星形超支化聚酯的合成及其光固化

紫外光固化具有快速反应、室温操作、低能消耗和无溶剂少污染等优点,现正以日益增长的速度应用于涂层和粘合剂等领域。然而,常规的线形光固化齐聚体具有缠结的柔性分子链结构,其粘度随着分子量的增大而快速增加,故其可加工性和应用受到很大的限制。     

可光固化星形超支化聚酯的合成与表征

描述了基于季戊四醇和１，２，４ 苯三甲酸酐，经由甲基丙烯酸缩水甘油酯和甲基丙烯酸酐改性的系列超支化聚酯的“发散”合成方法，即合成反应从“中心核”开始，逐步向外扩展，控制链增长，每个分子形成具有大约８，１２和１６个甲基丙烯酸酯双键的超支化臂。这种星形聚酯分子具有三维球状结构，不会产生分子链间的缠结，在辐射固化涂层和粘合剂等领域具有广阔的应用前景．     

超支化聚(胺酯)的分子设计及其制备

以丙烯酸甲酯和二乙醇胺为原料由Michael加成反应制得N ,N 二羟乙基 3 胺基丙酸甲酯单体 ,再用“准一步法”和“发散法”使之与 1 ,1 ,1 三羟甲基丙烷 (核 )反应合成一种新型超支化聚 (胺 酯 ) .以核磁共振和元素分析方法对N ,N 二羟乙基 3 胺基丙酸甲酯单体的分子结构进行了表征 .GPC测定表明合成的超支化聚 (胺 酯 )分子量分布窄 ,具有单分散性 ;粘度小于同分子量的线形分子 ;耐热性能较好 ,失重温度高于2 0 0℃ .     

Starburstr̀ dendrimers — Nanoscopic supermolecules according to dendritic rules and principles

Construction of dendritic macromolecules based on the mimicry of macroscopic branching patterns found in trees is reviewed. From this mimicry, synthetic strategies have been developed for the preparation of precise macromolecular building blocks referred to as Starburstr̀/Cascade dendrimers. These dendrimer constructions involve the amplifications of matter (mass) by organizing monomer units around initiator cores according to geometrically driven mathematical rules and principles. The predictable precision of mass and valency (i.e., number of reactive surface groups) displayed by these dendrimers, as a function of generation, validates their proposed role as fundamental nanoscopic building blocks (i.e., particle sizes of 10 −1000Å). This emerging area of “structure-controlled polymers” is defining a fourth new major class of macromolecular architecture. Ideal, defect free structures of Starburst^r̀ polyamidoamine (PAMAM) dendrimers (e.g., NH₃ core; generation = 2.0, MWt. 2,414) have been synthesized in kilogram quantities with overall yields of 60-70%. The precise masses and surface valencies associated with these dendrimer structures allow one to view these entities as “nanoscopic analogues” to atoms. As such, basic rules of chemical combination between dendrimers to give definite, stoichiometric compositions can be defined much as first noted by Dalton for atoms. The use of these nanoscopic building blocks (i.e., 10–1000Å species) to construct supramolecular/supermolecular structures such as nanoscopic compounds, clusters and macro-lattices will be reviewed. Registered trademark of Dendritech Inc.     

Synthesis of a novel one‐pot approach of hyperbranched polyurethanes and their properties

A new method for the synthesis of hyperbranched polymers involving the use of AB_x macromonomers containing linear units have been investigated. Two types of novel hyperbranched polyurethanes have been synthesized by a one‐pot approach. The structures of monomers and polymers were characterized by elemental analysis, ¹H NMR, ¹³C NMR, Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetric analysis. The hyperbranched polymers have been proven to be extremely soluble in a wide range of solvents. Polymer electrolytes were prepared with hyperbranched polymer, linear polymer as the host, and lithium perchlorate (LiClO₄) as the ion source. Analysis of the isotherm conductivity dependence of the ion concentration indicated that these hyperbranched polymers could function as a “solvent” for the lithium salt. The conductivity increased with the increasing concentration of hyperbranched polymers in the host polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 344–350, 2002     

Grafting of hyperbranched poly(amidoamine) onto waste tire rubber powder and its potential application as the curing agent for epoxy resin

To realize the high‐valued application of waste tire rubber (WTR), hyperbranched poly(amidoamine) (PAMAM) were synthesized from the surface of WTR powders to endow its chemical reactivity. The hyperbranched PAMAM‐grafted WTR powders containing a large amount of amine groups on their surface were obtained through “divergent procedure.” First, methyl methacrylate‐grafted WTR powders (MMA‐g‐WTR) were prepared by ozone‐induced grafting polymerization. Afterwards, Michael reaction and subsequent amidation reactions were carried out repetitively to obtain hyperbranched PAMAM chains grafted from the surface of the MMA‐g‐WTR powders. The resulting hyperbranched PAMAM‐grafted WTR powders exhibit good dispersibility in water. Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and thermogravimetric analysis demonstrate the successful grafting of hyperbranched PAMAM on WTR surface. The hyperbranched PAMAM‐grafted WTR powder could be utilize as curing agent and potential toughener for epoxy resin due to abundant amine groups and elastomeric feature of WTR. Differential scanning calorimetry shows that the hyperbranched PAMAM‐grafted WTR powders can be used as effective curing agent for epoxy resin. Copyright © 2011 John Wiley & Sons, Ltd.     

一种低代超支化聚醚的合成、表征及表面活性研究

以十二胺、丙烯酸甲酯和乙二胺为原料,甲醇为溶剂,采用发散合成法合成一种低代超支化分子骨架.采用1H NMR对分子骨架的结构进行了表征.在此基础上,以低代骨架为起始剂,分别与环氧乙烷、环氧丙烷加成制备了一种超支化聚醚,测定了它的表面张力、浊点,同时计算出了它的HLB值.结果表明:骨架的分子结构与所设计的结构相符,合成的聚醚具有典型表面活性剂的性质.     

Dendronized Hyperbranched Macromolecules: Soft Matter with a Novel Type of Segmental Distribution

Dendronization of a hyperbranched polyester with different generation dendrons leads to pseudo‐dendritic structures. The hyperbranched core is modified by the divergent coupling of protected monomer units to the functional groups. Compared to dendrimers, the synthetic effort is significantly less, but the properties are very close to those of high‐generation dendrimers. The number of functional groups, molar mass, and rheology behavior even in the early generation (G1–G4) pseudo‐dendrimers strongly resembles the behavior of dendrimers in higher generations (G5–G8). Comparison of the segmental and internal structure with perfect dendrimers is performed using SANS, dynamic light scattering and viscosity analysis, microscopy and molecular dynamics simulation. The interpretation of the results reveals unique structural characteristics arising from lower segmental density of the core, which turns into a soft nano‐sphere with a smooth surface even in the first generation.     

Chain‐Growth Click Polymerization of AB2 Monomers for the Formation of Hyperbranched Polymers with Low Polydispersities in a One‐Pot Process

Hyperbranched polymers are important soft nanomaterials but robust synthetic methods with which the polymer structures can be easily controlled have rarely been reported. For the first time, we present a one‐pot one‐batch synthesis of polytriazole‐based hyperbranched polymers with both low polydispersity and a high degree of branching (DB) using a copper‐catalyzed azide–alkyne cycloaddition (CuAAC) polymerization. The use of a trifunctional AB₂ monomer that contains one alkyne and two azide groups ensures that all Cu catalysts are bound to polytriazole polymers at low monomer conversion. Subsequent CuAAC polymerization displayed the features of a “living” chain‐growth mechanism with a linear increase in molecular weight with conversion and clean chain extension for repeated monomer additions. Furthermore, the triazole group in a linear (L) monomer unit complexed Cu^I, which catalyzed a faster reaction of the second azide group to quickly convert the L unit into a dendritic unit, producing hyperbranched polymers with DB=0.83.     

Triazatruxene-containing hyperbranched polymers: Microwave-assisted synthesis and optoelectronic properties

Hyperbranched polymer structures represent a class of high-functionality building blocks with excellent three-dimensional topology for the construction of highly substituted conjugated polymers. In this contribution, an efficient microwave synthesis protocol toward the synthesis of conjugated hyperbranched polymers is presented. A novel series of soluble hyperbranched polyfluorenes (PTF1-PTF3) incorporating triazatruxene moiety as the branch units with various branching degrees have thus been successfully constructed with good yields and high molecular weight via a facile “A2+B2+C3” approach. The structures of the hyperbranched polymers were confirmed by NMR and GPC. Their thermal, optical, and electrochemical properties of the hyperbranched polymers were also investigated. The results showed that introduction of triazatruxene units into the hyperbranched structure endowed the polymer with good thermal stability and highly amorphous properties. Photophysical investigation of PTFx revealed strong blue emission in both solution and solid states. Hyperbranched polymers with higher degree of branching and proper content of linear fluorene units exhibited better photophysical properties in terms of narrow emission spectra and relatively high quantum efficiency as well as improved thermal spectral stability. The triazatruxene branching unit also played a role in raising the HOMO energy levels relative to those of polyfluorenes that would help to improve the charge injection and transport properties. The incorporation of triazatruxene unit into hyperbranched polymers has thus explored an effective avenue for constructing optoelectronic polymers with improved functional characteristics.     

Novel Functional Conjugative Hyperbranched Polymers with Aggregation‐Induced Emission: Synthesis Through One‐Pot “A2+B4” Polymerization and Application as Explosive Chemsensors and PLEDs

With the aim to develop new tetraphenylethylene (TPE)‐based conjugated hyperbranched polymer, TPE units, one famous aggregation‐induced emission (AIE) active group, are utilized to construct hyperbranched polymers with three other aromatic blocks, through an “A₂+B₄” approach by using one‐pot Suzuki polycondensation reaction. These three hyperbranched polymers exhibit interesting AIEE behavior and act as explosive chemsensors with high sensitivity both in the nanoparticles and solid states. This is the first report of the AIE activity of the TPE‐based conjugated hyperbranched polymers. Their corresponding PLED devices also demonstrate good performance.     

Elaboration of corona functionalized regular unimolecular hyperbranched polystyrene nanoparticles

Functional arborescent graft polystyrenes prepared by the “graft-on-graft” technique, involving the iterative grafting of end functional polymer chains onto reactive polymer backbones were synthesized. The zero-generation comb polymers and then the first generation hyperbranched structures were obtained by the coupling reaction of living α-acetal polystyryllithium onto linear or comb chains of poly(chloroethyl vinyl ether) (PCEVE) of controlled D̄P̄_n and structure. Both the PS grafts and the PCEVE reactive backbones were synthesized individually by living polymerization techniques. Initiation of styrene polymerization from acetal functionalized lithium derivatives yield the ω-functionalization of all external polystyrene branches. Derivatization of these acetal branch termini allowed the generation of aldehyde, hydroxyl and carboxyl groups as well as the introduction of functional organic molecules at the periphery of the nanoparticles.     

On Crystallization in Polypropylene-Polyethylene Blends

Polymer blends are of interest both in terms of application and science.Althoughpolyethylene( PE) and polypropylene( PP) are both aliphatic hydrocarbons,because oftheir high molecular weight they might be expected to be of limited miscibility.Theyhave long been considered as immiscible,and indeed the miscibility of PP and linear lowdensity polyethylene( LLDPE) was found by electron microscopy to be very limited,sothat even at as low as 1 % of PP phase separated droplets of PP were observ…     

High-Resolution Transmission Electron Microscopy Re-examined as a Tool in Solid State Chemistry

Transmission electron microscopy (TEM) can be used with crystalline solids to obtain direct images of small structural groups comprising a few coordination polyhedra with resolution nearly down to atomic scale (“lattice imaging”). More exact knowledge of the conditions required for direct imaging, as well as improvements in the instruments themselves, have now made it possible to examine very small defect regions (microdomains), faults in the stacking sequence of structural groups or atom layers (planar or Wadsley defects), and isolated defects in narrowly delimited areas that may actually be below the dimensions of the unit cell. The structural principle of the very smallest ordered regions can even be determined when X-ray structure analysis proves unable to do this. “Block structures” are particularly suitable as models for the testing and further development of the high-resolution method; the detection of three-dimensional, two-dimensional, and one-dimensional defects has been studied on such structures.     

One‐step synthesis of hyperbranched polyethylene macroinitiator and its block copolymers with methyl methacrylate or styrene via ATRP

Block copolymers of hyperbranched polyethylene (PE) and linear polystyrene (PS) or poly(methyl methacrylate) (PMMA) were synthesized via atom transfer radical polymerization (ATRP) with hyperbranched PE macroinitiators. The PE macroinitiators were synthesized through a “living” polymerization of ethylene catalyzed with a Pd‐diimine catalyst and end‐capped with 4‐chloromethyl styrene as a chain quenching agent in one step. The macroinitiator and block copolymer samples were characterized by gel permeation chromatography, ¹H and ¹³C NMR, and differential scanning calorimetry. The hyperbranched PE chains had narrow molecular weight distribution and contained a single terminal benzyl chloride per chain. Both hyperbranched PE and linear PS or PMMA blocks had well‐controlled molecular weights. Slow initiation was observed in ATRP because of steric effect of hyperbranched structures, resulting in slightly broad polydispersity index in the block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3024–3032, 2010     

Functional Opals from Reactive Polymers: Complex Structures,Sensors, and Modified Photoluminescence

Summary: This paper describes the synthesis and properties of functional opal structures, so-called colloidal photonic crystals (CPCs), from a variety of reactive polymers. Photoprocessable opals are presented as well as opals with incorporated “smart” defect layers that can be actively addressed by external stimuli. In addition, opals with functional bio-macromolecular defects have been developed. They present a new class of materials for optical biomonitoring through shifts of the induced photonic defect mode. Strong modification of photoluminescence according to the photonic bandstructure is observed from opals with embedded exclusively luminescent defect layer.     

Hyperbranched methacrylates by self-condensing group transfer polymerization

The synthesis of hyperbranched methacrylates was achieved by self-condensing group transfer polymerization of 2-(2-methyl-1-triethylsiloxy-1-propenyloxy)ethyl methacrylate ( 1 ). “Back-biting” is shown to be the predominant side reaction. In spite of this, the compact nature of the hyperbranched molecules was demonstrated through SEC-viscosity measurements and comparison with a linear analogue. The degree of branching can be controlled by copolymerization with conventional monomers, e.g. MMA, and the living polymers can be used as macroinitiators for star-shaped polymers.     

Random Computer Generation of 3D Molecular Structures: Theoretical and Statistical Analysis

Summary: A computer program has been developed to generate three‐dimensional molecular structures randomly from a given collection of elementary chemical functional groups: the so‐called fragment database. The gradual assembly of the various fragments present in the database is performed according to a “self‐generation algorithm” (SGA). The latter is based on the covalent binding, step by step, between the unoccupied electronic valencies associated with the fragments of the database, and those of the growing molecular structure. When the number of electronic valencies of the molecular structure is zero, the growth process for this particular molecule is completed. It is shown that SGA is able to reproduce the asymmetric mass distributions of some natural colloids, like humic substances. In this article, particular attention is given to the analysis of the relationship existing between the fragment composition of the database and that of the collection of molecules generated. Mathematical expressions are derived and discussed, to understand the relationship between the proportions of the different types of fragments and the final composition of the generated molecular ensembles. For that purpose, a “pathway” formalism is proposed to describe exhaustively the whole set of generated molecules by specifying the distribution function of all of the fragments therein integrated. A statistical analysis that satisfactorily reproduces the predictions of the pathway model is extensively discussed.

Example of a three‐dimensional structure obtained with the “self‐generation algorithm” (SGA).     

Comparison of Loading Efficiency between Hyperbranched Polymers and Cross‐Linked Nanogels at Various Branching Densities

The effect of branching point structures and densities is studied between azido‐containing hyperbranched polymers and cross‐linked nanogels on their loading efficiency of alkynyl‐containing dendron molecules. Hyperbranched polymers that contained “T”‐shaped branching linkage from which three chains radiated out and cross‐linked nanogels that contained “X”‐shaped branching linkage with four radiating chains are synthesized in microemulsion using either atom transfer radical polymerization (ATRP) or conventional radical polymerization (RP) technique. Both polymers have similar density of azido groups in the structure and exhibit similar hydrodynamic diameter in latexes before purification. Subsequent copper‐catalyzed azide–alkyne cycloaddition reactions between these polymers and alkynyl‐containing dendrons in various sizes (G1–G3) demonstrate an order of dendron loading efficiencies (i.e., final conversion of alkynyl‐containing dendron) as hyperbranched polymers > nanogels synthesized by ATRP > nanogels synthesized by RP. Decreasing the branching density or using smaller dendron molecules increases the click efficiency of both polymers. When G2 dendrons with a molecular weight of 627 Da are used to click with the hyperbranched polymers composed of 100% inimer, a maximum loading efficiency of G2 in the loaded hyperbranched polymer is 58% of G2 by weight. These results represent the first comparison between hyperbranched polymers and cross‐linked nanogels to explore the effect of branching structures on their loading efficiencies.

     

Cycloaddition Reactions and Dendritic Polymer Architectures – A Perfect Match

Summery: The potential of cycloaddition (CA) reactions for the synthesis of dendritic polymers is pointed out. The [4 + 2] Diels Alder cycloaddition as well as 1,3-dipolar CA reactions including “click chemistry” are addressed, and the advantages of these reactions like high selectivity, thus high tolerance towards additional functionalities, high yields and synthesis under mild reaction conditions are highlighted. New perfectly branched dendrimers as well as hyperbranched polymers have been prepared and modified using the 1,3-dipolar cycloaddition reaction of azines with alkynes. The 1,3-dipolar CA reaction of bisazine with maleimides results in hyperbranched and thus, irregular and broadly distributed polymers though with a degree of branching of 100% due to special intermediate formation. The [4 + 2] Diels Alder cycloaddition was successfully applied for the synthesis of highly branched polyphenylene structures using the AB₂ + AB and the A₂ + B₃ approach. CA reactions are also very suitable for highly efficient polymer analogous reactions and thus, they can also be used to prepare complex polymer architectures like dendronized polymers.