A core-shell hybrid nanocomposites, possessing a hard core of nano titanium dioxide (n-TiO 2 ) and a soft shell of brushlike polystyrene (PS), were successfully prepared by surface-initiated atom transfer radical polymerization (ATRP) at 90 C in anisole solution using CuBr/PMDETA as the catalyst, in the presence of sacrificial initiator. FTIR, 1 H NMR, XPS, TEM, SEM, TGA, and DSC were used to determine the chemical structure, morphology, thermal properties, and the grafted PS quantities of the resulting products. TEM images of the samples provided direct evidence for the formation of a core-shell structure. The thermal stabilities of the grafted polymers were dramatically elevated relative to that of pristine PS according to TGA results. DSC results demonstrated that the TiO 2 -PS nanocomposites exhibited higher glass transition temperature (T g ) compared with pristine PS. The molecular weights of the free polymers formed by sacrificial initiator, which were similar to that of surface-attached polymers were measured by GPC instrument which showed that the molecular weights of PS were well controlled with a relatively narrow polydispersity index (PDI < 1.2).

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Abstract. Two methacrylate monomers containing azo and electronical push and pull structure, e.g. 2-Methyl-acrylic-acid-2-{[4-(4-cyano-phenylazo)-3-methyl-phenyl]-ethyl-amino-ethyl ester (MACP) with cyano substituted and 2-Methylacrylic-acid-2-{ethyl-[4-(4-methoxy-phenylazo)-3-methyl-phenyl]-amino}-ethyl ester (MAMP) with methoxy substituted, were synthesized and polymerized using 2-cyanoprop-2-yl dithiobenzoate (CPDB) as chain transfer agent and 2,2'-azobisisobutyronitrile (AIBN) as initiator. The results showed that the polymerization displayed characteristics of 'living'/controlled free radical polymerization. Thus, the obtained polymers, polyMACP (pMACP) and polyMAMP (pMAMP), had controlled molecular weights and narrow molecular weights distribution. The chain extension experiments of pMACP and pMAMP using styrene as the second monomer were successfully carried out. The photo-induced trans-cis-trans isomerization kinetic of pMACP and pMAMP in chloroform solution were described. Marked differences in rate for the trans-cis and cis-trans isomerization of pMACP and pMAMP were observed in chloroform solution due to the different electronic effects in these two polymers. Photoinduced birefringence and surface relief grating (SRG) of the pMACP and pMAMP were investigated in thin film state. Keywords: polymer synthesis, azopolymers, photo-induced birefringence, surface relief grating (SRG), reversible additionfragmentation chain transfer polymerization (RAFT)eXPRESS Polymer Letters Vol.2, No.8 (2008) [589][590][591][592][593][594][595][596][597][598][599][600][601] Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2008.71 polymers by linearly polarized (LP) photoexcitation of the azobenzene group, which undergoes trans-cis-trans isomerization [17,18] , giving rise, after repeated photoexcitation and isomerization cycles, to a net excess of azobenzene moieties oriented with their transition dipole moments perpendicularly to the direction of the pump electric field. The anisotropic distribution of chromophores provides birefringence and linear dichroism of the film can be erased by irradiation with depolarized or circularly polarized (CP) light, thus reproducing the original isotropy in the material. According to Rabek's report [19], azo compounds can be divided into three classes: azobenzene type, aminoazobenzene type and pseudo-stilbene type. Azobenzene containing compounds with electronical push and pull structures (pseudo-stilbene type) and aminoazobenzene type molecules can isomerize from cis configuration back to trans configuration very quickly at room temperature. However, the thermal cis-trans isomerization in azobenzene-type molecules is relatively slow, and it is even possible to isolate the cis isomer [20]. Typically, the azobenzene containing polymers can be obtained through two ways: incorporating azobenzene chromophores into the backbones directly during the polymerization process [21][22][23], and postpolymerization modification technique [24][25][26][27]. Generally, conv...

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