Synthesis and polymerizations of novelbisphosphonate- containing methacrylates

Abstract

In this study, two novel bisphosphonate-containing methacrylates (1 and 2) were synthesized from reaction of ethyl and tert-butyl -bromomethacrylates with 3,3-bis(diethoxyphosphoryl)propanoic acid. Their photopolymerizations using2,2’-dimethoxy-2-phenyl acetophenone (DMPA) as photoinitiator at 40 ˚C gave polymers in 44 and 64% yield. Thermal bulk polymerizations of 1 and 2 using 2,2’-azobis(isobutyronitrile) (AIBN) gave new water soluble bisphosphonate-containing polymers at23 and 25 % yield with Mn values of 83000 and 59500 g/mol for poly-1 and poly-2 respectively. Glass transition temperatures were observed for poly-1 and poly-2 at 75 and 85 ˚C.Thermal bulk and solution copolymerizations of 1 and 2 with poly(ethylene glycol) methyl ether methacrylate (PEGMA) (Mn= 950) in three different feed ratios (90:10, 70:30 and 50:50 mol% PEGMA:1 and PEGMA:2) were investigated using AIBN at 65 ˚C.Water soluble copolymers were obtained only at 70:30 and 50:50 mol % feed ratios in methanol. The lower molecular weight of the copolymers (10000-33000) compared to poly-PEGMA (230000) can be explained by the chain transfer ability of the synthesized monomers. The copolymer compositions determined from the integrated 1H NMR spectra of the copolymers indicated incorporation of the synthesized monomers into polymers. The attempts to hydrolyze bisphosphonate groups of monomers 1 and 2 with trimethylsilyl bromide (TMSBr) were not successful. However, one of the copolymers with50:50 mol% PEGMA: 2 in feed ratiowas hydrolyzed using the same reagent. The pH value of the aqueous solution of the hydrolyzed copolymer (5 wt %) was found to be 1.89.The interaction of this copolymer with hydroxyapatite (HAP), a model compound for bone, was investigated using FTIR spectroscopy.