Study Of Polymerization Technology On Hydroxy Terminated Polybutadiene With High Tacticity And Its Modification

The physical properties of hydroxyl terminated polybutadiene（HTPB）adhesive not only affect the cryogenic mechanical properties of solid propellants,but also affect their aging resistance and storage characteristic.With the continuous development of polymer synthesis technologies,the requirements for the highly tacticity of hydroxyl terminated polybutadiene become stricter.The studies indicate that we do not only need to effectively control the molecular weight and its distribution of polymer,but also need to effectively control the tacticity of hydroxyl terminated polybutadiene.The key factor in achieving the aforementioned controls is to vary the structure of polymer and choose the type of initiators by introduction of advanced polymerization technology.Therefore,this thesis focuses on how to synthesize hydroxyl terminated polybutadiene with highly tacticity and the relationship between the structures of Li-series and Ni-series initiators and the tacticity of synthesized hydroxyl terminated polybutadiene.The research contents and results are summarized as follows:（1）In order to reduce the association of alkyl lithium initiators in non-polar solvents and enhance the selectivity for 1,4 structure of hydroxyl terminated polybutadiene by alkyl lithium initiators during the polymerization of butadiene,a new alkyl lithium initiator was synthesized by introducing various steric hindrance structures into the molecular structure of initiator.The new type of alkyl lithium has a large steric resistance near the active center,which prevents the butadiene monomer from attackingγ-C at the beginning of polymerization,increases the 1,4 insertion by times and finally achieves the purpose of increasing the content of 1,4 structure.The obtained hydroxyl terminated polybutadiene has 1,4 content whcih is higher than 90%.Molecular weight distribution is less than 1.2 and a controllable molecular weight is obtained.This chapter discusses the factors of polymerization process on the synthesis of HTPB.The obtained optimal polymerization temperature and time are 50℃and4 h,respectively.The effect of the amount of alkyl lithium initiator on the polymerization was also discussed.It is found that the molecular weight of polymer fits the characteristics of living polymerization basically,so the pree control on molecule weight has been achieved.Polar solvents can significantly reduce the 1,4 content of hydroxyl terminated polybutadiene.The high 1,4 hydroxy-terminated polybutadiene will be of great application value in solid rocket propellant.（2）Based on the novel anionic alkyl lithium initiator with large hindrance,three hydroxyl terminated polybutadiene standard substances with different molecular weights were synthesized and their molecular weight and molecular weight distribution were measured accurately using SEC-MALLS and MALDI-TOF MS.According to the national specification for primary standard substance（JJG1006-94）,number-averaged molecular weight and molecular weight distribution of hydroxyl terminated polybutadiene with high 1,4 structure are subject to uniformity test by using the variance analysis.Through the establishment of statistical model and the calculations on uniformity and stability in storage in accordance with the Grubbs criterion,it is concluded that the three types of hydroxyl terminated polybutadiene with the molecular weight of 4000/6000/8000 synthesized by the self-made initiator meet the national standard so they can be used as an effective national first-level standard substance to guide the actual production process.（3）To solve the problem that the content of-1,4 structure in the obtained hydroxyl terminated polybutadiene by anionic polymerization is low,the catalytic system of butadiene rubber was transplanted and improved.An new kind of initiating system consisting of alkyl lithium-Nickel（II）naphthenate-Boron trifluoride diethyl etherate（Li-Ni-B）was obtained by introducing transition metal element Ni in the anionic polymerization system,which can obtained hydroxyl terminated polybutadiene with high-1,4 content via the excellent coordination capability of Ni.It has been found that as Li/Ni=10:1 and Li/B=1:2,the novel initiating system shows a good initiating activity for butadiene and obtains hydroxyl terminated polybutadiene with the content of-1,4 structure over 95%.The effects of polymerization time and temperature on hydroxyl terminated polybutadiene preparation process were discussed as well.It was found that the optimal polymerization time is 4 h and the optimal polymerization temperature is 50℃.（4）To improve the controlling capability for molecular weight by ternary initiator system and to obtained hydroxyl terminated polybutadiene with higher content of-1,4 structure,a new type of Ni complex containing acetoxyl group[Ni（η³-CH₂CHCHCH₂OOCCH₃）][BPh₄^F]was designed.This initiator was characterized by ¹H-NMR,which verifies that the target compound was successfully obtained.This chapter studies its application in the polymerization of butadiene.By studying the effect of catalyst’s skeleton structure and counterion on the initiation efficiency for hydroxyl terminated polybutadiene and the content of-1,4 structure in hydroxyl terminated polybutadiene,it has been found that cutting the conjugated system including oxygen and nickel atom,and introducing the counterion containing the electron-absorbing structure can effectively improve the initiation activity of hydroxyl terminated polybutadiene and increase the content of-1,4 structure.According to DSC results,hydroxyl terminated polybutadiene synthesized by the novel initiator[Ni（η³-CH₂CHCHCH₂OOCCH₃）][BPh₄^F]has lower glass-transition temperature than those synthesized by anionic polymerization and radical polymerization,which means that the mechanical properties of hydroxyl terminated polybutadiene with high-1,4 content is more excellent.Meanwhile,[Ni（η³-CH₂CHCHCH₂OOCCH₃）][BPh₄^F]also can effectively control the polymer`s molecular weight and molecular weight distribution.（5）In order to improve the low curing strength of hydroxyl terminated polybutadiene and overcome the poor controlling on tacticity of anion polymierzation,hydroxyl-terminated polystyrene-b-polybutadiene-b-polystyrene triblock copolymer（HO-SBS-OH）with high content of-1,4 structure was obtained by using self-synthesized initiator[Ni（η³-CH₂CHCHCH₂OOCCH₃）][BPh₄^F].FT-IR,¹H-NMR,and ¹³C-NMR results indicate that the polybutadiene segment of HO-SBS-OH co-polymer has a content of-1,4 structure over 90%,indicating the well achievement of the objective.Moreover,the hydroxyl group was successfully introduced at the ends of HO-SBS-OH.The DSC results show that the HO-SBS-OH synthesized with the novel catalyst has lower glass transition temperature（T_g）than the HO-SBS-OH synthesized with alkyl lithium as catalyst.Therefore,the HO-SBS-OH with high-1,4 content displays excellent low temperature mechanical properties and can increase the hard segment content of hydroxy-terminated polybutadiene after curing.（6）To study the applications of the hydroxyl-functionalizedπ-allyl nickel initiator in other monomers,two kinds ofπ-allyl nickel initiators containing protected hydroxy[Ni（η³-CH₂CHCH₂Ph OCH₃）（P）][BPh₄^F]and[Ni（η³-CH₂CHCH₂Ph O（CH₃）₂Si C（CH₃）₃）（PPh₃）][BAr₄^F]were first obtained.Single-crystal XRD analysis confirms that the Ni initiators possess a typicalπ-allyl structure with a protected hydroxyl group.The effect of counterion on the initiation activity was studied and it is found that the initiator has the higher initiating activity only if the counterion has the electron-withdrawing structure,indicating that electron-withdrawing group can highly increase the initiation activity.The Ni initiator was applied to synthesize hydroxyl-terminated poly（3-hexylthiophene）,hydroxyl-terminated polystyrene and hydroxyl-terminated butylacrylate.¹H-NMR spectra verify that the polymers contain silicon ether structure,indicating that the protected hydroxyl has been introduced.