| Polystyrene-b-polybutadiene-b-polystyrene (SBS) is widely used thermoplastic elatomers. One of the most important applications is used as a toughening agent for polyamide and epoxy resins and so on. But toughening effect on polyamides is not obvious through blending simply due to the poor compatibility between polar matrix and non-polar SBS. So the most used method is that polar group, maleic anhydride, is introduced into the SBS chains by melting grafting polymerization industrially. Maleic anhydride group in the SBS chains can react with amino group in the polyamide chains to improve their compatibility during screwing process.But there exist many defects in anionic polymerization and melting grafting polymerization like being suitable for few monomers and higher energy-consumption. So it is an interesting research topic to introduce maleic anhydride into the SBS chains directly in the process of synthesizeing block copolymer and improve the toughening effect of polyamides. The advent of reversible addition-fragmentation chain transfer radical polymerization (RAFT) in mini-emulsion system provides a new route to synthesize more (co)polymers with well-defined structure.In this study, based on synthsis of styrene/butadiene block copolymer modified by maleic anhydride as a polyamide toughening agent via RAFT (mini)emulsion polymerization, alternating copolymer of styrene and maleic anhydride teminated with RAFT functionality, poly(styrene-alt-maleic anhydride)-RAFT, is used as a macro RAFT agent to mediate (surfactant-free) miniemulsion polymerization and seeded emulsion polymerization. Maleic anhydride group is introduced into the molecular chains directly during synthesizing block copolymer. Therefore, with the target of synthesizing styrene/butadiene block copolymer modified by maleic anhydride which can be used for toughening polyamide, styrene/butadiene block copolymer with having maleic anhydride group was synthesized by RAFT-mediated bulk, miniemulsion polymerization and seeded emulsion polymerization. In this section, RAFT polymerization kinetics, living characters, morphologies and microphase separation were studied and its toughening effects, interface compatibility and water absorbency on polyamide-6 were also researched simply.The main researches of this thesis are as follow:1. Styrene RAFT miniemulsion polymerization mediated by poly(styrene-alt-maleic anhydride) macro RAFT agentPoly(styrene-alt-maleic anhydride) alternating copolymer terminated with dithioester group, which is obtained by RAFT polymerization, can be used as a macro-RAFT agent to mediate styrene polymerization in miniemulsion system stabilized by SDS. The results showed that styrene miniemulsion polymerization exhibited good controlled/living characters and the majority of molecular chains were terminated with dithioester group.Stable latexes were obtained by styrene RAFT polymerization in miniemulsion system stabilized by ammonolyzed SMA. The amount of ammonia had an obvious effect on the polymerization kinetics and living characters. Retardation appeared with increase of ammonia and the longer retardation time, the more the amount of ammonia. With lower degree of aminolysis, the polymerization exhibited relatively good controlled/living characters. Ammonia reacts with dithioester group to form thioamide and thiol, leading to the retardation and loss of living characters.Nanoparticles with core-shell structure were obtained via interfacially confined RAFT polymerization in miniemulsion system stabilized by ammonolyzed SMA macro RAFT agent. Ammonia has an obvious effect on the morphology of particles. Core-shell morphology is not obvious under lower degree of aminolysis and higher degree of aminolysis because of coupling reaction and homogeneous nucleation. Obvious core-shell morphology was clearly observed under certain degree of aminolysis, and particle size increases linearly with increase of ammonia.2. Synthesis of styrene/butadiene block copolymer modified by maleic anhydride via RAFT seeded emulsion polymerizationThe RAFT seeded emulsion polymerizations of butadiene were studied and effects of ratio of S/B, reaction temperature and polymerization type on polymerization kinetics, living characters, gel point, morphologies and polymer properties were mainly researched. Styrene/butadiene block copolymer could be synthesized via RAFT seeded emulsion polymerization. The polymerization proceeded slowly. Meanwhile, crosslinking and branching reaction appeared in the process of polymerization, leading to appearance of gel point. And gel point was affected obviously by feed ratio and reaction temperature. The higher the reaction temperature was, the earlier gel point appeared; the more the feed ratio of butadiene was, the lower the gel point was.The polymerization exhibited relatively good controlled/living characters before gel point. Due to the branching and crosslinking reaction the experimental Mns become larger than theoretical prediction approaching the gel point. The GPC results showed that feed ratio had no obvious influence on the molecular weight of polybutadiene before gelation.In the butadiene RAFT emulsion polymerization, particle morphology would change from lamellar, perforated concentric-spherical lamellar and core-shell structures with polystyrene shell and crosslinked polybutadiene core with increase of butadiene conversion. After styrene RAFT seeded emulsion polymerization, the final triblock copolymer particles modified by maleic anhydride possessed the morphology of three-layered core-shell structure which outer and inner layers are polystyrene and intermediate layer is crosslinked polybutadiene..For diblock copolymer of styrene and butadiene, the result of mechanical property showed the ultimate strength decreased from 9 MPa to 6 MPa and elongation at break increased from 240% to 350% as the increase of polybutadiene chain. But for triblock copolymer of styrene and butadiene, the largest stress was close to 18 MPa while elongation at break was only about 40% due to increase of crossling degree.3. Effect of styrene/butadiene block copolymer modified by maleic anhydride on toughening effect of PA6Toughening effect, compatibility and water absorbency of styrene/butadiene block copolymer modified by maleic anhydride on polyamide 6 were studied simply. The experimental results showed that styrene/butadiene block copolymer had toughening effect on polyamide 6 and the impact strength increased with increase of content of block copolymer. Styrene/butadiene block copolymers with more polybutadiene content have higher impact strength with the same content of rubber. When the rubber content exceeded 6%, the impact strength decreased. Compatibility between polyamide and unmodified block copolymer of styrene and butadiene was poor and the phase interface was obvious. Block copolymer of styrene and butadiene modified by maleic anhydride could improve the compatibility. Styrene/butadiene block copolymer modified by maleic anhydride and polyamide 6 would form homogeneous system due to the small molecular weight of block copolymer. And water absorbency decreased with increase of block copolymer content.RAFT miniemulsion polymerization mediated by alternating copolymer of styrene and maleic anhydride with narrow polydispersity index can introduce maleic anhydride group into the styrene/ butadiene block copolymer chains directly. Microphase separation of nanoparticles changes from conversions of monomers and polar group on the particle surface can improve the compatibility between resins and rubbers. This simple technique is readily scalable up and offers great opportunity to tune the compositions of different chains. And the results provide the basis for analyzing the effect on toughening polyamides. |
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