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We present a study of the random scission process of polymers, in which numerical simulations are com- bined with experimental investigations into the acid hydrolysis ofthepolysaccharidehyaluronan(HA),inparticularatpH1.1and 50 � C. As input for the simulations, an initial molecular weight distribution (MD(0)) and the hydrolysis rate constant (kh) are needed.The firstwasobtainedusingagarosegelelectrophoresis followed by densitometric analyses, by which we determined the evolution of the full molar-mass distribution during hydro- lysis. The rate constant was experimentally obtained by two independent techniques. Kinetic plots were obtained from both the number- and the weight-average molar mass (Mn and Mw, respectively), converted to degrees of polymerization (Nn and Nw, respectively),andfromthese,khvaluesforHAhydrolysiswerederived.Forconfirmation,khwasalsodeterminedfromtheevolution oftheconcentrationofreducingchainends.Experimentallydeterminedkhvalueswereusedasinputforthemodel,andtheevolution of MD during hydrolysis was simulated for various hypothetical MD(0) functions as well as for an experimentally determined MD(0) curve.Agreementbetweenexperimentalandsimulatedresultsdemonstratedconsistencyofthemodelandindicatesthatacidhydrolysisof hyaluronan can indeed be considered a random scission process. We show that for cases where the initial molar mass distribution is notoftheKuhn-type—whichisoftenthecase—thevalueforthekhdeterminedfromtheevolutionofMnismoreaccuratethanthat obtained from Mw.

The formation of soluble reversible coordination polymers with Zn2+ ions in aqueous solution was studied for two bifunctional ligands, differing in spacer length. Viscosity measurements were used to follow the formation of polymers as a function of the ratio between metal ions and ligands, the total ligand concentration, and the temperature. All the experimental findings could be reproduced and interpreted with a theoretical model that accounts for the formation of chains and rings. At low concentrations and at a 1:1 metal-to-ligand ratio, a large fraction of the ligand monomers are incorporated in small rings, with a small contribution to the viscosity. Rings are less important at higher concentrations or if one of the two components is in excess. The fraction of monomers in chains and rings could be estimated from 1H NMR measurements, which were in good agreement with the model predictions. With increasing temperature, the fraction of monomers in rings decreases. As a result, the reduced viscosity increases with increasing temperature

The photopolymerization of spin-coated films of diacetylene derivatives containing phthalimido or naphthaldiimido moieties has been studied by monitoring the increase in the optical absorption in the visible region on irradiation at 308 nm. The phthalimido derivatives form blue polymers with absorption maxima at ca. 630 nm, corresponding to a highly conjugated, close to planar polydiacetylene (PDA) backbone configuration. The naphthaldiimido derivative yields a red polymer with an absorption maximum at 535 nm, indicating a backbone structure with a substantially reduced degree of -bond conjugation. The initial, "low-dose" quantum yields for monomer conversion, based on the total number of photons absorbed at 308 nm, range from 2 to 20. Monomer conversions up to ca. 50re found. The polymerized films are found to be photoconductive using the time-resolved microwave conductivity technique (TRMC). Mobile charge carriers are suggested to be formed via the triplet state of the arylimido moieties which undergoes long-distance charge transfer to polydiacetylene chains to form the arylimido radical anion and the mobile PDA radical cation or "hole". A maximum value of 1.4 x 10-2 cm2/(V s) for the product of the quantum yield for charge carrier formation and the hole mobility is found. The photoconductivity of the "blue" polymer is approximately an order of magnitude larger than for the "red" variety. This is attributed to a higher mobility of PDA holes in the former compound, resulting from the higher degree of backbone conjugation. The lifetime of the mobile carriers extends well into the microsecond region, which is considerably longer than previously found on direct ionization of PDA chains.

Side-chain liquid crystalline polyelectrolytes containing terminal (cyanobiphenylyl)oxy moieties were obtained through hydrolysis of the corresponding poly(maleic anhydride-co-alkyl vinyl ether)s with spacer lengths of 6-12 methylene groups. All polymers display a liquid crystalline phase. The transition temperatures are lower for the more rigid poly(maleic anhydride-co-alkyl vinyl ether)s. The enthalpy gain associated with the phase transition decreases with increasing rigidity of the polymeric backbone and with decreasing spacer lengths. In aqueous solution all polyelectrolytes have two distinct apparent pK a values, 3.3 and 6.5, indicative for strong nearest neighbor interactions within a maleic acid moiety. At neutral pH a blue shift of the absorbance maximum is observed which increases with increasing spacer length. Above pH 8 the blue shift decreases, indicating a conformational transition of the polyelectrolytes from more compact microdomains to a more extended chain conformation.