Date of Award
Doctor of Philosophy (PhD)
Professor J.E. Guillet
The main objective of this thesis was to compare and contrast the behaviour of poly(N-isopropylacrylamide) (poly(NIPAM)) and its copolymers in organic solvents with their behaviour in water. Three fields of investigation were chosen: solution properties, photochemistry, and photophysics.
The experimental observations were based on a very careful examination of the reliability of the techniques of osmometry and viscosity. These techniques were used to determine the solution properties and the quantum yields of chain scission of copolymers of NIPAM with methyl vinyl ketone and methyl isopropenyl ketone. The possibility of determining the coefficients K and a in Mark-Houwink equation ([ƞ] = K Mª, in which [ƞ] is the intrinsic viscosity and M is the molecular weight of a polymer) for flexible polymers by a one-point technique, i.e., the determination of the intrinsic viscosity of one known molecular weight, was investigated using polystyrene and poly-(methyl methacrylate). The technique was applied to the studies of poly(NIPAM) in chloroform. A correlation between the Mark-Houwink coefficients K and a for rigid polymers was used for assessing the plausibility of the Mark-Houwink coefficients of some rigid carbazole containing methacrylate polymers.
The structure and sequence distribution of the different copolymers of NIPAM were also determined from the reactivity ratios. This latter study was necessary in order to determine the suitability of the copolymers for the photochemical and photophysical studies. The first studies were done in solutions and in solid films on the ketone copolymers and the second ones involved both steady state and transient fluorescent studies on copolymers of NIPAM with 1-naphthylmethyl methacrylate and 1-naphthyl methacrylate.
The studies on solution properties gave evidence of chain aggregation of the poly(NIPAM) in water. Furthermore, the stiffness parameter for poly(NIPAM) was found to be much larger than the ones of polystyrene and poly(methyl methacrylate). This stiffness increase was partially attributed to hydrogen bonding between water and the NIPAM chain.
The technique of viscosity was found to be reliable in the determination of scission numbers and solution properties if ultraviolet degradation was used as a way to obtain polymer fractions of known dispersity. This reliability was attributed to the facts that (1) chain scissions were obtained from the relative variation of molecule weight with the time of irradiation, (2) K and a are interdependent, and (3) the correction for heterogeneity was small and the activity of the degraded sample solutions, which were used for the solution properties determination, was constant.
The photochemistry of the ketone-NIPAM copolymers revealed an increase in quantum yield of chain scission (ɸcs) in water compared to dioxane and no variation of ɸcs in water with copolymer composition. The higher ɸcs in water was attributed to stabilization by water of an intermediate in the scission mechanism. This effect is in accord with the effects of polarity and hydrogen bonding in small molecule ketones. Other possibilities are discussed.
In films, the same copolymers showed a decrease of ɸcs as compared to the solution system. This was attributed to the restriction of chain mobility as the work was done below the glass transition temperature. Nevertheless, at this temperature, the quantum yield of carbonyl loss in films was still very important.
Different models for interpretation of excimer kinetics in copolymers were applied without success to a series of poly(NIPAM-1-NMA) copolymers in dichloromethane.
The photophysics of the naphthalene containing NIPAM copolymers showed that excimer formation in copolymers and their decay parameters were highly dependent on the solvent used for the experiment. A simplified kinetic mechanism was proposed in order to explain this solvent dependence. The decay parameters of the naphthalene copolymers were determined under different experimental conditions and for samples of different molecular weights and different contents of chromophores. There was concentration dependence of the parameters in water. This behaviour suggests intermolecular effects in water even at low chromophore concentration.
For the first time, it was systematically shown that photochemical and photophysical studies in water on chromophores not soluble in this medium were possible if these chromophores were attached to a water-soluble polymer.
Breton, Marcel Philippe, "Solution Properties Photochemistry and Photophysics of Poly(N-Isopropylacrylamide) and Its Copolymers" (1980). Open Access Dissertations and Theses. Paper 2029.