Synthesis Of PS-g-PA6 With Controlled Structure By Reactive Processing And Its Compatiblizing Efficiency

Polymer compatibilizing blending,block or graft copolymers pre-made are added or generated in-situ by reaction in the mixing process of the immsible polymers, offers an important route to prepare new materials with combinations of properties. The efficiencies of compatibilizer are believed to depend on their molecular architecture,molecular weight,composition and the interaction between the homopolymers and the copolymer block.Now the prevailing method of in-situ compatibilization results mainly from the formation of graft copolymer by the coupling reaction between two functional polymers.Therefore,it is very necessary to research the relationship of the structure and composition of graft copolymer and its compatibilizing efficiency.This thesis use the graft copolymer(PS-g-PA6) with polystyrene(PS) as backbone and polyamide 6(PA6) as grafts as the compatibilizer of PS/PA6 blend systems to establish the relationship of the structure and composition of graft copolymer and its compatibilizing efficiency,which is awfully significant to optimize the structure and composition of graft copolymer in order to achieve the high compatibilizing efficiency.This thesis is composed of three parts:(1) development of a novel reactive processing technology for synthesizing graft copolymer PS-g-PA6;(2) studying emulsification efficiency of PS-g-PA6 graft copolymers for PS/PA6 blends and the ability of stabilizing the phase morphology of PS/PA6 blend in the process of annealing;and(3) bringing forward the concept of tracer-emulsifier and extending an old concept(residence time distribution) in chemical engineering to polymer blending in order to study the morphology evolvement of polymer blends in continuous mixer. The results are as follows:1.The underlying chemistry for the synthesis of PS-g-PA6 graft copolymers was based on the use of a copolymer of styrene(St) and 3-isopropenyl-α,α-dimethylbenzene isocyanate(TMI),PS-co-TMI,to activate the polymerization ofε-caprolactam(CL) in the presence of sodiumε-caprolactam(NaCL) as an anionic catalyst.The structure of a graft copolymer is mainly determined by the following three parameters,backbone length,graft density,and graft chain length.The backbone length of the PS-g-PA6 depended only on the molar mass of the initial PS-co-TMI as the latter was not subjected to chain scission during the synthesis process.The PA6 graft density was determined by the TMI content in PS-co-TMI because all the isocyanate moieties had participated in the activation of the polymerization of CL. The PA6 graft chain length was controlled primarly by the PS-co-TMI/CL molar ratio.2.The efficiency of graft copolymers at compatibilizing the dispersed phase/matrix morphology of PS and PA6 blends and stabilizing the co-continuous morphology of the blends during quiescent annealing were studied.Results showed that it depended very much on its molecular architecture and/or composition.For graft copolymers with similar backbone and graft density,the longer the grafts,the higher their efficiency;for a given backbone/graft composition,graft copolymers having fewer and longer grafts were more efficient at comaptibilizing and stabilizing the morphology.3.Feeding mode had a very significant effect on the size of the dispersed phase domains at short mixing time and its effect decreased or became negligible at long mixing time.This indicates that feeding mode affected mostly the time necessary for the PS-g-PA6 compatibilizer to reach and emulsify the interfaces between PS and PA6. A good feeding mode should meet the following two requirements:first,the matrix should melt faster than the dispersed phase in order to avoid the phase inversion; second,the compatibilizer should be present as soon as the blending process starts, namely,the dispersed phase begins to melt.4.Building up an emulsification curve may not always be practical because of limited amounts of copolymers available.This is especially true for an industrial polymer blending process.A so-called concept of tracer-emulsifier was developed to solve the problem.Very small amounts of fluorecent moities such as anthracene were incorporated in PS-co-TMI.When the latter was used to activate the polymerization of CL,the resulting graft copolymer contained fluorescent moities.An original method for constructing the emulsification curve of a polymer blend in a continuous mixer such as a twin-screw extruder was developed based on the tracer-emulsifier concentration distribution(i.e.the residence time distribution) and the corresponding dispersed phase domain size distribution of the blend system.The resulting emulsification curves exhibited unique features that would open a new research field for polymer blending.