Mayo-Lewis Terminal Model Research Articles

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions.

Grafting density and graft distribution impact the chain dimensions and physical properties of polymers. However, achieving precise control over these structural parameters presents long-standing synthetic challenges. In this report, we introduce a versatile strategy to synthesize polymers with tailored architectures via grafting-through ring-opening metathesis polymerization (ROMP). One-pot copolymerization of an ω-norbornenyl macromonomer and a discrete norbornenyl comonomer (diluent) provides opportunities to control the backbone sequence and therefore the side chain distribution. Toward sequence control, the homopolymerization kinetics of 23 diluents were studied, representing diverse variations in the stereochemistry, anchor groups, and substituents. These modifications tuned the homopolymerization rate constants over 2 orders of magnitude (0.36 M-1 s-1 < khomo < 82 M-1 s-1). Rate trends were identified and elucidated by complementary mechanistic and density functional theory (DFT) studies. Building on this foundation, complex architectures were achieved through copolymerizations of selected diluents with a poly(d,l-lactide) (PLA), polydimethylsiloxane (PDMS), or polystyrene (PS) macromonomer. The cross-propagation rate constants were obtained by nonlinear least-squares fitting of the instantaneous comonomer concentrations according to the Mayo-Lewis terminal model. In-depth kinetic analyses indicate a wide range of accessible macromonomer/diluent reactivity ratios (0.08 < r1/r2 < 20), corresponding to blocky, gradient, or random backbone sequences. We further demonstrated the versatility of this copolymerization approach by synthesizing AB graft diblock polymers with tapered, uniform, and inverse-tapered molecular "shapes." Small-angle X-ray scattering analysis of the self-assembled structures illustrates effects of the graft distribution on the domain spacing and backbone conformation. Collectively, the insights provided herein into the ROMP mechanism, monomer design, and homo- and copolymerization rate trends offer a general strategy for the design and synthesis of graft polymers with arbitrary architectures. Controlled copolymerization therefore expands the parameter space for molecular and materials design.

Glycopolymers with glucosamine pendant groups: Copolymerization, physico-chemical and interaction properties

The synthesis of an unprotected glycomonomer, 2-{[( d-glucosamin-2- N-yl)carbonyl]oxy}ethyl acrylate (HEAGl) is firstly described as well as its copolymerization with methyl methacrylate by conventional free radical polymerization in DMSO solutions at 70 °C in a wide range of compositions. The reactions have been followed by in situ monitoring proton NMR which allows examining the system copolymerization kinetic as well as the variation of cumulative feed and copolymer compositions as a function of conversion. The monomer reactivity ratios have been calculated using the Mayo–Lewis terminal model and Kelen–Tüdös extended equation. The glass transition and thermal stability temperatures have been determined in statistical glycopolymers obtained at high degree of conversions. Finally, the ability of the water-soluble glycopolymers to interact with Con A lectin has been investigated.

Synthesis and characterization of functional gradient copolymers of glycidyl methacrylate and butyl acrylate

Epoxy-functional spontaneous gradient copolymers of glycidyl methacrylate (G) and n-butyl acrylate (B) were synthesized via atom transfer radical polymerization (ATRP). The copolymerization reactions were carried out in toluene solution at 70 °C, using methyl 2-bromopropionate (MBrP) as initiator and copper chloride with N, N, N′, N′′, N′′-pentamethyldiethylenetriamine (PMDETA) as the catalyst system. The kinetic behaviour of the statistical copolymerizations was studied in a wide composition interval with molar fractions of G ranging from 0.10 to 0.75. The synthesized copolymers were characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. 1H NMR was employed to determine the copolymer composition, demonstrating the gradient character of the copolymers along the main chain in the whole monomer conversion interval. Apart from this, the sequence distribution and stereoregularity were analyzed. These microstructural experimental data agreed well with those calculated from Mayo-Lewis terminal model (MLTM) and a Bernoullian statistic with an isotacticity parameter of σ G = 0.28 and a coisotacticity parameter of σ = 0.30.

Atom transfer radical copolymerization of glycidyl methacrylate and allyl methacrylate, two functional monomers

Bi-functional statistical copolymers, based on allyl methacrylate (AMA) and glycidyl methacrylate (GMA), were synthesized via atom transfer radical polymerization (ATRP). The polymerization reactions were carried out in a diphenyl ether solution at low temperature, 50 °C, using ethyl 2-bromoisobutyrate (EBrIB) as an initiator, and copper chloride with N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) as the catalyst. Different aspects of the copolymerization, such as the kinetic behaviour, crosslink density and gel fraction were studied. The sol fractions of the synthesized copolymers were characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. The reactivity ratios were calculated from the copolymer composition, determined by 1H NMR, and using the extended Kelen–Tüdös method. Values of 0.82 ± 0.04 and 1.22 ± 0.03 were obtained for AMA and GMA, respectively. The copolymer composition as a function of conversion degree for the different monomer molar fractions in the feed agreed with the theoretical values calculated from the Mayo–Lewis terminal model (MLTM).

Free‐radical copolymerization of ethyl α‐hydroxymethylacrylate with methyl methacrylate by reversible addition–fragmentation chain transfer

AbstractThe controlled free‐radical homopolymerization of ethyl α‐hydroxymethylacrylate and copolymerization with methyl methacrylate were performed in chlorobenzene at 70 °C by the reversible addition–fragmentation chain transfer polymerization technique with 2,2′‐azobisisobutyronitrile as the initiator. 2‐Phenylprop‐2‐yl dithiobenzoate and 2‐cyanoprop‐2‐yl dithiobenzoate were used as chain‐transfer agents in the homopolymerization, whereas only the former was used in the copolymerization. All reactions presented pseudolinear kinetics. The effect of the monomer feed ratio on the copolymerization kinetics was examined. The conversion level decreased when the proportion of ethyl α‐hydroxymethylacrylate in the monomer feed was larger. Kinetic studies indicated that the radical polymerizations proceeded with apparent living character according to experiments, demonstrating an increase in the molar mass with the monomer conversion and a relatively narrow molar mass distribution. All copolymers were statistical in chain structure, as confirmed by determinations of the monomer reactivity ratios. The monomer reactivity ratios were determined, and the Mayo–Lewis terminal model provided excellent predictions for the variations of the intermolecular structure over the entire conversion range. Additionally, the chemical modification of poly(ethyl α‐hydroxymethylacrylate) was carried out to introduce glucose pendant groups into the structure. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5618–5629, 2006

Synthesis and characterization of functional gradient copolymers of allyl methacrylate and butyl acrylate

AbstractFunctional spontaneous gradient copolymers of allyl methacrylate (A) and butyl acrylate (B) were synthesized via atom transfer radical polymerization. The copolymerization reactions were carried out in toluene solutions at 100 °C with methyl 2‐bromopropionate as the initiator and copper bromide with N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the catalyst system. Different aspects of the statistical reaction copolymerizations, such as the kinetic behavior, crosslinking density, and gel fraction, were studied. The gel data were compared with Flory's gelation theory, and the sol fractions of the synthesized copolymers were characterized by size exclusion chromatography and nuclear magnetic resonance spectroscopy. The copolymer composition, demonstrating the gradient character of the copolymers, and the microstructure were analyzed. The experimental data agreed well with data calculated with the Mayo–Lewis terminal model and Bernoullian statistics, with monomer reactivity ratios of 2.58 ± 0.37 and 0.51 ± 0.05 for A and B, respectively, an isotacticity parameter for A of 0.24, and a coisotacticity parameter of 0.33. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5304–5315, 2006

Synthesis and characterization of glycidyl methacrylate/butyl acrylate copolymers obtained at a low temperature by atom transfer radical polymerization

AbstractStatistical glycidyl methacrylate/butyl acrylate copolymerization, at three different feed monomer compositions (75:25, 50:50, and 25:75), was carried out under atom transfer radical polymerization conditions with ethyl 2‐bromoisobutyrate as an initiator, copper chloride as a catalyst, and N,N,N′,N″,N″‐pentamethyldiethylenetriamine as a ligand in 50% (v/v) toluene and diphenyl ether solutions and at 30 °C. Linear first‐order kinetics, linearly increasing molecular weight with conversion, and low polydispersities were observed for all the copolymerizations. The apparent propagation constant obtained for each molar fraction in the feed had similar values in the two solvents and increased as the glycidyl methacrylate molar fraction in the feed increased. The monomer reactivity ratios, 2.78 ± 0.32 for glycidyl methacrylate and 0.16 ± 0.07 for butyl acrylate, were estimated with the extended Kelen–Tüdos equation, and the copolymer compositions were determined by 1H NMR spectroscopy. The cumulative copolymer compositions as a function of conversion for the different molar fractions in the feed were quite consistent with the theoretically calculated values from the Mayo–Lewis terminal model. Moreover, the cure behavior of a copolymer with a commercial linear diamine was also analyzed by differential scanning calorimetry. A single exothermic peak was observed for a nonisothermal curing reaction, indicating the clear potential of the obtained copolymers for epoxy applications. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1807–1816, 2006

High-Throughput Synthesis and Screening of a Library of Random and Gradient Copoly(2-oxazoline)s

ReceiVed July 8, 2005 Introduction. The living cationic ring opening polymerization (CROP; see Scheme 1) of 2-oxazolines was discovered in 1966.1-3 After this discovery, the resulting biocompatible poly(2-oxazoline)s have been used for a wide variety of applications.4-6 Moreover, amphiphilic structures are easily accessible by the sequential polymerization of a hydrophilic monomer (e.g., 2-methylor 2-ethyl-2-oxazoline) and a hydrophobic monomer (e.g., 2-nonylor 2-phenyl-2oxazoline). Unlike block copoly(2-oxazoline)s, random copoly(2-oxazoline)s have not been extensively investigated so far. The possibility of copolymerizing different 2-oxazolines has been demonstrated by several groups;7-9 however, reactivity ratios have only been determined for copolymerizations involving 2-phenyl-2-oxazoline (PhOx).10 Due to the low reactivity of PhOx, the copolymerizations resulted in blocky structures instead of random or gradient copolymers. Moreover, the properties of copoly(2-oxazoline)s have not been studied in detail. Inspired by this lack of knowledge in the literature, we decided to investigate the synthesis and properties of a library of random copolymers from 2-methyl-2-oxazoline (MeOx), 2-ethyl-2-oxazoline (EtOx), and 2-nonyl-2-oxazoline (NonOx). Such systematical copolymerization studies and corresponding structure-property investigations are reported for the first time. In polymer science, this report is the first example of a high-throughput approach in which kinetic details, library synthesis, and property screening were investigated simultaneously, providing both fundamental and application-directed insights. Results and Discussion. The currently described work was preceded by detailed (automated parallel) kinetic investigation of the homopolymerizations of four monomers (MeOx, EtOx, NonOx, and PhOx) with four initiators at four molecular weights and two temperatures.11 The optimal conditions from this kinetic screening (polymerization with benzyl bromide as initiator at 100 °C in N,N-dimethylacetamide) were applied to synthesize copolymers from combinations of MeOx, EtOx, and NonOx utilizing a Chemspeed ASW2000 synthesis robot.12 For each combination, nine copolymers were synthesized with 0-100 mol % (steps of 12.5 mol %) of the second monomer, resulting in 27 parallel polymerizations. For each of the copolymerizations, the monomer conversion in time was investigated by automated sampling from the polymerization mixtures for GC analysis.13 The measured monomer-to-solvent ratios of the polymerization mixtures before heating (Figure 1) clearly demonstrate the gradual change in monomer composition for the different copolymerization series: With increasing mole fraction of the second monomer, the ratio of the second monomer to solvent increases linearly, and the ratio of the first monomer to solvent decreases linearly. Figure 2 (top row) depicts the resulting kinetic plots in time for the 50 mol % copolymerizations. Similar kinetic plots were obtained for all other copolymerizations (only one of the polymerizations failed during the library synthesis cq. kinetic screening). The linearity of the first-order kinetic plots (ln{[M]0/[M]t}) confirmed a constant concentration of living polymer chains as expected for a living polymerization. Moreover, monomodal GPC traces with narrow molecular weight distributions (PDI < 1.3) were obtained for the endsamples, which is indicative of a living polymerization mechanism, as well. The kinetic plots revealed a slightly faster consumption (higher reactivity) of MeOx, as compared to EtOx and NonOx. To further elucidate the copolymer compositions, the reactivity ratios (r1 ) k11/k12 and r2 ) k22/k21) were determined from the relation between the fraction of monomer A in the monomer feed (f1) and the incorporated fraction of monomer A in the polymer (F1) at both ∼20% and ∼60% monomer conversion (Figure 3.15, bottom row). For living polymerizations, the reactivity ratios should be calculated at higher monomer conversions (20% or higher) since different reactivities during the initiation process are commonly observed.15,16 Also for the polymerization of 2-oxazolines, it is well-known that the polymerization rate during initiation can be different from the final polymerization rate.17 In the first instance, the reactivity ratios were determined using the classical Mayo-Lewis terminal model (MLTM) utilizing nonlinear least-squares fitting of the data in Figure 2, bottom.18 However, the applied MLMT method is strictly only valid for 0% monomer conversion, and therefore, reliable reactivity ratios can only be determined from extrapolation of the data obtained at low monomer conversions up to ∼10%. To accurately determine the * Phone: +31 40 247 5303. Fax: +31 40 247 4186. E-mail: u.s.schubert@tue.nl. Scheme 1. Schematic Representation of the CROP of 2-Oxazolines Initiated with Benzyl Bromide 145 J. Comb. Chem. 2006, 8, 145-148

Copolymers of acrylic acid with 2-acryloyloxyethyl 2,4-dichlorophenoxyacetate: Synthesis and herbicide release

Free-radical copolymerization of acrylic acid with 2-acryloyloxyethyl 2,4-dichlorophenoxyacetate using 1.0 mol/L 1,4-dioxane solution and 1.5 × 10−2 mol/L of 2,2′ azobisisobutyronitrile as initiator has been carried out at 50°C. In addition to low conversion solution experiments performed to estimate the monomer reactivity ratios, three different copolymerizations over the whole range of conversions have been made. Theoretical values of cumulative copolymer composition, determined by the Mayo-Lewis terminal model, have been correlated with those experimentally obtained. Finally, the herbicide release in three different aqueous pH buffer solutions has been evaluated in heterogeneous phase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4238–4244, 2006

Nitroxide‐mediated free‐radical copolymerization of styrene with butyl acrylate

AbstractControlled free‐radical copolymerization of styrene (S) and butyl acrylate (BA) was achieved by using a second‐generation nitroxide, N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] nitroxide (DEPN), and 2,2‐azobisisobutyronitrile (AIBN) at 120 °C. The time‐conversion first‐order plot was linear, and the number‐average molecular weight increased in direct proportion to the ratio of monomer conversion to the initial concentration, providing copolymers with low polydispersity. The monomer reactivity ratios obtained were rS = 0.74 and rBA = 0.29, respectively. To analyze the convenience of applying the Mayo–Lewis terminal model, the cumulative copolymer composition against conversion and the individual conversion of each monomer as a function of copolymerization time were studied. The theoretical values of the propagating radical concentration ratio were also examined to investigate the copolymerization rate behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4168–4176, 2004

Sequence Distribution and Stereoregularity in Styrene/Butyl Methacrylate Copolymers Obtained at High Conversion by Stable Free-Radical Polymerization

13 C NMR spectra of styrene/butyl methacrylate copolymers prepared in bulk at 125°C using 2,2,6,6-tetramethyl-1-(1-phenylethoxy)piperidine as the initiator were analyzed. After assignment of the carbon resonances of the aromatic C-1 region, the Mayo-Lewis terminal model (MLTM) was tested by comparison of experimental and predicted values of configurational triad sequences. It follows that MLTM provides an excellent prediction across a wide conversion range for all comonomer feeds.

Kinetic study of the stable free‐radical copolymerization of styrene with butyl methacrylate

AbstractThe radical copolymerization of styrene and n‐butyl methacrylate mediated by 1‐phenyl‐1‐(2′,2′,6′,6′‐tetramethyl‐1′‐piperidinyl‐oxy)ethane in bulk at 125 °C has been analyzed over a wide range of conversions and monomer feed compositions. Monomer reactivity ratios have been determined, and the Mayo–Lewis terminal model provides excellent predictions for the variations of the intermolecular structure over the entire conversion range. The kinetic analysis of this copolymerization system indicates an apparent propagation rate coefficient independent of the monomer feed composition as well as a limiting conversion that decreases as the styrene monomer feed decreases. This fact is attributed to side reactions leading to unsaturated end groups and the accumulation of nonactive adducts of n‐butyl methacrylate. The number‐average molecular weights linearly increase with conversion, and the copolymers present narrow molecular weight distributions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2750–2758, 2002

Glass Transition Temperatures of Poly[(methyl methacrylate)-co-(butyl acrylate)]s Synthesized by Atom-Transfer Radical Polymerization

Glass transition temperatures Tg of methyl methacrylate/butyl acrylate copolymers obtained by means of atom-transfer radical polymerization are measured using differential scanning calorimetry. Due the nature of this polymerization method an increase in molecular weight is produced as the reaction progresses, which gives rise to an increase in Tg. Simultaneously, a composition gradient with the enrichment of butyl acrylate causes a decrease in Tg. These opposite effects almost compensate each other and, therefore, no influence on the molecular weight at M̄n < 10000 is found. This fact allows the application of the Johnston's equation and the Mayo-Lewis terminal model to describe and predict the variation in Tg with copolymer conversion for the copolymers and under the experimental conditions investigated.

Inter and intramolecular structure predictions in 2-hydroxyethyl methacrylate– tert-butyl acrylate copolymers obtained at high conversion

Radical copolymerization at 50°C of 2-hydroxyethyl methacrylate and tert-butyl acrylate in a 3 mol l −1 N, N′-dimethylformamide (DMF) solution has been analysed over a wide range of conversion and monomer feed compositions with the purpose of predicting the variation of inter and intramolecular structures. To do this, the previously obtained monomer reactivity ratios along with the coisotactic and statistical parameters were used. Overall copolymerization rate coefficients and individual monomer conversions for each monomer on the full range of conversion were also obtained. From the results obtained it follows that the Mayo–Lewis terminal model (MLTM) provides an excellent prediction across the complete conversion range for all comonomer feed compositions.

Low- and high-conversion studies of the free radical copolymerization of 2-hydroxyethyl methacrylate with styrene inN,N?-dimethylformamide solution

2-Hydroxyethyl methacrylate (HEMA) and styrene (S) have been copolymerized in a 3 mol . L -1 N,N'-dimethylformamide (DMF) solution using 2,2'azobis (isobutyronitrile) (AIBN) as an initiator over a wide composition and conversion range. From low-conversion experiments and 1 H-NMR analysis, the monomer reactivity ratios were determined according to the Mayo-Lewis terminal model. The comparison of the obtained results with those previously reported for copolymerization in bulk and in toluene reveals a relatively small but noticeable solvent effect that can be qualitatively explained by the bootstrap model. Cumulative copolymer composition as a function of conversion is satisfactorily described by the integrated Mayo-Lewis equation; overall copolymerization rate increases with increasing the HEMA/S ratio, and individual monomer conversion is closely related to the monomer molar fraction in the feed.

A kinetic study of free radical copolymerization of styrene/butyl acrylate

The free radical copolymerization at 50°C of styrene with butyl acrylate was carried out in bulk. Although the copolymer composition is well described by the Mayo-Lewis terminal model, the copolymerization rate is not. As many other systems recently examined, the data are well represented by the "implicit penultimate effect" model. Values of monomer and radical reactivity ratios are qualitatively rationalized in terms of the enthalpic and entropic models.

Kinetic study of high-conversion copolymerization of butyl acrylate with methyl methacrylate in solution

Butyl acrylate (BA) and methyl methacrylate (MMA) have been copolymerized in a 3 mol/L benzene solution using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator over a wide composition and conversion range. The overall copolymerization parameter kp/kt1/2 and the composition of the copolymer formed have been measured as a function of conversion. Theoretical values of the coupled parameter kp/kt1/2 calculated from the implicit penultimate unit model and those of cumulative copolymer composition, determined from the Mayo—Lewis terminal model, have been correlated with those experimentally obtained. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1961–1965, 1997