Construction Of “Quasi-block Copolymer” Induced By Stereocomplexation And Its Application As Compatibilizer For Immiscible Polymer Blends

Interfacial compatibilization and interfacial regulation of polymer materials,which are acknowledged as the core issue in terms of immiscible polymer blends,has attracting increasing attentions.Paradoxically,both the concept and advancement of interfacial compatibilization has been impeded since the emulsifier,either pre-made or in-situ formed during processing,is always linked by covalent bonds.Currently,noncovalent interactions are gaining attention due to the unique advantages such as relatively lower bonding energy,dynamic reversibility and selectivity,which brings new opportunities for the structure design of copolymers.Taking advantages of the noncovalent interaction between poly(L-lactide)(PLLA)and poly(D-lactide)(PDLA),“quasi-block copolymers”(q BCPs)can be achieved through melt blending.Then,the methodology is further applied into immiscible polymer blends to construct “interfacial q BCPs” between phases by the non-covalent “junction point”.The “interfacial q BCPs”is further applied to various immiscible polymer blends.A new conception,termed as“non-covalent compatibilization”,is thereby conceived based on the above results.The main achievements are as follows:(1)Construction of “quasi-block copolymer” based on stereocomplexation: Firstly,two kinds of graft copolymer,PMMA-g-PLLA and PS-g-PDLA,were prepared through reactive blending due to the in-situ ring-opening reaction between the terminal carboxyl groups of PLLA/PDLA and epoxide groups along the backbone of PMMA-co-GMA(MG)and PS-co-GMA(SG).Both the grafting density and grafting length can be regulated by adjusting the feed ratio and processing conditions.Then,the two products were used as pre-bonding units for subsequent processing.It can be envisaged that PS-“block”-PMMA connected by pseudo linkage was induced during compounding resulting from the complementary multiple hydrogen bonding interactions between PDLA and PLLA grafted moieties.Therefore,local segregation of PS-“block” and PMMA-“block” with nanometer size,which is resemble with classical BCPs,can be acquired.Interestingly,the refined morphology(from spherical micelles,lamellar,to co-continuous microstructure)can be obtained and facilely tuned by varying the length and ratio of enantiomeric PDLA/PLLA grafts.(2)The in-situ compatibilization of “interfacial q BCPs” for the immiscible PS/PMMA blends: PMMA-g-PLLA and PS-g-PDLA prepared above were further utilized as interfacial emulsifier for the immiscible PS/PMMA blends.The effects of graft copolymer content,blending methods,and processing conditions on phase structure and properties of the blends were systematically studied.Due to the specific physical entanglements between the enantiomeric grafts,sc linkage was in-situ formed,enabling the formation of “interfacial q BCPs” between PS and PMMA.The results showed that the in-situ generation of “interfacial q BCPs” can reduce the interfacial tension,enhance the interfacial bonding,and effectively increase the compatibility of PS/PMMA blends.(3)The in-situ compatibilization of “interfacial q BCPs” for POE/PBAT blends: In order to explore the universality of “non-covalent compatibilization”,the concept of“interfacial q BCPs” was introduced into poly(ethylene-1-octene)/poly(butyleneadipate-co-terephthalate)(POE/PBAT)blends.The effects of“interfacial q BCPs” concentration and the component composition on the structure and properties of the blends were systematically investigated.Firstly,POE-g-PLLA and PDLA-g-SG were prepared by reactive processing of POE-co-GMA(PS-co-GMA)and PLLA(PDLA),respectively.Then,the two products were incorporated into the POE/PBAT blends.It can be found that in-situ grafting of PBAT onto SG occurred between carboxyl group of PBAT and epoxy groups in SG mainchains.Meanwhile,specific non-covalent interaction between PLLA and PDLA is generated.Hence,“interfacial q BCPs” between POE and PBAT were in-situ formed.The results showed that the “interfacial q BCPs” can take the role of compatibilizer between phases and finally realize the optimization of properties.