Effect of pressure on free radical copolymerization kinetics. II. Novel methods of measuring monomer reactivity ratios under high-pressure conditions

Two new techniques for the determination of monomer reactivity ratios in copolymerization under high-pressure conditions have been developed, viz., the “sandwich” and the “quenching” method. Both methods are based on repeated quantitative gas chromatographic analysis of the reaction mixture during the low-pressure stages preceding and succeeding the high-pressure stage, of which the kinetics is under investigation. Application of the “sandwich” method implies the occurrence of reaction during both low-pressure stages and consequently the low-pressure kinetic data are required to obtain the transition points of low to high pressure and vice versa. These points constitute the initial and final conditions of the relevant high-pressure reaction. On the contrary, in the “quenching” method no reaction occurs during the low-pressure stages, owing to the lower temperature and the high activation energy of the initiator decomposition. As a consequence, the initial and final conditions of the high-pressure stage can be determined by a simple averaging procedure. Both methods have been tested for the ethylene—vinyl acetate copolymerization at 62°C and 600 kg/cm² with tert-butyl alcohol as solvent, and appear to lead to almost identical monomer reactivity ratios, although the “quenching” method is slightly preferred in case of copolymerization reactions. Both methods are particularly valuable when one of the reactants is gaseous or the reaction produces a gas. Further merits and drawbacks of both methods are discussed.     

Polymerization of cyclic acetals. II. Synthesis of amphiphilic block copolymers

The sequential copolymerization of 1,3,6-trioxacyclooctane (TOC) and 1,3-dioxolane (DOL) (B) with various vinyl monomers (A) was investigated. Under appropriate conditions amphiphilic block copolymers of the type AB and ABA were formed. The reaction mixtures and the isolated polymers were analyzed by GPC (double detection—IR and UV at 254 nm), IR, ¹H-, and ¹³C-NMR spectroscopy. Block copolymers with chosen molecular weights and low polydispersity could be obtained only by sequential copolymerization of p-methoxystyrene on “living” TOC. In the polymerization of DOL with α-methylstyrene and i-butyl vinyl ether (IBVE) transfer reactions take place to a larger degree.     

A new method of estimating monomer reactivity ratios in copolymerization by linear regression methods

Sequential gas-liquid chromotographic analysis of the reaction mixture throughout a copolymerization reaction in conjuction with the improved curve-fitting I (integrated form) method, which accounts for measurements errors in both variables, allows accurate estimation of the monomer reactivity ratios. In this article an alternative method is presented for estimating r values in copolymerization with linear regression only, which is especially suited to cases in which one or two of the r values is close to 1. In these cases the improved curve-fitting I method tends to converge slowly because of the numerical instability of the integrated copolymerization equation. The use of the new method is illustrated for the estimation of the r values for ethylene and vinyl acatate in benzene at 35 kg/cm² and 62°C. The linear regression method was also tried on other copolymerizations and the results are compared with those obtained from the improved curve-fitting I method. The limits of the applicability of the linear regression method were determined by simulated sequential sampling experiments. It appears that the new method is applicable when the product of the r values is between 0.001 and 2, provided both monomer conversions are large enough compared with the measurements error.     

Dependence of computed copolymer reactivity ratios on the calculation method. II. Effects of experimental design and error structure

Two calculation methods for estimating reactivity ratios, one method based on the differential Alfrey-Mayo equation and one based on the integrated form of this model, are compared with respect to precision and bias. Both methods are characterized by the use of information about the monomer feed composition only and are assumed to be valid up to high conversion. As only monomer feed composition has to be analyzed, several sampling designs are feasible. Two extreme designs can be distinguished. One consists of repetitive sampling of the initial and final monomer feed mixture, whereas the other consists of sequential sampling during the course of the reaction. The influence of both designs of the calculated r-values is investigated by means of simulation. In the present paper the second calculation method, based on the integrated form, is solved by a nonlinear least squares method considering errors in both variables. This method required additional information about the errorstructure of the data. As this information is mostly of approximate nature, the influence of misspecification of this error structure on the calculated r-values is also examined.     

Alternating copolymerization of maleic anhydride with allyl chloroacetate

Some regularities of radical alternating copolymerization of maleic anhydride with allyl chloroacetate are studied. The formation of donor–acceptor complexes between comonomers with complexing constant K_c = 0.052 L/mol is found using ¹H NMR spectroscopy. The kinetic parameters for this copolymerization reaction are found and the quantitative contribution of monomer complexes to chain-growth radical reactions is calculated. It is shown that either a “free-monomer” mechanism (dilute solutions) or a “mixed” mechanism (concentrated solutions) prevails for chain growth during radical copolymerization depending on total monomer concentration. It is found that inhibition of degradative chain transfer in the course of the reaction studied takes place owing to the presence of α-chlorine atom in the allyl chloracetate molecule and formation of charge transfer complex.     

Vacuum and oxidative pyrolysis of poly-p-xylylene. II. Chromatographic analysis and kinetics of reaction products

Reaction products of vacuum and oxidative degradation of poly-p-xylylene have been quantitatively determined by chromatographic analysis as function of time, temperature and oxygen pressure. Respective Arrhenius parameters were also ascertained for some of the reaction products and for the sums of all products. The energies of activation for the sums agree quite satisfactorily with the energies of activation obtained previously by uninterrupted experiments in quartz-spoon reaction vessels. The results found here can be described in terms of mechanisms previously postulated on the basis of the total loss in weight (or volatile production) data. Scission of “weak” links (due to abnormal structures) takes place followed by formation of various products. The whole process is governed by the initial chain scission reaction; however, the energies of activation for each of the products do not need to be identical with that of the chain scission reaction. Each product is formed by a reaction which has its own characteristic number average kinetic chain lengths; the latter have their specific energy of activation values. Oxidative degradation produces the same organic compounds as vacuum degradation and in addition CO, CO₂, and H₂O. Oxidized intermediate compounds are apparently fairly rapidly decarboxylated and decarbonylated. Oxidative chain scission is appreciably faster than that in vacuum. Almost simultaneous “weak” link and “normal” chain scission are taking place initiating the formation of a number of products.     

Photon correlation spectroscopy of crosslinked polystyrene networks in the swollen state: Influence of macromolecular polydispersity

We report measurements of the correlation function of light scattered from thermally excited longitudinal fluctuations in crosslinked polystyrene networks at equilibrium. In order to investigate the influence of the polydispersity of linear chain elements between successive branch points, we synthesized a network by means of anionic block copolymerization, using a mixture of two “precursor” polystyrenes of different molecular weights to initiate polymerization of a small amount of divinyl-benzene (DVB). The correlation function for fluctuations having a wave vector K, has the form of an exponential decay, exp (?Γ). The decay rate is given by Γ = D′K², where D′ represents the diffusion constant of longitudinal modes of the network. We also present measurements of the correlation function of light scattered from gels prepared by anionic block copolymerization of styrene and DVB with only one “precursor” polystyrene and by a free-radical process. In the latter case, the gels should have a wide distribution of linear chain lengths between branch points.     

Cationic copolymerization of racemic‐β‐butyrolactone with L,L‐lactide: One‐pot synthesis of block copolymers

Cationic copolymerization of racemic‐β‐butyrolactone (β‐BL) with l,l ‐lactide (LA) initiated by alcohol and catalyzed by trifluoromethanesulfonic acid proceeding by activated monomer (AM) mechanism was investigated. Although both comonomers were present from the beginning in the reaction mixture, polymerization proceeded in sequential manner, with poly‐BL formed at the first stage acting as a macroinitiator for the subsequent polymerization of LA. Such course of copolymerization was confirmed by following the consumption of both comonomers throughout the process as well as by observing the changes of growing chain‐end structure using ¹H NMR. ¹³C NMR analysis and thermogravimetry revealed the block structure of resulting copolymers. The proposed mechanism of copolymerization was confirmed by the studies of changes of ¹H NMR chemical shift of acidic proton in the course of copolymerization, providing an indication that indeed protonated species and hydroxyl groups are present throughout the process, as required for AM mechanism. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4873–4884     

Analysis of the Linear Methods for Determining Copolymerization Reactivity Ratios. V. Planning of Experiments

A method for planning of experiments has been elaborated which makes it possible to decide the adequacy of the two-parameter model of binary copolymerization. At the same time, the procedure provides equal and reasonably low relative errors of r₁ and r₂. In the approximate knowledge of the parameters and of the value of analytical error, the procedure furnishes the number of measurements and the monomer feed values necessary for the desired accuracy. It was obtained as a “rule of thumb” that, in spite of the erroneous practice, the points should be arranged uniformly within the range of copolymer composition instead of monomer composition. For the objective performance of retrospective evaluations, an “efficiency factor” has been introduced.     

Radical reactivity of α-trifluoromethylstyrene

α-Trifluoromethylstyrene (TFMST) does not undergo radical homopolymerization with azobis(isobutyronitrile) (AIBN) in bulk at 60°C. Low-temperature initiation was not effective either. Radical copolymerization of TFMST (M₂) with styrene (ST, M₁) has yielded monomer reactivity ratios as follows: r₁ = 0.60 and r₂ = 0.00. It has been found that the cyclohexyl radical generated by reaction of cyclohexylmercuric chloride with sodium borohydride adds to the β-carbon of TFMST 7.5 times faster than that of ST. Combination of the copolymerization analysis and the “mercury method” has allowed us to estimate Alfrey–Price Q and e parameters for TFMST to be 0.43 and 0.90, respectively. Thus, due to the strongly electron-withdrawing effect of the trifluoromethyl group, this styrene is highly electron deficient. In spite of the favorable electronic effect, however, the ceiling temperature appears very low, presumably due to the steric hindrance.     

A new arithmetic for linear free radical copolymerization

As a consequence of their method of production, polymer chains are polydisperse in size, composition and sequence distribution. In this work we present a new method of uniquely identifying these “polymer isomers” termed “Digital Encoding of Polymeric Chains”. The method involves replacing distinguishable features of the chain such as monomer units, branches, etc. with a number. This unique sequence of numbers provides a digital code, which, depending on the base of the arithmetic used (binary, ternary) can be translated into a unique decimal equivalent number. We have applied this technique to the case of binary copolymerization in a CSTR at steady state and show how the sequence spectra of the chain populations are conveniently obtained. Furthermore, the technique shows that rich information about the copolymerization kinetics, reactivity ratios and termination mode can be obtained from analysis of the short chains of the distribution. The implications for this in parameter estimation and controlled polymerization are discussed in this paper.     

“Living” free radical copolymerization of styrene and N-vinylcarbazole

Poly[styrene-co-(N-vinylcarbazole)] copolymers with controlled molecular weights and narrow polydispersities were synthesized by nitroxide-mediated “living” free radical copolymerization using an initiator/capping agent system consisting of benzoyl peroxide (BPO) and the stable nitroxyl radical 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO). The copolymerization behaves in a “living” fashion and allows the synthesis of poly[styrene-co-(N-vinylcarbazole)]/polystyrene block copolymers via a controlled chain-extension reaction of the prepared copolymers with styrene.     

Nucleosides. 130. Synthesis of 2′-Deoxy-2′-substituted- and 5′-Deoxy-5′-substituted-ψ-uridine Derivatives. Crystalline and Molecular Structure of 2′-Chloro-2′-deoxy-1,3-dimethyl-ψ-uridine. Studies Directed Toward the Synthesis of 2′-Deoxy-2′-substituted-arabino-Nucleosides. 1

A method was developed to prepare 5′-deoxy-5′-substituted-ψ-uridine derivatives 4 from 3′,5′-O-(1, 1, 3, 3-tetraisopropyldisiloxanyl)-1,3-dimethyl-ψ-uridine 1 via a silyl rearrangement reaction. Nucleophilic displacement of the mesyloxy function of 2′-O-mesyl-1,3-dimethyl-ψ-uridine 7 afforded products with the 2′-substituent in the “down” ribo configuration 8 . X-Ray crystallographic analysis of the 2′-chloro derivative 8a firmly established the molecular structure of 8 and provided evidence for neighboring group participation of the 4-carbonyl function of 7 during the nucleophilic reactions. Treatment of 1,3-dimethyl-ψ-uridine 11 with α-acetoxyisobutyryl chloride afforded a mixture from which two 2′-chloro-2′-deoxy-C-nucleosides were obtained. The major product (33% yield) was identical with 8 . The minor product (7% yield) was consequently assigned the arabino nucleoside 14 . This is the first direct introduction of a 2′-substituent in the “up” configuration in a preformed pyrimidine nucleoside.     

Preparation of remarkably tough polyHIPE materials via polymerization of oil‐in‐water HIPEs involving 1‐vinyl‐5‐aminotetrazole

Interconnected microcellular polymeric monoliths having unexpected high mechanical strength have been prepared using the high internal phase emulsion (HIPE) methodology. Oil‐in water concentrated emulsions of aqueous 1‐vinyl‐5‐amino [1,2,3,4]tetrazole (1‐VAT) mixed with a low molar ratio (7%) of N,N′‐methylenebisacrylamide as crosslinking agent were prepared using dodecane as dispersed phase and a mixture of hydrophilic surfactants. “Reverse” polyHIPE materials were obtained after radical copolymerization, solvent extraction, and drying. Their morphology, chemical composition, and physicochemical behavior are discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2942–2947, 2010     

Kinetics of Free Radical Copolymerization. IV. Rate of Initiation in the Copolymerization System Ethyl Acrylate-Styrene-Benzene

Dependence of the rate constant of initiation on the overall concentration and composition of monomer has been investigated in the free radical copolymerization of ethyl acrylate and styrene in bulk and in benzene solution at 50° C. The rate constant of initiation has been determined by the inhibition method using triphenyl-verdazil as the stable free-radical inhibitor. An equation has been derived to calculate the rate constant of initiation in a copolymerization system, where both monomers undergo a pseudounimolecular side reaction with the inhibitor. The rate constant of initiation in the copolymerization mixture is a linear composition of rate constants determined separately in the pure constituents of the system.     

Improved methods of estimating monomer reactivity ratios in copolymerization by considering experimental errors in both variables

Existing methods of calculating monomer reactivity ratios in copolymerization are reviewed briefly, evaluated, and classified according to their mathematical and computational similarities. More attention is paid to procedures based on the integrated copolymer equation with which calculation of r values is performed most often by electronic computer. Unfortunately, until now all procedures have shown shortcomings because the real-error structure of the observations has not been taken into account. A new algorithm that does account correctly for measurement errors in both variables is described. A computational method is illustrated for copolymerization data obtained from quantitative gas chromatographic analysis of the monomer feed throughout the reaction. It is shown that the actual error structure of the variables corresponds to the assumed error structure. Reliability of the estimates is substantially increased, compared with the existing methods. Standard deviations of the monomer reactivity ratios are given and appear to be in good agreement with reality.     

CH2XH→CH3X (X＝O, S, Se)异构化的量子拓扑研究

利用从头算和量子拓扑方法讨论了CH₂XH→CH₃X (X＝O, S, Se)异构化过程的反应机理. 着重从电子密度拓扑分析计算了反应进程中的各点, 讨论了反应进程中键的断裂和生成, 上述反应都经历了三元环过渡结构, 找到了这类反应的"能量过渡态"和"结构过渡态", 且结构过渡态均在能量过渡态之后出现. 三元结构过渡态结构出现的范围与反应热成正比.     

Time‐of‐flight mass spectrometry for time‐resolved measurements: Some developments and applications

In this paper, the time resolution for kinetic studies of reactions with mass spectrometric detection is characterized in detail, and it is shown how this allows faster kinetic processes to be determined. The time‐resolved technique used pulsed laser photolysis to initiate reaction and a time‐of‐flight mass spectrometer (TOFMS) to monitor progress, where the reactant gas was sampled by a sampling orifice and photoionized using pulsed, laser vacuum ultraviolet light before being analyzed by the TOFMS. Characterization of this setup has been carried out to identify the parameters that affect the time for “sampling,” which limits the fastest reactions that can be measured. A simple mathematical equation has been developed to correct for “sampling” delays (k_sampling～25, 000 s^?1), which extends the range of rate coefficients to be measured in a kinetic mass spectrometry reactor to k′ < 7000 s^?1. This method could be applied to any other kinetic mass spectrometry system where k_sampling can be measured; an important advantage since it allows the study of reactions over a wider range of conditions (e.g., larger concentrations of reagents/products can be used to minimize the contribution from wall losses). The system can produce reliable kinetic data whether monitoring reactant decay or product growth even when the reaction and sampling processes are occurring on a similar timescale (k′ < 7000 s^?1). Reproducible and reliable kinetic data have been obtained for the following reactions: SO + NO₂ → products (R1), ClSO + NO₂ → products (R2), where SO and ClSO were monitored under pseudo‐first‐order conditions, and HCO + O₂ → CO + HO₂ (R3), where CO was monitored by a [1+1] resonance enhanced ionization multiphoton ionization (REMPI) scheme with HCO reacting under pseudo–first‐order conditions. The limitations and potential developments of this setup are described. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 44: 532–545, 2012     

Cooperative motions in PVC studied by thermally stimulated currents: Comparison with A.C. dielectric derivative analysis

The thermally stimulated current–thermal sampling (TSC–TS) technique was used to study the broadened glass transition in conventional “atactic” poly(vinyl chloride), PVC. The activated parameters obtained from the TSC–TS data, mainly the apparent activation energy (E_a), characterize the breadth of glass transitions in a very sensitive way. These results are compared with those values of E_a obtained from the literature, using a recently proposed method of analyzing a.c. dielectric constants and their derivatives, over the temperature range of −100–130°C. Both techniques detect weak cooperative glass transition-like relaxations well below the main glass transition of ca. 80°C. As is the case with “atactic” PMMA, the data suggest that compositional heterogeneity related to a small fraction of predominantly isotactic sequences contribute to the broad glass transition extending ca. 60°C below the main glass transition in atactic PVC. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 913–918, 1998