Stanislaw Penczek

Kinetics and mechanism of cyclic esters polymerization initiated with Tin(II) octoate. 3. Polymerization of L, L-dilactide

Following our previous papers on the mechanism of cyclic esters polymerization induced by tin(II) octoate (Sn(Oct) 2 ) and particularly papers on ∈-caprolactone (CL), the present work shows that L,L-dilactide/Sn(Oct)2 does not differ mechanistically from the CL/Sn(Oct) 2 system. Sn atoms bonded through alkoxide groups to macromolecules were also observed by MALDI-TOF mass spectrometry. Formation of the actual initiator from Sn(Oct) 2 and a hydroxy group-containing compound (ROH) was envisaged by kinetic arguments. The appropriate experiments were carried out to show that some mechanisms put forward during the past few decades by several research groups were not sufficiently substantiated. Eventually, we conclude that L,L-dilactide/Sn(Oct)2 polymerization proceeds by simple monomer insertion into the ...-Sn-OR bond, reversibly formed in the reaction ...-SnOct + ROH ⇄ ...-Sn-OR + OctH, where ROH is either the low molar mass co-initiator (an alcohol, hydroxy acid, or H 2 O) or a macromolecule fitted with a hydroxy end group. These interconversions take place throughout the whole polymerization process. Sn(Oct) 2 itself does not play an active role in the polymerization.

Kinetics and mechanism of cyclic esters polymerization initiated with tin(II) octoate, 1. Polymerization of ε‐caprolactone

Following our previous papers on the mechanism of cyclic esters polymerization induced by tin(II) octoate (Sn(Oct)2) and particularly papers on e-caprolactone (CL), the present work shows that l,l-dilactide/Sn(Oct)2 does not differ mechanistically from the CL/Sn(Oct)2 system. Sn atoms bonded through alkoxide groups to macromolecules were also observed by MALDI−TOF mass spectrometry. Formation of the actual initiator from Sn(Oct)2 and a hydroxy group-containing compound (ROH) was envisaged by kinetic arguments. The appropriate experiments were carried out to show that some “mechanisms” put forward during the past few decades by several research groups were not sufficiently substantiated. Eventually, we conclude that l,l-dilactide/Sn(Oct)2 polymerization proceeds by simple monomer insertion into the ...−Sn−OR bond, reversibly formed in the reaction ...−SnOct + ROH ⇌ ...−Sn−OR + OctH, where ROH is either the low molar mass co-initiator (an alcohol, hydroxy acid, or H2O) or a macromolecule fitted with a hydro...

Cationic activated monomer polymerization of heterocyclic monomers

Abstract In the first part of this review the meaning of activation is discussed and selected examples of polymerizaton processes in which activation of monomer is required prior to actual propagation are presented. In some systems, activation of monomer proceeds with such a strong interaction between an activator and monomer that a new chemical entity is derived from the monomer. To describe the mechanism of such a process, the term ‘Activated Monomer Mechanism’ has been coined. The main part of the review is concerned with cationic Activated Monomer (AM) polymerization of cyclic ethers. In this process, cyclic ether is activated by formation of protonated species in the presence of a protic acid. Reaction of the protonated (activated) cyclic ether with hydroxyl group containing compounds leads to ring opening reforming the hydroxyl group. Several repetitions of such a reaction constitute a chain process. Thus, in AM polymerization of cyclic ethers hydroxyl group containing compounds act as initiator, protic acid is a catalyst, growing chain end is fitted with hydroxyl group and the charged species is a protonated monomer. The important feature of such a polymerization mechanism is that due to the absence of charged species at the growing chain end, back-biting leading to the formation of macrocyclics can be eliminated. The mechanism and kinetics of AM polymerization of cyclic ethers is discussed and the approach allowing one to determine the rate constant for propagation involving activated monomer species is outlined. The application of the AM concept to the copolymerization of cyclic ethers as well as to the polymerization of monomers containing both initiating (hydroxyl groups) and propagating (cyclic ether) functions within one molecule are presented. In the subsequent parts of the review, examples of cationic AM polymerization of other types of heterocyclic monomers, including cyclic acetals, cyclic esters (lactones), amines and amides (lactams), are given. Finally, the polyaddition of oxiranes to derivatives of phosphoric acid is discussed. Although this system does not conform to the AM polymerization scheme, it bears formal resemblance to earlier systems in such a sense that the activation of the cyclic ether is required for the reaction to occur.

Definitions of terms relating to the structure and processing of sols, gels, networks, and inorganic-organic hybrid materials (IUPAC Recommendations 2007)

This document defines terms related to the structure and processing of inorganic, polymeric, and inorganic-organic hybrid materials from precursors, through gels to solid products. It is divided into four sections - precursors, gels, solids, and processes - and the terms have been restricted to those most commonly encountered. For the sake of completeness and where they are already satisfactorily defined for the scope of this document, terms from other IUPAC publications have been used. Otherwise, the terms and their definitions have been assembled in consultation with experts in the relevant fields. The definitions are intended to assist the reader who is unfamiliar with sol-gel processing, ceramization, and related technologies and materials, and to serve as a guide to the use of standard terminology by those researching in these areas.

Branched polyether with multiple primary hydroxyl groups: polymerization of 3-ethyl-3-hydroxymethyloxetane

Cationic polymerization of 3-ethyl-3-hydroxymethyloxetane gives branched, soluble macromolecules with multiple glycolic end groups. There are approximately 3–4 “normal” units per one branched unit.

Terminology of polymers and polymerization processes in dispersed systems (IUPAC Recommendations 2011)

A large group of industrially important polymerization processes is carried out in dispersed systems. These processes differ with respect to their physical nature, mechanism of particle formation, particle morphology, size, charge, types of interparticle interactions, and many other aspects. Polymer dispersions, and polymers derived from polymerization in dispersed systems, are used in diverse areas such as paints, adhesives, microelectronics, medicine, cosmetics, biotechnology, and others. Frequently, the same names are used for different processes and products or different names are used for the same processes and products. The document contains a list of recommended terms and definitions necessary for the unambiguous description of processes, products, parameters, and characteristic features relevant to polymers in dispersed systems.

Block and random copolymers of ε-caprolactone

Abstract Conditions of the living homopolymerization of e-caprolactone (CL), lactides (LA), and of the homo-oligomerization of γ-butyrolactone (BL) are briefly described. Then block and random copolymerizations of CL with LA are shortly reviewed. The microstructure of the resulting copolyesters in relation to some peculiarities of these processes is discussed in more detail. It is also shown that the otherwise ‘non-polymerizable’ BL does form high molecular weight copolymers with CL, containing up to 50 mol% repeating units derived from BL. Their molecular weight is controlled by the concentrations of the consumed comonomers and the starting concentration of the initiator. NMR and DSC data indicate the random structure of copolymers. TGA traces of the BL/CL copolymers show that the presence of the γ-oxybutyryl repeating units randomly distributed within the poly(CL) chains improves the thermal stability of the latter.

Double‐Hydrophilic Block Copolymers with Monophosphate Ester Moieties as Crystal Growth Modifiers of CaCO3

The synthesis of double-hydrophilic block copolymers with a poly(ethylene glycol) block (PEG) and a block with pendant monophosphate ester groups based on a hydroxylated polybutadiene block (poly[2-(2- hydroxy ethyl)ethylene] (PHEE) with variable degrees of phosphate substitution (up to 40%) is described. It is shown that these block copolymers are very efficient scale inhibitors for CaCO 3 . The efficiency of these polymers is compared with block copolymers with an ionic block based on phosphorylated polyglycidol (PGL) with phosphorylation degrees up to 100%. The phosphorylated polyglycidols were also used to modify the morphology of CaCO 3 crystals. Instead of the typical rhombohedral calcite single crystals, superstructures of nanometer-sized particles are formed in the presence of these block copolymers when two different techniques were used: the fast double-jet technique and the slow Kitano-method. In the double-jet method, only spherical superstructures are obtained, whereas for the slower growth region covered by the Kitano method, complex cone-like or flower-like superstructures are formed.

On the mechanism of polymerization of cyclic esters induced by tin(II) octoate

Mechanism of initiation and propagation in polymerization of ϵ-caprolactone and L,L-dilactide induced with tin(II) octoate (Sn(Oct)2) and Sn(Oct)2/n-butyl alcohol system is presented. Tin(II) alkoxide bond formation is required in reaction of Sn(Oct)2 with hydroxyl group containing compound to form a true initiator. Then tin(II) alkoxide end group is an active centre in the further propagation.

Cationic ring-opening polymerization (CROP) major mechanistic phenomena

A number of todays accepted basic viewpoints related to cationic ring-opening polymerizations (CROP) were a matter of vivid disagreements between various research groups in the past. These controversies are described in this article and reasons of some differencies in opinions are explained. It is shown in which way we learned that polyacetals are not exclusively cyclic (as it was assumed), why CROP ions and ion pairs have similar reactivities, and why it was necessary to propose that CROP proceeds at certain conditions by Activated Monomer Mechanism. Among other subtle kinetic problems, application of the dynamic NMR and “temperature jump” techniques in determining rate constants of active species interconversions are discussed.