A Facile Synthesis of Cleavable Block Copolymers via Tandem Polymerizations of NMRP and ATRP

A functionalized compound, 4‐(2‐bromoisobutyryl)‐2,2,6,6‐tetra‐methylpiperidine‐1‐oxyl (Br‐TEMPO), was synthesized and used to synthesize block copolymers through tandem nitroxide‐mediated radical polymerization (NMRP) and atom transfer radical polymerization (ATRP). First, Br‐TEMPO was used to mediate the polymerization of styrene. The kinetics of polymerization proved a typical “living” nature of the reaction and the effectiveness in the mediation of polymerization of Br‐TEMPO. Then the PS‐Br macroinitiator was used to initiate atom transfer radical polymerization (ATRP). A series of acrylates were initiated by PS‐Br macroinitiators in typical ATRP processes at various conditions. The controlled polymerization of ATRP was also confirmed by molecular weight and kinetic analysis. Several cleavable block copolymers of PS‐b‐P(t‐BA), PS‐b‐P(n‐BA), and PS‐b‐PMA, with different molecular weights, were synthesized via this strategy. Relatively low polydispersities (<1.5) were observed and the molecular weights were in agreement with the theoretical ones. Hydrolysis of PS‐b‐P(t‐BA) was carried out, giving amphiphilic block copolymer PS‐b‐PAA without the cleavage of C‐ON bond or ester bond. All the block copolymers have two T_gs as demonstrated by DSC. A typical cleavable block copolymer of PS‐b‐PMA was cleaved by adding phenylhydrazine at 120°C to produce homopolymers in situ.     

Structure of Styrene and Acrylate Block Copolymers

Abstract

Using UV light as the energy source and polystyrene- (PS-) or polymethyl methacrylate- (PMMA-) macroinitiators with active aromatic or aliphatic thiyl end groups, PS-PMMA and PMMA-PEA (poly-ethyl acrylate) block copolymers were synthesized. The molecular weights of both block copolymers increased with increasing reaction time. The reactivity of macroinitiators depended on the type of thiyl groups and monomer and not on the length of the polymer chain. The most reactive were macroinitiators containing resonance stabilized non-substituted or substituted aromatic end groups. The decomposition of the macroinitiators took place over the formation of the thiyl radical and macroradical. The bond length, the bond dissociation energy, and the bond order of macroradical end groups were calculated. The most reactive monomer was ethyl acrylate; the less reactive was styrene. The structure, the molecular weight, and the T _g of the styrene-acrylate block copolymers were determined. The PMMA/PEA block copolymer had two of block's T _g s, the first at 105°C, the second at ?24°C, and a third at 16°C which probably represents contacting segments.     

One‐Step Synthesis of Multiphase Block Copolymers via Simultaneus Free Radical and Ring Opening Polymerization Using Poly(ethylene oxide) Possessing Azo Group

Multiphase block copolymers having the structure of poly(?‐caprolacton‐b‐etyhlene glycol‐b‐styrene‐b‐ethylene glycol‐b‐?‐caprolacton) were synthesized from poly(ethylene oxide) possesing azo group in the main chain by the combination of free radical polymerization (FRP) of styrene (S) and ring opening polymerization (ROP) of ?‐caprolacton (?‐CL) in one‐step. The block copolymers were characterized ¹H‐NMR and FT‐IR spectroscopy and gel permeation chromatography (GPC). ¹H‐NMR and FT‐IR spectroscopy and GPC studies of the obtained polymers indicate that multiphase block copolymers easily formed as a result of combination FRP and ROP in one‐step.     

Synthesis of Amphiphilic Block Copolypept(o)ides by Bifunctional Initiators: Making PeptoMicelles Redox Sensitive

In this work, the synthesis of polypeptoid‐block‐polypeptide copolymers (block copolypept(o)ides) based on bifunctional initiators is described, which introduces a distinct chemical entity at the connection between both blocks. With a view towards redox‐sensitive block copolypept(o)ides, a cystamine‐based initiator was used to synthesize polysarcosine macroinitiators with degrees of polymerization (X_n) between 100 and 200 displaying monomodal molecular weight distributions and dispersities (Đ) around 1.1 as determined by size exclusion chromatography. Block copolypept(o)ides with a poly(γ‐t‐butyloxycarbonyl‐l ‐glutamate) (PGlu(O^tBu)) block (X_n = 25 or 50) were synthesized by controlled N‐carboxyanhydride polymerization. Resulting block copolymers possess monomodal molecular weight distributions, dispersities around 1.2 and were applied to degradation studies. While block copolypept(o)ides are stable at 10 × 10⁻⁶ m , they degrade over time at GSH concentrations of 10 × 10⁻³ and 100 × 10⁻³ m . Furthermore, these disulfide‐containing block copolymers form PeptoMicelles, which degrade at intracellular GSH concentrations while remaining stable at extracellular GSH levels.

     

Poly(acrylate‐b‐styrene‐b‐isobutylene‐b‐styrene‐b‐acrylate) Block Copolymers via Carbocationic and Atom Transfer Radical Polymerizations

A series of polyacrylate‐polystyrene‐polyisobutylene‐polystyrene‐polyacrylate (X‐PS‐PIB‐PS‐X) pentablock terpolymers (X=poly(methyl acrylate) (PMA), poly(butyl acrylate) (PBA), or poly(methyl methacrylate) (PMMA)) was prepared from poly (styrene‐b‐isobutylene‐b‐styrene) (PS‐PIB‐PS) block copolymers (BCPs) using either a Cu(I)Cl/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) or Cu(I)Cl/tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) catalyst system. The PS‐PIB‐PS BCPs were prepared by quasiliving carbocationic polymerization of isobutylene using a difunctional initiator, followed by the sequential addition of styrene, and were used as macroinitiators for the atom transfer radical polymerization (ATRP) of methyl acrylate (MA), n‐butyl acrylate (BA), or methyl methacrylate (MMA). The ATRP of MA and BA proceeded in a controlled fashion using either a Cu(I)Cl/PMDETA or Cu(I)Cl/Me₆TREN catalyst system, as evidenced by a linear increase in molecular weight with conversion and low PDIs. The polymerization of MMA was less controlled. ¹H‐NMR spectroscopy was used to elucidate pentablock copolymer structure and composition. The thermal stabilities of the pentablock copolymers were slightly less than the PS‐PIB‐PS macroinitiators due to the presence of polyacrylate or polymethacrylate outer block segments. DSC analysis of the pentablock copolymers showed a plurality of glass transition temperatures, indicating a phase separated material.     

Coassembly of Metal and Titanium Dioxide Nanocrystals Directed by Monolayered Block Copolymer Inverse Micelles for Enhanced Photocatalytic Performance

Functional nanostructures of self‐assembled block copolymers (BCPs) incorporated with various inorganic nanomaterials have received considerable attention on account of their many potential applications. Here we demonstrate the two‐dimensional self‐assembly of anisotropic titanium dioxide (TiO₂) nanocrystals (NCs) and metal nanoparticles (NPs) directed by monolayered poly(styrene)‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) copolymer inverse micelles. The independent position‐selective assembly of TiO₂ NCs and silver nanoparticles (AgNPs) preferentially in the intermicelle corona regions and the core of micelles, respectively, for instance, was accomplished by spin‐coating a mixture solution of PS‐b‐P4VP and ex situ synthesized TiO₂ NCs, followed by the reduction of Ag salts coordinated in the cores of micelles into AgNPs. Hydrophobic TiO₂ NCs with a diameter and length of approximately 3 nm and 20–30 nm, respectively, were preferentially sequestered in the intermicelle nonpolar PS corona regions energetically favorable with the minimum entropic packing penalty. Subsequent high‐temperature annealing at 550 °C not only effectively removed the block copolymer but also transformed the TiO₂ NCs into connected nanoparticles, thus leading to a two‐dimensionally ordered TiO₂ network in which AgNPs were also self‐organized. The enhanced photocatalytic activity of the AgNP‐decorated TiO₂ networks by approximately 27 and 44 % over that of Ag‐free TiO₂ networks and randomly deposited TiO₂ nanoparticles, respectively, was confirmed by the UV degradation property of methylene blue.     

Synthesis and Self‐Assembly of Thermoresponsive Amphiphilic Biodegradable Polypeptide/Poly(ethyl ethylene phosphate) Block Copolymers

We report the design and synthesis of new fully biodegradable thermoresponsive amphiphilic poly(γ‐benzyl L ‐glutamate)/poly(ethyl ethylene phosphate) (PBLG‐b‐PEEP) block copolymers by ring‐opening polymerization of N‐carboxy‐γ‐benzyl L ‐glutamate anhydride (BLG? NCA) with amine‐terminated poly(ethyl ethylene phosphate) (H₂N? PEEP) as a macroinitiator. The fluorescence technique demonstrated that the block copolymers could form micelles composed of a hydrophobic core and a hydrophilic shell in aqueous solution. The morphology of the micelles as determined by transmission electron microscopy (TEM) was spherical. The size and critical micelle concentration (CMC) values of the micelles showed a decreasing trend as the PBLG segment increased. However, UV/Vis measurements showed that these block copolymers exhibited a reproducible temperature‐responsive behavior with a lower critical solution temperature (LCST) that could be tuned by the block composition and the concentration.     

Orthogonally Self‐Assembled Multifunctional Block Copolymers

We report the synthesis of telechelic poly(norbornene) and poly(cyclooctene) homopolymers by ring‐opening metathesis polymerization (ROMP) and their subsequent functionalization and block copolymer formation based on noncovalent interactions. Whereas all the poly(norbornene)s contain either a metal complex or a hydrogen‐bonding moiety along the polymer side‐chains, together with a single hydrogen‐bonding‐based molecular recognition moiety at one terminal end of the polymer chain. These homopolymers allow for the formation of side‐chain‐functionalized AB and ABA block copolymers through self‐assembly. The orthogonal natures of all side‐ and main‐chain self‐assembly events were demonstrated by ¹H NMR spectroscopy and isothermal titration calorimetry. The resulting fully functionalized block copolymers are the first copolymers combining both side‐ and main‐chain self‐assembly, thereby providing a high degree of control over copolymer functionalization and architecture and bringing synthetic materials one step closer to the dynamic self‐assembly structures found in nature.     

Block copolymer micelles with enzyme molecules at the interfaces

This research provides an efficient method for the fabrication of hybrid micelles with enzyme molecules at the interfaces. Amphiphilic block copolymer is synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization, and thiol‐modified porcine pancreatic lipase (PPL‐SH) is obtained by treatment of native PPL with Traut's reagent. PPL‐SH is conjugated to the block copolymer chains by thiol‐disulfide exchange reaction. In phosphate buffered saline, the bioconjugate self‐assembles into micelles with enzyme molecules at the interfaces between hydrophobic cores and hydrophilic coronae. The bioactivity of the enzyme molecules on the micelles are compared with the native enzyme. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2047–2052     

Perfluorocyclobutyl-containing Amphiphilic Block Copolymers Synthesized by RAFT Polymerization

Amphiphilic block copolymers containing hydrophobic perfluorocyclobutyl‐based (PFCB) polyacrylate and hydrophilic poly(ethylene glycol) (PEG) segments were prepared via reversible addition‐fragmentation chain transfer (RAFT) polymerization. The PFCB‐containing acrylate monomer, p‐(2‐(p‐tolyloxy)perfluorocyclobutoxy)‐phenyl acrylate, was first synthesized from commercially available compounds in good yields, and this kind of acrylate monomer can be homopolymerized by free radical polymerization or RAFT polymerization. Kinetic study showed the 2,2′‐azobis(isobutyronitrile) (AIBN) initiated and cumyl dithiobenzoate (CDB) mediated RAFT polymerization was in a living fashion, as suggested by the fact that the number‐average molecular weights (M_n) increased linearly with the conversions of the monomer, while the polydispersity indices kept less than 1.10. The block polymers with narrow molecular weight distributions (M_w/M_n≦1.21) were prepared through RAFT polymerization using PEG monomethyl ether capped with 4‐cyanopentanoic acid dithiobenzoate end group as the macro chain transfer agent (mPEG‐CTA). The length of the hydrophobic segment can be tuned by the feed ratio of the PFCB‐based acrylate monomer and the extending of the polymerization time. The micellization behavior of the block copolymers in aqueous media was investigated by the fluorescence probe technique.     

Preparation of Cross‐Linked Micelles from Glycidyl Methacrylate Based Block Copolymers and Their Usages as Nanoreactors in the Preparation of Gold Nanoparticles

This study reports the synthesis of poly(ethylene glycol)methyl ether‐block‐poly(glycidyl methacrylate) (MPEG‐b‐PGMA) diblock, and poly(ethylene glycol)methyl ether‐block‐poly(glycidyl methacrylate)‐block‐poly(methyl methacrylate) (MPEG‐b‐PGMA‐b‐PMMA) triblock copolymers via atom transfer radical polymerization and their self‐assembly behaviors in aqueous media by using acetone as cosolvent. These block copolymers formed near monodisperse core–shell micelles having cross‐linkable cores. Two types of cross‐linked micelles, namely spherical MPEG‐b‐PGMA core cross‐linked (CCL) micelles and MPEG‐b‐PGMA‐b‐PMMA interlayer cross‐linked (ILCL) micelles, were also successfully prepared from these block copolymers by using various bifunctional cross‐linkers such as hexamethylenediamine (HMDA), ethylenediamine (EDA), and 2‐aminoethanethiol (AET). Cross‐linking was successfully carried out via ring‐opening reactions of epoxy residues of hydrophobic‐cores with primary amine or thiol groups of bifunctional cross‐linkers. Finally, these cross‐linked micelles were successfully used as nanoreactors in the synthesis of gold nanoparticles (AuNPs) in aqueous media. Both CCL and ILCL micelles were found to be good stabilizers for AuNPs in aqueous media. Both CCL‐ and ILCL‐stabilized AuNP dispersions were stable for a long time without any size changes and flocculation at room temperature. These cross‐linked stabilized AuNPs exhibited good catalytic activities in the reduction of p‐nitrophenol. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 514–526.     

Modular Synthesis of Functional Block Copolymers

Summary: The free‐radical addition of ω‐functional mercaptans to the vinyl double bonds of 1,2‐polybutadiene‐block‐poly(ethylene oxide) copolymers was used for modular synthesis of well‐defined functional block copolymers. The modification reaction proceeds smoothly and yields quantitatively functionalized block copolymers (¹H NMR and FT‐IR spectroscopy) without disturbing the molecular‐weight distribution of the parent copolymer (PDI < 1.09, size exclusion chromatography).

The modular synthetic pathway towards the functional block copolymers reported here.     

K+‐Responsive Block Copolymer Micelles for Targeted Intracellular Drug Delivery

In this work, a novel type of block copolymer micelles with K⁺‐responsive characteristics for targeted intracellular drug delivery is developed. The proposed smart micelles are prepared by self‐assembly of poly(ethylene glycol)‐b‐poly(N‐isopropylacry‐lamide‐co‐benzo‐18‐crown‐6‐acrylamide) (PEG‐b‐P(NIPAM‐co‐B18C6Am)) block copolymers. Prednisolone acetate (PA) is successfully loaded into the micelles as the model drug, with loading content of 4.7 wt%. The PA‐loaded micelles display a significantly boosted drug release in simulated intracellular fluid with a high K⁺ concentration of 150 × 10⁻³m , as compared with that in simulated extracellular fluid. Moreover, the in vitro cell experiments indicate that the fluorescent molecules encapsulated in the micelles can be delivered and specifically released inside the HSC‐T6 and HepG2 cells responding to the increase of K⁺ concentration in intracellular compartments, which confirms the successful endocytosis and efficient K⁺‐induced intracellular release. Such K⁺‐responsive block copolymer micelles are highly potential as new‐generation of smart nanocarriers for targeted intracellular delivery of drugs.     

Au/CdS Hybrid Nanoparticles in Block Copolymer Micellar Shells

A polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) micellar structure with a P2VP core containing 5 nm CdS nanoparticles (NPs) and a PS shell formed in toluene that is a good solvent for PS block undergoes the core‐shell inversion by excess addition of methanol that is a good solvent for P2VP block. It leads to the formation of micellar shell‐embedded CdS NPs in the methanol major phase. The spontaneous crystalline growth of Au NPs on the CdS surfaces positioned at micellar shells without a further reduction process is newly demonstrated. The nanostructure of Au/CdS/PS‐b‐P2VP hybrid NPs is confirmed by transmission electron microscopy, energy‐dispersive X‐ray, and UV‐Vis absorption.

     

Hydration Changes during Thermosensitive Association of a Block Copolymer Consisting of LCST and UCST Blocks

Summary: Thermosensitive association of a diblock copolymer consisting of poly(3‐dimethyl(methacryloyloxyethyl) ammonium propane sulfonate) (PdMMAEAPS), as an upper critical solution temperature (UCST) block, and poly(N,N‐diethylacrylamide) (PdEA), as a lower critical solution temperature (LCST) block, has been investigated by using IR spectroscopy. The ν(CO) and ν(SO) bands of the PdMMAEAPS block and the amide I band of PdEA block critically changed at the UCST and LCST, respectively, indicating that the segmental interaction of each block is altered at each transition.

The double temperature responsiveness of a UCST block and LCST block containing diblock copolymer. Micelles form at temperatures both below the UCST and above the LCST of the blocks.     

Design of a Linear Poly(3‐hexylthiophene)/Fullerene‐Based Donor‐Acceptor Rod‐Coil Block Copolymer

Novel fullerene‐grafted poly(3‐hexylthiophene) (P3HT)‐based rod‐coil block copolymers have been synthesized. The regioregular P3HT rod block has been synthesized by a modified Grignard metathesis reaction (GRIM). An original in situ end‐capping reaction has been developed in order to convert the P3HT block into an efficient macro‐initiator for the nitroxide‐mediated radical polymerization (NMRP) of the coil block. Controlled radical polymerization of the second poly(butylacrylate‐stat‐chloromethylstyrene) [P(BA‐stat‐CMS)] block has been done through various conditions leading to different coil block lengths. The final electron donor‐acceptor block copolymer has been obtained after C₆₀ grafting in soft conditions. Copolymers have been characterized by ¹H NMR and size exclusion chromatography. Optical characterizations, before and after C₆₀ grafting, are reported.

     

Dimensional Control of Block Copolymer Nanofibers with a π‐Conjugated Core: Crystallization‐Driven Solution Self‐Assembly of Amphiphilic Poly(3‐hexylthiophene)‐b‐poly(2‐vinylpyridine)

With the aim of accessing colloidally stable, fiberlike, π‐conjugated nanostructures of controlled length, we have studied the solution self‐assembly of two asymmetric crystalline–coil, regioregular poly(3‐hexylthiophene)‐b‐poly(2‐vinylpyridine) (P3HT‐b‐P2VP) diblock copolymers, P3HT₂₃‐b‐P2VP₁₁₅ (block ratio=1:5) and P3HT₄₄‐b‐P2VP₁₁₅ (block ratio=ca. 1:3). The self‐assembly studies were performed under a variety of solvent conditions that were selective for the P2VP block. The block copolymers were prepared by using Cu‐catalyzed azide–alkyne cycloaddition reactions of azide‐terminated P2VP and alkyne end‐functionalized P3HT homopolymers. When the block copolymers were self‐assembled in a solution of a 50 % (v/v) mixture of THF (a good solvent for both blocks) and an alcohol (a selective solvent for the P2VP block) by means of the slow evaporation of the common solvent; fiberlike micelles with a P3HT core and a P2VP corona were observed by transmission electron microscopy (TEM). The average lengths of the micelles were found to increase as the length of the hydrocarbon chain increased in the P2VP‐selective alcoholic solvent (MeOH<iPrOH<nBuOH). Very long (>3 μm) fiberlike micelles were prepared by the dialysis of solutions of the block copolymers in THF against iPrOH. Furthermore the widths of the fibers were dependent on the degree of polymerization of the chain‐extended P3HT blocks. The crystallinity and π‐conjugated nature of the P3HT core in the fiberlike micelles was confirmed by a combination of UV/Vis spectroscopy, photoluminescence (PL) measurements, and wide‐angle X‐ray scattering (WAXS). Intense sonication (iPrOH, 1 h, 0 °C) of the fiberlike micelles formed by P3HT₂₃‐b‐P2VP₁₁₅ resulted in small (ca. 25 nm long) stublike fragments that were subsequently used as initiators in seeded growth experiments. Addition of P3HT₂₃‐b‐P2VP₁₁₅ unimers to the seeds allowed the preparation of fiberlike micelles with narrow length distributions (L_w/L_n <1.11) and lengths from about 100‐300 nm, that were dependent on the unimer‐to‐seed micelle ratio.     

Morphology Evolution of Block Copolymer Blend Thin Films Induced by Solvent Vapor Annealing

ABSTRACT

Self-assembly of binary block copolymer blends in thin film induced by solvent vapor annealing has been systematically studied. The diblock copolymers polystyrene-b-poly(2-vinylpyridine) with different molecular weights and volume fractions were blended with different molar ratios to cast thin films on silica substrate by spin coating. The films were annealed separately in the vapor of ethanol or toluene over time to induce morphology transformations from spheres, gyroids, and bicontinuous nanostructures, depending on the blending ratio, solvent selectivity, and annealing time, as investigated by atomic force microscopy and X-ray photoelectron spectroscopy. The formation and transformation mechanism of the self-assembly structure are discussed in the context of solvent-copolymer interactions. This study provides new insights into the simple manipulation of self-assembled nanostructures of block copolymer thin films.     

Gold‐Decorated Chiral Macroporous Films by the Self‐Assembly of Functionalised Block Copolymers

We describe a new and very versatile method to place chosen chemical functionalities at the edge of the pores of macroporous materials. The method is based on the synthesis and self‐assembly of inorganic block copolymers (BCPs) having chiral rigid segments bearing controllable quantities of randomly distributed functional groups. The synthesis of a series of optically active block copolyphosphazenes (PP) with the general formula [N?P(R‐O₂C₂₀H₁₂)_0.9(FG)_0.2]_n‐b‐[N?PMePh]_m (FG=‐OC₅H₄N ( 6 ), ‐NC₄H₈S ( 7 ), and ‐NC₄H₈O ( 8 )), was accomplished by the sequential living cationic polycondensation of N‐silylphosphoranimines, using the mono‐end‐capped initiator [Ph₃P?N?PCl₃][Cl] ( 3 ). The self‐assembly of the phosphazene BCPs 6 – 8 led to chiral porous films. The functionality present on those polymers affected their self‐assembly behaviour resulting in the formation of pores of different diameters (D_n=111 ( 6 ), 53 ( 7 ) and 77 nm ( 8 )). The specific functionalisation of the pores was proven by decorating the films with gold nanoparticles (AuNPs). Thus, the BCPs 6 and 7 , having pyridine and thiomorpholine groups, respectively, were treated with HAuCl₄, followed by reduction with NaBH₄, yielding a new type of block copolyphosphazenes, which self‐assembled into chiral porous films specifically decorated with AuNPs at the edge of the pores.     

Hairy Nanospheres by Gelation of Reactive Block Copolymer Micelles

Summary: A novel way to prepare polymer hair/polysilsesquioxane core hybrid nanospheres is presented based on a self‐assembly and gelation process of a reactive block copolymer, poly(ethylene oxide)‐block‐poly[3‐(trimethoxysilyl)propyl methacrylate] (PEO₁₁₃‐b‐PTMSPMA₂₀₆). Nanospheres of uniform size were obtained. Transmission electron microscopy (TEM), dynamic light scattering (DLS), and static light scattering (SLS) were employed to characterize the products.

Schematic of the PEO‐b‐PTMSPMA nanospheres formed here, the light gray part represents the PEO hairs, the dark parts are the polysilsesquioxane from the gelation of the PTMSPMA blocks of the self‐assembled sphere.