IPNs, synthesis

In order to provide a better basis for comparison, the IPN synthesis will be described first. 

Figure 4. Stress-strain curves for SIN S containing 40% castor oil elastomer (21). Discontinuous curve adapted from sequential IPN synthesis (1) COPEN (2) COPEUN (3) COPUN (4) 40/60 COPEN/PSN (S) 40/60 COPEUN/PSN (6) 40/60 COPUN/PSN (7) 40/60 COPUN/PSN...

We synthesized [13] IPNs composed of polyethylene oxide) (PEO) (polymer A) and poly(N-acryloylpyrrolidine) (PAPy) (polymer B). The IPN was synthesized by simultaneous crosslinked polymerization of APy and PEO. The overall reaction scheme for IPN synthesis by radical polymerization for APy (polymer A) and addition polymerization for PEO (polymer B) is shown in Fig. 3. This pair shows simple coacervation behavior in water. The IPN is constructed from PEO and PAPy networks as shown in Fig. 4. Chemically independent networks of polymer A and polymer B are interlocked and macroscopic phase separation in water swollen states is avoided. 

Semi-interpenetrating Polymer Network (Semi-IPN) Synthesis ... 

As can be seen from all of these works, sequential IPNs have been extensively used with silicone with various crosslinking reactions and polymers. As a result, attention must be paid to the influence of processing conditions, of the chemical nature of components (silicone and the other polymer), of the evolution of the material at each step of the IPN synthesis etc. Depending on the mastering of these parameters, reactivity, morphology and entanglement can be controlled and consequently targeted properties can be reached. 

FichetO et al. (2005) Polydimethylsiloxane-cellulose acetate butyrate IPN synthesis and kinetic study, Part I. Polymer 46 37-47... 

Abstract This article summarizes a large amount of work carried out in our laboratory on polysiloxane based Interpenetrating Polymer Networks (IPNs). First, a polydimethylsiloxane (PDMS) network has been combined with a cellulose acetate butyrate (CAB) network in order to improve its mechanical properties. Second, a PDMS network was combined with a fluorinated polymer network. Thanks to a perfect control of the respective rates of formation of each network it has been possible to avoid polymer phase separation during the IPN synthesis. Physicochemical analyses of these materials led to classify them as true IPNs according to Sperling s definition. In addition, synergy of the mechanical properties, on the one hand, and of the surface properties, on the other hand, was displayed. 

A novel approach to IPN synthesis was reported by Sperling and Arnts (I). They synthesized two polymer networks by simultaneous yet independent reactions in the same container at the same time. Complicated interactions were eliminated in the SIN s by combining free radical (acrylate) and condensation (epoxy) polymerization. The present work uses the basic technique of Sperling and Amts. 

Latex IPNs. Latex IPNs are the third type of IPNs and are manufactured according to the general schematic illustrated in Figure 3. Latex IPN synthesis involves the initial synthesis of a crosslinked seed polymer, usually in the form of an aqueous latex. The seed latex is then swollen with a second monomer/crosslinker/initiator system which is then polymerized "in situ" to form an aqueous IPN emulsion. Materials of this type are best suited to coating applications as illustrated by the development of "Silent Paint" by Sperling et al ( ). However, latex IPNs are limited to water emulsifiable monomer/polymer systems, most of which have fairly low service temperatures, less than 150 C. 

The previous section showed how IPNs and related materials can be synthesized. The several synthetic methods, such as sequential, simultaneous, latex, and thermoplastic IPN formation, will result in different morphologies. One of the main advantages of IPN synthesis relates to the ease of promoting dual phase continuity, i.e., for a... 

The important points developed in this section are that sequential IPN synthesis tends to make dual phase continuous materials. Eor both sequential and simultaneous syntheses, a metastable phase diagram can be developed to study the kinetics of phase separation and gelation, so that better control of the morphology can be attained. The thermoplastic IPNs depend on equal volume and viscosity ratios to attain the dual phase continuity. 

Let us now introduce the concept of degree of continuity of a phase. In the beginning of the IPN synthesis, polymer network I obviously exhibits continuity of both the network structure and its phase. When monomer II is uniformly swollen in, before polymerization of II, one phase also exists. Polymer network I is continuous (the sample is usually a swollen elastomer), and the monomer II is also distributed everywhere. Upon polymerization of II, phase separation takes place. Polymer network I is still continuous, but is partially or wholly excluded from some regions of space. Assuming the previous even distribution of monomer II, we have reason to believe polymer network II will exhibit some degree of chain continuity. Sometimes, polymer network II also appears to exhibit a degree of phase continuity. Usually, polymer network II has less continuity than polymer network I. A simple example of greater and lesser phase continuity in everyday life is chicken-wire in air. 

A third mode of IPN synthesis takes two latexes of linear polymers, mixes and coagulates them, and crosslinks both components simultaneously. The product is called an interpenetrating elastomeric network, lEN. There are, in fact, many different ways that an IPN can be prepared each yields a distinctive topology. 

Figure 7.14. Stress-strain curves for SINs containing 40% castor oil elastomer. Discontinuous curve adapted from the sequential IPN synthesis. ...

L. H. Sperling, J. A. Manson, G. M. Yenwo, N. Devia-Manjarres, J. Pulido, and A. Conde, Novel Plastics and Elastomers from Castor Oil Based IPN s A Review of an International Program, in Polymer Alloys, D. Klempner and K. C. Frisch, eds.. Plenum, New York (1977). Castor oil-urethane/polystyrene sequential IPNs. Synthesis, morphology, and mechanical behavior. Fatigue behavior. 

G. M. Yenwo, Synthesis, characterization, and Behavior of Interpenetrating Polymer Networks and Solution Graft Copolymers Based on Castor Oil and Polystyrene, Diss. Abstr. Int. B 37(11), 5788, (1977). Castor oil-urethane/PS sequential IPNs. Synthesis, morphology, glass transitions, mechanical properties. Ph.D. thesis. 

Figure 2 (15) outlines the two basic methods of IPN synthesis. In Figure 2, the boxes indicate monomers, the X s indicate cross-links, and the subscripts indicate whether it goes to make up polymer 1 or polymer 2. As in Figure 1, the lines indicate the polymers and the dots indicate cross-links. The Pi and P2 above the arrows indicate polymerization of polymer 1 and polymer 2, respectively. 

Latex IPNs are often made by sequential polymerization of two (or more) cross-linked polymers utilizing emulsion polymerization (71). For core-shell latex IPN synthesis, first a cross-linked seed latex of polymer 1 is synthesized (2). Then, a second monomer and cross-linker are added to the system, usually with no added surfactant. Often, a starved polymerization route is employed, ie, the rate of polymerization equals or exceeds the rate of monomer addition. This reduces the swelling of the seed latex by the monomer 2 mix, producing a two-layer latex having a spherical core, and an overlaying shell. Obviously, multiple shells can be added for different purposes. 

Das and coworkers studied the morphology and mechanical properties of NR/PMMA IPNs. Mathew studied solid NR and PS, intimately mixed by the sequential method of IPN synthesis. Semi-IPNs based on NR/PS where only the NR phase is crosslinked offer a binary polymer system network having the elastomeric properties of NR imparted to the hard brittle properties of PS. Schematically, the morphology of semi-IPNs can be represented as shown... 

Over the years, people have discovered many different ways of synthesizing IFN s. Figure 2 Illustrates the sequential IPN synthesis, top, and the simultaneous Interpenetrating network, SIN, synthesis, bottom. In the sequential synthesis, polymer network I Is swollen with monomer II plus crosslinker and activator, and polymerized In situ. The SIN synthesis begins with a mutual solution of both monomers or prepolymers and their respective crosslinkers, which are then polymerized simultaneously by noninterfering modes, such as stepwise and chain polymerizations. These methods have been used In the bulk, suspension, and latex states. Each will yield a distinguishable composition, even for the same polymer pair. 

Can Figures 13.20 and 13.21 be generalized to analyze a sequential IPN synthesis Assume that the urethane is polymerized first, then methyl methacrylate is swollen in, and then polymerized. What path is followed What are the requirements to cause phase separation first, and then gelation of the poly(methyl methacrylate) ... 

Pei Q, Inganas O (1992) Conjugated polymers and the bending cantilever method - electrical muscles and smart devices. Adv Mater 4(4) 277-278 Plesse C et al (2007) Poly(ethylene oxide)/polybutadiene based IPNs synthesis and characterization. Polymer 48(3) 696-703, Available at ht //linkinghub.elsevier.com/retrieve/pii/ S0032386106013085. Accessed 22 Feb 2013... 

The data obtained were used to calculate enthalpy, entropy and the Gibbs functions for the seq-IPNs synthesis. It was shown that the isotherms of diverse thermodynamic properties of interpenetrating polymer networks plotted versus their composition, in particular the molar fraction of the CPU per conditional mole, can be described by straight lines. This made it possible to estimate the thermodynamic behavior of the seq-IPNs of any compositions at standard pressure within a wide temperature range. It was determined [50] that at molar content > 0.50 of PCN in seq-IPNs studied AG°p (AG° of process) < 0 and this has allowed authors to conclude about thermodynamical miscibility of the components for seq-IPNs of these composition... 

The authors of ref [51] have confirmed the high homogeneity of these full seq-IPNs with PCN content > 40 wt. % of PCN. They explained this fact by strong chemical interactions (linking) of the components in these seq-IPNs, especially in ones with high PCN content and confirmed their conclusions by the FTIR data. They have proposed a scheme of covalent links formation during polycyanurate-polyurethane full seq-IPNs synthesis (cf Figure 24). 

Polyurethane/polycyanurate grafted semi-IPNs were prepared by polycyclotrimerization of dicyanate ester of bisphenol A (DCEBA) in the immediate presence of TPU, as described in Section 3.1. During semi-IPN synthesis, at... 

It is important that the viscoelastic properties of IPNs depend on the kinetic conditions and on the method of IPN synthesis [202], This question was thoroughly investigated for semi-IPNs based on cross-linked PU and linear PBMA. The latter polymer was introduced into the network in two different ways ... 

The dependence of the viscoelastic properties of IPNs based on PU and PUA on the segregation degree was shown in [88,256,257]. Taking into account the interconnection between the chemical kinetics and the kinetics of phase separation, various methods of IPN synthesis have been used, i.e., simultaneous and sequential methods. It is known that oHgourethane acrylate (OUA) in the presence of photoinitiators polymerizes at a high rate at room temperature, the reaction rate being much higher than that... 

By considering the reaction kinetics of the individual network or linear polymer formation in IPNs, one should also bear in mind that the data on the kinetics obtained for pure components could not be used to describe the IPN synthesis for three main reasons [51] ... 

In the course of the synthesis of both the sequential and the simultaneous networks, microphase separation of the system occurs as a result of the appearance of immiscibihty of growing chains of both network components. During IPN synthesis the kinetics of the formation of each network is different, primarily because of different formation mechanisms—in general, these mechanisms are polymerization and polyaddition. Usually one network is formed first and serves as a matrix for the formation of the second network. 

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