Acid-Enhanced Interfacial Polymer Layer Growth

Abstract

We report on the growth of interfacial multilayer structures formed from maleimidevinyl ether alternating copolymers. The thickness and density of these polymer layers can be controlled by adding acid to the interlayer cross-linking reaction. We have demonstrated this control for several different interlayer cross-linking strategies, where amide, ester, urea, and urethane interlayer covalent bonds are formed. For all reactions, the addition of concentrated acid during polymer layer deposition resulted in a 2-to 4-fold increase in the loading density of the polymer relative to the acid-free reaction, depending on the acid used and its concentration. These findings are consistent with acid catalysis (HCl) and/or dehydration (H 2 SO 4 ).

Covalent Layer‐by‐Layer Assembly Using Reactive Polymers

“…Examples of amide-bond-forming reactions that have proved particularly useful for covalent LbL assembly include reactions between amine-functionalized agents and building blocks functionalized with (i) anhydrides [66][67][68][69][70][71][72][73], (ii) acid chlorides [81,82], (iii) activated esters (e.g., polymers bearing reactive pentafluorophenyl ester groups) [74][75][76][77], and, in the presence of a carbodiimide coupling agent, (iv) carboxylic acids [78][79][80]. The reactivity of anhydride and acid chloride functionalities generally restricts the first two of these approaches to the use of aprotic organic solvents and film components that do not contain other protic groups that could lead to unwanted side reactions.…”

“…Amine-functionalized polymers and small molecules have also been used in combination with reactive building blocks bearing isocyanate [81,82], dichlorophosphazene [83], acrylate [84][85][86]147], alkyl halide [87,88], epoxide [89], or aldehyde groups [90][91][92][93][94][95][96][97][98] to fabricate covalent LbL films cross-linked with urea [81,82], phosphazene [83], amino-ester [84][85][86]147], alkyl amine [84][85][86][87][88], or Schiff base [90][91][92][93][94][95][96][97][98] (imine) linkages. Approaches based on reactions between amine-and aldehyde-functionalized components (to form imine or Schiff base linkages) have been particularly well studied because of the relatively fast and mild (aqueous) nature of these reactions, which also permits reactive immobilization of biomacromolecular agents such as proteins into cross-linked multilayers.…”

Understanding Molecular Interactions within Chemically Selective Layered Polymer Assemblies

“…ventional ionic zirconium bisphosphonate (ZP) interlayer linking chemistry, [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] where the phosphonates are sequestered by metal ion complex formation, we use the side groups of these polymer multilayers in their deprotected form 35,36 as active sites for metal ion uptake (Figure 3). 29 Covalent interlayer attachment is accomplished using adipoyl chloride.…”

“…After the desired number of layer deposition cycles, the phosphonate groups are deprotected using bromotrimethylsilane (BTMS). 35,36 Deprotection and hydrolysis renders a multilayer film capable of efficient metal ion uptake. Exposure of the deprotected multilayer to ZrOCl 2 solution results in rapid metal ion uptake, with ellipsometry, FTIR and X-ray photoelectron spectroscopy (XPS) data, each revealing significant changes in the multilayer structure after sorption of Zr…”

“…We use interfaces constructed with individual molecular layers of maleimide-vinyl ether alternating copolymers, where we control the identity of the polymer side group and the adlayer free volume. 29,[32][33][34][35][36][37][38] Understanding the structure and morphology of the polymer adlayers is central to the success of this work. We have created structural gradients normal to the substrate plane, where each layer in a polymer multilayer stack contains different polymer side groups, have achieved control over polymer layer density; and are in the process of developing reversible optical control over polymer layer porosity using photoisomerizable crosslinks between polymer layers.…”