Synthesis of carbosilane block copolymers by means of a living anionic polymerization of 1,1-diethylsilacyclobutane

Block polymerization of 1,1-diethylsilacyclobutane with styrene derivatives and methacrylate derivatives was investigated. Sequential addition of styrene to a living poly(1,1-diethylsilabutane), which was prepared from phenyllithium and 1,1-diethylsilacyclobutane in THF–hexane at −48°C, gave poly(1,1-diethylsilabutane)-b-polystyrene. Similarly, addition of 4-(tert-butyldimethylsiloxy)styrene to the living poly(1,1-diethylsilabutane) provided poly(1,1-diethylsilabutane)-b-poly(4-(tert-butyldimethylsiloxy)styrene). Poly(1,1-diethylsilabutane)-b-poly(methyl methacrylate) was obtained by treatment of living poly(1,1-diethylsilabutane) with 1,1-diphenylethylene followed by an addition of methyl methacrylate. Poly(1,1-diethylsilabutane)-b-poly(2-(tert-butyldimethylsiloxy)ethyl methacrylate) was also synthesized by adding 2-(tert-butyldimethylsiloxy)ethyl methacrylate to the living poly(1,1-diethylsilabutane) which was end-capped with 1,1-diphenylethylene in the presence of lithium chloride. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2699–2706, 1998     

Cisplatin-loaded polymer/magnetite composite nanoparticles as multifunctional therapeutic nanomedicine

Multifunctional nanocarriers with multilayer core-shell architecture were prepared by coating superparamagnetic Fe3O4 nanoparticles with diblock copolymer folate-poly（ethylene glycol）-b-poly（glycerol monomethacrylate） （FA-PEG-b- PGMA）, and triblock copolymer methoxy poly（ethylene glycol）-b-poly（2-（dimethylamino） ethyl methacrylate）-b- poly（glycerol monomethacrylate） （MPEG-b-PDMA-b-PGMA）. The PGMA segment was attached to the surfaces of Fe304 nanoparticles, and the outer PEG shell imparted biocompatibility. In addition, folate was conjugated onto the surfaces of the nanocarriers. Cisplatin was then loaded into the nanocarrier by coordination between the Pt atom in cisplatin and the amine groups in the inner shell of the multilayer architecture. The loaded cisplatin showed pH-responsive release： slower release at pH 7.4 （i.e. mimicking the blood environment） and faster release at more acidic pH （i.e. mimicking endosome/lysosome conditions）. All of the cisplatin-loaded nanoparticles showed concentration-dependent cytotoxicity in HeLa cells. However, the folate-conjugated cisplatin-loaded carriers exhibited higher cytotoxicity in HeLa cells than non-folate conjugated cisplatin-loaded carriers.     

Epitaxial single crystal surface patterning and study of physical and chemical environmental effects on crystal growth

For designing the responsive polymer brushes, and tuning the local and chemical surface responses to the external stimuli, the epitaxial single crystals were patterned by combination of bared surfaces of poly(ethylene glycol) (PEG) substrate, polymer homo-brushes constructed from poly(ethylene glycol)-b-polystyrene (PEG-b-PS) as well as poly(ethylene glycol)-b-poly(methyl methacrylate) (PEG-b-PMMA), and PEG-b-PS/PEG-b-PMMA mixed-brush channels. To achieve this target, various single crystals and epitaxial structures grown from dilute solutions through self-seeding approach were utilized as seeds to fabricate the next channels. The characteristics and morphologies of different channels were detectable by atomic force microscopy (AFM). The influence of chemical (solvent quality and interaction of substrate with different brushes) and physical (presence of brushes from another type in their vicinity) environments on crystallization was studied. Due to the effect of chemical environment, the PS brushes hampered the growth of PEG crystals at M _n ^PS?=?10,000 g/mol. However, the PMMA brushes allowed PEG crystals to grow completely at M _n ^PMMA =13,100 g/mol, and indicated their hindrance at higher molecular weights (here, M _n ^PMMA?=?17,100 g/mol). It was feasible to neutralize the mentioned hindrance through fabricating the channels with brushes having the highest hindrance (M _n ^PS?=?14,800 g/mol and M _n ^PMMA?=?17,100 g/mol), and altering the physical environment from homo- to mixed-brush morphology. The characteristics (thickness, tethering density, and domain size) of developed channels from a certain material, in all arrangements and in various channels were in good agreement with those of corresponding non-epitaxial single crystals grown under the same conditions.     

Facile synthesis of thermoresponsive block copolymers of N-isopropylacrylamide using heterogeneous controlled/living nitroxide-mediated polymerizations in supercritical carbon dioxide

A new protocol for preparation of thermoresponsive poly(N-isopropylacrylamide, NIPAM) containing block copolymers is described. It involves two successive heterogeneous controlled/living nitroxide-mediated polymerizations (NMPs) in supercritical carbon dioxide (scCO₂) using N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)]nitroxide (SG1), as the nitroxide. Precipitation NMPs give narrow dispersity macroinitiators (MIs), and a first report of the controlled/living polymerization of N,N-dimethylacrylamide (DMA) in scCO₂ is described. The MI is then used in an inverse suspension NMP of NIPAM in scCO₂ resulting in the efficient preparation of block copolymers containing DMA, tert-butyl acrylate and styrene. Aqueous cloud point temperature analysis for poly(DMA)-b-poly(NIPAM) and poly(acrylic acid)-b-poly(NIPAM) shows a significant dependence on poly(NIPAM) chain length for a given AB block copolymer.     

Combination of living anionic polymerization and ATRP via ��click�� chemistry as a versatile route to multiple responsive triblock terpolymers and corresponding hydrogels

A combination of anionic polymerization, atom transfer radical polymerization (ATRP) and ??click?? chemistry was used to construct trishydrophilic ABC triblock terpolymers composed of a pH-sensitive A block, a water-soluble B block and two different thermo-sensitive C blocks without any block sequence limitation problems. First, an azido end-functionalized poly(2-vinylpyridine)-block-poly(ethylene oxide) (P2VP-b-PEO-N₃) diblock copolymer was synthesized by anionic polymerization. In a second step, poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methacrylate) (POEGMA) were synthesized via ATRP using an alkyne functionalized initiator. The resulting polymers were attached to the P2VP-b-PEO-N₃ diblock copolymer using the 1,3-dipolar Huisgen cycloaddition (??click?? chemistry). For the ??click?? step, P2VP-b-PEO-N₃ diblock copolymers with either an azidoacetyl or a 2-azidoisobutyryl group were tested. In the latter case, however, a side reaction involving the cleavage of the formed ??click?? product via nucleophilic substitution occurred, preventing a permanent attachment of PDMAEMA or POEGMA to the P2VP-b-PEO-N₃ diblock copolymer. Finally, P2VP-b-PEO-b-POEGMA (with POEGMA=P(MEO₂MA-co-MEO_8.5MA)) and P2VP-b-PEO-b-PDMAEMA triblock terpolymers were successfully synthesized and used to construct stimuli-responsive hydrogels. A concentrated solution of P2VP₅₆-b-PEO₃₇₀-b-P[(MEO₂MA)₈₉-co-(MEO_8.5MA)₇] showed a gel?Csol?Cgel transition at pH?7 upon temperature increase, whereas in the case of P2VP₅₆-b-PEO₃₇₀-b-PDMAEMA₇₀, a gel?Csol or a weak gel?Cstrong gel transition was observed, depending on the applied pH. Finally, the addition of trivalent hexacyanocobaltate(III) ions to the P2VP₅₆-b-PEO₃₇₀-b-PDMAEMA₇₀ solution induced an upper critical solution temperature for the PDMAEMA block, which led to gel formation. This allows for the construction of light-sensitive hydrogels, utilizing the photo-aquation of hexacyanocobaltate(III) ions.     

Controlled radical polymerization of methacrylates of various structures in the presence of the AIBN-FeCl3-N,N-dimethylformamide catalytic system

The controlled radical polymerization of methyl methacrylate, 2-ethoxyethyl methacrylate, and tert-butyl methacrylate conducted via atom-transfer radical polymerization in the presence of the AIBN-FeCl₃· 6H₂O-N,N-dimethylformamide catalytic system is studied. For all the systems under study, the rate of reaction is first order with respect to the monomer concentration. The number-average molecular mass of the polymers linearly increases with conversion, and their polydispersity indexes are below 1.6. The rate of polymerization decreases in the following sequence: 2-ethoxyethyl methacrylate > methyl methacrylate > tert-butyl methacrylate. The presence of ω-terminal chlorine atoms in polymer macromolecules is confirmed by ¹H NMR spectroscopy and through the block copolymerization of methyl methacrylate with a poly(ethoxyethyl methacrylate)-based macroinitiator.     

Ion conductivity studies of blends of poly(methyl methacrylate)-g-poly(ethylene glycol) and poly(ethylene glycol) complexed with LiCF3 SO3

Polymer electrolytes which are adhesive, transparent, and stable to atmospheric moisture have been prepared by blending poly(methyl methacrylate)-g-poly(ethylene glycol) with poly(ethylene glycol)/LiCF₃ SO₃ complexes. The maximum ionic conductivities at room temperature were measured to be in the range of 10⁻⁴ to 10⁻⁵ s cm⁻¹. The clarity of the sample was improved as the graft degree increased for all the samples studied. The graft degree of poly(methyl methacrylate)-g-poly(ethylene glycol) was found to be important for the compatibility between the poly(methyl methacrylate) segments in poly(methyl methacrylate)-g-poly(ethylene glycol) and the added poly(ethylene glycol), and consequently, for the ion conductivity of the polymer electrolyte. These properties make them promising candidates for polymer electrolytes in electrochromic devices. © 1996 John Wiley & Sons, Inc.     

Thermal degradation of a heteroarm starlike polymer with fullerene C60 core

The mechanism of thermal degradation of a 12-arm starlike polymer with fullerene C₆₀ core and equal number of polystyrene and poly(tert-butyl methacrylate) arms was studied by thermal desorption mass spectrometry. Thermal characteristics of the heteroarm stars were compared with those of six-arm starlike fullerene-containing polystyrenes and linear poly(tert-butyl methacrylate).     

Synthesis of urethane—acrylic multi-block copolymers via electrochemically mediated ATRP

The electrochemically mediated atom transfer radical polymerisation (eATRP) of n-butyl acrylate was investigated under a variety of catalyst concentrations. Poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate) copolymers were prepared via electrochemically mediated atom transfer radical polymerisation (eATRP) using only 7 × 10^?6 mole % of Cu^II complex. The successful chain extension and formation of penta-block copolymers confirmed the living nature of the poly(alkyl acrylates) prepared by eATRP. In this work, the tri-block and penta-block urethane-acrylate copolymers were synthesised for the first time by using tertiary bromine-terminated polyurethane macro-initiators as transitional products reacting with n-butyl acrylate, and subsequently with tert-butyl acrylate in the presence of the Cu^IIBr₂/TPMA catalyst complex. The results of ¹H NMR spectral studies support the formation of tri-block poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate) copolymers, and penta-block poly(tert-butyl acrylate)-block-poly(n-butyl acrylate)-block-polyurethane-block-poly(n-butyl acrylate)-block-poly(tert-butyl acrylate) copolymers.     

Anionic polymerization of methyl methacrylate and tert-butyl acrylate initiated with the YCl3/lithium amide/nBuLi systems

The anionic polymerization of methyl methacrylate (MMA) was initiated with a mixture of lithium amide of various secondary amines and nBuLi in the presence of YCl₃, where an Y-ate complex was formed and an amide ligand on Y attacked MMA nucleophilically. In THF at −78 °C, PMMAs with narrow molecular weight distributions were obtained in high yields. The presence of a secondary amino group derived from the initiator at the polymer chain end was confirmed by MALDI-TOF-MS analyses. The initiating system using indoline as a secondary amine was effective for block copolymerization of MMA with tert-butyl acrylate (tBA), giving poly(MMA-b-tBA)s with narrow molecular weight distributions.     

Preparation of polyethylene block copolymers by a combination of postmetallocene catalysis of ethylene polymerization and atom transfer radical polymerization

The synthesis of block copolymers consisting of a polyethylene segment and either a poly(meth)acrylate or polystyrene segment was accomplished through the combination of postmetallocene-mediated ethylene polymerization and subsequent atom transfer radical polymerization. A vinyl-terminated polyethylene (number-average molecular weight = 1800, weight-average molecular weight/number-average molecular weight =1.70) was synthesized by the polymerization of ethylene with a phenoxyimine zirconium complex as a catalyst activated with methylalumoxane (MAO). This polyethylene was efficiently converted into an atom transfer radical polymerization macroinitiator by the addition of α-bromoisobutyric acid to the vinyl chain end, and the polyethylene macroinitiator was used for the atom transfer radical polymerization of n-butyl acrylate, methyl methacrylate, or styrene; this resulted in defined polyethylene-b-poly(n-butyl acrylate), polyethylene-b-poly(methyl methacrylate), and polyethylene-b-polystyrene block copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 496–504, 2004     

Synthesis of a photoactive gemini surfactant and its use in AGET ATRP miniemulsion polymerisation and UV curing

A novel photoactive gemini surfactant was easily synthesised in high yields. The multi-functional molecule can be used as a gemini surfactant, a benzophenone type photoinitiator, and as an ATRP initiator. Poly(methyl methacrylate) (PMMA) and poly(methyl methacrylate)-block-poly(allyl methacrylate) (PMMA-b-PAMA) were prepared using the photoactive gemini surfactant as an ATRP initiator under soap-free miniemulsion polymerisation conditions. Kinetic results of the miniemulsion polymerisation of methyl methacrylate (MMA) indicate that the reaction has controlled/living characteristics. UV curing was performed by irradiation of the linear PMMA-b-PAMA polymer, in which PMMA-b-PAMA containing a benzophenone moiety functioned as a macromolecular photoinitiator.     

Synthesis of graft copolyimides via controlled radical polymerization of methacrylates with a polyimide macroinitiator

The atom-transfer radical polymerization of methyl methacrylate and tert-butyl methacrylate with a polyimide multicenter macroinitiator in the presence of a CuCl-2,2′-bipyridine catalytic system is investigated. The kinetic features of the process, the molecular-weight characteristics of the formed side chains, and the post-polymerization of methyl methacrylate with graft polyimides containing polymethacrylate side chains are studied. The conditions of controlled polymerization yielding graft copolyimides with narrowly dispersed living poly(methyl methacrylate) or poly(tert-butyl methacrylate) side chains of variable lengths are determined.     

Nanoparticle directed domain orientation in thin films of asymmetric block copolymers

We investigated the thin film morphology of two different asymmetric block copolymers (BCP), polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and poly(n-pentyl methacrylate)-block-poly(methyl methacrylate) (PPMA-b-PMMA), loaded with pre-synthesized iron oxide nanoparticles (NP). The chemical composition of the BCP constituents determines the strength of the interaction between polymer chains and nanoparticles. In the case of NP/PS-b-P4VP system, the nanoparticles interact preferentially with the P4VP block and hence localize selectively in the P4VP cylindrical microdomains. However, for the NP/PPMA-b-PMMA system, the nanoparticles have no significant preference for the copolymer blocks and segregate at the polymer/substrate interface. Interestingly, this changes the effective substrate surface energy and hence leads to a remarkable change in domain orientation from parallel to perpendicular with respect to the substrate. These results clearly demonstrate the importance of both enthalpic and entropic factors which determine spatial distribution of NP in BCP films and influence domain orientation.     

The use of the DPE radical polymerization method for the synthesis of chromophore-labelled polymers and block copolymers

Two analogues of diphenylethene carrying phenanthrene (1-(9-phenanthryl)-1-phenylethene (PPE)) and anthracene (1-(2-anthryl)-1-phenylethene (APE)) units were used in radical polymerization of styrene (St) and methyl methacrylate (MMA) at 80 °C using AIBN as initiator. Because of the nature of the polymerization, the resulting polymers possess the corresponding chromophoric groups. Using the methodology of a DPE system, these labelled polymers were further used for the synthesis of block copolymers. In this way poly(methyl methacrylate)-b-poly(styrene) and poly(methyl methacrylate)-b-poly(acrylonitrile) with molar masses of 60,000-90,000 g/mol were synthesized. Incorporation of the chromophoric groups into both homo- and block copolymers was confirmed by spectral measurements.     

New Segmented Copolymers by Combination of Atom Transfer Radical Polymerization and Ring Opening Polymerization

Atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP) were combined to synthesize various polymers with various structures and composition. Poly(ε-caprolactone)-b-poly(n-octadecyl methacrylate), PCL-PODMA, was prepared using both sequential and simultaneous polymerization methods. Kinetic studies on the simultaneous process were performed to adjust the rate of both polymerizations. The influence of tin(II) 2-ethylhexanoate on ATRP was investigated, which led to development of new initiation methods for ATRP, i.e., activators (re)generated by electron transfer (AGET and ARGET). Additionally, block copolymers with two crystalizable blocks, poly(ε-caprolactone)-b-poly(n-butyl acrylate)-b-poly(n-octadecyl methacrylate), PCL-PBA-PODMA, block copolymers for potential surfactant applications poly(ε-caprolactone)-b-poly(n-octadecyl methacrylate-co-dimethylaminoethyl methacrylate), PCL-P(ODMA-co-DMAEMA), and a macromolecular brush, poly(hydroxyethyl methacrylate)-graft-poly(ε-caprolactone), PHEMA-graft-PCL, were prepared using combination of ATRP and ROP.     

Structure and supramolecular structures of star-shaped fullerene-containing heteroarm polymers in deuterotoluene

Self-organization of star-shaped polymers containing six PS arms and six polar polymer arms on a common C₆₀ branching center is studied by means of small-angle neutron scattering in deuterotoluene. The results are compared with the corresponding characteristics of six-arm star-shaped fullerene-containing PSs. It is shown that the incorporation of additional polar arms into a six-arm macromolecule leads to its compression due to an increase in the degree of coiling of polar chains in the nonpolar solvent. In solution, heteroarm stars give rise to supramolecular structures in the form of clusters whose dimensions and density depend on the nature of the polar arms. Stars containing PS and poly(2-vinylpyridine) arms are weakly associated, and the mean number of particles in an associate is ∼1.3. Hybrid polymers containing PS and poly(tert-butyl methacrylate) arms demonstrate capability for mutual penetration that favors the appearance of large structures that have a diameter of ∼50 nm and that include up to 12 macromolecules. Hybrid stars containing PS and diblock copolymer (poly(2-vinylpyridine)-poly(tert-butyl methacrylate)) arms exhibit moderate self-organization that manifests itself in the formation of chain associates built from four macromolecules.     

Preparation of thermo-responsive polymer brushes on hydrophilic polymeric beads by surface-initiated atom transfer radical polymerization for a highly resolutive separation of peptides

Poly(N-isopropylacrylamide-co-N-tert-butylacrylamide) [P(IPAAm-co-tBAAm)] brushes were prepared on poly(hydroxy methacrylate) (PHMA) [hydrolyzed poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate)] beads having large pores by surface-initiated atom transfer radical polymerization (ATRP) and applied to the stationary phases of thermo-responsive chromatography. Optimized amount of copolymer brushes grafted PHMA beads were able to separate peptides and proteins with narrow peaks and a high resolution. The beads were found to have a specific surface area of 43.0 m²/g by nitrogen gas adsorption method. Copolymer brush of P(IPAAm-co-tBAAm) grafted PHMA beads improved the stationary phase of thermo-responsive chromatography for the all-aqueous separation of peptides and proteins.     

Synthesis,characterization, and modification of poly(tert-butyl methacrylate-b-alkyl methacrylate-b-tert-butyl methacrylate) by group transfer polymerization

Different poly(tert-butyl methacrylate) (PTBMA)-poly(alkyl methacrylate) (PAMA, alkyl=CH₃, n-C₄H₉) triblock copolymers were synthesized by group transfer polymerization. They were obtained by first preparing “living” PAMA using a difunctional initiator, followed by polymerization of TBMA in THF at room temperature, in the presence of a nucleophilic catalyst. The segment molecular weights and compositions of TBMA segment could be controlled by regulating the feed ratio of two monomers and the ratio of monomer to initiator. As supported by ¹H-NMR, IR analysis, and titration, the PTBMA blocks could be quantitatively hydrolyzed into poly(methacrylic acid) (PMAA) blocks whereas the PAMA blocks were not hydrolyzed. The water-soluble amphiphiles prepared by neutralization of the PMAA block displayed surface-active behavior in water, which was characterized by a critical micelle concentration. The thermogravimetric analysis demonstrated the loss of tert-butyl groups. © 1992 John Wiley & Sons, Inc.