Low Molecular Weight Analogues Research Articles

Kinetics of complex formation of tetracyanoethylene with poly‐N‐vinyl carbazole and polynaphthyl methacrylate and the corresponding low molecular weight donors

AbstractThe complex formation of tetracyanoethylene with poly‐N‐vinyl carbazole, polynaphthyl methacrylate and the corresponding low molecular weight analogues, N‐ethylcarbazole and naphthyl methacrylate resp., in chloroform solution proceeds at a considerable rate and is accompanied by change in the absorption spectra in the visible region.The rates of donor‐acceptor complex formation in mole ratios of 1 : 1 at room temperature are studied by means of spectrophotometric “stopped‐flow” technique. The apparent rate constants of complex formation for all complexes are of the order of 104l · mole−1 · sec−1. Their values do not depend on the molecular weight of the donors. The apparent rate constants of the formation of tetracyanoethylene complexes of poly‐N‐vinyl carbazole and N‐ethylcarbazole are slightly greater than those of polynaphthyl methacrylate and naphthyl methacrylate, which shows that the rate of complex formation is influenced by the electron donating capacity of the complex forming units.

The thermal decomposition of hydrocarbon copolymers—II. Products of copolymers incorporating α-methyl styrene

The products of the thermal decomposition of a series of copolymers of structure ▪ with n = 1, 3, 4, 5, 6, and 10 have been investigated. The volatile product consists largely of low molecular weight analogues of the parent polymer with α-methyl styrene as the major constituent of the volatile liquid fraction. Mechanisms are postulated to account for the formation of most of the volatile products; the importance of secondary chemical reactions is emphasized.

Equilibrium ring concentrations and the statistical conformations of polymer chains: Part 4. Calculation of cyclic trimer content of poly(ethylene terephthalate)

The equilibrium concentration of cyclic trimer in poly(ethylene terephthalate) ( pet) melts is calculated by the Jacobson and Stockmayer theory using rotational isomeric state models to describe the conformational statistics of the corresponding linear chains. The Williams and Flory rotational isomeric state model of pet is used for the calculations, together with a model which incorporates structural information made available by a recent study of internal rotation in ethyl formate. This latter model takes into account all the intramolecular interactions within monomeric units by considering interactions that depend on rotations about monads, diads and triads of skeletal bonds. The models define 26244 discrete conformations for the acyclic trimer (CO.C 6H 4.CO.O.CH 2.CH 2.O) 3. The probability that such a chain will intramolecularly cyclize is calculated by computing the total number of conformations that have terminal atoms in close proximity for ring closure, each conformation being accorded a statistical weight based on molecular structural information relating to low molecular weight analogues and on estimates of the steric and electrostatic attractions and repulsions between non-bonded atoms of the chain. The rotational isomeric state models predict the cyclic trimer content of pet melts at 570 K to be 0.1–0.5% by weight (compared with the experimental value of 1·4%) and they give values of the ratio [ 〈r 2〉 0 M ] ∞ of the unperturbed mean-square end-to-end distance of pet to its molecular weight of 0.9–0.6Å 2(g mol.wt.) −1 at 303K (compared with the experimental value of 1·0).

Synthetic polymer analogues of enzymes characterized by esterase activity

IT ~AS been reported [1, 2] that poly-4-vinylpyridines (poly-4-VP), partially alkylated with 2-(2'-ehloroethyl)pyridine or benzyl chloride, exert high catalytic activity in hydrolysis of the ester bond, which is 2.5-3.5 times greater than the catalytic activity of low molecular weight analogues. We explained this by the formation in macromolecular spheres of local cavities of polymer catalysts (PC), each of which incorporates a nueleophile (unalkylated pyridine ring) and is surrounded by hydrophobie groups, which have an increased affinity for the substrate. This paper describes results of detailed investigation of the relations of the action of similar PC containing different substituents: methyl, ethyl, propyl, isopropyl, butyl, isobutyl and isoamyl. As is well known, some of these substituents are contained in a-aminoacids (valine, alanine, leucine) and are often situated in direct proximity to active enzyme groups.

Relative Reactivities of Elements of Polymer Chains, Determined by Their Transformation in Solution, Initiated by Dicumyl Peroxide

AbstractThe kinetics of the degradation of polyisobutylene and polystyrene initiated by dicumyl peroxide in the undiluted state and in solvents of different composition has been studied. The degradation process was experimentally investigated by a viscosimetric method. The kinetic expression of the degradation carried out in such a way gives also the relative values of the rates of reaction of hydrogen atoms in polymers with radicals of the peroxide used, determined for polyisobutylene, polyethylene, polystyrene, and n‐heptane. The reactivities of CH3, CH2, and CH groups, calculated from the results, are in the ratio 1:6:17; the methine hydrogens of the polystyrene benzylidene groups are three times more reactive than hydrogens of the analogous ethylidene groups of polypropylene. The reactivity of the low molecular weight model substance, n‐heptane, is about 30% greater than would be expected from the sum of the reactivities of its elements determined from polymers. This fact suggests that the ability of macromolecules to enter into substitution reactions with free radicals is less than that of low molecular weight analogues.

Nuclear magnetic resonance studies of polymer solutions. I. Poly(methyl methacrylates)

AbstractThe microscopic interactions of solvent with the diastereoisomeric units of isotactic and syndiotactic poly(methyl methacrylate) have been studied by high‐resolution nuclear magnetic resonance. The changes in chemical shifts in various solvents were compared with those of low molecular weight analogs, methyl acetate, and methyl propionate. These changes are caused mainly by the ring‐current effect, which has been found to be larger for the low molecular weight analogs than for the polymer. This is especially true when the protons on the polymer backbone are compared with the corresponding ones in the low molecular weight compounds. As one changes from a chloroform solvent to an aromatic solvent, the displacements of the chemical shifts of the polymer can be expressed as percentages of the corresponding shifts of methyl acetate. For syndiotactic poly(methyl methacrylate) in chlorobenzene, benzene, and α‐chloronaphthalene, respectively, the percentages are 82, 93, 75 for ester protons; 35, 29, 17 for the backbone methylene protons; and 18, 6.7, 0 for the backbone α‐methyl protons. For isotactic poly(methyl methacrylate) in chlorobenzene and benzene, respectively, the percentages are 71, 76 for the ester protons; 41, 38 for the backbone methylene protons; and 41, 32 for the backbone α‐methyl protons. These results are discussed in terms of the local stereochemistry of the polymer systems. The exploitation of procedures of this sort in revealing details of polymer behavior in solution indicates dramatic possibilities for future investigations.

Cationic and free‐radical polymerization of optically active 1‐olefins

AbstractThe AlCl3‐initiated cationic polymerization of optically active 1‐olefins yields polymers of varying optical rotatory power. Polymers of (+)‐3‐methyl‐1‐pentene and (−)‐4‐methyl‐1‐hexene prepared between −78 and −55°C. in CH2Cl2 or n‐heptane are almost completely optically inactive. Under identical reaction conditions (+)‐5‐methyl‐1‐heptene gives polymers of significant optical rotatory power. Alternating SO2copolymers of the same olefins, formed in reactions which proceed through free‐radical intermediates, yield optically active products with specific rotations similar to those of low molecular weight analogs. These results are consistent with a cationic polymerization mechanism in which the growing chain undergoes intramolecular hydride shift and the asymmetric carbon atoms are converted into carbonium ions. The data also provide evidence for the lack of rearrangement in free‐radical polymerization. By comparing the specific rotations of the cationic and free‐radical polymers, the extent of rearrangement during cationic polymerization can be estimated. The calculations show that the 1,2‐polymer in cationic poly‐3‐methyl‐1‐pentene is less than 2%, the sum of 1,2‐ and 1,3‐polymer in cationic poly‐4‐methyl‐1‐hexene is less than 4%, and the sum of 1,2‐, 1,3‐, and 1,4‐polymer in cationic poly‐5‐methyl‐1‐heptene is 14–20%.

Mean Activity Coefficient of Polyelectrolytes. III. Measurements of Hydrochlorides of Polyethylenimine and Its Low Molecular Weight Analogs1

Mean Activity Coefficient of Polyelectrolytes. III. Measurements of Hydrochlorides of Polyethylenimine and Its Low Molecular Weight Analogs¹

Structural Characterization of Natural Rubber Vulcanizates

Abstract The three principal approaches used in the structural resolution of sulfur vulcanizates of natural rubber are described and exemplified by their application to three systems: an unaccelerated sulfur system and two mercaptobenzothiazole (MBT)-accelerated sulfur systems, one of which makes very efficient use and the other inefficient use of the sulfur crosslinking. The ultimate aim of such studies is to relate vulcanizate structure to the physical properties and aging behavior of the vulcanizates during service. The first approach, which gives an overall measure of the structural complexity of the network, involves the determination of the crosslinking efficiency, (E), that is, the number of sulfur atoms combined in the network for each physically-effective, chemical crosslink formed. Crosslinking efficiencies of networks vary with increasing cure time from ca. 6-1.16 for the efficient-MBT system to 55-40 for the unaccelerated sulfur system. Between these extremes, it is found that variations of reactant concentrations and of temperature and time of cure lead to large variations in crosslinking efficiency and therefore of network complexity. Related work not reported here indicates that the latter features are also dependent on the type of accelerator used. More detailed information on network structure is obtained from analysis of reaction products of low molecular weight analogs of natural rubber with the vulcanizing agent and ancillary ingredients. Such studies reveal that the poor efficiency of the unaccelerated sulfur system is due to sulfur being combined wastefully in (i) long polysulfidic crosslinks of alkenyl t-alkyl structure, (ii) vicinal crosslinks which behave physically as one crosslink, and (iii) a large proportion of cyclic monosulfide groups which constitute an important modification of the main rubber chains. Conjugated triene groups, cis, trans-isomerized isoprene units, and main chain scission represent other possible types of modification. In contrast with this complex network, efficiently-cured MBT-accelerated sulfur vulcanizates contain, at early stages of cure, polysulfidic crosslinks of dialkenyl type which decrease with time to mainly monosulfide crosslinks; conjugated triene units are also present but little or no cyclic monosulfides, vicinal crosslinks, or main chain scission. Other accelerated sulfur vulcanizates possess structures intermediate between these two extremes, except that the crosslinks are generally of dialkenyl type and pendent groups terminated by accelerator residues constitute an additional possible type of modification. Knowledge from model olefin studies of the different types of sulfurated groups present in vulcanizates has led to the development of the third experimental approach, i.e. use of chemical reagents (‘chemical probes’) to determine specific groups. This approach is exemplified by reaction with actual vulcanizates of triphenylphosphine which removes sulfur atoms in excess of one or two from polysulfides; as cure proceeds in unaccelerated sulfur vulcanization, the proportion of combined sulfur present in cyclic sulfide groups rises from 75% to 95% while the average number of sulfur atoms in each crosslink unit falls from 12–13 to 2–4. Comparable data for the efficient MBT system confirm the essential simplicity of the network in this case.

Molecular motion in polystyrene and some substituted polystyrenes

AbstractProton magnetic resonance spectra of nine substituted polystyrenes: polymers of o‐methyl, m‐methyl, p‐methyl, p‐chloro‐, 2,4‐dimethyl‐, α,β,β′‐trideutero‐, β‐ deutero‐, 2,6‐dimethyl‐4‐tert‐butyl‐, and p‐tert‐butylstyrene, in addition to five polystyrene samples differing in molecular weight (M̄n's from 1.25 × 105 to ∼35 × 105) or tacticity have been obtained at temperatures from 77 to above 400°Kg. Measurements have also been made on p‐tert‐butyltoluene, 2,4‐dimethylstyrene, and 2,6‐dimethyl‐4‐tert‐butylstyrene. All polymers studied were found to exhibit single‐component derivative line shapes and to undergo rapid motional narrowing with increasing temperature in the region of the glass transition; in this region the line width for atactic polystyrene was found to be essentially independent of molecular weight. At lower temperatures a gradual line narrowing effect was also observed for some of the polymers, even near 77°K., and is attributed to limited phenyl or substituted phenyl group oscillation. This effect was apparent for polystyrene, poly‐α,β,β′‐trideutero‐, poly‐β‐deutero‐ poly‐p‐chloro, and poly‐p‐methylstyrene, less apparent for the o‐ and m‐methyl compounds and the p‐tert‐butyl‐substituted polymer, and absent for the 2,4‐dimethyl and the 2,6‐dimethyl‐4‐tert‐butyl polymers. By a comparison of experimental second moments with approximate ones obtained from theory, it is concluded that rotation of all methyl groups attached directly to benzene ring for all polymers studied is taking place at 77°K. For both p‐tert‐butylsubstituted polymers and the low molecular weight analogs, a motional narrowing process occurs in the ≤77° to 150°K. region, and for all but 2,6‐dimethyl‐4‐tert‐butylstyrene this is attributed to rotation of the methyl groups in the tert‐butyl part of the molecule; for the latter compound, onset of rotation of one of the methyl groups attached directly to the ring in addition to the methyl in the tert‐butyl part is responsible for the line narrowing. The contributions of various proton interactions to the total second moment of polystyrene and its derivatives are discussed.

Ionic grafting

AbstractCation initiated polymerizations of various monomers were carried out in the presence of several polystyrene derivatives in an effort to obtain graft copolymers. No success was achieved in grafting with vinyl butyl ether, vinyl ethyl ether, isobutylene, N‐vinylpyrrolidone, or pinene under the particular experimental conditions employed. In the experiments involving vinyl n‐butyl ether, the presence of the various polystyrenes appeared to have no effect on the polymerization of this monomer or on the DP of the polyvinylbutyl ethers obtained. However, when styrene was polymerized in the presence of poly‐p‐methoxystyrene (PPMS), graft copolymer was readily obtained. The success of this reaction demonstrates the feasibility of preparing graft copolymers by an ionic mechanism and yields additional proof of an ionic chain transfer reaction with aromatic species in which the latter are incorporated into the chain. Data obtained on the styrene‐PPMS system are discussed in terms of a simple kinetic scheme. The molecular termination constant of PPMS was found to be only 1/67th of that of p‐methylanisole, a low molecular weight analogue. The low chain transfer effectiveness of PPMS is believed to be due to constraints placed on the availability of the transfer sites which are linked in a polymeric chain.