Synthesis of photocleavable poly(methyl methacrylate‐block‐d‐lactide) via atom‐transfer radical polymerization and ring‐opening polymerization

The synthesis and characterization of a photocleavable block copolymer containing an ortho‐nitrobenzyl (ONB) linker between poly(methyl methacrylate) and poly(d ‐lactide) blocks is presented here. The block copolymers were synthesized via atom transfer radical polymerization (ATRP) of MMA followed by ring‐opening polymerization (ROP) of d ‐Lactide and ROP of d ‐lactide followed by ATRP of MMA from a difunctional photoresponsive ONB initiator, respectively. The challenges and limitations during synthesis of the photocleavable block copolymers using the difunctional photoresponsive ONB initiator are discussed. The photocleavage of the copolymers occurs under mild conditions by simple irradiation with 302 nm wavelength UV light (Relative intensity at 7.6 cm: 1500 μW/cm²) for several hours. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4309–4316     

Peptide block copolymers by N‐carboxyanhydride ring‐opening polymerization and atom transfer radical polymerization: The effect of amide macroinitiators

The synthesis of polypeptide‐containing block copolymers combining N‐carboxyanhydride (NCA) ring‐opening polymerization and atom transfer radical polymerization (ATRP) was investigated. An amide initiator comprising an amine function for the NCA polymerization and an activated bromide for ATRP was used. Well‐defined polypeptide macroinitiators were obtained from γ‐benzyl‐L ‐glutamate NCA, O‐benzyl‐serine NCA, and N‐benzyloxy‐L ‐lysine. Subsequent ATRP macroinitiation from the polypeptides resulted in higher than expected molecular weights. Analysis of the reaction products and model reactions confirmed that this is due to the high frequency of termination reactions by disproportionation in the initial phase of the ATRP, which is inherent in the amide initiator structure. In some cases selective precipitation could be applied to remove unreacted macroinitiator to yield well‐defined block copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Combining atom‐transfer radical polymerization and ring‐opening polymerization through bifunctional initiators derived from hydroxy benzyl alcohol—Preparation and characterization of initiators,macroinitiators, and block copolymers

A simple, one‐step procedure has been developed for the preparation of bifunctional initiators capable of polymerizing monomers suitable for atom‐transfer radical polymerization (ATRP) and ring‐opening polymerization (ROP). These bifunctional initiators were employed for making narrow disperse poly(styrene) macroinitiators, which were subsequently used for the ROP of various lactides to yield poly(styrene‐block‐lactide) copolymers. Thermogravimetric analysis (TGA) of these block copolymers are interesting in that it shows a two‐step degradation curve with the first step corresponding to the degradation of poly(lactide) segment and the second step associated with the poly(styrene) segment of the block copolymer. This nature of the block copolymer makes it possible to estimate the block copolymer content by TGA in addition to the ¹H NMR spectroscopic analysis. Thus, this study for the first time highlights the possibility of making porous materials by thermal means which are otherwise obtained by base hydrolysis. The bifunctional initiators were prepared by the esterification of 3‐hydroxy, 4‐hydroxy, and 3,5‐dihydroxy benzyl alcohols with α‐bromoisobutyryl bromide and 2‐bromobutyryl bromide. A mixture of products was obtained, which were purified by column chromatography. The esterified benzyl alcohols were employed in the polymerization of styrene under copper (Cu)‐catalyzed ATRP conditions to yield macroinitiators with low polydispersity. These macroinitiators were subsequently used in the ROP of L ‐, DL ‐, and mixture of lactides. The formation of block copolymers was confirmed by gel permeation chromatography (GPC), spectroscopic and thermal characterizations. The molecular weight of the block copolymers was always higher than the macroinitiator, and the GPC chromatogram was symmetrical indicating the uniform initiation of ROP by the macroinitiators. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 102–116, 2008     

Synthesis,characterization, and micellization of an epoxy‐based amphiphilic diblock copolymer of ϵ‐caprolactone and glycidyl methacrylate by enzymatic ring‐opening polymerization and atom transfer radical polymerization

Amphiphilic diblock copolymer polycaprolactone‐block‐poly(glycidyl methacrylate) (PCL‐b‐PGMA) was synthesized via enzymatic ring‐opening polymerization (eROP) and atom transfer radical polymerization (ATRP). Methanol first initiated eROP of ?‐caprolactone (?‐CL) in the presence of biocatalyst Novozyme‐435 under anhydrous conditions. The resulting monohydroxyl‐terminated polycaprolactone (PCL–OH) was subsequently converted to a bromine‐ended macroinitiator (PCL–Br) for ATRP by esterification with α‐bromopropionyl bromide. PCL‐b‐PGMA diblock copolymers were synthesized in a subsequent ATRP of glycidyl methacrylate (GMA). A kinetic analysis of ATRP indicated a living/controlled radical process. The macromolecular structures were characterized for PCL–OH, PCL–Br, and the block copolymers by means of nuclear magnetic resonance, gel permeation chromatography, and infrared spectroscopy. Differential scanning calorimetry and wide‐angle X‐ray diffraction analyses indicated that the copolymer composition (?‐CL/GMA) had a great influence on the thermal properties. The well‐defined, amphiphilic diblock copolymer PCL‐b‐PGMA self‐assembled into nanoscale micelles in aqueous solutions, as investigated by dynamic light scattering and transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5037–5049, 2007     

Synthesis,characterization, and thermal properties of dendrimer‐star,block‐comb copolymers by ring‐opening polymerization and atom transfer radical polymerization

Novel and well‐defined dendrimer‐star, block‐comb polymers were successfully achieved by the combination of living ring‐opening polymerization and atom transfer radical polymerization on the basis of a dendrimer polyester. Star‐shaped dendrimer poly(?‐caprolactone)s were synthesized by the bulk polymerization of ?‐caprolactone with a dendrimer initiator and tin 2‐ethylhexanoate as a catalyst. The molecular weights of the dendrimer poly(?‐caprolactone)s increased linearly with an increase in the monomer. The dendrimer poly(?‐caprolactone)s were converted into macroinitiators via esterification with 2‐bromopropionyl bromide. The star‐block copolymer dendrimer poly(?‐caprolactone)‐block‐poly(2‐hydroxyethyl methacrylate) was obtained by the atom transfer radical polymerization of 2‐hydroxyethyl methacrylate. The molecular weights of these copolymers were adjusted by the variation of the monomer conversion. Then, dendrimer‐star, block‐comb copolymers were prepared with poly(L ‐lactide) blocks grafted from poly(2‐hydroxyethyl methacrylate) blocks by the ring‐opening polymerization of L ‐lactide. The unique and well‐defined structure of these copolymers presented thermal properties that were different from those of linear poly(?‐caprolactone). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6575–6586, 2006     

Organic/inorganic hybrid nanospheres coated with palladium/P4VP shells from surface‐initiated atom transfer radical polymerization

Crosslinked poly(4‐vinylbenzyl chloride) (PVBC) nanospheres of about 160 nm were first synthesized by emulsion copolymerization of 4‐vinylbenzyl chloride (VBC) in the presence of a crosslinking agent, p‐divinylbenzene. Subsequent modification of the nanosphere surfaces via surface‐initiated atom transfer radical polymerization of 4‐vinylpyridine, using the VBC units of PVBC on the nanosphere surface as the macroinitiators, produced a well‐defined and covalently tethered poly(4‐vinylpyridine) (P4VP) shells of 24–27 nm in thickness. Activation of the P4VP shells in a PdCl₂ solution, followed by reactions with CO or H₂S gas, gave rise to the corresponding P4VP composite shells containing densely dispersed palladium metal or palladium sulfide nanoparticles. The chemical composition of the nanosphere surfaces at various stages of surface modification was characterized by X‐ray photoelectron spectroscopy. Field emission scanning electron microscopy and transmission electron microscopy were used to characterize the morphology of the organic/inorganic hybrid nanospheres coated with palladium/P4VP shells. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2119–2131, 2008     

Block and random copolymers as surfactants for dispersion polymerization. I. Synthesis via atom transfer radical polymerization and ring‐opening polymerization

Atom transfer radical polymerization (ATRP) and ring‐opening polymerization (ROP) were combined to synthesize poly(?‐caprolactone‐co‐octadecyl methacrylate‐co‐dimethylaminoethyl methacrylate) copolymers possessing a triblock or random block structure. Various synthetic pathways (sequential or simultaneous approaches) were investigated for the synthesis of both copolymers. For the preparation of these copolymers, an initiator with dual functionality for ATRP/anionic ring‐opening polymerization, 2‐hydroxyethyl 2‐bromoisobutyrate, was used. Copolymers were prepared with good structural control and low polydispersities (weight‐average molecular weight/number‐average molecular weight < 1.2), but one limitation was identified: the dimethylaminoethyl methacrylate (DMAEMA) block had to be synthesized after the ?‐caprolactone block. ROP could not proceed in the presence of DMAEMA because the complexation of the amine groups in poly(dimethylaminoethyl methacrylate) deactivated tin(II) hexanoate, which was used as a catalyst for ROP. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1498–1510, 2005     

Synthesis of diblock copolymers by combination of organocatalyzed ring‐opening polymerization and atom transfer radical polymerization using trichloroethanol as a bifunctional initiator

This study reports an application of trichloroethanol (TCE) as a bifunctional initiator for the synthesis of block copolymers (BCPs) by organocatalyzed ring‐opening polymerization (OROP) and atom transfer radical polymerization (ATRP). TCE was employed to synthesize a low dispersity poly (valerolactone) macroinitiator, which was subsequently used for the ATRP of tert‐butyl methacrylate. While it is known that TCE can serve as an initiator in ATRP, the ability to induce polymerization under OROP is reported for the first time. The formation of well‐defined BCPs was confirmed by gel permeation chromatography and ¹H NMR. Computational studies were performed to obtain a molecular‐level understanding of the ring‐opening polymerization mechanism involving TCE as initiator. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 563–569     

Synthesis of poly(tetrahydrofuran)‐b‐polystyrene block copolymers from dual initiators for cationic ring‐opening polymerization and atom transfer radical polymerization

A dual initiator (4‐hydroxy‐butyl‐2‐bromoisobutyrate), that is, a molecule containing two functional groups capable of initiating two polymerizations occurring by different mechanisms, has been prepared. It has been used for the sequential two‐step synthesis of well‐defined block copolymers of polystyrene (PS) and poly(tetrahydrofuran) (PTHF) by atom transfer radical polymerization (ATRP) and cationic ring‐opening polymerization (CROP). This dual initiator contains a bromoisobutyrate group, which is an efficient initiator for the ATRP of styrene in combination with the Cu(0)/Cu(II)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalyst system. In this way, PS with hydroxyl groups (PS‐OH) is formed. The in situ reaction of the hydroxyl groups originating from the dual initiator with trifluoromethane sulfonic anhydride gives a triflate ester initiating group for the CROP of tetrahydrofuran (THF), leading to PTHF with a tertiary bromide end group (PTHF‐Br). PS‐OH and PTHF‐Br homopolymers have been applied as macroinitiators for the CROP of THF and the ATRP of styrene, respectively. PS‐OH, used as a macroinitiator, results in a mixture of the block copolymer and remaining macroinitiator. With PTHF‐Br as a macroinitiator for the ATRP of styrene, well‐defined PTHF‐b‐PS block copolymers can be prepared. The efficiency of PS‐OH or PTHF‐Br as a macroinitiator has been investigated with matrix‐assisted laser desorption/ionization time‐of‐flight spectroscopy, gel permeation chromatography, and NMR. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3206–3217, 2003     

Self‐assembly of star‐shaped polystyrene‐block‐polypeptide copolymers synthesized by the combination of atom transfer radical polymerization and ring‐opening living polymerization of α‐amino acid‐N‐carboxyanhydrides

The self‐assembling nature and phase‐transition behavior of a novel class of triarm, star‐shaped polymer–peptide block copolymers synthesized by the combination of atom transfer radical polymerization and living ring‐opening polymerization of α‐amino acid‐N‐carboxyanhydride are demonstrated. The two‐step synthesis strategy adopted here allows incorporating polypeptides into the usual synthetic polymers via an amido–amidate nickelacycle intermediate, which is used as the macroinitiator for the growth of poly(γ‐benzyl‐L ‐glutamate). The characterization data are reported from analyses using gel permeation chromatography and infrared, ¹H NMR, and ¹³C NMR spectroscopy. This synthetic scheme grants a facile way to prepare a wide range of polymer–peptide architectures with perfect microstructure control, preventing the formation of homopolypeptide contaminants. Studies regarding the supramolecular organization and phase‐transition behavior of this class of polymer‐block‐polypeptide copolymers have been accomplished with X‐ray diffraction, infrared spectroscopy, and thermal analyses. The conformational change of the peptide segment in the block copolymer has been investigated with variable‐temperature infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2774–2783, 2006     

Controlled/living polymerization of 2‐(diethylamino)ethyl methacrylate and its block copolymer with tert‐butyl methacrylate by atom transfer radical polymerization

Polymerization of 2‐(diethylamino)ethyl methacrylate (DEAEMA) via homogeneous atom transfer radical polymerization under various reaction conditions is described. The effects of the initiators and solvents were examined. With 1,1,4,7,10,10‐hexamethyl triethylenetetramine/copper(I) chloride/p‐toluenesulfonyl chloride as the ligand/catalyst/initiator system in methanol, poly(DEAEMA) with a polydispersity index as low as 1.07 was synthesized. Kinetic studies demonstrated the polymerization was very well controlled and exhibited the living characteristic of the process. Well‐defined block copolymers of DEAEMA and tert‐butyl methacrylate (tBMA) were successfully synthesized. The copolymers could be synthesized with equally good results by starting with either p(DEAEMA) or p(tBMA) as the macroinitiators. However, only the macroinitiators terminated with chlorine should be used. The corresponding macroinitiators with bromine as a transferable group did not yield well‐defined copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2688–2695, 2003     

Functionalization of three‐dimensionally ordered macroporous cross‐linked polystyrene by atom‐transfer radical polymerization of hydroxyethyl methacrylate and subsequent derivatization

The surface‐initiated atom‐transfer radical polymerization (ATRP) technique was applied to the graft polymerization of 2‐hydroxyethyl methacrylate (HEMA) from three‐dimensionally ordered macroporous crosslinked polystyrene (3DOM CLPS) on which the initiator (benzyl chloride) was immobilized onto the pore wall of 3DOM CLPS by chloromethylation of benzene ring. By the adjustment of the monomer concentration or graft polymerization time, the thickness of grafted polymer layers can be controlled. FTIR analysis confirms that the graft polymerization of HEMA via ATRP had been taken place at the pore wall of 3DOM CLPS. SEM images of PHEMA‐grafted 3DOM CLPS show that the ordered structure is well preserved after graft polymerization and the grafted layers are dense and homogeneous. The maximum thickness of grafted layer is up to 35 nm and the corresponding percent weight increase is 102.8% in this study. Moreover, the PHEMA layers were further functionalized in high yield via their reactive hydroxyl groups under gentle condition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7950–7959, 2008     

Synthesis of well‐defined amphiphilic polymethylene‐b‐poly(ε‐caprolactone)‐b‐poly(acrylic acid) triblock copolymer via a combination of polyhomologation,ring‐opening polymerization,and atom transfer radical polymerization

Well‐defined amphiphilic polymethylene‐b‐poly(ε‐caprolactone)‐b‐poly(acrylic acid) (PM‐b‐PCL‐b‐PAA) triblock copolymers were synthesized via a combination of polyhomologation, ring‐opening polymerization (ROP), and atom transfer radical polymerization (ATRP). First, hydroxyl‐terminated polymethylenes (PM‐OH; M_n = 1100 g mol^?1; M_w/M_n = 1.09) were produced by polyhomologation followed by oxidation. Then, the PM‐b‐PCL (M_n = 10,000 g mol^?1; M_w/M_n = 1.27) diblock copolymers were synthesized via ROP of ε‐caprolactone using PM‐OH as macroinitiator and stannous octanoate (Sn(Oct)₂) as a catalyst. Subsequently, the macroinitiator transformed from PM‐b‐PCL in high conversion initiated ATRPs of tert‐butyl acrylate (^tBA) to construct PM‐b‐PCL‐b‐P^tBA triblock copolymers (M_n = 11,000–14,000 g mol^?1; M_w/M_n = 1.24–1.26). Finally, the PM‐b‐PCL‐b‐PAA triblock copolymers were obtained via the hydrolysis of the P^tBA segment in PM‐b‐PCL‐b‐P^tBA triblock copolymers. The chain structures of all the polymers were characterized by gel permeation chromatography, proton nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Porous films of such triblock copolymers were fabricated by static breath‐figure method and observed by scanning electron microscope. The aggregates of PM‐b‐PCL‐b‐PAA triblock copolymer were studied by transmission electron microscope. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of stable “gold nanoparticle–polymeric micelle” conjugates: A new class of star “molecular chimera” that self‐assemble into linear arrays of spherical micelles

Stable and aggregation‐free “gold nanoparticle–polymeric micelle” conjugates were prepared using a new and simple protocol enabled by the hydrogen bonding between surface‐capping ligands and polymeric micelles. Individual gold nanoparticles were initially capped using a phosphatidylthio–ethanol lipid and further conjugated with a star poly(styrene‐block‐glutamic acid) copolymer micelle using a one‐pot preparation method. The morphology and stability of these gold–polymer conjugates were characterized using transmission electron microscopy (TEM) and UV–vis spectroscopy. The self‐assembly of this class of polymer‐b‐polypeptide in aqueous an medium to form spherical micelles and further their intermicelle reorganization to form necklace‐like chains was also investigated. TEM and laser light scattering techniques were employed to study the morphology and size of these micelles. Polymeric micelles were formed with diameters in the range of 65–75 nm, and supermicellular patterns were observed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3570–3579, 2007     

Synthesis and self‐assembling of poly(N‐isopropylacrylamide‐block‐poly(L‐lactide)‐block‐poly(N‐isopropylacrylamide) triblock copolymers prepared by combination of ring‐opening polymerization and atom transfer radical polymerization

Novel thermo‐responsive poly(N‐isopropylacrylamide)‐block‐poly(l ‐lactide)‐block‐poly(N‐isopropylacylamide) (PNIPAAm‐b‐PLLA‐b‐PNIPAAm) triblock copolymers were successfully prepared by atom transfer radical polymerization of NIPAAm with Br‐PLLA‐Br macroinitiator, using a CuCl/tris(2‐dimethylaminoethyl) amine (Me₆TREN) complex as catalyst at 25 °C in a N,N‐dimethylformamide/water mixture. The molecular weight of the copolymers ranges from 18,000 to 38,000 g mol^?1, and the dispersity from 1.10 to 1.28. Micelles are formed by self‐assembly of copolymers in aqueous medium at room temperature, as evidenced by ¹H NMR, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The critical micelle concentration determined by fluorescence spectroscopy ranges from 0.0077 to 0.016 mg mL^?1. ¹H NMR analysis in selective solvents confirmed the core‐shell structure of micelles. The copolymers exhibit a lower critical solution temperature (LCST) between 32.1 and 32.8 °C. The micelles are spherical in shape with a mean diameter between 31.4 and 83.3 nm, as determined by TEM and DLS. When the temperature is raised above the LCST, micelle size increases at high copolymer concentrations due to aggregation. In contrast, at low copolymer concentrations, decrease of micelle size is observed due to collapse of PNIPAAm chains. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3274–3283     

Synthesis of a novel liquid crystal rod–coil star block copolymer consisting of poly(methyl methacrylate) and poly{2,5‐bis[(4‐methoxy‐phenyl)oxycarbonyl] styrene} via atom transfer radical polymerization

A bromine capped star‐shaped poly(methyl methacrylate) (S‐PMMA‐Br) was synthesized with CuBr/sparteine/PT‐Br as a catalyst and initiator to polymerize methyl methacrylate (MMA) according to atom transfer radical polymerization (ATRP). Then, with S‐PMMA‐Br as a macroinitiator, a series of new liquid crystal rod–coil star block copolymers with different molecular weights and low polydispersity were obtained by this method. The block architecture {coil‐conformation of the MMA segment and rigid‐rod conformation of 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl] styrene segment} of the four‐armed rod–coil star block copolymers were characterized by ¹H NMR. The liquid‐crystalline behavior of these copolymers was studied by differential scanning calorimetry and polarized optical microscopy. We found that the liquid‐crystalline behavior depends on the molecular weight of the rigid segment; only the four‐armed rod–coil star block copolymers with each arm's M_n,_GPC of the rigid block beyond 0.91 × 10⁴ g/mol could form liquid‐crystalline phases above the glass‐transition temperature of the rigid block. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 733–741, 2005