Acetal homopolymers

Homopolymer. Acetal homopolymers are prepared from formaldehyde and consist of high-molecular-weight linear polymers of formaldehyde. 

Poly(vinyl alcohol) used to manufacture the poly(vinyl acetal)s is made from poly(vinyl acetate) homopolymer (see Vinyl polymers, vinyl alcohol polymers Vinyl POLYMERS, vinyl acetate polymers). Hydrolysis of poly(vinyl acetate) homopolymer produces a polyol with predominandy 1,3-glycol units. The polyol also contains up to 2 wt % 1,2-glycol units that come from head-to-head bonding during the polymeri2ation of vinyl acetate monomer. Poly(vinyl acetate) hydrolysis is seldom complete, and for some appHcations, not desired. For example, commercial PVF resins may contain up to 13 wt % unhydroly2ed poly(vinyl acetate). Residual vinyl acetate units on the polymer help improve resin solubiHty and processibiHty (15). On the other hand, the poly(vinyl alcohol) preferred for commercial PVB resins has less than 3 wt % residual poly(vinyl acetate) units on the polymer chain. 

Poly(vinyl acetate) homopolymers adhere well to porous or ceUulosic surfaces, eg, wood, paper, cloth, leather (qv), and ceramics (qv). Homopolymer films tend to creep less than copolymer or terpolymer films. They are especially suitable in adhesives for high speed packaging operations. 

Properties of plastic LDPE LLDP E HDPE PP PVC (flexible ) PS ABS Polyacryhc (glazing) Polycarbonat e (glazing) Epoxy (minera 1 fihed) Acetal homopolym er... 

Acetals. Acetal resins (qv) are polymers of formaldehyde and are usually called polyoxymethylene [9002-81-7]. Acetal homopolymer was developed at Du Pont (8). The commercial development of acetal resins required a pure monomer. The monomer is rigorously purified to remove water, formic acid, metals, and methanol, which act as chain-transfer or reaction-terminating agents. The purified formaldehyde is polymerized to form the acetal homopolymer the polymer end groups are stabilized by reaction with acetic anhydride to form acetate end groups (9). 

Whilst the Vicat test usually gives the higher values the differences are quite modest with many polymers (e.g. those of types A, B and C). For example, in the case of the polycarbonate of bis-phenol A (Chapter 20) the heat distortion temperatures are 135-140°C and 140-146°C for the high and low stress levels respectively and the Vicat softening point is about 165°C. In the case of an acetal homopolymer the temperatures are 100, 170 and 185°C respectively. With nylon 66 the two ASTM heat distortion tests give values as different as 75 and 200°C. A low-density polyethylene may have a Vicat temperature of 90°C but a heat distortion temperature below normal ambient temperatures. 

Figure 19.5. Effect of annealing on room temperature crystallinity of acetal homopolymer resin. (Films moulded at 210°C, quenched to 50 C.) (After Hammer et al")...

Property ASTM test Acetal homopolymer Acetal copolymer Unit... 

Acetal homopolymer resins show outstanding resistance to organic solvents, no effective solvent having yet been found for temperatures below 70°C. Above this temperature some phenolic materials such as the chlorophenols are effective. Stress cracking has not been encountered in organic solvents. Swelling occurs with solvents of similar solubility parameter to that of the polymer (8 = 22.4 MPa ). 

Figure 19.8. Effect of humidity, time and temperature on the water absorption of acetal homopolymer resin (Delrin). (Du Pont Trade Literature).

Figure 19.9. Effect of absorbed water on the dimensions of acetal homopolymer resins ( Delrin ). (Du...

PVA Particles. Dispersions were prepared in order to examine stabilization for a core polymer having a glass transition temperature below the dispersion polymerization temperature. PVA particles prepared with a block copolymer having M PS) x 10000 showed a tendency to flocculate at ambient temperature during redispersion cycles to remove excess block copolymer, particularly if the dispersion polymerization had not proceeded to 100 conversion of monomer. It is well documented that on mixing solutions of polystyrene and poly(vinyl acetate) homopolymers phase separation tends to occur (10,11), and solubility studies (12) of PS in n-heptane suggest that PS blocks with Mn(PS) 10000 will be close to dissolution when dispersion polymerizations are performed at 3 +3 K. Consequently, we may postulate that for soft polymer particles the block copolymer is rejected from the particle because of an incompatibility effect and is adsorbed at the particle surface. If the block copolymer desorbs from the particle surface, then particle agglomeration will occur unless rapid adsorption of other copolymer molecules occurs from a reservoir of excess block copolymer. 

Masamoto J, Matsuzaki K, Iwaisako T, Yoshida K, Kagawa K, Nagahara H (1993) Development of a new advanced process for manufacturing polyacetal resins. Part 3. End-capping during polymerization for manufacturing acetal homopolymer and copolymer. J Appl Polym Sci 50 1317-1329... 

End-capping -of acetal copolymer [ACETAL RESINS] (Voll) -of acetal homopolymer [ACETAL RESINS] (Voll)... 

Poly(vinyl acetate) emulsions can be used in high speed gluing equipment. Poly(vinyl acetate) homopolymers adhere well to porous or cellulosic... 

Homopolymer. Acetal homopolymers are prepared from formaldehyde and consist of high-molecular-weight linear polymers of formaldehyde. The trimer of formaldehyde is shown to the left and the structure of the polymer is shown at the right, below. 

Emulsion Polymerization A typical recipe is give in Table I. Emulsion polymerization was carried out at 60°C under a nitrogen atmosphere using a batch process. Theoretical solids content in all the formulations was 25%, and generally the conversions were better than 98%. A polyvinyl acetate homopolymer and two poly (vinyl acetate-butyl acrylate) copolymers having VA/BA composition of 85/15 and 70/30 were prepared according to the above procedure. 

Plastics for which the adhesion of coatings may be improved by plasma pre-treatment are reported to be polyethylene, polypropylene, polycarbonates, polyacetals, polyaromatic esters, polyimides, polyamides, polyphenylene ether, polyacrylates, acetal homopolymer, and poly(ether imide). 

Acetal (homopolymer) Acetone 1. Abrasion. Sand with 280-grit emery cloth followed by solvent degreasing. 2. Satinizing technique. Immerse the part in the following for 5-30 s at 80-120°C Perchloroethylene 96.85 1,4 Dioxane 3.0 /7-Toluenesulfonic acid 0.05 Cab-o-Sil (Cabot Corp.) 0.10 Transfer the part immediately to an oven at 120°C for 1 min. Wash in hot water. Dry in air at 120°C. For general-purpose bonding For maximum bond strength. Recommended by DuPont... 

They include vinyl acetate homopolymers and all copolymers in which vinyl acetate is the major constituent (50% or greater). The major PVAc copolymers are vinyl acetate-ethylene (VAE) and vinyl acetate-acrylic ester (vinyl acrylic). Vinyl acetate-versatic acid (vinyl versatate) and vinyl acetate- maleate are major PVAc copolymer emulsions used. 

Polyvinyl acetate homopolymer emulsion. High molecular weight, large particle size resin. May be used with thermosetting resins, starches, softeners, nondurable water repellents and plasticizers. Base for adhesives. T(g) 28C. 

Modified polyvinyl acetate homopolymer emulsion especially reacted to provide hand modification and impart bulk to fibers. 

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