Syndissertation And Characterization Of High Performance Cis-polybutadiene Rubber Based On Modified Rare Earth Catalytic System

Cis-polybutadiene rubber(BR)has many advantages,such as high elasticity,good abrasion resistance,low temperature resistance,and good flex durability.It is an important material for the manufacture of tire and other rubber products.With the development of society,the performance of the BR can no longer meet the requirements of energy saving,safety,environmental protection and durability.Based on the actual demand of the synthetic rubber industry,this dissertation established a catalytic system for high cis narrow distribution BR by modifying the main catalyst,neodymium salt(NdS).At the same time,for the requirements of BR in specific application field,three products were developed:low rolling resistance BR,environmentally friendly and easy processing BR,and high flex durability BR.The detailed research works were listed as follows:(1)Modifier(M)was selected to modify NdS,which solved the problem that NdS could not be completely dissolved in hexane,and a transparent homogeneous catalyst was obtained.The optimum dosage of M was[M]/[Nd]=0.5.Under this condition,the catalytic activity was increased by 2.3 times,and the molecular weight distribution index of the polymer was less than 2.3.(2)Based on modified NdS(NdM),the effect of homogeneous agent(Bdcat dosage,diisobutylaluminum hydride(DIBAH)dosage,sesquiethylaluminum chloride(EASC)dosage and catalyst preparation conditions on catalyst solubility,catalytic activity and Bd polymerization were investigated.The molecular weight,molecular weight distribution(MWD),microstructure and sequence distribution of BR were characterized by GPC,FTIR and 13C-NMR.The results showed that a homogeneous catalyst was obtained by adding a little Bdcat during the preparation of the catalyst.Too much EASC([Cl]/[Nd]?3.8)would result in a heterogeneous catalyst;higher dosage of DIBAH or EASC,higher preparation temperature and longer preparation time would improve the catalytic activity;lower dosage of DIBAH,higher dosage of EASC,higher preparation temperature and longer preparation time would increase the molecular weight of BR and narrow its MWD;higher dosage of DIBAH would lead to the reduction of cis-1,4-content.Appropriate catalyst preparation conditions were[Al]/[Nd]=13-20,[Cl]/[Nd]=3.0,[Bdcat]/[Nd]=10-90,Tal=30-50?,tal=30-60 min,Ta2=50?,ta2=120 min.Under these conditions,a homogeneous catalyst which had high activity(2.88(Kg BR)·(g Nd)-1·h-1)),strong stereoselectivity and good stability was obtained.The molecular weight can be adjusted(Mn=4.6×104-3.1×105 g·mol-1),and the MWD was narrow(<2.3)and the cis-1,4-content was higher than 97%.(3)The Bd polymerization process catalyzed by NdM/DIBAH/EASC/Bdcat system was studied.It was found that the average molecular weight had a linear relationship with the conversion rate,which showed the characteristics of living polymerization;the polymerization product had a narrow molecular weight distribution and the lowest molecular weight distribution index was 1.5;the average number of polymer chains(Np)produced by each neodymium atom was above 7.This indicated that the system studied in this dissertation belonged to reversible coordination chain transfer polymerization,and the chain transfer reaction was reversible.The polymer chain obtained by chain transfer could be "reactivated" to become the active chain,and continued to propagate by reacting with the monomer,which would equal the chain length and narrow the MWD.The influencing factors of chain transfer reaction were investigated based on the polymerization mechanism.The results showed that the chain transfer reaction was basically determined by the dosage of DIBAH,and the relationship between Np and DIBAH was linear.Based on this mechanism,a formula for designing the molecular weight of BR was established,and the relative error between the experimental and design values was<10%.(4)Two kinds of narrow MWD BR were designed and synthesized in a 10 L reactor under NdM/DIBAH/EASC/Bdcat system,which confirmed the previous results again.The effect of molecular weight distribution on the application performance of BR was investigated.The results showed that the MWD had little effect on t10 and t90.The vulcanization rate of narrow MWD BR was slightly slower and the scorch time was slightly shorter.The narrow MWD was beneficial to increase the tensile stress,elongation at break,tear resistance and abrasion resistance of BR,and was beneficial to reduce rolling resistance.When the MWD index was decreased from 2.62 to 2.21 and 1.83,the rolling resistance was reduced by 16%and 24%,respectively.(5)Based on the NdM/DIBAH/EASC/Bdcat catalytic system,the effects of DIBAH dosage,catalyst dosage and polymerization temperature on the syndissertation of liquid BR(LBR)were investigated.Appropriate catalyst preparation conditions were[Al]/[Nd]=20-30,[Nd]/[Bd]=2.5×10-4-5.0×10-4,Tp=20?.LBR sample was synthesized in a 10 L reactor.Its number average molecular weight was 1.63×104 g-mol-1,and cis-1,4-content was 94.1%.Then,an environmentally friendly and easy processing BR which was prepared in solution by in-situ blending with LBR.The appropriate dosage of LBR is about 30 phr.Its mechanical properties and abrasion resistance were comparable to the ordinary BR which had operating oil,and the elongation at break and the wet-skid resistance were slightly improved.(6)Based on NdM,n-butylmagnesium(Mg)as the alkylating agent,the effects of Mg dosage,Bdcat dosage,catalyst preparation conditions and polymerization conditions on the solubility,catalytic activity and Bd polymerization were investigated.The molecular weight,distribution,microstructure and crystallization behavior of the polymerization products were characterized by GPC,FTIR and DSC.The results showed that when[Mg]/[Nd]=4-8,[Bdcat]/[Nd]=10-90,a homogeneous catalyst could be obtained with comparatively higher catalytic activity.The preparation temperature and time have little effect on the polymerization of Bd.When the polymerization temperature is 50?,TPB trans-1,4-content was about 95%.Higher polymerization temperature would lead to the trans-1,4-content reduction.TPB contained monoclinic phase crystal and hexagonal phase crystal at room temperature,and the crystal melting temperature was 44.4? and 96.6?,respectively.