Heterogeneous Grafting Of Mono Epoxy Terminated Polydimethylsiloxane Onto Gelatin And Preparation Of Gradient Film

Considering the ideal film for protein–based materials‘ coating, such as bone or leather, one side should closely contact with collagen molecules on the surface of the materials; however, the other which is exposed to the air would be expected to possess the surface hydrophobicity, ventilate and safe. For this purpose, PDMS–E grafted gelatin(PGG) seems an ideal candidate. PDMS with low glass transition temperature(Tg) can impart the desired flexibility, hydrophobicity, and safety when exposed to the air.In the paper, narrow distribution polydimethylsiloxane was synthesized by anionic polymerization, and then α-[3-(2, 3-epoxy-propoxy) propyl]-ω-butyl- polydimethy siloxanes(PDMS-E) was prepared by allyl glycidyl ether(AGE) and PDMS-H. A gradient film with flexibility and hydrophobicity was prepared using PDMS-E grafted gelatin(PGG). The results included:1. The heterogeneous reaction between gelatin and PDMS-E were carried out by ring-opening reaction between –NH2 groups and epoxy groups. The expose of the –NH2 groups and epoxy groups in interface was a key role in determing the extents of reaction. Surfactant received considerable attention to promote compatibility because of their ability to impart significant changes to the interfacial, rheological and physico-chemical properties of gelatin systems. The self-assembly of the gelatin/anionic surfactants in a phase-separating system has the potential to affect the reaction. The surfactants, including sodium heptyl sulfate(SHepS), sodium octyl sulfate(SOS), sodium decyl sulfate(SDec S), sodium undecyl sulfate(SUS), sodium dodecyl sulfate(SDS), sodium tetradecyl sulfate(STS), sodium hexadecyl sulfate(SHxaS), sodium dodecyl sulfonate(SDSo), sodium tetradecyl sulfonate(STSo), were chose for studying the interactions between gelatin and surfactants in semidilute unentangled solution, firstly. In addition, complex models were created.The formation mechanisms of gelatin/SDS/STSo/SDBS complex were discussed. The results show that phase separation occured after SDS interacts with gelatin in semidilute unentangled solution. A higher hydrophobicity of the hydrophobic segment in gelatin chains caused a tighter packing in the core of the aggregate. Hydrophilic segments, such as lysine and arginine residues of gelatin, should arrange at the gelatin/water boundary. The structural evolution of the aggregates in gelatin/surfactant mixed solution was driven by the electrostatic attraction, hydrogen bonding and hydrophobic interaction among gelatin, surfactant and water molecules. The hydrophilic segments bound in the micelle palisade layer, which prevented a fraction of the hydrophobic core from contacting with water. It was clearly shown that the extension of gelatin chains with well-ordered arrangemented at the boundary, as shown in the transmission electron microscopy(HR-TEM) results. The changes in viscosity indicated the strong molecular interactions in gelatin-SDBS system. It was suggested that SDBS not only caused intramolecular self-association but improves intermolecular cross-linking. The reason may be that SDBS monomer could not contact during the repulsive interactions of π-electron cloud but presented near the surface of the micelle.The results showed that When STSo was added, the extension of the gelatin chains can be caused and hydrophilic segments tend to arrange at the interface. Well-defined arrangement of gelatin chains at the boundary was observed. Conductivity measurement indicated the reduction of interfacial free energy of gelatin-sulfonate surfactant system. Molecular dynamics simulations conclusions confirmed that the length of hydrophobic alkyl chain played a crucial role in contributing to the decrease of energies. The results indicated that the conversion rate of free-NH2 group were affected by the types and concentration of surfactants. In short, a well-ordered arrangement of hydrophilic segments in gelatin chains in the interfacial region, which played an important role in improving the PDMS-E grafting gelatin reaction at interface. After parallel test and orthogonal test, we found that the conversion rate of free-NH2 groups minished in order of STSo, SDS, SDBS. When the concentration of SDS was 6 %(ws/wg) and Mw of PDMS-E = 1140, the conversion rate of free-NH2 groups reached the max peak values at 6 %(ws/wg) in SDS system. The orthogonal conditions were that temperature was 50℃, time was 14 h, pH = 10.2, and material ratios(molepoxy gropus: molamino groups) is 1:0.82. The electrostatic and hydrophobic interactions among components played key role in deterning the microphase speration structure of PGG films. Hybrid polymer films were prepared by casting aqueous solutions, including gelatin, PGG or their mixtures with surfactants. Supramolecular structure of gelatin, which was decided by the sophisticated interand intra-molecular interactions, significantly affected the self-assembly and phase behavior of PGG. Interestingly, the supramolecular organization of PGG could be tuned finely by negatively charged surfactants, such as SDS and STSo, as revealed by high-resolution HR-TEM, scanning electron microscopy(SEM), light microscopy(LM), and atomic force microscopy(AFM). SEM images exhibited the presence of spherical aggregates in PGG/SDS films while hexagonal array was observed in PGG/STSo films. The results of LM revealed that when PGG/STSo solution was dried, a successive structural transformation from spheres to hexagons, via sticks and butterfly-shaped aggregates as intermediates, was observed. However, the morphologies of the aggregates formed in PGG/SDS system did not exhibit any obvious change upon drying. Attenuated total reflection–fourier transform infrared spectra combined with AFM observations indicated that the secondary structure and aggregation behavior of gelatin was modified with the change in the electrostatic and hydrophobic interactions, leading to the formation of diversified solid-state structures of PGG.3. Composition gradients films in longitudinal orientation prepared via macromolecular self-assembling with solvent supporting. The reaction solution was separated by low temperature(-10 °C) centrifugation, and interlayer, a creamy white paste, was confirmed to be PDMS-E grafted gelatin(PGG) polymer. Firstly, deionized water( ~ 2 mL) was added to the creamy white paste under stirring for 2 h, and then, original gelatin solution(5 %, wt) was added at 1:1(v / v). The mixtures were allowed to further stir for 0.5 h. Subsequently, the mixtures were blended with ethanol or acetone or tetrahydrofuran at varying water–to–solvent volume ratios. After stirring for 30 seconds, the mixtures were placed on the gelatin substrate and deposited for 12 h within a closed environment. AFM and HR-TEM results indicated that rectangular aggregates were formed in ethanol/water mixed solvent, but in other solvent mixture systems, such as and methanol/water, acetone/water, and THF/water, no typical ordered aggregation structures were created. HR–TEM images showed that uniform sphere aggregates were observed at 1/3(v / v). Also, no typical ordered aggregation structures were created from other solvent mixtures, including methanol/water, acetone/water, and THF/water. The results indicated that the selection of proper solvent was the key role in determing the formation of the ordered structure. X–ray photoelectron spectroscopy revealed that PDMS chains full filled with the surface of the film, and a maximum intermolecular hydrogen bonds between ethanol and PDMS exhibited at X = 3, which provided an appropriate thermally environment for inducing phase separation. The results of HR–TEM showed that gelatin chains self–assembled to cyclic aggregates which tended to deposit on the gelatin substrate driven by polymer–substrate interactions. Moreover, PGG aggregates migrated to air–liquid interface driven by low free energy of PDMS chain. After the interaction between polymer and air/substrate induced migration procedure, the concentration gradients of PDMS composition in longitudinal orientation in the film were confirmed by scanning electron microscopy–energy dispersive spectroscopy with line scan. Dynamic mechanical analysis and contact angle results illustrated that the gradient film possesses good flexibility and surface hydrophobicity. It was expected that the presented straightforward fabrication method was applicable to other macromolecules chimera systems for generating new materials.