Structure and elasticity of polyurethane networks. 5. Effect of diluent in the formation of model networks of poly(oxypropylene)triol and 4,4-methylenebis(phenyl isocyanate)

Ilavský, M.; Dušek, Karel

doi:10.1021/ma00162a006

Cited by 60 publications

(44 citation statements)

References 12 publications

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“…Their effect is expressed through dilution because it is known from gelation theory that networks formed in solution have a lower crosslinking density than when prepared in bulk. 21,22 Note that f w is 8-100% higher than f n , and the difference is higher in polyols with lower OH numbers. The gel points shown in Table A.II were calculated for 100% conversion in the stoichiometric polyol/diisocyanate systems and in the absence of cyclization.…”

Section: Structures Of Polyols With Different Oh Contentsmentioning

confidence: 99%

Network structure and properties of polyurethanes from soybean oil

Petrovìć

Yang

Zlatanić

et al. 2007

J of Applied Polymer Sci

128

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Vegetable oils are very heterogeneous materials with a wide distribution of triacylglycerol structures and double-bond contents. The hydrogenation of epoxidized soybean oil (ESO) produces polyols having a functionality distribution related to that of soybean oil. Therefore, these polyols are convenient substances for studying the impact of structural heterogeneity on network formation and properties. Polyols of hydroxyl numbers ranging from 225 to 82 mg KOH/g and weight-average functionalities ranging from 4.4 to 2.7 were obtained by the variation of the time of hydrogenation of ESO. An analysis of the functionality distribution in polyols shows that gel points with diisocyanates vary from 54 to 76% conversion. The molecular weights of the network chains of polyurethanes prepared from these polyols and diphenyl methane diisocyanate varied from 688 to 1993. Polyols with hydroxyl numbers above 200 mg KOH/g gave glassy polymers, whereas those below that value gave rubbers. The heterogeneity of polyols had a negative effect on the elastic properties only at low crosslinking densities.

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Section: Structures Of Polyols With Different Oh Contentsmentioning

confidence: 99%

Network structure and properties of polyurethanes from soybean oil

Petrovìć

Yang

Zlatanić

et al. 2007

J of Applied Polymer Sci

128

View full text Add to dashboard Cite

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“…23 and 24 when the correct monomer molecular weights and densities are used to approximate the ideal crosslinking densities. [36,37] In these equations, E theo is the theoretical Young's modulus; R is the gas constant; T is the temperature in Kelvin; and ρ x is the ideal crosslinking density (assuming no cyclization). Equation 20 was used to calculate ρ x where the moles of tetrathiol monomer directly equate to twice the moles of crosslinks, and the polymerization volume was calculated from the monomer molecular weight, monomer functionality, and monomer density (1.28 g/mL and 1.09 g/mL for the tetrathiol and PEG, respectively).…”

Section: Calculating the Extent Of Primary Cyclization And Predictingmentioning

confidence: 99%

Development and characterization of degradable thiol-allyl ether photopolymers

Rydholm

Reddy

Anseth

et al. 2007

Polymer

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Degradable thiol-ene photopolymer networks were formed through radically mediated step growth reactions. Variations in the network structure were used to alter the initial and temporal moduli, mass loss profiles, and equilibrium swelling ratios. Mass loss rates varied with changes in the solvent concentration, monomer molecular weight, average monomer functionality, and concentration of degradable linkages. The time required for the networks to degrade completely ranged from 1.20 ± 0.01 to 24.5 ± 0.1 days, which corresponded to hydrolysis rates of 0.18 ± 0.01 and 0.021 ± 0.0003 days -1 . Initial moduli also varied considerably as a function of network structure, ranging from 150 ± 35 to nearly 5000 ± 100 kPa, and initial equilibrium swelling ratios ranged from 2.5 ± 0.01 to 18.7 ± 2. Collectively, these results demonstrate how the material properties and the mass loss behavior of thiol-ene networks can be independently tuned for specific applications.

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“…Such increase is expected since it is known that the efficiency of crosslinking increases with decreasing dilution at network formation due to the decreasing cyclization. 18 On the other hand, strong decrease in modulus G 1 with increasing salt concentration Xs suggests that ionic comonomer, though having two double bonds, does Scheme 1.…”

Section: Effect Of Preparation Conditions On the Network Structurementioning

confidence: 99%

Phase Transition in Swollen Gels XXIII. Effect of the Positive Charge Concentration on the Collapse and Mechanical Behavior of Poly(1-vinyl-2-pyrrolidone) Gels

Mamytbekov

Bouchal

Ilavský

et al. 1998

Polym J

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ABSTRACT:The swelling and mechanical behavior of ionized networks of copolymers of 1-vinyl-2-pyrrolidone, ionic comonomer, N,N-dimethyl-N,N-diallylammonium chloride (molar fraction of salt Xs = 0--0.27) and crosslinker, 3,3'-ethylidenebis(l-vinyl-2-pyrrolidone) was investigated in water-acetone mixtures and aqueous NaCl solutions. The networks were prepared by a radiation copolymerization method. At xs2:0.038, the first-order phase transition (collapse) was observed. While the critical acetone concentration in the mixture at collapse, ac = 76 vol%, is independent of x, the extent of the collapse (jumpwise change in the gel volume), .1, increases with increasing salt concentration. The jumpwise change in the gel volume is accompanied by a similar change in equilibrium modulus. The swelling and mechanical behavior of ionized networks in aqueous NaCl solutions were also measured. The expected decrease in the swelling and the increase in the modulus with increasing electrolyte concentration CNaC1 was found. The theory of swelling equilibria of polyelectrolyte networks, in which the effect of electrostatic interactions of the charges on the chain and a limited chain extensibility were included, semiquantitatively describes the swelling data provided an effective concentration of the charges (lower than xs) was introduced. Mechanical behavior of networks is predominantly determined by their degree of swelling.KEY WORDS Vinylpyrrolidone Networks / Polyelectrolytes / Swelling Equilibria / Mechanical Behavior / First-Order Phase Transition / Collapse Phenomenon / Swollen polymer networks carrying low amounts of charges on the chain (1-10 mol %), when subjected to a change in the external parameters (temperature, composition of the mixed solvent, electric field and the like), undergo a first-order phase transition (collapse), at which the jumpwise change in volume of the gel can be from 10 to 1000 times. 1 -4 SANS experiments showed that in the expanded state, the chains have a coil shape, while in the collapsed state they are in globular form.5 It has been shown,2 both experimentally and theoretically, that the conditions of network formation (concentration of cross linker and diluent) and of the charge concentration have a great influence on the appearance and extent of the collapse. The jump in volume is accompanied by a jump in other physical properties, such as shear modulus, refractive index, dielectric permittivity, and the like. 2 Due to these changes, these systems are considered for use in various devices, sensors, mechanochemical actuators, 6, 7 etc. Most experimental results were obtained with charged poly(acrylamide) (PAAm), poly(N-isopropylacrylamide) (PIPAAm), and poly(N,N-diethylacrylamide) (PDEAAm) hydrogels. 1 -3 ,8 While in PAAm gels, the collapse can be brought about by the changes in the solvent composition, in PIPAAm and PDEAAm gels the transition can be induced in water, by a temperature change. With all these systems, the networks had to be prepared at high dilution (the volume fraction of polymer ...

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Structure and elasticity of polyurethane networks. 5. Effect of diluent in the formation of model networks of poly(oxypropylene)triol and 4,4-methylenebis(phenyl isocyanate)

Cited by 60 publications

References 12 publications

Network structure and properties of polyurethanes from soybean oil

Network structure and properties of polyurethanes from soybean oil

Development and characterization of degradable thiol-allyl ether photopolymers

Phase Transition in Swollen Gels XXIII. Effect of the Positive Charge Concentration on the Collapse and Mechanical Behavior of Poly(1-vinyl-2-pyrrolidone) Gels

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