Synthesis Of Star Polystyrene And Styrene-Acrylonitrile Copolymer By Retarded Anionic Polymerization

SAN resins (styrene-acrylonitrile copolymers) are thermoplastics that have excellent combination property and collaborative performance of two components including styrene and arylonitrile. At present SAN resins are mainly prepared by continuous bulk polymerization attributed to radical copolymerization mechanism. Living anionic polymerization of styrene and acrylonitrile can be achieved using inexpensive initiating systems in the absence of solvent at elevated temperature after the developed of NaH/i-Bu3Al retarded anionic polymerization (RAP) initiating system. RAP makes the anionic polymerization competitive with industrial radical processes. Therefore, anionic styrene-acrylonitrile copolymers are the development trend of them.In this paper, taking ethylbenzene as solvent, star polystyrene (cs-PS) was synthesized by "core-first" method with multi-sodium (m-Na) obtained from NaH/i-Bu3Al,styrene and divinylbenzene (DVB) as initiator for the first time. The reaction kinetics of four kinds of monomers in divinylbenzene with polystyrene sodium and styrene in m-Na system have been determined. The effect of [DVB]/[NaH] on the molecular parameters was studied. Star polystyrene (as-PS) was also prepared by "arm-first" method with NaH/i-Bu3Al as initiator, and DVB as coupling agent. The influence of [DVB]/[NaH] on the molecular parameters was investigated.Star styrene-acrylonitrile copolymer (as-SAN) was also prepared by "arm-first" method with NaH/i-Bu3Al as initiator, and DVB as coupling agent for the first time. The reaction kinetics of two monomers using two feeding method have been investigated. The effect of temperature and feeding ratio on the single-step polymerization reaction was studied. Star styrene-acrylonitrile copolymer (cs-SAN) was synthesized by "core-first" method with pre-made m-Na as initiator via single-step and dropping polymerizations. The effect of [DVB]/[NaH] on the molecular parameters using two feeding method was studied.The reaction kinetics of styrene in m-Na system and the influence of THF on reaction have been determined in dropping polymerization.The experimental results showed that:the polymerization rates of PSNa with four components and monomer concentration belong to first-order kinetics relationship; The polymerization rates of styrene with m-Na and monomer concentration belong to first-order kinetics relationship, too. With increasing DVB/Na, the molecular weight and the average arm number of cs-PS increased, and the molecules weight distribution was widened obviously comparing with as-PS.The highest monomer conversion (35%) can be obtained using "arm first" method when the mass ratio of styrene and acrylonitrile is 3/1 at 120℃, which is the optimal single-step polymerization condition. The best dropping polymerization condition that the monomer conversion can up to 80.3%is obtained at 105℃when m(St)/m(AN) is 3/1. S-S units increased with the proportion of styrene increasing and copolymers still have random sequence distribution. The addition of THF can make the anion dissociate using "core-first" method.and the optimal feeding value is [THF]/[Na]=5; The molecular weight and molecular weight distribution of cs-SAN increased with [DVB]/[NaH] increasing.