Study of Linear and Cyclic Graft Polystyrenes with Identical Backbone Contour in Dilute Solutions: Preparation, Characterization, and Conformational Properties
Jianing Zhou, Jinxian Yang, M. Ishaq, Lianwei Li
Abstract
Exploring the difference in the topology–structure–conformation relationship for linear and cyclic graft polymers is an interesting topic. In this work, two libraries of linear graft (l-PPA-g-PS, with a linear backbone) and cyclic graft (c-PPA-g-PS, with a cyclic backbone) polystyrenes with low ratios of the backbone-to-sidechain contour length (rc, from 1.26 to 6.22) and various grafting densities (σ, from 0.16 to 0.86) have been studied as models. Atomic force microscopy (AFM) characterization has indicated ellipsoidal and spherical morphologies for both l-PPA-g-PS and c-PPA-g-PS with no significant difference. By comparing the absolute (Mw,abs) and apparent (Mw,app) molar masses, it is found that Mw,abs/Mw,app varies from 1.5 to 3.5 and gradually increases with σ. By measuring gh1/2 (gh1/2 = Rh,graft/Rh,linear), it is found that the two topologies have different compactness of conformation. By following the temperature-dependent interchain aggregation in cyclohexane, it is found that the cyclic backbone feature can suppress the interchain association and be more susceptible to graft density than linear graft polymers. The present study has clearly showed that the cyclic graft topology can potentially display unique structural and conformational properties, which can be attributed to the topological advantages such as more compact conformation and significant isotropic features.