Summary: A new 2‐oxazoline monomer with a Boc protected amino function, 2‐[N‐Boc‐5‐aminopentyl]‐2‐oxazoline; (Boc‐AmOx), was synthesized from commercially available compounds. With an initiator salt system (N‐methyl‐2‐methyl‐2‐oxazolinium triflate; MeOxOTf), the monomer could be converted via living cationic ring‐opening polymerization to well‐defined homopolymers with narrow molar mass distributions and targeted polymer chain length. After a quantitative deprotection, poly(2‐oxazoline)s with pendant amino functions were obtained. In order to vary the polymer functional group density and solubility of the polymer, copolymerization with different monomer ratios of Boc‐AmOx and 2‐ethyl‐2‐oxazoline (EtOx) was performed. Ex‐situ NMR spectroscopy studies verified the randomness of the cationic copolymerization. The accessibility of the pendant amino side functions was confirmed in polymer analog thiourea formation with different isothiocyanates, such as benzyl isothiocyanate (BzNCS), or a fluorescence dye, tetramethyl rhodamine isothiocyanate (TRITC). A cross‐linking reaction with a bifunctional isothiocyanate (Ph(NCS)2) resulted in poly(2‐oxazoline) hydrogels. magnified image

A protected aldehyde-functionalized 2-oxazoline, 2-[3-(1,3)-dioxolan-2-ylpropyl]-2-oxazoline (DPOx), was synthesized from commercially available compounds in high yields. The polymerization of DPOx with different initiators proceeds via a living ionic mechanism; thus, the polymers were of low polydispersity and the degree of polymerization could be precisely adjusted. Copolymerization with 2-methyl-2-oxazoline gave water-soluble statistical copolymers. Hydrolysis of the homo- and copolymers resulted in well-defined, aldehyde-bearing poly(2-oxazoline)s. The aldehyde side functions reacted quantitatively with an amino-oxy compound to form the corresponding oxime.

Amphiphilic lipopolymers are known to form 2D thermoreversible gels at the air-water interface. Recently, we have reported surface rheology and film balance experiments on poly(ethylene glycol) (PEG) lipopolymers of different molecular weights, which indicated that a sufficient cross-sectional area mismatch between polymer and lipid moieties is necessary to form stable 2D gels (J. Coffman and C. Naumann, Macromolecules 2002, 35, 1835). In the current studies, we have investigated the influence of the hydrophobic anchor on the gelation properties by surface rheology and film balance technique. Experiments on PEG lipopolymers carrying saturated and partially unsaturated alkyl chains and on poly[(2-n-nonyl-2-oxazoline)x-b-(2-methylor 2-ethyl-2-oxazoline)y] (NxMy or NxEy) diblock copolymers of different block length show that the gel formation is not merely the result of the area mismatch between hydrophilic and hydrophobic moieties of the amphiphile (cone shape), but that a sufficient strength of van der Waals interaction within the hydrophobic moiety is necessary for the 2D gel to form, thus verifying earlier predictions that an alkyl chain condensation is a necessary precursor for the gelation process to occur. We also present neutron reflectometry data on PEG lipopolymers above and below the alkyl chain condensation and gelation transitions, which, in agreement to previous neutron and X-ray scattering experiments, reveal that both transitions occur after surface micelles of lipopolymers are formed at the air-water interface. On the basis of these findings, we assume that the gelation process of lipopolymers at the air-water interface is caused by a surface micellization of lipopolymers, which can be seen as the 2D analogue to the 3D gel formation observed for polymeric colloids with grafted polymer chains, such as copolymers and star polymers.

A new 2‐oxazoline monomer with a protected thiol group, 2‐[2‐(4‐methoxybenzylsulfanyl)ethyl]‐2‐oxazoline, MOB‐SOx, was synthesized from commercially available compounds. MOB‐SOx and 2‐ethyl‐2‐oxazoline (EtOx) were simultaneously polymerized yielding well defined copolymers with narrow molar mass distributions and target polymer chain length. The copolymerization was initiated by N‐methyl‐2‐methyl‐2‐oxazolinium triflate (MeOxOTf). After quantitative deprotection, poly(2‐oxazoline) with pendant thiol groups was obtained. The thiol groups were quantitatively added to the double bond of N‐phenyl‐acrylamide (PhA) and benzylmaleimide (BzM). Graft copolymers were obtained by reaction of those SH containing polymers with poly(2‐methyl‐2‐oxazoline)s bearing acrylamide (PMeOx10A) and maleimide (PMeOx10M) as terminal reactive groups.magnified image