Pieparation Of Smart Polysiloxane Materiats Through Aza-michael Addition

Polysiloxanes are one kind of appealing material for clinical and medical treatments,because of its outstanding physiological inertness,non-toxicity,and biocompatibility.However,traditional polysiloxanes show poor hydrophilicity and insensitivity to the environment,which limit the use of the materials in smart fields.Furthermore,tranditional midification methodes of polysiloxane are always low-efficient,more side products,and leading several side-effect to properities of polysiloxane.Aza-Michael addition,a high efficient,no-side products,catalyst-free and high function group tolerance and high conversions at room temperature couping reaction,provide us a alterinative to extablish sarmt polysiloxane systems.Traditional poly(N-isopropylacrylamine)based thermo-responsive polymers have been intensively investigated over the past decade.However,inherent C-C backbones make the improvement of their sensitiveness too hard.Acrylamide had been used as comonomer to extend their phase separation temperature and make them easy functional for further applications,which resulted in a potential cytotoxicity and hysteresis.Herein,we report a strategy to synthesize a series of high-sensitive stimuli-responsive polysiloxanes(TRPSis)via a facile,highly efficient,catalyst-free aza-Michael addition of poly(aminopropylmethylsiloxane)(PAPMS)with N-isopropylacrylamide(NIPAAm).The TRPSis structures are systematically characterized using FT-IR,1H NMR and 13C NMR.The effects of N-isopropyl amide group(NIPAs)content in PAPMS,pH,and salinity on the responsive properties of TRPSis are examinated in detail.The as-prepared TRPSis show high sensitive respond to three changes of thermo-,pH-,and salinity,where the phase separation occurred within 0.3 ? due to their flexible Si-O-Si backbones,and lower critical phase separation(LCST)changed from 14.7 ? to 57.0 ? at varied NIP As contents.Surpringly,the TRPSis exhibit effectively hydrogen bond-derived loading(up to 74 wt.-%)and temperature-dependent release of hydrophobic drugs(ibuprofen).The present methodology may open a route for developing high-sensitive multi-stimuli-responsive polymers.The TRPSis,synthesized by the catalyst-free aza-Michael addition of PAPMS with NIPAAm,exhibited LCST-type phase separation in H20 and high critical solution temperature(UCST)-type in several non-aqueous solvents(e.g.,acetonitrile,ethylene carbonate,ethyl acetate,butyl acetate,and their mixed solvents).The UCST of TRPSis in acetonitrile increased from 34.2 ? to 62.7 ?with the decrease of N-isopropyl content from 100%to 20%.The results are in line with the finding that the UCST-type phase separation was derived from the intense hydrogen bonding interaction of the amino and carbonyl groups of TRPSis.Additionally,the phase separation behavior of TRPSis transformed from LCST-to UCST-type in H20-acetonitrile and H20-ethylene carbonate mixed solvents as the water content decreased.At high water content,the LCST of TRPSis increased with the addition of organic solvents(ethanol,acetonitrile,and ethylene carbonate)and the UCST decreased when water was added in organic solvents.The results indicated that the LCST and UCST of a thermo-responsive polymer were caused by the synergistic effect of hydrogen bonding and compatibilization.The UCST of TRPSis show distinct tendencies in acetonitrile/ethylene carbonate and acetonitrile/ethyl acetate mixed solvents:TRPSis exhibited higher UCST in mixed solvent than in the pure one in the former solvent,whereas,TRPSis exhibited lower UCST in mixed solvents than in the pure one in the later solvent,.The Hansen solubility parameter was applied to explain the phenomenon and reveal the relationship between the phase separation mechanism of TRPSis and solubility parameter of solvents quantitatively.This smart polysiloxane could serve as a promising candidate for the all-in-one application of intelligent catalyst,extraction in non-aqueous conditions.Two kinds of thermo-and light-responsive polysiloxanes with N-isopropyl amides and azobenzene(Azo)or salicylideneaniline(SA)as functionalities at the pendent groups were synthesized.The synthesis was conducted through a facile,effective,and catalyst-free aza-Michael addition of PAPMS with NIPAAm and N-azobenzcnc acrylamide or N-salicylaldehyde acrylamide.The as-prepared polysiloxanes exhibited LCST-type phase transition in water,that is reversible and can be controlled by temperature-and light-controlled.Higher values for the LCST were measured after irradiation of the polymer solutions due to the higher polarity of cis-Azo and keto-SA.The differences in LCST between the irradiated and the non-irradiated polysiloxane aqueous solutions increased linearly with the increase in Azo and SA units(up to 3.4 ? and 9.8 ? respectively).A novel type of highly uniform polymer microspheres poly(urea-siloxane)(PUSs)was prepared through the precipitation polymerization of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane(APTMDS)with isophorone diisocyanate(IPDI)in H20-acetone mixed solvent.No additives such as surfactant and initiator were used.The effects of monomer ratios,H20/acetone ratios,and monomer concentrations on the yields and morphologies of the PUSs were investigated.Results indicated that PUSs sizes can be regulated from 2.14 ?pm to 7.11 ?m by varying monomer ratios,monomer concentrations and H2O/acetone ratios.Hydrogen bonds between polyurea units,polyurea and APTMDS moieties which were identified as the main effects of the products,endowed the materials with good elasticity.The structures and morphologies of the materials were characterized by FT-IR,NMR,and SEM,and the thermal properties were characterized by TGA and DSC analyses.Then,the PUSs were modified by TRPSis through two steps aza-Michael addition,and its controllable hydrophilic/hydrophobic surface property was studied.