The influence of steric factors on the mechanism of copolymerization of phenylvinyl alkyl ethers and maleic anhydride

By assuming that the initial rate of copolymerization (R_p) of phenylvinyl alkyl ether (I) and maleic anhydride (MAn) equals the sum of the rate of polymerization of free monomers R_p(f) and CT complex monomers R_p(CT) the reactivity ratios k_1c/k₁₂ and k_2c/k₂₁ were calculated for copolymerization of I(R = Me, n-Pr, iso-Pr, and sec-Bu) and MAn from the change of copolymerization rate with monomer feed at a constant total monomer concentration. From the equation R_p = R_p(f) + R_p(CT) were calculated R_p(f) and R_p(CT) by applying the generalized model described by Shirota and coworkers and it was found that the participation of CT complex monomers increases with an increase in total monomer concentration in the feed. It was also found that the degree of CT complex monomer participation depends largely on the steric factors. In the copolymerization of I which contains bulky isopropyl or sec-butyl group even in the dilute solutions, copolymerization proceeds by the addition of CT complex monomers.     

Polymerization Kinetics of Water-Soluble N-Vinyl Monomers in Aqueous and Organic Solution

Summary: Free-radical batch polymerization (FRP) of N-vinyl pyrrolidone (NVP) and N-vinyl formamide (NVF) monomers in aqueous solution as well as NVP polymerization in organic (n-butanol) solution has been studied. The differences found in rate of monomer conversion with monomer and solvent choice correlates well with the differences in values of the propagation rate coefficients (k_p) and their variation with monomer concentration measured in independent pulsed-laser polymerization studies, a result demonstrating that a generalized understanding of water-soluble vinyl monomers can be obtained once their k_p differences have been accounted for. A reasonable representation of polymer molecular mass averages and the complete molecular mass distributions for the three systems was obtained by assuming that the rate coefficient for transfer to monomer, polymer, and organic solvent also vary as a function of monomer concentration.     

In vitro degradation characteristics of poly(anhydride-imides) containing pyromellitylimidoalanine

The in vitro degradation characteristics of poly(anhydride-imides) containing pyromellitylimidoalanine, with either 1,6-bis(carboxyphenoxy)hexane (CPH) or sebacic acid (SA) were assessed. The copolymers contained up to 50 mol % of the imide monomer, pyromellitylimidoalanine (PMA-ala). Degradation was pH sensitive, being enhanced under basic conditions. Control of degradation times from 2 days to 2 months was achieved by the selection of appropriate monomer units in the polymer backbone. Monomers were chosen based on their solubility in aqueous media, as well as how they influenced the hydrophobicity and crystallinity of the polymer matrices. Polymer degradation was followed by ultraviolet spectroscopy and high-pressure liquid chromatography. Increasing the amount of imide monomer, PMA-ala, and the use of SA (rather than CPH) as the comonomer increased the degradation rate of the polymer matrices. © 1996 John Wiley & Sons, Inc.     

Side chain liquid crystalline composites,occurrence of interdigitated bilayer smectic C phases

We report on the results of X-ray investigations in two series of polymer monomer composites, PM6Rm-33 and PMnR12-33, which consist of mixtures of achiral liquid crystalline side chain polymers and their monomers. These mixtures present a unique integration of monomer in the polymeric base which assists in modifying their properties and forming homogenous composites. X-ray measurements for all the investigated composites indicate the existence of bilayered smectic C phases (SmC₂). In several composites, the interlayer distance of the SmC₂ phase abnormally increases with cooling; this is associated with the aliphatic interdigitation at the tail-to-tail interface being more prominent when longer aliphatic tails are present.     

Some probability relations in multicomponent copolymers

It was previously shown that for a stationary random copolymer of A, B, and C, we have in general p(AB) + p(AC) = p(BA) + p(CA), etc., in place of p(AB) = p(BA) which is valid for a stationary binary copolymer. Here, p(AB) for example, is the probability that a randomly picked pair of consecutive comonomers in the polymer consists of an A followed by a B. For a stationary ternary copolymer produced by a first-order Markovian addition mechanism, we show that P_ABP_BCP_CA/P_ACP_CBP_BA = k, where k is a constant characteristic of a particular set of three monomers but independent of its composition. Here, P_AB is the conditional probability of finding a monomer of B given that its immediate predecessor is an A. We further show that if the individual rate constants of the monomer additions involved take a special form such as used in the Alfrey-Price Q–e scheme, then we have k = 1 irrespective of the kinds of monomers, and in addition we have p(AB) = p(BA), p(AC) = p(CA), etc. Thus, although these latter results were previously proposed by Ham as an alternative basis to supplant the Q–e scheme, they may rather be regarded as mathematical consequences of special assumptions adopted for the form of the individual rate constants. For a stationary random copolymer of four components A, B, C, and D, we have p(AB) + p(AC) + p(AD) = p(BA) + p(CA) + p(DA), etc., in general. For a first-order Markovian four-component copolymer, we show that there are seven different combinations of the conditional probabilities that are constants (k1, k2,…, k1) independent of the monomer composition. Again, if we assume the same special form for the rate constants involved, we find that all the seven constants k1, k2, …, k7 reduce to unity and p(XY) = p(YX) for X,Y, = A, B, C, D.     

Topochemical Polymerization of 1,3‐Diene Monomers and Features of Polymer Crystals as Organic Intercalation Materials

From the viewpoint of controlled polymer synthesis, topochemical polymerization based on crystal engineering is very useful for controlling not only the primary chain structures but also the higher‐order structures of the crystalline polymers. We found a new type of topochemical polymerization of muconic and sorbic acid derivatives to give stereoregular and high‐molecular weight polymers under photo‐, X‐ray, and γ‐ray irradiation of the monomer crystals. In this article, we describe detailed features and the mechanism of the topochemical polymerization of diethyl‐(Z,Z)‐muconate as well as of various alkylammonium derivatives of muconic and sorbic acids, which are 1,3‐diene mono‐ and dicarboxylic acid derivatives, to control the stereochemical structures of the polymers. The polymerization reactivity of these monomers in the crystalline state and the stereochemical structure of the polymers produced are discussed based on the concept of crystal engineering, which is a useful method to design and control the reactivity, structure, and properties of organic solids. The reactivity of the topochemical polymerization is determined by the monomer crystal structure, i.e. the monomer molecular arrangement in the crystals. Polymer crystals derived from topochemical polymerization have a high potential as new organic crystalline materials for various applications. Organic intercalation using the polymer crystals prepared from alkylammonium muconates and sorbates is also described.     

Alternating copolymerization of α-methylstyrene and maleic anhydride

Alternating copolymers of α-methylstyrene (α-MeSt) and maleic anhydride (MAn) were prepared by free-radical-initiated polymerization in bulk, benzene, or butanone as solvents. By applying the generalized model described by Shirota and co-workers, the reactivity ratios k_1c/k₁₂ and k_2c/k₂₁ were calculated from the change of copolymerization rate with monomer feed at constant total monomer concentration. From the equation R_p = R_p(f) + R_p(CT) were calculated R_p(f) and R_p(CT), and it was found that in benzene the reaction proceeds predominantly by the addition of CT-complex monomers, while in butanone, cross propagation of free monomers predominates. Termination occurs predominantly by homotermination of α-MeSt macro free radicals, k_t22, although the cross termination k_t21 is also operative.     

Synthesis of ordered polymer by direct polycondensation. VIII. Ordered polymer from two nonsymmetric monomers

The ordered (-aacdbbdc-) polymer was prepared by the direct polycondensation of a pair of symmetric monomers (XabX), 4,4′-(oxydi-p-phenylene)dibutanoic acid (XaaX) and 2-methoxyisophthalic acid (XbbX), with a nonsymmetric monomer (YcdY), 4-aminobenzhydrazide, using the condensing agent diphenyl (2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonate ( 1 ). The polymerization was carried out by a one-pot procedure, that is, mixing the dicarboxylic acids, condensing agent 1 and triethylamine in NMP for 2 h at room temperature, followed by the addition of 4-aminobenzhydrazide. This polymerization proceeded smoothly, yielding the ordered polymer with an inherent viscosity of 0.34 dL g⁻¹. The microstructure of the ordered polymer was confirmed by comparing the authentic ordered polymer in their ¹³C-NMR spectrum. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2309–2314, 1998     

Comparative study of the absolute reactivity of vinyl monomers: Kinetics of polymerization of vinyl monomers initiated by Mn3+–thiodiglycolic acid redox system

The kinetics and mechanism of polymerization of methacrylic acid (MAA) and ethyl acrylate (EA) initiated by the redox system, Mn³⁺–thiodiglycolic acid (TDGA) were investigated in the 15–35°C temperature range. The polymerization kinetics of both the monomers followed the same mechanism, viz., initiation by primary radical and termination by Mn³⁺–thiodiglycolic acid complex. The rate coefficients k_i/k₀ and k_p/k_t were related to the monomer reactivity and polymer radical reactivity, respectively. It was observed that both monomer reactivity and polymer radical reactivity followed the same order, viz., EA > MAA. The polymer radical reactivity varied inversely with the Q values of the monomers.     

Microstructure and fracture behavior of semicrystalline polymer–clay nanocomposites

The relationships between the microstructure and the fracture behavior of three polymer/clay nanocomposites were studied. Two different polymer matrices were chosen, namely polyamide‐6 and polyethylene (compatibilized with PE‐g‐MA or PE‐g‐PEo), to reach very different clay dispersion states. The microstructure was characterized in terms of polymer crystallinity, orientation of the polymer crystalline lamellae, clay dispersion state, and orientation of the clay tactoids. The mechanical behavior was characterized by tensile tests. The essential work of fracture (EWF) concept was used to determine the fracture behavior of the nanocomposites. Both tensile and EWF tests were performed in two perpendicular directions, namely longitudinal and transversal. It is shown that the fracture behaviors of the matrices mainly depend on the polymer crystalline lamellae orientation. For the nanocomposites, the relationships between the matrix orientation, the clay dispersion states, the values of the EWF parameters (w_e and βw_p), and their anisotropy are discussed. The results show that the lower the average clay tactoid thickness, the lower is the decrease of fracture performance for the nanocomposite and the more consumed energy as longer the path of the crack. Besides, a linear dependence of the anisotropy of the EWF parameters of the nanocomposites on the average clay aspect ratio is found. The more exfoliated the structure is, the less pronounced the anisotropy of the EWF parameters. Interestingly, it is thought that the average clay aspect ratio is the parameter representing the clay dispersion state that governs the fracture anisotropy of the nanocomposites (as the elastic properties determined by tensile tests). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1820–1836, 2008     

Raman spectroscopic studies of the solid-state polymerization of diacetylenes. II. Thermal polymerization of 1,6-di-p-methoxybenzene-sulfonyloxy-2,4-hexadiyne

The Raman spectra of 1,6-di-p-methoxybenzene-sulfonyloxy-2,4-hexadiyne (MBS) have been recorded during thermal polymerization. The spectra are similar to those of the related p-toluene-sulfonyloxy monomer but indicate a higher strain in the initially formed MBS polymer chains. Despite this similarity, the polymerization kinetics for the two monomers are markedly different. The polymerization behavior of MBS shows that the polymer chain initiation and propagation are practically independent of lattice strain. Possible causes for this independence are discussed.     

Diffusion coefficients of the monomer and oligomers in hydroxyethyl methacrylate

The diffusion coefficients are reported of rubbery ternary systems consisting of the polymer, its monomer analogue (i.e., the saturated equivalent of the monomer), and trace quantities of oligomers (dimer, trimer, tetramer and hexamer) for 2‐hydroxyethyl methacrylate (HEMA). These have been obtained with pulsed‐field‐gradient NMR spectroscopy with a polymer weight fraction (f_p) of 0 ≤ f_p ≤ 0.4. The oligomers are macromonomers synthesized with a cobalt catalytic chain‐transfer agent. The diffusion coefficients are about an order of magnitude smaller than those for monomers such as methyl methacrylate; this effect is ascribed to hydrogen bonding in HEMA. The diffusion coefficient D_i of an i‐meric oligomer has been fitted with moderate accuracy by an empirical universal scaling relation, D_i(f_p)/D₁(f_p) ≈ i, previously found to provide an adequate fit to corresponding data for styrene and for methyl and butyl methacrylates. The approximate empirical scaling relation seems to hold for a remarkably wide range of types of monomer/polymer systems. These results are of use in modeling rates and molecular weight distributions in free‐radical polymerization, particularly for termination (which is chain‐length‐dependent and is controlled by the diffusion coefficient of chains of the low degrees of polymerization studied here). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2491–2501, 2003     

Para-ordered polybenzimidazole

A series of novel AB monomers such as 2-[p-carboxyphenyl]-5,6-diaminobenzimidazole hydrochloride have been synthesized. In addition, a new aromatic monomer, 1,3-diamino-4,6-bis(p-toluenesulfonamido)benzene has been prepared in high purity and substituted for 1,2,4,5-tetraaminobenzene in a polymerization with terephthalic acid. Homopolymerization of the AB monomers, and polycondensation of monomer with terephthalic acid in polyphosphoric acid, produced the rod-like para-oriented polymer, poly[1,7-dihydrobenzo(1,2-d: 4,5-d)diimidazole-2,6-diyl-1,4-phenylene]. The yellow polymer was completely soluble in methanesulfonic acid (MSA) and PPA, exhibiting intrinsic viscosities as high as 5 dl/g in MSA, and a blue opalescence in solution. Polymerization at temperatures above 225°C caused crystallization and subsequent precipitation to occur. Polymer thus obtained was completely insoluble in MSA and possessed a high degree of crystallinity as demonstrated by x-ray analysis.     

Homogeneous ion-exchange membranes of improved flexibility

Poly(styrenesulfonic acid) ion-exchange membranes having various degrees of porosity and flexibility have been prepared by using aliphatic and aromatic esters of p-styrenesulfonic acid. The membranes formed from the aliphatic ester monomers were found to exhibit an increase in water uptake, permeability, and flexibility with increase in the size of the alcohol group of the ester monomer. With membranes formed from the phenyl and β-naphthyl ester monomers the reverse trend was indicated. The flexibility of the membranes formed from the aromatic ester monomers was much greater than that obtained with the aliphatic esters.     

Propagation kinetics in free-radical polymerizations

The combination of pulsed laser initiated polymerizations (PLP) with analysis of the generated polymer by size-exclusion chromatography (SEC) yields reliable individual rate coefficients for polymerizations of a large number of monomers in bulk and in solution. PLP-SEC experiments carried out in the presence of scCO₂ as a solvent show no unambiguous trend: while a significant reduction of k_p is seen for some monomers, e.g. acrylates, k_p for monomers such as vinyl acetate and styrene is not affected. It is suggested that the influence of CO₂ on acrylate k_p is not a true kinetic effect and that the experimental findings may be understood in terms of the occurrence of local monomer concentrations in the vicinity of the propagating radical. It is discussed that such local monomer concentrations may also contribute to a better understanding of why k_p increases with ester size within the acrylate or within the methacrylate family, and why k_p frequently is influenced by the initiating laser pulse repetition rate.     

Preparation and thermal behavior of poly-p-phenylene diacrylic acid dimethyl ester

The photopolymerization behavior of p-phenylene diacrylic acid dimethyl ester (p-PDA Me) crystal and the thermal behavior of the resultant poly-p-PDA Me were investigated. From the kinetic study of polymerization at various temperatures a topochemical process via a stepwise mechanism was observed. Continuous change from monomer to polymer crystals was demonstrated by x-ray diffraction pattern and DSC analysis. Crystallinity of the reacting phase was maintained at an extremely high degree during the polymerization process in support of monomer crystal lattice control. Thermal study on as-polymerized poly-p-PDA Me crystal confirmed that the thermal reaction was a polymer crystal lattice-controlled depolymerization, which was followed by miscellaneous processes that involved vaporization, sublimation, and deterioration of the oligomeric or monomeric units of p-PDA Me. Thermal stability was dependent on the molecular weight. All the results are compared with those of four-center-type photopolymerization in the crystalline state.     

Photosensitive chiral dopants with high twisting power

Abstract

Quantitative investigations of E,Z-photoisomerization of chiral dopants (?)-2-arylidene-p-menthanones were carried out using solvents of different nature and various liquid crystalline matrices.     

Synthesis and mesomorphic behaviour of novel chiral nematic side chain liquid crystalline polysiloxanes

A series of novel thermotropic side chain liquid crystalline polymers was synthesized by grafting copolymerization of a mesogenic monomer, 4-allyloxybenzoyl-4′?-(4-n-alkylbenzoyl)–p-benzenediol bisate and a chiral monomer, menthyl undecylenate. The mesogenic monomers exhibited nematic threadlike textures during heating and cooling. The polymers showed thermotropic liquid crystalline properties with a broad mesomorphic region over a range of 100°C. The polymers exhibited a cholesteric mesophase with a colourful Grand-Jean texture when the content of chiral units was greater than 15?mol?%; the others exhibited nematic threadlike textures. All of the polymers were thermally stable over 300°C, and most were laevorotatory as the chiral monomer.     

Studies of some bioactive N-p-methacrylamidobenzoic esters

Preparations of four typical bioactive esters of N-p-methacrylamidobenzoic monomers and their reactive polymers as immobilized trypsin carriers are described. N-p-methacrylamidobenzoic active ester monomers containing ? COONB, ? COOSu, ? COOObt, or ? COOBT group can react with an aliphatic amine such as benzylamine at room temperature to give an identical product, N-benzyl-p-methacrylamidobenzamide. However, only monomers with ? COOObt or ? COOBT group can also react with an aromatic amine such as aniline to give N-phenyl-p-methacrylamidobenzamide. These monmoers polymerized readily in solution with azobisisobutyronitrile as free-radical initiator; the polymers were used to immobilize trypsin. Among the four different active esters for the immobilization of trypsin, thE HONB and HOSu active ester showed rather higher bioactivities than the HOObt or HOBT active ester under the same conditions. Both P(MABONB)-trypsin and P(MABOSu)-trypsin matrices possess higher biological activities by about four or three times that of P(MABOObt)-trypsin or P(MABOBT)-trypsin matrices, respectively. It is proposed that these rather high bioactivities may be attributed to the “specific” aminolysis of reactive polymer with ? COONB or ? COOSu active ester group by aliphatic amino substituents.     

Substitution effects on the molecular structures and the longitudinal molecular polarizabilities of all‐trans polyacetylene oligomers of increasing size

AM1 calculations have been performed on all‐trans polyacetylene (PA) oligomers with an increasing number of unit cells to study the effect of donor or acceptor groups capped at opposite ends of PA chains, substituents included in the monomers, substituents' number and position in the monomers, on the molecular structures, and the static longitudinal polarizabilities (α_L) and second‐order hyperpolarizabilities (γ_L). Substitution of CH₃, Cl, or F group at opposite ends of an oligomer results in an increase of α_L and γ_L, but the substitution effects on Δα_L(N) and Δγ_L(N) are very small. The asymptotic limit values are unaffected by the substitution. F substituent included in the monomer of an oligomer enhances the Δα_L(N) and Δγ_L(N) values, especially at large N, but including monomers with CH₃ or Cl substituents substantially reduces the Δα_L(N) and Δγ_L(N) values. We alter the number of F substituents included in the monomers of oligomers and find that including two F substituents in the monomer leads to the larger enhancement of Δγ_L(N). The effect of F substituents' position in the monomers of oligomers on Δα_L and Δγ_L is obvious. The results may be helpful for the design of new materials for applications in nonlinear optics, particularly in the area of poled polymer films. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001