Polydopamine – A Versatile Coating for Surface‐Initiated Ring‐Opening Polymerization of Lactide to Polylactide

Abstract

An effi cient way for covering various surfaces with poly(lactic acid) (PLA) is discussed. In a fi rst step, the material is coated with polydopamine (PDA) by air oxidation of dopamine. The resulting PDA layer acts as an initiator for ring-opening polymerization (ROP) of lactide resulting in an outer PLA shell. Since PDA sticks to almost every solid material, the methodology has a wide scope. The strategy is demonstrated with magnetic nanoparticles and non-magnetic powders.can be achieved by ring-opening polymerization (ROP) of lactide in the presence of the material to be covered. There are materials where PLA does not stick or the adhesion is not strong enough. In such cases, a primary adhesive coating is advised that anchors to the material to be covered on the one hand and binds the PLA on the other hand. The most effi cient linkage of PLA is achieved when covalent bonds are formed by surface-initiated ROP. Here, nucleophilic reactive groups at the surface initiate the ROP and fi x the growing PLA chain covalently. In this way, magnetite NPs (MNPs) stabilized by glycolic acid were treated with lactide in the presence of tin(II) 2-ethylhexanoate under microwave conditions. [ 13 ] In a similar manner, MNPs covered with oleic acid underwent a ligand exchange by ω-hydroxy carboxylic acids and were subsequently covered with PLA by tin dioctanoatecatalyzed ROP of L -lactide. [ 14 ] In both cases, the PLA shell anchors by the help of the carboxylate groups of the initial ω-hydroxycarboxylic acid. Since anchoring of carboxylate to magnetite is not very strong and thus reversible, the search for better primary coverage of MNPs is still desired. Furthermore, the application of poisonous tin dioctanoate causes limitations if biomedical applications are considered. In an alternative approach, MNPs were stabilized by glyceryl phosphate or ascorbyl phosphate and then treated with lactide in the presence of 4-( N , N -dimethylamino)pyridine (DMAP). [ 15 ]

Chemistry of Polydopamine – Scope, Variation, and Limitation

“…In this process, a less likely amide formation of the acid groups with the N‐atom in position 1 of indole units was assumed concluded from FTIR spectra. PDA surfaces mediate ring‐opening polymerization of lactide to polylactic acid most likely by involvement of the amino groups of PDA …”

Chemistry of polydopamine analogues

“…Routes of PDA post functionalization utilizing quinone, catechol or primary amino groups as reactive sites …”

“…78 Primary amino groups of PDA can serve as initiator for organocatalytic ring opening polymerization (ROP) of lactide to polylactic acid. 44 As an initial step of this polymerization, acylation of the amino group by the lactide occurred, which was followed by ring opening of further lactide molecules. In this way, polylactic acid was linked to the surface of magnetic and non-magnetic materials like iron, magnetic nanoparticles, silica or titanium.…”

“…The diazo-transfer achieved with triflyl azide Examples of pathways of nucleophilic attacks (bent arrows) at quinone moieties in PDA leading to PDANA. Recent exploitation of primary amino groups of PDA in syntheses of PDANA 9,44,45,78,79.…”

One‐Pot Formation of ZnO‐graft‐Poly(d,l‐Lactide) Hybrid Systems via Microwave‐Assisted Polymerization of d,l‐Lactide in the Presence of ZnO Nanoparticles

“…[ 10 ] A vast number of publications claim that a previous functionalization of the nanoparticles with hydroxy-or amino-ended molecules is generally required, followed by ROP of lactide catalyzed commonly by stannous octanoate. [4][5][6]8,[11][12][13][14][15] Several drawbacks arise from this process including a multistep hydroxyl-or aminofunctionalization reaction associated with a time-consuming procedure (several days) and the use of a tin catalyst leading to by-products (Sn(OH) 2 and SnO, among others) that are diffi cult to get rid of and potentially cytotoxic. [ 16 ] Therefore, there is a need for new methodologies to generate PLA-functionalized nanoparticles that involve innocuous initiation systems.…”