Polymer Brushes Derived from Polymer Single Crystals

Polymer brushes are polymer chains densely tethered to substrates or interfaces. Different from free polymer chains, these tethered brushes exhibit unique chain conformations and behaviors, and can be widely used for different applications due to their special properties. Traditional methods for polymer brush synthesis include "grafting-to" and "grafting-from", both with intrinsic limitations. In this dissertation, polymer single crystals (PSCs) were used as templates to synthesize polymer brushes. Polymer brushes can be obtained on single crystal surface by crystallization of block copolymers, or by coupling PSCs with functional chain ends onto a substrate. Due to the regular chain packing in PSCs and the programmable crystal growth, polymer brushes derived from PSCs can possess controllable grafting density, tethering points, and brush architectures. In this dissertation, a series of polymer brushes with various chain compositions/architectures were synthesized via the PSC-templating method. The first example is the synthesis of patterned poly(ethylene oxide) (PEO) gradient brushes. The grafting density of PEO brushes was precisely tuned by co-crystallization of end dissimilar PEO polymers, and various gradient patterns were obtained by programming the PEO crystal growth. Block-copolymer brushes using poly(L-lactic acid)-b-poly(ethylene oxide) (PLLA-b-PEO) were synthesized by using PSCs of a triblock copolymer with a long tethering segment to obtain a high grafting efficiency. Binary poly(ethylene oxide) (PEO) / polystyrene (PS) mixed brushes were synthesized using poly(lactic acid) (PLA) stereocomplex single crystals as the templates. Stereocomplex structure prevented the formation of macrophase separation of the two immiscible polymers, and resulted in a homogeneous mixing of two polymer brushes. The resulting mixed PEO/PS brushes exhibited the characteristic ripple and dimple phase structures in response to different solvents. Lastly, patterned poly(4-vinylpyridine) (P4VP) brushes on PEO single crystals were used to assemble gold nano particles (AuNPs) into free standing frame structure with precisely tunable sizes. The synthesized AuNP frames exhibited special optical property, which was observed only in gold nano rods but not AuNPs, indicating the importance of a controlled assembly structure in discovering new properties of NPs. Keywords: polymer, polymer brush, polymer crystallization, polymer single crystal