Latex IPNs

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. 

Thermoplastic elastomers AB crosslinked copolymers Sequential IPNs Latex lENs... 

R. A. Dickie and S. Newman, Rubber-Modified Thermosets and Processes, U.S. Pat. 3,833,682 (1974). Semi-I and IPN latexes with reactive shells. Graded composition latexes containing rubber cores. Thermoset expoxies, etc. containing reactive latexes. One of three closely related patents. See U.S. Pat. 3,833, 683 (1974) and 3,856,883 (1974). 

O. B. Johnson and S. S. Labana, Thermoset Molding Powders from Hydroxy-Functional Graded Elastomer Particles and Monoblocked Diisocyanate and Molded Article, U.S. Pat. 3,659,003 (1972). Acrylic/methacrylic IPNs. Latex-based, rubber-toughened plastics. 

Hyperbranched polyurethanes are constmcted using phenol-blocked trifunctional monomers in combination with 4-methylbenzyl alcohol for end capping (11). Polyurethane interpenetrating polymer networks (IPNs) are mixtures of two cross-linked polymer networks, prepared by latex blending, sequential polymerization, or simultaneous polymerization. IPNs have improved mechanical properties, as weU as thermal stabiHties, compared to the single cross-linked polymers. In pseudo-IPNs, only one of the involved polymers is cross-linked. Numerous polymers are involved in the formation of polyurethane-derived IPNs (12). 

Silicone co-polymer networks and IPNs have recently been reviewed.321 The development of IPNs is briefly described, and the definitions of the main (non-exclusive) classes of the IPNs are cited. Examples of latex IPNs, simultaneous and sequential IPNs, semi-IPNs, and thermoplastic IPNs are provided. The use of silicone-silicone IPNs in studies of model silicone networks is also illustrated. Networks in which siloxane and non-siloxane components are connected via chemical bonds are considered co-polymer networks, although some other names have been applied to such networks. Today, some of the examples in this category should, perhaps, be discussed as organic-inorganic hybrids, or nanocomposites. Silicone IPNs are discussed in almost all of the major references dealing with IPNs.322-324 Silicone IPNs are also briefly discussed in some other, previously cited, reviews.291,306... 

The main path of the research employed both methods of synthesis in turn. At first, the graduate students Yenwo and Pulido explored the use of sequential IPN s based on castor oil urethanes and polystyrene (12-16). At the same time, the graduate student Devia, working in Colombia, explored an alternate synthetic route using latex technology (17). Since nothing was known about the behavior of such materials, their collective objective was to provide a map upon which further efforts could be intelligently based. This effort has now been reviewed (18). 

OP/HSP - Opaque Polymer HARP - High Aspect Ratio Polymer IPN - Interpenetrating Network PELC - Polymer Encapsulated Latex ML - Multilobe ... 

A few papers dealing with silicone latex IPNs have appeared. Frisch et al. [ 111 ] patented a process whereby two emulsions were prepared the first contained a hydroxyl-terminated PDMS and stannous octoate, the second a crosslinked polyurethane, poly(urethaneurea) or polyacrylate latex. The two lattices were blended and a film was cast and cured at 120 °C. The mechanical properties were found to be enhanced, especially in the case of the polyacrylate/PDMS IPN. Noteworthy is the fact that semi-IPNs such as the thermally stable... 

PTFE/PDMS can be obtained via a similar process [112]. PTFE chains are trapped in the PDMS network during casting. Jones et al. [113] also patented a process where adipic acid and hexane diamine (or f -caprolactam [114]) were added to a silicone latex leading to the formation of a polyamide/PDMS semi-IPN. 

In a more recent patent (45), Ryan prepared poly (n-butyl acrylate)/ poly (methyl methacrylate) latex semi-IPN s of the first kind. These materials were then blended into linear poly (vinyl chloride) and became a ternary polymer mixture. 

In a related patent (46) Amagi et al. synthesized a triple latex IPN. In brief, polymer 1 was a crosslinked SBR, polymer 2 was a crosslinked styrene-methyl methacrylate copolymer, and polymer 3 was a crosslinked poly (methyl methacrylate). All three were sequentially synthesized on the same latex particle. The latex material was then mechanically blended with linear poly (vinyl chloride). Also, Torvik (47) blended together four polymers that had different glass transition temperatures. 

Because the unique properties of IPNs arise from the intimate mixing of the component polymer systems, the synthetic methodology used to produce these materials is critical. Presently, there are three main routes utilized to produce IPNs simultaneous, sequential and latex. The method employed is determined by the component polymers selected, polymerization mechanisms, miscibility and the anticipated end use of the IPN. 

An early attempt to utilize the vibration absorbing effect of an IPN mixture was made by Sperling et al (4), who produced Silent Paint, of which one layer was an IPN. Hourston et al (5) illustrated typical IPN behavior in a 1 1 weight ratio Polyethylacrylate/Polyethylme-thacrylate latex IPN. A continued need for similar types of materials has prompted investigation of all polymeric materials known to be effective energy absorbers. 

The monomers, styrene, and methyl methacrylate (Aldrich) and ethyl methacrylate and n-butyl acrylate (Fluka) were purified prior to use. The crosslinking agent used in the synthesis of these semi-1-IPNs was tetraethyleneglycol dimethacrylate (Fluka). The emulsion polymerisation (90 C) was initiated with ammonium persulphate/sodium metabisulphite (both from BDH) and the resulting latex, which was prepared by a seed and feed procedure, was stabilised with sodium dioctyl sulfosuccinate (OT75 from Cyanamid). 

Sound and vibration damping research with IPNs began in the early 1970 s and resulted in the formation of a constrained layer damping system with the inner damping layer a latex IPN paint (3 ). The constrained layer system results in a shearing effect within the IPN layer along with flexural and extensional motions as the composite panel vibrates. The added shear mechanism, not present in extensional applications, increases the amount of energy that is dissipated in each vibrational cycle. 

It is apparent from Figure 3 that the "Silent Paint" formulation enables useful damping over a temperature range from -20 to +50 C, as evidenced by a nearly constant percent critical damping. Transitions in the epoxy material immediately above the latex IPNs transitions increase the effective damping range to to +90 C. 

The submicroscopic emulsion polymerized form of IPN s would be expected to differ in mechanical properties from the counterpart bulk polymerized form in that (1) The latex particles are not crosslinked one to another allowing movement of one latex particle past another. (2) In bulk IPN s (10) it was shown that polymer I forms the continuous or more continuous phase while in latex IPN s polymer II tends to form the more continuous phase (1). 

All latex IPN s were synthesized by two-stage emulsion polymerization techniques (1 18) as follows To 300 ml of deionized deaerated stirre 3 waTer at 60°C were added 50 ml of a 10% (W/V) solution of sodium lauryl sulfate followed by 5 ml of a 5% (w/V) solution of potassium persulfate. The calculated quantity of comonomer was added at a rate of about 2 ml per minute. When the first monomer was fully added a minimum of one hour was allowed to elapse. Then a new portion of initiator was added but no new soap followed by the second charge of comonomers under similar reaction conditions. 

Two important departures from standard procedures should be noted (1) all monomers contained 0.4% (W/V) of cross-linking agent tetraethylene glycol dimethacrylate necessary to form the IPN. (2) No new soap was added for the second stage polymerization to discourage the formation of new particles. Total polymer concentration of the completed latexes was about 30% (W/V). 

IPN s of 54/46 poly(methyl methacrylate)/poly(ethyl acrylate) were prepared by both the latex and bulk (10) routes. Both IPN s contained 0,4% (W/V) tetraethylene glycol dimethacrylate (TEGDM) crosslinking agent in each polymer. Samples of the latex IPN were film formed on glass petri dishes, All samples were vacuum dried at 60°C to constant weight. 

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