Effects Of End-groups And Fost-treatment On The Structure And Properties Of Polyphenylene Sulfide

Polyphenylene sulfide(PPS),as a thermoplastic crystalline polymer,has excellent thermal stability,chemical corrosion resistance and mechanical properties,and is widely used in high-end electronic packaging,dust removal and filtration,automotive and aerospace applications.There still exist some shortcomings such as poor toughness,easy to oxidize and crosslink when heating and low reactivity of original end groups,so PPS is often modified in practice through filling,blending,copolymerization,grafting,etc.Carboxyl-terminated PPS were synthesized from PPS,p-chlorobenzoic acid as modifier,NaOH as additive and NMP as solvent in this work.The structure of PPS was identified by FT-IR,end group content determination,and high temperature gel permeation chromatography.The optimal conditions for PPS modification were determined as follows:the molar ratio of PPS end groups:modifier:assistant agent was 1:1.75:7,reaction temperature 265℃,rotational speed 350rpm,and reaction time 200min,the end group conversion could reach 40-60%.The pyrolysis products and the mechanism of the modified samples were analyzed by pyrolysis-GC/MS.CO2,2,6-dimethyl-3,5-diphenylpyran-4-thione and phenyl ether in the pyrolysis products are characteristic and used to identify the presence of introduced end groups.According to pyrolysis products,the mechanism of end modified PPS is suggested as follows:the end groups remove to generate CO2 and free radicals which attack the main polymer chain and promote the random fracture of the chain.The radicals generate thiophenol,polycyclic and biphenyl derivatives through coupling,rearrangement and cyclization.By means of TGA,DSC,the influence of the introduced end groups and different scrubbing methods on the thermal performance of PPS was analyzed.Thermogravimetric performance,thermal decomposition kinetics,melting point and crystallinity are investigated.The results show that functional end groups can reduce the thermal stability and thermal decomposition energy of PPS slightly,and the reduction extent from high to low is PPS-BZA<PPS-PAA<PPS-HNA<PPS-PAD,PPS-ADH<PPS-ATP,and PPS-MPO<PPS-TPO.Moreover the melting point and crystallization temperature increase,the crystallinity increases,and improvement order is PPS-BZA>PPS-PAA>PPS-HNA>PPS-PAD>PPS-ADH>PPS-ATP,PPS-MPO>PPS-TPO.The more end groups are introduced,the higher the melting point and crystallinity will be.The thermal stability and melting/crystallization of modified PPS were different between water washing and water washing followed by 0.1%acetic acid solution scrubbing.Modified PPS washed with acid solution was improved in terms of thermogravimetry,melting point and crystallinity,while the thermal decomposition energy was slightly increased.