Study On Long-chain Branched Polymers For Leather Filling-Retanning From Trihydroxymethylpropane Maleates

Current linear polymer retanning-filling agents are increasingly unable to fulfil requirements of manufacturing high-quality leathers. Classical hyperbranched polymers, which have been used as alternatives, are not suitable to treat skins due to poor flexibility or mechanical properties resulted from its impact structure. Focusing on above dilemma, we employed unsaturated multi-functional monomers to polymerize with usual vinyl monomers to prepare long-chain branched polymers as retanning&filling agents for leather-making via traditional free radical polymerization.Tri-hydroxymethylpropane(TMP) is employed to react with maleic anhydride(MA) to produce mono-trihydroxymethylpropane maleates(MTPMs). Optimized reaction conditions are obtained by determinating mono-esterification rate of MA: reaction temperature 90℃and time 240 min for MTPM-20, MTPM-25 and MTPM-30; MTPM-30-C is prepared by addition of 0.2%(wt%) catalyst without producing diester of maleates. The average double bond functionality(ADF) of MTPM-20,MTPM-25,MTPM-30 and MTPM-30-C are calculated by esterification rate and NMR, results are respectively 2.0,2.5,2.7(2.8) and 3.0. Mole percentages of mono-trihydroxymethylpropane tri-maleates(M3) in aforementioned MTPMs determined by 13CNMR are 20.8%、37.6%、67.5%and 91.9%, respectively。Series of long-chain branched polymers(LBPs) are synthesized by aqueous copolymerization of MTPMs with MAA via free radical polymerization. The optimized conditions:n(MAA)/n(MTPM)= 18:1, APS 6.0%(wt%),temperature 83-85℃, time 3h, feeding methodⅢ(MAA and APS simultaneously added after MTPMs addition) and degree of neutralization for monomers 0.6. NMR and low angle laser light scattering(LALLS) are employed to characterize the architecture of LBPs. The results of LALLS show that intrinsic viscosity([η]) and molecular weight(Mw) relationships for LBPs do not follow a power law relationship, from which the branched architectures of LBPs are identified. The results of LALLS indicate that Mw of LBPs is located in the range from 15000g/mol to 27000g/mol, Mw/Mn 1.3-1.6.The branched architectures of LBPs are characterized by probability of branching (Pb) and branching factor g’, the results of both determinations reveal that degree of branching increases with the increasing of ADF of MTPMs.The effects of pH and shear rates on the aqueous viscosity of LBP25 are investigated, the results show that its rheological behavior comes close to Newtonian fluid and its aqueous viscosities display a minimum at pH-6.0. The results of DSC show that LBP molecules have nearly same flexibility as that of poly-methacrylic acid due to their close Tgs(LBPs:279～290℃, poly-MAA:279.71℃). The results of TGA/DTG manifest that each of LBPs has a two-stage decomposition from 50℃to 650℃and has thermal stability suitable for leather-making.LBPs are used to treat chrome-tanned sheepskins, the treated leathers are evaluated and the results indicate that LBPs, which perform well in filling and retanning leathers, produce result leathers excellent softness, plumpness and flexibility without effecting the dyeing of leathers. The LBP-25 polymer has better application properties than both other LBPs and Baytigan AR and ART-Ⅱ.