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Pinprayoon O.,University of Manchester | Groves R.,Synthomer Ltd. | Lovell P.A.,University of Manchester | Tungchaiwattana S.,University of Manchester | Saunders B.R.,University of Manchester
Soft Matter | Year: 2011

Although conventional ionomers have been studied for more than 40 years, reports of ionomers prepared using aqueous core-shell nanoparticle dispersions are lacking. In this study we examine the structure and properties of new soft core-shell elastomeric nanoparticles and ionomer films. The nanoparticles consist of a soft poly(Bd) (Bd is 1,3-butadiene) core and a poly(Bd-co-MAA) shell (MAA is methacrylic acid). The nanoparticles were prepared by sequential emulsion polymerisation and were characterised using photon correlation spectroscopy, TEM, PSDA (particle size distribution analysis) and potentiometric titration. Robust ionomer films were formed by casting mixed core-shell nanoparticle/ZnO dispersions at room temperature. The ZnO particles provided aqueous Zn2+ which neutralised the carboxylate groups and imparted ionic crosslinking. The mechanical properties of the films were investigated using DMTA (dynamic mechanical thermal analysis) and stress-strain measurements. Neutralisation substantially increased the film modulus values. This was ascribed to the formation of a poly(Bd-co-MAA)/Zn2+-rich layer that moved inwards from the periphery of the nanoparticles as the degree of neutralisation increased. In contrast to conventional ionomers, the mechanical properties of the present films depend on ionic crosslinking within a honeycomb-type continuous phase that percolates the film. The storage and tensile moduli for the films increased linearly with neutralisation. The films studied here are a new class of nanostructured ionomers and the results obtained should be generally applicable to other films comprising soft-core-shell nanoparticles containing surface carboxylate groups. © 2011 The Royal Society of Chemistry. Source

Tungchaiwattana S.,University of Manchester | Liu R.,University of Manchester | Liu R.,Zhengzhou University of Light Industry | Halacheva S.,University of Manchester | And 3 more authors.
Soft Matter | Year: 2013

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 star-like 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 pKa 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 pKa. MG/M1-PNP heteroaggregate formation occurred over a wide pH-range and also in the presence of 0.2 M NaNO3. The heteroaggregates exhibited temperature-dependent hydrodynamic diameters and zeta potentials. Concentrated MG/M1-PNP dispersions formed self-supporting 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. © 2013 The Royal Society of Chemistry. Source

Tungchaiwattana S.,University of Manchester | Musa M.S.,University of Manchester | Yan J.,University of Manchester | Lovell P.A.,University of Manchester | And 2 more authors.
Soft Matter | Year: 2014

Ionomers are polymers which contain ionic groups that are covalently bound to the main chain. The presence of a small percentage of ionic groups strongly affects the polymer's mechanical properties. Here, we examine a new family of nanostructured ionomer films prepared from core-shell polymer nanoparticles containing acrylonitrile (AN), 1,3-butadiene (Bd) and methacrylic acid (MAA). Three new AN-containing dispersions were investigated in this study. The core-shell nanoparticles contained a PBd core. The shells contained copolymerised Bd, AN and MAA, i.e., PBd-AN-MAA. Three types of crosslinking were present in these films: covalent crosslinks (from Bd); strong physical crosslinks (involving ionic bonding of RCOO- and Zn2+) and weaker physical crosslinks (from AN). We examined and compared the roles of AN and ionic crosslinking (from added Zn2+) on the structure and mechanical properties of the films. The FTIR spectroscopy data showed evidence for RCOOH-nitrile hydrogen bonding with tetrahedral geometry. DMTA studies showed that AN copolymerised within the PBd-AN-MAA phase uniformly. Tensile stress-strain data showed that inclusion of AN increased elasticity and toughness. Analysis showed that about 33 AN groups were required to provide an elastically-effective chain. However, only 1.5 to 2 ionically bonded RCOO - groups were required to generate an elastically-effective chain. By contrast to ionic bonding, AN inclusion increased the modulus without compromising ductility. Our results show that AN is an attractive, versatile, monomer for increasing the toughness of nanostructured ionomers and this should also be the case for other nanostructured polymer elastomers. This journal is © the Partner Organisations 2014. Source

Tungchaiwattana S.,University of Manchester | Groves R.,Synthomer Ltd. | Lovell P.A.,University of Manchester | Pinprayoon O.,University of Manchester | Saunders B.R.,University of Manchester
Journal of Materials Chemistry | Year: 2012

Ionomers are polymers containing a low mole fraction of ionic groups bound to the polymer backbone. These ionic groups produce major changes in their structure and mechanical properties. Recently, we introduced a new family of crosslinked poly(Bd)/poly(Bd-co-MAA) core shell nanoparticles (1,3-butadiene and methacrylic acid) that could be ionically crosslinked and cast as nanostructured ionomer films from aqueous dispersions [Pinprayoon et al., Soft Matter, 2011, 7, 247]. The MAA units in the core-shell particles were neutralised by Zn 2+. Here, we explore the structure-property relationships for these new architecturally controlled nanocomposites by investigating 6 new poly(Bd)/poly(Bd-co-MAA) dispersions and films. In this study we varied the extent of covalent crosslinking in the core and the shell at constant ionic crosslinking for the first time. We used dynamic mechanical thermal analysis to establish a general phase map for the new nanostructured ionomers. Stress-strain data show that our nanostructured films have well controlled, and adjustable, modulus and strain at break values. The data show that the core-shell nanoparticle geometry allows the often observed trade-off between elasticity and ductility to be tuned in a manner that is not possible for conventional ionomers. We show that the chain transfer agent (CTA) concentrations used during the preparation of the nanoparticle cores and shells can be used to independently tune the mechanical properties of the films. This is due to variation of the extents of covalent crosslinking. The results of this study should apply to other covalently crosslinked core-shell nanoparticles containing RCOOH groups in the particle shells. © The Royal Society of Chemistry 2012. Source

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