Thermoresponsive copolymers continue to attract a great deal of interest in the literature. In particular, those based on ethylene oxide-containing methacrylates have excellent potential for biomaterial applications. Recently, some of us reported a study of thermoresponsive cationic graft copolymers containing poly(N-isopropylacrylamide), PNIPAm, (Liu et al., Langmuir, 24, 7099). Here, we report an improved version of this new family of copolymers. In the present study, we replaced the PNIPAm side chains with poly(2-(2-methyoxyethoxy)ethylmethacrylate), PMeO(2)MA. These new, nonacrylamide containing, cationic graft copolymers were prepared using atom transfer radical polymerization (ATRP) and a macroinitiator. They contained poly(trimethylamonium)-aminoethyl methacrylate and PMeO(2)MA, i.e., PTMA(+)(x)-g-(PMeO(2)MA(n))(y). They were investigated using variable-temperature turbidity, photon correlation spectroscopy (PCS), electrophoretic mobility, and (1)H NMR measurements. For one system, four critical temperatures were measured and used to propose a mechanism for the thermally triggered changes that occur in solution. All of the copolymers existed as unimolecular micelles at 20 °C. They underwent reversible aggregation with heating. The extent of aggregation was controlled by the length of the side chains. TEM showed evidence of micellar aggregates. The thermally responsive behaviors of our new copolymers are compared to those for the cationic PNIPAm graft copolymers reported by Liu et al. Our new cationic copolymers retained their positive charge at all temperatures studied, have high zeta potentials at 37 °C, and are good candidates for conferring thermoresponsiveness to negatively charged biomaterial surfaces.

We demonstrate a new, scalable, simple, and generally applicable two-step method to prepare hollow colloidosomes. First, a high volume fraction oil-in-water emulsion was prepared. The oil phase consisted of CH2Cl2 containing a hydrophobic structural polymer, such as polycaprolactone (PCL) or polystyrene (PS), which was fed into the water phase. The water phase contained poly(vinylalcohol), poly(N-isopropylacrylamide), or a range of cationic graft copolymer surfactants. The emulsion was rotary evaporated to rapidly remove CH2Cl2. This caused precipitation of PCL or PS particles which became kinetically trapped at the periphery of the droplets and formed the shell of the hollow colloidosomes. Interestingly, the PCL colloidosomes were birefringent. The colloidosome yield increased and the polydispersity decreased when the preparation scale was increased. One example colloidosome system consisted of hollow PCL colloidosomes stabilized by PVA. This system should have potential biomaterial applications due to the known biocompatibility of PCL and PVA.

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Heteroaggregation of dispersions has attracted much interest in the literature, especially when one or more components are stimulus responsive. Here, we study binary mixtures of microgels (MG) and starlike copolymers for the first time. The study investigated the use of complementary hydrogen bonding between carboxylic acid and amide groups to construct heteroaggregates and gels that contained temperature-and pH-responsive components. The pH-responsive MG contained methacrylic-acid and had an apparent pK a of 8.2. Two new star-like copolymers were introduced which comprised a cationic backbone with poly(N-isopropylacrylamide) side-chains. They are abbreviated as M1-PNP. A combination of complementary hydrogen bonding and hydrophobic interactions was shown to cause formation of heteroaggregates for mixed MG/M1-PNP dispersions at room temperature and at pH values less than the MG pK a . MG/M1-PNP heteroaggregate formation occurred over a wide pH-range and also in the presence of 0.2 M NaNO 3 . The heteroaggregates exhibited temperature-dependent hydrodynamic diameters and zeta potentials. Concentrated MG/M1-PNP dispersions formed selfsupporting hybrid gels at 45 C and gel formation also occurred over a wide pH range. The gels contained 80% MG with respect to total polymer content and were remarkably ductile. They had yield strains greater than or equal to 290%. There was evidence that the elasticity and ductility of the hybrid gels were controlled by the MG and M1-PNP components, respectively. The new M1-PNP star-like copolymers introduced here had superior temperature-triggered gel-formation properties compared to related copolymers and should be a versatile system for conferring temperature-responsive gelation properties to polymer colloids containing carboxylic acid groups.