscopy and DSC studies.

     

Synthesis of Processable Inorganic‐Organic Hybrid Polymers Based on Poly(silsesquioxanes): Grafting from Polymerization Using ATRP

Inorganic‐organic hybrid polymers have been synthesized utilizing atom transfer radical polymerization (ATRP) from a functionalized poly(methylsilsesquioxane) (PMSSQ) macroinitiator. Different polymeric ATRP initiators were prepared by co‐condensation of functionalized trichlorosilanes with methyltrimethoxysilane. Various vinyl monomers have been successfully grafted from these macroinitiators, demonstrating a highly variable synthetic concept, which offers the chance to synthesize a wide spectrum of inorganic‐organic hybrid polymers. All synthesized polymers were soluble in various organic solvents. Spin‐coating these hybrid materials onto various substrates could produce stable and adherent surface coatings. Successful surface functionalization could be achieved on silicon, glass, metals or polymeric materials.

     

Synthesis of Double‐Hydrophilic BAB Triblock Copolymers via RAFT Polymerisation and their Thermoresponsive Self‐Assembly in Water

Triblock copolymers of poly(N‐isopropylacrylamide)‐block‐poly(N,N‐dimethylacrylamide)‐block‐poly(N‐isopropylacrylamide) were synthesised via RAFT polymerisation using a symmetrical bistrithiocarbonate. Keeping the block length of the permanently hydrophilic middle block constant, the length of the poly(N‐isopropylacrylamide) block was varied broadly. The thermoresponsive aggregation of the polymers in water was studied by ¹H NMR, turbidimetry, and dynamic light scattering. The complex aggregation behaviour was block length dependent and occurred under kinetic control. Importantly, different information on the hydrophilic‐hydrophobic transition of the poly(N‐isopropylacrylamide) block was obtained using the various analytical methods and could not be directly correlated.

     

Synthesis and ATRP Activity of New TREN‐Based Ligands

Summary: Ligands suitable for atom transfer radical polymerization (ATRP) were prepared by the Michael addition of several acrylates (allyl, benzyl, butyl, 2‐ethylhexyl, and 3‐(dimethoxymethylsilyl)propyl acrylates) with tris(2‐aminoethyl)amine (TREN). These ligands, readily prepared from inexpensive precursors, were used for the preparation of catalyst complexes suitable for polymerization of (meth)acrylates and styrene, providing activity comparable to catalysts currently used for these monomers. Catalysts containing ligands with a dimethoxymethylsilyl substituent were examined for copper removal after the reaction mixture was contacted with silica gel.

     

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).     

Block Copolymers from Organomodified Siloxane‐Containing Macroinitiators by Atom Transfer Radical Polymerization

Alternating copolymers of 1,3‐diisopropenylbenzene and 1,1,3,3‐tetramethyldisiloxane were synthesized by hydrosilylation–polyaddition. These linear copolymers were functionalized at both ends with 2‐bromoisobutyryl or benzyl chloride moieties. Subsequently, the obtained organomodified siloxane‐containing macroinitiators were successfully used for the preparation of ABA‐type block copolymers by atom transfer radical polymerization (ATRP) of styrene and tert‐butyl acrylate. The high chain‐end functionality of the macroinitiators was confirmed by ¹H NMR analysis of the macroinitiators and GPC measurements of the obtained ABA‐type block copolymers. The macroinitiator peaks disappeared in GPC traces after ATRP, and the obtained block copolymers showed a significantly narrower molecular‐weight distribution than the macroinitiators.

Synthesis of ABA‐type block copolymers by means of ATRP using organomodified siloxane‐containing, benzyl chloride functionalized macroinitiators.     

Cross‐Linked Nano‐Objects Containing Aldehyde Groups: Synthesis via RAFT Dispersion Polymerization and Application

Pure cross‐linked spherical micelles, nanowires, and vesicles are successfully fabricated from poly(2‐hydroxypropyl methacrylate‐b‐p‐(methacryloxyethoxy)benzaldehyde)s (PHPMA–b–PMAEBAs) through reversible addition‐fragmentation chain transfer dispersion polymerization of MAEBA in methanol using PHPMA as a macro‐CTA and subsequent cross‐linking. The cross‐linking reaction is conducted by stirring a mixture of 1,4‐butanediamine and the resultant nano‐objects in methanol at room temperature. For all polymerizations with feed molar ratios of MAEBA/PHPMA ranging from 75/1 to 240/1, the monomer MAEBA conversions are almost complete, and block copolymers with controlled molecular weight are obtained. The transmission electron microscopy, dynamic light scattering, and gel permeation chromatography results reveal that the following three factors significantly influence the morphology of the nano‐objects: the feed molar ratio of MAEBA/PHPMA, the copolymer concentration, and the degree of polymerization of PHPMA. The cross‐linked nano‐objects are very stable in good solvents, the spheres and nanowires slightly decrease in size after cross‐linking, whereas the vesicles slightly increase in size. The cross‐linked nano‐objects are stable in neutral solutions, but they dissociate in weekly acidic solutions. The loading of 1‐pyrenemethylamine (PMA) into the vesicles and the unloading of PMA from the vesicles are studied.

     

Synthesis and Characterization of Well‐Defined Mid‐Chain Functional Macrophotoinitiators of Polystyrene by Combination of ATRP and “Click” Chemistry

A combination of ATRP and “click” chemistry is employed for efficient preparation of a novel well‐defined mid‐chain functional macrophotoinitiator of polystyrene. Bromo‐terminated polystyrene (PSt‐Br) is prepared by ATRP of styrene using a methyl‐2‐bromopropanoate initiator with CuBr/PMDETA. Subsequently, PSt‐Br is converted to PSt‐N₃ by a simple nucleophilic substitution reaction. A dialkyne‐functionalized photoinitiator (alkyne‐PI‐alkyne) is synthesized using a dihydroxy‐functional photoinitiator and propargyl bromide. Then the “click” reaction between PSt‐N₃ and alkyne‐PI‐alkyne is performed by Cu(I) catalysis. Spectroscopic studies reveal that low‐polydispersity polystyrene with the desired photoinitiator functionality in the middle of the chain (PSt‐PI‐PSt) is obtained.