Microspheres by dispersion polymerization of lactides and ϵ-caprolactone

Polyester microspheres were synthesized by the ring-opening polymerization of lactides (racemate or optically active L,L-isomer) and ϵ-caprolactone. Polymerizations were carried out in the 1,4-dioxane-heptane mixed solvents in the presence of poly(dodecyl acrylate)-g-poly(ϵ-caprolactone) (poly(DA-CL)) used as surface-active agent. Polymerizations were initiated with tin(II) 2-ethylhexanoate (lactides), diethylaluminum ethoxide or sodium trimethylsilanolate (ϵ-caprolactone). In the studies of the polymerization of lactides, relations were determined between diameters, the distribution of diameters of synthesized microspheres, and the structure of poly(DA-CL). It was found that it is possible, depending on thermal treatment of microspheres after synthesis, to obtain polylactide microspheres differing in the degree of crystallinity. Kinetics of the dispersion pseudoanionic and anionic polymerizations of ϵ-caprolactone were also investigated and the results of these studies were compared with the data for the corresponding polymerizations of ϵ-caprolactone in solution.     

Polymerizations with contribution of covalent and ionic species

The similarities and dissimilarities between the ring-opening and vinyl cationic polymerizations are discussed for systems with simultaneous presence of covalent and ionic species. The common denominator in comparing kinetics of polymerization of these systems is the comparison of the total times of polymerization with the time elapsing when a given macromolecule is active (i.e. ionic) and inactive (e.g. covalent in cationic vinyl and ring-opening polymerization). In the cationic ring-opening polymerization the reactivation of covalent species proceeds mostly by intramolecular nucleophilic dipole-dipole reaction (conformationally assisted) involving the chain unit adjacent to growing ester chain end. This reaction is fast (e.g. in THF polymerization) and is responsible for covalent ion-pair interconversion. In the cationic vinyl polymerization this path does not exist but covalent species (esters) can be faster ionized by using of the nucleophile, increasing thus the rate of exchange between esters and ions. This process provides one of the possible ways for converting the non-living polymerization into the living-dormant process. The cationic polymerizations are then compared with covalent (pseudoanionic) polymerization of cyclic esters, initiated with covalent metal alkoxides like R₂AlOR' or Al(OR)₃.     

Intra- and intermolecular chain transfer to macromolecules with chain scission. The case of cyclic esters

Chain transfer to macromolecules with chain scission is the most often observed “side” reaction in the polymerization of heterocyclics. In our previous works we analysed quantitatively the intramolecular chain transfer to the own macromolecule (back-biting). This paper gives a general treatment of the kinetics of polymerization with propagation and intermolecular chain transfer to macromolecules, accompanied with chain scission. The numerical solution developed allows determining the k_p/k_tr ratio from the dependence of m̄_w/m̄_n on monomer conversion. This treatment was applied to the polymerization of L,L-lactide and k_p/k_tr ratios were measured for covalent alcoholate active species bearing Al, Fe, Ti, Sm, and La. In this way selectivities of active species (expressed with k_p/k_tr) were for the first time measured and finally correlated with the atomic number of the corresponding metal atoms, related to the strength of the bond involved in the monomer addition.     

Kinetics of ε-caprolactone polymerization on dialkylaluminum alkoxides

Polymerization of ε-caprolactone initiated with dialkylaluminum alkoxides is a living system; formation of macrocyclics is fully depressed. Polymerization initiated with diethylaluminum alkoxide and diisobutylaluminum alkoxide proceeds on monomeric (deaggregated) active species, reversibly aggregating into trimers for the former and into dimers for the latter initiator. Kinetic treatment of this system allowed to determine simultaneously the aggregation-deaggregation equilibrium constant and the rate constant of propagation. Propagation most probably proceeds with insertion (pseudoanionically). Application of amines, complexing the growing species, allowed to break down the aggregates; polymerization became firstorder in initiator. Only secondary amines complexed strongly enough with growing species, the tertiary ones did not affect polymerization, at least up to the ratio 2:1 ([amine]/[initiator]^o). Rate constants of propagation in all of the studied^o systems, whether aggregated or not, have been found to be the same and equal to 0, 04 1·mol⁻¹·s⁻¹ at 25° in THF solvent. This value is approx. 10² times lower than for ion-pairs at these conditions. Moreover, rate constants are almost the same for the growing species …-OAl(C₂H₅)₂ and …-OAl(i-C₄H₉)₂, although aggregation is very much influenced by the size of the alkyl groups.     

L,L‐Lactide and ε‐Caprolactone Block Copolymers by a ‘Poly(L,L‐lactide) Block First’ Route

L,L ‐lactide (LA) and ε‐caprolactone (CL) block copolymers have been prepared by initiating the poly(ε‐caprolactone) (PCL) block growth with living poly(L,L ‐lactide) (PLA*). In the previous attempts to prepare block copolymers this way only random copolyesters were obtained because the PLA* + CL cross‐propagation rate was lower than that of the PLA–CL* + PLA transesterification. The present paper shows that application of Al‐alkoxide active centers that bear bulky diphenolate ligands results in efficient suppression of the transesterification. Thus, the corresponding well‐defined di‐ and triblock copolymers could be prepared.

     

Molecular dynamics in stiff ionene below glass transition

Temperature dependences of proton and fluorine second moments and spin-lattice relaxation time T₁ below glass transition were measured in glassy “I-Do,Pip-Me-BF₄” ionene. The existence of motions of methyl groups and segments linking the cationic centers, namely piperidinium rings and trimethylene groups, for the polymeric part of ionene were established. Isotropic rotation of the counter-ion was evidenced and its limited diffusion suggested. To interpret the proton and fluorine relaxation data, a Davidson-Cole distribution of correlation times was assumed.     

R(4, 5) = 25

The Ramsey number R(4, 5) is defined to be the least positive integer n such that every n-vertex graph contains either a clique of order 4 or an independent set of order 5. With the help of a long computation using novel techniques, we prove that R(4, 5) = 25. © 1995 John Wiley & Sons, Inc.     

On the closure in W1q of the attainable subspace of linear time lag systems

This paper presents the necessary and sufficient condition for the closedness in the topology of W₁^q(T ? 1, T; Rⁿ) of the set of all complete final states x_{[T ? 1,T]} of a linear retarded system, which can be attained by L^p controls. The criterion is fully computable. The analyticity of the matrix coefficients of the system equation is assumed. A number of related results are presented, including a criterion for the closedness of the set of all trajectories of a nondelayed linear system with measurable coefficients.     

2α-Hydroxy-3α-[N-alkyl(aryl)]-pinanoamines. Part II. Synthesis and the nature of some pinanoamines and crystal and molecular structure of 2α-hydroxy-3α-(N-n-butyl)-pinanoamine hydrochloride

Several optically pure representatives of 2-hydroxy-3-[N-alkyl (aryl)] pinanoamines, potential chiral auxiliaries in organic synthesis, were obtained. In addition, a structural examination of 2-hydroxy-3-(N-n-butyl)-pinanoamine hydrochloride was conducted. Results of these studies confirm the structure of the amines obtained and the correctness of the proposed reaction pathway.Crystal data: C₁₂H₂₈NOCl,P2₁/c,a=13.196(1),b=8.562(1),c=14.276(1) Å,=110.41(3)°,R=0.034 for 2046 reflections.Part I,J. Cryst. Spec. Res. (1989)19, 535.     

Interaction of proteins with polymeric latexes

Syntheses, modifications and properties of latexes containing polyacrolein, suitable for the covalent immobilization of proteins, are described. Results of the studies of physical adsorption and covalent attachment of human serum albumin and gamma globulins are discussed. Procedures allowing immobilization of the enzyme, horseradish peroxidase, are described. Changes in protein molecules, owing to their contact with latex particles, are analyzed. Applicability of polyacrolein containing latexes for diagnostic purposes is discussed.