Synthesis And Properties Of Benzophenone Based Polymeric Photoinitiators

UV curing is a processing technology,where the photoinitiator(PI)produces active intermediates under the irradiation of UV light source,initiates polymerization or cross-linking reaction of oligomers and monomers,and realizes the rapid transformation of materials from liquid to solid.Photoinitiator is one of the key components of the photo-curing system,which plays a decisive role in the reaction rate and degree of photo curing.Traditional low molecular photoinitiators usually crack and produce residue fragments during the photo curing reaction.These residues may be volatile organic compounds(VOCs),or may migrate to the product surface.These substances are usually toxic and odorous,which may not only stimulate the skin,but are also declared with toxicity and carcinogenicity.Potential adverse effects on the health of both producers and users still exist,which limits the application of photoinitiator in some fields.Therefore,inhibiting the migration of photoinitiators in photo cured products and reducing the VOC emission are of great significance for the expansion of the application field of photoinitiators.Compared with low molecular photoinitiators,macromolecular photoinitiators are usually characterized by low volatility and low migration rate,which are well performed in reducing the VOC emission of photoinitiators in curing process and the migration to the surface in cured products,so as to reduce the toxicity.At the same time,macromolecular photoinitiators have enough photoinitiator groups.If well dispersed,the initiating activity of macromolecular photoinitiators is basically equivalent to that of low molecular photoinitiators.However,the molecular weight of the existing so-called"macromolecular photoinitiators"is below 1000,and there is still a hidden danger of residue volatilization and migration.In view of this,a series of main chain polymeric photoinitiators were synthesized by molecular design and polymerization control;Subsequently,the photolysis behavior,thermal stability and degradability of polymeric photoinitiators were studied by ~1H NMR,UV absorption spectra,FTIR,GPC,DSC,TGA and film weight loss rate;Finally,the polymeric photoinitiator and benzophenone(BP)were applied to the UV curing of polyethylene glycol diacrylate(PEGDA)and the UV crosslinking of ultra-high molecular weight polyethylene(UHMWPE).Their initiation activity,mobility and crosslinking effects were evaluated and compared by means of UV absorption spectra and gel test.The details are as follows:(1)A series of polymeric photoinitiators were designed and synthesized.A series of poly(decylene benzophenonedicarboxylate-co-adipate)(PDBA)polymeric photoinitiators of different composition were prepared with 1,10-decanediol,adipic acid and benzophenone-4,4'-dicarboxylic acid(BDA)as comonomer and functional monomer via polycondensation.The structure was characterized using ~1H NMR and FTIR.The molecular weight and thermal properties were determined and evaluated by GPC and DSC.The results showed that PDBAs are polymeric photoinitiators in type of polyester with benzophenone structure in main chain and M_w of 5.6?9.9kg/mol.(2)The degradation properties of polymeric photoinitiators were studied and evaluated.The UV absorption characteristics and UV photolysis behavior of PDBA and BP were studied and compared by UV spectra.The changes of structure and molecular weight of PDBA before and after photolysis were studied by FTIR,~1H NMR and GPC.The thermal stability of PDBA before and after photolysis was investigated by DSC and TGA.At the same time,the water degradation and enzymatic degradation behavior at different p H of PDBA was studied.The results showed that the optical activity of PDBA is basically similar to that of BP,the 5%thermogravimetric temperature is obviously higher than BP,and has good hydrolysis ability under acidic or enzymatic conditions.(3)The polymeric photoinitiator PDBA synthesized above and BP were used for photo curing of PEGDA and photo crosslinking of UHMWPE.The results showed that PDBA showed similar activity to BP when initiating the curing of PEGDA and the UV crosslinking of UHMWPE,and the migration rate of PDBA in the cured film was apparently lower than that of BP.The elongation at break of UHMWPE decreased and the elastic modulus increased with the addition of PDBA and UV irradiation.