This paper takes poly2-hydroxyethyl methacrylate (PHEMA) as an example, the effects of linear and branched structures on the microrheological properties of polymers are studied to further supplement and further understand the importance of microrheological properties for optimising material properties and expanding the scope of application. The experimental results show that the higher the molecular weight of linear PHEMA, the higher the storage modulus and the higher the complex viscosity; the higher the degree of branching of branched PHEMA, the lower the storage modulus and the lower the complex viscosity. The mean square displacement of tracer particles in isopropanol solutions of linear and branched PHEMA has a good linear relationship with the lag time, and the slope of the curve of linear PHEMA(0.74 ~ 0.86) is smaller than that of branched PHEMA(0.91 ~ 0.95). The loss factor of linear PHEMA is lower than that of branched PHEMA.
Xuefei Leng,Zhiyong Wei,Yufei Bian,Yingying Ren,Yurong Wang,Qinyi Wang,Yang Li
Three series of narrowly dispersed comb-like graft poly(L-lactide) (PLLA) with controlled graft length and graft density have been facilely synthesized and characterized. The structural information was determined by means of 1H NMR, GPC, and viscometry, demonstrating the well-defined grafted structure. The effects of grafting parameters on rheological properties, thermal and crystallization behaviors were investigated systematically to illustrate the structure–property relationships. By the analysis of the rheological behavior, the increase of graft length and graft density can both lead to an elevated value of zero-viscosity (η0), enhanced complex modulus (G*) and increased complex viscosity (η*). Comparatively, graft density contributes more to the improvement of rheological properties than graft length does. For thermal properties, DSC results show that the glass transition temperature (Tg), the melting temperature (Tm) and the crystallization enthalpy (ΔHm) of graft PLLA increase with the chain length and decrease with the graft density. Furthermore, spherulite morphologies and growth rates were studied by polarized microscopy (POM), and the observation revealed a remarkable improvement of radius growth rate of the spherulites (G) when graft density increased. The results indicate that G depends more on the molecular weight of each arm (Mn,arm) than the total Mn.
Bing Meng,Jingjing Deng,Qing Liu,Zhihua Wu,Wei Yang
Poly(butyl acrylate) was prepared by the free radical polymerization of butyl acrylate as an initiator in the presence of 2,2′-Azoisobu-tyronitrile (AIBN) and the average molecular weight , polydispersity and thermal stability were evaluated. PLA and PBA were melt blended using a Haake Rheometer, and the light transmission, thermal properties, dynamic rheological properties, mechanical properties , phase morphology of blends and toughening mechanism were investigated. Dynamic rheology, SEM and DSC results show that the PLA is partial miscible with PBA. The PBA component improved the crystallization ability of PLA and the crystallinity of PLA increased with content of PBA (<15 wt.%). With the increase of PBA, the tensile strength and modulus of the blend decreased slightly while the elongation at break and toughness were dramatically increased. With the addition of PBA, the failure mode changes from brittle fracture of neat PLA to ductile fracture of the blend. Rheological results revealed the complex viscosity and melt elasticity of the blends decreased with increasing content of PBA and phase segregation occurred at loading above 11 wt.% PBA. UV–vis light transmittance showed that PLA/PBA blends with a high transparency, and the transmittance decreased with the amount of PBA.
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