Synthesis and characterization of the environmental‐sensitive hyperbranched polymers as novel carriers for controlled drug release

Novel hyperbranched polymers, which contain a hydrophobic branched poly(p‐(chloromethy)styrene) (PCMS) core and poly(N,N‐dimethylaminoethyl methacrylate) (PDMA) shell that exhibited environmental sensitivity, have been synthesized by atom transfer radical polymerization (ATRP). At first, a hyperbranched polymer (PCMS) core is obtained via ATRP of p‐(chloromethy)styrene (CMS), which may act as an “inimer”‐monomer and initiator. Then the modified hyperbranched polymers having different average arm length consisting of PCMS and PDMA are synthesized by ATRP using anterior PCMS as macroinitiators. Their macromolecular structures are characterized by FTIR and ¹H NMR. Using chlorambucil as a model drug, the behaviors of the controlled drug release from the environmental‐sensitive hyperbranched polymers with different average chain length of PDMA and degree of branching are studied. The data demonstrate that the rate of the drug release can be effectively controlled by pH value, and these environmental‐sensitive hyperbranched polymers have the potential to be used as novel carriers in some controlled drug release systems in the future. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 311–316, 2006     

Dendritic polyamines: simple access to new materials with defined treelike structures for application in nonviral gene delivery

Polycationic dendrimers are interesting nonviral vectors for in vitro DNA delivery. We describe a simple approach to the synthesis of dendritic polyamines with different molecular weights and adjustable flexibility (degrees of branching; DB). Both parameters influence the transfection efficiency and the cell toxicity of the polymer. Functionalization of hyperbranched polyethylenimine (PEI) by a two-step procedure generated fully branched pseudodendrimers (analogues of polypropylenimine (PPI) and polyamidoamine (PAMAM) dendrimers). The DNA transfection efficiencies observed for these polymers depended on the cell line investigated. The highest efficiencies were observed for polymers whose unfunctionalized PEI cores had molecular weights in the range M(w)=6000-25 000 g mol(-1). The cytotoxicity of the dendrimers generally rises with increasing core size. The data collected for NIH/3T3 and COS-7 cells indicate a maximum transfection efficiency at around 60 % branching for the PPI analogues, and at a PEI-core molecular weight of M(w)=25 000 g mol(-1). PAMAM functionalization of PEI (M(w)=5000 and 21 000 g mol(-1)) leads to polymers with little or no cytotoxity in the cell lines investigated.     

Synthesis and characterization of a thermotropic liquid crystalline hyperbranched polyester

BACKGROUND: Hyperbranched polymers have received increasing attention in the fields of medicine, homogeneous catalysis and materials science. Hydroxyl‐functional aliphatic polyesters are one of the most widely investigated families of hyperbranched polymers. The research reported here is based on the preparation of a novel hyperbranched polyester and the modification of its terminal hydroxyl groups by biphenyl mesogenic units. RESULTS: 2,2,6,6‐Tetramethylolcyclohexanol as a core and 8‐[4′‐propoxy(1,1‐biphenyl)yloxy]octanoic acid as a mesogenic unit were synthesized. A hyperbranched polyester (HPE) was synthesized in one step and subsequently substituted by reaction of its terminal hydroxyl groups with the biphenyl mesogenic units to yield a novel liquid crystalline hyperbranched polyester (HPE‐LC). The chemical structures of all compounds were confirmed using Fourier transform infrared, ¹H NMR and ¹³C NMR spectroscopy. The thermal behavior and the mesogenic properties of the biphenyl mesogenic unit and HPE‐LC were investigated using differential scanning calorimetry, polarized optical microscopy and wide‐angle X‐ray diffraction. The results demonstrated that the degree of branching of the HPE is ca 0.63. Both HPE‐LC and the biphenyl mesogenic unit exhibit mesomorphic properties, but HPE‐LC has a lower isotropic transition temperature and a wider transition temperature range than the biphenyl mesogenic unit. CONCLUSION: A novel liquid crystalline hyperbranched polyester was successfully synthesized, which exhibits mesomorphic properties. This polymer has good solubility in highly polar solvents and good thermal stability. Copyright © 2009 Society of Chemical Industry     

Synthesis and characterization of hyperbranched polytriazole via an ‘A2 + B3’ approach based on click chemistry

BACKGROUND: The ‘A₂ + B₃’ type of polymerization has been demonstrated to be an alternative route towards hyperbranched polymers. Some highly crosslinked hyperbranched polymers have been prepared via copper(I)‐catalyzed click reactions of multivalent azides and alkynes. To obtain hyperbranched polymers without gelation and develop the A₂ + B₃ type of polymerization based on click reactions, the specific reaction conditions need to be investigated. RESULTS: In this work, a hyperbranched polytriazole (hb‐PTA) was synthesized through the A₂ + B₃ approach using a click reaction. 4‐N,N′‐bis(2‐azidoethyl)amino‐4′‐nitroazobenzene and 1,3,5‐tris(alynyloxy)benzene were synthesized for use as the A₂ and B₃ monomers, respectively. This was a ‘one‐pot’ polymerization carried out using a slow‐addition method. The obtained hb‐PTA was soluble in common organic solvents. The molecular structure was characterized using ¹H NMR, Fourier transform infrared and gel permeation chromatography analyses. The degree of branching of hb‐PTA was determined to be around 0.50. CONCLUSION: The hb‐PTA was successfully synthesized via the A₂ + B₃ approach based on a click reaction. The polymerization conducted in dilute solution adopting slow addition of A₂ to B₃ resulted in hb‐PTA in the absence of gelation. The obtained hb‐PTA exhibited high thermal stability. Copyright © 2008 Society of Chemical Industry     

Syntheses, characterization, and energy transfer properties of benzothiadiazole-based hyperbranched polyfluorenes

A series of benzothiadiazole-based (BT) hyperbranched polyfluorene copolymers with various branching degrees (5-40%) were designed and synthesized. TGA and film annealing tests showed the substantial thermal stability of these highly branched polymers. The optical performance of the polymers in solutions and as films, and their electrochemical properties were characterized. The energy transfer (ET) processes in these hyperbranched conjugated polymers, both in solutions and in the solid state, were also investigated. With the change of the solution concentration and the branching degree, the energy transfer efficiency of the polymers varied in solutions and the main photoluminescence (PL) peaks changed from blue to green region. As films, only green light emitted from BT units. In addition, the PL efficiency of the films decreased dramatically with the increase of branching degrees. All these features demonstrated that highly branched structure would effectively impede the intra- and interchain energy migration, especially in solutions, and remarkably influence the ET process in the solid state, which resulted in low PL efficiency.     

Synthesis of well‐defined dendritic hyperbranched polymers by iterative methodologies using living/controlled polymerizations

This review presents firstly the synthesis of various dendritic hyperbranched polymers with well‐defined structures by generation‐based growth methodologies using living/controlled polymerization. Secondly, the synthesis of dendritic hyperbranched poly(methyl methacrylate)s (PMMAs) and their functionalized block copolymers using a novel iterative methodology is described. The methodology involves a two‐reaction sequence in each iterative process: (a) a linking reaction of α‐functionalized living anionic PMMA with tert‐butyldimethylsilyloxymethylphenyl (SMP) groups with benzyl bromide (BnBr)‐chain‐end‐functionalized polymer and (b) a transformation reaction of the SMP groups into BnBr functions. This reaction sequence is repeated several times to construct high‐generation (maximum seventh generation) dendritic hyperbranched polymers. Similar branched architectural block copolymers have also been synthesized by the same iterative methodology using other α‐functionalized living anionic polymers. Surface structures of the resulting dendritic hyperbranched block copolymers composed of PMMA and poly(2‐(perfluorobutyl)ethyl methacrylate) segments have been characterized using X‐ray photoelectron spectroscopy and contact angle measurements. Solution behaviors of dendritic hyperbranched PMMAs with different generations and branch densities are discussed based on their intrinsic viscosities, g′ values and R_h values. Copyright © 2007 Society of Chemical Industry     

Influence of polymerization procedure on polymer topology and other structural properties in highly branched polymers obtained by A2 + B3 approach

Computational studies were carried out to investigate the influence of polymerization procedure on the topology and various macromolecular characteristics of the highly branched polymers formed by the reaction of A₂ and B₃ type monomers through step-growth polymerization reactions. The influence of three different polymerization procedures on the properties of the polymers formed was investigated, namely, (i) slow addition of A₂ over B₃, (ii) slow addition of B₃ over A₂, and (iii) mixed A₂ + B₃. Topology, degree of branching, number and weight average molecular weights, and polydispersity index of the polymers were determined using Monte Carlo simulations, assuming different levels of cyclization ratios during the reactions. Interestingly model polymers obtained by the slow addition of B₃ over A₂ produced much higher degree of branching or truly hyperbranched polymers, when compared with the other two methods, which mainly resulted in linear growth with slight branching.     

Preparation of epoxy‐ended hyperbranched polymers with precisely controllable degree of branching by thiol‐ene Michael addition

Epoxy‐ended hyperbranched polymers (EHPs) have a wide range of applications due to their outstanding performances. Because their microstructures are not positively identified, it is very difficult to ascertain the reinforcing and toughening mechanisms of EHPs and their interface interaction with other matrixes. Controllable synthesis of EHPs with precise degree of branching (DB) remains to be a major challenge. Here, a method for preparing novel nitrogen‐phosphor skeleton epoxy‐ended hyperbranched polymers (NPEHP) with controllable DB by a thiol‐ene Michael addition between thiol‐ended hyperbranched polymers (NPHSH) and glycidyl methacrylate have been firstly reported. NPHSH is synthesized by an esterification between hydroxyl‐ended hyperbranched polymers (NPHOH) and 3‐mercaptopropionic acid. NPHOH is prepared by a thiol‐ene Michael addition between methacrylate group of a monomer and thiol group of linear monomer (AB) and/or branched monomer (AB₂). The molar ratio between the AB and AB₂ monomers controls the DB of the products. The ¹H NMR spectra analysis of NPHOH shows that their experimentally determined DBs are very close to their theoretical values, indicating good controllability of their DBs. The narrow molecular weight distributions of NPHOH, NPHSH, and NPEHP suggest high efficiency of the thiol‐ene Michael addition. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44277.     

Hyperbranched poly(methyl methacrylate)s prepared by miniemulsion polymerization and their (non)-Newtonian flow behaviors

Miniemulsion polymerization is most suitable for the targeted synthesis of vinyl copolymers than the conventional emulsion polymerization, because in miniemulsion polymerization each monomer nanodroplet is a nanoreactor, and the monomers in each droplet are in situ converted to the corresponding polymers. Soluble and hyperbranched poly(methyl methacrylate)s (PMMA) were prepared with quantitative monomer conversion and without gelation by the miniemulsion copolymerization with di- and tri-acrylate and mediated with 1-dodecyl thiol (DDT). DDT acted both as a gelation prohibitor and as a reactive cosurfactant. The PMMAs with varied “X” or “Ж” shaped branches, depending on the di- and tri-functional acrylate used as the branching agent, are characterized and interpreted in terms of the repeating units per part, parts and branches per macromolecule, average molecular weight, latex particle size and size distribution. Effects of topology changes of the branched PMMAs on the rheological behaviors are observed for the first time: from Newtonian flow for the densely branched PMMAs to the non-Newtonian flow with pronounced shear thickening for the PMMA samples with high-molecular-weight and longer parts.     

基于自缩合自由基聚合超支化聚合物的制备及表征

与线型聚合物相比,超支化聚合物存在高度支化结构从而使其具有许多突出性能,在很多领域具有广阔的应用前景.以同时含有一个双键和两个原子转移自由基聚合(ATRP)引发点的丙烯酸(2,3-二(2-溴代)丙酰氧基)丙酯单体,通过调节丙烯酸(2,3-二(2-溴代)丙酰氧基)丙酯/丙烯酸正丁酯的物质的量比,以溴化亚铜(CuBr)/五...     

Evaluation of different branching functions used in the determination of random branching by GPC

Three branching functions are evaluated for use in the measurement of random branching by GPC. Initial evaluations of the functions g^1/2, g^3/2, and h³ were made by computer simulations of GPC experiments using published data of lightly and highly randomly branched polymers. Actual GPC experiments were then performed on characterized samples of lightly and highly branched styrene–divinylbenzene copolymers. The results indicate that h³ adequately predicts branching and molecular weight at all branching densities, whileg^1/2 is accurate only for lightly branched polymers and g^3/2 is accurate only for highly branched polymers. A means for predicting the M–[η] curve for branched polymers from the M–[η] calibration curve for linear polymer is proposed.     

Hyperbranched homo and thermoresponsive graft copolymers by using ATRP‐macromonomer initiators

Macromonomer initiators behave as macro cross‐linkers, macro initiators, and macromonomers to obtain branched and cross‐linked block/graft copolymers. A series of new macromonomer initiators for atom transfer radical polymerization (MIM‐ATRP) based on polyethylene glycol (M_n = 495D, 2203D, and 4203D) (PEG) were synthesized by the reaction of the hydroxyl end of mono‐methacryloyl polyethylene glycol with 2‐bromo propanoyl chloride, leading to methacryloyl polyethylene glycol 2‐bromo propanoyl ester. Poly (ethylene glycol) functionalized with methacrylate at one end was reacted with 2‐bromopropionyl chloride to form a macromonomeric initiator for ATRP. ATRP was found to be a more controllable polymerization method than conventional free radical polymerization in view of fewer cross‐linked polymers and highly branched polymers produced from macromonomer initiators as well. In another scenario, ATRP of N‐isopropylacrylamide (NIPAM) was initiated by MIM‐ATRP to obtain PEG‐b‐PNIPAM branched block/graft copolymers. Thermal analysis, FTIR, ¹H NMR, TEM, and SEM techniques were used in the characterization of the products. They had a thermo‐responsive character and exhibited volume phase transition at ～ 36°C. A plasticizer effect of PEG in graft copolymers was also observed, indicating a lower glass transition temperature than that of pure PNIPAM. Homo and copolymerization kinetics were also evaluated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Facile synthesis and characterization of star‐shaped polystyrene: self‐condensing atom transfer radical copolymerization of N‐[4‐(α‐bromoisobutyryloxy)phenyl]maleimide and styrene

BACKGROUND: Generation of stars around in situ formed cores provides a facile approach to star‐shaped polymers. Therefore the self‐condensing atom transfer radical copolymerization (SCATRCP) of N‐[4‐(α‐bromoisobutyryloxy)phenyl]maleimide (BiBPM) and a large excess of styrene (St) was investigated. RESULTS: BiBPM and St formed a charge transfer complex (CTC), which underwent the SCATRCP, leading to the branched core initiating the atom transfer radical polymerization of St, finally giving star‐shaped polystyrene (PS). Kinetic and structural study showed that a higher dosage of BiBPM resulted in an enhanced polymerization rate, a higher degree of branching and a larger number of short PS arms. Differential scanning calorimetry suggested that the glass transition temperature of the star‐shaped PS decreased with molecular weight. Melt rheometry showed that even a slightly branched architecture of the PS led to a significantly lower viscosity; both the melt flow index and the activation energy increased with the degree of branching. CONCLUSION: Due to the preferential consumption of BiBPM and formation of a CTC, even a very low dosage of BiBPM could lead to star‐shaped PS, which, in comparison with linear analogues, could possess much better melt fluidity. Copyright © 2008 Society of Chemical Industry     

Novel synthesis of branched polystyrenes by quasi‐living radical copolymerization using photofunctional inimer

Branched polystyrenes were prepared by quasi‐living radical copolymerization of N,N‐diethylaminodithiocarbamoylmethylstyrene (inimer: DTCS) with styrene under UV irradiation. DTCS monomers play an important role in this copolymerization system as an inimer capable of initiating living radical polymerization of the vinyl group. Two monomers (DTCS and styrene) showed equal reactivity toward both propagating species, and the copolymer composition was the same as the comonomer feed. This result means that both the branching and chain length of the hyperbranched molecules can be controlled statistically by the feed monomer ratios. The compact nature of the branched macromolecules is demonstrated by viscosity measurements compared to the linear analogues. © 2001 Society of Chemical Industry     

Preparation of heat‐resistant branched poly(styrene‐alt‐NPMI) by ATRP with divinylbenzene as the branching agent

Heat‐resistant branched poly(styrene‐alt‐NPMI) has been prepared via atom transfer radical polymerization (ATRP) of styrene (St) and N‐phenyl maleimide (NPMI) with divinylbenzene (DVB) as the branching agent in anisole at 80°C. Gas chromatography (GC) was used to determine the conversion of the reactants. Triple detection gel permeation chromatography (TD‐GPC) was used to analyze the copolymers. The results show that the polymerization yields primary chains predominately in the early stages and the formation of branched molecules occurs mainly when conversion is higher than 50%. As expected, higher dosage of DVB in our investigation range favors the formation of polymers with higher degree of branching. All the resulting branched poly(styrene‐alt‐NPMI)s have glass transition temperature (T_g) above 175°C, extrapolated initial weight loss temperature (T_i) above 410°C and statistic heat‐resistant index above 200°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

超支化聚合物及其自组装研究进展

介绍了超支化聚合物的结构性质特点及合成方法,主要有缩聚反应、乙烯基自缩合反应(SCVP)、开环聚合等;概述了超支化聚合物的自组装及其应用研究情况,如在生物医药、修饰碳纳米管及其它领域的实际应用现状。     

Aliphatic polyamidoamine hyperbranched polymers/layered silicate nanocomposites

Polyamidoamine hyperbranched polymer (Hyp)/clay nanocomposites were synthesized by using both of montmorillonite and laponite clays. Poly amidoamine hyperbranched polymer (Hyp) was prepared by one‐pot polymerization via couple monomer methodology. Afterward, the amino ends of Hyp were modified with methyl methacrylate (MMA), styrene (St) and butyl methacrylate (n‐BuMA) polymers which were previously prepared via ATRP (atom transfer radical polymerization) to form the corresponding new hyperbranched polymers Hyp₁, Hyp₂ and Hyp₃. Those formed polymers were inserted into the modified clay, such as montmorillonite and laponite to form their nanocomposites. The formed polymer/clay nanocomposites were characterized via XRD, TEM, and thermal analyses. The formed hyperbranched polymers generally showed intercalation behavior more than the exfoliation one mostly because of the bulkiness of the hyperbranched skeleton. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Solution properties of hyperbranched polymers and synthetic application for amphiphilic star‐hyperbranched copolymers by grafting from hyperbranched macroinitiator

Hyperbranched polystyrenes (PS) were prepared by living radical photopolymerization of N,N‐diethyldithiocarbamoylmethylstyrene (DTCS) as an inimer under UV irradiation. Branched PS with an average chain length between branching points of four styrene units was also prepared by living radical copolymerization of DTCS with styrene. The ratio of radius of gyration to hydrodynamic radius R_G/R_H for these hyperbranched polymers was in the range 0.82–0.89 in toluene. The translational diffusion coefficient D(C) showed a constant value in the range of 0–14 × 10^?3 g ml^?1 in toluene. It was found from these dilute solution properties that hyperbranched PSs formed a unimolecular structure even in a good solvent because of their compact nature. These hyperbranched PSs exhibited large amounts of photofunctional carbamate (DC) groups on their outside surfaces. Subsequently, we derived amphiphilic star‐hyperbranched copolymers by grafting from hyperbranched macroinitiator with 1‐vinyl‐2‐pyrrolidinone. These star‐hyperbranched copolymers were soluble in water and methanol. © 2001 Society of Chemical Industry     

Synthesis and thermal properties of randomly branched poly(butylene isophthalate) containing sodium sulfonate groups

Randomly branched poly(butylene isophthalate) samples containing sodium sulfonate groups were prepared from dimethyl isophthalate, 3,5‐bis(carbomethoxycarbonyl) benzene sulfonate, tris(hydroxyethyl) isocyanurate, and 1,4‐butanediol, according to the well‐known two‐stage polycondensation procedure. The polymers, containing various amounts of branching units and ionic groups, demonstrated to be soluble in the most common organic solvents, an evidence that gelation was not reached under the polymerization conditions adopted. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. The sulfonate as well as the branching units had only a limited effect on the thermal stability, which slightly decreased with respect to pure poly(butylene isophthalate). The analysis carried out using DSC technique showed that the T_m of the copolymers decreased with increasing counit content, differently from T_g, which, on the contrary, increased. Baur's equation was found to describe well the T_m‐composition data. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1374–1379, 2006