Synthesis And Properties Of Thermo-responsive Copolymers Based On N-isopropylacrylamide

In this thesis,thermo-responsive polymers,including P(NIPAM-co-NEAM)chemical crosslinked hydrogels and P(NIPAM-co-HOPOMA)linear copolymer,were synthesized and their properties have been investigated.The main achievements in this thesis are shown in the follow.1.Hydrogels with different monomer ratio of NIPAM and N-ethylacrylamide(NEAM)have been synthesized in solvent mixture of methanol and water with solvent composition fixed at methanol:water = 1:1(v:v).Elemental analysis,SEM,AFM and rheometer were applied to analyse the compositions,structures,swelling/deswelling properties and rheological properties.It indicates that the structures of those hydrogels changed from porous hydrogel connected by microgels to microgel connected networks with the increase of NIPAM content due to the different cononsolvency behaviors of PNIPAM and PNEAM in methanol-water mixture with same solvent composition,resulted in the improvement of porousity and hydrophobicity in hydrogels,consequently,properties such as swelling/deswelling properties,cononsolvency behavior and mechanical properties changed.The relationship between the monomer composition,structure and properties were demonstrated in detail as below.(1)Only one phase transition temperature existed in the hydrogels,and it decreases with the increase of NIPAM content;(2)With the increase of NIPAM content,swelling ratio of hydrogels firstly does not change too much when NIPAM content is less than 30%,and then increased rapidly from 30% to 80%,but decreased dramatically from 80% to 100% due to the competitive effect of porousity and hydrophobicity;(3)The deswelling rate of hydrogels increased with the increase of NIPAM content as the porousity increased;(4)From the atomic force microscopy(AFM)results,Young's modulus decreased with the increase of NIPAM content,but the surface roughness increased with the increase of NIPAM content;(5)Rheological properties show thatwith the increase of NIPAM content,the compression stress at break behaves as Gaussian curve,while the compression strain at break behaves as Gaussian curve before but increased again in the last.2.Hydrogels with fixed monomer ratio of NIPAM and NEAM as monomer ratio of NIPAM:NEAM=5:5 in mole but the solvent composition varied have been prepared.Elemental analysis,SEM,AFM and rheometer were used to characterize the copolymer hydrogels.It indicates that the structures of those hydrogels changed with the increase of methanol mole fraction x_m in the methanol-water mixture during synthesis due to the different phase separation of monomer fixed copolymer hydrogels in different solvent composition resulted from cononsolvency behavior,resulted in improvement of porousity and lower chain density in hydrogels,in consequence,different properties,such as swelling/deswelling properties,cononsolvency behavior and mechanical properties.The relationship between the solvent composition,structure and properties were demonstrated in detail as follow.(1)There is no influence of x_m on phase separation temperature of these hydrogels;(2)With the increase of x_m,swelling ratio of hydrogels firstly increased rapidly from 0 to 0.21,but then only varied in a small range while x_m keep increasing due to the change of porousity and chain density;(3)The deswelling rate of hydrogels changed in accordance with porousity,firstly increased but then decreased with the increase of x_m;(4)From the atomic force microscopy(AFM)results,Young's modulus decreased with the increase of x_m due to the competelive effects of porousity and chain density;(5)Rheological properties show that with the increase of x_m,the compression stress at 65% of compression strain at break,storage modulus and compression modulus all behave in line with Young's modulus from AFM.3.The monomer,named as HOPOMA,which contains the functional group of 3,4-HOPO,has been synthesized from maltol,and then copolymerized with N-isopropylacrylamide(NIPAM),which are thermo-responsive.Based on results(such as conversion,molecular weight,and molecular weight distribution)from different polymerization methods of reverse addition-fragmentation chain transfer(RAFT)polymerization and conventional free radical polymerization,conclusion can be made that RAFT polymerization is more suitable than the conventional free radical polymerization for the polymerization of NIPAM-HOPOMAsystem.1H-NMR,TGA,DSC and rheological results show that with the introduction of HOPOMA,the copolymer becomes more unstable than the PNIPAM homopolymer,and the glass transition temperature(Tg)increased compared to PNIPAM homopolymer,and interestingly,the copolymer solution behaves two LCST while HOPOMA is not thermo-responsive.