Step-growth polymerization—basics and development of new materials

2004 ◽  
Author(s):  
Zhiqun He ◽  
Eric A . Whale
Keyword(s):  
Molecular Weight ◽  
Degree Of Polymerization ◽  
Average Degree ◽  
Chain Growth ◽  
Side Reactions ◽  
Growth Processes ◽  
Molecular Weights ◽  
Reactive Groups ◽  
Step Growth ◽  
Step Growth Polymerization

Step-growth polymerization is often referred to as condensation polymerization, since often—but by no means always—small molecules such as water are released during the formation of the polymer chains. There are a number of differences in the way polymerization occurs in step-growth polymerization compared to chain-growth processes, and these have marked practical implications. The most obvious difference is that, as the name implies, the polymer chain grows in a step-wise fashion; the initial stage of the reaction involves the conversion of monomers to dimers and from these other lower molecular weight oligomers. It is only as the reaction nears completion that significant quantities of higher molecular weight material can be formed. Thus, in order to obtain effective molecular weights, the reaction must proceed almost to completion, indeed the molecular weight (in terms of the number average degree of polymerization xn) of the polymer can be linked to the extent of reaction (p) using eqn (1). Thus, in the simplest case of a difunctional (AB) monomer, when 50% of the available groups have reacted, the number average degree of polymerization is only 2. The consequence of eqn (1) is that high molecular weights in step-growth polymerizations are associated with highly efficient reactions that do not have side-reactions. Notwithstanding this, the types of molecular weights associated with chain-growth processes are not encountered in these processes (except in the case of monomers with more than two reactive groups where hyper-branched or even cross-linked polymers are possible). There is an additional complication, namely the role of cyclization. Kricheldorf has recently shown that under perfect conditions cyclization is the ultimate fate of any polymerization reaction. Thus, under extremely high conversions the prediction given by eqn (1) would overestimate the actual molecular weights produced. Molecules that undergo step-growth polymerization must have at least two reactive functional groups. If the functionality is greater than this, for example, trifunctional, then hyperbranched polymers or even cross-linked systems can be formed. Commonly, this involves the reaction of two different reactive difunctional monomers.

The formation of cyclic oligomers during step-growth polymerization

2004 ◽  
Author(s):  
Abderrazak Ben Haida ◽  
Philip Hodge
Keyword(s):  
Molecular Weight ◽  
Linear Molecule ◽  
Side Reactions ◽  
Order Process ◽  
Polymer Properties ◽  
End Groups ◽  
Cyclic Oligomers ◽  
Linear Molecules ◽  
Step Growth ◽  
Step Growth Polymerization

Step-growth polymerization is controlled both by the efficiency of the synthetic routes chosen (as indicated in Chapter 4) and by statistical considerations. In particular, the formation of the desired polymer is almost always accompanied by a cyclic oligomer fraction. As the dilution increases, the chances of cyclization also increase, since polymerization is a second-order process involving the reaction between linear species, whereas cyclization, involving the (intramolecular) reaction between the two ends of a linear molecule, is inherently a first-order process. Cyclization is a particular feature of the early stages of a step-growth polymerization (up to extents of reaction of 98–99%), where a proportion of the end groups that react are on the same molecule. Hence, cyclics form. Since the chances of meeting of the end groups decrease rapidly as the distance between them increases, the cyclics are of relatively low molecular weight, that is, they are oligomers. Further reaction leads mainly to linear molecules, although at extremely high conversions the number of end groups is quite small and intramolecular reactions essentially terminate the process, such that it might be expected that all chains ultimately cyclize. Practically though, the levels of conversion necessary to obtain these very large rings are extremely high and difficult to obtain (either by virtue of side reactions, monomer imperfections, or simply the level of viscosity of high molecular weight polymer solutions). What is usually obtained, therefore, is a mixture of cyclics and linear molecules. However, since cyclic oligomers often differ considerably in, for example, solubility compared to their high molar mass linear homologues, separation is often relatively straightforward. The commercial importance of polymers produced by step-growth polymerization gives a particular significance to understanding the nature of such materials. The presence of cyclic oligomers can be detrimental to the polymer properties since their presence could cause problems during processing. For instance, cyclic oligomers of polyethylene terephthalate (PET) tend to migrate to the surface of spun fibres and, under certain conditions, they crystallize to produce a surface ‘bloom’ which interferes with subsequent dyeing. More recently, it is the reverse of cyclization, namely ring-opening polymerization, which has been a particular focus of attention.

General procedures in chain-growth polymerization

2004 ◽  
Author(s):  
Najib Aragrag ◽  
Dario C. Castiglione
Keyword(s):  
Free Radical ◽  
Ring Opening ◽  
Point Of View ◽  
Polymerization Process ◽  
Undergraduate Teaching ◽  
Chain Growth ◽  
Reaction Conditions ◽  
Growth Processes ◽  
Reagent Purity ◽  
Step Growth

This chapter is intended to provide a general introduction to the laboratory techniques used in polymer synthesis, by focusing on some relatively well-known polymerizations that occur by chain-growth processes. In this way some of the more commonly used procedures in polymer chemistry are described. Due to the nature of the intermediates produced, such as free radicals, carbanions, carbocations, together with a range of organometallic species, the techniques often involve handling compounds in the complete absence of oxygen and moisture. Because of this the best results may require quite sophisticated equipment and glassware; however, it is our intention to show that the general procedures are accessible to any reasonably equipped laboratory, and indeed some of the techniques are suitable for use in an undergraduate teaching laboratory. Chain-growth polymerization involves the sequential step-wise addition of monomer to a growing chain. Usually, the monomer is unsaturated, almost always a derivative of ethene, and most commonly vinylic, that is, a monosubstituted ethane, 1 particularly where the growing chain is a free radical. For such monomers, the polymerization process is classified by the way in which polymerization is initiated and thus the nature of the propagating chain, namely anionic, cationic, or free radical; polymerization by coordination catalyst is generally considered separately as the nature of the growing chain-end may be less clear and coordination may bring about a substantial level of control not possible with other methods. Ring-opening polymerizations exhibit many of the features of chain-growth polymerization, but may also show some of the features expected from stepgrowth polymerizations. However, it is probably fair to say that from a practical point of view the techniques involved are rather similar or the same as those used in chain-growth processes and consequently some examples of ring-opening processes are provided here. It is particularly instructive to consider the requirements of chain-growth compared to step-growth processes in terms of the demands for reagent purity and reaction conditions.

Polymer characterization

2004 ◽  
Author(s):  
Ian L. Hosier ◽  
Alun S. Vaughan
Keyword(s):  
Molecular Weight ◽  
Electrode Materials ◽  
Polymeric Materials ◽  
Optical Nonlinearity ◽  
Polymer Science ◽  
New Materials ◽  
Wide Range ◽  
Step Growth ◽  
Step Growth Polymerization ◽  
Increasing Demand

Polymer science is, of course, driven by the desire to produce new materials for new applications. The success of materials such as polyethylene, polypropylene, and polystyrene is such that these materials are manufactured on a huge scale and are indeed ubiquitous. There is still a massive drive to understand these materials and improve their properties in order to meet material requirements; however, increasingly polymers are being applied to a wide range of problems, and certainly in terms of developing new materials there is much more emphasis on control. Such control can be control of molecular weight, for example, the production of polymers with a highly narrow molecular weight distribution by anionic polymerization. The control of polymer architecture extends from block copolymers to other novel architectures such as ladder polymers and dendrimers. Cyclic systems can also be prepared, usually these are lower molecular weight systems, although these also might be expected to be the natural consequence of step-growth polymerization at high conversion. Polymers are used in a wide range of applications, as coatings, as adhesives, as engineering and structural materials, for packaging, and for clothing to name a few. A key feature of the success and versatility of these materials is that it is possible to build in properties by careful design of the (largely) organic molecules from which the chains are built up. For example, rigid aromatic molecules can be used to make high-strength fibres, the most highprofile example of this being Kevlar®; rigid molecules of this type are often made by simple step-growth polymerization and offer particular synthetic challenges as outlined in Chapter 4. There is now an increasing demand for highly specialized materials for use in for example optical and electronic applications and polymers have been singled out as having particular potential in this regard. For example, there is considerable interest in the development of polymers with targeted optical properties such as second-order optical nonlinearity, and in conducting polymers as electrode materials, as a route towards supercapacitors and as electroluminescent materials. Polymeric materials can also be used as an electrolyte in the design of compact batteries.

THE VISCOSITY – MOLECULAR WEIGHT RELATION FOR POLY-levo-2,3-BUTANEDIYL o-PHTHALATE

1948 ◽  
Vol 26b (12) ◽  
pp. 783-797
Author(s):  
R. W. Watson ◽  
N. H. Grace
Keyword(s):  
Molecular Weight ◽  
High Purity ◽  
Molecular Orientation ◽  
Degree Of Polymerization ◽  
Solution Viscosity ◽  
Dilute Solution ◽  
Molecular Weights ◽  
Complex Relation ◽  
End Group ◽  
Long Chain

The inherent viscosities of dilute solutions of acidic polyesters of high purity have been compared with number average molecular weights accurately determined by end-group titration. For unfractionated resins with a degree of polymerization from 2 to 11 [Formula: see text] the viscosity – molecular weight relation is linear in chloroform at 25 °C. Where [Formula: see text], K = 1.923 × 10−5 and β = 0.0176. For fractionated polyesters from DP 5 to 8, K = 1.959 × 10−6 and β = 0.0161. For unfractionated resins with a DP > 11, molecular weights increase more rapidly than inherent viscosities. Above [Formula: see text] for fractionated resins linearity is resumed, and the slope increases. Several attempts have been made to explain this complex relation. Apparently the short chains remain linear, and the formation of anisotropic fibers at a DP close to 100 establishes a degree of molecular orientation in the long-chain superpolyesters. Isomerization of levo-diol to the diastereoisomer during polycondensation is without effect on the dilute solution viscosity of the resulting resin. Preferential degradation of the longer chains is assumed to be partially responsible for the decreasing slope from DP 11 to 65. As yet it has not been possible to assess the roles played by changes in size distribution, and variation in solvation with increasing chain length, but the data point to a curved viscosity – molecular weight relation in chloroform at 25 °C.

Study on the Reaction of TDI and PPG with Organo-Tin Mixed Catalyst

2011 ◽  
Vol 418-420 ◽  
pp. 13-17
Author(s):  
Su Ran Liao ◽  
Yuan Wei ◽  
Yu Qi Zhang ◽  
Meng Zhang ◽  
Gao Fei Feng
Keyword(s):  
Molecular Weight ◽  
Hydrogen Bonding ◽  
Average Molecular Weight ◽  
Polypropylene Glycol ◽  
Number Average Molecular Weight ◽  
Mixed Catalyst ◽  
Back Titration ◽  
Step Growth ◽  
Step Growth Polymerization ◽  
Polymerization Conditions

The study of polyurethanes are of continuing interest due to their excellent physical properties. In this study, the reaction kinetics and polymerization conditions in two-step process of toluene diisocyante (TDI) and polypropylene glycol (PPG) with organo-tin mixed catalyst were investigated by di-n-butylamine back-titration. It was showed that the reaction obeyed the second-order equation of step-growth polymerization, the rate constants of TDI and PPG reaction at 50, 60 and 70°C were 0.0922, 0.3373 and 0.5828 kg•mol-1•min-1，respectively. The activation energy obtained from the result was 71.63 kJ•mol-1. The number average molecular weight (Mn) and molecular-weight distribution (Mw/Mn) of the polyurethane were 45175 and 1.53, respectively, and the content of hydrogen bonding in the N-H group from Fourier transform infrared spectrum (FTIR) was 80.75%, which manifested that the large amount of N-H were present in hydrogen bonding.

scholarly journals New 1,2,3-Triazole Containing PolyestersviaClick Step-Growth Polymerization and Nanoparticles Made of Them

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Tengiz Kantaria ◽  
Temur Kantaria ◽  
Giorgi Titvinidze ◽  
Giuli Otinashvili ◽  
Nino Kupatadze ◽  
...  
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Sodium Azide ◽  
Dicarboxylic Acids ◽  
Solution Concentration ◽  
One Pot ◽  
Bromoacetic Acid ◽  
Aliphatic Polyesters ◽  
Step Growth ◽  
Step Growth Polymerization

High-molecular-weight AA-BB-type aliphatic polyesters were synthesizedviaCu(I)-catalyzed click step-growth polymerization (SGP) following a new synthetic strategy. The synthesis was performed between diyne and diazide monomers in an organic solvent as one pot process using three components and two stages. The dipropargyl esters of dicarboxylic acids (component 1) were used as diyne monomers, di-(bromoacetic acid)-alkylene diesters (component 2) were used as precursors of diazide monomers, and sodium azide (component 3) was used for generating diazide monomers. The SGP was carried out in two steps: at Step  1 dibromoacetates interacted with two moles of sodium azide resulting in diazide monomers which interacted in situ with diyne monomers at Step  2 in the presence of Cu(I) catalyst. A systematic study was done for optimizing the multiparameter click SGP in terms of the solvent, duration of both Step  1 and Step  2, solution concentration, catalyst concentration, catalyst and catalyst activator (ligand) nature, catalyst/ligand mole ratio, and temperature of both steps of the click SGP. As a result, high-molecular-weight (MWup to 74 kDa) elastic film-forming click polyesters were obtained. The new polymers were found suitable for fabricating biodegradable nanoparticles, which are promising as drug delivery containers in nanotherapy.

METAL OXIDE TRIALKYLSILYLOXIDE POLYMERS (POLYTRIALKYLSILOXANOMETALLOXANES): PART I. TITANIUM OXIDE TRIMETHYLSILYLOXIDE POLYMERS

1963 ◽  
Vol 41 (3) ◽  
pp. 629-635 ◽  
Author(s):  
D. C. Bradley ◽  
C. Prevedorou-Demas
Keyword(s):  
Molecular Weight ◽  
Metal Oxide ◽  
Titanium Oxide ◽  
Degree Of Polymerization ◽  
Average Degree ◽  
Degree Of Hydrolysis ◽  
Controlled Conditions

Tetrakis-(trimethylsilyloxy)-titanium Ti(OSiMe3)4 has been hydrolyzed under controlled conditions in dioxane. The initial products of hydrolysis undergo facile disproportionation, e.g. 3Ti2O(OSiMe3)6 → 4Ti(OSiMe3)4 + polymeric Ti2O3(OSiMe3)2. Molecular weight determinations were made on the titanium oxide trimethylsilyloxide polymers (polytrimethylsiloxanotitanoxanes) obtained by thermal disproportionation. Structures have been suggested for the polymers on the basis of the variation of number-average degree of polymerization with the degree of hydrolysis.

scholarly journals Tuning the Properties of High Molecular Weight Chitosans to Develop Full Water Solubility Within a Wide pH Range

2020 ◽  
Author(s):  
Anderson Fiamingo ◽  
Sergio Paulo Campana Filho ◽  
Osvaldo Novais Oliveira Junior
Keyword(s):  
Molecular Weight ◽  
Biomedical Applications ◽  
Random Distribution ◽  
Water Solubility ◽  
Aqueous Media ◽  
Degree Of Polymerization ◽  
Molecular Weights ◽  
H Nmr ◽  
Wide Ph Range ◽  
Ph Range

<p>The preparation of chitosans soluble in physiological conditions has been sought for years, but so far solubility in non-acidic aqueous media has only been achieved at the expense of lowering chitosan molecular weight. In this work, we applied the multistep ultrasound-assisted deacetylation process (USAD process) to β-chitin and obtained extensively deacetylated chitosans with high molecular weights (Mw ≥ 1,000,000 g mol<sup>-1</sup>). The homogeneous <i>N</i>-acetylation of a chitosan sample resulting from three consecutive USAD procedures allowed us to produce chitosans with a high weight average degree of polymerization (DPw ≈ 6,000) and tunable degrees of acetylation (DA from 5 to 80%). <i>N</i>-acetylation was carried out under mild conditions to minimize depolymerization, while preserving a predominantly random distribution of 2-amino-2-deoxy-D-glucopyanose (<i>GlcN</i>) and 2-acetamido-2-deoxy-D-glucopyanose (<i>GlcNAc</i>) units. This close to random distribution, inferred with deconvolution of nuclear magnetic resonance (<sup>1</sup>H NMR) spectra, is considered as responsible for the solubility within a wide pH range. Two of the highly <i>N</i>-acetylated chitosans (DA ≈ 60 % and ≈ 70 %) exhibited full water solubility even at neutral pH, which can expand the biomedical applications of chitosans. </p>

Controlled/‘living’ polymerization methods

2004 ◽  
Author(s):  
Wayne Hayes ◽  
Steve Rannard
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Chain Transfer ◽  
Living Polymerization ◽  
Degree Of Polymerization ◽  
Polymer Chains ◽  
Chain Growth ◽  
Living Polymerizations ◽  
Living Nature

Chain-growth polymerizations such as free-radical polymerizations are characterized by four key processes:(i) initiation, (ii) propagation, (iii) chain transfer, and (iv) termination. If it is possible to minimize the contribution of chain transfer and termination during the polymerization, it is possible to achieve a level of control over the resulting polymer and achieve a predetermined number average molecular weight and a narrow molecular weight distribution (polydispersity). If such an ideal scenario can be created, the number of polymer chains that are produced is equal to the number of initiator groups; the polymerization will proceed until all of the monomer has been consumed and the polymer chain ends will remain active so that further addition of monomer will lead to continued polymerization. This type of polymerization was termed a ‘living’ polymerization by Szwarc in 1956 and represents one of the ultimate goals of synthetic polymer chemists. Flory determined that in the absence of termination, the number of propagating polymer chains must remain constant and that the rate of polymerization for each growing chain must be equal. In this situation, the number average degree of polymerization (DPn) and hence the molecular weight of the polymer can be predicted by simple consideration of the monomer to initiator ratio (see eqns (1) and (2), respectively). Several key criteria are used to elucidate the ‘living’ nature of a polymerization. For a polymerization to be considered ‘living’, the rate of initiation must exceed the rate of propagation. Therefore, all the propagating polymer chains are formed simultaneously and grow at the same rate. If this situation did not occur, the first chains formed would be longer than those initiated later and the molecular weight distribution of the propagating chains would broaden. In addition, an ideal ‘living’ or ‘immortal’ polymerization must not exhibit any termination of the propagating polymer chains over the lifetime of the reaction. Consequently, ‘living’ polymerizations are characterized by very narrow molecular weight distributions (Mw/Mn < 1.2).

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