Effects Of Cyclodextrins And Other Additives On Cloud Points Of Several Neutral Thermosensitive Homopolymers

In the past four decades, many thermosensitive polymers were synthesized.Some have lower critical solution temperature, and some have upper critical solutiontemperature. It was found that many factors can affect the cloud point of athermosensitive polymer, but the effect of macrocyclic molecules on the cloud pointof a thermosensitive homopolymer was rarely reported. Recently, Ritter’s group andour group have reported the effect of cyclodextrins (CDs) on the cloud point of thethermosensitive polymers bearing a tertiary amine group at each repeating unit. Forexample, the addition of randomly-methylated-cyclodextrin (RM--CD) increasesthe cloud point of a poly(2-(dimethylamino)ethyl methacrylate)(PDMAEMA)solution. However, because the tertiary amino groups of PDMAEMA can beprotonated at neutral pH, we have to carry out related experiments in buffersolutions with pH9.18. In this dissertation, we chose several neutral thermosensitivehomopolymers, and successfully synthesized several neutral thermosensitivehomopolymers with chiral groups. The effect of CDs on the cloud points of thesethermosensitive homopolymers was systematically investigated. In addition, theeffects of pH and CDs on the cloud point of PiPAAm solution containing anamphoteric compound, para-aminobenzoic acid, were investigated. In Chapter2, we studied the effects of differently sized CDs on the cloud pointof four neutral thermosensitive polymers with similar structures. Fivethermosensitive polymers were synthesized. The effects of differently sized CDs onpoly(N-propylmethylacrylamide)(PnPMAm) were investigated.-CD increased thecloud point of a PnPMAm solution; by contrast,-CD or-CD did not affect thecloud point of the PnPMAm solution. The cloud point of the PnPMAm solutionincreased gradually with an increase in the concentration of-CD. Two-dimensionalNMR data shown that-CD and side groups of PnPMAm formed inclusioncomplexes. Then, we compared the effect of the differently sized CDs on the cloudpoints of four polymers with similar structures. As for PiPAAm, neither-CD nor-CD affected its cloud point. On the basis of the effects of the differently sized CDson the cloud points of five polymers solutions and the correspondingtwo-dimensional NMR data, we inferred that steric hindrance by the main chain ofPiPAAm might be responsible for the bulky CD being unable to form a complexwith the short isopropyl group.In Chapter3, we studied the effects of CDs on the cloud points of three pairs ofchiral thermosensitive homopolymers solutions. Based on the structures of someknown thermosensitive polymer, we synthesized three pairs of chiral polymerspoly(N-((L)-1-(methoxymethyl)propyl)methacrylamide)(P(L-MMPMA)) andpoly(N-((D)-1-(methoxymethyl)propyl)methacrylamide)(P(D-MMPMA));poly(N-((R)-2-ethoxypropyl)methacrylamide)(P(R)EPMA) andpoly(N-((S)-2-ethoxypropyl)methacrylamide)(P(S)EPMA);poly(N-(R)-tetrahydrofurfurylmethacrylamide)(P(R)THFMA) andpoly(N-(S)-tetrahydrofurfurylmethacrylamide)(P(S)THFMA). We characterizedtheir structures, molecular weights, Tg, and specific rotation with NMR, GPC, DSC,and polarimeter, respectively. Through measuring variation of transmittances of thechiral polymer solutions with an increase in temperature, it was found that thesolutions of these chiral polymers all had cloud points. Thus, synthesizing isomers of a known thermosensitive polymer is a new way of obtaining new thermosensitivepolymers. We studied the effects of differently sized CDs on the cloud points of thechiral thermosensitive polymers. The research results are described in the followingsentences.(1) None of three CDs affected the cloud points of a P(L-MMPMA)solution and a P(D-MMPMA) solution;(2)-CD increased the cloud points of aP(R)EPMA solution and a P(S)EPMA solution, and neither RM--CD or-CDaffected the cloud points of the solutions;(3)-CD, RM--CD and-CD allincreased cloud points of a P(R)THFMA solution and a P(S)THFMA solution, butthe effect of-CD on the cloud point was greater than those of RM--CD and-CD.(4) The effects of CDs on cloud points of solutions of each pair of polymerenantiomers were approximately equal. These chiral thermosensitive polymersmight be used at cloud-point extraction of chiral compounds or analog of proteins.In Chapter4, we studied the multiple responses of the mixed solution ofPiPAAm and an amphoteric compound, para-aminobenzoic acid (PABA). WhenPABA was added into PiPAAm solution, the cloud points decreased with theincrease of the concentration of PABA. For the solution of PABA/PiPAAm=3:1, thecloud point of the solution firstly decreased, then reached a plateau, and thenincreased, finally reached another plateau with increase of pH value. It was foundthat the un-ionized form of PABA decreased the cloud points of PiPAAm solutions;by contrast, the cationic form and anionic form of PABA had little effect on thecloud points. In contrast,-amino acids, another kind of amphoteric compound, didnot affect the cloud points of PiPAAm solutions. This was because-amino acidsexisted in the zwitterionic form at pH between pKa1and pKa2. On basis of the effectof isobutyric acid on the cloud points of PiPAAm solutions, we inferred that thehydrogen bonds between un-ionized form of PABA and PiPAAm played animportant role in the decrease of the cloud points of PiPAAm solutions.-CD couldinclude the un-ionized form of PABA, so that the cloud point increased when-CDwas added into the mixed solutions of PABA and PiPAAm. As for a mixed solution of-CD, PiPAAm and PABA, the cloud point of the solution did not change withthe increase of the pH value.