Tuning Polymer Thickness: Synthesis and Scaling Theory of Homologous Series of Dendronized Polymers

Abstract

The thickness of dendronized polymers can be tuned by varying their generation g and the dendron functionality X. Systematic studies of this effect require (i) synthetic ability to produce large samples of high quality polymers with systematic variation of g, X and of the backbone polymerization degree N, (ii) a theoretical model relating the solvent swollen polymer diameter, r, and persistence length, lambda, to g and X. This article presents an optimized synthetic method and a simple theoretical model. Our theory approach, based on the Boris-Rubinstein model of dendrimers predicts r approximately n(1/4)g(1/2) and lambda approximately n(2) where n = [(X - 1)(g) - 1]/(X - 2) is the number of monomers in a dendron. The average monomer concentration in the branched side chains of a dendronized polymer increases with g in qualitative contrast to bottle brushes whose side chains are linear. The stepwise, attach-to, synthesis of X = 3 dendronized polymers yielded gram amounts of g = 1-4 polymers with N approximately = 1000 and N approximately = 7000 as compared to earlier maxima of 0.1 g amounts and of N approximately = 1000. The method can be modified to dendrons of different X. The conversion fraction at each attach-to step, as quantified by converting unreacted groups with UV labels, was 99.3% to 99.8%. Atomic force microscopy on mixed polymer samples allows to distinguish between chains of different g and suggests an apparent height difference of 0.85 nm per generation as well as an increase of persistence length with g. We suggest synthetic directions to allow confrontation with theory.

Modeling Nanosized Single Molecule Objects: Dendronized Polymers Adsorbed onto Mica

“…The structure of a homologous series of neutral DPs composed of a poly(methacrylic acid) backbone, whose repeat units are regularly branched dendrons of generation g containing both amide and aromatic groups (Scheme 1), was investigated at the nanometer level by atomic force microscopy (AFM) and transmission electron microscopy (TEM) [2][3][4] and at the atomistic level using molecular dynamics (MD)…”

Living Radical Polymerization by the RAFT Process – A Third Update

“…G [415] MMA [415] St [415] MA [415] tBA [415] NIPAm [415] DMAm [415] MA-b-tBA [415] MA-bDMAm [415] G* [388,416] 310 [417] St [418] 4VP [388] BA [416] tBA [416] EHA [416] LA [416] PEGA [416] NIPAm [267] 137…”

Synthetic regimes due to packing constraints in dendritic molecules confirmed by labelling experiments

“…This effect arises in the vicinity of the so-called de Gennes dense packing limit 30 , at g ' g max , because the bulkier reaction products cannot be accommodated within the available free volume. In turn, the onset of this effect at g max occurs because the mass of an ideal dendron grows exponentially with g while its maximum span increases only linearly 10,[12][13][14][15] . For g4g max the exponential growth of mass, associated with perfectly regular branching, is impossible.…”