Prepaartion And Properties Of Core-shell Polymer Composite Particles

Core-shell micro/nanospheres are defined as composite particles with double-layers ormulti-layer structure. Several methods have been developed for preparing such particles.These methods can be divided into two broad categories according to whether the formulationrequires a polymerization reaction or not. The former can be achieved using monomers asstart material via various polymerization methods while the latter can be achieved using asystemic prepared or modified natural polymer as a start material via its self-assembly.Core-shell particles can be used as encapsulation materials for active agents and drug carriersbecause of their unique chemical structures, surface functionalities and easily-controlledparticle size and its distribution. In this paper, five kinds of micro/nanoparticles includingmicrocapsules were prepared as following with the control of morphology, particle size andits distribution investigated as well. The properties and applications of the preparedmicrospheres in controlled release system were also studied.1. The monodispersed P(St-PEG) nanospheres were prepared by emulsifier-freeemulsion polymerization of styrene (St) using a novel azo-type poly(ethylene glycol)macroinitiator (VPE) in water. The particle size of the nanospheres can be controlled from70to178nm by changing the concentration and molecule weight of VPE. The as-preparednanospheres with PSt as core and PEG as shell showed uniform morphology and excellentmonodispersity. The recipe of polymerization was highly simplified due to the multi-functionof VPE as initiator, emulsifier and stabilizer.2. Poly(tert-butyl methacrylate) macrointermediates ended by bromine atom(PtBMA-Br) were synthesized by atom transfer radical polymerization (ATRP) usingethylbromopropionate (EPN-Br) as initiator in bulk in the presence ofN,N,N′,N″,N″-pentamethyl diethylenetriamine (PMDETA) as a single ligand. A newmacromonomer (MAA-PtBMA) was successfully prepared via end-group nucleophilicsubstitution of methacrylic acid to obtain a high efficiency of C=C incorporation. Then, thePtBMA graft polystyrene (PtBMA-g-PSt) microspheres were prepared by dispersioncopolymerization of MAA-PtBMA macromonomers with St using2,2‘-azobisisobutyronitrile(AIBN) as free radical initiator in ethanol. The PtBMA-g-PSt microspheres showed uniformmorphology and excellent monodispersity. PMAA-g-PSt microspheres with PSt as core andPMAA as shell could be abtained after the resulting PtBMA-g-PSt microspheres directionalhydrolyzed. The size of microspheres could be controlled form1.2to2.18μm by adjustingthe molecular weight and feeding amount of macromonomer.3. Polystyrene (PSt) microspheres with diameter of375nm to be used as the seeds forseeded emulsion polymerization were prepared via emulsion polymerization using potassiumpersulfate (KPS) as initiator in ethanol-water mixed solvents. Emulsifier-free seeded emulsioncopolymerization of styrene (St) with acrylonitrile (AN) was carried out in the presence ofethylene glycol monomethoxymonomethacrylate (PEGm) macromonomer as reactivestabilizer and2,2‘-azobisisobutyronitrile (AIBN) as initiator to obtain submicron-sized PEGmgraft styrene-co-acrylonitrile (PEGm-g-PSAN) composite particles. Microspheres with uniform morphology could be obtained using AN as monomer, while microspheres withunique morphology using AN together with St as monomers. The morphology of themicrospheres also could be controlled by changing the concentration of PEGm， totalconcentration of St and AN, initiator type and the monomer feeding method as well.4. A novel trimethylene carbonate derivative5-(2-methoxyethyoxymethyl)-5-methyl-[1,3]-dioxa-2-one (TMCM-MOE1OM) was prepared by four steps using1,1,1-Tris(hydroxylmethyl)ethane (THME) as start material. The polymerization of TMCM-MOE1OM wasinitiated by benzaldehyde in CH2Cl2with1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) ascatalyst to obtain the homopolymer poly{5-(2-methoxyethyoxymethyl)-5-methyl-[1,3]-dioxa-2-one}[P(TMCM-MOE1OM)]. An amphiphilic block copolymer P (TMCM-MOE1OM)-b-PLLA was systhesised via the ring opening polymerization of l-lactide (LLA)initiated by the prepared homopolymer. The ratio of hydrophobic to hydrophilic component ofthe resulting block copolymer was6:1. The hydrophilic properties of the P(TMCM-MOE1OM) segment resulted in microspheres using acetonitrile/water as solvent pair by aselective solvent evaporation process. The size of P (TMCM-MOE1OM)-b-PLLAmicrospheres could be controlled from174to1000nm by changing the adding amount ofwater. The loading amount of hydrophilic drug model, cyclophosphamide monohydrate (CPh)in the surface of the microspheres was200μg/mg. A sustained release of CPh from themicrospheres was obtained after an obvious burst release of about50%during the initialperiod.5. Uniformed solid polymer-fragrance composite microspheres (PFCM) with spheremorphology and satisfied fluidity were prepared via in situ polymerization usingurea-formaldehyde resin (UF) as shell material in the presence of Tween-80and hydrochloricacid (1:50) acting as emulsifier and catalyst, respectively. The amount of embedded fragrancereached32%. The resulting PFCM microspheres performed thermo stability andcontrolled-release behavior based on thermogravimetry (TG) analysis. The fragranced plasticprepared with the prepared PFCM microspheres was proved to be scented stably and stronglywith its longevity prolonged above1year without any negative effect on its mechanicalproperty. The weight lose of fragrance during the process was reduced below10%.All these prepared core-shell polymer composite microspheres have potentialapplications in various fields. Some of them can be used as drug carrier and encapsulationmaterial of fragrance for controlled release system, which have been proved.