We report on the synthesis of telechelic poly(N-isopropylacrylamides) (PNIPAM) via nitroxide-mediated controlled polymerization, putting a focus on the introduction of defined end group moieties into telechelic poly(N-isopropylacrylamide) and poly(n-butyl acrylates). Various functional groups, linked to the central nitroxide-initiator via a triazole moiety resulting from an azide/alkyne-“click” reaction were probed with N-isopropylacrylamide and n-butyl acrylate as monomers in terms of efficiency and livingness. Functional groups on the initiator include a 1,2-dihydroxyalkyl moiety and a barbituric acid moiety as well as a phenyl moiety. Those initiators with a 1,2,3-1H-triazole moiety directly bound to the initiator group displayed a poor initiating quality toward N-isopropylacrylamide, whereas an ester bridge as linker between the initiator molecule and the functional group showed highly living character with respect to N-isopropylacrylamide and n-butyl acrylate as probed by kinetic experiments. Effects based upon internal hydrogen-bonding effects are made responsible rather than purely stereoelectronic effects, as proven by force-field calculations. MALDI time-of-flight mass spectrometry was used to prove the incorporation of the respective end groups into the telechelic PNIPAM polymers. Finally, the versatility of the method was demonstrated via a “grafting-from” approach of PNIPAM from magnetic iron oxide nanoparticles via a surface-bound initiator, resulting in an excellent control of molecular weight and thus thickness of the polymeric shell around the magnetic nanoparticles.

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Summary: Supramolecular gels, made from the combination of telechelic poly (ethyleneglycols) (PEG's) and trivalent poly(isobutylenes) with terminal matching hydrogen bonds were prepared and their rheological properties were investigated. Addition of poly(N-isopropylacrylamide) as thermosensitive polymer was included into the gel-capsules in amounts of 10 w%, producing gels with strongly thermallyresponsive properties. Additionally, dansyl-dyes with two different endgroups (either an hydrophobic endgroup or a multiple hydrogen bond) were encapsulated into the gels as mimicks for pharmaceutically active substances. Monitoring their diffusion by UV-dependent measurements allowed to tune the diffusion and thus the release properties of the gel. The generated supramolecular gels will allow the selective encapsulation and triggered release of various pharmaceuticals and biologically active targets.

The polymorphism of isotactic polypropylene (iPP) in combination with the strong response of this polymer to nucleation can be utilized for expanding the application range of this versatile polymer. Based on three “case studies” related to β-iPP pressure pipes, ethylene-propylene (EP) random copolymers for thin-wall injection molding and transparency and sterilization resistance of cast films we demonstrate ways of combining polymer composition, nucleation and process settings to achieve the desired application performance. The importance of considering interactions between polymer design, nucleation and processing parameters for designing application properties is highlighted.

Of all crystal modifications of isotactic polypropylene (iPP), the β-phase has received particular attention in both academia and industry because of the toughness increase resulting from its formation. Several novel nucleating agents have been presented and studied in recent years, most prominently the 'lanthanum complex' WBG. The majority of these studies are based only on one type of iPP, mostly an iPP homopolymer, despite the fact that chain irregularities are known to affect β-phase formation negatively. In the present study, several different iPP homo-and copolymers based on Ziegler-Natta and single-site catalysts differing mostly in chain defect concentration were used to evaluate the sensitivity of a 'reference' nucleating agent, quinacridonequinone, as well as WBG to chain structure effects. The results in terms of crystal structure, as well as mechanics, indicate a much greater sensitivity of WBG, resulting in a massively reduced β-phase formation for SSC-iPP hompolymers and ZN-iPP random copolymers with ethylene. An increase of γ-phase content in nucleation of the polymers with least regular chain structure hints at some duality for WBG as also observed for other β-nucleating agents before.