Synthesis of hybrid dendritic‐linear block copolymers with dendritic initiators prepared by convergent living anionic polymerization

Hybrid dendritic‐linear block copolymers were made in one‐pot by convergent living anionic polymerization. Dendritic polystyrene macroinitiators were synthesized by slowly adding a mixture of either vinylbenzyl chloride (VBC) or 4‐(chlorodimethylsilyl)styrene (CDMSS) and styrene (1 : 10 molar ratio of coupling agent to styrene) to a solution of living polystyryllithium. The addition was ceased prior to the addition of a stoichiometric amount of coupling agent to retain a living chain end. To the living dendritically branched polystyrene was then added either styrene or isoprene to polymerize a linear block from the dendritic polystyrene. The resulting copolymers were characterized by gel permeation chromatography coupled with multiangle laser light scattering (GPC‐MALLS), which clearly demonstrated the formation of diblock copolymers. The diblock copolymers were further characterized by ¹H NMR, which showed the presence of the two blocks in the case of dendritic polystyrene‐block‐linear polyisoprene. The measurement of intrinsic viscosity showed that the dilute solution properties of the block copolymers are greatly influenced by the dendritic portion. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 152–161, 2001     

Synthesis and photophysical characterization of amphiphilic dendritic–linear–dendritic block copolymers

Amphiphilic dendritic–linear–dendritic triblock copolymers based on hydrophilic linear poly(ethylene oxide) (PEO) and hydrophobic dendritic carbosilane were synthesized with a divergent approach at the allyl end groups of diallyl‐terminated PEO. Their micellar characteristics in an aqueous phase were investigated with dynamic light scattering, fluorescence techniques, and transmission electron microscopy. The block copolymer with the dendritic moiety of a third generation could not be dispersed in water. The block copolymers with the first (PEO–D ‐Si‐1G) and second (PEO–D ‐Si‐2G) generations of dendritic carbosilane blocks formed micelles in an aqueous phase. The critical micelle concentrations of PEO–D ‐Si‐1G and PEO–D ‐Si‐2G, determined by a fluorescence technique, were 27 and 16 mg/L, respectively. The mean diameters of the micelles of PEO–D ‐Si‐1G and PEO–D ‐Si‐2G, measured by dynamic light scattering, were 170 and 190 nm, respectively, which suggests that the micelles had a multicore‐type structure. The partition equilibrium constants of pyrene in the micellar solution increased with the increasing size of the dendritic block (e.g., 7.68 × 10⁴ for PEO–D ‐Si‐1G and 9.57 × 10⁴ for PEO–D ‐Si‐2G). The steady‐state fluorescence anisotropy values (r) of 1,6‐diphenyl‐1,3,5‐hexatriene were 0.06 for PEO–D ‐Si‐1G and 0.09 for PEO–D ‐Si‐2G. The r values were lower than those of the linear polymeric amphiphiles, suggesting that the microviscosity of the dendritic micellar core was lower than that of the linear polymeric analogues. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 918–926, 2001     

Controlling surfaces and interfaces with functional polymers: Preparation and functionalization of dendritic–linear block copolymers via metal catalyzed “living” free radical polymerization

The preparation and chemical modification of dendritic–linear block copolymers with surface functionalized dendritic components are presented. Isophthalate ester-functionalized dendrons featuring benzylic halide groups at their focal points have been used for the metal catalyzed “living” radical polymerization of styrene. The molecular weight of the dendritic–linear block copolymers determined by MALDI-TOF and Size Exclusion Chromatography was found to be accurately controlled up to molecular weights of ca. 30,000 a.m.u., with polydispersities less than 1.2. Subsequent functional group modifications of the peripheral ethyl ester groups of the dendritic block have been successfully carried out leading to carboxylic acids, butyl amides, benzyl alcohols, benzyl halides, and also accelerated generation growth via transesterification with a first generation dendritic alcohol. Several of these new dendritic–linear block copolymers exhibit interesting aggregation characteristics as evidenced by ¹H-NMR spectroscopic studies. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1–10, 1998     

Synthesis and MALDI‐TOF analysis of dendritic‐linear block copolymers of lactides: Influence of architecture on stereocomplexation

Formation of a stereocomplex from polylactide copolymers can be tuned by changing the size and the chain topology of the second block in the copolymer. In particular, the use of a dendritic instead of linear architecture is expected to destabilize the cocrystallisation of polylactide blocks. With this idea in mind, dendritic‐linear block copolymers were synthesized by ring‐opening polymerization (ROP) of lactides using benzyl alcohol dendrons of generation 1–3 as macroinitiators and stannous octoate as catalyst. Polymers with controlled and narrow molar mass distribution were obtained. The MALDI‐TOF mass spectra of these dendritic‐linear block copolymers show well‐resolved signals. Remarkably, 10% or less of odd‐membered polymers are present, indicating that ester‐exchange reactions which occur classically parallel to the polymerization process, were in these conditions, very limited. Thermal analysis of polyenantiomers of generation 1–3 and the corresponding blends were examined. The blend of a pair of enantiomeric dendritic‐linear block copolymers exhibit a higher melting temperature than each copolymer, characteristic for the formation of a stereocomplex. Melting temperatures are strongly dependent on the dendron generation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6782–6789, 2006     

Synthesis and properties of polydimethylsiloxane-containing block copolymers via living radical polymerization

Polydimethylsiloxane (PDMS) block copolymers were synthesized by using PDMS macroinitiators with copper-mediated living radical polymerization. Diamino PDMS led to initiators that gave ABA block copolymers, but there was low initiator efficiency and molecular weights are somewhat uncontrolled. The use of mono- and difunctional carbinol–hydroxyl functional initiators led to AB and ABA block copolymers with narrow polydispersity indices (PDIs) and controlled number-average molecular weights (M_n's). Polymerization with methyl methacrylate (MMA) and 2-dimethylaminoethyl methacrylate (DMAEMA) was discovered with a range of molecular weights produced. Polymerizations proceeded with excellent first-order kinetics indicative of living polymerization. ABA block copolymers with MMA were prepared with between 28 and 84 wt % poly(methyl methacrylate) with M_n's between 7.6 and 35 K (PDI <1.30), which show thermal transitions characteristic of block copolymers. ABA block copolymers with DMAEMA led to amphiphilic block copolymers with M_n's between 9.5 and 45.7 K (PDIs of 1.25–1.70), which formed aggregates in solution with a critical micelle concentration of 0.1 g dm⁻³ as determined by pyrene fluorimetry experiments. Monocarbinol functional PDMS gave AB block copolymers with both MMA and DMAEMA. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1833–1842, 2001     

Amphiphilic well-defined degradable star block copolymers by combination of ring-opening polymerization and atom transfer radical polymerization: Synthesis and application as drug delivery carriers

Atom transfer radical polymerization (ATRP) is one of the most popular advanced polymerization techniques in macromolecular science, allowing the synthesis of tailor-made polymers with controlled molecular weight, architecture, composition, and functionality. The combination of ATRP and ring-opening polymerization (ROP) provides a straightforward route for the preparation of polymers exhibiting both targeted and well-defined features and biodegradability, which is very interesting for the development of new materials for biomedical applications. Among the different types of polymer architectures, amphiphilic star block copolymers (BCPs) represent a very attractive one, due to their high degree of functionality at the molecular surface, low hydrodynamic volume and higher encapsulation ability, compared to molecular systems based on linear polymers. This review article highlights the research focused on the synthesis of amphiphilic well-defined degradable star BCPs by combination of ROP and ATRP, with particular focus on the development of polymers for biomedical applications, such as anticancer drug delivery, diagnosis therapy, or photodynamic therapy, which is the most investigated field regarding these polymers.     

新型线状-树枝状两亲嵌段共聚物的合成

本文设计合成了一系列由不同链长的聚丙烯酸(PAA)为亲水嵌段和不同代数聚苄醚树枝体(Dendr.PBE)为疏水嵌段的杂化共聚物(PAA-Dendr.PBE)。     

Synthesis of novel asymmetric dendritic‐linear‐dendritic block copolymers via “living” anionic polymerization of ethylene oxide initiated by dendritic macroinitiators

The first synthesis of asymmetric dendritic‐linear‐dendritic ABC block copolymers, that contain a linear B block and dissimilar A and C dendritic fragments is reported. Third generation poly(benzyl ether) monodendrons having benzyl alcohol moiety at their “focal” point were activated by quantitative titration with organometallic anions and the resulting alkoxides were used as initiators in the “living” ring‐opening polymerization of ethylene oxide. The reaction proceeded in controlled fashion at 40–50 °C affording linear‐dendritic AB block copolymers with predictable molecular weights (M_w = 6000–13,000) and narrow molecular weight distributions (M_w/M_n = 1.02–1.04). The propagation process was monitored by size‐exclusion chromatography with multiple detection. The resulting “living” copolymers were terminated by reaction either with HCl/tetrahydrofuran or with a reactive monodendron that differed from the initiating dendron not only in size, but also in chemical composition. The asymmetric triblock copolymers follow a peculiar structure‐induced self‐assembly pattern in block‐selective solvents as evidenced by size‐exclusion chromatography in combination with multi‐angle light scattering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5136–5148, 2007     

Controlled ring-opening polymerization of cyclic carbonates and lactones by an activated monomer mechanism

This article reviews recent topics in the controlled synthesis of polycarbonates and polylactones with small polydispersity indices by activated monomer cationic ring-opening polymerizations, especially with new initiator systems, such as alcohol/protonic acid and boron alkoxide/protonic acid. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2190–2198, 2002     

Anionic ring-opening polymerization behavior of trans-cyclohexene carbonate using metal tert-butoxides: Construction of living anionic ring-opening polymerization by lithium tert-butoxide

Anionic ring-opening polymerization (ROP) behavior of trans-cyclohexene carbonate (CHC) using metal alkoxides as initiators was investigated. As a result, lithium tert-butoxide-initiated ROP of CHC with a high-monomer concentration (10 M) at low temperature (−15 to −10°C) proceeded to afford a poly(trans-cyclohexene carbonate) (PCHC) without undesired side reactions such as mainly backbiting. The suppression of side reactions enables the control of the molecular weight (M_n = 2400–6100) of PCHC with low molar-mass dispersity values (M_w/M_n = 1.16–1.22). Furthermore, by increasing the feed ratio of the monomer to the initiator, the molecular weight increases proportionally, indicating a controllable polymerization. The results of a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis, a kinetic study, and a chain extension experiment suggested a living nature of this ROP using lithium tert-butoxide.     

Novel synthesis of rod‐coil block copolymers by combination of coordination polymerization and ATRP

Combination of coordination polymerization and atom transfer radical polymerization (ATRP) was applied to a novel synthesis of rod‐coil block copolymers. The procedure included the following steps: (1) monoesterification reaction of ethylene glycol with 2‐bromoisobutyryl bromide yielded a α‐bromo, ω‐hydroxy bifunctional initiator, (2) CpTiCl₃ (bifunctional initiator) catalyst was prepared from a mixture of trichlorocyclopentadienyl titanium (CpTiCl₃) and bifunctional initiator. Coordination polymerization of n‐butyl isocyanate initiated by such catalyst provided a well‐defined macroinitiator, poly(n‐butyl isocyanate)‐Br (PBIC‐Br), and (3) ATRP method of vinyl monomers using PBIC‐Br provided rod (PBIC)‐coil block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4037–4042, 2007     

A TEMPO-mediated “living” free-radical approach to ABA triblock dendritic linear hybrid copolymers

Dumbbell-shaped ABA triblock copolymers composed of benzyl ether dendrons and polystyrene as the A and B blocks, respectively, were prepared using 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) -mediated “living” free-radical polymerization. A new bis-dendritic unimolecular initiator, compound 3, was employed to study the efficiency of ABA triblock formation under standard TEMPO-mediated polymerization conditions. By this design, the central B block of the ABA triblock copolymer was grown into the bis-dendritic unimolecular initiator. The ABA triblock copolymer products were separated from their by-products, AB diblock copolymers, by column chromatography on silica gel. The isolated copolymers were characterized using gel permeation chromatography and proton nuclear magnetic resonance spectroscopy as complimentary techniques. That the dendritic-linear AB diblock copolymer was obtained in a mixture with ABA triblock material indicates that TEMPO-terminated dendron counter-radical 5 is an imperfect mediator of this free-radical polymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3748–3755, 1999     

Precise synthesis of olefin block copolymers using a syndiospecific living polymerization system

This feature article summarizes the synthesis of novel olefin block copolymers using fast syndiospecific living homo- and copolymerization of propylene, higher 1-alkene, and norbornene with ansa-fluorenylamidodimethyltitaniumbased catalyst according to the authors’ recent results. The catalytic synthesis of monodisperse polyolefin and olefin block copolymer was also described using this living system.     

Synthesis of block and graft copolymers of styrene by raft polymerization,using dodecyl‐based trithiocarbonates as initiators and chain transfer agents

A series of dodecyl‐based monofunctional trithiocarbonate chain transfer agents (CTAs) were successfully synthesized, toward the reversible addition‐fragmentations chain transfer (RAFT) polymerization of styrene. The CTAs were used as initiators for RAFT polymerization, in the absence of the conventional free radical initiator, at higher temperature. Polystyrene (PS) of narrow polydispersity index (PDI) is synthesized. Subsequently, poly(styrene‐b‐benzyl methacrylate) diblock and poly(styrene‐b‐benzyl methacrylate‐b‐2‐vinyl pyridine) triblock copolymers were synthesized from the PS macro‐RAFT agent by simply heating with the second and third monomer, respectively. These experiments suggest that it should be possible to control the RAFT polymerization initiated by a CTA through the adjustment of the temperature of polymerization in such manner that initiation is tailored to proceed at faster rate (at higher temperature) in comparison to propagation (lower temperature). For the specific CTAs studied in this work, the polymerization rate of styrene was high in the case of the reinitiating cyano (CN)‐substituted group (R group) compared to the other groups studied. The results further show that 4‐cyano pentanoic acid group is superior to the other R groups used for the RAFT polymerization of styrene, especially based on the polydispersity at a given conversion as well as the variation in the expected and experimental number‐average‐molecular weights. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of amphiphilic star block copolymers via diethyldithiocarbamate‐mediated living radical polymerization

(AB)_f star block copolymers were synthesized by the radical polymerization of a poly(t‐butyl acrylate)‐block‐poly(methyl methacrylate) diblock macroinitiator with ethylene glycol dimethacrylate in methanol under UV irradiation. Diblock macroinitiators were prepared by diethyldithiocarbamate‐mediated sequential living radical copolymerization initiated by (4‐cyano‐4‐diethyldithiocarbamyl)pentanoic acid under UV irradiation. The arm number (f) was controlled by the variation of the initial concentration of the diblock initiator. It was found from light scattering data that such star block copolymers (f ≥ 344) not only took a spherical shape but also formed a single molecule in solution. Subsequently, we derived amphiphilic [arm: poly(acrylic acid)‐block‐poly(methyl methacrylate)] star block copolymers by the hydrolysis of poly(t‐butyl acrylate) blocks. These amphiphilic star block copolymers were soluble in water because the external blocks were composed of hydrophilic poly(acrylic acid) chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3321–3327, 2006     

Synthesis and characterization of graft copolymers based on polyepichlorohydrin via reversible addition-fragmentation chain transfer polymerization

In this study, synthesis of poly(epichlorohydrin-g-methyl methacrylate) graft copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization was reported. For this purpose, epichlorohydrin was polymerized by using HNO₃ via cationic ring-opening mechanism. A RAFT macroinitiator (macro-RAFT agent) was obtained by the reaction of potassium ethyl xanthogenate and polyepichlorohydrin. The graft copolymers were synthesized using macro-RAFT agent as initiator and methyl methacrylate as monomer. The synthesis of graft copolymers was conducted by changing the time of polymerization and the amount of monomer-initiator concentration that affect the RAFT polymerization. The effects of these parameters on polymerization were evaluated via various analyses. The characterization of the products was determined using ¹H-nuclear magnetic resonance (¹H-NMR), Fourier-transform infrared spectroscopy, gel-permeation chromatography, thermogravimetric analysis, elemental analysis, and fractional precipitation techniques. The block lengths of the graft copolymers were calculated by using ¹H-NMR spectrum. It was observed that the block length could be altered by varying the monomer and initiator concentrations.     

Controlled synthesis of amphiphilic block copolymers with pendant glucose residues by living cationic polymerization

Amphiphilic block copolymers of vinyl ethers (VEs) of the type —[CH₂CH(OCH₂CH₂OR)]_m—[CH₂CH(OiBu)]_n—were synthesized by living cationic polymerization, where R is a D-glucose residue, and m and n are the degrees of polymerization (m = 20–50; n = 11–89). To obtain them, sequential living block copolymerization of isobutyl vinyl ether (IBVE) and the vinyl ether carrying 1,2:5,6-diisopropylidene-D -glucose residue was conducted by using the HCl adduct of IBVE, CH₃CH(OiBu)Cl, as initiator in conjunction with zinc iodide. These precursor block copolymers had a narrow molecular weight distribution (M̄_w/M̄_n ∼ 1.1) and a controlled composition. Treatment of them with a trifluoroacetic acid/water mixture led to the target amphiphiles. The solubility of the amphiphilic block copolymers in various solvents depended strongly on composition or the m/n ratio. Their solvent-cast thin films were observed, under a transmission electron microscope, to exhibit various microphase-separated surface morphologies such as spheres, cylinders, and lamellae, depending on composition. © 1997 John Wiley & Sons, Inc.     

Amphiphilic block copolymers by a combination of anionic polymerization and selective post-polymerization functionalization

Anionic polymerization is the oldest known living/controlled polymerization methodology that leads to well defined macromolecules. It has been also used, with considerable success, for the synthesis of amphiphilic block copolymers (AmBC), a class of functional copolymers having interesting self-assembling properties and high potential for applications in various technological fields. The use of mild and effective post-polymerization functionalization/chemical modification reactions on block copolymers has substantially increased the synthetic capabilities of anionic polymerization methodologies, toward the creation of a variety of AmBC. In this feature article we review work done on these directions in the last ten years. Some perspectives and future work on this particular field of polymer science are also discussed.     

Sequential photodecomposition of bisacylgermane type photoinitiator: Synthesis of block copolymers by combination of free radical promoted cationic and free radical polymerization mechanisms

A block copolymer of cyclohexene oxide (CHO) and styrene (St) was prepared by using bifunctional visible light photoinitiator dibenzoyldiethylgermane (DBDEG) via a two‐step procedure. The bifunctionality of the photoinitiator pertains to the sequential photodecomposition of DBDEG through acyl germane bonds. In the first step, photoinitiated free radical promoted cationic polymerization of CHO using DBDEG in the presence of diphenyliodonium hexafluorophosphate (Ph₂I⁺PF) was carried out to yield polymers with photoactive monobenzoyl germane end groups. These poly(cyclohexene oxide) (PCHO) prepolymers were used to induce photoinitiated free radical polymerization of styrene (St) resulting in the formation of poly(cyclohexene oxide‐block‐styrene) (P(CHO‐b‐St)). Successful blocking has been confirmed by a strong change in the molecular weight of the prepolymer and the block copolymer as well as NMR, IR, and DSC spectral measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4793–4799, 2009