Study On Synthesis Of Stimuli-responsive Polymers-based Pesticide Carriers And Property Of Controlled Release

Technology of controlled-release for pesticide can reasonably regulate the release of active ingredients according to the requirements of prevention and control,thereby increasing the utilization of pesticides,extending the duration of persistence.It provides a feasible way to solve the conflict between increasing agricultural output and pesticide pollution.As a pivotal component for the pesticide controlled-release technology,drug carriers have attracted intense attention due to their wide applications.A series of release systems including inorganic carrier materials,natural polymer materials and synthesized polymer materials have been reported in the literatures.Inorganic carrier materials and natural polymer materials have limitation in controlling the release rates toward different pesticide active ingredients,while the synthesized polymer materials often require the pre-preparation of polymer micelles,which would increased the cost of the carrier.To solve these problems,two microsphere carriers,i.e.,SiO₂@PAM core-shell microspheres and P?DMOEM-co-AM?microspheres,were designed and synthesized via a simple distillation precipitation polymerization using acrylamide?AM?as monomers,pH-sensitive di-?methacryloyloxy ethoxy?methane?DMOEM?as cross-linking agent,respectively.Taking indole-3-acetic acid?IAA?as a pesticide model molecule,the controlled-release performance of the synthesized carriers were systematically studied and the main research contents are as follows.1.Synthesis and controlled release performance of crosslinked PAM microspheres.The P?DMOEM-co-AM?microspheres was synthesized by a distillation precipitation polymerization with acrylamide?AM?as monomer,azobisisobutyronitrile?AIBN?as initiator in the presence of a pH-responsive cross-linking agent?DMOEM?.The size of the polymer microspheres depends on the degree of crosslinking.The cross-linked microspheres with cross-linking agent content of 50 wt%shows a uniform diameter size of 1.5?m as confirmed by SEM.The P?DMOEM-co-AM?carrier has good loading capacity up to 424?g/mg.The drug-loaded P?DMOEM-co-AM?crosslinked microspheres released slowly in the EtOH/H₂O?v/v=1:5?solution at pH=5 and the release rate of IAA was 20%for 48 h.In a solution of EtOH/H₂O?v/v=1:5?at pH=3 and pH=2,the corresponding IAA release rates were 44%and 63%for 48 h,respectively.2.Synthesis and controlled release performance of SiO₂@PAM microspheres.SiO₂nanospheres with the diameter of about 200 nm confirmed by TEM were first synthesized by sol-gel method.Then double bonds were introduced into the surface of SiO₂ nanospheres to yield functionalized SiO₂-MPS nanospheres.The narrowly dispersed functional polymer SiO₂@PAM microspheres were subsequently prepared by the polymerization of acrylamide?AM?in the presence of a pH-responsive cross-linking agent?DMOEM?,from the surface of SiO₂-MPS template microspheres via a distillation precipitation polymerization.Narrowly dispersed SiO₂@PAM microspheres with different shell thicknesses in the range of 2²9 nm can be obtained by controlling the content of crosslinke.The degradation properties of SiO₂@PAM core-shell microspheres under acidic conditions were studied by dynamic light scattering?DLS?.The particle size of SiO₂@PAM core-shell microspheres decreased from1223 nm to 673 nm upon stirring them in pH=2 CH₃COOH/CH₃COONa buffer solution for48 h,indicating the significant degradation behavior.SiO₂@PAM microspheres with a crosslinker content of 40 wt%exhibit high loading capacity of about 596?g/mg.The drug-loaded SiO₂@PAM crosslinked microspheres released slowly in the EtOH/H₂O?v/v=1:5?solution at pH=5 and the release rate of IAA was 25%for 48 h.The corresponding IAA release rates were 39%and 74%,respectively,in a solution of EtOH/H₂O?v/v=1:5?at pH=3 and pH=2 for 48 h.The resultant pesticide carriers showed obvious pH-dependent controlled-release performance,and they have higher release rate in lower pH solution.They should be potential for the applications in the prevention and control of pests in agriculture.