Synthesis And Properties Of Polymeric Thermal Stabilizers Containing Organotin Units In PVC Resin

As one of the five general plastics,polyvinyl chloride(PVC) was used in many fields,such as water pipes,floor and roof tiles,packing films,and sheets.However,due to its intrinsic thermal instability of PVC,dehydrochlorination happens at the processing temperature.During the thermal degradation of PVC,labile chlorine atoms start the reaction and HCl is released from the PVC,which makes conjugated double bonds formed,ultimately leading to discoloration and severe crosslinking.On the other hand,HCl during thermal degradation acts as auto-catalyst resulting in the loss of mechanical properties of PVC.Hence,the application of heat stabilizers is prerequisite for PVC processing.Heat stabilizers reduce thermal degradation of PVC in two ways:1.HCl enters to reaction by scavenging;2.labile chlorine atoms are substituted and conjugated double bond formation is prevented.As present,lead salt,metal soap and organotin are widely used as heat stabilizers.Many of the most effective heat stabilizers for this polymer contain toxic heavy metals,while alternative safe stabilizer systems are less effective to block degradation of PVC.Organotin still require further improvement in order to achieve a comparable price/performance.Hence,research on highly efficient, non-toxic,low cost heat stabilizer would provide new insights.In this paper,a series of polymers containing dialkyltin maleate units were designed and synthesized,which could improve thermal stability of PVC,and also offer a 'green', environmentally benign solution.Due to the drawbacks of small molecular heat stabilizers,such as migration and poor dispersion,a series of polymeric stabilizers were designed for excellent compatibility with PVC containing the starting effect groups and the long-term effect groups.These stabilizers could inhibit the thermal decomposition at the early stage,and meanwhile prolong the long-term heat stability of PVC.Besides,the polymeric stabilizers compatible with PVC would be homogeneously dispersed during the processing.It could be desirable to decrease the content of high cost metal in the heat stabilizers as least as effective.Dibutyltin maleate(DBTO),dioctyltin maleate(DOTO),N-phenyl maleimide(NPMI), N-(p-chlorophenyl) maleimide(N-p-ClPMI),N-(p-nitrophenyl) maleimide(N-p-NOPMI) with unsaturated groups were synthesized using dibutyltin oxide,dioctyltin oxide,maleic anhydride, aniline,p-chloroaniline,p-nitroaniline as raw materials,respectively.Then dibutyltin male,ate/styrene bipolymer[P(DBTM/St)],dibutyltin maleate/styrene/methyl acrylate terpolymer[P(DBTM/St/MA)],dibutyltin maleate/styrene/N-phenyl maleimide terpolymer [P(DBTM/St/NPMI)],dibutyltin maleate/styrene/N-(p-chlorophenyl) maleimide terpolymer [P(DBTM/St/NClPMI)],dibutyltin maleate/styrene/N-(p-nitrophenyl) maleimide terpolymer [P(DBTM/St/NNOPMI)],dioctyltin maleate/styrene biopolymer[P(DOTM/St)],dioctyltin maleate/styrene/methyl acrylate terpolymer[P(DOTM/St/MA)],dioctyltin maleate/styrene/ N-phenyl maleimide terpolymer[P(DOTM/St/NPMI)],dioctyltin maleate/styrene/ N-(p-ehlorophenyl) maleimide terpolymer[P(DOTM/St/NC1PMI)],dioctyltin maleate/styrene/N-(p-nitrophenyl) maleimide terpolymer[P(DOTM/St/NNOPMI)]were synthesized using DBTO,DOTO,PMI,N-p-ClPMI,N-p-NOPMI,styrene and methyl acrylate as monomers,respectively.The polymers were characterized by means of Fourier transfer infrared spectroscopy(FT-IR),proton nuclear magnetic resonance spectroscopy(~1H NMR), inductively coupled plasma atomic emission spectroscopy(ICP) and gel permeation chromatography(GPC).The effect of above polymeric stabilizers on the thermal stability of PVC was analyzed by Congo red test.The order of the thermal stability of copolymers containing dibutyltin maleateunits is as follows:P(DBTM/St/MA)＞P(DBTM/St)＞P(DBTM/St/NPMI)＞P(DBTM/St/NClPMI)＞P(DBTM/St/NNOPMI);The order of the thermal stability of copolymers containing dioctyltin maleateunits is as follows:P(DOTM/St/MA)＞P(DOTM/St)＞P(DOTM/St/NPMI)＞P(DOTM/St/NClPMI)＞P(DOTM/St/NNOPMI).The dehydrochlorination of PVC was discussed by means of acidimeter.The order of the inhibition ofcopolymers containing dibutyltin maleate units is as follows:P(DBTM/St/MA)＞P(DBTM/St)＞P(DBTM/St/NPMI)＞P(DBTM/St/NClPMI)＞P(DBTM/St/NNOPMI);The order of the inhibition of copolymers containing dioctyltin maleate units is as follows: P(DOTM/St/MA)＞P(DOTM/St)＞P(DOTM/St/NPMI)＞P(DOTM/St/NClPMI)＞P(DOTM/St/ NNOPMI).The discoloration and thermal aging of PVC was studied in a circulating air oven.The order of the stabilizing effect of copolymers containing dibutyltin maleateunits is as follows:P(DBTM/St/MA)＞P(DBTM/St)＞P(DBTM/St/NPMI)＞P(DBTM/St/NClPMI)＞P(DBTM/St/NNOPMI);The order of the stabilizing effect of copolymers containing dioctyltin maleateunits is as follows:P(DOTM/St/MA)＞P(DOTM/St)＞P(DOTM/St/NPMI)＞P(DOTM/St/NClPMI)＞P(DOTM/St/NNOPMI).Using the theoretical calculation of Gibbs free energy and Hildebrand mixing enthalpy equation,the solubility parameter of the polymeric heat stabilizers was obtained in order to estimate the compatibility of PVC with copolymers containing dibutyltin maleate units and dioctyitin maleate units.The effect of the compatibility on the thermal stability of the PVC stabilizing system was thoroughly explored.It is obtained that thermal stability was increased with excellent compatibility.The mechanical properties of PVC samples were measured with a servocontrolled testing machine.The effect of the filler dispersion in the PVC upon the tensile strength was observed by scan electron microscopy(SEM).It is shown that the tensile strength was increased with favorable dispersion.The order of the tensile strength of the PVC samples with copolymers containing dibutyltin maleateunits is as follows:P(DBTM/St/MA)＞P(DBTM/St)＞P(DBTM/St/NPMI)＞P(DBTM/St/NC1PMI)＞P(DBTM/St/NNOPMI);The order of the tensile strength of the PVC samples with copolymers containing dioctyltin maleate units is: P(DOTM/St/MA)＞P(DOTM/St)＞P(DOTM/St/NPMI)＞P(DOTM/St/NClPMI)＞P(DOTM/St/NNOPMI).A kinetic study was carried out on the thermogravimetric analyzer(TG/DTG).The pyrolysis activation energy of PVC with copolymers containing dialktyltin maleate units is increased by 5-15 kJ/mol compared with pure PVC.That was attributed to stabilization effect of heat stabilizers.Dehydrochlodnation to form conjugated polyene of PVC stable system was studied on UV spectrometer.It is shown that the thermal stabilizer could effectively inhibit the formation of conjugated polyene on the PVC backbone.Through the infrared spectrometer,it is confirmed that the labile chlorine atoms were substituted and the ester groups were introduced into the PVC.Furthermore,a mechanism for the stabilizing action of the synthesized stabilizers was proposed.It is concluded that in the series of the polymeric thermal stabilizers synthesized in this paper,PVC stabilizing systems containing P(DBTM/St/MA) and P(DOTM/St/MA) with the best thermal stability and excellent mechanical properties,might promise candidates for widespread application in the future.