The controlled radical polymerization (CRP) technique reversible addition−fragmentation chain transfer (RAFT) has potential for preparing functional (co)polymers directly in an aqueous environment. Hydrolysis and aminolysis can eliminate the active end groups necessary for maintaining “livingness” in water. These reactions have not previously been evaluated with respect to their effect on aqueous RAFT polymerizations. Herein we determine rate constants of hydrolysis and aminolysis for representative water-soluble chain transfer agents (CTAs) cyanopentanoic acid dithiobenzoate (CTP) and the macro-chain-transfer agents (macro-CTAs) of poly(sodium 2-acrylamido-2-methylpropanesulfonate) (AMPSX) and poly(acrylamide) (AMX) at selected pH values. Rates of hydrolysis and aminolysis both increase with increasing pH and decrease with increasing molecular weight of the dithioester. On the basis of these rate constants, mathematical relationships have been developed to predict the number of living chain ends and the molecular weight with competitive hydrolysis. Utilizing this approach, predictions of molecular weight at specific conversions are in agreement with experimental values determined by SEC/MALLS.

We discuss the synthesis and characterization of polyacrylamide (PAM) homopolymers with carefully controlled molecular weights (MWs). PAM was synthesized via free-radical solution polymerization under conditions that yield highly linear polymer with minimal levels of hydrolysis. The MW of the PAM homopolymers was controlled by the addition of sodium formate (NaOOCH) to the polymerization medium as a conventional chain-transfer agent. MWs and polydispersity indices (PDIs) were determined via size exclusion chromatography/multi-angle laser light scattering analysis; for polymerizations carried out to high conversion, PAM MWs ranged from 0.23 to 6.19 ϫ 10 6 g/mol, with most samples having PDI Ϸ2.0. Zero-shear intrinsic viscosities of the polymers were determined via low-shear viscometry in 0.514 M NaCl at 25°C. Data derived from the polymer characterization were used to determine the chaintransfer constant to NaOOCH under the given polymerization conditions and to calculate Mark-Houwink-Sakurada K and a values for PAM in 0.514 M NaCl at 25°C.

The relationships between drag reduction performance and polymer parameters including chemical structure, molecular weight, hydrodynamic volume, associations, and solvent nature were examined using synthetic water-soluble copolymers. Copolymer models were tailored to be systematically responsive to changes in electrolyte addition and included polyelectrolytes, polyampholytes, hydrophobically modified polymers, and uncharged, hydrophilic polymers. Commercial poly(ethy1ene oxide) (PEO) and copolymers of acrylamide with the comonomers sodium 3-(acrylamido)-3-methylbutanoate (NaAMB), sodium 2-(acrylamido)-2-methylpropanesulfonate (NaAMPS), [2-(acrylamido)-2-methylpropyl]dimethylammonium chloride (AMPDAC), and diacetone acrylamide (DAAM) synthesized in our laboratories were tested for drag reduction effectiveness using a rotating disk and a tube flow apparatus. Hydrodynamic volume as determined by viscometry and light scattering was monitored in deionized water and 0.514 M NaCl for particular compositions and molecular weights. Drag reduction performance was greatly affected by the nature of polymer/polymer and polymer/solvent interactions, generally increasing with hydrodynamic volume. Enhanced drag reduction behavior observed for the associating DAAM copolymers is proposed to be due to changes in water structuring in turbulent flow. IntroductionThe reduction of drag in turbulent flow produced by addition of small concentrations of high molecular weight polymers has been studied for over 40 years.' Studies of polymers of varying structures have shown that drag reduc-

Experimental solution intrinsic viscosity responses to temperature and polymer molecular weight variations were used to test the modeling capability of a simplified intrinsic viscosity equation. The multiple linear equation contains three parameters that are related to the thermodynamic properties of a polymer solution. Simple linear regression was used to produce an intrinsic viscosity equation containing unique fitted parameters for each of three solutions. These parameters describe the polymer coil size at unperturbed conditions and the polymer coil expansion capabilities of the solvent as a function of fluid temperature and molecular weight.

A comparative study of pH-responsive polyzwitterions (PZs) with polyampholyte or polybetaine architectures was conducted with well-defined model polymer systems. Low-charge-density PZs, including ampholytic terpolymers composed of acrylamide (AM), sodium 3-acrylamido-3-methylbutanoate, and (3-acrylamidopropyl-)trimethylammonium chloride and carboxybetaine copolymers composed of AM and 3-(3-acrylamidopropyldimethylammonio)propionate, were prepared via free-radical polymerization in 0.5M NaCl to yield ter-and copolymers with random termonomer and comonomer distributions. Sodium formate was used as a chain-transfer agent during the polymerizations to eliminate the effects of the monomer feed composition on the degree of polymerization (DP) and to suppress gel effects and broadening of the molecular weight distributions. The polymer compositions were determined via 13 C-NMR spectroscopy, and the residual counterion content was determined via elemental analysis for Na ϩ and Cl Ϫ . The molecular weights (MWs) and polydispersity indices (PDIs) were determined via size exclusion chromatography/multi-angle laser light scattering (SEC-MALLS); the polymer MWs ranged from 1.4 to 1.5 ϫ 10 6 g/mol, corresponding to DPs of 1.6 -1.9 ϫ 10 4 repeat units, with all the polymers exhibiting PDIs less than or equal to 2.1. The intrinsic viscosities determined from SEC-MALLS data and the Flory-Fox relationship agreed with the intrinsic viscosities determined via low-shear dilute-solution viscometry. Data from the SEC-MALLS analysis were used to analyze the radius of gyration/molecular weight (R g -M) relationships and the Mark-Houwink-Sakurada intrinsic viscosity/ molecular weight ([]-M) relationships for the PZs. The R g -M and []-M relationships and viscometric data revealed that under size exclusion chromatography conditions, the poly[acrylamide-co-3-(3-acrylamidopropyldimethylammonio)propionate] betaine copolymers had more open, random-coil conformations and greater polymer-solvent interactions than the ampholytic poly[acrylamide-co-sodium 3-acrylamido-3-methylbutanoate-co-(3-acrylamidopropyl)-trimethylammonium chloride] terpolymers. The pH-and salt-responsive dilute-solution viscosity behavior of the PZs was examined to assess the effects of the polymer structure and composition on the solution properties. The polyampholyte terpolymers had greater solution viscosities and more pronounced stimuli-responsiveness than the polybetaine copolymers because of their stronger intramolecular interactions and increased chain stiffness.