Surface-incited Controlled/Living Radical Polymerization To Prepare Functional Polymer Films

The ability to modify and functionlize filter membrane has got a lot ofattention, and the bio-functionlization of polymer substract has been anotherhotspot. Covalent tethering of functional brushes by surface incitedcontrolled/living radical polymerization (SI-CRP) on polymer film surfacewithout any destruction of bulk properties is of crucial importance to impartnew surface performances. In SI-CRP, well defined dense and structurepolymer brush grows from the initiator immobilized on polymer surface toprepare the functional polymer film, and most polymer film surface is inert.Therefore, the initiator immobilization is quite important. In this thesis, theinitiator immobilization strategies and the applications of functional polymercomposite film was studied in detail, which enriched the SI-CRP techniques,and developed three new initiator immobilization methods to fabricatefunctional polymer composite film. The main contents were listed as followed:1. A simple and highly efficient method to initiate surface incited radicalpolymerization by plasma treatment on polycarbonate track-etched (PCTE)membrane was studied. The PCTE membranes was pretreated via plasma andoxidized by air to induce peroxy bond, and subseguently thermal-graftcopolymerization of acrylic acid (AAc) was carried out. Under the highefficient initiating, AAc monomer solution (2wt%) could be polymerized toprepare pH sensitive PCTE membrane after3h.2. A facile two-step method was first developed for the covalentimmobilization of ATRP initiators on the surface of Nylon membrane and itsinside pores. The Nylon membrane was firstly functionalized bypolydopamine, the bromoalkyl initiator was then immobilized on thepolydopamine functionalized Nylon membrane surface in a two-stepsolid-phase reaction, followed by ATRP of acrylic acid (AA) in a aqueoussolution. The resulting Nylon membranes with grafted PAA side chains werecharacterized and studied by XPS and SEM. The results showed that thegrafted PAA polymers were formed uniformly inside the pores throughout theentire membrane thickness. With increase in the pore-filling ratio, the porediameters of PAA-grafted membranes became smaller. An approximatelylinear increase in graft yield (GY) of the grafted PAA chains withpolymerization time was observed, indicating that the chain growth from thePCL-Br surface was consistent with a "controlled" and well-defined process. The Nylon-g-PAAc membranes exhibit rapid and reversible response of theflux to the environmental pH as pH is switched between3and9.3. An alternative aminolysis-based method was developed for thecovalent immobilization of ATRP initiators on the polycaprolactone (PCL)film surfaces. It is possible to introduce free amino and hydroxyl groups onPCL film surfaces through the aminolysis reaction, and is followed with thereaction of2-bromoisobutyryl bromide (BIBB) to produce the ATRP initiatorspecies. Well-defined PDMAEMA brushes were subsequently prepared viasurface-initiated ATRP from the initiator functionalized PCL surfaces. Thecell-adhesion property on the functionalized PCL surface could be controlledby adjusting the ratio of PDMAEMA/gelatin and the gene transfectionproperty on the immobilized cells was dependent on the density of theimmobilized cells. With the good cell-adhesive nature of gelatin and theefficient gene transfection on the dense immobilized cells, the incorporatingthe suitable of PDMAEMA/gelatin complexes onto PCL surfaces could endowthe PCL substrates new and interesting properties for potential tissue enginering applications.4. The gelatin-functionalized PCL film surfaces are prepared viaSI-ATRP of GMA. The gelatin-functionalized PCL film surfaces exhibitexcellent cell-adhesion ability to both adherent and suspension cells. Theattached adherent cells demonstrate the characteristic elongated morphologieswith good spreading capability, while the attached suspension cells can maintain the original status of the round morphologies without spreading. Thegelatin coupled on the PCL surface could be used to absorb the cationicvector/plasmid deoxyribonucleic acid (pDNA) complexes via electrostaticinteraction. The local gene transfection property on the immobilized cells isdependent on both the density of the immobilized cells and the loading typesof pDNA complexes. The transfection efficiency of different assemblemethods of pDNA complex was compared. With the pre-and post-loadingsandwitch-like gene transfection, the gelatin-functionalized PCL film surfacecan substantially enhance the transfection properties to different cell lines. Thepresent study is very useful to spatially control local gene delivery and directcellular functions within PCL-based tissue scaffolds.5. The photo-induced one-step method was first developed for thecovalent immobilization of ATRP initiators on the C-H group-containingsubstrates such as biaxially oriented polypropylene (BOPP). The ATRPinitiators could be patterned immobilized by using of metal mask. The C-Hbonds of precise location of inert polymer surfaces were readily transferred tobromoalkyl initiator with the present of metal mask, followed by ATRP of2-(dimethylamino) ethyl methacrylate (DMAEMA) and glycidyl methacrylate(GMA) respectively to produce the resultant patterned BOPP-g-PDMAEMAand BOPP-g-PGMA films. The epoxy groups of the PGMA microdomainscould be aminated for covalently coupling IgG, while the PDMAEMAmicrodomains were used for immobilizing IgG via electronic interactions. The resultant IgG-coupled microdomains could interact with the correspondingtarget proteins, anti-IgG.6. The biggest drawback of ATRP is the use of copper, and it is moreserious when it applied in the biomedicine. A novel none-copper ATRPsystem collaborated by UV and BIXAN semipinacol radicals is exploed tosolve this problem. Preliminary results shows that under the low lightintensity of2mW/cm2, an approximately linear increase in GY of the graftedPDMAEMA chains with polymerization time was observed, indicating thatthe chain growth from the BOPP-BHAP surface was consistent with a"controlled" process. Through some comparison experiments, the role ofBHAP and BXIAN was studied. The controlled/living character wasconfirmed by the homopolymerization in solution under similar condition.7. The Low density polyethylene (LDPE) film surface was conjugatedwith PEGMA from the "dormant" ITXSP groups for forming antifoulingbackground, and subsequently block polymerized the copolymer of PGMAand (PGMA-Polylysine) from the ITXSP sits at the end of PEGMA chains.The epoxy groups of the GMA prior were aminated with cell-adhesive proteinPoly lysine to protect epoxy groups from ring-opening reaction. Thefunctionalized LDPE film surfaces both exhibit excellent antifouling andcell-adhesion property at different location. The attached adherent cellsdemonstrate the characteristic elongated morphologies with good spreadingcapability. The present study is very useful to spatially control local cell attachment and direct cellular functions within LDPE-based tissue scaffolds.The design and microfabrication of the active patterning on polymer substratesvia surface-initiated photochemical modification is of crucial importance indeveloping novel functional materials.