Journal of Polymer Science: Polymer Symposia最新文献

Two new methods of predicting free radical polymerizability of allyl monomers have been developed. MINDO/3 calculations of eigenvalues for the C—H bond a to the atlyl substituent allow comparison of relative bond strengths. Monomers known to undergo degradative chain transfer display more positive eigenvalues correlating with weaker α-C—H bonds. Polymerizable monomers have more negative eigenvalues and stronger α-C—H bonds. The latter possess strongly polarized or protonated substituents not capable of resonance stabilization of a chain-terminating allyl radical. The inductive effect of such substituents on the ¹³C NMR peaks of the vinyl carbons is the basis for the empirical spectroscopic method. Allyl compounds display β-carbon peaks farther downfield than the γ-carbon peaks. Polymerizable monomers generally have β peaks shifted upfield and γ peaks shifted downfield from those of poor monomers. This effect brings the two peaks closer together in the spectrum. Thus, the smaller the Δδ value (δ_β − δ_γ), the more likely the monomer is to polymerize well. Monomers with intermediate eigenvalues or Δδ values may polymerize with difficulty or only under special conditions. Combined use of the theoretical and empirical techniques can allow prediction of inherent polymerizability and can facilitate evaluation of reaction media most favorable to polymer formation.

Equilibrium phase studies were carried out on the ternary system of polystyrene-poly butadiene-toluene at 23°C and 1 atm. Narrow and broad molecular weight distribution (MWD) samples of polystyrene and polybutadiene were employed, and their binodal curves were established. Expressions were derived to calculate X2i values for both monodisperse (narrow MWD) and polydisperse polymers. Typical interaction parameters determined from (lie experimental data are presented. It is concluded that monodisperse expressions can be used for polydisperse polymers using the number-average molecular weight.

Three copolymers of poly(acrylic acid-co-vinylamine) containing 12% (SP12). 30% (SP30), and 52% (SP52) amino groups were synthesized from poly(acrylic acid) by means of the Schmidt reaction. These copolymers were analyzed by C-13 NMR and the results compared wiih the previously analyzed homopolymers. The various comonomer sequence distributions were identified by means of peak areas. It was determined thai (1) the reactivity was not significantly influenced by the triad taciicity of the parent poly(acrylic acid), (2) the final copolymer is characterized by an essentially alternating sequence, and (3) there is extensive lactam formation between neighboring carboxyl and amino groups. In terms of nearest neighbor effects, the relative rales of amine formation are k₁/k₀ ≈ 0.3 and k₂/k₀ ≈ 0. A C-13 NMR pH titration of SPI2 showed that the carboxyl group with a neighboring amino group is more acidic man a carboxyl group flanked by two carboxyl groups.

Dipheny-2-pyridylmethyl methacrylate (D2PyMA) was anionically polymerized with several organolithium complexes of chiral ligands such as (-)-sparteine (Sp), (S,S)-( + )- and (R,R)-(-)-2,3-dimethoxy-1,4-bis(dimethylamino)butane [(+)- and (- )-DDB], (S)-(-)-1 - methyl-2-(piperi-dinomethyl)pyrrolidine (MPP), (S,S)-( + )-3,4-dimethoxy-N-(2-(dimethylamino)ethyl)pyrrolidine (DDEP), and (S,S)-(+ )-N-benzyl-3,4-dimethoxypyrrolidine (BDP) in toluene at low temperature. Sp complexes gave a polymer of low optical activity. DDB was a better chiral ligand, and its complex, particularly the complex with N,N'-diphenylethylenediamine monolithium amide (DPEDA-Li), was effective in preparing a polymer of high optical rotation. A THF-soluble portion of the polymer obtained with (-)-DDB-DPEDA-Li showed [α]^25/365 about - 1400°, which was comparable to that of poly(triphenylmethyl methacrylate) (PTrMA) with pure one-handed helical structure. However, in the polymerization with DDB-DPEDA-Li, optical rotation of the polymer depended greatly on polymerization conditions, such as monomer and initiator concentrations, reaction temperature, and polar additives. Fractionation by THF and/or gel permeation chromatography of the obtained polymers revealed that poly(diphenyl-2-pyridylmethyl methacrylate) (PD2PyMA) consisted of a mixture of (+)- and (-)- polymers which probably were not enantiomeric to each other. DDEP-DPEDA-Li and DDEP-fluorenyllithium complexes were also efficient chiral initiators that gave polymer of the same or higher optical rotation in comparison with DDB complexes. The optical rotation of PD2PyMA in CHCl₃-2,2,2-trifluoroethanol (90:10) slowly changed with time. Optically active PD2PyMA coated on macroporous silica gel resolved racemic compounds as a chiral stationary phase for high-performance liquid chromatography (HPLC).

We have carried out an in-depth study of the alkali metal ion binding characteristics of a model ionophoric macromolecule, poly(4′-vinylbenzo 18-crown-6), P18C6. Ion selective electrode potentiometry has been utilized to determine stability constants for complexstion of K⁺, Na⁺, and Cs⁺ to P18C6 in methanol/water (80/20)_w. Our results show that (he intrinsic binding constants, K_n, of P18C6 towards K⁺C1⁻ and Na⁺Cl⁻ are identical to that of the monomeric analog, benzo-18-crown-6.

In the absence of supporting electrolyte, the apparent binding constant of benzo-18-crown-6 is greater than (hat of P18C6. At low tonic strength the binding of K⁺ to P18C6 depends strongly on the fraction of crown moieties bound. P18C6 binds K⁺C1⁻ and Na⁺Cl⁻ with a stoichiometry of 2 mol of crown per mole of M⁺ . This binding, however, is not sandwich mode. The binding of K⁺Cl⁻, K⁺NO₃ and K⁺ClO₄⁻ to P18C6 in methanol/water differs significantly, with K_N(K⁺ClO₄⁻1 being nearly an order of magnitude greater than K_N(K⁺Cl⁻). Cs⁺ is bound to P1SC6 with a stoichiometry of ∼3 mol of crown per mole of Cs⁺, and the ion is bound cooperatively in a sandwich geometry.

The anionic polymerization of α,α-disubstituted four-membered lactams (3-hexyl-3-methyl-2-azetidinone, I and 3-butyl-3-methyl-2-azetidinone, II) was found to follow a more complicated kinetics than could be expected. The apparent order of polymerization with respect to the monomer was not constant and increased from zero at the beginning of polymerization to two towards its end. Therefore, it is justified to correlate only the initial rate of polymerization with the concentrations of reactants.

Racemic or chiral bifunctional oligoethers of the type H—(O—CH(CH₃)—CH₂—)_n—Cl, n = 4-10, have been prepared by reacting racemic or optically active propylene oxide with teiraphenyl porphyrin (TPPH₂)—AlEt₂Cl initiator sysfem. The synthesized products were characterized by IR, elemental analysis, VPO, GPC, and ¹H and ¹³CNMR techniques. The oligomers purified by fractional distillation exhibit narrow MW distributions (M̄_w/M̄_n ≈ 1.03). Chiroptical properties of the oligomers and their derivatives were examined and compared with those of high molecular weight polyfpropylene oxide). Different possibilities of applicadons of these oligomers are presently under study.

Both conventional and inverse emulsion polymerization comprise the emulsification of an immiscible monomer in a continuous medium followed by polymerization with a free radical initiator to give a colloidal sol of polymer particles. Both processes give “emulsion polymerization kinetics,” i.e., a proportionality of both the polymerization rate and polymer molecular weight to the number of particles instead of the inverse relationship between rate and molecular weight observed for mass, solution, and suspension polymerization. The emulsion polymerization process can be divided into particle nucleation and particle growth stages and can be carried out using batch, semicontinuous, or continuous processes. Seeded emulsion polymerization can be used to avoid the particle nucleation stage in all three processes. The many mechanisms proposed for the initiation of emulsion polymerization can be divided into four categories according to the locus of particle initiation: (i) monomer-swollen micelles; (ii) adsorbed emulsifier layer; (iii) aqueous phase; (iv) monomer droplets. These general principles are applied to: (i) the preparation of monodisperse latexes by seeded emulsion polymerization; (ii) the locus of particle initiation for various monomers and initiators; (iii) emulsion copolymerization; (iv) core-shell emulsion copolymerization; (v) polymerization in fine monomer droplets; (vi) inverse emulsion polymerization.

We discuss the results of Monte Carlo simulations of a recent kinetic percolation model applicable to free radical initiated copolymerization of bifunctional and tetrafunctional units in the presence of a solvent. We find that the critical exponent for gelation and the critical amplitudes are unchanged by the inclusion of solvent and mobility. We also obtain relations for the dependence of the critical conversion and the maximum value of the suscepiibility on the fraction of tetrafunctional monomers, solvent concentration, and initiator concentration.

The statistical basis of the entropic repulsion of dissolved random-flight polymer chains from impenetrable passive barriers is described. The application of these ideas to the partial exclusion of linear and branched polymer chains from micropores and to the polymer concentration profile near a barrier is reviewed with emphasis on the mean projection of the chain as a measure of the exclusion effect.