The Isotactic Polystyrene High Vacuum Anionic Synthesis And Its Integration Rubber,

In this dissertation, based on high vacuum techniques, t-Butyllithium (t-BuLi) were used as initiator, sodium dodecylbenzenesulfonate (SDBS) as structure modifier for the styrene anionic polymerization in hydrocarbon media and their influence on polystyrene microstructure has been investigated. The influence on the stereoregulation of other parameters of this initiating system, such as the ratio of initiator, the concentration of living seeds, reaction temperature as well as that of the type of regulator has also been investigated.1-lithio-1,3-diphenylbutane (LDPB) and sodium 4-methylbenzenesulfonate (SMBS) was used as simplified models of the grow chain (PSLi) and SDBS respectively. The quantum chemistry calculations, density functional theory (DFT), on these two models were performed to stimulate the molecular state of this initiating system. On the basis of both research metioned above, combing with the data from ultra-violet spectrum, the structural features and statistics, the possible structure of PSLi/SDBS complexes and the stereoregualtion mechanisms of isotactic polystyrene (iPS) were discussed. By the anionic polymerization technique for living advantage, diblock copolymers of polybutadiene-block-isotactic polystyrene (PB-b-iPS) and polyisoprene-block-isotactic polystyrene (PI-b-iPS) have been successfully prepared. And their practical application in integrative rubber was also preliminary studied.The experimental results indicated that the iPS can be obtained in nonpolar solvent (e.g. hexane) at 30℃or above in the presence of SDBS. The reaction time was saved dramaticly and the conversion of monomer reached nearly 100%. The PS samples were fractionated by extraction using boiling methyl ethyl ketone (MEK) into 80℃MEK insoluble and 25℃MEK soluble fractions. Unfortunately, the 80℃MEK insoluble fraction was not complete highly isotactic and the 25℃MEK soluble fraction was also not entire atactic polystyrene. The mmmm pentad content of these two fractions was about 50% and 10% respectively. These results clearly differ from those described by other publishers. The SDBS content exerted a great influence on the anionic polymerization of styrene. The low [SDBS]/[t-BuLi] ratio gave a markedly increased polymerization rate and isotactic PS microstructure. While at the high [SDBS]/[t-BuLi] ratio a sharp decrease both in isotactic content and polymerization rete was observed. Reaction temperature showed a significant influence on PS isotacticity. Especially, decreasing the temperature to improve the isotacticity was just the opposite to what we wishes. There was no noticeable change in siotactic content by varying the concentration of living seeds. The influence of sulfonate derivatives on stereoregulation of iPS was characterized by:distinctly influence of metal counterion and the length of alkyl chain, slightly influence of sulfonate and sulfate. The coordination of the SDBS with t-BuLi or PSLi is stronger than with toluene and tetraphenylethylene but weaker with tetrahydrofuran (THF). The solvent displayed obvious influence on PS isotacticity. No other than atactic polystyrene was obtained in THF. However, isotactic PS was observed in toluene, cyclohexane and hexane. The relative highest isotacticity was obtained in cyclohexane.DFT calculations on LDPB indicated that ion pairs of LDPB with the Li position in the pro-meso (pro-m) and pro-racemic (pro-r) differ in energy due to the interaction with the penultimate phenyl group with the pro-r complexes being favored. Furthermore, DFT calculations in vacuum or in cyclohexane on possible inter-or intra-molecular ion pair epimerization of LDPB suggested that these processes were slow on the polymerization time scale. In contrast to the ion pairs, the formation of pro-(S) and pro-(R) monomer presentation may well be reversible and rapid on the polymerization time scale. The calculations of LDPB-styrene complexes indicated a preference for pro-r structures. The calculations also indicated the formation of very stable pro-m or pro-r LDPB dimers that appear unable to form stable styrene complexes consistent with a well known lack of reactivity of PSLi dimers under these conditions indicating that the propagating species is the pro-m or pro-r LDPB (PSLi) monomeric ion pair. The DFT calculations also indicated that the styrene attacks cation-side ("syn") as the corresponding "anti" attack results in much higher energy intermediates. DFT calculations on sodium 4-methylbenzene sulfonate (SMBS) as a model for SDBS indicated that the formation of 2:1 LDPB:SMBS and or 1:1 complexes was indeed plausible. Furthermore, DFT calculations in vacuum and in cyclohexane showed that, in contrast with the model LDPB styrene complexes, the pro-m SMBS-LDPB-styrene complexes are now favored.The research on the structure of SDBS/PSLi complexes and the propagating mechanism of iPS was summarized as below. Addition of SDBS yielded a dramaticly n-butyllithium maximum absorption wavelength shift to long-wave band. In nopolar solvent, one SDBS molecule could interact with two t-BuLi molecules to form the corresponding 2:1 complexes. The highest reactivity of SDBS/t-BuLi was observed in 2:1 complexes and the relative reactivity decreased in the order SDBS/(t-BuLi)2> SDBS/t-BuLi> (t-BuLi)2. The nonassociated PSLi was being in a dynamic equilibrium with a high proportion of associated contact PSLi ion pairs that appear to be the only propagation site resulting the isotactic structure in PS. The statistic calculation on PS samples indicated that the 80℃MEK insoluble was consistent with the Bernoullian statistic but the unfractionated and 25℃MEK soluble fraction was neither in agreement with the Bernoullian statistic nor with the 1st-order Markov statistic. The complexes formed by coordination of styrene with the 1:1 SDBS/PSLi complexes suggested that the pro-m structure was preferred. Repeated pro-(R) or pro-(S) monomer presentation will lead to isotactic polymers.The elementary study on the practical application of iPS in integrative rubber indicated that the change of propagating sites had faint influence on the stereoregulation of PS. In virtue of the living character of the anionic polymerization, PB-b-iPS, PI-b-iPS diblock copolymers have been successfully prepared. The expected structure of the micelle-like aggregates was resulted from an inner iPS block surrounded by the corresponding soft block shell. The size of such an aggregate was nanoscale and easy to control their diameter. The polybutadiene-b-polystyrene-b-polybutadiene (BSB) was also prepared in cyclohexane. After treated with hexane, it also can form micelle-like aggregates composed of an inner PS block surrounded by the PB shell. The low temperature vulcanization of BSB indicated that their mechanical properties are bad due to the insufficient crosslink. The PI-b-iPS used as the replacement of carbon black showed a limited ability of reinforcing the styrene-butadiene rubber (SBR). The main reason was lack of effective crosslink between iPS core and SBR matrix. The PI-b-iPS vulcanized directly still displayed the bad mechanical properties as almost iPS core contributing reinforcement was destroyed.