Photoinitiated Thermoresponsive Aqueous Dispersion Polymerization-Induced Self-Assembly

Polymerization-Induced Self-Assembly(PISA)is a new method for efficiently and rapidly synthesis block copolymer nanoparticles with complex structure,which has good industrial prospects due to the characteristics of polymerization and assembly proceed simultaneously and scalable synthesis.Certain specific nanoparticles prepared by PISA have stimulus-responsive behavior,and the thermoresponse is the most common.PISA for producing nanoparticles which include thermoresponsive block is named polymerization-induced thermal self-assembly(PITSA)by Sumerlin and coworkers.PITSA has LCST limit and need post-polymerization cross-linking to stabilize the shape.Poly(diacetone acrylamide)(PDAAM)is hydrophobic and not thermoresponsive,but existing literatures show that the PDAAM-based nanoparticles show morphology transition with temperature changing.Thus,we report thermally insensitive hydrophobic block-based photoinitiated thermoresponsive aqueous dispersion polymerization-induced self-sssembly which is different from PITSA.Firstly,we synthesis the PHPMA38-b-PDAAMn nanoparticles via photoinitiated RAFT aqueous dispersion polymerization-induced self-sssembly that is Photo-PISA at 25?.The core-forming and the stabilizer blocks dehydrate on the n value increasing above the low critical dissolution chain length(LCSCL)and the nanoparticles only form lamellae due to the higher interfacial tension and the lower curvature.The lamellae cannot evolve to higher order vesicles structure due to the frozen chain.We discuss the reaction temperature dependence of the Photo-PISA.The PHPMA30-b-PDAAMn nanoparticles synthesised at 60?.Nanoparticles show a morphology transtion consistent with the traditional PISA.The increase of the reaction temperature improves the mobility of the polymer chains,reduces the interfacial tension and increases the curvature.Assemblies form spheres,and then occur the evolution of spheres-worms-lamellae-vesicles.Increasing temperature is beneficial for lamellae to vesicles transtion,and the assemblies are thermoresponsive.Unlike PITSA,this thermoresponsive Photo-PISA has no LCST limit,and not need cross-linking.Then the thermoresponsive behavior is further explored.The PHPMA30-b-PDAAM450 nanoparticles synthesized at different temperatures are the clusters of spheres(25?),tubes/vesicles(35?,45?)and thick-walled vesicles(60?),indicating that assemblies are themoresponsive.Based on the above studies,the effect of solid content is explored.In the same temperature range,reducing solid content from 20%w/w to 15%w/w,vesicles at 45? are more uniform smaller,and regular,indicating that reducing the solid content to prevent the collision of nanoparticles can control the shape.Next the space steric effect of the stablizer is studied.We synthesis PHPMA38-b-PDAAM560 nanoparticles at the same temperature range and solid content with maintaining the f value,vesicles at 450C are smaller than PHPMA30-b-PDAAM450.Increase in temperature yields heterogeneous and larger vesicles.All these indicate that the length of the stablizer can effect the shape of nanoparticles,the shape and size uniformity are indeed temperature-tunable.Last,the in-situ thermoresponsive morphology transtision is investigated.We synthesis PHPMA38-b-PDAAM90 and PHPMA38-b-PDAAM100 vesicles at 70 0C.The reversible in-situ vesicles-lamellae and vesicles-worms morphology transitions occur during temperature changing.In summary,we proposed the concept of LCSCL,the lamellae evolution at 25?,the morphology transition,and the reversible transition of morphology.It is different from the existing PITSA in the following 3 aspects:(1)There is no LCST limit and not need cross-linking.(2)Higher temperature can improve the chain mobility and the formation of spheres,which then evolve to worms-lamellae-vesicles.Moreover,the temperature and the solid content and stablizer length all can effect the shape and size uniformity of the assemblies.(3)Change temperature can cause the reversible in-situ morphology transitions of vesicles-lamellae and vesicles-worms.Based on these studies,we successfully establish a new thermoresponsive aqueous dispersion Photo-PIS A based on hydrophobic block.