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1、Coreshell polymers:a review,RSC Adv.,2013,3,15543-15565,Reporter:Rui Niu Jianwu Guo Xiaobo Teng 2013.11.20,Content,1.Introduction2.Classifications3.Preparation of core-shell4.Development of latex particle morphology of CPS5.Characterizations 6.Recent study on core-shell polymers7.Applications8.concl
2、usion,1.Introduction,In1961,Hughes and Brown investigated the physical properties of coreshell polymer(CSP)and their interesting morphology.This class of material has attracted much attention because of the combination of superior properties not possessed by the individual components.The systems mig
3、ht combine the characteristics and properties of both shell and core where the surface properties of the shell are translated to the core,imparting new functionality to the CSP.Macromolecules,2003,36(6),19881993.,CSPs are structured composite particles consisting of at leasttwo different components,
4、one in principle forms the core and another forms the shell of the particles.,2.Classification,Core shell polymers(CSPs),State,Hydrogels,NIPAM,Non-NIPAM,Conventionalmonomer,Acrylamide derivatives,Size,Nano,Micro,Non-Hydrogels,Non-aqueous,Organic-inorganic,Single,2.1 Coreshell polymer hydrogels,Prope
5、rty:CSP hydrogels have been produced either to modify the stability and physical properties of the polymers or to impart stimuli-responsive properties to responsive particles.,Application:CSP hydrogels made of smart materials have widespread applications,especially in biomedical areas,as their respo
6、nse to surrounding environmental changes such as temperature and pH,etc.,Adv.Drug Delivery Rev.,1996,18(2),219267.Macromolecules,1998,31(25),89128917.,2.1.1 NIPAM based CSP hydrogels,32,switchable or smart materials,poly(N-isopropylacrylamide PNIPAM)has been extensively used as a main component in C
7、SP hydrogels due to its thermoresponsive properties.,Macromolecules,1998,31(25),89128917,Langmuir,2004,20(11),43304335,J.Colloid Interface Sci.,2012,376(1),97106.,2.1.2 Non-NIPAM CSP hydrogel,non-NIPAM CSPs(conventional monomer),hydrophilic AAm,hydrophilic AAc,hydrophobic MMA,hydrophobic St.,produce
8、 responsive CSPs,non-NIPAM CSPs(acrylamide derivatives),NIPMAM,NNPAM,N-ethylacrylamide,N-vinylisobutylacrylamide,used to polymerize temperature-sensitive microgels,2.2 Non-hydrogel coreshell polymer,Non Hydrogels,Non-aqueous,Organic-inorganic,Single,Core:solid polymer particle or rubberShell:hard po
9、lymerUsed:paints,coating applications,pigments,binder,Used：nanotechnology and biomedical applications,such as a signal-molecular template,live-cell imaging,drug carrier and drug release.,Def:non-cross linked CSPs consisting of amphiphilic block or graft polymers in which hydrophobic and hydrophilic
10、segments are covalently connected with the dendritic or hyperbranched core-shell.,在下面介绍,J.Am.Chem.Soc.,2010,132(35),1221812221,synthesis of new functional materials for light-emitting devices,solar cells,photodetectors,biomedical and sensor applications.,Core,surfactant,poly(ethylene oxide),poly(vin
11、yl benzyl chloride),poly(vinyl pyrrolidone),polymer,different copolymers,poly(styrene acrylic acid),Shell,metals,metal oxides,metal chalcogenides,silica,Adv.Mater.,2009,21(5),509534.,J.Mater.Chem.,2012,22(22),1137011378.,Used,Inorganicorganic CSPs,butadiene,styrene,3.Preparation of coreshell polymer
12、s,CSPs are typically prepared by a series of consecutive,emulsion,dispersion or precipitation polymerization sequences with different monomer type.,CSP particles,multi-step,One-stage reaction:a facile method to prepare polymer particles with coreshell morphology.,seed particles as a core material,se
13、cond or third stage monomer is polymerized in the seed latex particles,Disadvantage:expensive,timeconsuming,Chim.Acta,2003,496(12),5363.,Macromolecules,2009,42(13),45114519.,consecutive emulsion,Dispersion polymerization：a class of larger particles and irregular shape of polymer particles were produ
14、ced in precipitation polymerization.polymer particles in the range of 115 m.The formed polymers are insoluble in continuous phase.,Based on ploymerization classes,emulsion polymerization:the main process for the preparation of commercial emulsion,which involves a monomer that has limited solubility
15、in water.particle diameter is typically within the range of 110 m.,Macromolecules,2009,42(13),45114519,Part A:Polym.Chem.,2001,39(19),34343442,Example Fig.3 illustrates common methods to prepare CSPs described by Li and Stover.,emulsion polymerization using reactive surfactants,Two-stage emulsion po
16、lymerization was the first general method,step-wise heterocoagulation of smaller cationic polymer particles onto larger anionic,heat treatment.,block copolymers can be used to produce coreshell type polymer nanospheres via block copolymerization.,3.1 Emulsion polymerization,Emulsion polymerization s
17、ynthesized process is commonly used to produce water based resins with a variety of physicochemical and colloidal properties.,Characterized:emulsified monomer droplets(1-10 um in diameter)dispersed in a continuous aqueous phase with the assistance of an oil-in-water surfactant at the very beginning
18、of polymerization.The emulsion polymerization technique is a commercially and technologically important reaction system.This technique continues to grow through its versatile reaction and its ability to tailor the properties of the emulsion polymer produced.,Emulsion polymerization,semi-batch proces
19、s,batch process,The most significant difference between batch and semi-batch emulsion polymerization,Semi-batch process allows two types of feed stream,M(monomer)feed and E(emulsion)feeds,Batch processes are of limited versatility for producing emulsion and are mainly use in academic research with s
20、imple reaction formulations.,Advantage of Semi-bath:(1)Good temperature control with extra cooling of polymerization process.(2)Easy to control polymerization rate by keeping process starved.(3)Flexible control of molecular weight.(4)Good polymer composition control.,Example one,Lin et al.prepared t
21、hermoresponsive CSPs of P(NIPAM-co-AAc)or poly(NIPAM-co-SA)copolymer using batch process surfactant-free emulsion copolymerization(SFEP).,Example two,Fig.6 A schematic representation of the copolymerization and cross-linking reaction mechanism of AN with NIPAM in sodium dodecyl sulfate(SDS)micelles.
22、,Serrano-Medina prepared nano/microgels of poly(P(NIPAM-co-PEGMEMA-co-2MBA)by one-stage surfactant free emulsion polymerization(SFEP),The high sensitivity of these P(NIPAM-co-AAc)microgels to small changes in pH and temperature suggest that they could be useful in drug delivery applications,Example
23、three,Fig.7 Schematic representation of the formation of the coreshell NPs by semi-batch emulsion polymerization.Reproduced from ref.83 by permission of American Chemical Society.,Ni et al.synthesized hybrid nanoparticles(NPs)with a polystyrene core and a hybrid copolymer shell in a two step process
24、:emulsion polymerization of styrene and subsequent copolymerization of styrene with-methacryloxypropyltri-methoxysilane(MPS).,3.2 Dispersion polymerization,This technique allows synthesis of micro particles in the range of 115microns.Most of the ingredients in this process,including surfactant,initi
25、ators and monomers,are soluble in continuous organic phase and which form polymers that are insoluble in continuous phase.,Example,Li et al.reported the preparation of narrowly distributed nanogels by two-stages dispersion polymerization.,First,the core particles composed of PNIPAM were synthesized
26、and then the core particles were used as nuclei in the following stage for subsequent shell addition of poly(4-vinylpyridine)(P4VP)(四乙烯基吡啶).,3.3 Other techniques to prepare coreshell polymers,Example one,three-step synthesis approach was used to prepare thermoresponsive CSP by Xiao et al.,A single-m
27、olecular particle of hyperbranched conjugatedpolyelectrolyte(HCPE)was synthesized by Pu et al.,Example two,Fig.9 shows a schematic illustration of the synthesis routes of single-molecular nano-particles multi-HPBPEA-g-PNIPAM,Three-step synthesis approach was used to prepare thermoresponsive CSP by C
28、ai and Liu to synthesize a novel single-molecular/unimolecularnanoparticle,multihyperbranchedpoly2-(2-bromopropionyl)oxy)ethyl acrylate)-g-poly(Nisopropylacrylamide(HPBPEA-g-PNIPAM),via atom transfer radical polymerization(ATRP).,Mu et al.prepared a monodisperse and multilayer coreshell(MMLCS)via su
29、rface cross-linking emulsion polymerization.,Example three,Fig.10 shows the preparation of multilayer coreshell(MMLCS)emulsion via surface cross-linking emulsion polymerization.The PBA core was synthesized by seed polymerization using the PBA seed at 75 2for 3.5 h.,GMA:甲基丙烯酸缩水甘油酯BA：丁基丙烯酸酯,Example fo
30、ur,Thermosensitive PStPNIPAM coreshell particles were synthesized using photoemulsion polymerization technique.,This new synthesis strategy may Produce a thermosensitive shell of PNIPAM networks with morehomogeneous cross-linking density.,Example five,5 mol%NIPAM,Kim et al.fabricated monodisperse co
31、reshell microgels based PNIPAM by capillary microfluidic technique.,Used to develop novel biomaterials forapplications in drug delivery,artificialmuscles,and cancer therapy.,Fig.12 Drop formation of pre-microgel drops in a capillary microfluidic device.（毛细管装置中微凝胶的液滴状微流动图示意图）,4.Development of latex p
32、article morphology of CSP,Affected by many variables,cross-linking,radical penetration,diffusion,processing,polarity of monomers,batch processing,semi-batch processing,4.1 Effect of cross-linking,Durant et al.have predicted the effect of cross-linked seed latex particles on equilibrium particle morp
33、hology of two component particles,which is considered to be occluded morphology(OCC),inverse coreshell(ICS)and coreshell(CS)structures.,Sheu et al.prepared core-shelllatices by seeded emulsionpolymerization of styrene(St)into polystyrene(PSt)laticeswith varying amounts of DVB cross-linker.,Example o
34、ne,Example two,Fig.14.PSt formed a homogeneous shell on uncross-linked PSt seed.The morphology of the shell changed to a snowman structure when PSt seed was cross-linked with around 0.2%of DVB.At 6%of DVB the shape of the shell changed into a raspberry structure.,4.2 Radical penetration and diffusio
35、n,Fig.15 Possible particle morphologies produced from differing radical penetration depth.Reproduced from ref.100 and 104 by permission of Elsevier and Taylor&Francis.,monomers,Latex particle,penetrates,Ivarsson et al.and Jo nsson studied the influence of the relative difference apparent between gla
36、ss transition temperature,Tg,and reaction temperature within particle on the ability of oligomeric radicals.,One hand,On the other hand,polymer radicals may be restricted to the periphery of the particles when the radical flux is high enough and the monomer feed is slow enough for glassy seed polyme
37、rs,but probably not for low Tg seed polymers.,5.Characterizations,6.Recent study on coreshell polymers,Coreshell polymers have attracted enormous research interest,both from the point of view of fundamental science and for prospective applications.In addition,the unique properties of CSP attracted s
38、cientists to study and developed new microgel systems and re-investigated older systems using advanced techniques and methods.,Example one,Yu et al.prepared monodisperse CSmicrospheres composed of a PNIPAM-co-PHEMA by microfluidic emulsification,freeradical polymerization and ATRP.,Example two,Lee e
39、t al.demonstrated that coreshell poly(styrene/pyrrole)P(St/Py)particles were successfully prepared by using Fe3+-catalyzed oxidative polymerization with emulsifier-free emulsion polymerization in aqueous medium.The resulting P(St/Py)particles showed excellent electrical conductivity(2.21 Scm-1)due t
40、o the coreshell morphology.,Fig.26(a)shows a schematic for the formation of coreshell P(St/Py)particles and(b)the detailed reaction mechanism of pyrrole monomers via Fe3+-catalyzed oxidative polymerization.,Example three,Zhang et al.reported a facile method to create a living in situ gelling system
41、for controlled formation of hydrogels from a hyperbranched polymer(BAP)with disulfide-linked coreshell structures.,Contribution:they developed an inverse emulsion technique to obtain micro or nanodroplets of a disulfide-linked coreshell BAP.To produce fine-tunable micro/nano drug carriers,having bro
42、ad implications in diagnostics and therapeutic delivery systems,Fig.27(A)Schematic illustration of the core/shell separation process dissociation of the shells and cross-linking of the cores and(B)schematic depiction of the synthetic approach to controlled formation of(multilayered)hydrogel particle
43、s.,Example four,a,Schematic illustration of a core-shell microgel which undergoes three regions of different swelling behavior(completely reversible process).b,corresponding classification of previously mentioned regions in an exemplary Rh(T)-diagram of a core-shell microgel system with 10 mol%cross
44、-linked cores.In region I we find a restricted shell collapse,while region II covers the linear swelling behavior.Region III indicates the occurrence of an active core collapse.,Zeiser et al.PNIPMAM-co-PNNPAM.In the region between 25 and 41,the response of the particles is directly proportional to t
45、he temperature。,Example five,Peng et al.studied a novel approach for preparing hollow PSt particles by seed emulsion polymerization.The particles are composed of PNIPAM-co-PSt and Hollow particles have shown potential applications in drug delivery,catalysts,controlled release etc.,Fig.30 Preparation
46、 of hollow particles with PNIPAM microgels as the cores.,CSP features,7.Applications,External stimuli(temperature,ionic strength,pH,external stress solvent nature),8.Conclusion,The combination of a core in the center surrounded by the shell seems to have unique properties of both the materials of th
47、e core and the shell.,(3)Morphological analysis of CSPs is the most important data that can provide detailed information about internal structure which leads to an estimation of their properties.,(2)Applications of CSPs are expanding in various areas such as impact modifiers,surface coatings,printin
48、g,catalysis,pollution control,sensing,and drug delivery in biomedical applications.,(4)NIPAM is the most commonly used monomer to prepare CSPs,due to its high response to the environmental change.,(5)The environmental responses of CSPs,such as thermoresponse and pH sensitivity,are the most important characteristic for drug delivery applications.,(6)According to the literature,emulsion polymerization seems to be the most used technique to prepare CSPs in different size.,谢谢,Thank you!,
