Study On Highly Transparent And High Impact Styrene/Butadiene Copolymers

In this paper,a series of linear and star liquid butadiene/styrene polymers was synthesized with cyclohexane as solvent,n-BuLi as initiator,THF as structure controller by anionic polymerization.The molecular weight,polydispersity index and microstructure of the polymers were determined by GPC,FT-IR,¹H-NMR and ¹³C-NMR.The polymers mentioned above were epoxidized by in-situ formic acid-hydrogen peroxide method with toluene as solvent. Linear and star liquid epoxidized polymers with different microstructures(b-ELBSC), (t-ELBSC),(r-ELBSC) and(s-ELPB) were synthesized.The effects of hydrogen peroxide amount,reaction temperature and time,styrene content and sequence structure on epoxy degree of ELBSC were investigated.The rules of the coupling reaction with ELBSC and CH₃Si(OCH₃)₃ as coupling agent were researched.The effect of coupling reaction temperature,coupling reaction time,and amount of coupling agent and THF on the polybutadienelithium coupling reaction were investigated.Star-comb,linear-comb and star 3-arm styrene/butadiene copolymers were developed with s-ELPB,ELBSC,epoxidized soybean oil and CH₃Si(OCH₃)₃ as coupling agent.The effects of molecular weight,styrene content,block length,sequence structure,charging times and dosage ratio of initiator on the microstructure of star-comb B/S copolymers were investigated.Consequently,the mechanical properties of the star-comb B/S copolymers were tested.The epoxidation results showed that epoxy value can be modulated by the amount of hydrogen peroxide added.The epoxy value of ELBSC was maximum when H₂O₂/LBSC (mol)=0.6,epoxy time was 120min and epoxy temperature was 50℃.It was found that the coupling efficiency was maximum when Epoxy group/ n-BuLi (mol)=1.With the amount of ELBSC increasing,the relative number of arms decreased, average number of arms passes through the maximum,and the molecular weight distribution becomes broader at the beginning and then turns to be narrower.The coupling efficiency passes through the maximum at the mole ratio of THF/n-BuLi is 1.The number of arms and the molecular weight distribution do not change much at different amount of THF.The higher the temperature of coupling reaction,the higher the coupling efficiency,and the temperature of coupling reaction does not affect much on the number of arms and the molecular weight distribution.With the increase of the coupling reaction time,the coupling efficiency enhances, but it increases slowly after thirty minutes.The coupling reactions are considered to be completed approximately within thirty mintues.The time of coupling reaction does not have much effect on the number of arms and the molecular weight distribution.The mechanical properties of the star-comb B/S copolymers show that with the increasing of the molecular weight,the impact strength increased,and the tensile strength and the elongation at break decreased.The impact strength and the tensile strength are both good when the molecular weight is between 80 and 200 thousands,THF/Li is between 10 and 30, Li₁/Li₂=1:2.The impact performance order is:s-ELPB＞ELBSC＞CH₃Si(OCH₃)₃＞epoxidized soybean oil.