Controlled Thiol‐Ene Functionalization of Polyferrocenylsilane‐block‐Polyvinylsiloxane Copolymers

A general route for the controlled functionalization of polyferrocenylsilane‐block‐polyvinylsiloxane copolymers, which should be transferable to other silicone‐based materials, is developed utilizing the photoinitiated thiol‐ene reaction. Poly(ferrocenyldimethylsilane)₅₄‐block‐poly(methylvinylsiloxane)₅₁₀ (PFDMS₅₄‐b‐PMVS₅₁₀) is synthesized via sequential living anionic polymerization and quantitatively functionalized with a range of thiols, with the aim of tuning the solubility of the resulting materials for self‐assembly studies or incorporating more complex functionality for subsequent applications. When functionalization is attempted using a deficit of thiol, the photoinitiator 2,2‐dimethoxy‐2‐phenylacetophenone, used to accelerate the radical reaction, is found to cause significant cross‐linking of the polysiloxane chain. Reproducible percentage thiol‐ene functionalization of the polysiloxane block can be achieved by the use of PFDMS₅₃‐b‐PMVS₅₈/PDMS₄₄₄ (PDMS = polydimethylsiloxane), prepared by the copolymerization of cyclic siloxane monomers, [Me(CH?CH₂)SiO]₃ and [Me₂SiO]₃, to tune the vinyl group incorporation pre‐functionalization.

     

Allyl End‐Functionalized Poly(ethylene oxide)‐block‐poly(methylidene malonate 2.1.2) Block Copolymers: Synthesis,Characterization, and Chemical Modification

Summary: Poly(ethylene oxide)‐block‐poly(methylidene malonate 2.1.2) block copolymer (PEO‐b‐PMM 2.1.2) bearing an allyl moiety at the poly(ethylene oxide) chain end was synthesized by sequential anionic polymerization of ethylene oxide (EO) and methylidene malonate 2.1.2 (MM 2.1.2). This allyl functional group was subsequently modified by reaction with thiol‐bearing functional groups to generate carboxyl and amino functionalized biodegradable block copolymers. These end‐group reactions, performed in good yields both in organic media and in aqueous micellar solutions, lead to functionalized PEO‐b‐PMM 2.1.2 copolymers which are of interest for cell targeting purposes.

Synthetic route to α‐allyl functionalized PEO‐b‐PMM 2.1.2 copolymers.     

Synthesis and Characterization of Amphiphilic Poly(ethylene oxide)‐block‐poly(hexyl methacrylate) Copolymers

We describe the preparation of amphiphilic diblock copolymers made of poly(ethylene oxide) (PEO) and poly(hexyl methacrylate) (PHMA) synthesized by anionic polymerization of ethylene oxide and subsequent atom transfer radical polymerization (ATRP) of hexyl methacrylate (HMA). The first block, PEO, is prepared by anionic polymerization of ethylene oxide in tetrahydrofuran. End capping is achieved by treatment of living PEO chain ends with 2‐bromoisobutyryl bromide to yield a macroinitiator for ATRP. The second block is added by polymerization of HMA, using the PEO macroinitiator in the presence of dibromobis(triphenylphosphine) nickel(II), NiBr₂(PPh₃)₂, as the catalyst. Kinetics studies reveal absence of termination consistent with controlled polymerization of HMA. GPC data show low polydispersities of the corresponding diblock copolymers. The microdomain structure of selected PEO‐block‐PHMA block copolymers is investigated by small angle X‐ray scattering experiments, revealing behavior expected from known diblock copolymer phase diagrams.

SAXS diffractograms of PEO‐block‐PHMA diblock copolymers with 16, 44, 68 wt.‐% PEO showing spherical (A), cylindrical (B), and lamellae (C) morphologies, respectively.     

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.

     

Methacrylic Polymers Containing Optically Active Side‐Chain Carbazole: Synthesis,Characterization and Photoconductive Properties

Two novel optically active polymethacrylates bearing in the side chain a cyclic chiral group of one prevailing absolute configuration linked to the carbazole chromophore, deriving from the related monomers (S)‐(?)‐3‐methacryloyloxy‐N‐[3‐(9‐ethylcarbazolyl)]pyrrolidine [(S)‐(?)‐MECP] and (S)‐(+)‐2‐methacryloyloxy‐N‐[3‐(9‐ethylcarbazolyl)]succinimide [(S)‐(+)‐MECSI], have been prepared and characterized with the aim to obtain materials suitable to photoconductive applications. Poly[(S)‐(?)‐MECP] and poly[(S)‐(+)‐MECSI] exhibit remarkable thermal stability, with glass transition temperature around 200 °C and decomposition temperatures in the range 330–350 °C. Spectroscopic, thermal and chiroptical characterizations indicate the occurrence of dipolar interactions among the side chain moieties and the presence of chiral conformation at least for chain segments of the macromolecules. The photoconductive properties are discussed in terms of extent of conjugation in the side chain based on the electron‐acceptor or electron‐donator properties of the optically active ring linked to the carbazole group.

     

Selectivity of PEO‐block‐PPO Diblock Copolymers in the Microwave‐Accelerated,Anionic Ring‐Opening Polymerization of Propylene Oxide with PEG as Initiator

Diblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) were synthesized by the anionic ring‐opening polymerization of propylene oxide (PO), with controlled microwave heating in sealed vessels. A detailed study was carried out to investigate the effects of different parameters on the formation of unwanted byproducts. Parameters that were considered include temperature; the concentration of NaH, monomer and hydroxy groups in the feed; and the polarity of the reaction medium. A continuous decrease of internal pressure during the sealed‐vessel experiment reflected the consumption of PO monomer and the completion of the reaction was confirmed by a drop of the internal pressure to zero when reactions were performed in bulk. The products were characterized by using different chromatographic techniques. A comparison of the reaction times and composition of the polymers prepared by microwave and conductive heating is given.

     

Synthesis of Diene‐Functionalized Macromonomers via Functionalization with Hexa‐1,3,5‐triene

The reaction of poly(styryl)lithium (PSLi) with hexa‐1,3,5‐triene (HXT) was studied as a route to diene‐functionalized macromonomers. When PSLi was reacted with 1.5 molar equivalents of HXT for 2.5 h at ?10 °C in toluene, it was found that the diene‐functionalized macromonomer was obtained in high yield; however, oligomerization of the HXT was observed by matrix‐assisted laser absorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). Oligomerization was eliminated by running the reaction with only 1.2 molar equivalents of HXT to PSLi and allowing the reaction to run for 15 min at ?10 °C in toluene. The resulting polymer exhibited high diene chain‐end functionality and no oligomerization was observed by MALDI‐TOF MS. ¹³C NMR spectroscopy and the attached‐proton test (APT), along with calculated chemical shifts, showed the presence of both the 1,2‐ and 1,4‐addition chain‐end structures. Further analysis by the reaction of the functional polymer with maleic anhydride indicated that 18 wt.‐% of the product was unreactive, either because of a 1,4‐addition chain‐end structure or a nonfunctional polymer. The structure of the maleic anhydride‐modified polymer was determined by MALDI‐TOF MS and ¹³C NMR spectroscopy. Preliminary work on the reactivity of the diene‐functionalized macromonomers was performed by the addition of a large excess of PSLi to a solution of macromonomer followed by characterization by size‐exclusion chromatography (SEC).

The formation of hexa‐1,3,5‐triene‐functionalized polystyrenes and their reaction with maleic anhydride.     

Model ω‐Functionalized Linear Polystyrenes with One,Two, and Three Sulfobetaine End Groups: Synthesis,Characterization, and Association Behavior

Three series of ω‐functionalized polystyrenes (PS) with different molecular weights, the first consisting of dimethylamino end‐capped PSs and the other two of ω‐branched PSs end‐capped with two and three low‐molecular‐weight (M _n ～ 500 g · mol^?1) dimethylamino ω‐functionalized polybutadienes (PB), were synthesized by high‐vacuum anionic polymerization techniques using the functional initiator ([3‐(dimethylaminopropyl)]lithium) and chlorosilane linking chemistry. The ω‐dimethylamino polymers (precursors) were molecularly characterized by size‐exclusion chromatography, low‐angle laser light scattering (LALLS), membrane osmometry, and NMR spectroscopy. The characterization results indicate a high degree of molecular and structural homogeneity. The dimethylamino end groups were transformed to the highly polar sulfozwitterionic ones (see Figure) by reaction with cyclopropanosultone. The mono‐, di‐, and tri‐zwitterion capped polymers were found by LALLS, dynamic light scattering (DLS) and viscometry, to associate in carbon tetrachloride, a good nonpolar solvent for the PS tail. In contrast, results on dimethylamino‐capped precursors show no evidence of aggregation. Aggregation numbers increase in decalin compared with those in carbon tetrachloride. At constant molecular weight of the parental PS, the degree of association increases with increasing number of functional groups and for a given number of functional groups with decreasing molecular weight of the PS tail. Temperature‐dependent light scattering measurements in decalin indicate that aggregation persists at the highest temperature investigated.

A schematic representation of the materials investigated in this study.     

Avoiding Disulfides: Improvement of Initiation and End‐Capping Reactions in the Synthesis of Polysulfide Block Copolymers

In episulfide polymerisation, the exchange between thiols and disulfides results in a chain transfer, which may compromise the control over molecular weight and molecular weight distribution. Self‐assemblable polysulfide structures have found promising applications as bionanomaterials (responsive nanoparticles or vesicles, surface films, etc.), but the necessary precise molecular control may indeed be jeopardised by the presence of disulfides. We here discuss in depth the role of disulfides as chain transfer agents and present some robust solutions, aiming at minimising the presence of disulfides and optimising synthetic procedures.

     

Successive Synthesis of Multiarmed and Multicomponent Star‐Branched Polymers by New Iterative Methodology Based on Linking Reaction between Block Copolymer In‐Chain Anion and α‐Phenylacrylate‐Functionalized Polymer

A series of multiarmed and multicomponent miktoarm (μ‐) star polymers have been successfully synthesized by developing a new iterative methodology based on a specially designed linking reaction of the block copolymer in‐chain anions, whose anions are positioned between the blocks, with α‐phenylacrylate (PA)‐functionalized polymers. The iterative methodology involves the following two reaction steps: a) introduction of two different polymer segments by the linking reaction of a block copolymer in‐chain anion with a PA‐functionalized polymer and b) regeneration of the PA reaction site. By repeating this reaction sequence, two different polymer segments are advantageously and successively introduced into the μ‐star polymer. In practice, repetition of the reaction sequence affords well‐defined 3‐arm ABC, 5‐arm ABCDE, 7‐arm ABCDEFG, and even 9‐arm ABCDEFGHI μ‐star polymers, composed of polystyrene, polystyrenes substituted with functional groups, polyisoprene, and poly(alkyl methacrylate) arms, respectively.

     

Hairy Nanoparticles with Hard Polystyrene Cores and Soft Polydimethylsiloxane Shells: One‐Pot Synthesis by Living Anionic Polymerization and Characterization

Hairy core–shell nanoparticles have emerged as a unique class of polymeric nanocomposites. Hairy nanoparticles (HNPs) with hard polystyrene (PS) cores and soft polydimethylsiloxane (PDMS) shells have been synthesized by living anionic polymerization via “one‐pot synthesis” approach. The size and composition of both core and shell components can be controlled. The synthetic approach produces an entirely new class of HNPs. Differential scanning calorimetry thermograms of the core–shell nanoparticles show two distinct transition temperatures corresponding to a glass transition temperature (T_g) of PS segment and a melting transition temperature (T_m) of PDMS segment indicating the formation of a phase separated system. The synthesized HNPs show different morphologies dependent on the content of PDMS due to the fusion of particles. Solvents play a crucial role in the fusion of particles. Diethyl ether can reduce the fusion of particles and generate almost uniform particles. The HNPs can self‐assemble into hierarchical suprastructures. The HNPs may have potential applications in emerging industries such as high‐density microelectronic materials and lithography.

     

Synthesis of Upper Rim Functionalized Calixarene‐Based Poly(norbornenes)

A modified synthesis of 25‐allyl‐26,27,28‐trihydroxycalix[4]arene is reported. This calix[4]arene was utilized to prepare calix[4]arenes containing norbornene and calix[4]arene containing azo dyes and norbornene on their upper rims. The calixarene monomers were reacted with Grubbs' second generation catalyst to give poly(norbornenes) containing calixarenes. The poly(norbornenes) were determined to possess molecular weights between 45 100 and 116 200 with PDIs between 1.4 and 1.9. Thermal analysis showed that the azo dye containing polymers were less thermally stable than the non‐azo dye containing polymers with decompositions beginning at 140 °C and 395 °C, respectively. The azo dye containing polymers displayed λ_max at 430 nm in THF solutions that underwent a bathochromic shift to 520 nm when acidified with HCl_(g), due to the formation of the azonium ion.

     

Double‐Gyroid Morphology of a Polystyrene‐block‐Poly(ferrocenylethylmethylsilane) Diblock Copolymer: A Route to Ordered Bicontinuous Nanoscale Architectures

A polystyrene‐block‐poly(ferrocenylethylmethylsilane) diblock copolymer, displaying a double‐gyroid morphology when self‐assembled in the solid state, has been prepared with a PFEMS volume fraction ?_PFEMS = 0.39 and a total molecular weight of 64 000 Da by sequential living anionic polymerisation. A block copolymer with a metal‐containing block with iron and silicon in the main chain was selected due to its plasma etch resistance compared to the organic block. Self‐assembly of the diblock copolymer in the bulk showed a stable, double‐gyroid morphology as characterised by TEM. SAXS confirmed that the structure belonged to the Ia d space group.

     

Photoresponsive New Polysiloxanes with 4‐Substituted Azobenzene Side‐Groups. Synthesis,Characterization and Kinetics of the Reversible Trans‐Cis‐Trans Isomerization

New polydimethylsiloxanes with p‐substituted azobenzene side‐groups were synthesized. Thin films and solutions exhibit a photochemical trans‐cis isomerization of the azobenzene groups, followed by their cis‐trans thermal relaxation in the dark. In films, relaxation rates were found to be 100–1 000 times slower than the rates of photoisomerization, the former being very sensitive to the electron‐acceptor character of the substituents. in solution, the rates of cis‐trans relaxation are lower than those obtained for the solid state. This is ascribed to the dipolar intramolecular interactions between cis chromophores, which are favored in solution.

     

Synthesis of Polystyrene‐block‐Poly(methyl methacrylate) with Fluorene at the Junction: Sequential Anionic and Controlled Radical Polymerization from a Single Carbon

Polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) has been synthesized by sequential anionic and reverse atom transfer radical polymerization (ATRP) or a variation of nitroxide mediated polymerization (NMP) from a single initiating site, specifically the 9‐carbon on 2,7‐dibromofluorene or fluorene. The addition of the second arm (PS) relied on thermal decomposition of 2,2′‐azoisobutyronitrile (AIBN) to generate radicals, abstracting the 9‐H on the polymer‐bound fluorene species to form the initiating radical. Styrene was not present in the reaction mixture when AIBN was decomposed, preventing competition between addition across the monomeric alkene and hydrogen abstraction from the fluorene. After 1 h, styrene was introduced and mediation of the subsequent radical polymerization was achieved by the presence of CuCl₂/ligand or TEMPO. Characterization of the diblock copolymers by gel permeation chromatography (GPC) revealed substantial shifts in number average molecular weight ( ) values compared to the anionically prepared PMMA macroinitiator, while polydispersity indices (PDI's) remained relatively low (typically < 1.5). Characterization by UV detection with GPC (at 310 nm) verified that the diblock polymer is chromophore‐bound, which was further verified by UV‐vis spectroscopy of the isolated diblock.

     

Well‐Defined Cyclohexene Oxide Mid‐Chain Functional Polystyrene Macromonomer: Synthesis,Characterization and Photoinitiated Cationic Homo‐ and Copolymerization

In this article, we present the results of a study of the preparation of a cyclohexene oxide (CHO) mid‐chain functional macromonomer via ATRP of styrene (St) and epoxidation on work‐up with 3‐chloroperoxybenzoic acid. The ATRP initiator, Br? CH? Br, was synthesized by the condensation of 3‐cyclohexene‐1,1‐dimethanol with 2‐bromopropanoyl bromide. The ATRP of St with Br? CH? Br and Cu(I)/bpy yielded well‐defined polystyrene with a cyclohexene mid‐chain group (PSt? CH? PSt). Epoxidation of the PSt? CH? PSt was performed using 3‐chloroperoxybenzoic acid. GPC, IR and ¹H NMR analyses revealed that a low polydispersity macromonomer of polystyrene with CHO functionality at the mid‐chain (PSt? CHO? PSt) was obtained. The photoinduced cationic polymerization of PSt? CHO? PSt yielded comb‐shaped and graft copolymers.

     

Polythiophene Diblock Copolymer with Different Solvent Affinities of the Side‐Chain Substituents: Solvatochromism and Effect on the Electronic Conjugation

A new diblock copolymer composed of a regioregular block of poly[3‐[2‐(2‐methoxyethoxy)ethoxy]methylthiophene], bearing as side‐chain a hydrophilic substituent, and a regioregular block of poly[3‐(1‐octyloxy)thiophene], is prepared and characterized. The properties are compared with those of a related copolymer composed of poly(3‐hexylthiophene) and poly(3‐alkoxythiophene) blocks. The solvatochromic properties of these materials in solution are investigated by absorption and emission spectroscopy upon gradual addition of a poor solvent, and compared with those of the parent regioregular homopolymers. The experimental results are interpreted in terms of electronic interactions between the blocks. It is found that the different hydrophilicity of the side chain plays a crucial role for the electronic communication between blocks in poly(3‐alkylthiophene)‐block‐poly(3‐alkoxythiophene) copolymers.

     

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,Characterization, and Thermal Properties of Block Copolymers Containing Poly(styrene‐co‐4‐vinylpyridine) and Poly(styrene‐co‐butyl acrylate) by Controlled Radical Polymerization

Radical polymerization of styrene and mixtures of styrene and 4‐vinylpyridine was performed in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) producing polymers with controlled molecular weights and molecular weight distributions. The living nature of these polymers was confirmed by using them as macroinitiators in the block copolymerization of styrene and butyl acrylate. The thermal properties of the synthesized statistical diblock copolymers measured by differential scanning calorimetry indicated that a phase‐separated morphology was exhibited in most of the block copolymers. The results were confirmed by transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS) showing microphase‐separated morphology as is known for homo A‐B diblock polymers.

SAXS of a block copolymer synthesized from S/V 70:30 macroinitiators (03) with one detected T_g.     

Novel Polyesteramide‐Based Diblock Copolymers: Synthesis by Ring‐Opening Copolymerization and Characterization

Block copolymers based on a polyesteramide sequence and a polyether block were synthesized in bulk at 250 °C by ring‐opening copolymerization (ROP) of ε‐caprolactone (CLo) and ε‐caprolactam (CLa) as initiated by Jeffamine® M1000, i.e., ω‐NH₂ copoly[(ethylene oxide)‐co‐(propylene oxide)] copolymer [P(EO‐co‐PO)‐NH₂]. For an initial molar ratio of [CLa]₀/[CLo]₀ = 1, the copolymerization allowed for the formation of a diblock copolymer with a statistical polyesteramide sequence, as evidenced by ¹³C NMR. Investigation of the ROP mechanism highlighted that CLo was first polymerized, leading to the formation of a diblock copolymer P(EO‐co‐PO)‐b‐PCLo‐OH, followed by CLa hydrolysis to aminocaproic acid that inserted into the ester bonds of PCLo via aminolysis and subsequent condensation reactions. The outcome is the selective formation of P(EO‐co‐PO)‐b‐P(CLa‐co‐CLo)‐OH diblock copolymers where the composition and length of the polyesteramide sequence can be fine‐tuned by the [CLa]₀/[CLo]₀ and ([CLa]₀ + [CLo]₀)/[P(EO‐co‐PO)‐NH₂]₀ initial molar ratios.