A new approach for the synthesis of model amphiphilic polymer co-networks (ACNs) based on a heterocomplementary coupling reaction of a 2-(4-nitrophenyl)-benzoxazinone terminated tetra-arm polycaprolactone star (tetra-PCL) with an amino-terminated tetra-arm polyethylene glycol star (tetra-PEG) is presented. The reaction conditions (solvent, concentration, and temperature) were varied widely. Reaction kinetics and gelation were analyzed with high-resolution NMR spectroscopy and computer simulations. The results agree with a nearly homogeneous mixture where local composition fluctuations affect kinetics only after most of the molecules are attached to the gel. Viscometry, dynamic light scattering data, and literature data for the solubility parameters were combined to provide estimates for the Flory−Huggins interaction parameter of the two star polymers in toluene, chloroform, and THF as solvents. These estimates allow one to collapse equilibrium swelling data in different solvents on a universal curve. Multiple quantum NMR analysis shows an enhanced formation of double connections between the same pair of stars as compared to preceding work on tetra-PEG gels made by the same cross-linking strategy but with a different coupling reaction. Besides this last observation, the remaining results indicate that the networks possess a near model-like structure with only a small fraction of pending arms as the most relevant type of network defects.
A new approach to hybrid model network formation based upon heterocomplementary end‐linking of four‐arm star poly‐ε‐caprolactone (PCL) and linear polypropylene glycol (PPG) precursors is demonstrated. Specifically, hydroxy‐terminated PCL(OH)4 and an amino‐terminated linear PPG(NH2)2 are reacted with a bifunctional coupling agent containing one carboxylic acid chloride group and one oxazinone group. PCL(OH)4 is first reacted with the former in a solution, and the so‐obtained oxazinone‐terminated intermediate is then reacted with PPG(NH2)2 to form a network both in the solution and in the melt. A strong effect of electron‐withdrawing groups on the reactivity of the oxazinone group, and thus on the network formation, is evidenced. Network structure and properties are studied by swelling experiments and low‐field multiple‐quantum (MQ) NMR, which confirm the successful formation of hybrid networks and provide information on the significant network inhomogeneities. On the methodological side, a reliable approach to MQ NMR data analysis for networks of variable degree of inhomogeneity is discussed.
PA6/PPO 70/30 blends were reactively compatibilized using carboxylated polystyrene (PS) and poly(styrene-block-4-methylstyrene) with various degrees of carboxylation. The high carboxylation of PS (up to about 50%) caused a decrease of dispersed PPO dimensions with a simultaneous deterioration of properties, especially of toughness and elongation. The best mechanical behavior was found for PS with 1% degree of carboxylation and for neat PS. On the other hand, degrees of carboxylation higher than 50% caused an increase in particle size. This was most significant for block copolymers, where a marked change in size and shape occurred, from spherical particles of about 1 m in size to large, elongated particles about 50 m long or a similar rough cocontinuous structure. The deteriorated mechanical behavior is tentatively explained by unsuitable properties of the reactively formed compatibilizer and thus of the interface. The enhanced rigidity of highly carboxylated poly(4-methylstyrene) chains (and its product of grafting with PA6), causing its decreased emulsification ability together with the expected rigid interface, which probably suppresses breakup of the PPO phase, may be responsible for the increase of the dispersed PPO dimensions found.
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