Perspective Automatic continuous online monitoring of polymerization reactions (ACOMP)

Transcription

1 Polymer International Polym Int 57: (28) Perspective Automatic continuous online monitoring of polymerization reactions (ACOMP) Alina M Alb, Michael F Drenski and Wayne F Reed Physics Department, Tulane University, New Orleans, LA 7118, USA Abstract: A brief overview of the principles and associated instrumentation used to monitor polymerization reactions by automatic continuous online monitoring of polymerization reactions (ACOMP) is presented. ACOMP can be used as an analytical method in R&D, as a tool for reaction optimization at the bench and pilot plant level and, eventually, for feedback control of full-scale reactors. ACOMP measures in a model-independent fashion the evolution of average molar mass and intrinsic viscosity, monomer conversion kinetics and, in the case of copolymers, also the average composition drift and distribution. A summary of areas of ACOMP application is given, which include free radical and controlled radical homo- and copolymerization, polyelectrolyte synthesis, heterogeneous phase reactions, including emulsion polymerization, adaptation to batch and continuous reactors, and modifications of polymers. Finally, a brief sketch of two novel complementary methods is given: automatic continuous mixing (ACM) and simultaneous multiple sample light scattering (SMSLS). 27 Society of Chemical Industry Keywords: polymerization reaction monitoring; light scattering; polymerization kinetics; copolymerization; polyelectrolyte; living polymerization; emulsion polymerization INTRODUCTION Monitoring polymerization reactions is useful from several perspectives. At the fundamental level, information on monomer conversion kinetics and evolution of molar mass and other polymer properties can help in understanding the mechanisms involved in specific reactions, which can accelerate the process of new polymer discovery and development. At the bench and pilot plant level, reaction monitoring allows optimization of reactions in terms of reagents and reaction conditions. Monitoring can also lead to identification of any unusual events (e.g. microgelation due to phase separation or crosslinking) and allow corrective actions to be taken (e.g. addition of quenching or other reagents). Finally, when implemented with feedback control in full-scale industrial reactors, polymerization reaction monitoring is expected to yield consistently higher product quality, including on-command polymers of desired properties, and make the most efficient use of energy, non-renewable resources, petroleumbased products and plant and personnel time, while reducing the amount of greenhouse gas emissions per kilogram of product. When reached, these latter goals will have significant environmental, economic, and technological impact. A variety of methods in situ, online and atline are used for monitoring polymerization reactions, most of which focus on one aspect, such as monomer conversion. Widespread methods include infrared spectroscopy and Raman scattering. 1 5 In most cases, empirical models must be developed to correlate reagent concentrations with spectral features. Other monitoring techniques include calorimetry, rheology, turbidimetry, densitometry and electron spin resonance. Methods involving periodic withdrawals of discrete aliquots abound, including literal attempts to adapt SEC directly to polymerization monitoring. 6 The SEC approach has not enjoyed wide application in basic research or industrial reactor control, due chiefly to the inherent complexity, long delay times, sensitive instrumentation and expense of SEC itself. AUTOMATIC CONTINUOUS ONLINE MONITORING OF POLYMERIZATION REACTIONS (ACOMP) BACKGROUND What is ACOMP? ACOMP is a non-chromatographic method that relies on continuous extraction, dilution and conditioning of a small stream of reactor contents such that light scattering, viscometric, spectroscopic and other measurements made on the diluted stream are dominated by single macromolecular properties and not intermolecular interactions. Hence, measurements of conversion, composition, weight-average molar Correspondence to: Wayne F Reed, Physics Department, Tulane University, New Orleans, LA 7118, USA wreed@tulane.edu (Received 6 March 27; accepted 15 June 27) Published online 18 September 27; DOI: 1.12/pi Society of Chemical Industry. Polym Int /27/$3.

2 Perspective mass (M w ) and intrinsic viscosity [η] w, etc., are not dependent on empirical or inferential models. Furthermore, the detection portion of ACOMP provides a flexible platform to which virtually any desired detector can be added and its signals integrated into ACOMP s massive data gathering and analysis capabilities. ACOMP is a very broadly applicable method that has been already demonstrated to work effectively for many different types of reactions in different types of reactors. Some guiding principles of ACOMP The basic principles of ACOMP are the following. (1) The monitoring is always adapted to the chemistry. The chemistry is never interfered with or changed to suit the monitoring. (2) The quality of data obtained by each instrument is optimized through proper online sample conditioning. (3) Measurements are made at the most fundamental level possible (single scattering events, dilute regime viscosity and spectroscopy, etc.) and these are designed to obtain model-free primary quantities, such as conversion, composition, molar mass, intrinsic viscosity, etc. The use of empirical and inferential models and calibration schemes is thereby avoided. (4) Obtaining high-quality data with model-free primary quantities allows the richness of the ACOMP results to be used for building chemical, physical and mechanistic models to any degree of elaboration desired, and for potential control of reactions. Comparing ACOMP with in situ methods such as near-infrared (NIR) and Raman analyses While ACOMP gives the comonomer conversions, which NIR) and Raman techniques also do, ACOMP additionally monitors the evolution of M w and [η] w, average polymer properties of critical importance in the ultimate characterization and utilization of the polymers. A seeming advantage of Raman and NIR compared to ACOMP is that probes for the former can often be put inside the reactor, avoiding ACOMP s complex withdrawal, dilution and conditioning steps. The in situ probes also eliminate the delay times inherent to ACOMP, which are typically in the range 5 3 s. However, whether a probe is inserted into a reactor or a tube for withdrawal is inserted for ACOMP, access into the reactor is required in either case, and hence all techniques are invasive to this degree. Furthermore, probes inside reactors can easily foul and lead to erroneous data. Working at high concentrations in the reactor normally requires that empirical models and calibrations be used to interpret data, 7 and other phenomena can intervene (e.g. scattering effects of emulsions) that dominate the detector s response over the desired phenomenon (e.g. monomer conversion). In fact, calibration difficulties with Raman spectroscopy are well known, and whole articles are devoted to them. 8 In contrast, the ACOMP front end (extraction, dilution and conditioning, such as filtration, debubbling, phase inversion, etc.) is a flexible platform specifically designed to deal with the conversion of real, often dirty and non-ideal reactor contents into a highly conditioned, dilute and continuous sample stream on which absolute, modelindependent measurements can be made. ACOMP instrumentation: the front end This refers to the ensemble of pumps, mixing stages and conditioning elements that ultimately produce the diluted, conditioned stream, which continuously feeds the detection train. Extraction of liquid from the reactor typically ranges from.1 to.5 ml min 1, depending on the application. Many different approaches have been taken for the front end. One system uses two HPLC pumps, one for reactor extraction and the other for dilution, and a highpressure mixing chamber. This arrangement supplies a reliable, diluted, conditioned stream up to reactor viscosities of only about 3 cp. To deal with very high reactor viscosities, up to 1 6 cp, a two-stage mixing system was introduced, which consists of (1) a reactor extraction pump capable of withdrawing high-viscosity fluids, such as a gear pump; (2) a mixing stage at atmospheric pressure, which also allows any bubbles created by exothermicity or other processes in the reaction to be exhaled and excluded from the detector stream; and (3) a highpressure mixing stage which allows for further dilution after the low-pressure stage. This normally involves five pumps. ACOMP instrumentation: the back end or detector train There are no inherent limitations on which detectors can be used in ACOMP, and detector selection is made according to the needs of each monitoring situation. A standard configuration involves multi-angle light scattering (MALS), a differential refractive index (RI) detector, a UV-visible detector and a single-capillary viscometer. Infrared, fluorescence and conductivity detectors are other examples of instruments that can be incorporated. Typically, the concentration of the continuous, dilute, conditioned stream produced by the front end is in the range 1 4 to 1 2 gcm 3, i.e. corresponding to concentrations usually injected into SEC columns. The Tulane group developed a MALS instrument specifically to meet the demanding environment of ACOMP, and Brookhaven Instruments Corporation (BIC, Holtsville, NY) took a license from Tulane for this design and currently produces the BI- MwA (molecular weight analyzer) for ACOMP, SEC and batch applications ( MwAmw.html). Figure 1 shows a BI-MwA unit. RI detectors from Shimadzu Corp. ( shimadzu.com/products/lab/chromato/spd1avp. html) and from Waters Corp. have been typically used by the Tulane group. RI instruments from BIC Polym Int 57: (28) 391 DOI: 1.12/pi

3 AM Alb, MF Drenski, WF Reed Figure 1. Brookhaven Instruments BI-MwA, used in ACOMP, also for ACM, and standard multi-detector SEC. and Polymer Laboratories have also been successfully implemented. The Shimadzu dual wavelength UV-visible spectrometer (SPD 1AVvp model) has been a true workhorse for ACOMP. The Shimadzu PDA-2, a temperature-controlled photodiode array spectrometer, has recently been introduced into the ACOMP train, producing significantly higher performance, especially for copolymerization monitoring. A very simple custom-built single-capillary viscometer design has been adopted for use with ACOMP. It should be noted that, although ACOMP produces a continuously measurable sample stream, this stream can also be measured intermittently rather than continuously. Hence, since the sample stream concentrations are in the ideal range of SEC, it is possible to connect an automatic diverter valve and injector loop to the ACOMP sample stream and make periodic, automatic injections into SEC columns interposed between the front-end outlet stream and the detector train. This might be desirable in certain specialty applications. It is also possible to connect the diverter valve, columns and separate detectors, after the primary ACOMP detector train, and hence have simultaneous data from the continuous detectors and the periodic SEC results. extraction rate is provided via interface to a state-ofthe-art microfluidic controller (Bronkhorst, Inc.). The PMC includes an advanced design low-pressure mixing chamber. Several pressure and temperature sensors provide automatic feedback to the system to monitor its own performance, and an automatic clean cycle will make operation simpler and increase throughput. The software platform provides complete instrument control and analysis functions, including authentication, appropriate levels of security, over-the-net operating and monitoring capabilities and databasing for advanced storage and data mining. The National Instruments interface is open-ended and allows PL to easily adapt new instruments and sensors into the platform. The stock configuration is compatible with a variety of PL instruments (RI and viscometer), the Brookhaven BI-MwA MALS unit and Shimadzu UVvisible detectors. Typical ACOMP raw data Figure 3 shows data for a free radical terpolymerization of methyl methacrylate (MMA), butyl acrylate (BA) and styrene. The diluted monomer concentration in the detector train was approximately.1 g cm 3. The various signals can be understood as follows. During the first 2 s, pure solvent (BA) flows through the detectors. The three monomers are then added sequentially and the strong increments of RI and UV response for each are seen, whereas the light scattering (LS) (only the 9 data are shown) and viscometer do not respond to the dilute monomer solution. At 9 s the initiator is added (2,2 - azobisisobutyronitrile) and the reaction begins. The Commercial availability of complete ACOMP platforms from Polymer Laboratories Ltd (now a Division of Varian, Inc) In 24 Polymer Laboratories (PL, Shropshire, UK) took a license to ACOMP and related technologies from Tulane University. PL has developed a fully professionalized, modular ACOMP platform which is now available for distribution as the PL Process Monitoring and Control platform (PMC; The PL system, a working prototype of which is shown in Fig. 2, includes many improvements over the Tulane research versions. The standard PL configuration includes dual low- and high-pressure mixing stages, with a heavy duty Zenith gear pump providing reactor extraction and fast recirculation through a temperature-controlled loop from which the desired Figure 2. First complete commercial prototype of an ACOMP unit, the Polymer Laboratories (now a division of Varian, Inc.) PMC. 392 Polym Int 57: (28) DOI: 1.12/pi

4 Perspective decrease in the UV marks the conversion of the monomers into terpolymer, whereas the RI signal increases because dn/dc is higher for the polymeric form than dn/dc of the corresponding monomer. The increase in LS and viscosity corresponds to the buildup of polymer in the reactor as conversion proceeds. These signals allow model-independent calculation of comonomer conversion kinetics, weight-average molar mass, intrinsic viscosity and average composition drift and distribution. Results of ACOMP analyses on this type of raw ACOMP data for different reaction scenarios are presented below. ACOMP APPLICATIONS Classic free radical homopolymerization One of the most straightforward applications of ACOMP is the monitoring of free radical homopolymerization reactions. The first published ACOMP work involved the free radical polymerization of vinyl pyrrolidone (VP).9 ACOMP has been used to determine monomer conversion and chain transfer kinetics,1 to obtain measures of polydispersity even though no chromatographic columns are used,11 to seek deviations from ideality (such as scavenging by impurities)12 and to monitor continuous reactors.13 In this latter application the approach to the steady state after changing reaction conditions, e.g. to change from one grade of product to another, is precisely monitored, as well as any fluctuations away from steady-state operation due to any number of effects, such as feed rates, changing temperature or initiator conditions, etc. ACOMP has also been used to monitor reactions in pressurized reactors. Living reactions for well-controlled low polydispersity polymers Anionic polymerization was the first well-developed type of living polymerization that can lead to low polydispersity, and gradient and multi-block 3 reaction starts 6 14 RI 2 15 CRP.4 2 Visc.(-1V).3 add BA LS9.2 1 Mw (g/mole) (6%BA, 2.5% excess [SG1] T=12 ) LS9, Viscosity add Styrene.5 RI, UV@265nm Copolymerization reactions ACOMP has begun to contribute powerfully to the monitoring of copolymerization reactions. Without any model-dependent assumptions, the evolution of the average composition, molar mass and intrinsic viscosity distributions can be followed, as well as the composition drift. Hence, the copolymer is born characterized. From this, if desired, model-dependent quantities such as reactivity ratios and sequence length distributions can be computed. Online monitoring of copolymerization reduces the need for tedious and expensive post-mortem analyses using coupled fractionation methods and also allows for possible reaction control MMA base. free radical polymerization (3%BA, 7%THF BPO=1%BA (w/w), T=6 C) UV.1 solvent Mw (g/mole).6 structures. Recently, enormous strides have been made in finding more robust, economical routes to living polymerization. These include the family of controlled free radical polymerization (CRP) mechanisms, including nitroxide-mediated polymerization (NMP),14 atom transfer radical polymerization (ATRP)15 and reversible addition-fragmentation chain transfer (RAFT).16 Additionally, ring-opening polymerization (ROP)17 and ring-opening metathesis polymerization (ROMP)18 methodologies have expanded the synthetic routes available for preparing well-defined polymers. Figure 4 shows the striking difference between classic free radical polymerization, where Mw can decrease with conversion, and living-type polymerization leading to a linear increase of mass with conversion (NMP of BA). Successful monitoring of NMP,19 ATRP2 and ROMP21 reactions has been demonstrated, and allows the kinetics and evolution of molar mass to be followed, as well as deviations from ideal living behavior due to unwanted reactions such as termination22 and chain transfer. ACOMP is ideally suited to accompany and accelerate the development and applications of living polymerization reactions t (s) Figure 3. Typical ACOMP data. Terpolymerization of MMA/BA/styrene. Polym Int 57: (28) DOI: 1.12/pi f Figure 4. Controlled radical polymerization versus free radical polymerization: Weight-average molecular mass Mw as function of monomer conversion f. Solid circles for free radical data are SEC results for manually withdrawn reaction aliquots. 393

5 AM Alb, MF Drenski, WF Reed The first comprehensive demonstration of ACOMP capabilities in this area were made on a traditional styrene/mma copolymerization. 23 Recently, the use of a full spectrum UV-visible photodiode array detector (Shimadzu PDA-2) has allowed ACOMP to monitor copolymer reactions where the comonomers have only slightly different spectra. 24 This method is very promising for monitoring multiple acrylic comonomers. It was immediately applied to the copolymerization of N- methacryloxysuccinimide (MASI) with other acrylic monomers. 25 There was a large contrast in composition drift and M w versus conversion between the free radical copolymerization of MASI/MMA and MASI/BA. The reactivity ratios, determined in model-dependent fashion from ACOMP, yielded for MASI/MMA r MASI =.69, r MMA = 1.32, and for MASI/BA r MASI = 1.89, r BA =.53. The greater reactivity ratio difference in the MASI/BA pair leads to greater composition drift than in the MASI/MMA case, and an unusual increase in M w for the MASI/BA versus conversion. This latter is not fully understood, but may relate to the differences in reactivity ratios and/or mid-chain branching reactions. It is important to differentiate between copolymerization in free radical versus living contexts. In the former, since chains are initiated, propagate and terminate very rapidly compared to the time for total monomer conversion, there is a distribution of composition among the chains. For living copolymerization, in contrast, since each chain ideally lives the duration of the entire conversion process, each chain records and bears the same average composition drift as the reaction proceeds. These are sometimes referred to as gradient copolymers. The NMP mediated gradient copolymerization of styrene and BA was recently monitored by ACOMP, yielding the average composition gradient of the chains, as well as conversion kinetics and the evolution of M w and [η] w. 26 Other areas of current activity involve block copolymerization and synthesis of copolymeric polyelectrolytes. Figure 5 shows comonomer conversions and M w for a free radical copolymerization of the sodium salt of vinyl benzene sulfonic acid (VB) and acrylamide (Aam). This leads to a striking two-phase reaction, in which the VB and Aam copolymerize in the first phase, and then, the VB being exhausted, large homopolymeric chains of PAam are produced; i.e. a blend of copolymeric polyelectrolyte and neutral PAam results. Also shown in the figure is the instantaneous weight average mass M w,inst, which can be obtained from the cumulative M w by differentiation: M w,inst (f ) = d[fm w (f )]/df, where f is the fractional conversion of monomer. Heterogeneous phase polymerization Heterogeneous phase polymerizations include emulsions, suspensions, slurries and other media. The first application of ACOMP in this area involved the monomer conversion f VB t (s) M w,inst f Aam M w Figure 5. Free radical copolymerization of VB and Aam led to the two-phase production of a blend of copolymeric polyelectrolyte (VB/Aam) and homopolymeric PAam. inverse emulsion phase polymerization of polyacrylamide. Several new capabilities of ACOMP resulted from this, including use of breaker surfactants during dilution to help create phase inversion, measurement of time needed to create the inversion, use of viscometric detection to eliminate the effects on detection of debris and large colloid particles and preliminary use of heterogeneous time-dependent static light scattering (HTDSLS) to see between the colloids and debris, and recover the scattering background from the polymer. 27 HTDSLS was recently introduced in order to simultaneously characterize solutions containing both polymers and colloids. 28 A large current effort is being devoted to monitoring emulsion polymerization reactions, with and without surfactant. A significant advance concerns the simultaneous monitoring of both emulsion particle properties (e.g. particle size using light scattering) and the characteristics of the soluble polymer and monomer components. Step-growth reactions ACOMP has been applied to the step-growth of polyurethane, and the step-growth production of polyamines using a small molar percentage of hexafunctional monomers to promote branching and crosslinking. 29 In this latter case there is a very rapid and dramatic divergence of M w when conversion is >99%. The polyelectrolytes produced in this way are used for water purification, so the greater the mass the higher their flocculating efficiency. Hence, the motivation is to drive M w as high as possible without reaching the stage of catastrophically linking the entire reactor contents into a macroscopic gel. ACOMP allows the rapid M w increase in this stage to be carefully monitored. M w (g/mole) 394 Polym Int 57: (28) DOI: 1.12/pi

6 Perspective Post-polymerization modifications Frequently, desirable properties can be imparted to polymers by modifying them after they are formed. There are many types of post-polymerization modifications, including hydrolysis, quaternization, sulfonation, carboxylation, PEGylation, the adding of specific moieties by click chemistry, etc. ACOMP is ideally suited to monitoring such modifications by homing in on the physical or chemical changes that accompany the modifications. A recent example is the base hydrolysis of polyacrylamide (PAAM), which turns it into a polyelectrolyte of increasing charge density as hydrolysis proceeds. By selecting an ACOMP diluent of low to moderate ionic strength, the evolution of the polyelectrolyte properties, in terms of polymer coil expansion, increased intrinsic viscosity and strong interparticle correlations, is clearly monitored. 3 Another study in progress involves grafting reactions of styrene onto polybutadiene. It is expected that ACOMP will offer an unprecedented means of discerning between grafting and homopolymerization reactions, unexpected side reactions and unraveling the relationship between the chemical reactions and the concomitant development of physical phase separations. The area of ACOMP monitoring of postpolymerization modification is currently targeted as a priority area in the Tulane research group. strength due to the decrease in electrostatic excluded volume, manifested in A 2 and A 3, while the viscosity decreases due to the shrinkage of the polyelectrolyte coil with increasing ionic strength. The inset shows the values of the electrostatically enhanced A 2 and A 3 obtained from the experiments. Simultaneous multiple sample light scattering (SMSLS). 35,36 While ACOMP gives a detailed characterization of a polymer reaction, it is not suited for high-throughput screening of many samples simultaneously, where the goal is not high-quality characterization of each sample, but rather testing to see which samples meet certain criteria. In this context SMSLS can be used to follow processes in polymer solutions such as aggregation, degradation, dissolution and polymerization. It is envisioned that long-term stability of hundreds of products, e.g. polymers in given concentrations and solvents, or pharmaceutical formulations, will now be feasible, whereas use of a traditional, single-sample light scattering instrument would be totally impractical. In terms of polymerization reactions, it has been demonstrated that SMSLS can (1) determine if a reaction occurs at all, (2) give an indication of the time scale for the reaction to occur if it occurs, (3) give a rough idea of the average polymer mass, and (4) signal any mechanistic hallmarks or peculiarities via the timedependent light scattering signature. 37 RELATED, COMPLEMENTARY METHODS While ACOMP represents a versatile tool for online characterization, other techniques provide useful complements. SEC with coupled LS and viscosity detectors has become routine, and is gradually replacing reliance on older column calibration techniques. ACOMP results are often cross-checked with SEC, usually with excellent agreement. Automated continuous mixing (ACM) for equilibrium and quasi-equilibrium measurements of multicomponent solutions. 31 ACM has proven to be both a useful complement to ACOMP and a rapid means for detailed characterization of multicomponent systems. Gradient pumps are used to create selected paths in the composition space of the solution, and light scattering and viscosity data are gathered over the path, and the RI and/or UV detectors are used to compute the solute concentrations at each point of the path. Examples include determination of effects of added electrolyte on polyelectrolyte dimensions, interactions and hydrodynamics, 32,33 ion-specific effects and interactions of surfactants, polymers, aromatic molecules and electrolytes. 34 Figure 6 gives an example of ACM data showing the effect of increasing electrolyte (NaCl) concentration on the LS and viscosity of a highly charged, linear polyelectrolyte, sodium hyaluronate (HA). As expected, the scattering increases with increased ionic OUTLOOK ACOMP is in a vigorous phase of widening its range of applications and providing many modular approaches to a very wide variety of polymerization reactions. Some of the current reaction focus areas include polymerization reactions in emulsions, postpolymerization modification reactions, copolymeric polyelectrolytes and living copolymerization reactions Raw Light Scattering (V) (9 ) A 3 (mol-ml 2 /g 3 ) Viscosity [I] (M) [NaCl] (M) Light Scattering A 2 = hollow circles A 3 = solid squares Figure 6. Increase in light scattering and decrease in solution viscosity in a solution containing a linear polyelectrolyte (HA), as the ionic strength increases. Inset shows the determinations of A 2 and A 3 resulting from the raw data. (Adapted from reference 32)..1.1 A 2 (mol - ml/g 2 ) 3 Raw Viscosity (V) Polym Int 57: (28) 395 DOI: 1.12/pi

7 AM Alb, MF Drenski, WF Reed for producing polymers of precise architectures. Initial efforts to use the massive ACOMP data stream for controlling reactions have now begun, and promise to be a major area of growth. Control can be achieved through modulating process-critical parameters, such as temperature and reagent flow rate in batch, semibatch and continuous reactors, in response to the ACOMP data stream. A related area involves the attempt to relate the macromolecular distributions and kinetics furnished by ACOMP to the macroscopic properties of the end products. An important longer term goal is to combine the control potential of ACOMP with such knowledge of how macromolecular distributions correlate to end product properties to produce on-command polymers of desired properties; the producer could, in principle, select the desired end product properties (e.g. processability, impact-resistance, rheology control, associative behavior) which are relatable to macromolecular distributions, and dial the distributions into a feedback control system on the reactor piloted by ACOMP to produce the desired end product. In parallel, the dynamic partnership with PL is an important means to continue the technological transfer to their evolving commercial ACOMP/PMC platforms. Similarly, relations with BIC have led to improvements in light scattering detection. The growing number of polymer producers entering into research collaborations has allowed a significant amount of the work to focus on reactions and processes of immediate and long-term industrial interest. The Tulane Center for Polymer Reaction Monitoring and Characterization (PolyRMC) was established in the summer of 27 (website: < PolyRMC will formally group together the ensemble of new characterization methods and instrumentation platforms, and allow multiple projects of both fundamental and applied interest to be carried out. An important training dimension is also envisioned for PolyRMC. ACKNOWLEDGEMENTS Support over the years has derived from the US National Science Foundation s Chemical and Transport Systems program, from the Louisiana Board of Regents and from the National Aeronautics and Space Administration via the Tulane Institute for Macromolecular Engineering and Science (TIMES). Private sponsors in the instrument sector include Polymer Laboratories (now a division of Varian), Brookhaven Instruments Corporation and Shimadzu Corp. Industrial sponsors include Arkema, Inc., Total SA, International Specialty Products, Inc., Firmenich SA and Degussa. Vital contributions have been made from many collaborators at universities in the USA, France, Brazil, Germany and Turkey. REFERENCES 1 Long TE, Liu HY, Schell BA, Teegarden DM and Uerz DS, Macromolecules 26:6237 (1993). 2 Shaikh S and Puskas JE, Polym News 28:71 (23). 3 Storey RF, Donnalley AB and Maggio TL, Macromolecules 31:1523 (1998). 4 Lachenal G, J Near IR Spectrosc 6:299 (1998). 5 Aldridge PK, Kelly JJ, Callis JB and Burns DH, Anal Chem 65:3581 (1993). 6 Ponnuswarmy S, Shah SL and Kiparissides C, JLiquidChromatogr 9:2411 (1986). 7 Elizalde O, Asua JM and Leiza JR, Appl Spectrosc 59:128 (25). 8 Reis MM, Araujo PHH, Sayer C and Giudici R, J Appl Polym Sci 93:1136 (24). 9 Florenzano FH, Strelitzki R and Reed WF, Macromolecules 31:7226 (1998). 1 Grassl B, Alb A and Reed WF, Macromol Chem Phys 22:2518 (21). 11 Reed WF, Macromolecules 33:7165 (2). 12 Giz A, Giz H, Brousseau JL, Alb A and Reed WF, Macromolecules 34:118 (21). 13 Grassl B and Reed WF, Macromol Chem Phys 23:586 (22). 14 Hawker CJ, Bosman AW and Harth E, Chem Rev 11:3661 (21). 15 Matyajzewski K and Xia J, Chem Rev 11:2921 (21). 16 Moad G, Rizzardo E and Thang SH, Aust J Chem 58:378 (25). 17 Dechy-Cabaret O, Martin-Vaca B and Bourissou D, Chem Rev 14:6147 (24). 18 Grubbs RH, Handbook of Metathesis. John Wiley (23). 19 ChauvinF,AlbAM,BertinD,TordoPandReedWF,Macromol Chem Phys 23:229 (2). 2 Mignard E, Lutz JF, LeBlanc T, Matyjaszewski K, Guerret O and Reed WF, Macromolecules 38:9556 (25). 21 Alb AM, Enohnyaket P, Craymer JF, Eren T, Coughlin EB and Reed WF, Macromolecules 4:444 (27). 22 Drenski MF, Mignard E and Reed WF, Macromolecules 39:8213 (26). 23 Giz A, Koc AO, Catalgil-Giz H, Alb AM and Reed WF, Macromolecules 35:6557 (22). 24 Alb AM, Enohnyaket P, Drenski MF, Head A, Reed AW and Reed WF, Macromolecules 39:575 (26). 25 Alb AM, Enohnyaket P, Shunmugam R, Tew GN and Reed WF, Macromolecules 39:8283 (26). 26 Mignard E, Leblanc T, Bertin D, Guerret O and Reed WF, Macromolecules 37:966 (24). 27 Alb AM, Farinato R, Calbick J and Reed WF, Langmuir 22:831 (26). 28 Schimanowski R, Strelitzki R, Mullin DA and Reed WF, Macromolecules 32:755 (1999). 29 Farinato RS, Calbick J, Sorci GA, Florenzano FH and Reed WF, Macromolecules 38:1148 (25). 3 Paril A, Alb AM and Reed WF, Macromolecules 4:449 (27). 31 Strelitzki R and Reed WF, J Appl Polym Sci 73:2359 (1999). 32 Bayly EE, Brousseau J-L and Reed WF, Int J Polym Char Anal 7:1 (22). 33 Sorci GA and Reed WF, Macromolecules 35:5218 (22). 34 Sorci GA and Reed WF, Langmuir 18:353 (22). 35 Reed WF, US Patent (23). 36 Drenski MF and Reed WF, Polym Mater Sci Eng 88:34 (23). 37 Alb AM, Drenski MF, Mignard E and Reed WF, Macromolecules 37:2578 (24). 396 Polym Int 57: (28) DOI: 1.12/pi