| In recent years,As the state control of VOCs by governments and people has been strengthened,the application of traditional solvent-based polyurethanes has restricted.A new type of green non-toxic materials,namely water-based polyurethanes,is favored.Waterborne polyurethane has been improved and continues to make breakthroughs in the application field,which has a tendency to replace solvent-based polyurethanes.However,anionic waterborne polyurethanes are commonly used in the market,and in order to obtain sufficient hydrophilicity,it is often necessary to add an organic amine compound as neutralizing agents to form quaternary ammonium salt ions.Because organic amines have large odor,are volatile,and have certain toxicity,the volatilization of organic amines in the process of film formation of anionic waterborne polyurethane emulsions weakens its green environmental characteristics.As a hydrophilic polymer widely used in the field of medicine and food,polyvinylpyrrolidone(PVP)has good biocompatibility and physical optical properties.PVP has not been reported as hydrophilic segments to synthesize waterborne polyurethane.By using PVP instead of dimethylolpropionic acid(DMPA)as hydrophilic segments in the synthesis of waterborne polyurethane,organic amine neutralizing agents could be invalidated.This nonionic polyurethane that combines with PVP chains has characteristics of good biocompatibility,stable chemistry property and good filming property,enabling achieve the development of new applications for waterborne polyurethanes.In the present situation,the synthesis of nonionic waterborne polyurethane is mainly obtained by using polyethylene glycol(PEG)as hydrophilic segments.There are no reports about the synthesis of nonionic waterborne polyurethane using other water-soluble polymers,such as hydroxyl functionalized PVP or Polyacrylamide(PAM),as hydrophilic segments.However,one of the major challenges of PVP as hydrophilic segments is the functionalization of its hydroxyl group by free radical polymerization.It is limited to the special non-conjugated vinyl structure of the monomeric vinylpyrrolidone(NVP).It is often difficult to introduce reactive functional groups when conventional free radical polymerization methods are used to synthesize PVP.It has also become difficult to make PVP composite with other polymers.An effective route to obtain a PVP having a terminated-hydroxyl group at the end of molecular chains is to add functional chain transfer agents such as an alcohol or a mercapto alcohol compound in the polymerization to thereby synthesize a terminal hydroxyl group PVP even a single-end dihydroxy PVP.The position of the hydrophilic segment of the nonionic polyurethane also has an effect on the performance.It is optimal to be located on the side chain of main polyurethane chains,and the free movement of hydrophilic chains can ensure sufficient hydrophilic effect.Therefore,the molecular chain structure of the single-ended bis-hydroxy group is suitable.In this paper,with isopropanol and isopropoxyethanol were used as solvents respectively,different mercapto compounds were used as functional chain transfer agents,low molecular weight PVP were synthesized by free radical solution polymerization.Then,the hydrophilic polymers were used to synthesize nonionic waterborne polyurethane dispersions.Molecular structure and molecular weight of polymers were conducted by nuclear magnetic resonance spectroscopy(NMR),laser dissociation matrix assisted time-of-flight mass spectrometer(MALDI-TOF MS),also were studied by Fourier transform infrared spectrometer(FTIR).Particle sizes of WPU dispersions was measured by nanoparticle size laser particle size analyzer.The characterization,the mechanism of polymerization in monomer NVP solution and the influencing factors of PVP molecular weight was also investigated.Electrolyte resistance,low temperature resistance of non-ionic waterborne polyurethane was also tested.The main research contents are summarized as follows:(1)Synthesis and characterization of hydroxylated terminational polyvinylpyrrolidoneTwo different alcohol compounds,isopropanol and isopropoxyethanol,were used as solvents,thioglycerol and mercaptoethanol were added as chain transfer agents in monomers solution,respectively.Two different end group structures of PVP with terminal hydroxyl groups were all obtained by azobisisobutyronitrile(AIBN)as initiator.Structural analysis found that isopropoxyethanol is more suitable for the synthesis of PVP of the primary hydroxyl group.Using toluene diisocyanate(TDI),polytetrahydrofuran ether glycol(PTMG)to obtain prepolymers,primary hydroxyl functional PVP,1,4-butanediol(BDO),trimethylolpropane(TMP)were reacted with the prepolymers to prepare nonionic polyurethane dispersion with different particle size.The results show that the nonionic polyurethane emulsion has good electrolyte resistance and low temperature resistance,and with the increase of PVP addition,the stability of the emulsion is enhanced,and the characteristics of the nonionic polyurethane are more prominent.(2)Synthesis and characterization of single-ended bis-hydroxy terminational PVPIn order to overcome the weakness of low molecular weight and hydrophilicity of the polyurethane prepared by the mono hydroxy functional PVP,toluene was used as polymerization solvent,and a certain amount of thioglycerol was added as chain transfer agents under the initiation of AIBN to obtain polymers products containing a bis-hydroxy PVP molecule chains.The analysis found that the molecular weight distribution of PVP synthesized by this method is wide,and its hydroxyl value increases with the increase of thioglycerol amount.The functional polymers were then introduced into polyurethane system to successfully prepare nonionic polyurethane emulsion without adding any DMPA.Furthermore,the stability of the emulsion was further tested.It was found that the emulsion prepared by controlling the amount of PVP in the range of 40%to 60%,was stable and the electrolyte resistance and freeze-thaw stability were also better than others. |
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