Multifunctional Initiator Research Articles

Preparation and ionic conductive properties of all‐solid polymer electrolytes based on multiarm star block polymers

AbstractA series of star block polymers with a hyperbranched core and 26 arms are successfully synthesized by atom transfer radical polymerization of styrene (St), and poly(ethylene glycol) methyl ether methacrylate from a hyperbranched polystyrene (HBPS) multifunctional initiator. All‐solid polymer electrolytes composed of these multiarm star polymers and lithium salts are prepared. The influences of polyoxyethylene (PEO) side‐chain length, PEO content, lithium salt concentration and type, and the structure of polymer on ionic conductivity are systematically investigated. The resulting polymer electrolyte with the longest PEO side chains exhibits the best ionic conductive properties. The maximum conductivity is 0.8 × 10−4 S cm−1 at 25°C with EO/Li = 30. All the prepared multiarm star block polymers possess good thermal stability. The mechanical property is greatly improved owing to the existence of polystyrene blocks in the multiarm star polymer molecules, and flexible films can be obtained by solution‐casting technique. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Synthesis, Characterization, and Biocompatibility of Biodegradable Hyperbranched Polyglycerols from Acid-Cleavable Ketal Group Functionalized Initiators

Herein we report the synthesis of biodegradable hyperbranched polyglycerols (BHPGs) having acid-cleavable core structure by anionic ring-opening multibranching polymerization (ROMBP) of glycidol using initiators bearing dimethyl and cyclohexyl ketal groups. Five different multifunctional initiators carrying one to four ketal groups and two to four hydroxyl groups per molecule were synthesized. The hydroxyl carrying initiators containing one ketal group per molecule were synthesized from ethylene glycol. An alkyne-azide click reaction was used for synthesizing initiators containing multiple cyclohexyl ketal linkages and hydroxyl groups. The synthesized BHPGs exhibited monomodal molecular weight distributions and polydispersity in the range of 1.2 to 1.6, indicating the controlled nature of the polymerizations. The polymers were relatively stable at physiological pH but degraded at acidic pH values. The polymer degradation was dependent on the type of ketal structure present in the BHPG; polymers with cyclohexyl ketal groups degraded at much slower rates than those with dimethyl ketal groups at a given pH. Good control of polymer degradation was achieved under mild acidic conditions by changing the structure of ketal linkages. A precise control of the molecular weight of the degraded HPG was achieved by controlling the number of ketal groups within the core, as revealed from the gel permeation chromatography (GPC) analyses. The decrease in the polymer molecular weights upon degradation was correlated well with the number of ketal groups in their core structure. Our data support the suggestion that glycidol was polymerized uniformly from all hydroxyl groups of the initiators. BHPGs and their degradation products were highly biocompatible, as measured by blood coagulation, complement activation, platelet activation, and cell viability assays. The controlled degradation profiles of these polymers together with their excellent biocompatibility make them suitable for drug delivery and bioconjugation applications.

Double Responsive Hydrogels based on Tertiary Amine Methacrylate Star Block Copolymers

Abstract Double hydrophilic stimuli-responsive star block copolymers with poly(2-(dimethylamino)ethyl methacrylate) (PDMA) inner blocks and poly(2-(diethylamino)ethyl methacrylate) (PDEA) outer blocks were synthesized using ATRP. Different multifunctional initiators based on sugar scaffolds were employed in a core-first approach with sequential polymerization of both blocks yielding stars with 4 and 6 arms, respectively, and varying length of the PDEA outer block. The star block copolymers show pH- and temperature-responsive aggregation as revealed by dynamic light scattering and turbidimetry. The impact of pH, PDEA block length and arm number on the gelation behavior was investigated by tube inversion and rheology.

Mechanism of Formation of Partially Crosslinked Polyacrylamide Complexes

A new type of partially crosslinked polyacrylamide (PCPAM) which displays promising application in enhanced oil recovery (EOR) has been synthesized via aqueous solution polymerization under adiabatic conditions. Based on methods of real-time infrared monitoring, two-dimensional infrared correlation spectroscopy, and dynamic rheology measurement, an unusual complex formation mechanism of the PCPAM with the multifunctional initiator system is clearly disclosed. A process forming branched structures from three functional dimethylaminoethyl methacrylate (DMAEMA) was exhibited, which was supported by high-resolution Fourier transform infrared (FTIR) information. Furthermore, an interesting reaction process, dominated by reaction dynamics, is proposed. By viscosity matching, a great number of coupling terminations will be generated from the branched end chains which will result in the formation of partially crosslinked structures, whereas lots of branched structures were retained under quick gelling conditions. Consequently, the relative number of branched and crosslinked structures in PCPAM was not only mainly determined by the viscosity of the system but also by the content of DMAEMA.

Star‐Like Polymers of tert‐Butyl Acrylate via Controlled Radical Polymerization – Synthesis and Properties

AbstractSummary: Star polymers with different numbers and lengths of poly(tert‐butyl acrylate) arms were obtained by the core‐first method via atom transfer and iodine mediated radical polymerization. Multifunctional initiators with different numbers of initiating groups (from 3 to 28) were used to initiate the polymerization of tert‐butyl acrylate, yielding stars with different numbers of arms. The structures of the stars were characterized by NMR and gel permeation chromatography with refractive index, multiangle laser light scattering and viscosimetric detectors.

Synthesis and characterization of star-shaped poly (lactide-co-glycolide) and its drug-loaded microspheres

The star-shaped poly (lactide-co-glycolide) (PLGA) was synthesized via the ring-opening polymerization of d,l-lactide and glycolide, with pentaerythritol as a multifunctional initiator and stannous 2-ethyl hexanoate as a catalyst. The structures of these polymers were characterized by 13C-NMR spectroscopy, while the molecular weight and polydispersity index (PDI) were determined by gel permeation chromatography (GPC). The glass transition temperature (Tg) of copolymer was determined by differential scanning calorimetry (DSC). Bovine serum albumin (BSA) loaded microspheres were fabricated using star-shaped PLGA by a W/O/W double emulsion solvent evaporation method. The results of characterization demonstrated that the particle size of the PLGA microspheres were about 80–150 μm, the maximum loading capacity and encapsulation efficiency of BSA-loaded microspheres were 67.51 μg/(mg microspheres) and 78.39%, respectively, which were better than linear PLGA. The in vitro release profiles of BSA in phosphate buffer saline (PBS) lasted for 37 h. Drug release profiles can be affected by polymer molecular weight and the ratio of polymer to drug. The maximum release percentage was 80%.

PH-Controlled Exponential and Linear Growing Modes of Layer-by-Layer Assemblies of Star Polyelectrolytes

We report the unique layer-by-layer (LbL) assembly behavior of pH-sensitive star-shaped polyelectrolytes with both linear and exponential growth modes controlled by star architecture and assembly conditions. Cationic poly[2-(dimethylamino)ethyl methacrylate] and anionic poly(acrylic acid) stars were synthesized via "core-first" atom-transfer radical polymerization (ATRP) based on multifunctional initiators, in addition to their linear analogues. We demonstrated the LbL growth behavior as a function of deposition pH (ranging from 5 to 7), number of layers (up to 30 bilayers), and the method of assembly (dip- vs spin-assisted LbL). The spin-assisted LbL assembly makes it possible to render smoother and thinner LbL films with parameters controlled by the shear rate and pH conditions. In contrast, for dip-assisted LbL assembly, the pH-dependent exponential growth was observed for both linear and star polyelectrolytes. In the case of linear/linear pair, the exponential buildup was accompanied with a notable surface segregation which resulted in dramatic surface nonuniformity, "wormlike" heterogeneous morphology, and dramatic surface roughening. In contrast, star/linear and star/star LbL films showed very uniform and smooth surface morphology (roughness below 2.0 nm on the scale of 10 μm × 10 μm) with much larger thickness reaching up to 1.0 μm for 30 bilayers and rich optical interference effects. Star polyelectrolytes with partially screened charges and high mobility caused by compact branched architecture appear to facilitate fast diffusion and exponential buildup of LbL films. We suggest that the fast buildup prevents long-range lateral diffusion of polyelectrolyte star components, hinders large-scale microphase separation, and thus leads to unique thick, smooth, uniform, transparent, and colorful LbL films from star polyelectrolytes in contrast to mostly heterogeneous films from traditional linear counterparts.

Morphology and properties of miktoarm star styrene-butadiene rubber

In order to obtain the optimized structure rubber, a novel miktoarm star styrene-butadiene rubber (MS-SBR) was initiated by a multifunctional macromolecular initiator with polydiene arm and Sn-C bond. The properties of MS-SBR were investigated with respect to the morphology, mechanical properties, and dynamic viscoelasticity in comparison with those of the blends, natural rubber (NR)/star styrene-butadiene random rubber(S-SBR) blend rubber and cis-1,4-polybutadiene rubber (cis-BR)/S-SBR blend rubber. The samples were analyzed using transmission electron microscopy (TEM), dynamic mechanical thermal analyzer (DMTA), and mechanical properties test. The analysis results show that MS-SBR possesses the desired combination of low rolling resistance and high antiskid resistance, and is promising for application in high performance tire tread.

Synthesis, characterization, and rheological properties of hybrid titanium star‐shaped poly(n‐butyl acrylate)

AbstractThe synthesis of hybrid star‐shaped polymers was carried out by atom transfer radical polymerization of n‐butyl acrylate from a well‐defined multifunctional titanium‐oxo‐cluster initiator. Conditions were identified to prevent possible side reactions among monomer, polymer, and the titanium‐oxo‐cluster ligands. Polymerizations provided linear first‐order kinetics and the evolution of the experimental molecular weight is also linear with the conversion. 1H DOSY NMR and cleavage of the polymeric branches from the multifunctional initiator by hydrolysis were used to (i) prove the star‐shaped structure of the polymer, and (ii) demonstrate that the shoulder observed on size exclusion chromatograms is not due to a noncontrolled polymerization but to ungrafting of polymeric branches during analysis. Rheological properties of the hybrid star‐shaped poly(n‐butyl acrylate) were studied in the linear regime and show that the Ti‐oxo‐cluster not only increases significantly the viscosity of the polymer relative to its ungrafted arm but has a rheological signature which is qualitatively different from that of stars with organic cores suggesting that the Ti cluster reduces significantly the molecular mobility of the star. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis of star polymethyl acrylate by SET-LRP at ambient temperature

The star-shaped polymethyl acrylate (PMA) was synthesized by single electron transfer living radical polymerization (SET-LRP) at 30 °C in dimethyl sulfoxide, using 2,2-dibromomethyl-1,3-dibromopropane as the multifunctional initiator, Cu0 powder and tris-(2-dimethylamino ethyl)amine (Me6-TREN) as catalyst. The structure of polymer was analyzed by 1H NMR, and the results showed that the star-shaped PMA had perfect chain ends (–Br) retention. In addition, the polymerization proceeded smoothly and the time dependence of ln([M]0/[M]) was linear, which could indicate a first order propagation rate with respect to both radicals and monomer concentration, the polymerization was the living polymerization. The Mn and Mw/Mn of polymer were being measured by Gel Permeation Chromatography. The kpapp = 0.0367 h−1 and the conversion was 36.3% at 16 h, meanwhile the MnGPC of the polymer was 13,300 and the Mw/Mn was 1.40.

Synthesis of well-defined structurally silica–nonlinear polymer core–shell nanoparticles via the surface-initiated atom transfer radical polymerization

We report on the synthesis of the well-defined structurally silica–nonlinear polymer core–shell nanoparticles via the surface-initiated atom transfer radical polymerization. At first, 3-(2-bromoisobutyramido)propyl(triethoxy)-silane (the ATRP initiator) was prepared by the reaction of 3-aminopropyltriethoxysilane with 2-bromoisobutyryl bromide. The ATRP initiator was covalently attached onto the nanosilica surface. The subsequent ATRP of HEMA from the initiator-attached SiO 2 surface was carried out in order to afforded functional nanoparticles bearing a hydroxyl moiety at the chain end, SiO 2-g-PHEMA-Br. The esterification reaction of pendent hydroxyl moieties of PHEMA segment with 2-bromoisobutyryl bromide afforded the SiO 2-based multifunctional initiator, SiO 2-g-PHEMA(-Br)-Br, bearing one bromine moiety on each monomer repeating unit within the PHEMA segment. Finally, the synthesis of SiO 2-g-PHEMA(-g-PSt)-b-PSt was accomplished by the ATRP of St monomer using SiO 2-g-PHEMA(-Br)-Br as multifunctional initiator. These organic/inorganic hybrid materials have been extensively characterized by FT-IR, XPS, TG, and TEM.

Statistical properties for the self-condensing vinyl polymerization in presence of multifunctional core initiators

The self-condensing vinyl polymerization system consisting of inimers and multifunctional core initiators is studied by the principle of statistical mechanics. From viewpoints of functional groups and polymers, two types of canonical partition functions are constructed and further are proved to be consistent with each other. In this way, the explicit expressions of equilibrium free energy and law of mass action concerning the polymerization are obtained, and then the equilibrium size distribution functions of hyperbranched polymers are given. With the help of the size distribution functions, the k-th mean square radii of gyration of hyperbranched polymers with and without a core are derived, respectively. In order to investigate the effect of core initiators on the statistical properties of the system, the number and functionality of core initiators have been explicitly taken into account, and the variations of relevant physical quantities against the conversion of vinyl groups under various conditions are presented. It is shown that the presence of core initiator results in a significant influence on average properties of the system, which can be explained from the competition between polymers with and those without a core initiator in their growth process.

Synthesis and thermal stability of star polymer with eight arms using polyhedral oligomeric silsesquioxane as a core

AbstractA Polyhedral oligomeric silsesquioxane (POSS) containing eight 3- chloropropyl groups was synthesized and incorporated into poly(methyl methacrylates) to form star polymer. First, octa(3-chloropropyl) POSS [(ClCH2CH2CH2)8Si8O12] was prepared by hydrolysis and condensation of 3- chloropropyltriethoxysilane, and then two star-shaped POSS/PMMA composites with different POSS content was synthesized at 110 °C, using octa(3-chloropropyl) POSS as an multifunctional initiator, CuCl and 2-2’ bipyridine (Bpy) as catalyst system. The structures of octa(3-chloropropyl) POSS and star-shaped POSS/PMMA composite were characterized by analytical methods including FTIR, NMR, GPC and XRD, with results showing that POSS molecule was successfully formed which accorded well with the reported work and was dispersed into PMMA matrix evenly by atom transfer radical polymerization method. The TGA results indicated that synthetic POSS molecule possessed good thermal stability, and the thermal stability of POSS/PMMA composite enhanced with the increase of POSS content, which is due to the incorporation of inorganic POSS molecule

Kinetic theory of self-condensing vinyl polymerization

This review introduces the kinetic theory of self-condensing vinyl polymerization (SCVP), including the SCVP of AB* inimers, the SCVP with non-equal reactivity between A* and B* groups, the SCVP in the presence of a small amount of multifunctional initiators, also the SCVP of both inimers and comonomers. The analytical expressions of various molecular parameters for the resulting hyperbranched polymers, such as the molecular size distribution function, the average molecular weight, the polydispersity index and the degree of branching, are reviewed systematically.

Stepwise Cleavable Star Polymers and Polymeric Gels Thereof

A multifunctional initiator 1 with chemically labile disulfide and ester groups bearing four bromoisobutyryl groups was prepared by esterification of bis(2-hydroxyethyl)disulfide with 2,2-bis(2-bro...

Thermal decomposition of 3,3,6,6,9,9-hexaethyl-1,2,4,5,7,8-hexaoxacyclononane in solution and its use in methyl methacrylate polymerization

The kinetics of the thermal decomposition reaction of diethylketone triperoxide (3,3,6,6,9,9-hexaethyl-1,2,4,5,7,8-hexaoxacyclononane, DEKTP) in ethylbenzene solution were studied in the temperature range of 120.0–150.0 °C and at an initial concentration range of 0.01–0.10 M. This peroxide was used as a new initiator in methyl methacrylate (MMA) polymerization process at high temperatures (110.0–140.0 °C) in ethylbenzene solution. The effects of initiator concentration and reaction temperature on the polymerization rate were investigated in detail. Thus, activation parameters of the solution polymerization process (ΔE d* = 83.3 kJ mol−1 and ΔE p* − ΔE t*/2 = 54.0 kJ mol−1) will be obtained. DEKTP can effectively act as initiator in MMA polymerization and its performance is similar to that presented by a multifunctional initiator resulting in high-molecular weight polymethylmethacrylate with a high reaction rate.

Synthesis and self‐assembly of well‐defined cyclodextrin‐centered amphiphilic A14B7 multimiktoarm star copolymers based on poly(ε‐caprolactone) and poly(acrylic acid)

AbstractNovel amphiphilic A14B7 multimiktoarm star copolymers composed of 14 poly(ε‐caprolactone) (PCL) arms and 7 poly(acrylic acid) (PAA) arms with β‐cyclodextrin (β‐CD) as core moiety were synthesized by the combination of controlled ring‐opening polymerization (CROP) and atom transfer radical polymerization (ATRP). 14‐Arm star PCL homopolymers (CDSi‐SPCL) were first synthesized by the CROP of CL using per‐6‐(tert‐butyldimethylsilyl)‐β‐CD as the multifunctional initiator in the presence of Sn(Oct)2 at 125 °C. Subsequently, the hydroxyl end groups of CDSi‐SPCL were blocked by acetyl chloride. After desilylation of the tert‐butyldimethylsilyl ether groups from the β‐CD core, 7 ATRP initiating sites were introduced by treating with 2‐bromoisobutyryl bromide, which further initiated ATRP of tert‐butyl acrylate (tBA) to prepare well‐defined A14B7 multimiktoarm star copolymers [CDS(PCL‐PtBA)]. Their molecular structures and physical properties were in detail characterized by 1H NMR, SEC‐MALLS, and DSC. The selective hydrolysis of tert‐butyl ester groups of the PtBA block gave the amphiphilic A14B7 multimiktoarm star copolymers [CDS(PCL‐PAA)]. These amphiphilic copolymers could self‐assemble into multimorphological aggregates in aqueous solution, which were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2961–2974, 2010

Anionic methods for synthesis of star polymers

Leading position among numerous methods for synthesis of star polymers is occupied, as regards their potential and diversity, by techniques based on the anionic polymerization. The review considers five basic approaches to application of the anionic polymerization mechanisms in relation to an agent used or procedure employed (methods with polyfunctional coupling agents, multifunctional initiators, polymerizing and nonpolymerizing divinyl agents; multistage methods, methods using C60 fullerene). All groups of syntheses are illustrated by examples, and advantages of methods for synthesis of various homo- and heteroarm star structures are demonstrated. Particular attention is given to syntheses with C60 fullerene. The potential of C60 fullerene as a coupling agent for “living” polymer chains and methods for conversion of polymeric derivatives of C60 (hexaadducts) to polyfunctional macroinitiators of anionic polymerization are described and techniques for functionalization of polymeric fullerene derivatives and their coupling into structures with a complex controllable architecture are presented.

Structure-Based Mutational Analysis of the Bovine Papillomavirus E1 Helicase Domain Identifies Residues Involved in the Nonspecific DNA Binding Activity Required for Double Trimer Formation

The papillomavirus E1 protein is a multifunctional initiator protein responsible for preparing the viral DNA template for initiation of DNA replication. The E1 protein encodes two DNA binding activities that are required for initiation of DNA replication. A well-characterized sequence-specific DNA binding activity resides in the E1 DBD and is used to tether E1 to the papillomavirus ori. A non-sequence-specific DNA binding activity is also required for formation of the E1 double trimer (DT) complex, which is responsible for the local template melting that precedes loading of the E1 helicase. This DNA binding activity is very poorly understood. We use a structure-based mutagenesis approach to identify residues in the E1 helicase domain that are required for the non-sequence-specific DNA binding and DT formation. We found that three groups of residues are involved in nonspecific DNA binding: the E1 beta-hairpin structure containing R505, K506, and H507; a hydrophobic loop containing F464; and a charged loop containing K461 together generate the binding surface involved in nonspecific DNA binding. These residues are well conserved in the T antigens from the polyomaviruses, indicating that the polyomaviruses share this nonspecific DNA binding activity.

Rapid Synthesis and MALDI‐ToF Characterization of Poly(ethylene oxide) Multiarm Star Polymers

AbstractMultiarm PEO star polymers with a purely aliphatic polyether structure have been synthesized using hyperbranched polyglycerol (PG) with different molecular weights as a multifunctional initiator. Different degrees of deprotonation of the initiator were studied with respect to molecular weight control. The results show that the degree of deprotonation is a crucial parameter for the synthesis of well‐defined polymers with controlled molecular weights. Partial deprotonation of the PG hydroxyl groups (5–8%) was proven to represent an optimum for the synthesis of star polymers with molecular masses close to the theoretical values. Molecular weights of the stars ranged between 9 000 and 30 000 g · mol−1. MALDI‐ToF spectra confirmed that the PEO arms in the star polymers possess homogeneous lengths.magnified image